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At least 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Low-temperature MnBi alloys: Electronic and magnetic properties, constitution, morphology and fabrication (Review article)

The article reviews the rich phenomena of physical properties of MnBi. The diverse phenomena include strong spin-orbit interaction, anomalous temperature dependence of the coercivity and the magneto-crystalline anisotropy field, unique magneto-optical properties. Issues addressed include the nature of the electronic ground states of MnBi, the electronic and magnetic structures, Fermi surface, magneto-crystalline anisotropy, x-ray magnetic dichroism. The discussion includes key experiments, such as optical and magneto-optical spectroscopic measurements, de Haas-van Alphen (dHvA) measurements, x-ray photoemission and x-ray absorption spectroscopy measurements as well as x-ray magnetic circular dichroism. The effect of the spin-orbit (SO) interaction and Coulomb repulsion U were found to be crucial for the Fermi surface, cyclotron masses, magneto-optical properties, and x-ray magnetic circular dichroism. The microscopic origin of unique magneto-crystalline anisotropy and giant Kerr effect in MnBi is analyzed in detail. The huge Kerr effect in MnBi is caused by the combination of a sizable magnetic moment on manganese, the large spin-orbit coupling of bismuth, and a strong hybridization between the manganese 3d and the bismuth 6p states. The magneto-optically active states are mainly the 6p states of Bi. We show that the observed temperature dependence of the magneto-crystalline anisotropy can be explained taking into account the spin-orbit interaction together with strong Coulomb electron-electron interaction. The SO coupling of Bi is equally responsible for the large magneto-crystalline anisotropy energy as is the exchange splitting of Mn. The fabrication, morphology, and constitution of low-temperature MnBi alloys in bulk, thin films, and nanoparticles are discussed. The nanocomposite permanent magnetic materials based on MnBi, (Co, Fe) and Nd 2 Fe 14 B are also discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2022

On the theory of nonhomogeneous nonequilibrium superconductivity in 2D systems with massless fermions

Here we analyze static and nonequilibrium superconducting properties of a 2D relativistic-like model system with local electron-electron interaction, Rashba spin-orbit interaction αR in presence of time-dependent in-plane magnetic field H(t). It is shown that similar to the 2D case with ordinary massive quasiparticle dispersion ε(k)~|k| 2 at large fields, such a system demonstrates a nonhomogeneous superconducting stripe phase with the order parameter Δ(r)=Δ(0)cos(2[μ B B×r]n/$\hbarυ_F$) (B is the magnetic induction, υF is the Fermi velocity, n is the normal to the plane, μ B is the Bohr magneton, and αR$\ll$υF) where the stripes are oriented along the B direction. In the considered system, the inter-stripe period L and the magnitude of the magnetic field B are related by a universal relation BL=$\hbarυ_F$/μ B ≃0.714∙10 -4 Tm. Contrary to the case of massive quasiparticles, where the condition α R ~υ F can be, in principle, satisfied by increasing α R or by charge doping (Fermi velocity decreasing), in a relativistic-like system, where υF is doping-independent and one-two orders of magnitude larger than typical Fermi velocity in the “standard” 2D systems, the stripe phase can be the ground state at a rather low doping level. We also analyzed the nonequilibrium properties of the system with a focus on the melting of the stripe order (when the magnetic field is quenched to a lower value) and stripe dynamics (when the field is rotated by 90° degrees) and found several notable results. In particular, it was shown that the stripe domains melt according to law R~1$\sqrt{t}$ at initial times, while at longer times they shrink exponentially. In the case of the flipped magnetic field, the stripe orientation gradually turns from x- to y-direction, and the intermediate “crossed-stripe” phase takes place during times of order of picoseconds. Such a crossed phase is built of periodic superconducting bubbles that potentially may have applications in modern ultrafast superconducting technologies.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Heterostructure design to achieve high quality, high density GaAs 2D electron system with g -factor tending to zero

Hydrostatic pressure is a useful tool that can tune several key parameters in solid state materials. For example, the Landé g-factor in GaAs two-dimensional electron systems (2DESs) is expected to change from its bulk value g ≃ -0.44 to zero and even to positive values under sufficiently large hydrostatic pressure. Although this presents an intriguing platform to investigate electron-electron interaction in a system with g = 0, studies are quite limited because the GaAs 2DES density decreases significantly with increasing hydrostatic pressure. Here, we show that a simple model, based on pressure-dependent changes in the conduction band alignment, quantitatively explains this commonly observed trend. Furthermore, we demonstrate that the decrease in the 2DES density can be suppressed by more than a factor of 3 through an innovative heterostructure design.

