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2021-03-15 | Design of Eutectic High Entropy Alloys | Eutectic high entropy alloys (EHEAs) are emerging as an exciting new class of
structural alloys as they have shown very promising mechanical properties.
However, how to design these alloys has been a challenge. In this work, a
simple approach is presented for designing EHEAs. The introduced approach uses
the composition of binary and ternary eutectic alloys for finding the
composition of EHEAs. The approach is based on the assumption that EHEAs are
originated from binary and ternary eutectic alloys. The approach is applied for
alloy systems Al-Co-Cr-Fe-Ni, Co-Cr-Fe-Ni, Co-Cr-Fe-Ni-Ti, and Co-Cr-Fe-Ni-Ta
and several EHEAs are predicted for these alloy systems. The predicted results
are verified with thermodynamic simulations and experimental data. The results
show that the introduced approach can be considered as a feasible and
easy-to-use method for designing EHEAs. Based on the developed approach, any
binary eutectic alloy can be used for designing multicomponent eutectic alloys. | 2103.08216v2 |
2019-03-19 | Composition dependence of magnetoresistance in Fe$_{1-x}$Ni$_{x}$ alloys | Resistance of Fe$_{1-x}$Ni$_x$(x=0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7 and 0.9)
has been measured using four probe method from 5K to 300K with and without a
longitudinal magnetic field of 8T. The zero field resistivity of x=0.1 and 0.9
alloys, predominant contribution to resistivity above near room temperature is
due to electron-phonon scattering, whereas for x=05 and 0.7 alloys
electron-magnon scattering is dominant. Alloys with x=0.1 and 0.9 exhibit
positive magnetoresistance(MR) from 5K to 300K. For x=0.5 and 0.7 alloys,
magnetoresistance changes sign from positive to negative with increase in
temperature. The temperature at which sign changes increase with Ni
concentration in the alloy. The field dependent magnetoresistance is positive
for x=0.1, 0.7 and 0.9 alloys whereas it is negative for x=0.5 alloy. MR
follows linear behaviour with field for x=0.1 alloy. MR of all other alloys
follow a second order polynomial in field. | 1903.08230v3 |
2020-10-06 | Short-range order in GeSn alloy | Group IV alloys have been long viewed as homogeneous random solid solutions
since they were first perceived as Si-compatible, direct-band-gap
semiconductors 30 years ago. Such a perception underlies the understanding,
interpretation and prediction of alloys' properties. However, as the race to
create scalable and tunable device materials enters a composition domain far
beyond alloys' equilibrium solubility, a fundamental question emerges as to how
random these alloys truly are. Here we show, by combining statistical sampling
and large-scale ab initio calculations, that GeSn alloy, a promising group IV
alloy for mid-infrared technology, exhibits a clear, short-range order for
solute atoms within its entire composition range. Such short-range order is
further found to substantially affect the electronic properties of GeSn. We
demonstrate the proper inclusion of this short-range order through canonical
sampling can lead to a significant improvement over previous predictions on
alloy's band gaps, by showing an excellent agreement with experiments within
the entire studied composition range. Our finding thus not only calls for an
important revision of current structural model for group IV alloy, but also
suggests short-range order may generically exist in different types of alloys. | 2010.02991v2 |
2021-08-25 | Predictive model of surface adsorption in dissolution on transition metals and alloys | Surface adsorption, which is often coupled with surface dissolution, is
generally unpredictable on alloys due to the complicated alloying and
dissolution effects. Herein, we introduce the electronic gradient and cohesive
properties of surface sites to characterize the effects of alloying and
dissolution. This enables us to build a predictive model for the quantitative
determination of the adsorption energy in dissolution, which holds well for
transition metals, near-surface alloys, binary alloys, and high-entropy alloys.
Furthermore, this model uncovers a synergistic mechanism between the d-band
upper-edge ratio, d-band width and s-band depth in determining the alloying and
dissolution effects on adsorption. Our study not only provides fundamental
mechanistic insights into surface adsorption on alloys but also offers a
long-sought tool for the design of advanced alloy catalysts. | 2108.11017v1 |
2021-09-21 | Sustainable low-cost method for production of High entropy alloys from alloy scraps | In this communication,we propose a sustainable way to produce high entropy
alloys from alloy scraps called Alloy mixing.We successfully demonstrate this
method using a near equimolar CrCuFeMnNi HEA. Alloy scraps (304L stainless
steel, Nichrome 80 and electrical wire grade Copper) obtained from various
sources were melted together using vacuum arc melting along with minor
additions of Mn and Cr to achieve the equiatomic composition.The alloy was
characterized using X-ray Diffraction (XRD) and Scanning Electron Microscopy,
which confirmed that the alloy produced through Alloy mixing exhibits a
microstructure similar to that of the alloy with the same composition produced
through conventional melting of pure elements | 2109.10276v2 |
2024-01-15 | High entropy alloys and their affinity to hydrogen: from Cantor to platinum group elements alloys | Properties of high entropy alloys are currently in the spotlight due to their
promising applications. One of the least investigated aspects is the affinity
of these alloys to hydrogen, its diffusion and reactions. In this study we
apply high-pressure at ambient temperature and investigate stress-induced
diffusion of hydrogen into the tructure of high entropy alloys HEA including
the famous Cantor alloy as well as less known, but nevertheless important
platinum group PGM alloys. By applying X-ray diffraction to samples loaded into
diamond anvil cells we perform a comparative investigation of these HEA alloys
in Ne and H2 pressure-transmitting media. Surprisingly, even under stresses far
exceeding conventional industrial processes both Cantor and PGM alloys show
exceptional resistance to hydride formation, on par with widely used industrial
grade CuBe alloys. Our observations inspire optimism for practical HEA
applications in hydrogen-relevant industry and technology e.g. coatings, etc,
particularly those related to transport and storage. | 2401.07802v1 |
2018-08-09 | Underlying burning resistant mechanisms for titanium alloy | The "titanium fire" as produced during high pressure and friction is the
major failure scenario for aero-engines. To alleviate this issue, Ti-V-Cr and
Ti-Cu-Al series burn resistant titanium alloys have been developed. However,
which burn resistant alloy exhibit better property with reasonable cost needs
to be evaluated. This work unveils the burning mechanisms of these alloys and
discusses whether burn resistance of Cr and V can be replaced by Cu, on which
thorough exploration is lacking. Two representative burn resistant alloys are
considered, including Ti14(Ti-13Cu-1Al-0.2Si) and
Ti40(Ti-25V-15Cr-0.2Si)alloys. Compared with the commercial non-burn resistant
titanium alloy, i.e., TC4(Ti-6Al-4V)alloy, it has been found that both Ti14 and
Ti40 alloys form "protective" shields during the burning process. Specifically,
for Ti14 alloy, a clear Cu-rich layer is formed at the interface between
burning product zone and heat affected zone, which consumes oxygen by producing
Cu-O compounds and impedes the reaction with Ti-matrix. This work has
established a fundamental understanding of burning resistant mechanisms for
titanium alloys. Importantly, it is found that Cu could endow titanium alloys
with similar burn resistant capability as that of V or Cr, which opens a
cost-effective avenue to design burn resistant titanium alloys. | 1808.02976v1 |
2020-03-23 | Plasma Surface Metallurgy of Materials Based on Double Glow Discharge Phenomenon | Plasma Surface Metallurgy/Alloying is a kind of surface metallurgy/alloying
to employ low temperature plasma produced by glow discharge to diffuse alloying
elements into the surface of substrate material to form an alloy layer. The
first plasma surface metallurgy technology is plasma nitriding invented by
German scientist Dr. Bernard Berghuas in 1930. He was the first person to apply
glow discharge to realize the surface alloying. In order to break the
limitation of plasma nitriding technology, which can only be applied to a few
non-metallic gaseous elements such as nitrogen, carbon, sulfur, the "Double
Glow Discharge Phenomenon"was found in 1978. Based on this phenomenon the
"Double Glow Plasma Surface Metallurgy Technology", also known as the "Xu-Tec
Process" was invented in 1980. It can utilize any chemical elements in the
periodic table including solid metallic, gas non-metallic elements and their
combination to realize plasma surface alloying, hence greatly expanded the
field of surface alloying. Countless surface alloys with high hardness, wear
resistance and corrosion resistance, such as high speed steels, nickel base
alloys and burn resistant alloys have been produced on the surfaces of a
variety of materials. This technology may greatly improve the surface
properties of metal materials, comprehensively improve the quality of
mechanical products, save a lot of precious alloy elements for human beings.
Based on the plasma nitriding technology, the Xu-Tec Process has opened up a
new material engineering field of "Plasma Surface Metallurgy". This Review
Article briefly presents the history of glow discharge and surface alloying,
double glow discharge phenomenon, basic principle and current status of Double
Glow Plasma Surface Metallurgy/Alloying. Industrial applications, advantages
and future potential of the Xu-Tec process are also presented. | 2003.10250v1 |
2014-08-01 | Hexagonal High-Entropy Alloys | We report on the discovery of a high-entropy alloy with a hexagonal crystal
structure. Equiatomic samples in the alloy system Ho-Dy-Y-Gd-Tb were found to
solidify as homogeneous single-phase high-entropy alloys. The results of our
electron diffraction investigations and high-resolution scanning transmission
electron microscopy are consistent with a Mg-type hexagonal structure. The
possibility of hexagonal high-entropy alloys in other alloy systems is
discussed. | 1408.0100v3 |
2016-01-03 | Depletion Gilding: An Ancient Method for Surface Enrichment of Gold Alloys | Ancient objects made of noble metal alloys, that is, gold with copper and/or
silver, can show the phenomenon of surface enrichment. This phenomenon is
regarding the composition of the surface, which has a percentage of gold higher
than that of the bulk. This enrichment is obtained by a depletion of the other
elements of the alloy, which are, in some manner, removed. This depletion
gilding process was used by pre-Columbian populations for their 'tumbaga', a
gold-copper alloy, to give it the luster of gold. | 1601.00845v1 |
2017-07-26 | Molecular dynamics study of plasticity in Al-Cu alloy nanopillar due to compressive loading | In this paper, compressive loading effects on the plasticity of Al-Cu alloy
varying the crystal orientation of Al and alloying element (Cu) percentage are
investigated using molecular dynamics approach. The alloying percentage of Cu
are varied up to 10% in <001>, <110> and <111> crystal loading direction of Al.
Our results indicate that the alloy nanopillar has highest first yielding
strength and strain along <110> and <001> direction, respectively. Further, the
dislocation density and dislocation interaction are studied to explain the
compressive stress strain behavior of the alloy nanopillar. | 1707.08404v2 |
2019-08-07 | DFT-based energy shifts screening of Na$_x$K$_{55-x}$ alloy clusters | Compositional effects in NaK alloy clusters have been studied using bond
order length strength notation and density functional theory calculations. The
results reveal binding energy shifts of the NaK alloy clusters under different
elemental compositions. Atomic arrangements that can be used to predict the
structures of stable experimental NaK alloys were also obtained. Our study of
these alloy nanoclusters has uncovered a trend correlating atomic position and
composition with binding energy. We believe this data will help in the
experimental preparation of alloy nanoclusters. | 1908.02421v1 |
2019-09-01 | Low activation, refractory, high entropy alloys for nuclear applications | Two new, low activation high entropy alloys (HEAs) TiVZrTa and TiVCrTa are
studied for use as in-core, structural nuclear materials for in-core nuclear
applications. Low-activation is a desirable property for nuclear reactors, in
an attempt to reduce the amount of high level radioactive waste upon
decommissioning, and for consideration in fusion applications.The alloy TiVNbTa
is used as a starting composition to develop two new HEAs; TiVZrTa and TiVCrTa.
