publicationDate stringlengths 1 2.79k | title stringlengths 1 36.5k ⌀ | abstract stringlengths 1 37.3k ⌀ | id stringlengths 9 47 |
|---|---|---|---|
2022-05-06 | Band lineup at hexagonal Si$_x$Ge$_{1-x}$/Si$_y$Ge$_{1-y}$ alloy interfaces | The natural and true band profiles at heterojunctions formed by hexagonal
Si$_x$Ge$_{1-x}$ alloys are investigated by a variety of methods: density
functional theory for atomic geometries, approximate quasiparticle treatments
for electronic structures, different band edge alignment procedures, and
construction of various hexagonal unit cells to model alloys and
heterojunctions. We demonstrate that the natural band offsets are rather
unaffected by the choice to align the vacuum level or the branch point energy,
as well as by the use of a hybrid or the Tran-Blaha functional. At interfaces
between Ge-rich alloys we observe a type-I heterocharacter with direct band
gaps, while Si-rich junctions are type-I but with an indirect band gap. The
true band lineups at pseudomorphically grown heterostructures are strongly
influenced by the generated biaxial strain of opposite sign in the two adjacent
alloys. Our calculations show that the type-I character of the interface is
reduced by strain. To prepare alloy heterojunctions suitable for active
optoelectronic applications, we discuss how to decrease the compressive biaxial
strain at Ge-rich alloys. | 2205.03287v1 |
2022-07-24 | MD simulations and experiments of plasma proteins adsorption to the biodegradable magnesium alloys to facilitate cell response | Once the magnesium alloy was implanted in the body, it was immediately
covered with plasma proteins. The coated alloy surface promoted the adsorption
and growth of osteoblasts. Herein, in vitro biological reactions of the ZK60
and AZ31 magnesium alloys were analyzed with and without plasma proteins
incubation. The plasma proteins adsorbed on the magnesium alloy were
characterized using mass spectrometry (MS). The MS results show that proteins
related to bone cells such as fibrinogen, vitronectin, fibronectin, and
prothrombin are prone to adsorbed on the surface of the alloys than other
proteins. These proteins restrain the degradation of Mg alloys and promote the
adsorption and growth of bone cells, which demonstrated by the immersion tests
and biocompatibility assays. Furthermore, molecular dynamics simulations were
used to analyze the details of the adsorptions of fibrinogen, fibronectin, and
prothrombin on ZK60 and AZ31at atomic level. It is revealed that the type of
residues adsorbed on the surface of the material has an important effect on
protein adsorption. | 2207.11639v1 |
2022-09-06 | Magnetization controlled by crystallization in soft magnetic Fe-Si-B-P-Cu alloys | Soft magnetic materials have low coercive fields and high permeability.
Recently, nanocrystalline alloys obtained using annealing amorphous alloys have
attracted much interest since nanocrystalline alloys with small grain sizes of
tens of nanometers exhibit low coercive fields comparable to that of amorphous
alloys. Since nanocrystalline soft magnetic materials attain remarkable soft
magnetic properties by controlling the grain size, the crystal grains'
microstructure has a substantial influence on the soft magnetic properties. In
this research, we examined the magnetic properties of Fe-Si-B-P-Cu
nanocrystalline soft magnetic alloys obtained by annealing amorphous alloys.
During crystallization, the observation findings reveal the correlation between
the generated microstructures and soft magnetic properties. | 2209.02225v1 |
2022-09-22 | Computational Design of Corrosion-resistant and Wear-resistant Titanium Alloys for Orthopedic Implants | Titanium alloys are promising candidates for orthopedic implants due to their
mechanical resilience and biocompatibility. Current titanium alloys in
orthopedic implants still suffer from low wear and corrosion resistance. Here,
we present a computational method for optimizing the composition of titanium
alloys for enhanced corrosion and wear resistance without compromising on other
aspects such as phase stability, biocompatibility, and strength. We use the
cohesive energy, oxide formation energy, surface work function, and the elastic
shear modulus of pure elements as proxy descriptors to guide us towards alloys
with enhanced wear and corrosion resistance. For the best-selected candidates,
we then use the CALPHAD approach, as implemented in the Thermo-Calc software,
to calculate the phase diagram, yield strength, hardness, Pourbaix diagram, and
the Pilling-Bedworth (PB) ratio. These calculations are used to assess the
thermodynamic stability, biocompatibility, corrosion resistance, and wear
resistance of the selected alloys. Additionally, we provide insights about the
role of silicon on improving the corrosion and wear resistance of alloys. | 2210.00845v1 |
2022-11-23 | The Mixing Thermodynamics and Local Structure of High-entropy Alloys from Randomly Sampled Ordered Configurations | A general method is presented for modeling high entropy alloys as ensembles
of randomly sampled, ordered configurations on a given lattice. Statistical
mechanics is applied post hoc to derive the ensemble properties as a function
of composition and temperature, including the free energy of mixing and local
structure. Random sampling is employed to address the high computational costs
needed to model alloys with a large number of components. Doing so also
provides rigorous convergence criteria, including the quantification of noise
due to random sampling, and an estimation of the number of additional samples
required to lower this noise to the needed/desired levels. This method is
well-suited for a variety of cases: i) high entropy alloys, where standard
lattice models are costly; ii) "medium" entropy alloys, where both the entropy
and enthalpy play significant roles; and iii) alloys with residual short-range
order. Binary to 5-component alloys of the group-IV chalcogenides are used as
case examples, for which the predicted miscibility shows excellent agreement
with experiment. | 2211.13066v1 |
2024-01-31 | Spark Plasma Sintering for high-speed diffusion welding of the ultrafine grained near-a Ti-5Al-2V alloy with high strength and corrosion resistance for nuclear engineering | The paper demonstrates the prospects of Spark Plasma Sintering (SPS) for the
high-speed diffusion welding of the high-strength ultrafine-grained (UFG)
near-a Ti-5Al-2V alloy. The effect of increased diffusion welding intensity in
the UFG Ti alloys is discussed also. The welds of the UFG near-a-Ti-5Al-2V
alloy obtained by SPS are featured by high density, strength, and corrosion
resistance. The rate of weld sealing in the UFG alloys has been shown to depend
on the heating rate non-monotonously (with a pronounced maximum). At the stage
of continuous heating and isothermic holding, the kinetics of the weld sealing
was found to be determined by the exponential creep rate, the intensity of
which in the coarse-grained (CG) alloys is limited by the diffusion rate in the
crystal lattice whereas in the UFG alloys it is limited by the grain boundary
diffusion rate. | 2401.17718v1 |
2024-02-27 | A survey of energies from pure metals to multi-principal element alloys | In materials science, a wide range of properties of materials are governed by
various types of energies, including thermal, physicochemical, structural, and
mechanical energies. In 2005, Dr. Frans Spaepen used crystalline
face-centered-cubic (fcc) copper as an example to discuss a variety of
phenomena that are associated with energies. Inspired by his pioneering work,
we broaden our analysis to include a selection of representative pure metals
with fcc, hexagonal close-packed (hcp), and body-centered cubic (bcc)
structures. Additionally, we extend our comparison to energies between pure
metals and equiatomic binary, ternary, and multi-principal element alloys
(sometimes also known as high-entropy alloys). Through an extensive collection
of data and calculations, we compile energy tables that provide a comprehensive
view of how structure and alloying influence the energy profiles of these
metals and alloys. We highlight the significant impact of constituent elements
on the energies of alloys compared to pure metals and reveal a notable
disparity in mechanical energies among materials in fcc-, hcp- and
bcc-structured metals and alloys. Furthermore, we discuss the underlying
mechanisms behind these patterns and discuss the implications for structural
transformations, providing insights into the broader context of these energy
variations. | 2402.17121v1 |
2015-05-16 | Substrate-free layer-number identification of two-dimensional materials: A case of Mo$_{0.5}$W$_{0.5}$S$_2$ alloy | Any of two or more two-dimensional (2D) materials with similar properties can
be alloyed into a new layered material, namely, 2D alloy. Individual monolayer
in 2D alloys are kept together by Van der Waals interactions. The property of
multilayer alloys is a function of their layer number. Here, we studied the
shear (C) and layer-breathing (LB) modes of Mo$_{0.5}$W$_{0.5}$S$_2$ alloy
flakes and their link to the layer number of alloy flakes. The study reveals
that the disorder effect is absent in the C and LB modes of 2D alloys, and the
monatomic chain model can be used to estimate the frequencies of the C and LB
modes. We demonstrated how to use the C and LB mode frequency to identify the
layer number of alloy flakes deposited on different substrates. This technique
is independent of the substrate, stoichiometry, monolayer thickness and complex
refractive index of 2D materials, offering a robust and substrate-free approach
for layer-number identification of 2D materials. | 1505.04236v1 |
2017-12-20 | Impact of disorder on the optoelectronic properties of GaN$_y$As$_{1-x-y}$Bi$_x$ alloys and heterostructures | We perform a systematic theoretical analysis of the nature and importance of
alloy disorder effects on the electronic and optical properties of
GaN$_{y}$As$_{1-x-y}$Bi$_{x}$ alloys and quantum wells (QWs), using large-scale
atomistic supercell electronic structure calculations based on the
tight-binding method. Using ordered alloy supercell calculations we also derive
and parametrise an extended basis 14-band \textbf{k}$\cdot$\textbf{p}
Hamiltonian for GaN$_{y}$As$_{1-x-y}$Bi$_{x}$. Comparison of the results of
these models highlights the role played by short-range alloy disorder --
associated with substitutional nitrogen (N) and bismuth (Bi) incorporation --
in determining the details of the electronic and optical properties. Systematic
analysis of large alloy supercells reveals that the respective impact of N and
Bi on the band structure remain largely independent, a robust conclusion we
find to be valid even in the presence of significant alloy disorder where N and
Bi atoms share common Ga nearest neighbours. Our calculations reveal that N-
(Bi-) related alloy disorder strongly influences the conduction (valence) band
edge states, leading in QWs to strong carrier localisation, as well as
inhomogeneous broadening and modification of the conventional selection rules
for optical transitions. Our analysis provides detailed insight into key
properties and trends in this unusual material system, and enables quantitative
evaluation of the potential of GaN$_{y}$As$_{1-x-y}$Bi$_{x}$ alloys for
applications in photonic and photovoltaic devices. | 1712.07693v2 |
2020-08-08 | Screening of generalized stacking fault energies, surface energies and intrinsic ductile potency of refractory multicomponent alloys | Body-centered cubic (bcc) refractory multicomponent alloys are of great
interest due to their remarkable strength at high temperatures. Meanwhile,
further optimizing the chemical compositions of these alloys to achieve a
combination of high strength and room-temperature ductility remains
challenging, which would require systematic predictions of the correlated alloy
properties across a vast compositional space. In the present work, we performed
first-principles calculations with the special quasi-random structure (SQS)
method to predict the unstable stacking fault energy ($\gamma_{usf}$) of the
$(1\bar10)[111]$ slip system and the $(1\bar10)$-plane surface energy
($\gamma_{surf}$) for 106 individual binary, ternary and quaternary bcc
solid-solution alloys with constituent elements among Ti, Zr, Hf, V, Nb, Ta,
Mo, W, Re and Ru. Moreover, with the first-principles data and a set of
physics-informed descriptors, we developed surrogate models based on
statistical regression to accurately and efficiently predict $\gamma_{usf}$ and
$\gamma_{surf}$ for refractory multicomponent alloys in the 10-element
compositional space. Building upon binary and ternary data, the surrogate
models show outstanding predictive ability in the high-order multicomponent
systems. The ratio between $\gamma_{surf}$ and $\gamma_{usf}$ is a parameter to
reflect the potency of intrinsic ductility of an alloy based on the Rice model
of crack-tip deformation. Therefore, using the surrogate models, we performed a
systematic screening of $\gamma_{usf}$, $\gamma_{surf}$ and their ratio over
112,378 alloy compositions to search for alloy candidates that may have
enhanced strength-ductile synergies. Search results were also confirmed by
additional first-principles calculations. | 2008.03591v1 |
2022-03-24 | Mode- and Space- Resolved Thermal Transport of Alloy Nanostructures | Nanostructured semiconducting alloys obtain ultra-low thermal conductivity as
a result of the scattering of phonons with a wide range of mean-free-paths
(MFPs). In these materials, long-MFP phonons are scattered at the nanoscale
boundaries whereas short-MFP high-frequency phonons are impeded by disordered
point defects introduced by alloying. While this trend has been validated by
simplified analytical and numerical methods, an ab-initio space-resolved
approach remains elusive. To fill this gap, we calculate the thermal
conductivity reduction in porous alloys by solving the mode-resolved Boltzmann
transport equation for phonons using the finite-volume approach. We analyze
different alloys, length-scales, concentrations, and temperatures, obtaining a
very large reduction in the thermal conductivity over the entire configuration
space. For example, a ~97% reduction is found for Al$_{0.8}$In$_{0.2}$As with
25% porosity. Furthermore, we employ these simulations to validate our recently
introduced "Ballistic Correction Model" (BCM), an approach that estimates the
effective thermal conductivity using the characteristic MFP of the bulk alloy
and the length-scale of the material. The BCM is then used to provide guiding
principles in designing alloy-based nanostructures. Notably, it elucidates how
porous alloys such as Si$_{x}$Ge$_{1-x}$ obtain larger thermal conductivity
reduction compared to porous Si or Ge, while also explaining why we should not
expect similar behavior in alloys such as Al$_{x}$In$_{1-x}$As. By taking into
account the synergy from scattering at different scales, we provide a route for
the design of materials with ultra-low thermal conductivity. | 2203.13279v1 |
2019-05-14 | Discovery of $ω$-free high-temperature Ti-Ta-X shape memory alloys from first principles calculations | The rapid degradation of the functional properties of many Ti-based alloys is
due to the precipitation of the $\omega$ phase. In the conventional
high-temperature shape memory alloy Ti-Ta the formation of this phase
compromises completely the shape memory effect and high (>100{\deg}C)
transformation temperatures cannot be mantained during cycling. A solution to
this problem is the addition of other elements to form Ti-Ta-X alloys, which
often modifies the transformation temperatures; due to the largely unexplored
space of possible compositions, very few elements are known to stabilize the
shape memory effect without decreasing the transformation temperatures below
100{\deg}C. In this study we use transparent descriptors derived from first
principles calculations to search for new ternary Ti-Ta-X alloys that combine
stability and high temperatures. We suggest four new alloys with these
properties, namely Ti-Ta-Sb, Ti-Ta-Bi, Ti-Ta-In, and Ti-Ta-Sc. Our predictions
for the most promising of these alloys, Ti-Ta-Sc, are subsequently fully
validated by experimental investigations, the new alloy Ti-Ta-Sc showing no
traces of $\omega$ phase after cycling. Our computational strategy is
immediately transferable to other materials and may contribute to suppress
$\omega$ phase formation in a large class of alloys. | 1905.05680v3 |
2019-09-17 | Sparking mashups to form multifunctional alloy nanoparticles | Synthesizing unconventional alloys remains challenging owing to seamless
interactions between kinetics and thermodynamics. High entropy alloys (HEAs),
for example, draw a fundamentally new concept to enable exploring unknown
regions in phase diagrams. The exploration, however, is hindered by traditional
metallurgies based on liquid-solid transformation. Vapor-solid transformation
that is permissible on pressure-temperature phase diagrams, offers the most
kinetically efficient pathway to form any desired alloy (e.g., HEA). Here, we
report that a technique called "sparking mashups", which involves a rapidly
quenched vapor source and induces unrestricted mixing for alloying 55 distinct
types of ultrasmall nanoparticles (NPs) with controllable compositions. Unlike
the precursor feed in wet chemistry, a microseconds-long oscillatory spark
controls the vapour composition, which is eventually retained in the alloy NPs.
