publicationDate stringlengths 1 2.79k | title stringlengths 1 36.5k ⌀ | abstract stringlengths 1 37.3k ⌀ | id stringlengths 9 47 |
|---|---|---|---|
1997-06-20 | Stationary perturbations and infinitesimal rotations of static Einstein-Yang-Mills configurations with bosonic matter | Using the Kaluza-Klein structure of stationary spacetimes, a framework for
analyzing stationary perturbations of static Einstein-Yang-Mills configurations
with bosonic matter fields is presented. It is shown that the perturbations
giving rise to non-vanishing ADM angular momentum are governed by a
self-adjoint system of equations for a set of gauge invariant scalar
amplitudes. The method is illustrated for SU(2) gauge fields, coupled to a
Higgs doublet or a Higgs triplet. It is argued that slowly rotating black holes
arise generically in self-gravitating non-Abelian gauge theories with bosonic
matter, whereas, in general, soliton solutions do not have rotating
counterparts. | 9706064v1 |
1999-06-22 | The generalization of the Regge-Wheeler equation for self-gravitating matter fields | It is shown that the dynamical evolution of perturbations on a static
spacetime is governed by a standard pulsation equation for the extrinsic
curvature tensor. The centerpiece of the pulsation equation is a wave operator
whose spatial part is manifestly self-adjoint. In contrast to metric
formulations, the curvature-based approach to gravitational perturbation theory
generalizes in a natural way to self-gravitating matter fields. For a certain
relevant subspace of perturbations the pulsation operator is symmetric with
respect to a positive inner product and therefore allows spectral theory to be
applied. In particular, this is the case for odd-parity perturbations of
spherically symmetric background configurations. As an example, the pulsation
equations for self-gravitating, non-Abelian gauge fields are explicitly shown
to be symmetric in the gravitational, the Yang Mills, and the off-diagonal
sector. | 9906090v1 |
1999-10-18 | Perturbation theory for self-gravitating gauge fields I: The odd-parity sector | A gauge and coordinate invariant perturbation theory for self-gravitating
non-Abelian gauge fields is developed and used to analyze local uniqueness and
linear stability properties of non-Abelian equilibrium configurations. It is
shown that all admissible stationary odd-parity excitations of the static and
spherically symmetric Einstein-Yang-Mills soliton and black hole solutions have
total angular momentum number $\ell = 1$, and are characterized by
non-vanishing asymptotic flux integrals. Local uniqueness results with respect
to non-Abelian perturbations are also established for the Schwarzschild and the
Reissner-Nordstr\"om solutions, which, in addition, are shown to be linearly
stable under dynamical Einstein-Yang-Mills perturbations. Finally, unstable
modes with $\ell = 1$ are also excluded for the static and spherically
symmetric non-Abelian solitons and black holes. | 9910059v1 |
2001-03-09 | The topology of the off-diagonal terms of the semiclassical form factor | The semiclassical origin of the logarithmic singularity at the Heisenberg
time of the symplectic form factor is deduced by combining the result of M.
Sieber and K. Richter for the first term of the loop-expansion in the
orthogonal case with the contribution that arises due to the spin.
We are able to make a quantitative statement about the topology of all
non-diagonal contributions in terms of integrals over SU(2) leading to the
conclusion that the same perturbative loop expansion is responsible for the
form factor in the region $0 < \tau < 2$ in the orthogonal and symplectic case
taking into account Kramers' degeneracy; the only difference being a phase
factor arising due to the spin. | 0103007v4 |
2006-01-11 | The i11/2 f5/2 and i11/2 p3/2 neutron particle-hole multiplets in 208Pb | Inelastic proton scattering via isobaric analog resonances allows to derive
rather complete information about neutron particle-hole states. We applied this
method to the doubly-magic nucleus 208Pb by measuring angular distributions of
208Pb(p, p') on top of the isobaric analog resonances in 209Bi with the Q3D
magnetic spectrograph at M\"unchen. We identify the six states of the i11/2
f5/2 multiplet and the four states of the i11/2 p3/2 multiplet in the energy
range 4.6 MeV < Ex < 5.3 MeV. Firm spin assignments for the ten states are
given, some of them new. Additional measurements of the reaction 207Pb(d, p)
confirm the fragmented i11/2 p1/2 multiplet. | 0601016v1 |
2006-11-10 | On the mixing strength in the two lowest 0- states in 208Pb | With a resolution of 3 keV, the two lowest 0- states in 208Pb are identified
by measurements of the reaction 207Pb(d, p) with the Muenchen Q3D magnetic
spectrograph in a region where the average level spacing is 6 keV. Precise
relative spectroscopic factors are determined. Matrix elements of the residual
interaction among one-particle one-hole configurations in a two-level scheme
are derived for the two lowest 0- states in 208Pb. The off-diagonal mixing
strength is determined as 105 +-10(experimental) +-40(systematic) keV.
Measurements of the reaction 208Pb(p,p') via isobaric analog resonances in
209Bi support the structure information obtained. | 0611013v1 |
2007-08-24 | Influence of the L21 ordering degree on the magnetic properties in Co2MnSi Heusler films | We report on the influence of the improved L21 ordering degree on the
magnetic properties of Co2MnSi Heusler films. Different fractions of the L21
phase are obtained by different post-growth annealing temperatures ranging from
350 degC to 500 degC. Room temperature magneto-optical Kerr effect measurements
reveal an increase of the coercivity at an intermediate annealing temperature
of 425 degC, which is a fingerprint of an increased number of pinning centers
at this temperature. Furthermore, Brillouin light scattering studies show that
the improvement of the L21 order in the Co2MnSi films is correlated with a
decrease of the saturation magnetization by about 9%. The exchange stiffness
constant of Co2MnSi, however, increases by about 8% when the L21 order is
improved. Moreover, we observe a drop of the cubic anisotropy constant K1 by a
factor of 10 for an increasing amount of the L21 phase. | 0708.3303v1 |
2008-09-29 | Hall effect in laser ablated Co_2(Mn,Fe)Si thin films | Pulsed laser deposition was employed to grow thin films of the Heusler
compounds Co_2MnSi and Co_2FeSi. Epitaxial growth was realized both directly on
MgO (100) and on a Cr or Fe buffer layer. Structural analysis by x-ray and
electron diffraction shows for both materials the ordered L2_1 structure. Bulk
magnetization was determined with a SQUID magnetometer. The values agree with
the Slater-Pauling rule for half-metallic Heusler compounds. On the films grown
directly on the substrate measurements of the Hall effect have been performed.
The normal Hall effect is nearly temperature independent and points towards a
compensated Fermi surface. The anomalous contribution is found to be dominated
by skew scattering. A remarkable sign change of both normal and anomalous Hall
coefficients is observed on changing the valence electron count from 29 (Mn) to
30 (Fe). | 0809.4978v1 |
2008-10-05 | Determination of exchange constants of Heusler compounds by Brillouin light scattering spectroscopy: application to Co$_2$MnSi | Brillouin light scattering spectroscopy from so-called standing spin waves in
thin magnetic films is often used to determine the magnetic exchange constant.
The data analysis of the experimentally determined spin-wave modes requires an
unambiguous assignment to the correct spin wave mode orders. Often additional
investigations are needed to guarantee correct assignment. This is particularly
important in the case of Heusler compounds where values of the exchange
constant vary substantially between different compounds. As a showcase, we
report on the determination of the exchange constant (exchange stiffness
constant) in Co$_2$MnSi, which is found to be $A=2.35\pm0.1$ $\mu$erg/cm
($D=575\pm20$ meV \AA$^2$), a value comparable to the value of the exchange
constant of Co. | 0810.0834v3 |
2008-11-27 | Electron correlations in Co$_2$Mn$_{1-x}$Fe$_x$Si Heusler compounds | This study presents the effect of local electronic correlations on the
Heusler compounds Co$_2$Mn$_{1-x}$Fe$_x$Si as a function of the concentration
$x$. The analysis has been performed by means of first-principles
band-structure calculations based on the local approximation to spin-density
functional theory (LSDA). Correlation effects are treated in terms of the
Dynamical Mean-Field Theory (DMFT) and the LSDA+U approach. The formalism is
implemented within the Korringa-Kohn-Rostoker (KKR) Green's function method.
In good agreement with the available experimental data the magnetic and
spectroscopic properties of the compound are explained in terms of strong
electronic correlations. In addition the correlation effects have been analysed
separately with respect to their static or dynamical origin. To achieve a
quantitative description of the electronic structure of
Co$_2$Mn$_{1-x}$Fe$_x$Si both static and dynamic correlations must be treated
on equal footing. | 0811.4625v1 |
2009-03-29 | The semiclassical origin of curvature effects in universal spectral statistics | We consider the energy averaged two-point correlator of spectral determinants
and calculate contributions beyond the diagonal approximation using
semiclassical methods. Evaluating the contributions originating from
pseudo-orbit correlations in the same way as in [S. Heusler {\textit {et al.}}\
2007 Phys. Rev. Lett. {\textbf{98}}, 044103] we find a discrepancy between the
semiclassical and the random matrix theory result. A complementary analysis
based on a field-theoretical approach shows that the additional terms occurring
in semiclassics are cancelled in field theory by so-called curvature effects.
We give the semiclassical interpretation of the curvature effects in terms of
contributions from multiple transversals of periodic orbits around shorter
periodic orbits and discuss the consistency of our results with previous
approaches. | 0903.5091v1 |
2010-11-10 | Ab initio prediction of ferrimagnetism, exchange interactions and Curie temperatures in Mn2TiZ Heusler compounds | The Heusler compounds Mn$_2$TiZ (Z = Al, Ga, In, Si, Ge, Sn, P, As, Sb) are
of large interest due to their potential ferrimagnetic properties and high spin
polarization. Here, we present calculations of the structural and magnetic
properties of these materials. Their magnetic moment follows the Slater-Pauling
rule $m = N_V - 24$. None of them is actually a perfect half-metallic
ferrimagnet, but some exhibit more than 90% spin polarization and Curie
temperatures well above room temperature. The exchange interactions are
complex, direct and indirect exchange contributions are identified. The Curie
temperature scales with the total magnetic moment, and it has a positive
pressure dependence. The role of the Z element is investigated: it influences
the properties of the compounds mainly via its valence electron number and its
atomic radius, which determines the lattice parameter. Based on these results,
Mn$_2$TiSi, Mn$_2$TiGe, and Mn$_2$TiSn are proposed as candidates for
spintronic applications. | 1011.2486v1 |
2010-11-26 | Weak itinerant ferromagnetism in Heusler type Fe2VAl0.95 | We report measurements of the magnetic, transport and thermal properties of
the Heusler type compound Fe2VAl0.95. We show that while stoichiometric Fe2VAl
is a non-magnetic semi-metal a 5% substitution on the Al-site with the 3d
elements Fe and V atoms leads to a ferromagnetic ground state with a Curie
temperature TC = 33+-3 K and a small ordered moment ms = 0.12 mB/Fe in
Fe2VAl0.95. The reduced value of the ratio ms/mp = 0.08, where mp = 1.4 mB/Fe
is the effective Curie-Weiss moment, together with the analysis of the
magnetization data M(H,T), show magnetism is of itinerant nature. The specific
heat shows an unusual temperature variation at low temperatures with an
enhanced Sommerfeld coefficient, g = 12 mJK-2mol-1. The resistivity, r(T), is
metallic and follows a power law behavior r(T) = r0+AT^n with n = 1.5 below TC.
With applying pressure, TC decreases with the rate of (1/TC)(dTC /dP) = -0.061
GPa-1. We conclude substitution on the Al-site with Fe and V atoms results in
itinerant ferromagnetism with a low carrier density. | 1011.5704v1 |
2011-02-25 | CuMn-V compounds: a transition from semimetal low-temperature to semiconductor high-temperature antiferromagnets | We report on a theoretical and experimental study of CuMn-V antiferromagnets.
Previous works showed low-temperature antiferomagnetism and semimetal
electronic structure of the semi-Heusler CuMnSb. In this paper we present
theoretical predictions of high-temperature antiferromagnetism in the stable
orthorhombic phases of CuMnAs and CuMnP. The electronic structure of CuMnAs is
at the transition from a semimetal to a semiconductor and we predict that CuMnP
is a semiconductor. We show that the transition to a semiconductor-like band
structure upon introducing the lighter group-V elements is present in both the
metastable semi-Heusler and the stable orthorhombic crystal structures. On the
other hand, the orthorhombic phase is crucial for the high N\'eel temperature.