Physics↗
DOE OSTI2020

False metals, real insulators, and degenerate gapped metals

This paper deals with a significant family of compounds predicted by simplistic electronic structure theory to be metals but are, in fact, insulators. This false metallic state has been traditionally attributed in the literature to reflect the absence of proper treatment of electron-electron correlation (“Mott insulators”) whereas, in fact, even mean-field like density functional theory describes the insulating phase correctly if the restrictions posed on the simplistic theory are avoided. Such unwarranted restrictions included different forms of disallowing symmetry breaking described in this article. As the science and technology of conductors have transitioned from studying simple elemental metals such as Al or Cu to compound conductors such as binary or ternary oxides and pnictides, a special class of degenerate but gapped metals has been noticed. Their presumed electronic configurations show the Fermi level inside the conduction band or valence band, yet there is an “internal band gap” between the principal band edges. The significance of this electronic configuration is that it might be unstable toward the formation of states inside the internal band gap when the formation of such states costs less energy than the energy gained by transferring carriers from the conduction band to these lower energy acceptor states, changing the original (false) metal to an insulator. The analogous process also exists for degenerate but gapped metals with the Fermi level inside the valence band, where the energy gain is defined by transfer of electrons from the donor level to the unoccupied part of the valence band. We focus here on the fact that numerous electronic structure methodologies have overlooked some physical factors that could stabilize the insulating alternative, predicting instead false metals that do not really exist (note that this is in general not a physical phase transition, but a correction of a previous error in theory that led to a false prediction of a metal). Such errors include: (i) ignoring spin symmetry breaking, such as disallowing magnetic spin ordering in CuBi2O4 or disallowing the formation of polymorphous spin networks in paramagnetic LaTiO 3 and YTiO 3 ; (ii) ignoring structural symmetry breaking, e.g., not enabling energy-lowering bond disproportionation (Li-doped TiO 2 , SrBiO 3 , and rare-earth nickelates), or not exploring pseudo-Jahn–Teller-like distortions in LaMnO 3 , or disallowing spontaneous formation of ordered vacancy compounds in Ba 4 As 3 and Ag 3 Al 22 O 34 ; and (iii) ignoring spin–orbit coupling forcing false metallic states in CaIrO 3 and Sr 2 IrO 4 . The distinction between false metals vs real insulators is important because (a) predicting theoretically that a given compound is metal even though it is found to be an insulator often creates the temptation to invoke high order novel physical effects (such as correlation in d-electron Mott insulators) to explain what was in effect caused by a more mundane artifact in a lower-level mean-field band theory, (b) recent prediction of exotic physical effects such as topological semimetals were unfortunately based on the above compounds that were misconstrued by theory to be metal, but are now recognized to be stable insulators not hosting exotic effects, and (c) practical technological applications based on stable degenerate but gapped metals such as transparent conductors or electrides for catalysis must rely on the systematically correct and reliable theoretical classification of metals vs insulators.

36 MATERIALS SCIENCE↗
DOE OSTI2020

A self-consistent field formulation of excited state mean field theory

In this work, we show that, as in Hartree-Fock theory, the orbitals for excited state mean field theory can be optimized via a self-consistent one-electron equation in which electron-electron repulsion is accounted for through mean field operators. In addition to showing that this excited state ansatz is sufficiently close to a mean field product state to admit a one-electron formulation, this approach brings the orbital optimization speed to within roughly a factor of two of ground state mean field theory. The approach parallels Hartree Fock theory in multiple ways, including the presence of a commutator condition, a one-electron mean-field working equation, and acceleration via direct inversion in the iterative subspace. When combined with a configuration interaction singles Davidson solver for the excitation coefficients, the self-consistent field formulation dramatically reduces the cost of the theory compared to previous approaches based on quasi-Newton descent.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Taming the fixed-node error in diffusion Monte Carlo via range separation