The resulting NPs range from binary to HEAs with marked thermal stability at
room temperature. We show that a nanosize-effect ensures such thermal stability
and mimics the role of mixing entropy in HEAs. This discovery contradicts the
traditional "smaller is less stable" view while enabling the elemental
combinations that have never been alloyed to date. We even break the
miscibility limits by mixing bulk-immiscible systems in alloy NPs. As powerful
examples, we demonstrate the alloy NPs as both high-performance fuel-cell
catalysts and building blocks for three-dimensional (3D) nanoprinting to
construct HEA nanostructure arrays of various architectures and compositions.
Our results form the basis of new rules for guiding HEA-NP synthesis and
advancing catalysis and 3D printing to new frontiers. | 1909.08147v2 |
2024-01-30 | Effect of the Sc/Zr ratio on the corrosion resistance of Al-Mg cast alloys | The results of investigations of the corrosion resistance of Al-Mg-Sc-Zr
alloys with varying Mg content and different Sc/Zr ratios are presented. The
objects of investigations were the Al-Mg-Sc-Zr alloys with total Sc + Zr
content of 0.32 wt%. The concentration of Sc and Zr in the alloys varied with
the increments of 0.02 wt%. The alloys were produced by induction casting. The
effect of annealing temperature on the microhardness and electrical resistivity
of the Al-Mg-Sc-Zr alloys was investigated. Corrosion tests were carried out in
a medium simulating intergranular corrosion in aluminum alloys. Electrochemical
studies and mass loss tests were performed. An increase in the Sc concentration
and a decrease in the Zr one were shown to result in an increase in the
corrosion rate. The primary Al3(ScxZr1-x) particles were found to have the main
effect on the corrosion resistance of Al-Mg-Sc-Zr alloys. The dependence of the
corrosion current on the annealing temperature of the Al-Mg-Sc-Zr alloy was
found to have a non-monotonous character (with a maximum). | 2401.17429v1 |
2024-02-19 | Hot carrier distribution engineering by alloying: picking elements for the desired purposes | Metal alloys hold the promise of providing hot carrier generation
distributions superior to pure metals in applications such as sensing,
catalysis and solar energy harvesting. Guidelines for finding the optimal alloy
configuration for a target application require understanding the connection
between alloy composition and hot carrier distribution. Here we present a
DFT-based computational approach to investigate the photo-generated hot carrier
distribution of metal alloys based on the joint density of states and the
electronic structure. We classified the metals by their electronic structure
into closed d-shell, open d-shell, p-block and s-block elements. It is shown
that combining closed d-shell elements enables modulating the distribution of
highly energetic holes typical of pure metals but also leads to hot carrier
production by IR light excitation and the appearance of highly energetic
electrons due to band folding and splitting. This feature arises as an emergent
property of alloying and is only unveiled when the hot carrier distribution
computation takes momentum conservation into account. The combination of closed
d-shell with open d-shell elements allows an abundant production of hot
carriers in a broad energy range, while alloying a closed d-shell elements with
an s-block element opens the door to hot electron distribution skewed toward
high energy electrons. The combination of d-shell with p-block elements results
in moderate hot carrier distribution whose asymmetry can be tuned by
composition. Overall, the obtained insights that connect alloy composition,
band structure and resulting carrier distribution provide a toolkit to match
elements in an alloy for the deliberate engineering of hot carrier
distribution. | 2402.12337v1 |
2004-04-29 | Aging-induced complex transformation behavior of martensite in Ni57.5Mn17.5Ga25 shape memory alloy | Ni57.5Mn17.5Ga25 shape memory alloy exhibits a complex transformation
behavior, appearing after aging. Aging in the austenitic state resulted in an
ordinary decrease of the martensitic transformation temperature. Contrary to
this, aging in the martensitic state brought about unusual features of the
martensitic transformation observed so far only in Ni-Ti alloys. | 0404698v1 |
2009-08-25 | Augmented space recursion code and application in simple binary metallic alloy | We present here an optimized and parallelized version of the {\sl augmented
space recursion code} for the calculation of the electronic and magnetic
properties of bulk disordered alloys, surfaces and interfaces, either flat,
corrugated or rough, and random networks. Applications have been made to bulk
disordered alloys to benchmark our code. | 0908.3532v1 |
2013-01-22 | First principles study of helium, carbon and nitrogen in austenite, dilute austenitic iron alloys and nickel | An extensive set of first-principles density functional theory calculations
have been performed to study the behaviour of He, C and N solutes in austenite,
dilute Fe-Cr-Ni austenitic alloys and Ni in order to investigate their
influence on the microstructural evolution of austenitic steel alloys under
irradiation. | 1301.5317v1 |
2018-01-10 | Microstructure and mechanical properties of Al-Cu alloy with 0.6%Fe produced with ultrasonic vibration and applied pressure | The combined effect of ultrasonic vibration (UT) and applied pressure (P) on
microstructure and mechanical properties of Al-5.0Cu-0.6Mn-0.6Fe alloy were
investigated. The best tensile properties produced by P+UT processing are UTS:
268MPa, YS: 192MPa, E.L.: 17.1%, respectively, which increasing by 64%, 59% and
307%, respectively, compare to the Non-treated alloy. | 1801.03246v1 |
2021-07-03 | Thin film of Al-Ga-Pd-Mn quasicrystalline alloy | Thin film quasicrystal coatings have unique properties such as very high
electrical and thermal resistivity and very low surface energy. A nano
quasicrystalline thin film of icosahedral Al-Ga-Pd-Mn alloy, has produced by
flash evaporation followed by annealing. Attempts will be made to discuss the
micromechanisms for the formation of quasicrystalline thin film in Al-Ga-Pd-Mn
alloys | 2107.01478v1 |
2018-12-26 | Formation and composition-dependent properties of alloys of cubic halide perovskites | Distinct shortcomings of individual halide perovskites for solar
applications, such as restricted range of band gaps, propensity of ABX3 to
decompose into AX+BX2, or oxidation of 2ABX3 into A2BX6 have led to the need to
consider alloys of individual perovskites. This creates a non-trivial
material-selection problem, spanning a continuum of three sets of compositions
(one for each sub lattice), and requiring control of phase-separation or
ordering in each alloyed subfield. Not surprisingly, material and structure
choices were made thus far mostly via trial-and-error explorations. We use
ideas from solid state theory of semiconductor alloys to analyze the behaviors
of the (FA,Cs)(Pb,Sn)I3 alloys system. Density functional calculations
utilizing specially constructed supercells (SQS) are used to calculate the
composition dependence of band gaps, energy of decomposition and alloy mixing
enthalpies. A number of trends are observed for A-site as well as for B-site
alloys. To understand the physical reasons that control these trends we
decompose the alloy properties into distinct physical terms: (i) the energies
associated with removing the octahedral deformations (tilting, rotations, B
site displacements), (ii) the energies of compressing the larger component and
expanding the smaller one to the alloy volume, (iii) the charge transfer
energies associated with placing the alloyed units onto a common lattice, and
finally, (iv) structural relaxation of all bonds within the cells., This
analysis clarifies the origin of the observed trends in bang gaps,
decomposition energies and mixing enthalpies. Unlike a number of previous
calculations we find that the a proper description of alloy physics requires
that even the pure, non-alloyed end-point compounds be allowed to develop local
environment dependent octahedral deformation that lowers significantly the
total energy and raises their band gaps. | 1812.10536v1 |
1999-02-22 | La substitution induced linear temperature dependence of electrical resistivity and Kondo behavior in the alloys, Ce_{2-x}La_{x}CoSi_{3} | The results of electrical resistivity, heat capacity and magnetic
susceptibility behavior of new class of alloys, Ce_{2-x}La_{x}CoSi_{3}, are
reported. The x= 0.0 alloy is mixed valent and La substitution for Ce (x= 0.25)
induces linear temperature dependence of resistivity at low temperatures, an
observation of relevance to the topic of non-Fermi liquid behavior. The
modifications of Kondo effect for all the alloys are also presented. | 9902298v1 |
2000-09-14 | c(2x2) Interface Alloys in Co/Cu Multilayers - Influence on Interlayer Exchange Coupling and GMR | The influence of a c(2x2) ordered interface alloy of 3d transition metals at
the ferromagnet/nonmagnet interface on interlayer exchange coupling (IXC), the
formation of quantum well states (QWS) and the phenomenon of Giant
MagnetoResistance is investigated. We obtained a strong dependence of IXC on
interface alloy formation. The GMR ratio is also strongly influenced. We found
that Fe, Ni and Cu alloys at the interface enhance the GMR ratio for in-plane
geometry by nearly a factor of 2. | 0009213v2 |
2001-03-23 | On the de Haas-van Alphen effect in inhomogeneous alloys | We show that Landau level broadening in alloys occurs naturally as a
consequence of random variations in the local quasiparticle density, without
the need to consider a relaxation time. This approach predicts
Lorentzian-broadened Landau levels similar to those derived by Dingle using the
relaxation-time approximation. However, rather than being determined by a
finite relaxation time $\tau$, the Landau-level widths instead depend directly
on the rate at which the de Haas-van Alphen frequency changes with alloy
composition. The results are in good agreement with recent data from three very
different alloy systems. | 0103476v1 |
2001-12-19 | Interesting magnetic properties of Fe$_{1-x}$Co$_x$Si alloys | Solid solution between nonmagnetic narrow gap semiconductor FeSi and
diamagnetic semi-metal CoSi gives rise to interesting metallic alloys with
long-range helical magnetic ordering, for a wide range of intermediate
concentration. We report various interesting magnetic properties of these
alloys, including low temperature re-entrant spin-glass like behaviour and a
novel inverted magnetic hysteresis loop. Role of Dzyaloshinski-Moriya
interaction in the magnetic response of these non-centrosymmetric alloys is
discussed. | 0112346v1 |
2004-03-10 | Monte Carlo Simulation of Surface De-alloying of Au/Ni(110) | Based on BFS model and using Monte Carlo simulation we confirms the
de-alloying in immiscible Au/Ni(110) system, and the critical Au coverage when
de-alloying happens is also consistent with experiments. At the same time our
simulation show that the structural phase transition will lead to the
saturation of the number of alloying Au atoms. | 0403259v2 |
2004-06-21 | Two-Phase Equilibrium in Small Alloy Particles | The coexistence of two phases within a particle requires an interface with a
significant capillary energy. We show that this entails changes in the nature
of alloy phase equilibria at small size. Most notably, the eutectic points in
alloy phase diagrams degenerate into intervals of composition where the alloy
melts discontinuously. | 0406477v2 |
2004-08-27 | Tunable magnetization damping in transition metal ternary alloys | We show that magnetization damping in Permalloy, Ni80Fe20 (``Py''), can be
enhanced sufficiently to reduce post-switching magnetization precession to an
acceptable level by alloying with the transition metal osmium (Os). The damping
increases monotonically upon raising the Os-concentration in Py, at least up to
9% of Os. Other effects of alloying with Os are suppression of magnetization
and enhancement of in-plane anisotropy. Magnetization damping also increases
significantly upon alloying with the five other transition metals included in
this study (4d-elements: Nb, Ru, Rh; 5d-elements: Ta, Pt) but never as strongly
as with Os. | 0408608v1 |
2004-11-06 | Curie temperature and quantum phase transitions in the Hubbard model with binary alloy disorder | Magnetic and electric properties of the Hubbard model with binary alloy
disorder are studied within the dynamical mean--field theory. A
paramagnet--ferromagnet phase transition and a Mott--Hubbard metal--insulator