Results of X-ray diffraction, magnetization, transport, and neutron diffraction
measurements we performed on chemically synthesized CuMnAs are consistent with
the theory predictions. | 1102.5373v1 |
2011-07-04 | Influence of tetragonal distortion on the topological electronic structure of the half-Heusler compound LaPtBi from first principles | The electronic structures of tetragonally distorted half-Heuselr compound
LaPtBi in the C1b structure are investigated in the framework of density
functional theory using the full potential linearized augmented plane with
local spin density approximation method. The calculation results show that both
the band structures and the Fermi level can be tuned by using either
compressive or tensile in-plane strain. A large bulk band gap of 0.3 eV can be
induced through the application of a compressive in-pane strain in LaPtBi with
the assumption of a relaxed volume of the unit cell. Our results could serve as
a guidance to realize topological insulators in half-Heusler compounds by
strain engineering. | 1107.0531v1 |
2011-07-25 | Half-Heusler semiconductors as piezoelectrics | One of the central challenges in materials science is the design of
functional and multifunctional materials, in which large responses are produced
by applied fields and stresses. A rapidly developing paradigm for the rational
design of such materials is based on the first-principles study of a large
materials family, the perovskite oxides being the prototypical case.
Specifically, first-principles calculations of structure and properties are
used to explore the microscopic origins of the functional properties of
interest and to search a large space of equilibrium and metastable phases to
identify promising candidate systems. In this paper, we use a first-principles
rational-design approach to demonstrate semiconducting half-Heusler compounds
as a previously-unrecognized class of piezoelectric materials, and to provide
guidance for the experimental realization and further investigation of
high-performance materials suitable for practical applications. | 1107.5078v2 |
2012-05-28 | Stationary Black Holes: Uniqueness and Beyond | The spectrum of known black-hole solutions to the stationary Einstein
equations has been steadily increasing, sometimes in unexpected ways. In
particular, it has turned out that not all black-hole-equilibrium
configurations are characterized by their mass, angular momentum and global
charges. Moreover, the high degree of symmetry displayed by vacuum and
electro-vacuum black-hole spacetimes ceases to exist in self-gravitating
non-linear field theories. This text aims to review some developments in the
subject and to discuss them in light of the uniqueness theorem for the
Einstein-Maxwell system. | 1205.6112v1 |
2012-07-27 | Half-Metallic Ferromagnetism in the Heusler Compound Co$_2$FeSi revealed by Resistivity, Magnetoresistance, and Anomalous Hall Effect measurements | We present electrical transport data for single-crystalline Co$_2$FeSi which
provide clear-cut evidence that this Heusler compound is truly a half-metallic
ferromagnet, i.e. it possesses perfect spin-polarization. More specifically,
the temperature dependence of $\rho$ is governed by electron scattering off
magnons which are thermally excited over a sizeable gap $\Delta\approx 100 K$
($\sim 9 meV$) separating the electronic majority states at the Fermi level
from the unoccupied minority states. As a consequence, electron-magnon
scattering is only relevant at $T\gtrsim\Delta$ but freezes out at lower
temperatures, i.e., the spin-polarization of the electrons at the Fermi level
remains practically perfect for $T\lesssim\Delta$. The gapped magnon population
has a decisive influence on the magnetoresistance and the anomalous Hall effect
(AHE): i) The magnetoresistance changes its sign at $T\sim 100 K$, ii) the
anomalous Hall coefficient is strongly temperature dependent at $T\gtrsim 100
K$ and compatible with Berry phase related and/or side-jump electronic
deflection, whereas it is practically temperature-independent at lower
temperatures. | 1207.6611v1 |
2012-09-29 | Realization of spin gapless semiconductors: the Heusler compound Mn2CoAl | Recent studies have reported an interesting class of semiconductor materials
that bridge the gap between semiconductors and halfmetallic ferromagnets. These
materials, called spin gapless semiconductors, exhibit a bandgap in one of the
spin channels and a zero bandgap in the other and thus allow for tunable spin
transport. Here, a theoretical and experimental study of the spin gapless
Heusler compound Mn2CoAl is presented. It turns out that Mn2CoAl is a very
peculiar ferrimagnetic semiconductor with a magnetic moment of 2 {\mu}B and a
high Curie temperature of 720 K. Below 300 K, the compound exhibits nearly
temperature-independent conductivity, very low, temperature-independent carrier
concentration, and a vanishing Seebeck coefficient. The magnetoresistance
changes sign with temperature. In high fields, it is positive and
non-saturating at low temperatures, but negative and saturating at high
temperatures. The anomalous Hall effect is comparatively low, which is
explained by the close antisymmetry of the Berry curvature for kz of opposite
sign. | 1210.0148v1 |
2012-10-22 | Fabrication and characterization of the gapless half-Heusler YPtSb thin films | Half-Heusler YPtSb thin films were fabricated by magnetron co-sputtering
method on MgO-buffered SiO2/Si(001) substrates. X-ray diffraction pattern and
Energy dispersive X-ray spectroscopy confirmed the high-quality growth and
stoichiometry. The temperature dependence of the resistivity shows a
semiconducting-type behavior down to low temperature. The Hall mobility was
determined to be 450 cm2/Vs at 300K, which is much higher than the bulk value
(300 cm2/Vs). In-plane magnetoresistance (MR) measurements with fields applied
along and perpendicular to the current direction show opposite MR signs, which
suggests the possible existence of the topological surface states. | 1210.5808v1 |
2012-12-13 | First-principles study of the structural stability of Mn3Z (Z=Ga, Sn and Ge) Heusler compounds | We investigate the structural stability and magnetic properties of cubic,
tetragonal and hexagonal phases of Mn3Z (Z=Ga, Sn and Ge) Heusler compounds
using first-principles density-functional theory. We propose that the cubic
phase plays an important role as an intermediate state in the phase transition
from the hexagonal to the tetragonal phases. Consequently, Mn3Ga and Mn3Ge
behave differently from Mn3Sn, because the relative energies of the cubic and
hexagonal phases are different. This result agrees with experimental
observations from these three compounds. The weak ferromagnetism of the
hexagonal phase and the perpendicular magnetocrystalline anisotropy of the
tetragonal phase obtained in our calculations are also consistent with
experiment. | 1212.3144v1 |
2013-02-08 | Superconductivity in the noncentrosymmetric half-Heusler compound LuPtBi : A possible topological superconductor | We report superconductivity in the ternary half-Heusler compound LuPtBi, with
Tc = 1.0 K and Hc2 = 1.6 T. The crystal structure of LuPtBi lacks inversion
symmetry, hence the material is a noncentrosymmetric superconductor.
Magnetotransport data show semimetallic behavior in the normal state, which is
evidence for the importance of spin-orbit interaction. Theoretical calculations
indicate that the strong spin-orbit interaction in LuPtBi should cause strong
band inversion, making this material a promising candidate for 3D topological
superconductivity. | 1302.1943v2 |
2013-02-11 | Phase stability of chromium based compensated ferrimagnets with inverse Heusler structure | Chromium based inverse Heusler compounds of the type Cr2YZ (Y=Co, Fe; Z=Al,
Ga, In, Si, Ge, Sn) have been proposed as fully compensated half-metallic
ferrimagnets. Such materials are of large interest for spintronics because they
combine small magnetic moment with high spin polarization over a wide
temperature range. We assess their thermodynamic stability by their formation
enthalpies obtained from density functional theory calculations. All compounds
under investigation are unstable. Cr2FeSi and Cr2CoAl are stable with respect
to the elemental constituents, but decompose into binary phases. Cr2FeGe,
Cr2CoGa, Cr2FeSn and Cr2CoIn are found to be unstable with respect to their
elemental constituents. We identify possible binary decompositions. | 1302.2487v2 |
2013-10-17 | Superconductivity and magnetic order in the non-centrosymmetric Half Heusler compound ErPdBi | We report superconductivity at $T_c = 1.22$ K and magnetic order at $T_N =
1.06$ K in the semi-metallic noncentrosymmetric Half Heusler compound ErPdBi.
The upper critical field, $B_{c2}$, has an unusual quasi-linear temperature
variation and reaches a value of 1.6 T for $T \rightarrow 0$. Magnetic order is
found below $T_c$ and is suppressed at $B{_M} \sim 2.5$ T for $T \rightarrow
0$. Since $T_c \simeq T_N$, the interaction of superconductivity and magnetism
is expected to give rise to a complex ground state. Moreover, electronic
structure calculations show ErPdBi has a topologically nontrivial band
inversion and thus may serve as a new platform to study the interplay of
topological states, superconductivity and magnetic order. | 1310.4592v1 |
2014-02-24 | Experimental realization of a semiconducting full Heusler compound: Fe2TiSi | Single-phase films of the full Heusler compound Fe2TiSi have been prepared by
magnetron sputtering. The compound is found to be a semiconductor with a gap of
0.4eV. The electrical resistivity has a logarithmic temperature dependence up
to room temperature due to Kondo scattering of a dilute free electron gas off
superparamagnetic impurities. The origin of the electron gas is extrinsic due
to disorder or off-stoichiometry. Density functional theory calculations of the
electronic structure are in excellent agreement with electron energy loss,
optical, and x-ray absorption experiments. Fe2TiSi may find applications as a
thermoelectric material. | 1402.5755v1 |
2014-03-11 | Spin Dependent Lifetimes and Spin-orbit Hybridization Points in Heusler Compounds | We present an ab initio calculation of the k and spin-resolved electronic
lifetimes in the half-metallic Heusler compounds Co(2)MnSi and Co(2)FeSi. We
determine the spin-flip and spin-conserving contributions to the lifetimes and
study in detail the behavior of the lifetimes around states that are strongly
spin-mixed by spin-orbit coupling. We find that, for non-degenerate bands, the
spin mixing alone does not determine the energy dependence of the (spin-flip)
lifetimes. Qualitatively, the lifetimes reflect the lineup of electron and hole
bands. We predict that different excitation conditions lead to drastically
different spin-flip dynamics of excited electrons and may even give rise to an
enhancement of the non-equilibrium spin polarization. | 1403.2590v2 |
2014-08-01 | NMR evidence for enhanced orbital diamagnetism in topologically nontrivial half-Heusler semimetals | 209Bi nuclear magnetic resonance (NMR) spectroscopy was employed to probe
potential spin-orbit effects on orbital diamagnetism in YPtBi and YPdBi
crystals. The observed opposite sign and temperature dependent magnitude of
209Bi NMR shifts of both crystals reveal experimental signatures of enhanced
orbital diamagnetism induced by spin-orbit interactions. This investigation
indicates that NMR isotropic shifts might be beneficial in search of
interesting spin-electronic phases among a vast number of topological
nontrivial half-Heusler semimetals. | 1408.0078v2 |
2014-08-02 | Bending strain-tunable magnetic anisotropy in Co2FeAl Heusler thin film on Kapton | Bending effect on the magnetic anisotropy in 20 nm Co$_{2}$FeAl Heusler thin
film grown on Kapton\textregistered{} has been studied by ferromagnetic
resonance and glued on curved sample carrier with various radii. The results
reported in this letter show that the magnetic anisotropy is drastically
changed in this system by bending the thin films. This effect is attributed to
the interfacial strain transmission from the substrate to the film and to the
magnetoelastic behavior of the Co$_{2}$FeAl film. Moreover two approaches to
determine the in-plane magnetostriction coefficient of the film, leading to a
value that is close to $\lambda^{CFA}=14\times10^{-6}$, have been proposed. | 1408.0379v1 |
2014-12-10 | Chemical disorder as engineering tool for spin-polarizationin Mn3Ga-based Heusler systems | Our study highlights spin-polarization mechanisms in metals, by focusing on
the mobilities of conducting electrons with different spins instead of their
quantities. Here, we engineer electron mobility by applying chemical disorder
induced by non-stoichiometric variations. As a practical example, we discuss
the scheme that establishes such variations in tetragonal Mn3Ga Heusler
material. We justify this approach using first-principles calculations of the
spin-projected conductivity components based on the Kubo-Greenwood formalism.
It follows that, in majority of the cases, even a small substitution of some
other transition element instead of Mn may lead to a substantial increase in
spin-polarization along the tetragonal axis. | 1412.3394v2 |
2015-03-15 | Magnetic structure of the antiferromagnetic half-Heusler compound NdBiPt | We present results of single crystal neutron diffraction experiments on the
rare-earth, half-Heusler antiferromagnet (AFM) NdBiPt. This compound exhibits
an AFM phase transition at $T_{\mathrm N}=2.18$~K with an ordered moment of
$1.78(9)$~$\mu_{\mathrm B}$ per Nd atom. The magnetic moments are aligned along
the $[001]$-direction, arranged in a type-I AFM structure with ferromagnetic
planes, alternating antiferromagnetically along a propagation vector $\tau$ of
$(100)$. The $R$BiPt ($R$= Ce-Lu) family of materials has been proposed as
candidates of a new family of antiferromagnetic topological insulators (AFTI)
with magnetic space group that corresponds to a type-II AFM structure where
ferromagnetic sheets are stacked along the space diagonal. The resolved
structure makes it unlikely, that NdBiPt qualifies as an AFTI. | 1503.04487v3 |
2015-04-13 | Magnetic and superconducting phase diagram of the half-Heusler topological semimetal HoPdBi | We report a study of the magnetic and electronic properties of the
non-centrosymmetric half-Heusler antiferromagnet HoPdBi ($T_N = 2.0$ K).