The new alloys exhibit comparable indentation hardness and modulus, to the
TiVNbTa alloy in the as-cast state. After heavy ion implantation the new alloys
show an increased irradiation resistance. | 1909.00373v1 |
2018-08-01 | Thick amorphous complexion formation and extreme thermal stability in ternary nanocrystalline Cu-Zr-Hf alloys | Building on the recent discovery of tough nanocrystalline Cu-Zr alloys with
amorphous intergranular films, this paper investigates ternary nanocrystalline
Cu-Zr-Hf alloys with a focus on understanding how alloy composition affects the
formation of disordered complexions. Binary Cu-Zr and Cu-Hf alloys with similar
initial grain sizes were also fabricated for comparison. The thermal stability
of the nanocrystalline alloys was evaluated by annealing at 950 {\deg}C (>95%
of the solidus temperatures), followed by detailed characterization of the
grain boundary structure. All of the ternary alloys exhibited exceptional
thermal stability comparable to that of the binary Cu-Zr alloy, and remained
nanocrystalline even after two weeks of annealing at this extremely high
temperature. Despite carbide formation and growth in these alloys during
milling and annealing, the thermal stability of the ternary alloys is mainly
attributed to the formation of thick amorphous intergranular films at high
temperatures. Our results show that ternary alloy compositions have thicker
boundary films compared to the binary alloys with similar global dopant
concentrations. While it is not required for amorphous complexion formation,
this work shows that having at least three elements present at the interface
can lead to thicker grain boundary films, which is expected to maximize the
previously reported toughening effect. | 1808.00507v5 |
2023-05-20 | Mechanical Property Design of Bio-compatible Mg alloys using Machine-Learning Algorithms | Magnesium alloys are attractive options for temporary bio-implants because of
their biocompatibility, controlled corrosion rate, and similarity to natural
bone in terms of stiffness and density. Nevertheless, their low mechanical
strength hinders their use as cardiovascular stents and bone substitutes. While
it is possible to engineer alloys with the desired mechanical strength,
optimizing the mechanical properties of biocompatible magnesium alloys using
conventional experimental methods is time-consuming and expensive. Therefore,
Artificial Intelligence (AI) can be leveraged to streamline the alloy design
process and reduce the required time. In this study, a machine learning model
was developed to predict the yield strength (YS) of biocompatible magnesium
alloys with an $R^2$ accuracy of 91\%. The predictive model was then validated
using the CALPHAD technique and thermodynamics calculations. Next, the
predictive model was employed as the fitness function of a genetic algorithm to
optimize the alloy composition for high-strength biocompatible magnesium
implants. As a result, two alloys were proposed and synthesized, exhibiting YS
values of 108 and 113 MPa, respectively. These values were substantially higher
than those of conventional magnesium biocompatible alloys and closer to the YS
and compressive strength of natural bone. Finally, the synthesized alloys were
subjected to microstructure analysis and mechanical property testing to
validate and evaluate the performance of the proposed AI-based alloy design
approach for creating alloys with specific properties suitable for diverse
applications. | 2305.12060v1 |
2008-11-02 | Ab-initio simulation and experimental validation of beta-titanium alloys | In this progress report we present a new approach to the ab-initio guided
bottom up design of beta-Ti alloys for biomedical applications using a quantum
mechanical simulation method in conjunction with experiments. Parameter-free
density functional theory calculations are used to provide theoretical guidance
in selecting and optimizing Ti-based alloys with respect to three constraints:
(i) the use of non-toxic alloy elements; (ii) the stabilization of the body
centered cubic beta phase at room temperature; (iii) the reduction of the
elastic stiffness compared to existing Ti-based alloys. Following the
theoretical predictions, the alloys of interest are cast and characterized with
respect to their crystallographic structure, microstructure, texture, and
elastic stiffness. Due to the complexity of the ab initio calculations, the
simulations have been focused on a set of binary systems of Ti with two
different high melting bcc metals, namely, Nb and Mo. Various levels of model
approximations to describe mechanical and thermodynamic properties are tested
and critically evaluated. The experiments are conducted both, on some of the
binary alloys and on two more complex engineering alloy variants, namely,
Ti-35wt.%Nb-7wt.%Zr-5wt.%Ta and a Ti-20wt.%Mo-7wt.%Zr-5wt.%Ta. | 0811.0157v1 |
2009-03-13 | Half-metallic ferrimagnetism in the [Sc$_{1-x}$V$_x$]C and [Sc$_{1-x} $V$_x$]Si alloys adopting the zinc-blende and wurtzite structures from first-principles | Employing first-principles calculations we study the structural, electronic
and magnetic properties of the [Sc$_{1-x}$V$_x$]C and [Sc$_{1-x}$V$_x$]Si
alloys. In their equilibrium rocksalt structure all alloys are non-magnetic.
The zincblende and wurtzite structures are degenerated with respect to the
total energy. For all concentrations the alloys in these lattice structures are
half-metallic with the gap located in the spin-down band. The total spin moment
follows the Slater-Pauling behavior varying linearly between the -1 $\mu_B$ of
the perfect ScC and ScSi alloys and the +1 $\mu_B$ of the perfect VC and VSi
alloys. For the intermediate concentrations V and Sc atoms have antiparallel
spin magnetic moments and the compounds are half-metallic ferrimagnets. At the
critical concentration, both [Sc$_{0.5}$V$_{0.5}$]C and [Sc$_{0.5}$V$_{0.5}$]Si
alloys present zero total spin-magnetic moment but the C-based alloy shows a
semiconducting behavior contrary to the Si-based alloys which is a
half-metallic antiferromagnet. | 0903.2331v1 |
2009-05-07 | Research of Mechanical Properties of Ni-Ti-Nb Alloyson Low Temperature and Restriction Behavior | Mechanical Properties of Ni-Ti-Nb alloys with these conditions of
cold-drawing, non-vacuum heat treatment and vacuum heat treatment were measured
at low temperature, and Mechanical Properties of Ni47Ti44Nb9 alloys of
restricting recover was compared with the one of alloys of non-restricting
recover, and these rules of the mechanical performance between them was
analyzed. Experiment indicates that, mechanical Properties of vacuum heat
treatment's alloys was more excellent than the other two (non-vacuum heat
treatment and cold-drawing), and the stress curves of alloys of restricting
recover haven't the evident yield band, and the stress of alloys of restricting
recover was higher than the ones of alloys of non-restricting recover, but the
stress of alloys of restricting recover was lower than the ones of alloys of
non-restricting recover. | 0905.0967v2 |
2012-05-07 | Gamma-irradiation influence on the initial magnetic conductivity of based on the system Fe-Si-B amorphous and nanocrystalline alloys | The dependence of initial magnetic permeability {\mu}i of based on the
Fe-Si-B amorphous and nanocrystalline alloys on the {\gamma}-irradiation dose
was investigated by the method of inductance factor determination. It was
determined that the alloying of amorphous Fe-Si-B alloys by nickel and
molybdenum increases the radiation sensitivity of the {\mu}i. Initial magnetic
permeability of nanocrystalline magnetic alloys is less sensitive to the action
of {\gamma}-irradiation as compared with the alloyed amorphous alloys. Has been
suggested that radiation influence on the initial magnetic permeability are
caused by creation of non-magnetic incorporation in structure of amorphous
alloys as well as amorphous matrix of nanocrystalline alloys. | 1205.1354v1 |
2013-07-15 | Characterization of Al and Mg Alloys from Their X-Ray Emission Bands | The valence states of Mg-Al alloys are compared to those of reference
materials (pure Mg and Al metals, and intermetallics). Two methods based on
X-ray emission spectroscopy are proposed to determine the phases and their
proportion: first, by analyzing the Al valence spectra of the Mg-rich alloys
and the Mg valence spectra of the Al-rich alloys; second, by fitting with a
linear combination of the reference spectra the Al spectra of the Al-rich
alloys and the Mg spectra of the Mg-rich alloys. This enables us to determine
that Al and Al3Mg2 are present in the 0-43.9 wt% Al composition range and Mg
and Al12Mg17 are present in the 62.5-100 wt% Al composition range. In the
43.9-62.5% Al range, the alloy is single phase and an underestimation of the Al
content of the alloy can be estimated from the comparison of the bandwidth of
the alloy spectrum to the bandwidths of the reference spectra. | 1307.3959v1 |
2013-11-06 | Characterization of poly- and single-crystal uranium-molybdenum alloy thin films | Poly- and single-crystal thin films of U-Mo alloys have been grown both on
glass and sapphire substrates by UHV magnetron sputtering. X-ray and Electron
Backscatter Diffraction data indicate that for single-crystal U1-xMox alloys,
the pure cubic uranium gamma-phase exists for x > 0.22 (10 wt.% Mo). Below 10
wt.% Mo concentration, the resulting thin film alloys exhibited a mixed
alpha-gamma uranium phase composition. | 1311.1430v1 |
2020-01-22 | The design of eutectic high entropy alloys in Al-Co-Cr-Fe-Ni system | In the present work, a simple approach is proposed for predicting the
compositions of eutectic high entropy alloys (EHEAs) in Al-Co-Cr-Fe-Ni system.
It is proposed that eutectic lines exist between certain eutectic alloys in
this system and, as a result, new eutectic or near-eutectic compositions can be
obtained by mixing the alloys which are located on the same eutectic line. The
approach is applied for a series of experimentally verified eutectic alloys and
new eutectic or near-eutectic alloys are designed for Al-Co-Cr-Fe-Ni system.
Furthermore, by investigating the compositions of verified eutectic alloys in
Al-Co-Cr-Fe-Ni system, compositional diagrams are proposed which show the
relations between the concentrations of constituent elements in eutectic
alloys. The compositional diagrams suggest that EHEAs are derived from binary
and ternary eutectic alloys. Moreover, the proposed diagrams can be considered
as convenient methods for evaluating the composition of EHEAs in Al-Co-Cr-Fe-Ni
system. | 2001.07954v1 |
2021-07-06 | A Transferable Machine-learning Scheme from Pure Metals to Alloys in Predicting Adsorption Energies | Alloys present the great potential in catalysis because of their adjustable
compositions, structures and element distributions, which unfortunately also
limit the fast screening of the potential alloy catalysts. Machine learning
methods are able to tackle the multi-variable issues but still cannot yet
predict the complex alloy catalysts from the properties of pure metals due to
the lack of universal descriptors. Herein we propose a transferable
machine-learning model based on the intrinsic properties of substrates and
adsorbates, which can predict the adsorption energies of single-atom alloys
(SAAs), AB intermetallics (ABs) and high-entropy alloys (HEAs), simply by
training the properties of transition metals (TMs). Furthermore, this model
builds the structure-activity relationship of the adsorption energies on alloys
from the perspective of machine learning, which reveals the role of the surface
atoms' valence, electronegativity and coordination and the adsorbates' valence
in determining the adsorption energies. This transferable scheme advances the
understanding of the adsorption mechanism on alloys and the rapid design of
alloy catalysts. | 2107.02599v1 |
2019-01-06 | Effect of copper content on thermal and mechanical properties of eutectoid zn-al alloy | Zn-Al alloys have become one of the major engineering alloys among
commercially available alloys. This study was conducted on eutectoid
composition of Zn-Al alloy with an observation of the effect of copper
addition. For this purpose, one eutectoid (Zn-22wt%Al) and three other alloys,
adding 1wt%, 3wt% and 5wt% copper with this eutectoid composition, were molded
in permanent metal mould. Microscopic studies exhibited varied grains which
confirmed the formation of different phases. Moreover, the formation of
different phases in micro study was supported by XRD analysis. Hardness of the
samples were tested on Rockwell B scale and it was observed that the hardness
of these alloys was substantially increased with the addition of copper. With
increasing amount of copper, phase changing temperature of the alloys reveals a
growing trend, which was observed by DTA analysis. From this study it was
concluded that addition of copper can significantly add to the mechanical
properties of Zn-Al alloys. | 1901.01519v2 |
2019-08-13 | Investigating the real-time dissolution of a compositionally complex alloy using inline ICP and correlation with XPS | The real-time dissolution of the single-phase compositionally complex alloy
(CCA), Al1.5TiVCr, was studied using an inline inductively coupled plasma
method. Compositionally complex alloys (CCAs), a term encompassing high entropy
alloys (HEAs) or multi-principal element alloys (MPEAs), are - in general -
noted for their inherently high corrosion resistance. In order to gain an
insight into the dissolution of Al1.5TiVCr alloy, atomic emission
spectroelectrochemistry was utilised in order to measure the ion dissolution of
the alloy during anodic polarisation. It was revealed that incongruent
dissolution occurred, with preferential dissolution of Al, and essentially no
dissolution of Ti, until the point of alloy breakdown. Results were correlated
with X-ray photoelectron spectroscopy, which revealed a complex surface oxide
inclusive of unoxidised metal, and metal oxides in disproportion to the bulk
alloying element ratio. | 1908.04493v1 |
2020-11-14 | The influence of alloying on the stacking fault energy of gold from density functional theory calculations | The generalized stacking fault (SFE) energy curves of pure gold (Au) and its
binary alloys with transition metals are determined from density functional
theory (DFT). Alloy elements Ag, Al, Cu, Ni, Ti, Zr, Zn, In, Ga, Sn, Mn, Cd,
Sn, Ta and Cr are substituted into Au at concentrations up to 4%. A comparison
of various proposed methodologies to calculate SFEs is given. The intrinsic SFE
decreases for all alloying elements from its value for pure Au, but SFE
energies (both stable and unstable) vary strongly with the distance of the
alloying element from the stacking fault region, and with alloy concentration.