transition are observed upon varying the alloy concentration. A disorder
induced enhancement of the Curie temperature is demonstrated and explained by
the effects of band splitting and subband filling. Different quantum phase
transitions driven by changes of the alloy concentration are identified. | 0411168v1 |
2006-11-26 | Critical cooling rate for the glass formation of ferromagnetic Fe40Ni40P14B6 alloy | Bulk ferromagnetic amorphous Fe-Ni-P-B alloys in rod shape were formed by a
rapid solidification technique. The largest amorphous specimen prepared had a
diameter of ~2.5 mm and the corresponding cooling rate for the glass formation
of this alloy system in our experiment can be estimate to be around 492.4 K/s
by the method of finite-difference numerical calculation. This value is on the
same order of magnitude as the critical cooling rate Rc of Fe40Ni40P14B6 alloy
estimated by the method of constructing the continuous-cooling-transformation
(CCT) curve. It is indicated that the heterophase impurities have been
eliminated well in our experiment. | 0611651v2 |
2006-12-14 | Magnetic order of FeMn alloy on the W(001) surface | We investigate theoretically the ground state of the FeMn binary alloy
monolayer on the W(001) surface, the stability of different magnetic
configurations (ferro/antiferromagnetic, disordered local moments, etc.) and
estimate concentrations at which a transition occurs between different magnetic
orders. The tight-binding linear muffin-tin orbital method combined with the
coherent potential approximation is used to treat the surface alloy
appropriately. We discuss the role of disorder on the phase transitions in
surface alloys composed from two different 3d transition metals. | 0612366v1 |
2007-01-26 | X-Ray diffraction studies on asymmetrically broadened peaks of heavily deformed Zirconium based alloys | The diffraction peaks of Zircaloy-2 and Zr-2.5%Nb alloys at various
deformations are found to be asymmetric in nature. In order to characterize the
microstructure from these asymmetric peaks of these deformed alloys, X-Ray
Diffraction Line Profile Analysis like Williamson-Hall technique, Variance
method based on second and fourth order restricted moments and Stephens model
based on anisotropic strain distribution have been adopted. The domain size and
dislocation density have been evaluated as a function of deformation for both
these alloys. These techniques are useful where the dislocation structure is
highly inhomogeneous inside the matrix causing asymmetry in the line profile,
particularly for deformed polycrystalline materials. | 0701645v1 |
1995-02-22 | Static displacements and chemical correlations in alloys | Recent experiments in metallic solid solutions have revealed interesting
correlations between static pair-displacements and the ordering behavior of
these alloys. This paper discusses a simple theoretical model which
successfully explains these observations and which provides a natural framework
for analyzing experimental measurements of pair-displacements and chemical
correlations in solid solutions. The utility and scope of this model is
demonstrated by analyzing results of experiments on $Ni-Fe$ and $Cr-Fe$ alloys
and results of simulations of $Cu-Au$ and $Cu-Ag$ alloys. | 9502005v1 |
2007-04-16 | Classical nucleation theory in ordering alloys precipitating with L12 structure | By means of low-temperature expansions (LTEs), the nucleation free energy and
the precipitate interface free energy are expressed as functions of the
solubility limit for alloys which lead to the precipitation of a stoichiometric
L12 compound such as Al-Sc or Al-Zr alloys. Classical nucleation theory is then
used to obtain a simple expression of the nucleation rate whose validity is
demonstrated by a comparison with atomic simulations. LTEs also explain why
simple mean-field approximation like the Bragg-Williams approximation fails to
predict correct nucleation rates in such an ordering alloy. | 0704.1988v1 |
2008-12-17 | Jahn-Teller like origin of the tetragonal distortion in disordered Fe-Pd magnetic shape memory alloys | The electronic structure and magnetic properties of disordered
Fe$_{x}$Pd$_{100-x}$ alloys $(50 < x < 85)$ are investigated in the framework
of density functional theory using the full potential local orbital method
(FPLO). Disorder is treated in the coherent potential approximation (CPA). Our
calculations explain the experimental magnetization data. The origin of the
tetragonal distortion in the Fe-Pd magnetic shape memory alloys is found to be
a Jahn-Teller like effect which allows the system to reduce its band energy in
a narrow composition range. Prospects for an optimization of the alloys'
properties by adding third elements are discussed. | 0812.3332v1 |
2011-04-08 | Diameter dependence of SiGe nanowire thermal conductivity | We theoretically compute the thermal conductivity of SiGe alloy nanowires as
a function of nanowire diameter, alloy concentration, and temperature,
obtaining a satisfactory quantitative agreement with experimental results. Our
results account for the weaker diameter dependence of the thermal conductivity
recently observed in Si$_{1-x}$Ge$_x$ nanowires ($x<0.1$), as compared to pure
Si nanowires. We also present calculations in the full range of alloy
concentrations, $0 \leq x \leq 1$, which may serve as a basis for comparison
with future experiments on high alloy concentration nanowires. | 1104.1570v1 |
2012-01-19 | Phase transformation in steel alloys for magnetocaloric applications; Fe$_{85-x}$Cr$_{15}$Ni$_{x}$ and Fe$_{85-x}$Cr$_{15}$Mn$_{x}$ as prototypes | We here show by first principles theory that it is possible to achieve a
structural and magnetic phase transition in common steel alloys like
Fe$_{85}$Cr$_{15}$, by alloying with Ni or Mn. The predicted phase transition
is from the ferromagnetic body centered cubic (bcc) phase to the paramagnetic
face centered cubic (fcc) phase. The relatively high average magnetic moment of
$\sim1.4\mu_{B}$/atom predicted at the transition suggests that stainless steel
potentially can present a magnetocaloric effect strong enough to make these
alloys good candidates for refrigeration applications operating at and around
room temperature. | 1201.4176v1 |
2014-04-03 | Magnetic and Thermodynamic properties of face-centered cubic Fe-Ni alloys | A model lattice ab initio parameterised Hamiltonian spanning a broad range of
alloy compositions and a large variety of chemical and magnetic configurations
has been developed for face-centered cubic Fe-Ni alloys. Thermodynamic and
magnetic properties of the alloys are explored using configuration and magnetic
Monte Carlo simulations in a temperature range extending well over 1000 K. | 1404.0888v1 |
2015-12-20 | Structure, elastic and bonding properties of hcp ZrxTi1-x binary alloy from first-principles calculations | First principles calculations were performed to study the structural,
elastic, and bonding properties of hcp ZrxTi1-x binary alloy. The special
quasi- random structure (SQS) method is employed to mimic the random hcp
ZrxTi1-x alloy. It is found that Bulk modulus, B, Young's modulus, E, and shear
modulus, G, exhibit decreasing trends as increasing the amount of Zr. A ductile
behavior ZrxTi1-x is predicted in the whole composition range. In terms of
Mulliken charge analisis, we found that the element Ti behaves much more
electronegative than Zr in hcp ZrxTi1-x alloy, and the charge transfer of an
atom is approximately linear to the amount of other element atom surrounding
it. | 1512.06408v1 |
2016-04-28 | Utilization of mechanical alloying method for flux growth of single crystalline BaFe$_2$(As$_{1-x}$P$_x$)$_2$ | Mechanical alloying method has been employed to prepare the Ba-Fe-As-P
precursors, necessary for the Ba-(As,P) flux growth of the single crystalline
BaFe$_2$(As$_{1-x}$P$_x$)$_2$. By alloying constituent elementals mechanically,
the Ba-(As,P) precursors are successfully formed at the room temperature within
one hour, significantly reducing preparation time. Using the mechanically
alloyed precursors, we have grown single crystals of
BaFe$_2$(As$_{1-x}$P$_x$)$_2$ with the sizes up to 5~mm $\times$ 5~mm $\times$
0.1~mm. | 1604.08375v1 |
2017-08-25 | Phase partitioning in a novel near equi-atomic AlCuFeMn alloy | A novel low cost, near equi-atomic alloy comprising of Al, Cu, Fe and Mn is
synthesized using arc-melting technique. The cast alloy possesses a dendritic
microstructure where the dendrites consist of disordered FCC and ordered FCC
phases. The inter-dendritic region is comprised of ordered FCC phase and
spinodally decomposed BCC phases. A Cu segregation is observed in the
inter-dendritic region while dendritic region is rich in Fe. The bulk hardness
of the alloy is ~ 380 HV, indicating significant yield strength. | 1708.07688v1 |
2018-03-02 | Probabilistic design of a molybdenum-base alloy using a neural network | An artificial intelligence tool is exploited to discover and characterize a
new molybdenum-base alloy that is the most likely to simultaneously satisfy
targets of cost, phase stability, precipitate content, yield stress, and
hardness. Experimental testing demonstrates that the proposed alloy fulfils the
computational predictions, and furthermore the physical properties exceed those
of other commercially available Mo-base alloys for forging-die applications. | 1803.00879v1 |
2017-04-06 | Thermoelectric power factor of Bi-Sb-Te and Bi-Te-Se alloys and doping strategy: First-principles study | By performing first principles calculations combined with Boltzmann transport
equations, we calculate the thermoelectric power factor (PF) of Bi-Sb-Te and
Bi-Te-Se ternary alloys as a function of alloy composition ratio, carrier
concentration, and temperature. The point defect formation energy calculations
also perform to search potential n-type dopant candidates in ternaries. | 1704.01723v1 |
2018-10-09 | Peculiar spectra of dark and bright excitons in alloyed nanowire quantum dots | Excitons in alloyed nanowire quantum dots have unique spectra as shown here
using atomistic calculations. The bright exciton splitting is triggered solely
by alloying and despite cylindrical quantum dot shape reaches over $15~\mu$eV,
contrary to previous theoretical predictions, however, in line with
experimental data. This splitting can however be tuned by electric field to go
below $1$~$\mu$eV threshold. The dark exciton optical activity is also strongly
affected by alloying reaching notable $1/3500$ fraction of the bright exciton
and having large out-of-plane polarized component. | 1810.03831v1 |
2018-10-24 | High Strain Rate Behaviour of Nano-quasicrystalline Al93Fe3Cr2Ti2 Alloy and Composites | In the present work, we demonstrate for the first time the outstanding
dynamic mechanical properties of nano-quasicrystalline Al93Fe3Cr2Ti2 at.% alloy
and composites. Unlike most crystalline aluminium-based alloys, this alloy and
composites exhibit substantial strain rate sensitivity and retain much of their
ductility at high rates of strain. This opens new pathways for use in
safety-critical materials where impact resistance is required. | 1810.10476v2 |
2019-04-05 | New high-entropy alloy superconductor Hf$_{21}$Nb$_{25}$Ti$_{15}$V$_{15}$Zr$_{24}$ | High-entropy alloys are a new class of alloys, and attract much attention due
to their unique properties. Since the discovery of a superconducting
high-entropy alloy (HEA) in 2014, the materials research on HEA superconductor
is a hot topic. We have found that Hf$_{21}$Nb$_{25}$Ti$_{15}$V$_{15}$Zr$_{24}$
body-centered-cubic (BCC) HEA is a new superconductor with the superconducting
critical temperature Tc of 5.3 K. We briefly discussed the comparison of
cocktail effect of Tc among BCC HEA superconductors. | 1904.03291v1 |
2019-04-10 | Enhancement of spin transparency by interfacial alloying | We report that atomic-layer alloying (intermixing) at a Pt/Co interface can
increase, by approximately 30%, rather than degrade the interfacial spin
transparency, and thereby strengthen the efficiency of the dampinglike
spin-orbit torque arising from the spin Hall effect in the Pt. At the same
time, this interfacial alloying substantially reduces fieldlike spin-orbit
torque. Insertion of an ultrathin magnetic alloy layer at
heavy-metal/ferromagnet interfaces represents an effective approach for
improving interfacial spin transparency that may enhance not only spin-orbit
torques but also the spin detection efficiency in inverse spin Hall
experiments. | 1904.05455v1 |