Magnetotransport measurements show HoPdBi has a semimetallic behaviour with a
carrier concentration $n=3.7 \times 10^{18}$ cm$^{-3}$ extracted from the
Shubnikov-de Haas effect. The magnetic phase diagram in the field-temperature
plane has been determined by transport, magnetization and thermal expansion
measurements: magnetic order is suppressed at $B_M\sim 3.6$ T for $T
\rightarrow 0$. Superconductivity with $T_c \sim 1.9$ K is found in the
antiferromagnetic phase. Ac-susceptibility measurements provide solid evidence
for bulk superconductivity below $T_c = 0.75$ K with a screening signal close
to a volume fraction of 100 %. The upper critical field shows an unusual linear
temperature variation with $B_{c2}(T \rightarrow 0) = 1.1$ T. We also report
electronic structure calculations that classify HoPdBi as a new topological
semimetal, with a non-trivial band inversion of 0.25 eV. | 1504.03181v1 |
2015-10-21 | Titanium Nitride as a Seed Layer for Heusler Compounds | Titanium nitride (TiN) shows low resistivity at room temperature, high
thermal stability and thus has the potential to serve as seed layer in magnetic
tunnel junctions. High quality TiN thin films with regard to the
crystallographic and electrical properties were grown and characterized by
X-ray diffraction and 4-terminal transport measurements. Element specific X-ray
absorption spectroscopy revealed pure TiN in the bulk. To investigate the
influence of a TiN seed layer on a ferro(i)magnetic bottom electrode, an
out-of-plane magnetized Mn2.45Ga as well as in- and out-of-plane magnetized
Co2FeAl thin films were deposited on a TiN buffer, respectively. The magnetic
properties were investigated using a superconducting quantum interference
device (SQUID) and anomalous Hall effect (AHE) for Mn2.45Ga. Magneto optical
Kerr effect (MOKE) measurements were carried out to investigate the magnetic
properties of Co2FeAl. TiN buffered Mn2.45Ga thin films showed higher
coercivity and squareness ratio compared to unbuffered samples. The Heusler
compound Co2FeAl showed already good crystallinity when grown at room
temperature. | 1510.06256v3 |
2015-10-23 | Laser-induced THz magnetization precession for a tetragonal Heusler-like nearly compensated ferrimagnet | Laser-induced magnetization precessional dynamics was investigated in
epitaxial films of Mn$_3$Ge, which is a tetragonal Heusler-like nearly
compensated ferrimagnet. The ferromagnetic resonance (FMR) mode was observed,
the precession frequency for which exceeded 0.5 THz and originated from the
large magnetic anisotropy field of approximately 200 kOe for this ferrimagnet.
The effective damping constant was approximately 0.03. The corresponding
effective Landau-Lifshitz constant of approximately 60 Mrad/s and is comparable
to those of the similar Mn-Ga materials. The physical mechanisms for the
Gilbert damping and for the laser-induced excitation of the FMR mode were also
discussed in terms of the spin-orbit-induced damping and the laser-induced
ultrafast modulation of the magnetic anisotropy, respectively. | 1510.06793v1 |
2015-10-27 | Spin-resolved Fermi surface of the localized ferromagnetic Heusler compound Cu$_2$MnAl measured with spin-polarized positron annihilation | We determined the bulk electronic structure in the prototypical Heusler
compound Cu$_2$MnAl by measuring the Angular Correlation of Annihilation
Radiation (2D-ACAR) using spin-polarized positrons. To this end, a new
algorithm for reconstructing 3D densities from projections is introduced that
allows us to corroborate the excellent agreement between our electronic
structure calculations and the experimental data. The contribution of each
individual Fermi surface sheet to the magnetization was identified, and summed
to a total spin magnetic moment of $3.6\,\pm\,0.5\,\mu_B/\mathrm{f.u.}$. | 1510.07808v1 |
2015-11-26 | Symmetry-protected ideal Weyl semimetal in HgTe-class materials | Ideal Weyl semimetals with all Weyl nodes exactly at the Fermi level and no
coexisting trivial Fermi surfaces in the bulk, similar to graphene, could
feature deep physics such as exotic transport phenomena induced by the chiral
anomaly. Here, we show that HgTe and half-Heusler compounds, under a broad
range of in-plane compressive strain, could be materials in nature realizing
ideal Weyl semimetals with four pairs of Weyl nodes and topological surface
Fermi arcs. Generically, we find that the HgTe-class materials with nontrivial
band inversion and noncentrosymmetry provide a promising arena to realize ideal
Weyl semimetals. Such ideal Weyl semimetals could further provide a unique
platform to study emergent phenomena such as the interplay between ideal Weyl
fermions and superconductivity in the half-Heusler compound LaPtBi. | 1511.08284v2 |
2016-04-05 | Composition induced metal-insulator quantum phase transition in the Heusler type Fe2VAl | We report the magnetism and transport properties of the Heusler compound
Fe2+xV1-xAl at -0.10 < x < 0.10 under pressure and a magnetic field. A
metal-insulator quantum phase transition occurred at x = -0.05. Application of
pressure or a magnetic field facilitated the emergence of finite
zero-temperature conductivity around the critical point, which scaled
approximately according to the power law. At x < -0.05, a localized
paramagnetic spin appeared, whereas above the ferromagnetic quantum critical
point at x = 0.05, itinerant ferromagnetism was established. At the quantum
critical points at x = -0.05 and 0.05, the resistivity and specific heat
exhibited singularities characteristic of a Griffiths phase appearing as an
inhomogeneous electronic state. | 1604.01114v2 |
2016-04-21 | Magnetic properties and Curie temperatures of disordered Heusler compounds: Co(1+x)Fe(2-x)Si | The local atomic environments and magnetic properties were investigated for a
series of Co(1+x)Fe(2-x)Si (0<x<1) Heusler compounds. While the total magnetic
moment in these compounds increases with the number of valance electrons, the
highest Curie temperature (Tc) in this series was found for Co1.5Fe1.5Si, with
a Tc of 1069 K (24 K higher than the well known Co2FeSi). 57Fe M\"ossbauer
spectroscopy was used to characterize the local atomic order and to estimate
the Co and Fe magnetic moments. Consideration of the local magnetic moments and
the exchange integrals is necessary to understand the trend in Tc. | 1604.06235v1 |
2016-10-18 | Magnetic properties of low-moment ferrimagnetic Heusler Cr2CoGa thin films grown by molecular beam epitaxy | Recently, theorists have predicted many materials with a low magnetic moment
and large spin-polarization for spintronic applications. These compounds are
predicted to form in the inverse Heusler structure, however, many of these
compounds have been found to phase segregate. In this study, ordered Cr2CoGa
thin films were synthesized without phase segregation using molecular beam
epitaxy. The present as-grown films exhibit a low magnetic moment from
antiferromagnetically coupled Cr and Co atoms as measured with SQUID
magnetometry and soft X-ray magnetic circular dichroism. Electrical
measurements demonstrated a thermally-activated semiconductor-like resistivity
with an activation energy of 87 meV. These results confirm spin gapless
semiconducting behavior, which makes these thin films well positioned for
future devices. | 1610.05808v1 |
2016-11-24 | Design of L2_1-type antiferromagnetic semiconducting full-Heusler compounds: A first principles DFT+GW study | Antiferromagnetic spintronics is an on-going growing field of research.
Employing both standard density functional theory and the $GW$ approximation
within the framework of the FLAPW method, we study the electronic and magnetic
properties of seven potential antiferromagnetic semiconducting Heusler
compounds with 18 (or 28 when Zn is present) valence electrons per unit cell.
We show that in these compounds G-type antiferromagnetism is the ground state
and that they are all either emiconductors (Cr$_2$ScP, Cr$_2$TiZn, V$_2$ScP,
V$_2$TiSi, and V$_3$Al) or semimetals (Mn$_2$MgZn and Mn$_2$NaAl). The
many-body corrections have a minimal effect on the electronic band structure
with respect to the standard electronic structure calculations. | 1611.08080v2 |
2017-03-03 | Discovery of Magnetic Antiskyrmions Beyond Room Temperature in Tetragonal Heusler Materials | Skyrmions, topologically stable spin textures, are of great interest for new
generations of spintronic devices. In general, the stabilization of skyrmions
has been achieved in systems with broken inversion symmetry, where the
asymmetric Dzyaloshinskii-Moriya interaction (DMI) modifies the uniform
magnetic state to a swirling state. Depending on the crystal symmetries, two
distinct types of skyrmions, Bloch and N\'eel types, have been observed
experimentally. Here, we present, the experimental manifestation of a special
type of spin-swirling, namely antiskyrmions, in a family of acentric tetragonal
Heusler compounds with D2d crystal symmetry. A spiral magnetic ground-state,
which propagates in the tetragonal basal plane, is transformed into a skyrmion
lattice-state under magnetic fields applied along the tetragonal axis over a
wide temperature interval. Direct imaging by Lorentz Transmission Electron
Microscopy (LTEM) shows field stabilized antiskyrmion lattices and isolated
antiskyrmions between 100 K and 400 K, and zero-field metastable antiskyrmions
at low temperatures. | 1703.01017v1 |
2017-03-06 | A first-principles DFT+GW study of spin-filter and spin-gapless semiconducting Heusler compounds | Among Heusler compounds, the ones being magnetic semiconductors (also known
as spin-filter materials) are widely studied as they offer novel
functionalities in spintronic/magnetoelectronic devices. The spin-gapless
semiconductors are a special case. They possess a zero or almost-zero energy
gap in one of the two spin channels. We employ the $GW$ approximation, which
allows an elaborate treatment of the electronic correlations, to simulate the
electronic band structure of these materials. Our results suggest that in most
cases the use of $GW$ self energy instead of the usual density functionals is
important to accurately determine the electronic properties of magnetic
semiconductors. | 1703.02142v2 |
2017-08-15 | Electronic fitness function for screening semiconductors as thermoelectric materials | We introduce a simple but efficient electronic fitness function (EFF) that
describes the electronic aspect of the thermoelectric performance. This EFF
finds materials that overcome the inverse relationship between $\sigma$ and $S$
based on the complexity of the electronic structures regardless of specific
origin (e.g., isosurface corrugation, valley degeneracy, heavy-light bands
mixture, valley anisotropy or reduced dimensionality). This function is well
suited for application in high throughput screening. We applied this function
to 75 different thermoelectric and potential thermoelectric materials including
full- and half-Heuslers, binary semiconductors and Zintl phases. We find an
efficient screening using this transport function. The EFF identifies known
high performance $p$- and $n$-type Zintl phases and half-Heuslers. In addition,
we find some previously unstudied phases with superior EFF. | 1708.04499v2 |
2017-09-13 | Hole-doped cobalt-based Heusler phases as prospective high-performance high-temperature thermoelectrics | Materials design based on first-principles electronic calculations has proven
a fruitful strategy to identify new thermoelectric materials with a favorable
figure of merit. Recent electronic structure calculations predict that in
cobalt-based half-Heusler systems a power factor higher than in CoTiSb can be
achieved upon p-type doping of CoVSn, CoNbSn, CoTaSn, CoMoIn, and CoWIn. Here,
using a first-principles approach and semi-classical Boltzmann transport
theory, we investigate the electrical and thermal transport properties of these
materials. The calculated thermal conductivity at room temperature of all the
systems is lower than that of CoTiSb, with CoMoIn and CoWIn having an almost
3-fold lower thermal conductivity than CoTiSb. We also provide conservative
estimates of the figure of merit for these systems which all turn out to be
higher than in CoTiSb and to have a maximum value for CoWIn. | 1709.04243v1 |
2018-01-24 | Origin of efficient thermoelectric performance in half-Heusler FeNb$_{0.8}$Ti$_{0.2}$Sb | A half-Heusler material FeNb$_{0.8}$Ti$_{0.2}$Sb has been identified as a
promising thermoelectric material due to its excellent thermoelectric
performance at high temperatures. The origins of the efficient thermoelectric
performance are investigated through a series of low-temperature (2 - 400 K)
measurements. The high data coherence of the low and high temperatures is
observed. An optimal and nearly temperature-independent carrier concentration
is identified, which is ideal for the power factor. The obtained single type of
hole carrier is also beneficial to the large Seebeck coefficient. The
electronic thermal conductivity is found to be comparable to the lattice