The compositional dependence of the SFE on the volume change associated with
alloying element is determined. This work demonstrates that the SFE is strongly
influenced by misfit strain caused by the alloying elements. Moreover, the
computed generalized SFE curves provide information valuable to developing an
understanding of the deformation behavior of Au and Au-alloys. | 2011.07305v1 |
2021-01-07 | Highly Distorted Lattices in Chemically Complex Alloys Produce Ultra-Elastic Materials with Extraordinary Elinvar Effects | Conventional crystalline alloys usually possess a low atomic size difference
in order to stabilize its crystalline structure. However, in this article, we
report a single phase chemically complex alloy which possesses a large atomic
size misfit usually unaffordable to conventional alloys. Consequently, this
alloy develops a rather complex atomic-scale chemical order and a highly
distorted crystalline structure. As a result, this crystalline alloy displays
an unusually high elastic strain limit (~2%), about ten times of that of
conventional alloys, and an extremely low internal friction (< 2E-4) at room
temperature. More interestingly, this alloy firmly maintains its elastic
modulus even when the testing temperature rises from room temperature to 900 K,
which is unmatched by the existing alloys hitherto reported. From an
application viewpoint, our discovery may open up new opportunities to design
high precision devices usable even under an extreme environment. | 2101.02382v1 |
2021-04-20 | Accelerated Discovery of Molten Salt Corrosion-resistant Alloy by High-throughput Experimental and Modeling Methods Coupled to Data Analytics | Insufficient availability of molten salt corrosion-resistant alloys severely
limits the fruition of a variety of promising molten salt technologies that
could otherwise have significant societal impacts. To accelerate alloy
development for molten salt applications and develop fundamental understanding
of corrosion in these environments, here we present an integrated approach
using a set of high-throughput alloy synthesis, corrosion testing, and modeling
coupled with automated characterization and machine learning. By using this
approach, a broad range of Cr-Fe-Mn-Ni alloys were evaluated for their
corrosion resistances in molten salt simultaneously demonstrating that
corrosion-resistant alloy development can be accelerated by thousands of times.
Based on the obtained results, we unveiled a sacrificial mechanism in the
corrosion of Cr-Fe-Mn-Ni alloys in molten salts which can be applied to protect
the less unstable elements in the alloy from being depleted, and provided new
insights on the design of high-temperature molten salt corrosion-resistant
alloys. | 2104.10235v1 |
2021-08-13 | Insight into Ideal Shear Strength of Ni-based Dilute Alloys using First-Principles Calculations and Correlational Analysis | The present work examines the effect of alloying elements (denoted X) on the
ideal shear strength for 26 dilute Ni-based alloys, Ni$_{11}$X, as determined
by first-principles calculations of pure alias shear deformations. The
variations in ideal shear strength are quantitatively explored with
correlational analysis techniques, showing the importance of atomic properties
such as size and electronegativity. The shear moduli of the alloys are affirmed
to show a strong linear relationship with their ideal shear strengths, while
the shear moduli of the individual alloying elements were not indicative of
alloy shear strength. Through combination with available ideal shear strength
data on Mg alloys, a potential application of the Ni alloy data is demonstrated
in the search for a set of atomic features suitable for machine learning
applications to mechanical properties. As another illustration, the predicted
Ni ideal shear strengths play a key role in a predictive multiscale framework
for deformation behavior of single crystal alloys at large strains, as shown by
simulated stress-strain curves. | 2108.06412v2 |
2021-10-18 | Equilibrium Phase Diagrams of Isostructural and Heterostructural Two-Dimensional Alloys from First Principles | Alloying is a successful strategy for tuning the phases and properties of
two-dimensional (2D) transition metal dichalcogenides (TMDCs). To accelerate
the synthesis of new TMDC alloys, we present a method for generating
temperature-composition equilibrium phase diagrams by combining
first-principles total energy calculations with thermodynamic solution models.
This method is applied to three representative 2D TMDC alloys: an isostructural
alloy, MoS2(1-x)Te2x, and two heterostructural alloys, Mo1-xWxTe2 and
WS2(1-x)Te2x. We show that the mixing enthalpy of the entire composition range
of these binary alloys can be reliably represented using a sub-regular solution
model fitted to the total energy of a small number of compositions that are
calculated using density-functional theory on special quasi-random structures.
The sub-regular solution model uses a cubic fit that captures three-body
effects that are important in these TMDC alloys having hexagonal structures. By
comparing both isostructural and heterostructural phase diagrams generated with
this method to those calculated with cluster expansion methods, we demonstrate
that this method can be used to rapidly design phase diagrams of TMDC alloys,
and related 2D materials. | 2110.09589v2 |
2023-09-09 | High-throughput screening of coherent topologically close-packed precipitates in hexagonal close-packed metallic systems | The nanoscale, coherent topologically close-packed (TCP) precipitate plates
in magnesium alloys are found beneficial to the strength and creep resistance
of alloys. However, the conventional trial-and-error method is too
time-consuming and costly, which impedes the application of TCP precipitates to
hcp-based metallic alloys. Here, we systematically screen the potential
coherent TCP precipitate plates in the three most common hcp alloys, magnesium
(Mg), titanium (Ti), and zirconium (Zr) alloys, using an efficient
high-throughput screening methodology. Our findings indicate that the
hcp-to-TCP structural transformations readily occur in Mg alloys, leading to
abundant precipitation of TCP plates. However, hcp-Ti and Zr alloys exhibit a
preference for hcp-to-bcc structural transformations, rather than the in situ
precipitation of TCP plates. These screening results are largely consistent
with experimental observations. The insights gained contribute to a deeper
understanding of precipitation behavior in various hcp-based alloys at the
atomic level and provide insightful reference results for designing novel
alloys containing TCP phases. | 2309.04822v2 |
2006-05-29 | Epitaxy of thin films of the Heusler compound Co2Cr0.6Fe0.4Al | Epitaxial thin films of the highly spin polarized Heusler compound
Co2Cr0.6Fe0.4Al are deposited by dc magnetron sputtering. It is shown by XRD
and TEM investigations how the use of an Fe buffer layer on MgO(100) substrates
supports the growth of highly ordered Co2Cr0.6Fe0.4Al at low deposition
temperatures. The as grown samples show a relatively large ordered magnetic
moment of mu = 3.0mu_B/f.u. providing evidence for a low level of disorder. | 0605698v2 |
2006-09-02 | A new diluted magnetic semiconductor: The half-metallic ferromagnet CoTi(1-x)FexSb | Half-Heusler compounds with 18 valence electrons are semi-conducting. It will
be shown that doping with electrons results in half-metallic ferromagnets,
similar to the case of diluted semi-conductors. CoTiSb is known to be a
semi-conducting Half-Heusler compound. Doping by Fe is expected to result in
ferromagnetic order. It was found that Ti can be replaced by up to about 10% Fe
while its crystal structure still remains C1b, which was proved by X-ray powder
diffraction. SQUID magnetometry revealed a magnetic moment of 0.32 mB per unit
cell at 5K. | 0609042v1 |
2006-10-17 | Surface and bulk properties of the Heusler compound Co2Cr0.6Fe0.4Al: a Moessbauer study | To explore its structural and magnetic properties, the Heusler compound
Co2Cr0.6Fe0.4Al was investigated using Moessbauer spectroscopy. The results of
both transmission and conversion electron Moessbauer spectroscopy (CEMS) are
analyzed to obtain insight into both the disorder effects as well as the
differences between bulk and surface properties. It was found that mechanical
treatment of the surfaces of bulk samples causes disorder and phase
segregation, effects that should be taken into consideration when performing
studies using surface-informative techniques. Results from bulk sample CEMS
measurements of Co2Cr0.6Fe0.4Al are used to interpret the thin film Moessbauer
spectra of this compound. | 0610480v1 |
2007-03-28 | Crystalline electric fields and the magnetic ground state of the novel Heusler intermetallic YbRh$_{2}$Pb | We have synthesized a new intermetallic compound with a distorted Heusler
structure, YbRh$_{2}$Pb. We present a study of the magnetic, thermal, and
transport properties. Heat capacity measurements revealed that YbRh$_{2}$Pb
orders magnetically below T$_{N}$=0.57 K from a paramagnetic state with
substantial crystal electric field splitting. Magnetic field further splits the
ground state, which leads to the suppression of magnetic order in YbRh$_{2}$Pb. | 0703765v2 |
1995-03-28 | THE UNIQUENESS THEOREM FOR ROTATING BLACK HOLE SOLUTIONS OF SELF-GRAVITATING HARMONIC MAPPINGS | We consider rotating black hole configurations of self-gravitating maps from
spacetime into arbitrary Riemannian manifolds. We first establish the
integrability conditions for the Killing fields generating the stationary and
the axisymmetric isometry (circularity theorem). Restricting ourselves to
mappings with harmonic action, we subsequently prove that the only stationary
and axisymmetric, asymptotically flat black hole solution with regular event
horizon is the Kerr metric. Together with the uniqueness result for
non-rotating configurations and the strong rigidity theorem, this establishes
the uniqueness of the Kerr family amongst all stationary black hole solutions
of self-gravitating harmonic mappings. | 9503053v1 |
1995-06-15 | Pulsation of Spherically Symmetric Systems in General Relativity | The pulsation equations for spherically symmetric black hole and soliton
solutions are brought into a standard form. The formulae apply to a large class
of field theoretical matter models and can easily be worked out for specific
examples. The close relation to the energy principle in terms of the second
variation of the Schwarzschild mass is also established. The use of the general
expressions is illustrated for the Einstein-Yang-Mills and the Einstein-Skyrme
system. | 9506027v1 |
1996-10-11 | No-Hair Theorems and Black Holes with Hair | The critical steps leading to the uniqueness theorem for the Kerr-Newman
metric are reexamined in the light of the new black hole solutions with
Yang-Mills and scalar hair. Various methods -- including scaling techniques,
arguments based on energy conditions, conformal transformations and divergence
identities -- are reviewed, and their range of application to selfgravitating
scalar and non-Abelian gauge fields is discussed. In particular, the no-hair
theorem is extended to harmonic mappings with arbitrary Riemannian target
manifolds. (This paper is an extended version of an invited lecture held at the
Journ\'ees Relativistes 96.) | 9610019v1 |
1997-03-06 | Mass formulae for a class of nonrotating black holes | In the presence of a Killing symmetry, various self-gravitating field
theories with massless scalars (moduli) and vector fields reduce to
sigma-models, effectively coupled to 3-dimensional gravity. We argue that this
particular structure of the Einstein-matter equations gives rise to quadratic
relations between the asymptotic flux integrals and the area and surface
gravity (Hawking temperature) of the horizon. The method is first illustrated
for the Einstein-Maxwell system. A derivation of the quadratic formula is then
also presented for the Einstein-Maxwell-axion-dilaton model, which is relevant
to the bosonic sector of heterotic string theory. | 9703015v1 |
1998-05-15 | On rotational excitations and axial deformations of BPS monopoles and Julia-Zee dyons | It is shown that Julia-Zee dyons do not admit slowly rotating excitations.