2019-07-03 | Dynamic magnetic features of a mixed ferro-ferrimagnetic ternary alloy in the form of AB$_p$C$_{1-p}$ | Dynamic magnetic features of a mixed ferro-ferrimagnetic ternary alloy in the
form of AB$_p$C$_{1-p}$, especially. The effect of Hamiltonian parameters on
the dynamic magnetic features of the system are investigated. For this aim, an
AB$_p$C$_{1-p}$ ternary alloy system was simulated within the mean-field
approximation based on a Glauber type stochastic dynamic and for simplicity, A,
B and C ions as SA = 1/2, SB = 1 and SC = 3/2, were chosen respectively. It was
found that in our dynamic system the critical temperature was always dependent
on the concentration ratio of the ternary alloy. | 1907.01850v1 |
2019-10-29 | Improvement in corrosion resistance and biocompatibility of AZ31 magnesium alloy by NH+2 ions | Magnesium alloys have been considered to be favorable biodegradable metallic
materials used in orthopedic and cardiovascular applications. We introduce NH+2
to the AZ31 Mg alloy surface by ion implantation at the energy of 50 KeV with
doses ranging from 1e16 ions/cm2 to 1e17 ions/cm2 to improve its corrosion
resistance and biocompatibility. Surface morphology, mechanical properties,
corrosion behavior and biocompatibility are studied in the experiments. The
analysis confirms that the modified surface with smoothness and hydrophobicity
significantly improves the corrosion resistance and biocompatibility while
maintaining the mechanical property of the alloy. | 1910.13265v1 |
2012-09-04 | Rapid Production of Accurate Embedded-Atom Method Potentials for Metal Alloys | The most critical limitation to the wide-scale use of classical molecular
dynamics for alloy design is the availability of suitable interatomic
potentials. In this work, we demonstrate a simple procedure to generate a
library of accurate binary potentials using already-existing single-element
potentials that can be easily combined to form multi-component alloy
potentials. For the Al-Ni, Cu-Au, and Cu-Al-Zr systems, we show that this
method produces results comparable in accuracy to alloy potentials where all
parts have been fitted simultaneously, without the additional computational
expense. Furthermore, we demonstrate applicability to both crystalline and
amorphous phases. | 1209.0619v1 |
2020-08-07 | Vibrational Entropy Investigation in High Entropy Alloys | The lattice dynamics for NiCo, NiFe, NiFeCo, NiFeCoCr, and NiFeCoCrMn medium
to high entropy alloy have been investigated using the DFT calculation. The
phonon dispersions along three different symmetry directions are calculated by
the weighted dynamical matrix (WDM) approach and compared with the supercell
approach and inelastic neutron scattering. We could correctly predict the trend
of increasing of the vibrational entropy by adding the alloys and the highest
vibrational entropy in NiFeCoCrMn high entropy alloy by WDM approach. The
averaged first nearest neighbor (1NN) force constants between various pairs of
atoms in these intermetallic are obtained from the WDM approach. The results
are discussed based on the analysis of these data. | 2008.03338v2 |
2016-03-11 | Alloy meets TLA+: An exploratory study | Alloy and TLA+ are two formal specification languages that are increasingly
popular due to their simplicity and flexibility, as well as the effectiveness
of their companion model checkers, the Alloy Analyzer and TLC, respectively.
Nonetheless, while TLA+ focuses on temporal properties, Alloy is better suited
to handle structural properties, requiring ad hoc mechanisms to reason about
temporal properties. Thus, both have limitations in the specification and
analysis of systems rich in both static and dynamic properties. This paper
explores the pros and cons of these two frameworks when handling this class of
systems through the step-by-step modeling, specification and verification of an
example. | 1603.03599v1 |
2019-05-13 | Application of the Statistical Moment Method to Melting Properties of Ternary Alloys with FCC Structure | The high-pressure melting properties of the ternary alloy AlCuSi with
face-centred cubic structure is theoretically investigated using the
statistical moment method. We calculate the melting temperature for the alloy
under pressure up to 80 GPa. The dependence of the melting temperature on the
content of alloying elements is also studied. Our results agree well with
previous experiments, simulations, and other theoretical calculations. | 1905.05047v2 |
2020-09-24 | Correlation of microdistortions with misfit volumes in High Entropy Alloys | The yield strengths of High Entropy Alloys have recently been correlated with
measured picometer-scale atomic distortions. Here, the root mean square
microdistortion in a multicomponent alloy is shown to be nearly proportional to
the misfit-volume parameter that enters into a predictive model of solute
strengthening. Analysis of two model ternary alloy families, face-centered
cubic Cr-Fe-Ni and body-centered cubic Nb-Mo-V, demonstrates the correlation
over a wide composition space. The reported correlation of yield strength with
microdistortion is thus a consequence of the correlation between
microdistortion and misfit parameter and the derived dependence of yield
strength on the misfit parameter. | 2009.11695v1 |
2020-11-24 | Phase Diagrams of Generalized Spin-S Magnetic Binary Alloys | Critical properties of the generalized spin-S magnetic binary alloys
represented by $A_{c}B_{1-c}$ have been investigated within the framework of
EFT. By inspecting the evolution of the phase diagrams with the concentration
for several spin values, general results have been obtained. Obtained results
cover the results obtained for special cases in the literature. Type of the
transition (first/second order), as well as the presence of the tricritical
point have been determined for general spin models. It has also been shown
that, the same critical concentration value exist in the system, regardless of
the spin value for binary alloy consist of half integer-integer spin alloy. | 2011.12330v1 |
2020-12-20 | Precipitate strengthening of pyramidal slip in Mg-Zn alloys | The mechanical properties of Mg-4wt.% Zn alloy single crystals along the
[0001] orientation were measured through micropillar compression at 23C and
100C. Basal slip was dominant in the solution treated alloy, while pyramidal
slip occurred in the precipitation hardened alloy. Pyramidal dislocations pass
the precipitates by forming Orowan loops, leading to homogeneous deformation
and to a strong hardening. The predictions of the yield stress based on the
Orowan model were in reasonable agreement with the experimental data. The
presence of rod-shape precipitates perpendicular to the basal plane leads to a
strong reduction in the plastic anisotropy of Mg. | 2012.10886v1 |
2021-02-03 | Predicting grain boundary energies of complex alloys from ab initio calculations | Investigating the grain boundary energies of pure fcc metals and their
surface energies obtained from ab initio modeling, we introduce a robust method
to estimate the grain boundary energies for complex multicomponent alloys. The
input parameter is the surface energy of the alloy, which can easily be
accessed by modern ab initio calculations based on density functional theory.
The method is demonstrated in the case of paramagnetic Fe-Cr-Ni alloys for
which reliable grain boundary data is available. | 2102.01972v1 |
2021-10-21 | Efficient, Systematic Estimation of Alloy Free Energy from Special Microscopic States | For classical discrete systems under constant composition typically refferred
to substitutional alloys, we propose calculation method of Helmholtz free
energy based on a set of special microscopic states. The advantage of the
method is that configuration of the special states are essentially independent
of energy and temperature, and they depend only on underlying lattice: The
special states can be known a priori without any thermodynamic information,
enabling systematic prediction of free energy for multicomponent alloys. We
confirm that by comparing to conventional thermodynamic simulation, information
about the special states provide reasonable predictive power above
order-disorder and phase-separating transition temperature for alloys with
many-body (up to 3-body) interactions. | 2110.10839v1 |
2021-12-24 | Analysis of Raman and Ellipsometric Responses of Nb$_{x}$W$_{1-x}$Se$_{2}$ alloys | The growth of transition metal dichalcogenide (TMDC) alloys provides an
opportunity to experimentally access information elucidating how optical
properties change with gradual substitutions in the lattice compared with their
pure compositions. In this work, we performed growths of alloyed crystals with
stoichiometric compositions between pure forms of NbSe2 and WSe2, followed by
an optical analysis of those alloys by utilizing Raman spectroscopy and
spectroscopic ellipsometry. | 2112.13063v1 |
2023-01-23 | Superconductivity in the Face Centered Cubic $\rm W_{n-x}Mo_{x}RhIrPt_{2}$ High Entropy Alloy | We report single phase superconducting face centered cubic (FCC)
intermetallic high entropy alloys (HEAs) synthesized via splat cooling. The
single phase materials fall at electron counts in the HEA superconductor alloy
family where structural stability and optimal superconducting electron counts
clash. The materials' superconducting properties follow the general trends
published for metallic alloys. Many of the superconducting characteristics are
summarized. Insights are provided as to why an FCC structure may be stable. | 2301.09678v2 |
2006-01-30 | Correlation in the transition metal based Heusler compounds Co$_2$MnSi and Co$_2$FeSi | Half-metallic ferromagnets like the full Heusler compounds with formula
X$_2$YZ are supposed to show an integer value of the spin magnetic moment.
Calculations reveal in certain cases of X = Co based compounds non-integer
values, in contrast to experiments. In order to explain deviations of the
magnetic moment calculated for such compounds, the dependency of the electronic
structure on the lattice parameter was studied theoretically. In local density
approximation (LDA), the minimum total energy of Co$_2$FeSi is found for the
experimental lattice parameter, but the calculated magnetic moment is about 12%
too low. Half-metallic ferromagnetism and a magnetic moment equal to the
experimental value of $6\mu_B$ are found, however, only after increasing the
lattice parameter by more than 6%.
To overcome this discrepancy, the LDA$+U$ scheme was used to respect on-site
electron correlation in the calculations. Those calculations revealed for
Co$_2$FeSi that an effective Coulomb-exchange interaction $U_{eff}=U-J$ in the
range of about 2eV to 5eV leads to half-metallic ferromagnetism and the
measured, integer magnetic moment at the measured lattice parameter. Finally,
it is shown in the case of Co$_2$MnSi that correlation may also serve to
destroy the half-metallic behavior if it becomes too strong (for Co$_2$MnSi
above 2eV and for Co$_2$FeSi above 5eV). These findings indicate that on-site
correlation may play an important role in the description of Heusler compounds
with localized moments. | 0601671v1 |
2007-10-30 | Searching for hexagonal analogues of the half-metallic half-Heusler XYZ compounds | The XYZ half-Heusler crystal structure can conveniently be described as a
tetrahedral zinc blende YZ structure which is stuffed by a slightly ionic X
species. This description is well suited to understand the electronic structure
of semiconducting 8-electron compounds such as LiAlSi (formulated
Li$^+$[AlSi]$^-$) or semiconducting 18-electron compounds such as TiCoSb
(formulated Ti$^{4+}$[CoSb]$^{4-}$). The basis for this is that [AlSi]$^-$
(with the same electron count as Si$_2$) and [CoSb]$^{4-}$ (the same electron
count as GaSb), are both structurally and electronically, zinc-blende
semiconductors. The electronic structure of half-metallic ferromagnets in this
structure type can then be described as semiconductors with stuffing magnetic
ions which have a local moment: For example, 22 electron MnNiSb can be written
Mn$^{3+}$[NiSb]$^{3-}$. The tendency in the 18 electron compound for a
semiconducting gap -- believed to arise from strong covalency -- is carried
over in MnNiSb to a tendency for a gap in one spin direction. Here we similarly
propose the systematic examination of 18-electron hexagonal compounds for
semiconducting gaps; these would be the "stuffed wurtzite" analogues of the
"stuffed zinc blende" half-Heusler compounds. These semiconductors could then
serve as the basis for possibly new families of half-metallic compounds,
attained through appropriate replacement of non-magnetic ions by magnetic ones.