thermal conductivity and becomes the dominant component above 200 K. These
findings again indicate that electron scattering plays a key role in the
electrical and thermal transport properties. The dimensionless figure of merit
is thus mainly governed by the electronic properties. These effects obtained at
low temperatures with the avoidance of possible thermal fluctuations together
offer the physical origin for the excellent thermoelectric performance in this
material. | 1801.07935v1 |
2018-01-25 | Heusler compounds -- how to tune the magnetocrystalline anisotropy | Tailoring and controlling magnetic properties is an important factor for
materials design. Here, we present a case study for Ni-based Heusler compounds
of the type Ni$_2$YZ with Y = Mn, Fe, Co and Z = B, Al, Ga, In, Si, Ge, Sn
based on first principles electronic structure calculations. These compounds
are interesting since the materials properties can be quite easily tuned by
composition and many of them possess a non-cubic ground state being a
prerequisite for a finite magnetocrystalline anisotropy (MAE). We discuss
systematically the influence of doping at the Y and Z sublattice as well of
lattice deformation on the MAE. We show that in case of Ni$_2$CoZ the phase
stability and the MAE can be improved using quaternary systems with elements
from group 13 and 14 on the Z sublattice whereas changing the Y sublattice
occupation by adding Fe does not lead to an increase of the MAE. Furthermore,
we studied the influence of the lattice ratio on the MAE. Showing that small
deviations can lead to a doubling of the MAE as in case of Ni$_2$FeGe. Even
though we demonstrate this for a limited set of systems the findings may carry
over to other related systems. | 1801.08511v1 |
2018-06-11 | Positron annihilation spectroscopy for the pure and Niobium doped ZrCo$_2$Sn Heusler compound | We perform spin-polarized two-dimensional angular correlation of annihilation
radiation (2D-ACAR) calculations for the recently predicted ZrCo$_2$Sn-Weyl
Heusler compound within the density functional theory using the generalized
gradient approximation (GGA) and its extension GGA+U. We confirm that within
the GGA+U method, a pair of Weyl-points are revealed, and that by doping with
Niobium, for the composition Nb$_{0.3}$Zr$_{0.7}$Co$_2$Sn, the Weyl points are
reaching the Fermi level. Our 2D-ACAR results indicate the existence of the
Weyl points, however, within the present calculation, it is uncertain if the
smearing at the Fermi level can be attributed to the positron wave function. | 1806.04093v1 |
2018-06-14 | Superconductivity in half-Heusler compound TbPdBi | We have studied the half-Heusler compound TbPdBi through resistivity,
magnetization, Hall effect and heat capacity measurements. A semimetal behavior
is observed in its normal state transport properties, which is characterized by
a large negative magnetoresistance below 100 K. Notably, we find the
coexistence of superconductivity and antiferromagnetism in this compound. The
superconducting transition appears at 1.7 K, while the antiferromagnetic phase
transition takes place at 5.5 K. The upper critical field $H_{c2}$ shows an
unusual linear temperature dependence, implying unconventional
superconductivity. Moreover, when the superconductivity is suppressed by
magnetic field, its resistivity shows plateau behavior, a signature often seen
in topological insulators/semimetals. These findings establish TbPdBi as a
platform for study of the interplay between superconductivity, magnetism and
non-trivial band topology. | 1806.05314v1 |
2018-11-12 | Interface spin polarization of the Heusler compound Co2MnSi probed by unidirectional spin Hall magnetoresistance | Many Heusler compounds are predicted to be ferromagnetic half metals in the
bulk, which makes them promising compounds for spintronics. However, for
devices the transport spin polarization at specific interfaces requires
optimization. We show that investigations of the unidirectional
magnetoresistance provide an alternative approach to access this quantity.
Based on a Wheatstone-bridge design we probed the unidirectional
magnetoresistance of Co2MnSi/(Ag, Cu, or Cr)(0.5 nm)/Pt (or Ta) multilayers and
separate the spin-dependent unidirectional spin Hall magnetoresistance from
other contributions. We demonstrated that by the insertion of a thin epitaxial
Ag layer the spin-dependent contribution is doubled corresponding to a
significant increase of the transport spin polarization, which is discussed in
the framework of highly spin polarized interface states. | 1811.04592v2 |
2020-01-22 | Characterization of rattling in relation to thermal conductivity: ordered half-Heusler semiconductors | The factors that affect the thermal conductivity of semiconductors is a topic
of great scientific interest, especially in relation to thermoelectrics. Key
developments have been the concept of the phonon-glass-electron-crystal (PGEC)
and the related idea of rattling to achieve this. We use first principles
phonon and thermal conductivity calculations in order to explore the concept of
rattling for stoichiometric ordered half-Heusler compounds. These compounds can
be regarded as filled zinc blende materials, and the filling atom could be
viewed as a rattler if it is weakly bound. We use two simple metrics, one
related to the frequency and the other to bond frustration and anharmonicity.
We find that both measures correlate with thermal conductivity. This suggests
that both may be useful in screening materials for low thermal conductivity. | 2001.08029v1 |
2021-07-15 | Microstructure manipulation by laser-surface remelting of a full-Heusler compound to enhance thermoelectric properties | There is an increasing reckoning that the thermoelectric performance of a
material is dependent on its microstructure. However, the
microstructure-properties relationship often remains elusive, in part due to
the complexity of the hierarchy and scales of features that influence transport
properties. Here, we focus on the promising Heusler-Fe2VAl compound. We
directly correlate microstructure and local properties, using advanced scanning
electron microscopy methods including in-situ four-point-probe technique for
electron transport measurements. The local thermal conductivity is investigated
by scanning thermal microscopy. Finally, atom probe tomography provides
near-atomic scale compositional analysis. To locally manipulate the
microstructure, we use laser surface remelting. The rapid quenching creates a
complex microstructure with a high density of dislocations and small, elongated
grains. We hence showcase that laser surface remelting can be employed to
manipulate the microstructure to reduce the thermal conductivity and electrical
resistivity, leading to a demonstrated enhancement of the thermoelectric
performance at room temperature. | 2107.07327v1 |
2017-05-11 | Pursuit of thermoelectric properties in a novel Half Heusler compound: HfPtPb | We explore the structural, electronic, mechanical and thermoelectric
properties of a new half Heusler compound, HfPtPb which is all metallic heavy
element and has been recently been proposed to be stable [Nature Chem 7 (2015)
308]. In the present work, we employ density functional theory and
semiclassical Boltzmann transport equations with constant relaxation time
approximation. The mechanical properties such as Shear modulus, Young modulus,
elastic constants, Poisson ratio, and shear anisotropy factor are investigated.
The elastic and phonon properties reveal that this compound is mechanically and
dynamically stable. Pugh and Frantsevich ratio demonstrates the ductile
behavior and Shear anisotropic factor reflects the anisotropic nature of
HfPtPb. The calculation of band structure predicts that this compound is
semiconductor in nature with band gap 0.86 eV. The thermoelectric transport
parameters such as Seebeck coefficient, electrical conductivity, and electronic
thermal conductivity and lattice thermal conductivity have been calculated as a
function of temperature. The highest value of Seebeck coefficient is obtained
for n-type doping at optimal carrier concentration. We predict the maximum
value of the figure of merit 0.25 at 1000 K. Our investigation suggests that
this material is n-type semiconductor. | 1705.04015v1 |
2017-05-23 | Integration of antiferromagnetic Heusler compound Ru$_2$MnGe into spintronic devices | We report on the first integration of an antiferromagnetic Heusler compound
acting as a pinning layer into magnetic tunneling junctions. The
antiferromagnet Ru$_2$MnGe is used to pin the magnetization direction of a
ferromagnetic Fe layer in MgO based thin film tunnelling magnetoresistance
stacks. The samples were prepared using magnetron co-sputtering. We investigate
the structural properties by X-ray diffraction and reflection, as well as
atomic force and high-resolution transmission electron microscopy. We find an
excellent crystal growth quality with low interface roughnesses of 1-3 \r{A},
which is crucial for the preparation of working tunnelling barriers. Using Fe
as a ferromagnetic electrode material we prepared magnetic tunneling junctions
and measured the magnetoresistance. We find a sizeable maximum
magnetoresistance value of 135%, which is comparable to other common Fe based
MTJ systems. | 1705.08420v1 |
2017-05-30 | Heteroepitaxial growth of tetragonal Mn$_{2.7-x}$Fe$_{x}$Ga$_{1.3}$ (0 $\leqslant$ x $\leqslant$ 1.2) Heusler films with perpendicular magnetic anisotropy | This work reports on the structural and magnetic properties of
Mn$_{2.7-x}$Fe$_{x}$Ga$_{1.3}$ Heusler films with different Fe content x (0
$\leqslant$ x $\leqslant$ 1.2). The films were deposited heteroepitaxially on
MgO single crystal substrates, by magnetron sputtering.
Mn$_{2.7-x}$Fe$_{x}$Ga$_{1.3}$ films with the thickness of 35 nm were
crystallized in tetragonal D0$_{22}$ structure with (001) preferred
orientation. Tunable magnetic properties were achieved by changing the Fe
content x. Mn$_{2.7-x}$Fe$_{x}$Ga$_{1.3}$ thins films exhibit high uniaxial
anisotropy Ku $\geqslant$ 1.4 MJ/m3, coercivity from 0.95 to 0.3 T and
saturation magnetization from 290 to 570 kA/m. The film with
Mn$_{1.6}$Fe$_{1.1}$Ga$_{1.3}$ composition shows high Ku of 1.47 MJ/m3 and
energy product ${(BH)_{max}}$ of 37 kJ/m3, at room temperature. These findings
demonstrate that Mn$_{2.7-x}$Fe$_{x}$Ga$_{1.3}$ films have promising properties
for mid-range permanent magnet and spintronic applications. | 1705.10668v1 |
2019-07-09 | Magnetic instabilities in doped Fe$_2YZ$ full-Heusler thermoelectric compounds | Thermoelectricity is a promising avenue for harvesting energy but large-scale
applications are still hampered by the lack of highly-efficient low-cost
materials. Recently, Fe$_2YZ$ Heusler compounds were predicted theoretically to
be interesting candidates with large thermoelectric power factor. Here, we show
that under doping conditions compatible with thermoelectric applications, these
materials are prone to an unexpected magnetic instability detrimental to their
thermoelectric performance. We rationalize the physics at the origin of this
instability, provide guidelines for avoiding it and discuss its impact on the
thermoelectric power factor. Doing so, we also point out the shortcomings of
the rigid band approximation commonly used in high-throughput theoretical
searches of new thermoelectrics. | 1907.04267v2 |
2012-09-17 | Nonlinear emission of spin-wave caustics from an edge mode of a micro-structured Co2Mn0.6Fe0.4Si waveguide | Magnetic Heusler materials with very low Gilbert damping are expected to show
novel magnonic transport phenomena. We report nonlinear generation of higher
harmonics leading to the emission of caustic spin-wave beams in a low-damping,
micro-structured Co2Mn0.6Fe0.4Si Heusler waveguide. The source for the higher
harmonic generation is a localized edge mode formed by the strongly
inhomogeneous field distribution at the edges of the spin-wave waveguide. The
radiation characteristics of the propagating caustic waves observed at twice
and three times the excitation frequency are described by an analytical
calculation based on the anisotropic dispersion of spin waves in a magnetic
thin film. | 1209.3669v2 |
2018-02-01 | Stability of Room Temperature Compensated Half-Metallicity in Cr-based Inverse-Heusler Compounds | Using three correlated band approaches, namely the conventional band approach
plus on-site Coulomb repulsion $U$, the modified Becke-Johnson functional, and
hybrid functional, we have investigated inverse-Heusler ferrimagnets
Cr$_2$Co${\cal Z}$ (${\cal Z}$=Al, Ga, In). These approaches commonly indicate
that the Cr$_2$CoAl synthesized recently is a precise compensated half-metal
(CHM), whereas Cr$_2$CoGa and Cr$_2$CoIn are ferrimagnets with a small moment.
This is also confirmed by the fixed spin moment approach. Analysis of the Bader
charge decomposition and the radial charge densities indicates that this
contrast is due to chemical differences among the ${\cal Z}$ ions.