By combining density-functional theory (DFT) and wave function theory via the range separation (RS) of the interelectronic Coulomb operator, we obtain accurate fixed-node diffusion Monte Carlo (FN-DMC) energies with compact multi-determinant trial wave functions. In particular, we combine here short-range exchange-correlation functionals with a flavor of selected configuration interaction known as configuration interaction using a perturbative selection made iteratively (CIPSI), a scheme that we label RS-DFT-CIPSI. One of the take-home messages of the present study is that RS-DFT-CIPSI trial wave functions yield lower fixed-node energies with more compact multi-determinant expansions than CIPSI, especially for small basis sets. Indeed, as the CIPSI component of RS-DFT-CIPSI is relieved from describing the short-range part of the correlation hole around the electron-electron coalescence points, the number of determinants in the trial wave function required to reach a given accuracy is significantly reduced as compared to a conventional CIPSI calculation. Importantly, by performing various numerical experiments, we evidence that the RS-DFT scheme essentially plays the role of a simple Jastrow factor by mimicking short-range correlation effects, hence avoiding the burden of performing a stochastic optimization. Considering the 55 atomization energies of the Gaussian-1 benchmark set of molecules, we show that using a fixed value of mu = 0.5 bohr(-1) provides effective error cancellations as well as compact trial wave functions, making the present method a good candidate for the accurate description of large chemical systems.

Scemama, Anthony↗
DOE OSTI2023

Ab initio calculations of low-energy quasiparticle lifetimes in bilayer graphene

Motivated by recent experimental results we calculate from first-principles the lifetime of low-energy quasiparticles in bilayer graphene (BLG). Here, we take into account the scattering rate arising from electron-electron interactions within the GW approximation for the electron self-energy and consider several p-type doping levels ranging from 0 to ρ ≈ 2.4 × 10 12 holes/cm 2 . In the undoped case we find that the average inverse lifetime scales linearly with energy away from the charge neutrality point, with values in good agreement with experiments. The decay rate is approximately three times larger than in monolayer graphene, a consequence of the enhanced screening in BLG. In the doped case, the dependence of the inverse lifetime on quasiparticle energy acquires a non-linear component due to the opening of an additional decay channel mediated by acoustic plasmons.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

Plasma channel produced by femtosecond laser pulses as a medium for amplifying electromagnetic radiation of the subterahertz frequency range

The electron energy distribution function in the plasma channel produced by a femtosecond laser pulse with a wavelength of 248 nm in atmospheric-pressure gases was considered. Conditions were determined whereby this channel may be employed for amplifying electromagnetic waves up to the terahertz frequency range over the energy spectrum relaxation time ∼10{sup -7} s. Gains were calculated as functions of time and radiation frequency. The effect of electron – electron collisions on the rate of relaxation processes in the plasma and on its ability to amplify the electromagnetic radiation was investigated. (interaction of laser radiation with matter)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2011