These semiconductors and semimetals with tunable charge carrier concentrations
could also be interesting in the context of magnetoresistive and thermoelectric
materials. | 0710.5769v1 |
2013-11-20 | Nuclear magnetic resonance study of thin Co$_2$FeAl$_{0.5}$Si$_{0.5}$ Heusler films with varying thickness | Type, degree and evolution of structural order are important aspects for
understanding and controlling the properties of highly spin polarized Heusler
compounds, in particular with respect to the optimal film growth procedure. In
this work, we compare the structural order and the local magnetic properties
revealed by nuclear magnetic resonance (NMR) spectroscopy with the macroscopic
properties of thin Co$_2$FeAl$_{0.5}$Si$_{0.5}$ Heusler films with varying
thickness. A detailed analysis of the measured NMR spectra presented in this
paper enables us to find a very high degree of $L2_1$ type ordering up to 81%
concomitantly with excess Fe of 8 to 13% at the expense of Al and Si. We show,
that the formation of certain types of order do not only depend on the
thermodynamic phase diagrams as in bulk samples, but that the kinetic control
may contribute to the phase formation in thin films. It is an exciting finding
that Co$_2$FeAl$_{0.5}$Si$_{0.5}$ can form an almost ideal $L2_1$ structure in
films though with a considerable amount of Fe-Al/Si off-stoichiometry.
Moreover, the very good quality of the films as demonstrated by our NMR study
suggests that the novel technique of off-axis sputtering technique used to grow
the films sets stage for the optimized performance of
Co$_2$FeAl$_{0.5}$Si$_{0.5}$ in spintronic devices. | 1311.5070v2 |
2015-11-09 | NMR Evidence for the Topologically Nontrivial Nature in a Family of Half-Heusler Compounds | Spin-orbit coupling (SOC) is expected to partly determine the topologically
nontrivial electronic structure of heavy half-Heusler ternary compounds.
However, to date, attempts to experimentally observe either the strength of SOC
or how it modifies the bulk band structure have been unsuccessful. By using
bulk-sensitive nuclear magnetic resonance (NMR) spectroscopy combined with
first-principles calculations, we reveal that 209Bi NMR isotropic shifts scale
with relativity in terms of the strength of SOC and average atomic numbers,
indicating strong relativistic effects on NMR parameters. According to
first-principles calculations, we further claim that nuclear magnetic
shieldings from relativistic p1/2 states and paramagnetic contributions from
low-lying unoccupied p3/2 states are both sensitive to the details of band
structures tuned by relativity, which explains why the hidden relativistic
effects on band structure can be revealed by 209Bi NMR isotropic shifts in
topologically nontrivial half-Heusler compounds. Used in complement to
surface-sensitive methods, such as angle resolved photon electron spectroscopy
and scanning tunneling spectroscopy, NMR can provide valuable information on
bulk electronic states. | 1511.02706v2 |
2016-08-09 | Compensated ferrimagnetic tetragonal Heusler thin films for antiferromagnetic spintronics | In recent years, antiferromagnetic spintronics has received much attention
since ideal antiferromagnets do not produce stray fields and are much more
stable to external magnetic fields compared to materials with net
magnetization. Akin to antiferromagnets, compensated ferrimagnets have zero net
magnetization but have the potential for large spin-polarization and strong out
of plane magnetic anisotropy, and, hence, are ideal candidates for high density
memory applications. Here, we demonstrate that a fully compensated magnetic
state with a tunable magnetic anisotropy is realized in Mn-Pt-Ga based
tetragonal Heusler thin films. Furthermore, we show that a bilayer formed from
a fully compensated and a partially compensated Mn-Pt-Ga layer, exhibits a
large interfacial exchange bias up to room temperature. The present work
establishes a novel design principle for spintronic devices that are formed
from materials with similar elemental compositions and nearly identical crystal
and electronic structures. Such devices are of significant practical value due
to their improved properties such as thermal stability. The flexible nature of
Heusler materials to achieve tunable magnetizations, and anisotropies within
closely matched materials provides a new direction to the growing field of
antiferromagnetic spintronics. | 1608.02887v1 |
2017-07-03 | Large magneto-Seebeck effect in magnetic tunnel junctions with half-metallic Heusler electrodes | Spin caloritronics studies the interplay between charge-, heat- and
spin-currents, which are initiated by temperature gradients in magnetic
nanostructures. A plethora of new phenomena has been discovered that promises,
e.g., to make wasted heat in electronic devices useable or to provide new
read-out mechanisms for information. However, only few materials have been
studied so far with Seebeck voltages of only some {\mu}V, which hampers
applications. Here, we demonstrate that half-metallic Heusler compounds are hot
candidates for enhancing spin-dependent thermoelectric effects. This becomes
evident when considering the asymmetry of the spin-split density of electronic
states around the Fermi level that determines the spin-dependent thermoelectric
transport in magnetic tunnel junctions. We identify Co$_2$FeAl and Co$_2$FeSi
Heusler compounds as ideal due to their energy gaps in the minority density of
states, and demonstrate devices with substantially larger Seebeck voltages and
tunnel magneto-Seebeck effect ratios than the commonly used Co-Fe-B based
junctions. | 1707.00505v2 |
2018-09-20 | Surface Majorana Flat Bands in $j=\frac{3}{2}$ Superconductors with Singlet-Quintet Mixing | Recent experiments have revealed the evidence of nodal-line superconductivity
in half-Heusler superconductors, e.g. YPtBi. Theories have suggested the
topological nature of such nodal-line superconductivity and proposed the
existence of surface Majorana flat bands on the (111) surface of half-Heusler
superconductors. Due to the divergent density of states of the surface Majorana
flat bands, the surface order parameter and the surface impurity play essential
roles in determining the surface properties. In this work, we studied the
effect of the surface order parameter and the surface impurity on the surface
Majorana flat bands of half-Heusler superconductors based on the Luttinger
model. To be specific, we consider the topological nodal-line superconducting
phase induced by the singlet-quintet pairing mixing, classify all the possible
translationally invariant order parameters for the surface states according to
irreducible representations of $C_{3v}$ point group, and demonstrate that any
energetically favorable order parameter needs to break time-reversal symmetry.
We further discuss the energy splitting in the energy spectrum of surface
Majorana flat bands induced by different order parameters and non-magnetic or
magnetic impurities. We proposed that the splitting in the energy spectrum can
serve as the fingerprint of the pairing symmetry and mean-field order
parameters. Our theoretical prediction can be examined in the future scanning
tunneling microscopy experiments. | 1809.07455v2 |
2021-07-10 | Anisotropic exchange and non-collinear antiferromagnets on a noncentrosymmetric fcc structure as in the half-Heuslers | One of the signatures of the face-centered cubic (fcc) antiferromagnet as a
typical example of a geometrically frustrated system is the large ground state
degeneracy of the classical nearest neighbor and next-nearest neighbor
Heisenberg (isotropic) model on this lattice. In particular, collinear states
are degenerate with non-collinear and non-coplanar ones: this degeneracy is
accidental and is expected to be lifted by anisotropic exchange interactions.
In this work, we derive the most general nearest and next-nearest neighbor
exchange model allowed by the space-group symmetry of the noncentrosymmetric
half-Heusler compounds, which includes three anisotropic terms: the so-called
Kitaev, Gamma and Dzyaloshinskii-Moriya interactions -- most notably, the
latter is allowed by the breaking of inversion symmetry in these materials and
has not been previously been studied in the context of the fcc lattice. We
compute the resulting phase diagram and show how the different terms lift the
ground state degeneracy of the isotropic model, and lay emphasis on finding
regimes where multi-q (non-collinear/non-coplanar) states are selected by
anisotropy. We then discuss the role of quantum fluctuations and the coupling
to a magnetic field in the ground state selection, and show that these effects
can stabilize non-coplanar (triple-q) states. These results suggest that some
half-Heusler antiferromagnets might host rare non-collinear/non-coplanar
orders, which may in turn explain the unusual transport properties detected in
these semimetals. | 2107.04906v2 |
2017-06-11 | First principles study of the structural phase stability and magnetic order in various structural phases of Mn$_2$FeGa | We investigate the structural and magnetic properties of Mn$_{2}$FeGa for
different phases(cubic, hexagonal and tetragonal) reported experimentally using
density functional theory. The relative structural stabilities, and the
possible phase transformation mechanisms are discussed using results for total
energy, electronic structure and elastic constants. We find that the phase
transformation form hexagonal to ground state tetragonal structure would take
place through a Heusler-like phase which has a pronounced electronic
instability. The electronic structures, the elastic constants and the
supplementary phonon dispersions indicate that the transition from the
Heusler-like to the tetragonal phase is of pure Jahn-Teller origin. We also
describe the ground state magentic structures in each phase by computations of
the exchange interactions. For Heusler-like and tetragonal phases, the
ferromagnetic exchange interactions associated with the Fe atoms balance the
dominating antiferromagnetic interactions between the Mn atoms leading to
collinear magnetic structures. In the hexagonal phase, the direction of atomic
moment are completely in the planes with a collinear like structure, in stark
contrast to the well known non-collinear magnetic structure in the hexagonal
phase of Mn$_{3}$Ga, another material with similar structural properties. The
overwhelmingly large exchange interactions of Fe with other magnetic atoms
destroy the possibility of magnetic frustration in the hexagonal phase of
Mn$_{2}$FeGa. This comprehensive study provides significant insights into the
microscopic physics associated with the structural and magnetic orders in this
compound. | 1706.03425v1 |
2019-05-22 | Ultra-low magnetic damping in Co 2 Mn-based Heusler compounds: promising materials for spintronic | The prediction of ultra-low magnetic damping in Co 2 MnZ Heusler half-metal
thin-film magnets is explored in this study and the damping response is shown
to be linked to the underlying electronic properties. By substituting the Z
elements in high crystalline quality films (Co 2 MnZ with Z=Si, Ge, Sn, Al, Ga,
Sb), electronic properties such as the minority spin band gap, Fermi energy
position in the gap and spin polarization can be tuned and the consequence on
magnetization dynamics analyzed. The experimental results allow us to directly
explore the interplay of spin polarization, spin gap, Fermi energy position and
the magnetic damping obtained in these films, together with ab initio
calculation predictions. The ultra-low magnetic damping coefficients measured
in the range 4.1 10-4-9 10-4 for Co 2 MnSi, Ge, Sn, Sb are the lowest values
obtained on a conductive layer and offers a clear experimental demonstration of
theoretical predictions on Half-Metal Magnetic Heusler compounds and a pathway
for future materials design. | 1905.08987v1 |
2020-02-07 | Engineering Co$_2$MnAl$_x$Si$_{1-x}$ Heusler compounds as a model system to correlate spin polarization, intrinsic Gilbert damping and ultrafast demagnetization | Engineering of magnetic materials for developing better spintronic
applications relies on the control of two key parameters: the spin polarization
and the Gilbert damping responsible for the spin angular momentum dissipation.
Both of them are expected to affect the ultrafast magnetization dynamics
occurring on the femtosecond time scale. Here, we use engineered Co2MnAlxSi1-x
Heusler compounds to adjust the degree of spin polarization P from 60 to 100%
and investigate how it correlates with the damping. We demonstrate
experimentally that the damping decreases when increasing the spin polarization
from 1.1 10-3 for Co2MnAl with 63% spin polarization to an ultra-low value of
4.10-4 for the half-metal magnet Co2MnSi. This allows us investigating the
relation between these two parameters and the ultrafast demagnetization time
characterizing the loss of magnetization occurring after femtosecond laser
pulse excitation. The demagnetization time is observed to be inversely
proportional to 1-P and as a consequence to the magnetic damping, which can be
attributed to the similarity of the spin angular momentum dissipation processes
responsible for these two effects. Altogether, our high quality Heusler
compounds allow controlling the band structure and therefore the channel for
spin angular momentum dissipation. | 2002.02686v1 |
2020-03-12 | Semi-adsorption-controlled growth window for half Heusler FeVSb epitaxial films | The electronic, magnetic, thermoelectric, and topological properties of
Heusler compounds (composition $XYZ$ or $X_2 YZ$) are highly sensitive to
stoichiometry and defects. Here we establish the existence and experimentally
map the bounds of a \textit{semi} adsorption-controlled growth window for
semiconducting half Heusler FeVSb films, grown by molecular beam epitaxy (MBE).