Additionally, in Cr$_2$CoAl, changing the volume by $\pm$ 5% or the ratio of
$c/a$ by $\pm$ 2% does not alter the CHM state, suggesting that this state is
robust even under application of moderate pressure or strain. Considering the
observed high Curie temperature of 750 K, our results suggest that Cr$_2$CoAl
is a promising candidate for robust high $T_C$ CHMs. Furthermore, the
electronic structure of the CHM Cr$_2$CoAl is discussed. | 1802.00125v2 |
2018-02-20 | Signature of a highly spin polarized resonance state at Co2MnSi(001)/Ag(001) interfaces | We investigated interfaces of halfmetallic Co2MnSi(100) Heusler thin films
with Ag(100), Cr(100), Cu and Al layers relevant for spin valves by high energy
x-ray photoemission spectroscopy (HAXPES). Experiments on Co2MnSi samples with
an Ag(100) interface showed a characteristic spectral shoulder feature close to
the Fermi edge, which is strongly diminished or suppressed at Co2MnSi (100)
interfaces with the other metallic layers. This feature is found to be directly
related to the Co2MnSi(100) layer, as reflected by control experiments with
reference non-magnetic films, i.e. without Heusler layer. By comparison with
HAXPES calculations, the shoulder feature is identified as originating from an
interface state related to a highly spin polarized surface resonance of Co2MnSi
(100). | 1802.07005v1 |
2018-08-21 | Negative longitudinal magnetoresistance as a sign of a possible chiral magnetic anomaly in the half-Heusler antiferromagnet DyPdBi | Magnetotransport investigation of a half-Heusler antiferromagnet DyPdBi
revealed hallmark features of Weyl semimetal: huge negative longitudinal
magnetoresistance and planar Hall effect. Both effects have recently been
linked to chiral magnetic anomaly - axial charge pumping between Weyl nodes.
Magnetoresistance (MR) of single crystals of DyPdBi is very pronounced. In
magnetic field longitudinal to electrical current direction it reaches -80% and
its relative difference with respect to that measured in transverse field
(expressed as anisotropic magnetoresistance) is extremely strong: -60% at 10K
and 14 T. The planar Hall effect in DyPdBi depends on temperature and magnetic
field in non-monotonous way, which has not been previously reported. We compare
magnetoresistance measured with voltage contacts on mid-line of the sample with
that measured with contacts on its edge, and show that the role of
current-jetting, an extrinsic source of anisotropic negative magnetoresistance,
is marginal. We discuss that nature of the compound and sample quality exclude
intrinsic sources of negative and anisotropic magnetoresistance other than weak
localization and the chiral magnetic anomaly. | 1808.06856v2 |
2020-08-07 | Magnetoelastic and Magnetostrictive Properties of Co$_2$XAl Heusler Compounds | We present a comprehensive first principles electronic structure study of the
magnetoelastic and magnetostrictive properties in the Co-based Co$_2$XAl (X =
V, Ti, Cr, Mn, Fe) full Heusler compounds. In addition to the commonly used
total energy approach, we employ torque method to calculate the magnetoelastic
tensor elements. We show that the torque based methods are in general
computationally more efficient, and allow to unveil the atomic- and
orbital-contributions to the magnetoelastic constants in an exact manner, as
opposed to the conventional approaches based on second order perturbation with
respect to the spin-orbit coupling. The magnetostriction constants are in good
agreement with available experimental data. The results reveal that the main
contribution to the magnetostriction constants, $\lambda_{100}$ and
$\lambda_{111}$, arises primarily from the strained-induced modulation of the
$\langle d_{x^2-y^2}|\hat{L}_z|d_{xy}\rangle$ and $\langle
d_{z^2}|\hat{L}_x|d_{yz}\rangle$ spin orbit coupling matrix elements,
respectively, of the Co atoms. | 2008.03005v1 |
2016-03-15 | Quasiparticle band structure of the almost-gapless transition-metal-based Heusler semiconductors | Transition-metal-based Heusler semiconductors are promising materials for a
variety of applications ranging from spintronics to thermoelectricity.
Employing the $GW$ approximation within the framework of the FLAPW method, we
study the quasi-particle band structure of a number of such compounds being
almost gapless semiconductors. We find that in contrast to the
\textit{sp}-electron based semiconductors such as Si and GaAs, in these systems
the many-body corrections have a minimal effect on the electronic band
structure and the energy band gap increases by less than 0.2~eV, which makes
the starting point density functional theory (DFT) a good approximation for the
description of electronic and optical properties of these materials.
Furthermore, the band gap can be tuned either by the variation of the lattice
parameter or by the substitution of the \emph{sp}-chemical element. | 1603.04677v1 |
2017-02-15 | Stability of Weyl points in magnetic half-metallic Heusler compounds | We employ {\it ab-initio} fully-relativistic electronic structure
calculations to study the stability of the Weyl points in the momentum space
within the class of the half-metallic ferromagnetic full Heusler materials, by
focusing on Co$_2$TiAl as a well-established prototype compound. Here we show
that both the number of the Weyl points together with their $k$-space
coordinates can be controlled by the orientation of the magnetization. This
alternative degree of freedom, which is absent in other topological materials
(e.g. in Weyl semimetals), introduces novel functionalities, specific for the
class of half-metallic ferromagnets. Of special interest are Weyl points which
are preserved irrespectively of any arbitrary rotation of the magnetization
axis. | 1702.04558v1 |
2019-03-28 | Surface resonance of the Heusler half metal Co2MnSi probed by SX-ARPES | Heusler compounds are promising materials for spintronics with adjustable
electronic properties including 100% spin polarization at the Fermi energy. We
investigate the electronic states of AlOx capped epitaxial thin films of the
ferromagnetic half metal Co2MnSi ex-situ by soft X-ray angular resolved
photoemission spectroscopy (SX-ARPES). Good agreement between the experimental
SX- ARPES results and photoemission calculations including surface effects was
obtained. In particular, we observed in line with our calculations a large
photoemission intensity at the center of the Brillouin zone, which does not
originate from bulk states, but from a surface resonance. This provides strong
evidence for the validity of the previously proposed model based on this
resonance, which was applied to explain the huge spin polarization of Co2MnSi
observed by angular-integrating UV-photoemission spectroscopy. | 1903.11840v1 |
2019-03-28 | Anisotropic Topological Hall Effect with Real and Momentum Space Berry Curvature in the Antiskrymion Hosting Heusler Compound Mn$_{1.4}$PtSn | The topological Hall effect (THE) is one of the key signatures of
topologically non-trivial magnetic spin textures, wherein electrons feel an
additional transverse voltage to the applied current. The magnitude of THE is
often small compared to the anomalous Hall effect. Here, we find a large THE of
0.9 $\mu\Omega$cm that is of the same order of the anomalous Hall effect in the
single crystalline antiskyrmion hosting Heusler compound Mn$_{1.4}$PtSn, a
non-centrosymmetric tetragonal compound. The THE is highly anisotropic and
survives in the whole temperature range where the spin structure is noncoplanar
(<170 K). The THE is zero above the spin reorientation transition temperature
of 170 K, where the magnetization will have a collinear and ferromagnetic
alignment. The large value of the THE entails a significant contribution from
the momentum space Berry curvature along with real space Berry curvature, which
has never been observed earlier. | 1903.12037v1 |
2019-05-25 | Magnetic 2D electron liquid at the surface of Heusler semiconductors | Conducting and magnetic properties of a material often change in some
confined geometries. However, a situation where a non-magnetic semiconductor
becomes both metallic and magnetic at the surface is quite rare, and to the
best of our knowledge has never been observed in experiment. In this work, we
employ first-principles electronic structure theory to predict that such a
peculiar magnetic state emerges in a family of quaternary Heusler compounds. We
investigate magnetic and electronic properties of CoCrTiP, FeMnTiP and CoMnVAl.
For the latter material, we also analyse the magnetic exchange interactions and
use them for parametrizing an effective spin Hamiltonian. According to our
results, magnetism in this material should persist at temperatures at least as
high as 155 K. | 1905.10541v1 |
2019-09-06 | The interplay of large two-magnon ferromagnetic resonance linewidths and low Gilbert damping in Heusler thin films | We report on broadband ferromagnetic resonance linewidth measurements
performed on epitaxial Heusler thin films. A large and anisotropic two-magnon
scattering linewidth broadening is observed for measurements with the
magnetization lying in the film plane, while linewidth measurements with the
magnetization saturated perpendicular to the sample plane reveal low Gilbert
damping constants of $(1.5\pm0.1)\times 10^{-3}$, $(1.8\pm0.2)\times 10^{-3}$,
and $<8\times 10^{-4}$ for Co$_2$MnSi/MgO, Co$_2$MnAl/MgO, and Co$_2$FeAl/MgO,
respectively. The in-plane measurements are fit to a model combining Gilbert
and two-magnon scattering contributions to the linewidth, revealing a
characteristic disorder lengthscale of 10-100 nm. | 1909.02738v2 |
2019-09-24 | Understanding the origin of the magneto-caloric effects in substitutional Ni-Mn-Sb-Z (Z=Fe, Co, Cu) compounds: insights from first-principles calculations | Ni-Mn based ternary Heusler compounds have drawn attentions lately as
significant magneto-caloric effects in some of them have been observed.
Substitution of Ni and Mn by other $3d$ transition metals in controlled
quantity have turned out to be successful in enhancing the effect and bring the
operational temperatures closer to the room temperature. Using density
functional theory calculations, in this work, we have systematically explored
the roles of various factors such as site occupancies, magnetic interactions,
and compositions associated with the constituents of Mn-excess Ni$_{2}$MnSb
Heusler compounds upon substitution of Ni and/or Mn by $3d$ transition metals
Fe, Co and Cu. Our calculations unveiled the physics behind the variations of
physical properties associated with the magneto-caloric effects, and thus
interpreted the available experimental results successfully. The work also
provided important information on the compounds and the composition ranges
where significant magneto-caloric effects may be realised and further
experimental investigations need to be done. | 1909.10667v1 |
2019-12-09 | Intrinsically high thermoelectric figure of merit of half-Heusler ZrRuTe | The electronic structure and thermoelectric properties of ZrRuTe-based
Half-Heusler compounds are studied using density functional theory (DFT) and
Boltzmann transport formalism. Based on rigorous computations of electron
relaxation time $\tau$ considering electron-phonon interactions and lattice
thermal conductivity $\kappa_l$ considering phonon-phonon interactions, we find
ZrRuTe to be an intrinsically good thermoelectric material. It has a high power
factor of $\sim 2\times 10^{-3}$ W/m-K$^{2}$ and low $\kappa_l\sim 10$ W/m-K at
800 K. The thermoelectric figure of merit $ZT \sim 0.13$ at 800 K is higher
than similar other compounds. We have also studied the properties of the
material as a function of doping and find the thermoelectric properties to be
substantially enhanced for $p$-doped ZrRuTe with the $ZT$ value raised to $\sim
0.2$ at this temperature. The electronic, thermodynamic, and transport
properties of the material are thoroughly studied and discussed | 1912.03883v3 |
2019-12-17 | Type-II Dirac states in full Heusler compounds XInPd2 (X = Ti, Zr and Hf) | We predict three full Heusler compounds XInPd2 (X = Zr, Hf and Ti) to be
potential candidates for type-II Dirac semimetals. The crystal symmetry of
these compounds have appropriate chemical environment with a unique interplay
of inversion, time reversal and mirror symmetry. These symmetries help to give
six pairs of type-II Dirac nodes on the C_4 rotation axis, closely located
at/near the Fermi level. Using first principle calculations, symmetry arguments
and crystal field splitting analysis, we illustrate the occurrence of such
Dirac nodes in these compounds. Bulk Fermi surfaces have been studied to
understand the Lorentz symmetry breaking and Lifshitz transition (LT) of Fermi
surfaces. Bulk nodes are projected on the (001) and (111) surfaces which form
the surface Fermi arcs, that can further be detected by probes such as angle
resolved photo-emission and scanning tunneling spectroscopy. By analyzing the
evolution of arcs with changing chemical potential, we prove the fragile nature
and the absence of topological protection of the Dirac arcs. Our predicted
compounds overcome the limitations of the previously reported PtTe2 class of
compounds. | 1912.07807v1 |
2020-03-06 | Unexpected band gap increase in the Fe2VAl Heusler compound | Knowing the electronic structure of a material is essential in energy
applications to rationalize its performance and propose alternatives. Materials
for thermoelectric applications are generally small-gap semiconductors and
should have a high figure of merit ZT. Even if the Fe2VAl Heusler compound has
a decent ZT, its conductive nature (semi-metal or semiconductor) is not yet
clarified especially at low temperature. In this paper, we focus our DFT
calculations on the effect of temperature on the bandgap of Fe2VAl. In contrast
to what is usually observed, we show that both the temperature increase and the
formation of thermally-activated Al/V inversion defects (observed
experimentally), open the bandgap. Such an unusual behavior is the key for
reconciling all bandgap measurements performed on the Fe2VAl compound using a
standard GGA functional and could be an efficient way for improving the
thermoelectric properties of this family of materials. | 2003.03166v1 |
2020-03-14 | Exceptionally large anomalous Hall effect due to anticrossing of spin-split bands in the antiferromagnetic half-Heusler compound TbPtBi | We have investigated magnetotransport properties and the topological
electronic structure of the half-Heusler compound TbPtBi. Our experiments
reveal an exceptionally large anomalous Hall effect (AHE) in the canted
antiferromagnetic state of TbPtBi with the anomalous Hall angle (AHA) reaching
~0.68-0.76, which is a few times larger than the previously reported record in
GdPtBi. First-principles electronic structure and the associated anomalous Hall
conductivity were computed in order to interpret the experimental results. Our
analysis shows that the AHE in TbPtBi does not originate from the Weyl points
but that it is driven by the large net Berry curvature produced by the
anticrossing of spin-split bands near the Fermi level in TbPtBi. | 2003.06688v1 |
2020-09-07 | Strain driven emergence of topological non-triviality in YPdBi thin films | Half-Heusler compounds exhibit a remarkable variety of emergent properties
such as heavy-fermion behaviour, unconventional superconductivity and
magnetism. Several of these compounds have been predicted to host topologically
non-trivial electronic structures. Remarkably, recent theoretical studies have
indicated the possibility to induce non-trivial topological surface states in
an otherwise trivial half-Heusler system by strain engineering. Here, using
magneto-transport measurements and first principles DFT-based simulations, we
demonstrate topological surface states on strained [110] oriented thin films of
YPdBi grown on (100) MgO. These topological surface states arise in an
otherwise trivial semi-metal purely driven by strain. Furthermore, we observe
the onset of superconductivity in these strained films highlighting the
possibility of engineering a topological superconducting state. Our results
demonstrate the critical role played by strain in engineering novel topological
states in thin film systems for developing next-generation spintronic devices. | 2009.03018v3 |
2020-12-08 | Importance of Electronic Correlation in the Intermetallic Half-Heusler Compounds | Low temperature scanning tunneling spectroscopy of HfNiSn shows a V^m(m < 1)
zero bias anomaly around the Fermi level. This local density of states with a
fractional power law shape is well known to be a consequence of electronic
correlations. For comparison, we have also measured the tunneling conductances
of other half-Heusler compounds with 18 valence electrons. ZrNiPb shows a
metal-like local density of states, whereas ZrCoSb and NbFeSb show a linear and
V^2 anomaly. One interpretation of these anomalies is that a correlation gap is
opening in these compounds. By analyzing the magnetoresistance of HfNiSn, we
demonstrate that at low temperatures, electron-electron scattering dominates.