This is achieved by investigating the complete set of stationary excitations
which can give rise to non-vanishing angular momentum. The relevant zero modes
are parametrized in a gauge invariant way and analyzed by means of a harmonic
decomposition. Since general arguments show that the solutions to the
linearized Bogomol'nyi equations cannot contribute to the angular momentum, the
relevant modes are governed by a set of electric and a set of non self-dual
magnetic perturbation equations. The absence of axial dipole deformations is
also established. | 9805061v1 |
2001-05-22 | Semiclassical evidence for the BGS-conjecture | Recently, M. Sieber and K. Richter achieved a breakthrough towards a proof of
the BGS-conjecture by calculating semiclassically a first correction to the
diagonal approximation of the orthogonal form factor for geodesic flow on a
Riemann surface of constant negative curvature. In this note, we try to
generalize the arguments. However, the solution proposed is not yet correct,
because also other geometries must be taken into account. | 0105052v3 |
2001-06-22 | Near action degeneracy of periodic orbits in systems with non-conventional time reversal | Recently, Sieber and Richter calculated semiclassically a first off-diagonal
contribution to the orthogonal form factor for a billiard on a surface of
constant negative curvature by considering orbit pairs having almost the same
action. For a generalization of this derivation to systems invariant under
non-conventional time reversal symmetry, which also belong to the orthogonal
symmetry class, we show in this paper that it is necessary to redefine the
configuration space in an appropriate way. | 0106035v1 |
2011-10-13 | Berry-curvatures and anomalous Hall effect in Heusler compounds | Berry curvatures are computed for a set of Heusler compounds using density
functional (DF) calculations and the wave functions that DF provide. The
anomalous Hall conductivity is obtained from the Berry curvatures. It is
compared with experimental values in the case of Co$_2$CrAl and Co$_2$MnAl. A
notable trend cannot be seen but the range of values is quite enormous. The
results for the anomalous Hall conductivities and their large variations can be
qualitatively understood by means of the band structure and the Fermi-surface
topology. | 1110.2878v1 |
2012-06-06 | Probing the superconducting state of the Heusler supercoductor: ZrNi$_2$Ga | Using both muon spin rotation and muon spin relaxation, the superconducting
ground state of the Heusler superconductor {ZrNi$_2$Ga} has been studied. The
temperature dependence of the magnetic penetration depth of {ZrNi$_2$Ga} is
consistent with a single isotropic gap s-wave BCS superconductor. The gap
energy is \Delta(0)=0.44(1) meV and the magnetic penetration depth, \lambda(0),
is 310(5) nm. Furthermore, we show evidence of a possible cross-over from an
square flux line lattice to a hexagonal lattice at low temperatures. No
evidence of time reversal symmetry breaking has been observed as might be
expected for a half metal superconductor. | 1206.1182v1 |
2012-10-19 | Search for spin gapless semiconductors: The case of inverse Heusler compounds | We employ ab-initio electronic structure calculations to search for spin
gapless semiconductors, a recently identified new class of materials, among the
inverse Heusler compounds. The occurrence of this property is not accompanied
by a general rule and results are materials specific. The six compounds
identified show semiconducting behavior concerning the spin-down band structure
and in the spin-up band structure the valence and conduction bands touch each
other leading to 100% spin-polarized carriers. Moreover these six compounds
should exhibit also high Curie temperatures and thus are suitable for
spintronics applications. | 1210.5355v1 |
2013-09-25 | Half metallic state and magnetic properties versus the lattice constant in Ti\raisebox{-.2ex}{\scriptsize 2}CoSn Heusler compound: an ab initio study | The half metallic properties of Ti\raisebox{-.2ex}{\scriptsize 2}CoSn
full-Heusler compound is studied within the framework of the density functional
theory with the Perdew Burke Ernzerhof generalized gradient approximation
(GGA). Structural optimization was performed and the calculated equilibrium
lattice constant is 6.340 A. The spin up band of compound has metallic
character and spin down band is semiconducting with an indirect gap of 0.598 eV
at equilibrium lattice constant. For the lattice parameter, ranging from 6.193
to 6.884 A the compound presents 100% spin polarization and a total magnetic
moment of 3$\mu_{B}$. | 1309.6437v1 |
2014-11-26 | Theoretical investigations of electronic structure and magnetism in Zr2CoSn full-Heusler compound | The half-metallic properties of a new and promising full-Heusler compound,
Zr2CoSn, are investigated by means of ab initio calculations within the Density
Functional Theory framework. The ferromagnetic ordered Hg2CuTi-type crystal
structure is energetically favorable and the optimized lattice parameter is
6.76 A. The total magnetic moment calculated is 3 uB/f.u. and follows a typical
Slater-Pauling dependence. The half metallicity disappears if the unit cell
volume is contracted by 5 %. | 1411.7154v1 |
2018-04-01 | First-principles study on thermoelectric properties of half-Heusler compounds CoMSb(M=Sc, Ti, V, Cr, and Mn) | We have performed systematic density functional calculations and evaluated
thermoelectric properties, See- beck coefficient and anomalous Nernst
coefficient of half-Heusler comounds CoMSb(M=Sc, Ti, V, Cr, and Mn). The
carrier concentration dependence of Seebeck coefficients in nonmagnetic
compounds are in good agreement with experimental values. We found that the
half-metallic ferromagnetic CoMnSb show large anomalous Nernst effect
originating from Berry curvature at the Brillouin zone boundary. These results
help to understanding for the mechanism of large anomalous Nernst coefficient
and give us a clue to design high performance magnetic thermoelectric
materials. | 1804.00297v1 |
2022-12-19 | Chiral surface superconductivity in half-Heusler semimetals | We propose the metallic and weakly dispersive surface states of half-Heusler
semimetals as a possible domain for the onset of unconventional surface
superconductivity ahead of the bulk transition. Using density functional theory
(DFT) calculations and the random phase approximation (RPA), we analyse the
surface band structure of LuPtBi and its propensity towards Cooper pair
formation induced by screened electron-electron interactions in the presence of
strong spin-orbit coupling. Over a wide range of model parameters, we find an
energetically favoured chiral superconducting condensate featuring Majorana
edge modes, while low-dimensional order parameter fluctuations trigger
time-reversal symmetry breaking to precede the superconducting transition. | 2212.09786v1 |
2013-09-07 | Defects and hyperfine interactions in binary Fe-Al alloys studied by positron annihilation and Mossbauer spectroscopies | The defects, the behavior of 3d electrons and the hyperfine interactions in
binary Fe-Al alloys with different Al contents have been studied by the
measurements of positron lifetime spectra, coincidence Doppler broadening
spectra of positron annihilation radiation and Mossbauer spectra. The results
show that on increasing the Al content in Fe-Al alloys, the mean positron
lifetime of the alloys increase, while the mean electron density of the alloys
decrease. The increase of Al content in binary Fe-Al alloys will decrease the
amount of unpaired 3d electrons; as a consequence the probability of positron
annihilation with 3d electrons and the hyperfine field decrease rapidly.
Mossbauer spectra of binary Fe-Al alloys with Al content less than 25at% show
discrete sextets, these alloys give ferromagnetic contribution at room
temperature. The M\"ossbauer spectrum of Fe70Al30 shows a broad singlet. As Al
content higher than 40 at%, the M\"ossbauer spectra of these alloys are
singlet, that is, the alloys are paramagnetic. The behavior of 3d electron and
its effect on the hyperfine field of the binary Fe-Al alloy has been discussed. | 1309.2673v1 |
2014-10-02 | Phase stability of ternary fcc and bcc Fe-Cr-Ni alloys | The phase stability of fcc and bcc magnetic binary Fe-Cr, Fe-Ni, Cr-Ni alloys
and ternary Fe-Cr-Ni alloys is investigated using a combination of density
functional theory (DFT), Cluster Expansion (CE) and Magnetic Cluster Expansion
(MCE). Energies, magnetic moments, and volumes of more than 500 alloy
structures are evaluated using DFT, and the most stable magnetic configurations
are compared with experimental data. Deviations from the Vegard law in fcc
Fe-Cr-Ni alloys, associated with non-linear variation of atomic magnetic
moments as functions of alloy composition, are observed. Accuracy of the CE
model is assessed against the DFT data, where for ternary alloys the
cross-validation error is smaller than 12 meV/atom. A set of cluster
interaction parameters is defined for each alloy, where it is used for
predicting new ordered alloy structures. Fcc Fe2CrNi phase with Cu2NiZn-like
structure is predicted as the global ground state with the lowest chemical
ordering temperature of 650K. DFT-based Monte Carlo (MC) simulations are used
for assessing finite temperature fcc-bcc phase stability and order-disorder
transitions in Fe-Cr-Ni alloys. Enthalpies of formation of ternary alloys
calculated from MC simulations at 1600K combined with magnetic correction
derived from MCE are in excellent agreement with experimental values measured
at 1565K. Chemical order is analysed, as a function of temperature and
composition, in terms of the Warren-Cowley short-range order (SRO) parameters
and effective chemical pairwise interactions. | 1410.0548v2 |
2020-05-11 | Microstructure, mechanical properties and aging behaviour of nanocrystalline copper-beryllium alloy | A complex study of aging kinetics for both coarse-grained and nanostructured
by severe plastic deformation Cu -- 2 wt% Be alloy is reported. It is shown
that aging of a coarse-grained alloy leads to continuous formation of nanosized
CuBe body centred cubic (bcc, CsCl -- type) semi-coherent particles with the
{220} Cu // {200} CuBe crystallographic orientation relationship. These
particles created significant internal stress fields and became obstacles for
dislocation glide that resulted in a change in the hardness from 95 Vickers
hardness (HV) for the solubilized alloy to 400 HV for the aged one. The severe
plastic deformation led to the formation of a single-phase nanograined
microstructure with an average grain size of 20 nm and 390 HV. It was found
that this grain size was slightly driven by grain boundary segregation. Further
aging of the nanocrystalline alloy led to the discontinuous formation of
precipitates on the former Cu grain boundaries and skipping of metastable
phases. Significant age hardening with a maximum hardness of 466 HV for the
aged nanostructured alloy was observed. Mechanical tests result revealed a
strong influence of microstructure and further aging on strength capability of
the alloy for both coarse-grained and nanostructured alloy. A good thermal
stability in the nanostructured alloy was also noticed. Theoretical
calculations of the hardness value for the CuBe phase are provided. It was
shown that Be as a light alloying elements could be used for direct change of
microstructure of severely deformed copper alloys. | 2005.04976v1 |
2017-10-13 | Unusual negative formation enthalpies and atomic ordering in isovalent alloys of transition metal dichalcogenide monolayers | Common substitutional isovalent semiconductor alloys usually form disordered
metastable phases with positive excess formation enthalpies ({\Delta}H). In
contrast, monolayer alloys of transition metal dichalcogenides (TMDs) MX2 (M =
Mo, W; X = S, Se) always have negative {\Delta}H, suggesting atomic ordering,
which is, however, not yet experimentally observed. Using first-principles
calculations, we find that the negative {\Delta}H of cation-mixed TMD alloys
results from the charge transfer from weak Mo-X to nearest strong W-X bonds and
the negative {\Delta}H of anion-mixed TMD alloys comes from the larger energy
gain due to the charge transfer from Se to nearest S atoms than the energy cost
due to the lattice mismatch. Consequently, cation-mixed and anion-mixed alloys
should energetically prefer to have Mo-X-W and S-M-Se ordering, respectively.
The atomic ordering, however, is only locally ordered but disordered in the
long range due to the symmetry of TMD monolayers, as demonstrated by many
energetically degenerate structures for given alloy compositions. Besides, the
local ordering and disordering effects on the macroscopic properties such as
bandgaps and optical absorptions are negligible, making the experimental
observation of locally ordered TMD alloys challenging. We propose to take the
advantage of microscopic properties such as defects which strongly depend on
local atomic configurations for experiments to identify the disordering and
local ordering in TMD alloys. Finally, quaternary TMD alloys by mixing both
cations and anions are studied to have a wide range of bandgaps for
optoelectronic applications. Our work is expected to help the formation and
utilization of TMD alloys. | 1710.05064v1 |
2024-01-15 | Impact of boron atom clustering on the electronic structure of (B,In)N alloys | Tailoring the electronic and optical properties of nitride-based alloys for
optoelectronic applications in the ultraviolet and red spectral range has
attracted significant attention in recent years. Adding boron nitride (BN) to
indium gallium nitride, (In,Ga)N, alloys, can help to control the lattice
mismatch between (In,Ga)N and GaN and may thus allow reduction of strain
related defect formation. However, understanding of the impact of BN on the
electronic properties of III-N alloys, in particular the influence of
experimentally observed boron atom clustering, is sparse. This work presents
first-principles calculations investigating the electronic properties of
(B,In)N alloys with boron contents between 2% and 7%. Special attention is paid
to the impact of the alloy microstructure. While the results show that the
lattice constants of such alloys largely agree with lattice constants
determined from a Vegard approximation, the electronic properties strongly
depend on the local boron atom configurations. For instance, if boron atoms are
dispersed throughout the structure and are not sharing nitrogen atoms, the band
gap of (B,In)N alloys is largely unaffected and stays close to the gap of
pristine InN. However, in the case of boron atom clustering, e.g., when boron
atoms are sharing nitrogen atoms, the band gap can be strongly reduced, often
leading to a metallic state in (B,In)N alloys. These strong band gap reductions
are mainly driven by carrier localization effects in the valence band. The
calculations thus show that the electronic structure of (B,In)N alloys strongly
depends on the alloy microstructure and that boron atom clustering plays an
important role in understanding the electronic and optical properties of these
emerging materials. | 2401.07623v1 |
2010-02-28 | Tunable Multifunctional Topological Insulators in Ternary Heusler Compounds | Recently the Quantum Spin Hall effect (QSH) was theoretically predicted and
experimentally realized in a quantum wells based on binary semiconductor
HgTe[1-3]. QSH state and topological insulators are the new states of quantum
matter interesting both for fundamental condensed matter physics and material
science[1-11]. Many of Heusler compounds with C1b structure are ternary
semiconductors which are structurally and electronically related to the binary
semiconductors. The diversity of Heusler materials opens wide possibilities for
tuning the band gap and setting the desired band inversion by choosing
compounds with appropriate hybridization strength (by lattice parameter) and
the magnitude of spin-orbit coupling (by the atomic charge). Based on the
first-principle calculations we demonstrate that around fifty Heusler compounds
show the band inversion similar to HgTe. The topological state in these
zero-gap semiconductors can be created by applying strain or by designing an
appropriate quantum well structure, similar to the case of HgTe. Many of these
ternary zero-gap semiconductors (LnAuPb, LnPdBi, LnPtSb and LnPtBi) contain the
rare earth element Ln which can realize additional properties ranging from
superconductivity (e. g. LaPtBi[12]) to magnetism (e. g. GdPtBi[13]) and
heavy-fermion behavior (e. g. YbPtBi[14]). These properties can open new
research directions in realizing the quantized anomalous Hall effect and
topological superconductors. | 1003.0193v1 |
2015-04-07 | Thermal Expansion of Ni-Ti-Sn Heusler and Half-Heusler Materials from First Principles Calculations and Experiments | We coupled first principles calculations and the quasiharmonic approximation
combined with experiments (X-Ray diffraction and dilatometry measurements) to
determine the thermal properties of NiTiSn (half-Heusler) and Ni2TiSn (Heusler)
compounds. These properties are important especially if they are to be used in
thermoelectric applications. First, the calculation of their mode Gruneisen
parameter shows that it is positive throughout the first Brillouin zone. This
suggests that these compounds undergo a regular thermal expansion. Then, the
calculation of the Ni2TiSn thermal expansion shows an excellent agreement, even
in the high temperature range, with our high energy powder X-Ray diffraction
measurements (ESRF) and dilatometry experiments. In the case of NiTiSn, this
agreement is less impressive. This could be due to stronger phonon-phonon
interactions that are not considered within the quasiharmonic approximation,
but also to the difficulty of making high-quality NiTiSn samples. Finally, the
constant-pressure and constant-volume heat capacities have been calculated for
both compounds and compared with the experimental data reported in the
literature. In particular, we have decomposed the constant-volume heat capacity
of Ni2TiSn into a purely electronic and a phonon-mediated contribution, and we
discuss each of them. | 1504.01606v1 |
2016-04-06 | Anomalous Hall effect in Weyl semimetal half Heusler compounds RPtBi (R = Gd and Nd) | Topological materials ranging from topological insulators to Weyl and Dirac
semimetals form one of the most exciting current fields in condensed-matter
research. Many half-Heusler compounds, RPtBi (R= rare earth) have been
theoretically predicted to be topological semimetals. Among various topological
attributes envisaged in RPtBi, topological surface states, chiral anomaly and
planar Hall effect have been observed experimentally. Here, we report on an
unusual intrinsic anomalous Hall effect (AHE) in the antiferromagnetic Heusler
Weyl semimetal compounds GdPtBi and NdPtBi that is observed over a wide
temperature range. In particular, GdPtBi exhibits an anomalous Hall
conductivity of up to 60 ohm-1cm-1 and an anomalous Hall angle as large as 23%.