We show that due to the high volatility of Sb, the Sb stoichiometry is
self-limiting for a finite range of growth temperatures and Sb fluxes, similar
to the growth of III-V semiconductors such as GaSb and GaAs. Films grown within
this window are nearly structurally indistinguishable by X-ray diffraction
(XRD) and reflection high energy electron diffraction (RHEED). The highest
electron mobility and lowest background carrier density are obtained towards
the Sb-rich bound of the window, suggesting that Sb-vacancies may be a common
defect. Similar \textit{semi} adsorption-controlled bounds are expected for
other ternary intermetallics that contain a volatile species $Z=$\{Sb, As,
Bi\}, e.g., CoTiSb, LuPtSb, GdPtBi, and NiMnSb. However, outstanding challenges
remain in controlling the remaining Fe/V ($X/Y$) transition metal
stoichiometry. | 2003.05971v2 |
2020-03-21 | Scaling of quadratic and linear magnetooptic Kerr effect spectra with L2$_1$ ordering of Co$_2$MnSi Heusler compound | The Heusler compound Co$_2$MnSi provides a crystallographic transition from
B2 to L2$_1$ structure with increasing annealing temperature $T_a$, being a
model system for investigating the influence of crystallographic ordering on
structural, magnetic, optic, and magnetooptic (MO) properties. Here, we present
quadratic magnetooptic Kerr effect (QMOKE) spectra depending on $M^2$ in
addition to the linear magnetooptic Kerr effect (LinMOKE) spectra being
proportional to $M$, both in the extended visible spectral range of light from
0.8\,eV to 5.5\,eV. We investigated a set of Co$_2$MnSi thin films deposited on
MgO(001) substrates and annealed from 300$^\circ$C to 500$^\circ$C. The
amplitude of LinMOKE and QMOKE spectra scales linearly with $T_a$, and this
effect is well pronounced at the resonant peaks below 2.0\,eV of the QMOKE
spectra. Furthermore, the spectra of the MO parameters, which fully describe
the MO response of Co$_2$MnSi up to the second order in $M$, are obtained
dependend on $T_a$. Finally, the spectra are compared to ab-initio calculations
of a purely L2$_1$ ordered Co$_2$MnSi Heusler compound. | 2003.09728v2 |
2020-03-25 | Establishing the carrier scattering phase diagram for ZrNiSn-based half-Heusler thermoelectric materials | Chemical doping is one of the most important strategies for tuning electrical
properties of semiconductors, particularly thermoelectric materials. Generally,
the main role of chemical doping lies in optimizing the carrier concentration,
but there can potentially be other important effects. Here, we show that
chemical doping plays multiple roles for both electron and phonon transport
properties in half-Heusler thermoelectric materials. With ZrNiSn-based
half-Heusler materials as an example, we use high-quality single and
polycrystalline crystals, various probes, including electrical transport
measurements, inelastic neutron scattering measurement, and first-principles
calculations, to investigate the underlying electron-phonon interaction. We
find that chemical doping brings strong screening effects to ionized
impurities, grain boundary, and polar optical phonon scattering, but has
negligible influence on lattice thermal conductivity. Furthermore, it is
possible to establish a carrier scattering phase diagram, which can be used to
select reasonable strategies for optimization of the thermoelectric
performance. | 2003.11222v3 |
2020-06-03 | Half-Heusler thermoelectric materials: NMR studies | We report $^{59}$Co, $^{93}$Nb, and $^{121}$Sb nuclear magnetic resonance
(NMR) measurements combined with density functional theory (DFT) calculations
on a series of half-Heusler semiconductors, including NbCoSn, ZrCoSb, TaFeSb
and NbFeSb, to better understand their electronic properties and general
composition-dependent trends. These materials are of interest as potentially
high efficiency thermoelectric materials. Compared to the other materials, we
find that ZrCoSb tends to have a relatively large amount of local disorder,
apparently antisite defects. This contributes to a small excitation gap
corresponding to an impurity band near the band edge. In NbCoSn and TaFeSb,
Curie-Weiss-type behavior is revealed, which indicates a small density of
interacting paramagnetic defects. Very large paramagnetic chemical shifts are
observed associated with a Van Vleck mechanism due to closely spaced $d$ bands
splitting between the conduction and valence bands. Meanwhile, DFT methods were
generally successful in reproducing the chemical shift trend for these
half-Heusler materials, and we identify an enhancement of the larger-magnitude
shifts, which we connect to electron interaction effects. The general trend is
connected to changes in $d$-electron hybridization across the series. | 2006.02013v1 |
2020-06-17 | Epitaxy, exfoliation, and strain-induced magnetism in rippled Heusler membranes | Single-crystalline membranes of functional materials enable the tuning of
properties via extreme strain states; however, conventional routes for
producing membranes require the use of sacrificial layers and chemical
etchants, which can both damage the membrane and limit the ability to make them
ultrathin. Here we demonstrate the epitaxial growth of the cubic Heusler
compound GdPtSb on graphene-terminated Al$_2$O$_3$ substrates. Despite the
presence of the graphene interlayer, the Heusler films have epitaxial registry
to the underlying sapphire, as revealed by x-ray diffraction, reflection high
energy electron diffraction, and transmission electron microscopy. The weak Van
der Waals interactions of graphene enable mechanical exfoliation to yield
free-standing GdPtSb membranes, which form ripples when transferred to a
flexible polymer handle. Whereas unstrained GdPtSb is antiferromagnetic,
measurements on rippled membranes show a spontaneous magnetic moment at room
temperature, with a saturation magnetization of 5.2 bohr magneton per Gd.
First-principles calculations show that the coupling to homogeneous strain is
too small to induce ferromagnetism, suggesting a dominant role for strain
gradients. Our membranes provide a novel platform for tuning the magnetic
properties of intermetallic compounds via strain (piezomagnetixm and
magnetostriction) and strain gradients (flexomagnetism). | 2006.10100v3 |
2020-11-06 | Thermoelectric power factor under strain-induced band-alignment in the half-Heuslers NbCoSn and TiCoSb | Band convergence is an effective strategy to improve the thermoelectric
performance of complex bandstructure thermoelectric materials. Half-Heuslers
are good candidates for band convergence studies because they have multiple
bands near the valence bad edge that can be converged through various band
engineering approaches providing power factor improvement opportunities.
Theoretical calculations to identify the outcome of band convergence employ
various approximations for the carrier scattering relaxation times (the most
common being the constant relaxation time approximation) due to the high
computational complexity involved in extracting them accurately. Here, we
compare the outcome of strain-induced band convergence under two such
scattering scenarios: i) the most commonly used constant relaxation time
approximation and ii) energy dependent inter- and intra-valley scattering
considerations for the half-Heuslers NbCoSn and TiCoSb. We show that the
outcome of band convergence on the power factor depends on the carrier
scattering assumptions, as well as the temperature. For both materials
examined, band convergence improves the power factor. For NbCoSn, however, band
convergence becomes more beneficial as temperature increases, under both
scattering relaxation time assumptions. In the case of TiCoSb, on the other
hand, constant relaxation time considerations also indicate that the relative
power factor improvement increases with temperature, but under the energy
dependent scattering time considerations, the relative improvement weakens with
temperature. This indicates that the scattering details need to be accurately
considered in band convergence studies to predict more accurate trends. | 2011.04288v1 |
2021-10-05 | Tuning the Parity Mixing of Singlet-Septet Pairing in a Half-Heusler Superconductor | In superconductors, electrons with spin ${s=1/2}$ form Cooper pairs whose
spin structure is usually singlet (${S=0}$) or triplet (${S=1}$). When the
electronic structure near the Fermi level is characterized by fermions with
angular momentum ${j=3/2}$ due to strong spin-orbit interactions, novel pairing
states such as even-parity quintet (${J=2}$) and odd-parity septet (${J=3}$)
states become allowed. Prime candidates for such exotic states are half-Heusler
superconductors, which exhibit unconventional superconducting properties, but
their pairing nature remains unsettled. Here we show that the superconductivity
in the noncentrosymmetric half-Heusler LuPdBi can be consistently described by
the admixture of isotropic even-parity singlet and anisotropic odd-parity
septet pairing, whose ratio can be tuned by electron irradiation. From
magnetotransport and penetration depth measurements, we find that carrier
concentrations and impurity scattering both increase with irradiation,
resulting in a nonmonotonic change of the superconducting gap structure. Our
findings shed new light on our fundamental understanding of unconventional
superconducting states in topological materials. | 2110.01819v2 |
2022-08-10 | Defect engineering and Fermi-level tuning in half-Heusler topological semimetals | Three-dimensional topological semimetals host a range of interesting quantum
phenomena related to band crossing that give rise to Dirac or Weyl fermions,
and can be potentially engineered into novel quantum devices. Harvesting the
full potential of these materials will depend on our ability to position the
Fermi level near the symmetry-protected band crossings so that their exotic
spin and charge transport properties become prominent in the devices. Recent
experiments on bulk and thin films of topological half-Heuslers show that the
Fermi level is far from the symmetry-protected crossings, leading to strong
interference from bulk bands in the observation of topologically protected
surface states. Using density functional theory calculations we explore how
intrinsic defects can be used to tune the Fermi level in the two representative
half-Heusler topological semimetals PtLuSb and PtLuBi. Our results explain
recent results of Hall and angle-resolved photoemission measurements. The
calculations show that Pt vacancies are the most abundant intrinsic defects in
these materials grown under typical growth conditions, and that these defects
lead to excess hole densities that place the Fermi level significantly below
the expected position in the pristine material. Directions for tuning the Fermi
level by tuning chemical potentials are addressed. | 2208.05415v2 |
2022-08-11 | Controlling the balance between remote, pinhole, and van der Waals epitaxy of Heusler films on graphene/sapphire | Remote epitaxy on monolayer graphene is promising for synthesis of highly
lattice mismatched materials, exfoliation of free-standing membranes, and
re-use of expensive substrates. However, clear experimental evidence of a
remote mechanism remains elusive. In many cases, due to contaminants at the
transferred graphene/substrate interface, alternative mechanisms such as
pinhole-seeded lateral epitaxy or van der Waals epitaxy can explain the
resulting exfoliatable single-crystalline films. Here, we find that growth of
the Heusler compound GdPtSb on clean graphene on sapphire substrates produces a
30 degree rotated epitaxial superstructure that cannot be explained by pinhole
or van der Waals epitaxy. With decreasing growth temperature the volume
fraction of this 30 degree domain increases compared to the direct epitaxial 0
degree domain, which we attribute to slower surface diffusion at low
temperature that favors remote epitaxy, compared to faster surface diffusion at
high temperature that favors pinhole epitaxy. We further show that careful
graphene/substrate annealing ($T\sim 700 ^\circ C$) and consideration of the
film/substrate vs film/graphene lattice mismatch are required to obtain epitaxy
to the underlying substrate for a variety of other Heusler films, including
LaPtSb and GdAuGe. The 30 degree rotated superstructure provides a possible
experimental fingerprint of remote epitaxy since it is inconsistent with the
leading alternative mechanisms. | 2208.05927v1 |
2022-10-14 | Anti-site disorder and Berry curvature driven anomalous Hall effect in spin gapless semiconducting Mn2CoAl Heusler compound | Spin gapless semiconductors exhibit a finite band gap for one spin channel
and closed gap for other spin channel, emerged as a new state of magnetic
materials with a great potential for spintronic applications. The first
experimental evidence for the spin gapless semiconducting behavior was observed
in an inverse Heusler compound Mn2CoAl. Here, we report a detailed
investigation of the crystal structure and anomalous Hall effect in the Mn2CoAl
using experimental and theoretical studies. The analysis of the high-resolution
synchrotron x-ray diffraction data shows anti-site disorder between Mn and Al
atoms within the inverse Heusler structure. The temperature-dependent
resistivity shows semiconducting behavior and follows Mooijs criteria for