The T^m(m < 1) temperature dependence of the conductivity confirms that the
electronic correlations are a bulk rather than a surface property. | 2012.04184v1 |
2021-06-24 | A first-principles investigation of band inversion in topologically nontrivial Na2AgX (X= As, Sb and Bi) full Heusler compounds | Topological nontrivial nature are the latest phases to be discovered in
condensed matter physics with insulating bulk band gaps and topologically
protected metallic surface states; they are one of the current hot topics
because of their unique properties and potential applications. In this paper,
we have highlighted a first-principles study of the structural stability and
electronic behavior of the Na${}_{2}$AgX (X= As, Sb and Bi) full Heusler
compounds, using the Full-Potential Linear Muffin-Tin Orbital (FP-LMTO) method.
We have originated that the Hg${}_{2}$CuTi structure is appropriate in all
studied materials. The negative values of the calculated formation energies
mean that these compounds are energetically stable. The band structure is
studied for the two cases relating the existence and the absence of
spin-orbital couplings, where all materials are shown to be topologically
non-trivial compounds. Spin orbital couplings were noticed to have no
significant effect on the electronic properties such as the topological order. | 2106.13184v1 |
2021-09-02 | A first-principles investigation of pressure induced topological phase transition in Half-Heusler AgSrBi | Topological Insulators (TI) are materials with novel quantum states which
exhibit a bulk insulating gap while the edge/surface is conducting. This has
been extensively explored in several Half-Heusler (HH) compounds hosting the
exotic TI behaviour. In the present work we employ, first-principles based
Density Functional Theory to perform thorough investigations of pressure
induced topological phase transition (TPT) in HH AgSrBi which belongs to the
F-43m space group. AgSrBi is intrinsically semi-metallic in nature which, under
isotropic pressure exhibits semi-metal to trivial insulator transition
retaining the cubic symmetry whereas, on breaking the cubic symmetry we observe
the much sought after non-trivial semi-metal to TI phase transition. We also
explore the effect of lowering crystal symmetry in realizing TI nature.
Following this we perform qualitative analysis of the electronic properties to
understand the origin of this non-trivial behavior followed by the quantitative
analysis of the Z$_2$ classification which indicates that AgSrBi is a strong TI
(i.e., Z$_2$ = (1, 101)). We thus, propose AgSrBi as a dynamically stable TI
which can be used as ultra-thin films thermoelectric and nanoelectronic
applications. | 2109.01108v1 |
2021-11-28 | Electronic properties of the Weyl semimetals Co$_2$MnX (X=Si, Ge, Sn) | Using first-principles electronic structure calculations, we show that
ferromagnetic Heusler compounds Co$_2$MnX (X= Si, Ge, Sn) present non-trivial
topological characteristics and belong to the category of Weyl semimetals.
These materials exhibit two topologically interesting band crossings near the
Fermi level. These band crossings have complex 3D geometries in the Brillouin
zone and are characterized by non-trivial topology as Hopf links and chain-like
nodal lines, that are protected by the perpendicular mirror planes. The
spin-orbit interaction split these nodal lines into several zero-dimensional
Weyl band crossings. Unlike previously known topologically non-trivial Heusler
materials, these majority-spin band crossings lie in the band gap of minority
spin bands, potentially facilitating its experimental realization. | 2111.14135v1 |
2021-12-16 | Spin Hall Conductivity and Anomalous Hall Conductivity in Full Heusler compounds | The spin Hall conductivity (SHC) and anomalous Hall conductivity (AHC) in
more than 120 full Heusler compounds are calculated using density functional
theory in a high-throughtput way. The electronic structures are mapped to the
Wannier basis and the linear response theory is used to get the conductivity.
Our results show that the mechanism under the SHC or AHC cannot be simply
related to the valence electron numbers or atomic weights, is related to the
very details of the electronic structure, which can only be obtained by
calculations. A high throughput calculation is efficient to screen out the
desired materials. According to our present results, Cu2CoSn, as well as
Co2MnAl and Co2MnGa are candidates in spintronic materials regarding to their
high SHC and AHC values, which can benefit the spin-torque-driven nanodevices. | 2112.08630v1 |
2021-12-18 | Structural, elastic, electronic and optical properties of the half-Heusler ScPtSb and YPtSb compounds under pressure | First-principles calculations using the plane-wave pseudopotential method
within the generalized gradient approximation method were performed to study
the pressure dependence of the structural, elastic, electronic and optical
properties for the half-Heusler compounds ScPtSb and YPtSb in a cubic
MgAgAs-type structure. The calculations were performed with the inclusion of
spin-orbit coupling. The calculated equilibrium lattice parameters are in good
agreement with the available experimental and theoretical values. The crystal
rigidity and mechanical stability were discussed using the elastic constants
and related parameters, namely bulk modulus, shear modulus, Debye temperature,
Poisson's coefficient, Young's modulus and isotropic sound velocities. The
calculated electronic band structures show that ScPtSb has an indirect gap of
$\Gamma-X $ type, whereas YPtSb has a direct band gap of $\Gamma -\Gamma $
type. Furthermore, the effect of pressure on the optical properties, namely the
dielectric function, absorption spectrum, refractive index, extinction
coefficient, reflectivity and energy-loss spectrum is investigated for both
compounds ScPtSb and YPtSb. | 2112.09940v1 |
2022-04-28 | Observation of Griffiths-like phase in the quaternary Heusler compound NiFeTiSn | The quaternary Heusler compound NiFeTiSn can be considered to be derived from
the exotic pseudogap-compound Fe2TiSn by the replacement of one Fe atom by Ni.
In contrast to Fe2TiSn, which shows a disorder-induced ferromagnetic phase, the
ground state of NiFeTiSn is antiferromagnetic with the signature of spin
canting. Interestingly, NiFeTiSn shows a Griffiths-like phase characterized by
isolated ferromagnetic clusters before attaining the antiferromagnetic state.
The Griffiths-like phase is possibly associated with the antisite disorder
between Fe and Ti sites as evident from our powder X-ray diffraction study. The
compound also shows rather an unusual temperature dependence of resistivity,
which can be accounted for by the prevailing structural disorder in the system.
NiFeTiSn turned out to be a rare example where a Griffiths-like phase is
observed in a semiconducting 3d transition metal-based intermetallic compound
with an antiferromagnetic ground state. | 2204.13462v1 |
2022-09-21 | Effect of Co Substitution on Ferrimagnetic Heusler compound Mn3Ga | Effect of Co substitution on Mn$_3$Ga is investigated using first-principles
study for structural and magnetic properties. Without Co, ferrimagnetic Heusler
compound Mn3Ga is in tetragonal phase. With Co substitution, depending on Co
concentration (x) Mn$_3$Ga prefers tetragonal (cubic) phase when x \leq 0.5 (x
\geq 0.5). Ferrimagnetism is robust regardless of x in both phases. While
magnetic moments of two Mn do not vary significantly with x, Co magnetic moment
in two phases exhibit different behaviors, leading to distinct features in
total magnetic moment (M_{tot}). When x \leq 0.5, in tetragonal phase, Co
magnetic moment is vanishingly small, resulting in a decrease of M_{tot} with
x. In contrast, when x \geq 0.5, in cubic phase, Co magnetic moment is roughly
1$\mu_B$, which is responsible for an increase of Mtot. Electronic structure is
analyzed with partial density of states for various x. To elucidate the
counterintuitively small Co moment, the magnetic exchange interaction is
investigated where exchange coefficient between Co and Mn is much smaller in x
\leq 0.5 case than x \geq 0.5 one. | 2209.10216v1 |
2022-11-23 | Molecular Beam Epitaxy of a Half-Heusler Topological Superconductor Candidate YPtBi | The search for topological superconductivity has motivated investigations
into materials that combine topological and superconducting properties. The
half-Heusler compound YPtBi appears to be such a material, however experiments
have thus far been limited to bulk single crystals, drastically limiting the
scope of available experiments. This has made it impossible to investigate the
potential topological nature of the superconductivity in this material.
Experiments to access details about the superconducting state require
sophisticated lithographic structures, typically based on thin films. Here we
report on the establishment of high crystalline quality epitaxial thin films of
YPtBi(111), grown using molecular beam epitaxy on Al2O3(0001) substrates. A
robust superconducting state is observed, with both critical temperature and
critical field consistent with that previously reported for bulk crystals.
Moreover we find that AlOx capping sufficiently protects the sample surface
from degradation to allow for proper lithography. Our results pave a path
towards the development of advanced lithographic structures, that will allow
the exploration of the potentially topological nature of superconductivity in
YPtBi. | 2211.13106v1 |
2023-04-12 | Large Violation of the Wiedemann Franz Law in Heusler, Ferromagnetic, Weyl Semimetal Co$_2$MnAl | The Wiedemann-Franz (WF) law relates the electronic component of the thermal
conductivity to the electrical conductivity in metals through the Lorenz
number. The WF law has proven to be remarkably robust, however violations have
been observed in many topological materials. In this work, we report
thermoelectric measurements conducted on Heusler, ferromagnetic, Weyl semimetal
Co$_2$MnAl which shows a drastic, temperature dependent violation of the WF law
below 300 K. We then discuss our result in the context of known physical
explanations for WF law violation. Both the magnitude and temperature
dependence of the violation in Co2MnAl are extreme, indicating that there may
be more than one effect contributing to the violation in this system. | 2304.05595v1 |
2023-12-06 | First-principles prediction of energy band gaps in 18-valence electron semiconducting half-Heusler compounds: Exploring the role of exchange and correlation | The choice of exchange functional is a critical factor in determining the
energy bandgap of semiconductors. Ab initio calculations using different
exchange functionals, including the conventional generalized-gradient
approximation (GGA) functionals, meta-GGA functionals, and hybrid functionals,
show significant differences in the calculated energy bandgap for
semiconducting half-Heusler compounds. These compounds, which have 18 valence
electrons per unit cell, are of great interest due to their thermoelectric
properties, making them suitable for energy conversion applications. In
addition, accounting for electronic correlations using the GW method also
affects the calculated energy bandgaps compared to standard GGA calculations.