Muon spin resonance (mu-SR) studies of GdPtBi indicate a sharp
antiferromagnetic transition (T_N) at 9 K without any noticeable magnetic
correlations above T_N. Our studies indicate that Weyl points in these
half-Heuslers are induced by a magnetic field via exchange-splitting of the
electronic bands at or near to the Fermi energy which is the source of the
chiral anomaly and the AHE. | 1604.01641v2 |
2018-01-09 | Epitaxial Heusler Superlattice Co2MnAl/Fe2MnAl with Perpendicular Magnetic Anisotropy and Termination-Dependent Half-Metallicity | Single-crystal Heusler atomic-scale superlattices that have been predicted to
exhibit perpendicular magnetic anisotropy and half-metallicity have been
successfully grown by molecular beam epitaxy. Superlattices consisting of
full-Heusler Co$_2$MnAl and Fe$_2$MnAl with one to three unit cell periodicity
were grown on GaAs (001), MgO (001), and Cr (001)/MgO (001). Electron energy
loss spectroscopy maps confirmed clearly segregated epitaxial Heusler layers
with high cobalt or high iron concentrations for samples grown near room
temperature on GaAs (001). Superlattice structures grown with an excess of
aluminum had significantly lower thin film shape anisotropy and resulted in an
out-of-plane spin reorientation transition at temperatures below 200 K for
samples grown on GaAs (001). Synchrotron-based spin resolved photoemission
spectroscopy found that the superlattice structure improves the Fermi level
spin polarization near the X point in the bulk Brillouin zone. Stoichiometric
Co$_2$MnAl terminated superlattice grown on MgO (001) had a spin polarization
of 95%, while a pure Co$_2$MnAl film had a spin polarization of only 65%. | 1801.02787v1 |
2018-01-11 | Structural, elastic, electronic, magnetic and thermoelectric properties of new quaternary Heusler compounds CoZrMnX (X=Al, Ga, Ge, In) | We have performed a comprehensive set of first principles calculations to
study the structural, elastic, electronic, magnetic and transport properties of
new quaternary Heusler compounds CoZrMnX (X =Al, Ga, Ge, In). The results
showed that all the quaternary Heusler compounds were stable in Type(I)
structure. CoZrMnX are elastically stable and relatively hard materials.
CoZrMnAl, CoZrMnGa, and CoZrMnIn are found to be ductile and CoZrMnGe is
brittle in nature. The calculated Debye temperatures of all compounds are
relatively high. The electronic structure calculations reveal that CoZrMnAl is
nearly half metallic, CoZrMnGa and CoZrMnIn are metallic, and CoZrMnGe is a
narrow indirect bandgap semiconductor. The calculated magnetic properties
implies that CoZrMnAl, CoZrMnGa, and CoZrMnIn are ferromagnetic while CoZrMnGe
is non-magnetic material. The CoZrMnAl is highly spin-polarized (96%) and
CoZrMnGe is non-spin-polarized. Seebeck coefficent (S) in CoZrMnGe is
relatively high (-106 {\mu}V/K at 650K) due to its semiconducting nature. The
calculated thermoelectric figure of merit CoZrMnGe is 0.1 at 600K and for
CoZrMnIn it is also 0.1 at 900 K. We hope our interesting results will inspire
experimentalist to synthesis the new quaternary Heusler compounds CoZrMnX (X
=Al, Ga, Ge, In). | 1801.03719v1 |
2018-03-01 | Observation of Dirac state in half-Heusler material YPtBi | The prediction of non-trivial topological electronic states hosted by
half-Heusler compounds makes them prime candidates for discovering new physics
and devices as they harbor a variety of electronic ground states including
superconductivity, magnetism, and heavy fermion behavior. Here we report normal
state electronic properties of a superconducting half-Heusler compound YPtBi
using angle-resolved photoemission spectroscopy (ARPES). Our data reveal the
presence of a Dirac state at the zone center of the Brillouin zone at 500 meV
below the chemical potential. We observe the presence of multiple Fermi surface
pockets including two concentric hexagonal and six half oval shaped pockets at
the gamma and K points of the Brillouin zone, respectively. Furthermore, our
measurements show Rashba-split bands and multiple surface states crossing the
chemical potential which are supported by the first-principles calculations.
Our finding of a Dirac state in YPtBi plays a significant role in establishing
half-Heusler compounds as a new potential platform for novel topological phases
and explore their connection with superconductivity. | 1803.00589v1 |
2017-02-27 | Large magnetocrystalline anisotropy in tetragonally distorted Heuslers: a systematic study | With a view to the design of hard magnets without rare earths we explore the
possibility of large magnetocrystalline anisotropy energies in Heusler
compounds that are unstable with respect to a tetragonal distortion. We
consider the Heusler compounds Fe$_2$YZ with Y = (Ni, Co, Pt), and Co$_2$YZ
with Y = (Ni, Fe, Pt) where, in both cases, Z = (Al, Ga, Ge, In, Sn). We find
that for the Co$_2$NiZ, Co$_2$PtZ, and Fe$_2$PtZ families the cubic phase is
always, at $T=0$, unstable with respect to a tetragonal distortion, while, in
contrast, for the Fe$_2$NiZ and Fe$_2$CoZ families this is the case for only 2
compounds -- Fe$_2$CoGe and Fe$_2$CoSn. For all compounds in which a tetragonal
distortion occurs we calculate the MAE finding remarkably large values for the
Pt containing Heuslers, but also large values for a number of the other
compounds (e.g. Co$_2$NiGa has an MAE of -2.11~MJ/m$^3$). The tendency to a
tetragonal distortion we find to be strongly correlated with a high density of
states at the Fermi level in the cubic phase. As a corollary to this fact we
observe that upon doping compounds for which the cubic structure is stable such
that the Fermi level enters a region of high DOS, a tetragonal distortion is
induced and a correspondingly large value of the MAE is then observed. | 1702.08150v1 |
2019-09-27 | Surface Reconstructions of Heusler Compounds in the Ni-Ti-Sn (001) System | As progress is made on thin-film synthesis of Heusler compounds, a more
complete understanding of the surface will be required to control their
properties, especially as functional heterostructures are explored. Here, the
surface reconstructions of semiconducting half-Heusler NiTiSn(001), and
Ni1+xTiSn(001) (x=0.0-1.0) are explored as a way to optimize growth conditions
during molecular beam epitaxy. Density functional theory (DFT) calculations
were carried out to guide the interpretation of the experimental results. For
NiTiSn(001) a c(2x2) surface reconstruction was observed for Sn rich samples,
while a (1x1) unreconstructed surface was observed for Ti-rich samples. A
narrow range around 1:1:1 stoichiometry exhibited a (2x1) surface
reconstruction. Electrical transport is used to relate the observed reflection
high energy electron diffraction (RHEED) pattern during and after growth with
carrier concentration and stoichiometry. Scanning tunneling microscopy and
RHEED were used to examine surface reconstructions, the results of which are in
good agreement with density functional calculations. X-ray photoelectron
spectroscopy was used to determine surface termination and stoichiometry.
Atomic surface models are proposed, which suggest Sn-dimers form in
reconstructed Ni1+xTiSn(001) half-Heusler surfaces (x<0.25) with a transition
to Ni terminated surfaces for x > 0.25. | 1909.12487v1 |
2020-02-11 | A simple model for vacancy order and disorder in defective half-Heusler systems | Defective half-Heusler systems X(1-x)YZ with large amounts of intrinsic
vacancies, such as Nb(1-x)CoSb, Ti(1-x)NiSb and V(1-x)CoSb, are a group of
promising thermoelectric materials. Even with high vacancy concentrations they
maintain the average half-Heusler crystal structure. These systems show high
electrical conductivity but low thermal conductivity arising from an ordered YZ
lattice, which conducts electrons, while the large amounts of vacancies on the
X sublattice effectively scatters phonons. Using electron scattering it was
recently observed that in addition to Bragg diffraction from the average cubic
half-Heusler structure, some of these samples show broad diffuse scattering
indicating short-range vacancy order while other samples show sharp additional
peaks, indicating long-range vacancy ordering. Here we show that both the short
and long-range ordering can be explained using the same simple model, which
assumes that vacancies on the X-sublattice avoid each other. The samples
showing long-range vacancy order are in agreement with the predicted
ground-state of the model, while short-range order samples are quenched
high-temperature states of the system. A previous study showed that changes in
sample stoichiometry affect whether the short or long-range vacancy structure
is obtained, but the present model suggests that thermal treatment of samples
should allow controlling the degree of vacancy order, and thereby the thermal
conductivity, without changes in composition. This is important as the
composition also dictates the amount of electrical carriers. Independent
control of electrical carrier concentration and degree of vacancy order should
allow further improvements in the thermoelectric properties of these systems. | 2002.04281v2 |
2020-11-16 | A high throughput search of efficient thermoelectric half-Heusler compounds | Half-Heusler compounds have emerged as promising thermoelectric materials
that offer huge compositional space to tune their thermoelectric performance. A
class of stable half Heusler compounds formed from elements of three specific
groups in the periodic table viz.
X$_{p}$X$'_{1-p}$Y$_{q}$Y$'_{1-q}$Z$_{r}$Z$'_{1-r}$ (with X, X$'$= Ti, Zr, Hf,
Y, Y$'$ = Ni, Pd, Pt and Z, Z$'$ = Ge, Sn, Pb and p, q, r = 0, 0.25, 0.75 and
1) via various stoichiometric isoelectronic elemental substitution at the X, Y
and Z sites respectively is investigated. Intelligent filters are employed at
each step of our high throughput density functional theory calculations to
filter compounds with improved figure of merit. While confirming several known
results, the calculations also reveal unknown pathways to improve the
thermoelectric performance of the compound class. The 50% X as well as Z site
substitution of the parent Heusler individually are found to marginally enhance
the power factor for both the $p$- and $n$-type doping, while leading to
considerable enhancement in the figure of merit (by $\sim$24 %) specifically
due to lowering of the lattice thermal conductivity because of increase in
lattice disorder in approximately the same cell volume. Furthermore, the
present study confirms the experimental scenario that Y site substitution does
not lead to enhancement of the powerfactor because of the breaking of band
degeneracies at the high symmetry points. This work will serve as a
consolidated cost effective guideline for experimentalist working with this
compound class on enhancing the powerfactor and figure of merit of the
compositions. | 2011.08134v1 |
2021-06-27 | Ferromagnetic Cr4PtGa17: A Novel Half-Heusler-Type Compound with a Breathing Pyrochlore Lattice | We describe the crystal structure and elementary magnetic properties of a
previously unreported ternary intermetallic compound, Cr4PtGa17, which
crystallizes in a rhombohedral unit cell in the noncentrosymmetric space group
R3m. The crystal structure is closely related to those of XYZ half-Heusler
compounds, where X, Y and Z are reported to be single elements only, occupying
three different face-centered cubic sublattices. The new material, Cr4PtGa17,
can be most straightforwardly illustrated by writing the formula as
(PtGa2)(Cr4Ga14)Ga (X=PtGa2, Y = Cr4Ga14, Z = Ga), that is, the X and Y sites
are occupied by clusters instead of single elements. The magnetic Cr occupies a
breathing pyrochlore lattice. Ferromagnetic ordering is found below TC ~61 K,
by both neutron diffraction and magnetometer studies, with a small, saturated
moment of ~0.25 muB/Cr observed at 2 K, making Cr4PtGa17 the first
ferromagnetically ordered material with a breathing pyrochlore lattice. A
magnetoresistance of ~140% was observed at 2 K. DFT calculations suggest that
the material has a nearly-half-metallic electronic structure. The new material,
Cr4PtGa17, the first realization of both a half-Heusler-type structure and a
breathing pyrochlore lattice, might pave a new way to achieve novel types of
half-Heusler compounds. | 2106.14296v2 |
2022-09-28 | First Principles Study of the Electronic Structure of the Ni$_2$MnIn/InAs and Ti$_2$MnIn/InSb interfaces | We present a first-principles study of the electronic and magnetic properties
of epitaxial interfaces between the Heusler compounds Ti$_2$MnIn and Ni$_2$MnIn
and the III-V semiconductors, InSb and InAs, respectively. We use density
functional theory (DFT) with a machine-learned Hubbard $U$ correction
determined by Bayesian optimization. We evaluate these interfaces for
prospective applications in Majorana-based quantum computing and spintronics.