disordered metal. Scaling behavior of the anomalous Hall resistivity suggests
that the anomalous Hall effect in the Mn2CoAl is primarily governed by
intrinsic mechanism due to the Berry curvature in momentum space. The
experimental intrinsic anomalous Hall conductivity (AHC) is found to be 35
S/cm, which is considerably larger than the theoretically predicted value for
ordered Mn2CoAl. Our first-principle calculations conclude that the anti-site
disorder between Mn and Al atoms enhances the Berry curvature and hence the
value of intrinsic AHC, which is in a very well agreement with the experiment. | 2210.07668v1 |
2023-07-26 | Giant spin-charge conversion in ultrathin films of the MnPtSb half-Heusler compound | Half-metallic half-Heusler compounds with strong spin-orbit-coupling and
broken inversion symmetry in their crystal structure are promising materials
for generating and absorbing spin-currents, thus enabling the electric
manipulation of magnetization in energy-efficient spintronic devices. In this
work, we report the spin-to-charge conversion in sputtered ultrathin films of
the half-Heusler compound MnPtSb with thickness (t) in the range from 1 to 6
nm. A combination of X-ray and transmission electron microscopy measurements
evidence the epitaxial nature of these ultrathin non-centrosymmetric MnPtSb
films, with a clear (111)-orientation obtained on top of (0001) single-crystal
sapphire substrates. The study of the thickness (t)-dependent magnetization
dynamics of the MnPtSb(t)/Co(5nm)/Au(5nm) heterostructure revealed that the
MnPtSb compound can be used as an efficient spin current generator, even at
film thicknesses as low as 1 nm. By making use of spin pumping FMR, we measure
a remarkable t-dependent spin-charge conversion in the MnPtSb layers, which
clearly demonstrate the interfacial origin of the conversion. When interpreted
as arising from the inverse Edelstein effect (IEE), the spin-charge conversion
efficiency extracted at room temperature for the thinnest MnPtSb layer reaches
{\lambda}IEE~3 nm, representing an extremely high spin-charge conversion
efficiency at room temperature. The still never explored ultrathin regime of
the MnPtSb films studied in this work and the discover of their outstanding
functionality are two ingredients which demonstrate the potentiality of such
materials for future applications in spintronics. | 2307.14516v1 |
2023-11-03 | Giant tunneling magnetoresistance in Fe$_2$CrSi/Fe$_2$TiSi/Fe$_2$CrSi magnetic tunnel junction | We propose a theoretical model for an all-Heusler magnetic tunnel junction
that uses two Heusler compounds: Fe$_2$CrSi and Fe$_2$TiSi, both of which can
be experimentally synthesized. Fe$_2$CrSi is a half-metallic ferromagnet,
making it a promising material for efficient spin injection in magnetic random
access memories and other spin-dependent devices. While, Fe$_2$TiSi is a
nonmagnetic semiconductor that has the same lattice structure and comparable
lattice constant with Fe$_2$CrSi, as it can be obtained by substituting the
$Y$-site atoms in Fe$_2$CrSi. By using Fe$_2$TiSi as a tunneling barrier
sandwiched by two pieces of semi-infinite Fe$_2$CrSi to construct an
all-Heusler magnetic tunnel junction, the interface disorder is naturally
reduced. Our calculations demonstrate that this magnetic tunnel junction can
exhibit a giant tunneling magnetoresistance of up to 10$^{9}$\% and remains
robust under finite bias voltage. These characteristics suggest that
Fe$_2$CrSi/Fe$_2$TiSi/Fe$_2$CrSi MTJ will be an ideal candidate for future
spintronic applications. More importantly, such a device model can keep such a
giant tunneling magnetoresistance at and beyond room temperature due to the
high Curie temperature of Fe$_2$CrSi. | 2311.01772v1 |
2018-11-06 | Probing alloy formation using different excitonic species: The particular case of InGaN | Since the early 1960s, alloys are commonly grouped into two classes,
featuring bound states in the bandgap (I) or additional, non-discrete band
states (II). Microscopic material parameters for class I alloys can directly be
extracted from photoluminescence (PL) spectra, whereas any conclusions drawn
for class II alloys usually remain indirect and limited to macroscopic
assertions. Nonetheless, here, we present a spectroscopic study on exciton
localization in a so-called mixed crystal alloy (class II) that allows us to
access microscopic alloy parameters. We study bulk In$_x$Ga$_{1-x}$N epilayers
at the onset of alloy formation (0 $\leq$ $x$ $\leq$ 2.4%) in order to
understand the material's particular robustness to defects. Based on an
in-depth PL analysis it is demonstrated how different excitonic complexes
(free, bound, and complex bound excitons) can serve as a probe to monitor the
dilute limit of class II alloys. From an $x$-dependent linewidth analysis we
extract the length scales at which excitons become increasingly localized,
meaning that they convert from a free to a bound particle upon alloy formation.
Already at x = 2.4% the average exciton diffusion length is reduced to 5.7
$\pm$ 1.3 nm at a temperature of 12 K, thus, detrimental exciton transfer
mechanisms towards non-radiative defects are suppressed. In addition, the
associated low temperature PL data suggests that a single indium atom does not
suffice in order to permanently capture an exciton. Micro-PL spectra even give
access to a forthright probing of silicon bound excitons embedded in a
particular environment of indium atoms, thanks to the emergence of a hierarchy
of individual, energetically sharp emission lines (full width at half maximum
$\approx$ 300 $\mu$eV). Consequently, the present study allows us to extract
first microscopic alloy properties formerly only accessible for class I alloys. | 1811.02348v1 |
2019-07-30 | Giant Enhancement of Solid Solubility in Monolayer BNC Alloys by Selective Orbital Coupling | Solid solubility (SS) is one of the most important features of alloys, which
is usually difficult to be largely tuned in the entire alloy concentrations by
external approaches. Some alloys that were supposed to have promising physical
properties could turn out to be much less useful because of their poor SS,
e.g., the case for monolayer BNC [(BN)1-x(C2)x] alloys. Until now, an effective
approach on significantly enhancing SS of (BN)1-x(C2)x in the entire x is still
lacking. In this article, a novel mechanism of selective orbital coupling
between high energy wrong-bond states and surface states mediated by the
specific substrate has been proposed to stabilize the wrong-bonds and in turn
significantly enhance the SS of (BN)1-x(C2)x alloys. Surprisingly, we
demonstrate that five ordered alloys, exhibiting variable direct quasi-particle
bandgaps from 1.35 to 3.99 eV, can spontaneously be formed at different x when
(BN)1-x(C2)x is grown on hcp-phase Cr. Interestingly, the optical transitions
around the band edges in these ordered alloys, accompanied by largely tunable
exciton binding energies of ~1 eV at different x, are significantly strong due
to their unique band structures. Importantly, the disordered (BN)1-x(C2)x
alloys, exhibiting fully tunable bandgaps from 0 to ~6 eV in the entire x, can
be formed on Cr substrate at the miscibility temperature of ~1200 K, which is
greatly reduced compared to that of 4500~5600 K in free-standing form or on
other substrates. Our discovery not only may resolve the long-standing SS
problem of BNC alloys, but also could significantly extend the applications of
BNC alloys for various optoelectronic applications. | 1907.12847v1 |
2023-02-15 | An experimental high-throughput to high-fidelity study towards discovering Al-Cr containing corrosion-resistant compositionally complex alloys | Compositionally complex alloys hold the promise of simultaneously attaining
superior combinations of properties, such as corrosion resistance,
light-weighting, and strength. Achieving this goal is a challenge due in part
to a large number of possible compositions and structures in the vast alloy
design space. High-throughput methods offer a path forward, but a strong
connection between the synthesis of an alloy of a given composition and
structure with its properties has not been fully realized to date. Here, we
present the rapid identification of corrosion-resistant alloys based on
combinations of Al and Cr in a base Al-Co-Cr-Fe-Ni alloy. Previously unstudied
alloy stoichiometries were identified using a combination of high-throughput
experimental screening coupled with key metallurgical and electrochemical
corrosion tests, identifying alloys with excellent passivation behavior. The
alloy native oxide performance and its self-healing attributes were probed
using rapid tests in deaerated 0.1 mol/L H2SO4. Importantly, a correlation was
found between the electrochemical impedance modulus of the exposure-modified
air-formed film and self-healing rate of the CCAs. Multi-element extended x-ray
absorption fine structure analyses connected more ordered type chemical
short-range order in the Ni-Al 1st nearest-neighbor shell to poorer corrosion
resistance. This report underscores the utility of high throughput exploration
of compositionally complex alloys for the identification and rapid screening of
a vast stoichiometric space. | 2302.07988v2 |
2023-06-14 | Neural network as a tool for design of amorphous metal alloys with desired elastoplastic properties | The development and implementation of the methods for designing amorphous
metal alloys with desired mechanical properties is one of the most promising
areas of modern materials science. Here, the machine learning methods appear to
be a suitable complement to empirical methods related to the synthesis and
testing of amorphous alloys of various compositions. In the present work, it is
proposed a method to determine amorphous metal alloys with mechanical
properties closest to those required. More than $50\,000$ amorphous alloys of
different compositions have been considered, and the Young's modulus $E$ and
the yield strength $\sigma_{y}$ have been evaluated for them by the machine
learning model trained on the fundamental physical properties of the chemical
elements. Statistical treatment of the obtained results reveals that the
fundamental physical properties of the chemical element with the largest mass
fraction are the most significant factors, whose values correlate with the
values of the mechanical properties of the alloys, in which this element is
involved. It is shown that the values of the Young's modulus $E$ and the yield
strength $\sigma_{y}$ are higher for amorphous alloys based on Cr, Fe, Co, Ni,
Nb, Mo and W formed by the addition of semimetals (e.g. Be, B, Al, Sn),
nonmetals (e.g. Si and P) and lanthanides (e.g. La and Gd) than for alloys of
other compositions. Increasing the number of components in alloy from $2$ to
$7$ and changing the mass fraction of chemical elements has no significantly
impact on the strength characteristics $E$ and $\sigma_{y}$. Amorphous metal
alloys with the most improved mechanical properties have been identified. In
particular, such extremely high-strength alloys include Cr$_{80}$B$_{20}$
(among binary), Mo$_{60}$B$_{20}$W$_{20}$ (among ternary) and
Cr$_{40}$B$_{20}$Nb$_{10}$Pd$_{10}$Ta$_{10}$Si$_{10}$ (among multicomponent). | 2306.08383v1 |
2024-03-20 | Effect of annealing on the hot salt corrosion resistance of the fine-grained titanium alpha-alloy Ti-2.5Al-2.6Zr obtained via cold Rotary Swaging | A hot salt corrosion (HSC) test was performed on the fine-grained titanium
alpha-alloy Ti-2.5Al-2.6Zr (Russian industrial alloy PT-7M). The
ultrafine-grained (UFG) microstructure in the titanium alpha-alloy was formed
via cold Rotary Swaging. The grain size and volume fraction of the
recrystallized microstructure in the alloy were varied by choosing appropriate
annealing temperatures and times. The microstructure and corrosion resistance
of UFG alloys were studied after 30 min of annealing at 500-700C and after 1000
h of annealing at 250C. Metallographic studies were carried out to investigate
the effects of annealing on the nature and extent of corrosive damage in the
titanium alpha-alloy Ti-2.5Al-2.6Zr. After HSC tests, surface analyses of the
titanium alpha-alloy samples were conducted using X-ray diffraction and
electron microscopy. During the HSC testing of the titanium alpha-alloy
Ti-2.5Al-2.6Zr, a competitive interaction between intergranular corrosion (IGC)
and pitting corrosion was observed. To the best of our knowledge, it was shown
for the first time that annealing affects the relationship among the IGC,
pitting corrosion and uniform corrosion rates of the titanium alloy. Prolonged
low-temperature annealing at 250C resulted in a more pronounced increase in the
uniform corrosion rate than short-term high-temperature annealing for 30 min at
500-700C. An in-depth analysis of the effect of the structure and phase
composition of the grain boundaries on the susceptibility of the alpha-alloy
Ti-2.5Al-2.6Zr to HSC was conducted. | 2403.13587v1 |
2007-10-11 | The value of long-range interactions parameter for some alloys | The critical behavior of some alloys are analyzed within the framework of
Heisenbergs model with long-range interaction. On based experimental values of
the critical exponent $\gamma$ we calculate the value of paerameter of
long-range interaction. | 0710.2196v1 |