The variations in calculated energy bandgaps are specific to each material when
using different functionals. Hence, a detailed investigation of the electronic
properties of each compound is necessary to determine the most appropriate
functional for an accurate description of the electronic properties. Our
results indicate that no general rules can be established and a comparison with
experimental results is required to determine the most appropriate functional. | 2312.03321v2 |
2023-12-28 | Possible Unconventional Surface Superconductivity in the Half-Heusler YPtBi | We report an extensive extensive study of the noncentrosymmetric half-Heusler
topological superconductor YPtBi, revealing unusual relation between bulk
superconductivity and the appearance of surface superconductivity at
temperatures up to 3 times the bulk transition temperature. Transport
measurements confirmed the low carrier density of the material and its bulk
superconducting transition, which was also observed in ac susceptibility
through mutual inductance (MI) measurements. However, a weak signature of
superconductivity in the MI measurements appeared much above the bulk
transition temperature, which was further observed in scanning tunneling
spectroscopy. Polar Kerr effect measurements suggest that while the bulk
superconductor may exhibit an unusual nodal superconducting state, only the
surface state breaks time reversal symmetry. Complementary tunneling
measurements on LuPtBi are used to establish the observations on YPtBi, while
density-functional theory (DFT) calculations may shed light on the origin of
this unusual surface state. | 2312.17213v1 |
2024-03-24 | Ideal spin-polarized Weyl-half-semimetal with a single pair of Weyl points in half-Heusler compounds XCrTe (X=K, Rb) | Realizing ideal Weyl semimetal state with a single pair of Weyl points has
been a long-sought goal in the field of topological semimetals. Here, we reveal
such a state in the Cr-based half-Heusler compounds XCrTe (X=K, Rb). We show
that these materials have a half metal ground state, with Fermi level crossing
only one spin channel. Importantly, the Fermi surface is clean, consisting of
the minimal number (i.e., a single pair) of spin-polarized Weyl points, so the
state represents an ideal Weyl half semimetal. We show that the locations of
the two Weyl points and the associated Chern vector can be flexibly tuned by
rotating the magnetization vector. The minimal surface Fermi arc pattern and
its contribution to anomalous Hall transport are discussed. Our finding offers
an ideal material platform for exploring magnetic Weyl fermions, which will
also facilitate the interplay between Weyl physics and spintronics. | 2403.16195v1 |
2005-02-16 | Dependence of the electronic structure of self-assembled InGaAs/GaAs quantum dots on height and composition | While electronic and spectroscopic properties of self-assembled
In_{1-x}Ga_{x}As/GaAs dots depend on their shape, height and alloy
compositions, these characteristics are often not known accurately from
experiment. This creates a difficulty in comparing measured electronic and
spectroscopic properties with calculated ones. Since simplified theoretical
models (effective mass, k.p, parabolic models) do not fully convey the effects
of shape, size and composition on the electronic and spectroscopic properties,
we offer to bridge the gap by providing accurately calculated results as a
function of the dot height and composition. Prominent results are the
following. (i) Regardless of height and composition, the electron levels form
shells of nearly degenerate states. In contrast, the hole levels form shells
only in flat dots and near the highest hole level (HOMO). (ii) In alloy dots,
the electrons' ``s-p'' splitting depends weakly on height, while the ``p-p''
splitting depends non-monotonically. In non-alloyed InAs/GaAs dots, both these
splittings depend weakly on height. For holes in alloy dots, the ``s-p''
splitting decreases with increasing height, whereas the ``p-p'' splitting
remains nearly unchaged. Shallow, non-alloyed dots have a ``s-p'' splitting of
nearly the same magnitude, whereas the ``p-p'' splitting is larger. (iii) As
height increases, the ``s'' and ``p'' character of the wavefunction of the HOMO
becomes mixed, and so does the heavy- and light-hole character. (iv) In alloy
dots, low-lying hole states are localized inside the dot. Remarkably, in
non-alloyed InAs/GaAs dots these states become localized at the interface as
height increases. This localization is driven by the biaxial strain present in
the nanostructure. | 0502409v1 |
2008-07-17 | Ab initio study of element segregation and oxygen adsorption on PtPd and CoCr binary alloy surfaces | The segregation behavior of the bimetallic alloys PtPd and CoCr in the case
of bare surfaces and in the presence of an oxygen ad-layer has been studied by
means of first-principles modeling based on density-functional theory (DFT).
For both systems, change of the d-band filling due to charge transfer between
the alloy components, resulting in a shift of the d-band center of surface
atoms compared to the pure components, drives the surface segregation and
governs the chemical reactivity of the bimetals. In contrast to previous
findings but consistent with analogous PtNi alloy systems, enrichment of Pt
atoms in the surface layer and of Pd atoms in the first subsurface layer has
been found in Pt-rich PtPd alloy, despite the lower surface energy of pure Pd
compared to pure Pt. Similarly, Co surface and Cr subsurface segregation occurs
in Co-rich CoCr alloys. However, in the presence of adsorbed oxygen, Pd and Cr
occupy preferentially surface sites due to their lower electronegativity and
thus stronger oxygen affinity compared to Pt and Co, respectively. In either
cases, the calculated oxygen adsorption energies on the alloy surfaces are
larger than on the pure components when the more noble components are present
in the subsurface layers. | 0807.2787v1 |
2009-11-28 | Band-gap bowing and p-type doping of (Zn, Mg, Be)O wide-gap semiconductor alloys: a first-principles study | Using a first-principles band-structure method and a special quasirandom
structure (SQS) approach, we systematically calculate the band gap bowing
parameters and \emph{p}-type doping properties of (Zn, Mg, Be)O related random
ternary and quaternary alloys. We show that the bowing parameters for ZnBeO and
MgBeO alloys are large and dependent on composition. This is due to the size
difference and chemical mismatch between Be and Zn(Mg) atoms. We also
demonstrate that adding a small amount of Be into MgO reduces the band gap
indicating that the bowing parameter is larger than the band-gap difference. We
select an ideal N atom with lower \emph{p} atomic energy level as dopant to
perform \emph{p}-type doping of ZnBeO and ZnMgBeO alloys. For N doped in ZnBeO
alloy, we show that the acceptor transition energies become shallower as the
number of the nearest neighbor Be atoms increases. This is thought to be
because of the reduction of \emph{p}-\emph{d} repulsion. The N$_{\rm{O}}$
acceptor transition energies are deep in the ZnMgBeO quaternary alloy
lattice-matched to GaN substrate due to the lower valence band maximum. These
decrease slightly as there are more nearest neighbor Mg atoms surrounding the N
dopant. The important natural valence band alignment between ZnO, MgO, BeO,
ZnBeO, and ZnMgBeO quaternary alloy is also investigated. | 0911.5375v1 |
2011-09-10 | Phonon dynamics of Zn(Mg,Cd)O alloy nanostructures and their phase segregation | In this paper we report phonon dynamics in chemically synthesized Zn1- xMgxO
(0\leqx\leq0.07) and Zn1-yCdyO (0\leqy\leq0.03) alloy nanostructures of sizes
~10 nm using non-resonant Raman and Fourier Transformed Infrared Spectroscopy
(FTIR). Substitution by Mg makes the unit cell compact while Cd substitution
leads to unit cell expansion. On alloying, both A1(LO) and E1(LO) mode of
wurtzite ZnO show blue shift for Zn1-xMgxO and red shift for Zn1-yCdyO alloy
nanostructures due to mass defect and volume change induced by the impurity
atoms. Significant shift has been observed in E1(LO) mode for Zn1-xMgxO (73
cm-1 for x = 0.07) and Zn1-yCdyO (17 cm-1 for y = 0.03) nanostructures. The
variation in Zn(Mg,Cd)-O bond length determined from the blue (red) shift of IR
bands on alloying with Mg (Cd) is consistent with their respective ionic sizes
and the structural changes predicted by X-ray diffraction study. However, on
progressive alloying one can detect phase segregation (due to presence of
interstitial Mgand Cd ions) in the alloy nanostructures for relatively higher
Mg and Cd concentrations. This is confirmed by the gradual absence of the
characteristic IR and Raman bands of wurtzite ZnO near 400-600 cm-1 as well as
by X-Ray and TEM studies. | 1109.2252v1 |
2013-10-22 | Master equation approach to the theory of diffusion in alloys and calculations of enhancement factors for tracer solvent and tracer solute diffusion in FCC alloys | The earlier-suggested master equation approach is used to develop the
consistent statistical theory of diffusion in alloys using the five-frequency
model of FCC alloys as an example. Expressions for the Onsager coefficients in
terms of microscopic interatomic interactions and some statistical averages are
presented. We discuss methods of calculations of these averages using both the
mean-field and the pair-cluster approximation to describe influence of
vacancy-solute and solute-solute interactions, and both the nearest-neighbor
and the second-shell approximation to describe vacancy correlation effects. The
methods developed are used for calculations of enhancement factors which
determine the concentration dependence of tracer self-diffusion and tracer
solute diffusion in dilute FCC alloys. For the tracer self-diffusion, we show
that some significant contribution to the enhancement factor related to the
thermodynamic activity of vacancies was missed in the previous treatments of
this problem. It implies that the most of existing estimates of parameters of
the five-frequency model for real alloys should be revised. For the tracer
solute diffusion, the expression for the enhancement factor seems to be
presented for the first time. The results obtained are used to estimate the
microscopic parameters important for diffusion, including the vacancy-solute
interaction, in several FCC alloys for which necessary experimental data are
available. | 1310.5808v2 |
2016-11-19 | Alloying, de-alloying and reentrant alloying in (sub-)monolayer growth of Ag on Pt(111) | An in-situ nanoscopic investigation of the prototypical surface alloying
system Ag/Pt(111) is reported. The morphology and the structure of the
ultrathin Ag-Pt film is studied using Low Energy Electron Microscopy during
growth at about 800 K. An amazingly rich dynamic behaviour is uncovered in
which stress relieve plays a governing role. Initial growth leads to surface
alloying with prolonged and retarded nucleation of ad-islands. Beyond 50%
coverage de-alloying proceeds, joined by partial segregation of Pt towards the
centre of large islands in violent processes. Upon coalescence the irregularly
shaped vacancy clusters are filled by segregating Pt, which then take a compact
shape (black spots). As a result at around 85% coverage the strain of the
initially pseudo-morphological film is almost completely relieved and
Pt-segregation is at its maximum. Further deposition of Ag leads to transient
re-entrant alloying and recovery of the pseudo-morphological layer. The black
spots persist even in/on several layers thick films. Ex-situ atomic force
microscopy data confirm that these are constituted by probably amorphous
Pt(-rich) structures. The (sub-)monolayer films are very much heterogeneous. | 1611.06354v1 |
2017-12-06 | Exploration of the High Entropy Alloy Space as a Constraint Satisfaction Problem | High Entropy Alloys (HEAs), Multi-principal Component Alloys (MCA), or
Compositionally Complex Alloys (CCAs) are alloys that contain multiple
principal alloying elements. While many HEAs have been shown to have unique
properties, their discovery has been largely done through costly and
time-consuming trial-and-error approaches, with only an infinitesimally small
fraction of the entire possible composition space having been explored. In this
work, the exploration of the HEA composition space is framed as a Continuous
Constraint Satisfaction Problem (CCSP) and solved using a novel Constraint
Satisfaction Algorithm (CSA) for the rapid and robust exploration of alloy
thermodynamic spaces. The algorithm is used to discover regions in the HEA
Composition-Temperature space that satisfy desired phase constitution
requirements. The algorithm is demonstrated against a new (TCHEA1) CALPHAD HEA
thermodynamic database. The database is first validated by comparing phase
stability predictions against experiments and then the CSA is deployed and
tested against design tasks consisting of identifying not only single phase
solid solution regions in ternary, quaternary and quinary composition spaces
but also the identification of regions that are likely to yield
precipitation-strengthened HEAs. | 1712.02442v3 |
2017-12-26 | The effect of Si addition on the microstructure and tensile properties of casting Al-5.0Cu-0.6Mn-1.2Fe alloys | In this work, we studied the effect of Si on the microstructure and tensile
properties of the as-cast Al-5.0Cu-0.6Mn-1.2Fe alloys which were produced by
casting with or without applied pressure. The results show that the addition of
Si can significantly influence the microstructure and tensile properties of the
alloys. For the alloys produced without pressure, the addition of Si can