In both interfaces, states from the Heusler penetrate into the gap of the
semiconductor, decaying within a few atomic layers. The magnetic interactions
at the interface are weak and local in space and energy. Magnetic moments of
less than 0.1 $\mu_B$ are induced in the two atomic layers closest to the
interface. The induced spin polarization around the Fermi level of the
semiconductor also decays within a few atomic layers. The decisive factor for
the induced spin polarization around the Fermi level of the semiconductor is
the spin polarization around the Fermi level in the Heusler, rather than the
overall magnetic moment. As a result, the ferrimagnetic narrow-gap
semiconductor Ti$_2$MnIn induces a more significant spin polarization in the
InSb than the ferromagnetic metal Ni$_2$MnIn induces in the InAs. This is
explained by the position of the transition metal $d$ states in the Heusler
with respect to the Fermi level. Based on our results, these interfaces are
unlikely to be useful for Majorana devices but could be of interest for
spintronics. | 2209.14101v3 |
2023-02-07 | Colossal anomalous Hall and Nernst effect from the breaking of nodal-line symmetry in Cu2CoSn Weyl semimetal: A first-principles study | The presence of topological band crossings near the Fermi energy is essential
for the realization of large anomalous transport properties in the materials.
The topological semimetals (TSMs) host such properties owing to their unique
topological band structure such as Weyl points or nodal lines (NLs), that is
protected by certain symmetries of the crystal. When the NLs break out in the
system due to perturbation in Hamiltonian, a large Berry curvature arises in
the surrounding area of the gapped NL. In the present work, we studied
anomalous transport properties of Cu2CoSn compound, which has a cubic Heusler
crystal structure (space group: Fm-3m). The Cu2CoSn full Heusler compound
possesses three NLs in the absence of spin-orbit coupling close to the Fermi
level. These NLs gap out with the consideration of the SOC and a large Berry
curvature observed along the gapped NLs. The integral of Berry curvature gives
the intrinsic anomalous Hall conductivity (AHC) about 1003 S/cm and the
anomalous Nernst conductivity (ANC) of about 3.98 A/m-K at the Fermi level.
These values of AHC and ANC are comparable to the largest reported values for
the Co2MnGa Heusler compound. Therefore, Cu2CoSn becomes a newborn member of
the family of full Heusler compounds, which possesses giant AHC and ANC that
can be useful for the spintronics application. | 2302.03279v1 |
2023-02-09 | Spin-polarized two-dimensional electron/hole gas at the interface of non-magnetic semiconducting half-Heusler compounds: Modified Slater-Pauling rule for half-metallicity at the interface | Half-Heusler compounds with 18 valence electrons per unit cell are well-known
non-magnetic semiconductors. Employing first-principles electronic band
structure calculations, we study the interface properties of the half-Heusler
heterojunctions based on FeVSb, CoTiSb, CoVSn, and NiTiSn compounds, which
belong to this category of materials. Our results show that several of these
heterojunction interfaces become not only metallic but also magnetic. The
emergence of spin-polarization is accompanied by the formation of
two-dimensional electron gas (2DEG) or hole gas (2DHG) at the interface. We
qualitatively discuss the origin of the spin polarization at the interfaces on
the basis of the Stoner model. For the cases of magnetic interfaces where
half-metallicity is also present, we propose a modified Slater-Pauling rule
similar to the one for bulk half-metallic half-Heusler compounds. Additionally,
we calculate exchange parameters, Curie temperatures and magnetic anisotropy
energies for magnetic interfaces. Our study, combined with the recent
experimental evidence for the presence of 2DEG at CoTiSb/NiTiSn heterojunctions
might motivate future efforts and studies toward the experimental realization
of devices using the proposed heterojunctions. | 2302.04563v1 |
2023-03-17 | Intrinsic and extrinsic anomalous transport properties of Heusler ferromagnets Fe$_2$CoAl and Fe$_2$NiAl from first principles | Recently, Heusler ferromagnets have been found to exhibit unconventional
anomalous electric, thermal, and thermoelectric transport properties. In this
study, we employed first-principles density functional theory calculations to
systematically investigate both intrinsic and extrinsic contributions to the
anomalous Hall effect (AHE), anomalous Nernst effect (ANE), and anomalous
thermal Hall effect (ATHE) in two Heusler ferromagnets: Fe$_2$CoAl and
Fe$_2$NiAl. Our analysis reveals that the extrinsic mechanism originating from
disorder dominates the AHE and ATHE in Fe$_2$CoAl , primarily due to the steep
band dispersions across the Fermi energy and corresponding high longitudinal
electronic conductivity. Conversely, the intrinsic Berry phase mechanism,
physically linked to nearly flat bands around the Fermi energy and gapped by
spin-orbit interaction band crossings, governs the AHE and ATHE in Fe$_2$NiAl.
With respect to ANE, both intrinsic and extrinsic mechanisms are competing in
Fe$_2$CoAl as well as in Fe$_2$NiAl. Furthermore, Fe$_2$CoAl and Fe$_2$NiAl
exhibit tunable and remarkably pronounced anomalous transport properties. For
instance, the anomalous Nernst and anomalous thermal Hall conductivities in
Fe$_2$NiAl attain giant values of 8.29 A/Km and 1.19 W/Km, respectively, at
room temperature. To provide a useful comparison, we also thoroughly
investigated the anomalous transport properties of Co$_2$MnGa. Our findings
suggest that Heusler ferromagnets Fe$_2$CoAl and Fe$_2$NiAl are promising
candidates for spintronics and spin-caloritronics applications. | 2303.09812v2 |
2023-06-07 | Searching for ductile superconducting Heusler X2YZ compounds | Heusler compounds have always attracted a great deal of attention from
researchers thanks to a wealth of interesting properties for technological
applications. They are intermetallic ductile compounds, and some of them have
been found to be superconducting. With this in mind, we perform an extensive
study of the superconducting and elastic properties of the cubic (full-)Heusler
family. Starting from thermodynamically stable compounds, we use ab initio
methods for the calculation of the phonon spectra, electron-phonon couplings,
superconducting critical temperatures and elastic tensors. By analyzing the
statistical distributions of these properties and comparing them to
anti-perovskites we recognize universal behaviors that should be common to all
conventional superconductors while others turn out to be specific to the
material family. The resulting data is used to train interpretable and
predictive machine learning models, that are used to extend our knowledge of
superconductivity in Heuslers and to provide an interpretation of our results.
In total, we discover a total of 8 hypothetical materials with critical
temperatures above 10 K, to be compared with the current record of Tc = 4.7 K
in this family. Furthermore, we expect most of these materials to be highly
ductile, making them potential candidates for the manufacture of wires and
tapes for superconducting magnets. | 2306.04439v1 |
2023-09-14 | Chemical-substitution-driven giant anomalous Hall and Nernst effects in magnetic cubic Heusler compounds | Chemical substitution efficiently optimizes the physical properties of
Heusler compounds, especially their anomalous transport properties, including
anomalous Hall conductivity (AHC) and anomalous Nernst conductivity (ANC). This
study systematically investigates the effect of chemical substitution on AHC
and ANC in 1493 magnetic cubic Heusler compounds using high-throughput
first-principles calculations. Notable trends emerge in Co- and Rh-based
compounds, where chemical substitution effectively enhances the AHC and ANC.
Intriguingly, certain chemically substituted candidates exhibit outstanding
enhancement in AHCs and ANCs, such as (Co$_{0.8}$Ni$_{0.2}$)$_2$FeSn with
considerable AHC and ANC values of $-2567.78$ S cm$^{-1}$ and $8.27$ A
m$^{-1}$K$^{-1}$, respectively, and (Rh$_{0.8}$Ru$_{0.2}$)$_2$MnIn with an AHC
of $1950.49$ S cm$^{-1}$. In particular, an extraordinary ANC of $8.57$ A
m$^{-1}$K$^{-1}$ is identified exclusively in Rh$_2$Co$_{0.7}$Fe$_{0.3}$In,
nearly double the maximum value of $4.36$ A m$^{-1}$K$^{-1}$ observed in the
stoichiometric Rh$_2$CoIn. A comprehensive band structure analysis underscores
that the notable enhancement in ANC arises from the creation and modification
of the energy-dependent nodal lines through chemical substitution. This
mechanism generates a robust Berry curvature, resulting in significant ANCs.
These findings emphasize the pivotal role of chemical substitution in
engineering high-performance materials, thereby expanding the horizons of
transport property optimization within Heusler compounds. | 2309.07722v3 |
2023-10-24 | Tuning the topological character of half-Heusler systems: A comparative study on Y$T$Bi ($T$ = Pd, Pt) | Half-Heusler systems host a plethora of different ground states, especially
with non-trivial topology. However, there is still a lack of spectroscopic
insight into the corresponding band inversion in this family. In this work, we
locally explore the half-Heuslers Y$T$Bi ($T =$ Pt and Pd) by means of scanning
tunneling microscopy/spectroscopy. From our analysis of the (120) surface
plane, we infer that the increase of the spin--orbit coupling upon going from
Pd to Pt is the main player in tuning the surface states from trivial to
topologically non-trivial. Our measurements unveil a ($2 \times 1$)
reconstruction of the (120) surface of both systems. Using density functional
theory calculations, we show that the observed different behavior of the local
density of states near the Fermi level in these two materials is directly
related to the presence of metallic surface states. Our work sheds new light on
a well known tunable family of materials and opens new routes to explore the
presence of topological states of matter in half-Heusler systems and its
microscopic observation. | 2310.15708v1 |
2023-11-10 | Strong-coupling superconductivity of the Heusler-type compound ScAu2Al: Ab-initio studies | The ScAu$_2$Al superconducting Heusler-type compound was recently
characterized to have the highest critical temperature of $T_c = 5.12$ K and
the strongest electron-phonon coupling among the Heusler family. In this work,
the electronic structure, phonons, electron-phonon coupling, and
superconductivity of ScAu$_2$Al are studied using \textit{ab initio}
calculations. The spin-orbit coupling significantly changes the electronic
structure removing the van Hove singularity from the vicinity of the Fermi
level. In the phonon spectrum, low frequency acoustic modes, additionally
softened by the spin-orbit interaction, strongly couple with electrons, leading
to the electron-phonon coupling constant $\lambda=1.25$, a record high among
Heuslers. The density functional theory for superconductors is then used to
analyze superconducting {state in this two-band superconductor}. The effect of
spin fluctuations (SF) on superconductivity is also analyzed. The calculated
critical temperatures of $T_c = 5.16$ K (4.79 K with SF) agree very well with
the experiment, confirming the electron-phonon mechanism of superconductivity
and showing a weak spin-fluctuations effect. The superconducting gaps formed on
two Fermi surface sheets exhibit moderate anisotropy. Their magnitudes confirm
the strong coupling regime, as the reduced average values are $2\Delta_1/k_BT_c
\simeq 4.1$ and $2\Delta_2/k_BT_c \simeq 4.3$. Anisotropy of the gaps and large
spread in their values significantly affect the calculated quasiparticle
density of states. | 2311.06075v3 |
2006-11-07 | Calculated electronic and magnetic properties of the half-metallic, transition metal based Heusler compounds | In this work, results of {\it ab-initio} band structure calculations for
$A_2BC$ Heusler compounds that have $A$ and $B$ sites occupied by transition
metals and $C$ by a main group element are presented. This class of materials
includes some interesting half-metallic and ferromagnetic properties. The
calculations have been performed in order to understand the properties of the
minority band gap and the peculiar magnetic behavior found in these materials.