2008-11-03 | Ab initio calculation of structural and electronic properties of Al$_x$Ga$_{1-x}$N and In$_x$Ga$_{1-x}$N alloys | Using the density functional theory (DFT) with the generalized gradient
approximation (GGA), the structural and electronic properties of wurtzite AlN,
GaN, InN, and their related alloys, Al$_x$Ga$_{1-x}$N and In$_x$Ga$_{1-x}$N,
were calculated. We have performed accurate {\it ab initio} total energy
calculations using the full--potential linearized augmented plane wave
(FP--LAPW) method to investigate the structural and electronic properties. In
both alloys we found that the fundamental parameters do not follow Vegard's
law. The lattice parameters, $a, c,$ and $u$, for the Al$_x$Ga$_{1-x}$N alloy
are found to exhibit downward bowing, while for In$_x$Ga$_{1-x}$N there is an
upward bowing for the $a$ and $c$ parameters and a downward bowing for the
internal parameter, $u$. Furthermore, we found that for both alloys, the band
gap value does not follow Vegard's law. As a by--product of our electronic band
structure calculations, the effective masses of the binary compounds as well as
their related alloys were calculated. We show that the calculated properties
for the binary compounds, as well as for the studied alloys, show good
agreement with most of the previously reported results. Finally, using the
frozen phonon approach, the A$_1(TO)$ mode for the different systems studied in
this work was calculated. Our calculations show good agreement with
experimental values reported for the binary compounds. For the ternary alloys,
our calculations reproduce experimental values for Al$_x$Ga$_{1-x}$N as well as
theoretical predictions for In$_x$Ga$_{1-x}$N. | 0811.0380v1 |
2009-08-30 | Measurement of spin memory lengths in PdNi and PdFe ferromagnetic alloys | Weakly ferromagnetic alloys are being used by several groups in the study of
superconducting/ferromagnetic hybrid systems. Because spin-flip and spin-orbit
scattering in such alloys disrupt the penetration of pair correlations into the
ferromagnetic material, it is desirable to have a direct measurement of the
spin memory length in such alloys. We have measured the spin memory length at
4.2 K in sputtered Pd0.88Ni0.12 and Pd0.987Fe0.013 alloys using methods based
on current-perpendicular-to-plane giant magnetoresistance. The alloys are
incorporated into hybrid spin valves of various types, and the spin memory
length is determined by fits of the Valet-Fert spin-transport equations to data
of magnetoresistance vs. alloy thickness. For the case of PdNi alloy, the
resulting values of the spin memory length are lsf(PdNi) = 2.8 +/- 0.5 nm and
5.4 +/- 0.6 nm, depending on whether or not the PdNi is exchange biased by an
adjacent Permalloy layer. For PdFe, the spin memory length is somewhat longer,
lsf(PdFe) = 9.6 +/- 2 nm, consistent with earlier measurements indicating lower
spin-orbit scattering in that material. Unfortunately, even the longer spin
memory length in PdFe may not be long enough to facilitate observation of
spin-triplet superconducting correlations predicted to occur in
superconducting/ferromagnetic hybrid systems in the presence of magnetic
inhomogeneity. | 0908.4375v1 |
2010-04-14 | Spectral properties of discrete alloy-type models | We discuss recent results on spectral properties of discrete alloy-type
random Schr\"odinger operators. They concern Wegner estimates and bounds on the
fractional moments of the Green's function. | 1004.2385v1 |
2010-08-31 | Internal friction study of dislocation dynamics in thermally aged Fe-1%Cu-C alloys | Internal friction study of dislocation dynamics in thermally aged Fe-1%Cu-C
alloys. | 1008.5262v3 |
2012-01-05 | The influence of transition metal solutes on dislocation core structure and values of Peierls stress and barrier in tungsten | Several transition metals were examined to evaluate their potential for
improving the ductility of tungsten. The dislocation core structure and Peierls
stress and barrier of $1/2<111>$ screw dislocations in binary
tungsten-transition metal alloys (W$_{1-x}$TM$_{x}$) were investigated using
first principles electronic structure calculations. The periodic quadrupole
approach was applied to model the structure of $1/2<111>$ dislocation. Alloying
with transition metals was modeled using the virtual crystal approximation and
the applicability of this approach was assessed by calculating the equilibrium
lattice parameter and elastic constants of the tungsten alloys. Reasonable
agreement was obtained with experimental data and with results obtained from
the conventional supercell approach. Increasing the concentration of a
transition metal from the VIIIA group, i.e. the elements in columns headed by
Fe, Co and Ni, leads to reduction of the $C^\prime$ elastic constant and
increase of elastic anisotropy A=$C_{44}/C^\prime$. Alloying W with a group
VIIIA transition metal changes the structure of the dislocation core from
symmetric to asymmetric, similar to results obtained for W$_{1-x}$Re$_{x}$
alloys in the earlier work of Romaner {\it et al} (Phys. Rev. Lett. 104, 195503
(2010))\comments{\cite{WRECORE}}. In addition to a change in the core symmetry,
the values of the Peierls stress and barrier are reduced. The latter effect
could lead to increased ductility in a tungsten-based
alloy\comments{\cite{WRECORE}}. Our results demonstrate that alloying with any
of the transition metals from the VIIIA group should have similar effect as
alloying with Re. | 1201.1245v2 |
2012-02-15 | Monte Carlo simulations of the structure of Pt-based bimetallic nanoparticles | Pt-based bimetallic nanoparticles have attracted significant attention as a
promising replacement for expensive Pt nanoparticles. In the systematic design
of bimetallic nanoparticles, it is important to understand their preferred
atomic structures. However, compared with unary systems, alloy nanoparticles
present more structural complexity with various compositional configurations,
such as mixed-alloy, core-shell, and multishell structures. In this paper, we
developed a unified empirical potential model for various Pt-based binary
alloys, such as Pd-Pt, Cu-Pt, Au-Pt, and Ag-Pt. Within this framework, we
performed a series of Monte Carlo (MC) simulations that quantify the
energetically favorable atomic arrangements of Pt-based alloy nanoparticles: an
intermetallic compound structure for the Pd-Pt alloy, an onion-like multi-shell
structure for the Cu-Pt alloy, and core-shell structures (Au@Pt and Ag@Pt) for
the Au-Pt and Ag-Pt alloys. The equilibrium nanoparticle structures for the
four alloy types were compared with each other, and the structural features can
be interpreted by the interplay of their material properties, such as the
surface energy and heat of formation. | 1202.3277v2 |
2013-09-06 | Interplay of force constants in the lattice dynamics of disordered alloys : An ab-initio study | A reliable prediction of interatomic force constants in disordered alloys is
an outstanding problem. This is due to the need for a proper treatment of
multisite (atleast pair) correlation within a random environment. The situation
becomes even more challenging for systems with large difference in atomic size
and mass. We propose a systematic density functional theory (DFT) based study
to predict the ab-initio force constants in random alloys. The method is based
on a marriage between special quasirandom structures (SQS) and the augmented
space recursion (ASR) to calculate phonon spectra, density of states (DOS) etc.
bcc TaW and fcc NiPt alloys are considered as the two distinct test cases.
Ta-Ta (W-W) bond distance in the alloy is predicted to be smaller (larger) than
those in pure Ta (W), which, in turn, yields stiffer (softer) force constants
for Ta (W). Pt-Pt force constants in the alloy, however, are predicted to be
softer compared to Ni-Ni, due to a large bond distance of the former. Our
calculated force constants, phonon spectra and DOS are compared with
experiments and other theoretical results, wherever available. Correct trend of
present results for the two alloys pave a path for further future studies in
more complex alloy systems. | 1309.1589v2 |
2016-09-21 | Magnetic Susceptibility of Dirac Fermions, Bi-Sb Alloys, Interacting Bloch Fermions, Dilute Nonmagnetic Alloys, and Kondo Alloys | Wide ranging interest in Dirac Hamiltomian is due to the emergence of novel
materials, namely, graphene, topological insulators and superconductors, the
newly-discovered Weyl semimetals, and still actively-sought after Majorana
fermions in real materials. We give a brief review of the relativistic Dirac
quantum mechanics and its impact in the developments of modern physics. The
quantum band dynamics of Dirac Hamiltonian is crucial in resolving the giant
diamagnetism of bismuth and Bi-Sb alloys. Quantitative agreement of the theory
with the experiments on Bi-Sb alloys has been achieved, and physically
meaningful contributions to the diamagnetism has been identified. We also treat
relativistic Dirac fermion as an interband dynamics in uniform magnetic fields.
For the interacting Bloch electrons, the role of translation symmetry for
calculating the magnetic susceptibility avoids any approximation to second
order in the field. The magnetic susceptibility of Hubbard model and those of
Fermi liquids are readily obtained as limiting cases. The expressions for
magnetic susceptibility of dilute nonmagnetic alloys give a firm theoretical
foundation of the empirical formulas used in fitting experimental results. For
completeness, the magnetic susceptibility of dilute magnetic or Kondo alloys is
also given for high and low temperature regimes. | 1609.06419v1 |
2018-01-01 | Structural Disorder and Electronic Structure in Alloyed SrTiO3/SrFeO2.5 Compounds: A Theoretical Study | Many mixed ionic/electronic conductors (MIECs) applied in fuel cell
electrodes can be considered as alloys between perovskite oxides and ordered
oxygen vacancy compounds. For example, in the model MIEC (STF), low oxygen
diffusion barrier exist in SrTiO3 lattice, when it has been mixed with SrFeO2.5
with intrinsic oxygen deficiency, the ionic conductivity can be greatly
improved. Meanwhile, the electronic conductivity can be optimized by
controlling the defect chemistry of the alloy. However, the configurational
space is too large in such alloys so that it is difficult for direct atomic
modeling, which hinders in-depth understanding and predictive modeling. In this
work, we present a cluster expansion model to describe the energetics of the
disordered SrTiO3/SrFeO2.5 alloy within the full solid solution composition
space Sr(Ti1-x,Fex)O3-0.5x (0<x<1). Cluster expansion Monte Carlo simulations
have been performed to search the lowest energy atomic configurations and
investigate the origin of lattice disorder. With representations of realistic
configurations, the electronic structures of such alloys at different
stoichiometry have also been examined. We find that the band gap evolution with
composition calculated using our atomic model is consistent with experiment
measurement. Meanwhile, the band edge analysis elucidate that electronic
conductivity within such alloy can be facilitated by the Fe/Ti cation disorder.
Taking SrTiO3/SrFeO2.5 alloy as an example, the generalized computational
framework applied here can be extended to other relevant MIEC material systems. | 1801.00456v2 |
2018-01-07 | Platelet-zone in an age-hardening Mg-Zn-Gd alloy | The structure of a unique platelet zone with a three close-packed layer
thickness, which occurred in a Mg-1at.%Zn-2at.%Gd alloy annealed at low
temperatures (<~500K), has been determined based on scanning transmission
electron microscopy and first principles calculations. | 1801.02115v1 |
2018-02-27 | Anisotropic Thermal Transport in Phase-Transition Layered 2D Alloys WSe2(1-x)Te2x | Transition metal dichalcogenide (TMD) alloys have attracted great interests
in recent years due to their tunable electronic properties, especially the
semiconductor-metal phase transition, along with their potential applications
in solid-state memories and thermoelectrics. However, the thermal conductivity
of layered two-dimensional (2D) TMD alloys remains largely unexplored despite
that it plays a critical role in the reliability and functionality of
TMD-enabled devices. In this work, we study the temperature-dependent
anisotropic thermal conductivity of the phase-transition 2D TMD alloys
WSe2(1-x)Te2x in both the in-plane direction (parallel to the basal planes) and
the cross-plane direction (along the c-axis) using time-domain
thermoreflectance measurements. In the WSe2(1-x)Te2x alloys, the cross-plane
thermal conductivity is observed to be dependent on the heating frequency
(modulation frequency of the pump laser) due to the non-equilibrium transport
between different phonon modes. Using a two-channel heat conduction model, we
extracted the anisotropic thermal conductivity at the equilibrium limit. A
clear discontinuity in both the cross-plane and the in-plane thermal
conductivity is observed as x increases from 0.4 to 0.6 due to the phase
transition from the 2H to Td phase in the layered 2D alloys. The temperature
dependence of thermal conductivity for the TMD alloys was found to become
weaker compared with the pristine 2H WSe2 and Td WTe2 due to the atomic
disorder. This work serves as an important starting point for exploring phonon
transport in layered 2D alloys. | 1802.10009v2 |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.