promote the formation of Chinese script {\alpha}-Fe, suppress the precipitation
of plate-like Al3(FeMn) and Chinese script Al6(FeMn) and increase the volume
percent of porosity, resulting in a remarkable decrease in the ultimate tensile
strength (UTS) and yield strength (YS). For the alloys produced with a pressure
of 75 MPa, the addition of Si can also promote the formation of fine Chinese
script {\alpha}-Fe and high number density Al2Cu ({\theta}) phases, resulting
in a slight increase in UTS and YS. The strength and elongation of the alloys
increases with increasing applied pressure at the same Si level, which are
attributed to the elimination of porosity, grain refinement strengthening and
solid-solution strengthening. The alloy with addition of 1.1 % Si produced
under the applied pressure of 75 MPa shows the best tensile properties, where
the UTS, YS and elongation is 237 MPa, 140 MPa and 9.8%, respectively. | 1712.09177v2 |
2018-06-08 | Band gap and band offset of Ga$_2$O$_3$ and (Al$_x$Ga$_{1-x}$)$_2$O$_3$ alloys | Ga$_2$O$_3$ and (Al$_x$Ga$_{1-x}$)$_2$O$_3$ alloys are promising materials
for solar-blind UV photodetectors and high-power transistors. Basic key
parameters in the device design, such as band gap variation with alloy
composition and band offset between Ga$_2$O$_3$ and
(Al$_x$Ga$_{1-x}$)$_2$O$_3$, are yet to be established. Using density
functional theory with the HSE hybrid functional, we compute formation
enthalpies, band gaps, and band edge positions of (Al$_x$Ga$_{1-x}$)$_2$O$_3$
alloys in the monoclinic ($\beta$) and corundum ($\alpha$) phases. We find the
formation enthlapies of (Al$_x$Ga$_{1-x}$)$_2$O$_3$ alloys are significantly
lower than of (In$_x$Ga$_{1-x}$)$_2$O$_3$, and that (Al$_x$Ga$_{1-x}$)$_2$O$_3$
with $x$=0.5 can be considered as an ordered compound AlGaO$_3$ in the
monoclinic phase, with Al occupying the octahedral sites and Ga occupying the
tetrahedral sites. The direct band gaps of the alloys range from 4.69 to 7.03
eV for $\beta$-(Al$_x$Ga$_{1-x}$)$_2$O$_3$ and from 5.26 to 8.56 eV for
$\alpha$-(Al$_x$Ga$_{1-x}$)$_2$O$_3$. Most of the band offset of the
(Al$_x$Ga$_{1-x}$)$_2$O$_3$ alloy arises from the discontinuity in the
conduction band. Our results are used to explain the available experimental
data, and consequences for designing modulation-doped field effect transistors
(MODFETs) based on (Al$_x$Ga$_{1-x}$)$_2$O$_3$/Ga$_2$O$_3$ are discussed. | 1806.03360v2 |
2019-11-14 | Electronic structure evolution in dilute carbide Ge$_{1-x}$C$_{x}$ alloys and implications for device applications | We present a theoretical analysis of electronic structure evolution in the
highly-mismatched dilute carbide group-IV alloy Ge$_{1-x}$C$_{x}$. For ordered
alloy supercells, we demonstrate that C incorporation strongly perturbs the
conduction band (CB) structure by driving hybridisation of $A_{1}$-symmetric
linear combinations of Ge states lying close in energy to the CB edge. This
leads, in the ultra-dilute limit, to the alloy CB edge being formed primarily
of an $A_{1}$-symmetric linear combination of the L-point CB edge states of the
Ge host matrix semiconductor. Our calculations describe the emergence of a
"quasi-direct" alloy band gap, which retains a significant admixture of
indirect Ge L-point CB edge character. We then analyse the evolution of the
electronic structure of realistic (large, disordered) Ge$_{1-x}$C$_{x}$ alloy
supercells for C compositions up to $x = 2$%. We show that short-range alloy
disorder introduces a distribution of localised states at energies below the Ge
CB edge, with these states acquiring minimal direct ($\Gamma$) character. Our
calculations demonstrate strong intrinsic inhomogeneous energy broadening of
the CB edge Bloch character, driven by hybridisation between Ge host matrix and
C-related localised states. The trends identified by our calculations are
markedly different to those expected based on a recently proposed
interpretation of the CB structure based on the band anti-crossing model. The
implications of our findings for device applications are discussed. | 1911.06186v1 |
2021-07-13 | A pathway towards high throughput Quantum Monte Carlo simulations for alloys: A case study of two-dimensional (2D) $GaS_xSe_{1-x}$ | The study of alloys using computational methods has been a difficult task due
to the usually unknown stoichiometry and local atomic ordering of the different
structures experimentally. In order to combat this, first-principles methods
have been coupled with statistical methods such as the Cluster Expansion
formalism in order to construct the energy hull diagram, which helps to
determine if an alloyed structure can exist in nature. Traditionally, density
functional theory (DFT) has been used in such workflows. In this work we
propose to use chemically accurate many-body variational Monte Carlo (VMC) and
diffusion Monte Carlo (DMC) methods to construct the energy hull diagram of an
alloy system, due to the fact that such methods have a weaker dependence on the
starting wavefunction and density functional, scale similarly to DFT with the
number of electrons, and have had demonstrated success for a variety of
materials. To carry out these simulations in a high-throughput manner, we
propose a method called Jastrow sharing, which involves recycling the optimized
Jastrow parameters between alloys with different stoichiometries. We show that
this eliminates the need for extra VMC Jastrow optimization calculations and
results in a significant computational cost savings (on average 1/4 savings of
total computational time). Since it is a novel post-transition metal
chalcogenide alloy series that has been synthesized in its few-layer form, we
used monolayer $GaS_xSe_{1-x}$ as a case study for our workflow. By extensively
testing our Jastrow sharing procedure for monolayer $GaS_xSe_{1-x}$ and
quantifying the cost savings, we demonstrate how a pathway towards chemically
accurate high-throughput simulations of alloys can be achieved using many-body
VMC and DMC methods. | 2107.06128v1 |
2021-03-20 | Towards Superior High Temperature Properties in Low Density AlCrFeNiTi Compositionally Complex Alloys | Three novel precipitation strengthened bcc alloys which exhibit a smooth
microstructural gradient with composition have been fabricated in bulk form by
induction casting. All three alloys are comprised of a mixture of disordered
A2-(Fe, Cr) and L2$_1$-ordered (Ni, Fe)$_{2}$AlTi type phases both as-cast and
after long-term annealing at 900 $^{\circ}$C. The ratio of disordered to
ordered phase, primary dendrite fraction, and overall microstructural
coarseness all decrease as Cr is replaced by Al and Ti. Differences in phase
composition are quantified through domain averaged principal component analysis
of energy dispersive spectroscopy data obtained during scanning transmission
electron microscopy. Bulk tensile testing reveals retained strengths of nearly
250 MPa up to 900 $^{\circ}$C for the alloys which contain a nanoscale
maze-like arrangement of ordered and disordered phases. One alloy, containing a
duplex microstructure with ductile dendritic regions and highly creep resistant
interdendritic regions, shows a promising balance between high temperature
ductility and strength. For this alloy, tension creep testing was carried out
at 700, 750, and 800 $^{\circ}$C for a broad range of loading conditions and
revealed upper bound creep rates which surpass similar ferritic superalloys and
rival those of several conventionally employed high temperature structural
alloys, including Inconel 617 and 718, at much lower density and raw material
cost. | 2103.11173v1 |
2021-03-25 | Design of a V-Ti-Ni alloy with superelastic nano-precipitates | Stress-induced martensitic transformations enable metastable alloys to
exhibit enhanced strain hardening capacity, leading to improved formability and
toughness. As is well-known from transformation-induced plasticity (TRIP)
steels, however, the resulting martensite can limit ductility and fatigue life
due to its intrinsic brittleness. In this work, we explore an alloy design
strategy that utilizes stress-induced martensitic transformations but does not
retain the martensite phase. This strategy is based on the introduction of
superelastic nano-precipitates, which exhibit reverse transformation after
initial stress-induced forward transformation. To this end, utilizing ab-initio
simulations and thermodynamic calculations we designed and produced a
V45Ti30Ni25 (at%) alloy. In this alloy, TiNi is present as nano-precipitates
uniformly distributed within a ductile V-rich base-centered cubic (bcc) beta
matrix, as well as being present as a larger matrix phase. We characterized the
microstructure of the produced alloy using various scanning electron microscopy
(SEM) and transmission electron microscopy (TEM) methods. The bulk mechanical
properties of the alloy are demonstrated through tensile tests, and the
reversible transformation in each of the TiNi morphologies were confirmed by
in-situ TEM micro-pillar compression experiments, in-situ high-energy
diffraction synchrotron cyclic tensile tests, indentation experiments, and
differential scanning calorimetry experiments. The observed transformation
pathways and variables impacting phase stability are critically discussed | 2103.13978v2 |
2022-02-28 | Machine learning-enabled high-entropy alloy discovery | High-entropy alloys are solid solutions of multiple principal elements,
capable of reaching composition and feature regimes inaccessible for dilute
materials. Discovering those with valuable properties, however, relies on
serendipity, as thermodynamic alloy design rules alone often fail in
high-dimensional composition spaces. Here, we propose an active-learning
strategy to accelerate the design of novel high-entropy Invar alloys in a
practically infinite compositional space, based on very sparse data. Our
approach works as a closed-loop, integrating machine learning with
density-functional theory, thermodynamic calculations, and experiments. After
processing and characterizing 17 new alloys (out of millions of possible
compositions), we identified 2 high-entropy Invar alloys with extremely low
thermal expansion coefficients around 2*10-6 K-1 at 300 K. Our study thus opens
a new pathway for the fast and automated discovery of high-entropy alloys with
optimal thermal, magnetic and electrical properties. | 2202.13753v1 |
2019-08-07 | Comparison of first principles and semi-empirical models of the structural and electronic properties of Ge$_{1-x}$Sn$_{x}$ alloys | We present and compare three distinct atomistic models -- based on first
principles and semi-empirical approaches -- of the structural and electronic
properties of Ge$_{1-x}$Sn$_{x}$ alloys. Density functional theory calculations
incorporating Heyd-Scuseria-Ernzerhof (HSE) and modified Becke-Johnson (mBJ)
exchange-correlation functionals are used to perform structural relaxation and
electronic structure calculations for a series of Ge$_{1-x}$Sn$_{x}$ alloy
supercells. Based on HSE calculations, a semi-empirical valence force field
(VFF) potential and $sp^{3}s^{\ast}$ tight-binding (TB) Hamiltonian are
parametrised. Comparing the HSE, mBJ and TB models, and using the HSE results
as a benchmark, we demonstrate that: (i) mBJ calculations provide an accurate
first principles description of the electronic structure at reduced
computational cost, (ii) the VFF potential is sufficiently accurate to
circumvent the requirement to perform first principles structural relaxation,
and (iii) TB calculations provide a good quantitative description of the alloy
electronic structure in the vicinity of the band edges. Our results also
emphasise the importance of Sn-induced band mixing in determining the nature of
the conduction band structure of Ge$_{1-x}$Sn$_{x}$ alloys. The theoretical
models and benchmark calculations we present inform and enable predictive,
computationally efficient and scalable atomistic calculations for disordered
alloys and nanostructures. This provides a suitable platform to underpin
further theoretical investigations of the properties of this emerging
semiconductor alloy. | 1908.02833v1 |
2020-03-04 | Physics-informed machine learning for composition-process-property alloy design: shape memory alloy demonstration | Machine learning (ML) is shown to predict new alloys and their performances
in a high dimensional, multiple-target-property design space that considers
chemistry, multi-step processing routes, and characterization methodology
variations. A physics-informed featured engineering approach is shown to enable
otherwise poorly performing ML models to perform well with the same data.
Specifically, previously engineered elemental features based on alloy
chemistries are combined with newly engineered heat treatment process features.
The new features result from first transforming the heat treatment parameter
data as it was previously recorded using nonlinear mathematical relationships
known to describe the thermodynamics and kinetics of phase transformations in
alloys. The ability of the ML model to be used for predictive design is
validated using blind predictions. Composition - process - property
relationships for thermal hysteresis of shape memory alloys (SMAs) with complex
microstructures created via multiple
melting-homogenization-solutionization-precipitation processing stage
variations are captured, in addition to the mean transformation temperatures of
the SMAs. The quantitative models of hysteresis exhibited by such highly
processed alloys demonstrate the ability for ML models to design for physical
complexities that have challenged physics-based modeling approaches for
decades. | 2003.01878v3 |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.