Among the interesting aspects of the electronic structure of the materials are
the contributions from both $A$ and $B$ atoms to states near the Fermi energy
and to the total magnetic moment. The magnitude of the total magnetic moment,
which depends as well on the kind of $C$ atoms, shows a trend consistent with
the Slater-Pauling type behavior in several classes of these compounds. The
localized moment in these magnetic compounds resides at the $B$ site. Other
than in the classical Cu$_2$-based Heusler compounds, the $A$ atoms in Co$_2$,
Fe$_2$, and Mn$_2$ based compounds may contribute pronounced to the total
magnetic moment. | 0611179v1 |
2009-04-27 | Exchange stiffness in Co$_{2}$-based Heusler compounds | We determine the spin wave exchange stiffness $D$ and the exchange constant
$A$ for the full Heusler compound \CFS using Brillouin light scattering
spectroscopy. We find an extraordinarily large value of $D=715\pm20$ meV
\AA$^2$ ($A=31.5\pm1.0$ pJ/m) which is, to the best of our knowledge, only
surpassed by the intermetallic compound Fe$_{53}$Co$_{47}$ (J. Appl. Phys.
\textbf{75}, 7021 (1994)). Furthermore, we provide a systematization of the
exchange stiffnesses determined for a variety of Co$_2$-based Heusler
compounds. We find that for the investigated compounds, the exchange stiffness
is a function of the valence electron concentration and the crystallographic
ordering. The exchange stiffness increases when the valence electron
concentration and/or the amount of the L2$_1$ ordering increase. A qualitative
explanation for the dependence on the valence electron concentration is
provided. | 0904.4194v1 |
2010-04-07 | Single-Dirac-cone Z2 topological insulator phases in distorted Li2AgSb-class and related quantum critical Li-based spin-orbit compounds | We have extended our new materials class search for the experimental
realization of Z2 topological insulators from binary [Bi2Se3-class, Xia et.al.,
Nature Phys. 5, 398 (2009)] and the ternary [Half-Heusler class, Lin et.al.,
arXiv:1003.0155v1 (2010); arXiv:1003.2615v1 (2010)] series to non-Heusler
Li-based ternary intermetallic series Li2M'X ($M'$=Cu, Ag, and Au, $X$=Sb and
Bi) with CuHg2Ti-type structure. We discovered that the distorted-Li2AgSb is a
lightweight compound harboring a 3D topological insulator state with Z2=-1
although the groundstate lies near a critical point, whereas the related
Li2CuSb-type compounds are topologically trivial. Non-Heusler ternary Li2M'X
series (with a number of variant compounds) we identified here is a new
platform for deriving novel stoichiometric compounds, artificial
quantum-well/heterostructures, nano-wires, nano-ribbons and nanocrystals. We
have grown some of these bulk materials (experimental results will be reported
separately). | 1004.0999v1 |
2010-07-31 | Half-Heusler Compounds as a New Class of Three-Dimensional Topological Insulators | Using first-principles calculations within density functional theory, we
explore the feasibility of converting ternary half-Heusler compounds into a new
class of three-dimensional topological insulators (3DTI). We demonstrate that
the electronic structure of unstrained LaPtBi as a prototype system exhibits
distinct band-inversion feature. The 3DTI phase is realized by applying a
uniaxial strain along the [001] direction, which opens a bandgap while
preserving the inverted band order. A definitive proof of the strained LaPtBi
as a 3DTI is provided by directly calculating the topological Z2 invariants in
systems without inversion symmetry. We discuss the implications of the present
study to other half-Heusler compounds as 3DTI, which, together with the
magnetic and superconducting properties of these materials, may provide a rich
platform for novel quantum phenomena. | 1008.0057v1 |
2010-11-05 | Magnetic microstructure and magnetotransport in Co2FeAl Heusler compound thin films | We correlate simultaneously recorded magnetotransport and spatially resolved
magneto optical Kerr effect (MOKE) data in Co2FeAl Heusler compound thin films
micropatterned into Hall bars. Room temperature MOKE images reveal the
nucleation and propagation of domains in an externally applied magnetic field
and are used to extract a macrospin corresponding to the mean magnetization
direction in the Hall bar. The anisotropic magnetoresistance calculated using
this macrospin is in excellent agreement with magnetoresistance measurements.
This suggests that the magnetotransport in Heusler compounds can be adequately
simulated using simple macrospin models, while the magnetoresistance
contribution due to domain walls is of negligible importance. | 1011.1417v1 |
2011-07-31 | Room-temperature generation of giant pure spin currents using Co$_2$FeSi spin injectors | Generation, manipulation, and detection of a pure spin current, i.e., the
flow of spin angular momentum without a charge current, are prospective
approaches for realizing next-generation spintronic devices with ultra low
electric power consumptions. Conventional ferromagnetic electrodes such as Co
and NiFe have so far been utilized as a spin injector for generating the pure
spin currents in nonmagnetic channels. However, the generation efficiency of
the pure spin currents is extremely low at room temperature, giving rise to a
serious obstacle for device applications. Here, we demonstrate the generation
of giant pure spin currents at room temperature in lateral spin valve devices
with a highly ordered Heusler-compound Co$_2$FeSi spin injector. The generation
efficiency of the pure spin currents for the Co$_2$FeSi spin injectors reaches
approximately one hundred times as large as that for NiFe ones, indicating that
Heusler-compound spin injectors enable us to materialize a high-performance
lateral spin device. The present study is a technological jump in spintronics
and indicates the great potential of ferromagnetic Heusler compounds with half
metallicity for generating pure spin currents. | 1108.0156v2 |
2011-11-03 | Estimation of the spin polarization for Heusler-compound thin films by means of nonlocal spin-valve measurements: Comparison of Co$_{2}$FeSi and Fe$_{3}$Si | We study room-temperature generation and detection of pure spin currents
using lateral spin-valve devices with Heusler-compound electrodes, Co$_{2}$FeSi
(CFS) or Fe$_{3}$Si (FS). The magnitude of the nonlocal spin-valve (NLSV)
signals is seriously affected by the dispersion of the resistivity peculiarly
observed in the low-temperature grown Heusler compounds with ordered
structures. From the analysis based on the one-dimensional spin diffusion
model, we find that the spin polarization monotonically increases with
decreasing the resistivity, which depends on the structural ordering, for both
CFS and FS electrodes, and verify that CFS has relatively large spin
polarization compared with FS. | 1111.0742v2 |
2012-10-17 | GW study of the half-metallic Heusler compounds Co2MnSi and Co2FeSi | Quasiparticle spectra of potentially half-metallic Co2MnSi and Co2FeSi
Heusler compounds have been calculated within the one-shot GW approximation in
an all-electron framework without adjustable parameters. For Co2FeSi the
many-body corrections are crucial: a pseudogap opens and good agreement of the
magnetic moment with experiment is obtained. Otherwise, however, the changes
with respect to the density-functional-theory starting point are moderate. For
both cases we find that photoemission and x-ray absorption spectra are well
described by the calculations. By comparison with the GW density of states, we
conclude that the Kohn-Sham eigenvalue spectrum provides a reasonable
approximation for the quasiparticle spectrum of the Heusler compounds
considered in this work. | 1210.4776v1 |
2012-10-29 | Modified Becke-Johnson potential investigation of half-metallic Heusler compounds | We have investigated the electronic structures of various potentially
half-metallic Heusler compounds with the Tran-Blaha modified Becke-Johnson
(TB-mBJLDA) potential within the density functional theory. The half-metallic
gaps are considerably enhanced with respect to values from the
Perdew-Burke-Ernzerhof (PBE) functional. In particular the unoccupied densities
of states are modified by mBJLDA, and agreement with experiment is considerably
worse than for PBE. The agreement of the densities of states can be improved by
reducing the Tran-Blaha parameter c. However, ground state properties such as
the hyperfine fields are more accurately described by PBE than by mBJLDA.
Despite its success for ionic and covalent semiconductors and insulators, we
conclude that mBJLDA is not a suitable approximation for half-metallic Heusler
compounds. | 1210.7738v1 |
2012-11-02 | Interface characterization of Co2MnGe/Rh2CuSn Heusler multilayers | All-Heusler multilayer structures have been investigated by means of high
kinetic x-ray photoelectron spectroscopy and x-ray magnetic circular dichroism,
aiming to address the amount of disorder and interface diffusion induced by
annealing of the multilayer structure. The studied multilayers consist of
ferromagnetic Co$_2$MnGe and non-magnetic Rh$_2$CuSn layers with varying
thicknesses. We find that diffusion begins already at comparably low
temperatures between 200 $^{\circ}$C and 250 $^{\circ}$C, where Mn appears to
be most prone to diffusion. We also find evidence for a 4 {\AA} thick
magnetically dead layer that, together with the identified interlayer
diffusion, are likely reasons for the small magnetoresistance found for
current-perpendicular-to-plane giant magneto-resistance devices based on this
all-Heusler system. | 1211.0489v2 |
2013-03-03 | High spin polarization of the anomalous Hall current in Co-based Heusler compounds | Based on first principles density functional calculations of the intrinsic
anomalous and spin Hall conductivities, we predict that the charge Hall current
in Co-based full Heusler compounds Co$_2$XZ (X = Cr and Mn; Z = Al, Si, Ga, Ge,
In and Sn) except Co$_2$CrGa would be almost fully spin-polarized even although
Co$_2$MnAl, Co$_2$MnGa, Co$_2$MnIn and Co$_2$MnSn do not have a half-metallic
band structure. Furthermore, the ratio of the associated spin current to the
charge Hall current is slightly larger than 1.0. This suggests that these
Co-based Heusler compounds, especially Co$_2$MnAl, Co$_2$MnGa and Co$_2$MnIn
which are found to have large anomalous and spin Hall conductivities, might be
called anomalous Hall half-metals and could have valuable applications in
spintronics such as spin valves as well as magnetoresistive and spin-torque
driven nanodevices. These interesting findings are discussed in terms of the
calculated electronic band structures, magnetic moments and also anomalous and
spin Hall conductivities as a function of the Fermi level. | 1303.0509v1 |
2013-07-11 | Large Linear Magnetoresistance and Shubnikov-de Hass Oscillations in Single Crystals of YPdBi Heusler Topological Insulators | We report the observation of a large linear magnetoresistance (MR) and
Shubnikov-de Hass (SdH) quantum oscillations in single crystals of YPdBi
Heusler topological insulators. Owning to the successfully obtained the
high-quality YPdBi single crystals, large non-saturating linear MR of as high
as 350% at 5K and over 120% at 300 K under a moderate magnetic field of 7 T is
observed. In addition to the large, field-linear MR, the samples exhibit
pronounced SdH quantum oscillations at low temperature. Analysis of the SdH
data manifests that the high-mobility bulk electron carriers dominate the
magnetotransport and are responsible for the observed large linear MR in YPdBi
crystals. These findings imply that the Heusler-based topological insulators
have superiorities for investigating the novel quantum transport properties and
developing the potential applications. | 1307.3022v1 |
2013-07-25 | Plasmon dispersions in simple metals and Heusler compounds | We present a comprehensive study of plasmon dispersions in simple metals and
Heusler compounds based on an accurate ab-initio evaluation of the momentum and
frequency dependent dielectric function in the random-phase approximation.
Using a momentum-dependent tetrahedron method for the computation of the
dielectric function, we extract and analyze "full" and "intraband" plasmon
dispersions: The "full" plasma dispersion is obtained by including all bands,
the intraband plasma dispersion by including only intraband transitions. For
the simple metals silver and alu- minum, we show that the intraband plasmon
dispersion has an unexpected downward slope and is therefore markedly different
from the results of an effective-mass electron-gas model and the full plasmon
dispersion. For the two Heusler compounds Co2FeSi and Co2MnSi, we present
spectra for the dielectric function, their loss functions and plasmon
dispersions. The latter exhibit the same negative intraband plasmon dispersion
as found in the simple metals. We also discuss the influence of spin-mixing on
the plasmon dispersion. | 1307.6844v1 |
2013-10-17 | A new class of topological insulators from I-III-IV half-Heusler compounds with strong band inversion strength | In this paper, by first principle calculations, we investigate systematically
the band topology of a new half-Heusler family with composition of
I(A)-III(A)-IV(A). The results clearly show that many of the I-III-IV
half-Heusler compounds are in fact promising to be topological insulator
candidates. The characteristic feature of these new topological insulators is
the naturally strong band inversion strength (up to -2eV) without containing
heavy elements. Moreover, we found that both the band inversion strength and
the topological insulating gap can be tailored through strain engineering, and
therefore would be grown epitaxially in the form of films, and useful in
spintronics and other applications. | 1310.4696v1 |
2014-08-25 | Nanograined half-Heusler semiconductors as advanced thermoelectrics: an ab-initio high-throughput statistical study | Nanostructuring has spurred a revival in the field of direct thermoelectric
energy conversion. Nanograined materials can now be synthesized with higher
figures of merit (ZT) than the bulk counterparts. This leads to increased
conversion efficiencies. Despite considerable effort in optimizing the known
and discovering the unknown, technology still relies upon a few limited
solutions. Here we perform ab-initio modeling of ZT for 75 nanograined
compounds obtained by filtering down the 79,057 half-Heusler entries available
in the AFLOWLIB.org repository according to electronic and thermodynamic
criteria. For many of the compounds the $ZT$s are markedly above those
attainable with nanograined IV and III-V semiconductors. About 15% of them may
even outperform ZT~2 at high temperatures. Our analysis elucidates the origin
of the advantageous thermoelectric properties found within this broad material
class. We use machine learning techniques to unveil simple rules determining if
a nanograined half-Heusler compound is likely to be a good thermoelectric given
its chemical composition. | 1408.5859v1 |
2015-02-06 | Long-term stability of phase-separated Half-Heusler compounds | Half-Heusler (HH) compounds have shown high Figure of merits up to 1.5. The
key to these high thermoelectric efficiencies is an intrinsic phase separation,
which occurs in multicomponent Half-Heusler compounds and leads to an
significantly reduction of the thermal conductivity. For commercial
applications, compatible n- and p-type materials are essential and their
thermal stability under operating conditions, e.g. for an automotive up to 873
K, needs to be guaranteed. For the first time, the long-term stability of n-
and p-type HH materials is proved. We investigated HH materials based on the
Ti0.3Zr0.35Hf0.35NiSn-system after 500 cycles (1700 h) from 373 to 873 K. Both
compounds exhibit a maximum Seebeck coefficient of S around 210 muV/K and an
intrinsic phase separation into two HH phases. The dendritic microstructure is
temperature resistant and maintained the low thermal conductivity values (kappa
less than 4 W/Km). Our results emphasize that phase-separated HH compounds are
suitable low cost materials and can lead to enhanced thermoelectric
efficiencies beyond the set benchmark for industrial applications. | 1502.01828v1 |
2015-06-11 | Magnetism in tetragonal manganese-rich Heusler compounds | A comprehensive study of the total energy of manganese-rich Heusler compounds
using density functional theory is presented. Starting from a large set of
cubic parent systems, the response to tetragonal distortions is studied in
detail. We single out the systems that remain cubic from those that most likely
become tetragonal. The driving force of the tetragonal distortion and its
effect on the magnetic properties, especially where they deviate from the
Slater--Pauling rule, as well as the trends in the Curie temperatures, are
highlighted. By means of partial densities of states, the electronic structural
changes reveal the microscopic origin of the observed trends. We focus our
attention on the magnetocrystalline anisotropy and find astonishingly high
values for tetragonal Heusler compounds containing heavy transition metals
accompanied by low magnetic moments, which indicates that these materials are
promising candidates for spin-transfer torque magnetization-switching
applications. | 1506.03735v1 |
2015-07-30 | First principle investigations of the structural, electronic and magnetic properties of the new zirconium based full-Heusler compounds, Zr2MnZ (Z = Al, Ga and In) | The crystal structure, electronic and magnetic properties of the new
full-Heusler compounds Zr2MnZ (Z=Al, Ga, In), were studied within the Density
Functional Theory (DFT) framework. The materials exhibit unique properties that
connect the spin gapless semiconducting character with the completely
compensated ferrimagnetism. In magnetic configurations, Zr2MnZ (Z=Al, Ga, In)
crystallize in inverse Heusler structure, are stable against decomposition and
have zero magnetic moment per formula unit properties, in agreement with
Slater-Pauling rule. The Zr2MnAl compound presents spin gapless semiconducting
properties with a energy band gap of 0.41 eV in the majority spin channel and a
zero band gap in the minority spin channel. By substituting Ga or In elements,
for Al in Zr2MnAl, semiconducting pseudo band gaps are formed in the majority
spin channels due to the different neighborhood around the manganese atoms,
which decreases the energy of Mn's triple degenerated anti-bonding states. | 1507.08605v2 |
2015-11-10 | Large low-field positive magnetoresistance in nonmagnetic half-Heusler ScPtBi single crystal | High-quality nonmagnetic half-Heusler ScPtBi single crystals were synthesized
by a Bi self-flux method. This compound was revealed to be a hole-dominated
semimetal with a large low-field magnetoresistance up to 240% at 2K in a
magnetic field of 1T. Magneto-transport measurements demonstrated that the
large low-field magnetoresistance effect resulted from the coexistence of
field-induced metal-semiconductor transition and weak-antilocalization effect.
Moreover, Hall measurements indicated that ScPtBi single crystal showed a high
mobility over a wide temperature region even up to room temperature (4050
cm2V-1s-1 at 2K - 2016 cm2V-1s-1 at 300K). These findings not only suggest the
nonmagnetic ScPtBi semimetal a potential material candidate for applications in
high-sensitivity magnetic sensors, but also are of great significance to
comprehensively understand the rare-earth based half-Heusler compounds. | 1511.03017v1 |
2016-01-28 | LaPtSb: a half-Heusler compound with high thermoelectric performance | The electronic and transport properties of the half-Heusler compound LaPtSb
are investigated by performing first-principles calculations combined with
semi-classical Boltzmann theory and deformation potential theory. Compared with
many typical half-Heusler compounds, the LaPtSb exhibits obviously larger power
factor at room temperature, especially for the n-type system. Together with the
very low lattice thermal conductivity, the thermoelectric figure of merit (ZT)
of LaPtSb can be optimized to a record high value of 2.2 by fine tuning the
carrier concentration. | 1601.07690v4 |
2016-04-13 | Ultralow Thermal Conductivity in Full-Heusler Semiconductors | Semiconducting half- and, to a lesser extent, full-Heusler compounds are
promising thermoelectric materials due to their compelling electronic
properties with large power factors. However, intrinsically high thermal
conductivity resulting in a limited thermoelectric efficiency has so far
impeded their widespread use in practical applications. Here, we report the
computational discovery of a class of hitherto unknown stable semiconducting
full-Heusler compounds with ten valence electrons ($X_2YZ$, $X$=Ca, Sr, and Ba;
$Y$= Au and Hg; $Z$=Sn, Pb, As, Sb, and Bi) through high-throughput $ab-initio$
screening. These new compounds exhibit ultralow lattice thermal conductivity
$\kappa_{\text{L}}$ close to the theoretical minimum due to strong anharmonic
rattling of the heavy noble metals, while preserving high power factors, thus
resulting in excellent phonon-glass electron-crystal materials. | 1604.03827v2 |
2016-04-18 | Itinerant G-type antiferromagnetism in D0$_3$-type V$_3$Z (Z=Al, Ga, In) compounds: A first-principles study | Heusler compounds are widely studied due to their variety of magnetic
properties making them ideal candidates for spintronic and magnetoelectronic
applications. V$_3$Al in its metastable D0$_3$-type Heusler structure is a
prototype for a rare antiferromagnetic gapless behavior. We provide an
extensive study on the electronic and magnetic properties of V$_3$Al, V$_3$Ga
and V$_3$In compounds based on state-of-the-art electronic structure
calculations. We show that the ground state for all three is a G-type itinerant
antiferromagnetic gapless semiconductor. The large antiferromagnetic exchange
interactions lead to very high N\'eel temperatures, which are predicted to be
around 1000 K. The coexistence of the gapless and antiferromagnetic behaviors
in these compounds can be explained considering the simultaneous presence of
three V atoms at the unit cell using arguments which have been employed for
usual inverse Heusler compounds. We expect that our study on these compounds to
enhance further the interest on them towards the optimization of their growth
conditions and their eventual incorporation in devices. | 1604.05137v1 |
2017-07-10 | Inflated nodes and surface states in superconducting half-Heusler compounds | Two topics of high current interest in the field of unconventional
superconductivity are non-centrosymmetric superconductors and multiband
superconductivity. Half-Heusler superconductors such as YPtBi exemplify both.
In this paper, we study bulk and surface states in nodal superconducting phases
of the half-Heusler compounds, belonging to the $A_1$ ($s+p$-like) and $T_2$
($k_zk_x+ik_zk_y$-like) irreducible representations of the point group. These
two phases preserve and break time-reversal symmetry, respectively. For the
$A_1$ case, we find that flat surface bands persist in the multiband system. In
addition, the system has dispersive surface bands with zero-energy crossings
forming Fermi arcs, which are protected by mirror symmetries. For the $T_2$
case, there is an interesting coexistence of point and line nodes, known from
the single-band case, with Bogoliubov Fermi surfaces (two-dimensional nodes).
There are no flat-band surface states, as expected, but dispersive surface
bands with Fermi arcs exist. If these arcs do not lie in high-symmetry planes,
they are split by the antisymmetric spin-orbit coupling so that their number is
doubled compared to the inversion-symmetric case. | 1707.02739v2 |
2018-01-31 | Unconventional superconductivity and Surface pairing symmetry in Half-Heusler Compounds | Signatures of nodal line/point superconductivity have been observed in
half-Heusler compounds, such as LnPtBi (Ln = Y, Lu). Topologically non-trivial
band structures, as well as topological surface states, has also been confirmed
by angular-resolved photoemission spectroscopy in these compounds. In this
work, we present a systematical classification of possible gap functions of
bulk states and surface states in half-Heusler compounds and the corresponding
topological properties based on the representations of crystalline symmetry
group. Different from all the previous studies based on four band Luttinger
model, our study starts with the six-band Kane model, which involves both four
p-orbital type of {\Gamma}8 bands and two s-orbital type of {\Gamma}6 bands.
Although the {\Gamma}6 bands are away from the Fermi energy, our results reveal
the importance of topological surface states, which originate from the band
inversion between {\Gamma}6 and {\Gamma}8 bands, in determining surface
properties of these compounds in the superconducting regime by combining
topological bulk state picture and non-trivial surface state picture. | 1801.10286v1 |
2018-03-27 | Subamorphous thermal conductivity of crystalline half-Heusler superlattices | The quest to improve the thermoelectric figure of merit has mainly followed
the roadmap of lowering the thermal conductivity while keeping unaltered the
power factor of the material. Ideally an electron-crystal phonon-glass system
is desired. In this work, we report an extraordinary reduction of the
cross-plane thermal conductivity in crystalline (TiNiSn):(HfNiSn) half-Heusler
superlattices. We create SLs with thermal conductivities below the effective
amorphous limit, which is kept in a large temperature range (120-300 K). We
measured thermal conductivity at room temperature values as low as 0.75 W/(m
K), the lowest thermal conductivity value reported so far for half-Heusler
compounds. By changing the deposition conditions, we also demonstrate that the
thermal conductivity is highly impacted by the way the single segments of the
superlattice grow. These findings show a huge potential for thermoelectric
generators where an extraordinary reduction of the thermal conductivity is
required but without losing the crystal quality of the system. | 1803.09920v2 |
2020-01-20 | Ab initio design of quaternary Heusler compounds for reconfigurable magnetic tunnel diodes and transistors | Reconfigurable magnetic tunnel diodes and transistors are a new concept in
spintronics. The realization of such a device requires the use of materials
with unique spin-dependent electronic properties such as half-metallic magnets
(HMMs) and spin-gapless semiconductors (SGSs). Quaternary Heusler compounds
offer a unique platform to design within the same family of compounds HMMs and
SGSs with similar lattice constants to make coherent growth of the consecutive
spacers of the device possible. Employing state-of-the-art first-principles
calculations, we scan the quaternary Heusler compounds and identify suitable
candidates for these spintronic devices combining the desirable properties: (i)
HMMs with sizable energy gap or SGSs with spin gaps both below and above the
Fermi level, (ii) high Curie temperature, (iii) convex hull energy distance
less than 0.20 eV, and (iv) negative formation energies. Our results pave the
way for the experimental realization of the proposed magnetic tunnel diodes and
transistors. | 2001.07029v1 |
2017-04-04 | Model Hamiltonian and Time Reversal Breaking Topological Phases of Anti-ferromagnetic Half-Heusler Materials | In this work, we construct a generalized Kane model with a new coupling term
between itinerant electron spins and local magnetic moments of
anti-ferromagnetic ordering in order to describe the low energy effective
physics in a large family of anti-ferromagnetic half-Heusler materials.
Topological properties of this generalized Kane model is studied and a large
variety of topological phases, including Dirac semimetal phase, Weyl semimetal
phase, nodal line semimetal phase, type-B triple point semimetal phase,
topological mirror (or glide) insulating phase and anti-ferromagnetic
topological insulating phase, are identified in different parameter regions of
our effective models. In particular, we find that the system is always driven
into the anti-ferromagnetic topological insulator phase once a bulk band gap is
open, irrespective of the magnetic moment direction, thus providing a robust
realization of anti-ferromagentic topological insulators. Furthermore, we
discuss the possible realization of these topological phases in realistic
anti-ferromagnetic half-Heusler materials. Our effective model provides a basis
for the future study of physical phenomena in this class of materials. | 1704.01138v1 |
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