A step closer to visualizing the electron___phonon interplay

The origin of the very high superconducting transition temperature (Tc) in ceramic copper oxide superconductors is one of the greatest mysteries in modern physics. In the superconducting state, electrons form pairs (known as Cooper pairs) and condense into the superfluid state to conduct electric current with zero resistance. For conventional superconductors, it is well established that the 2 electrons in a Cooper pair are 'bonded' by lattice vibrations (phonons), whereas in high-Tc superconductors, the 'glue' for the Cooper pairs is still under intense discussion. Although the high transition temperature and the unconventional pairing symmetry (d-wave symmetry) have led many researchers to believe that the pairing mechanism results from electron-electron interaction, increasing evidence shows that electron-phonon coupling also significantly influences the low-energy electronic structures and hence may also play an important role in high-Tc superconductivity. In a recent issue of PNAS, Carbone et al. use ultrafast electron diffraction, a recently developed experimental technique, to attack this problem from a new angle, the dynamics of the electronic relaxation process involving phonons. Their results provide fresh evidence for the strong interplay between electronic and atomic degrees of freedom in high-Tc superconductivity. In general, ultrafast spectroscopy makes use of the pump-probe method to study the dynamic process in material. In such experiments, one first shoots an ultrafast (typically 10-100 fs) 'pumping' pulse at the sample to drive its electronic system out of the equilibrium state. Then after a brief time delay ({Delta}t) of typically tens of femtoseconds to tens of picoseconds, a 'probing' pulse of either photons or electrons is sent in to probe the sample's transient state. By varying {Delta}t, one can study the process by which the system relaxes back to the equilibrium state, thus acquiring the related dynamic information. This pump-probe experiment is reminiscent of the standard method used by bell makers for hundreds of years to judge the quality of their products (hitting a bell then listening to how the sound would fade away), albeit the relevant time scale here is way beyond tens of femtoseconds. Traditionally, ultrafast spectroscopy was carried out to study gas-phase reactions, but it has also been applied to study condensed phase systems since the development of reliable solid-state ultrafast lasers approximately a decade ago. In addition, the ability to control pulse width, wavelength, and amplification of the output of Ti:Sapphire lasers has further increased the capability of this experimental method. During the past decade, many ultrafast pump-probe experiments have been carried out in various fields by using different probing methods, such as photo-resistivity, fluorescence yield, and photoemission, and they have revealed much new information complementary to the equilibrium spectroscopy methods used before. Carbone et al. used the photon-pump, electron (diffraction)-probe method. The pumping photon pulse first drives the electrons in the sample into an oscillating mode along its polarization direction. Then during the delay time, these excited electrons can transfer excess energy to the adjacent nuclei and cause crystal lattice vibration on their way back to the equilibrium state. An ultrashort electron pulse is shot at the sample at various time delays {Delta}t and the diffraction pattern is collected. Because the electron diffraction pattern is directly related to the crystal lattice structure and its motion, this technique provides a natural way to study the electron-phonon coupling problem. Furthermore, by adjusting the pump pulse's relative polarization with respect to the Cu-O bond direction, Carbone et al. were able to acquire the electron-phonon coupling strength along different directions. Focusing on the lattice dynamic along the c axis, Carbone et al. found that the c-axis phonons in the optimally-doped Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} (Bi2212) are coupled to the electrons with different strength along different directions within the CuO{sub 2} plane. The coupling strength reaches its largest value along the 2 Cu-O bond directions and becomes the weakest along the bisector of the angle formed by the 2 Cu-O bonds. As pointed out by Carbone et al., these observations agree well with the calculated coupling strength between electrons and the buckling phonons. Furthermore, their observation of this anisotropic electron-phonon coupling also agrees with results from angle-resolved photoemission (ARPES), which measures the equilibrium-state properties of materials. In ARPES measurements, electron-phonon coupling manifests itself as a kink anomaly in the band dispersion and a corresponding sudden broadening in the spectral width.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Many-body interactions in quasi-freestanding graphene

The Landau-Fermi liquid picture for quasiparticles assumes that charge carriers are dressed by many-body interactions, forming one of the fundamental theories of solids. Whether this picture still holds for a semimetal such as graphene at the neutrality point, i.e., when the chemical potential coincides with the Dirac point energy, is one of the long-standing puzzles in this field. Here we present such a study in quasi-freestanding graphene by using high-resolution angle-resolved photoemission spectroscopy. We see the electron-electron and electron-phonon interactions go through substantial changes when the semimetallic regime is approached, including renormalizations due to strong electron-electron interactions with similarities to marginal Fermi liquid behavior. These findings set a new benchmark in our understanding of many-body physics in graphene and a variety of novel materials with Dirac fermions.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Distinguishing attosecond electron–electron scattering and screening in transition metals

Electron–electron interactions are the fastest processes in materials, occurring on femtosecond to attosecond timescales, depending on the electronic band structure of the material and the excitation energy. Such interactions can play a dominant role in light-induced processes such as nano-enhanced plasmonics and catalysis, light harvesting, or phase transitions. However, to date it has not been possible to experimentally distinguish fundamental electron interactions such as scattering and screening. Here, we use sequences of attosecond pulses to directly measure electron–electron interactions in different bands of different materials with both simple and complex Fermi surfaces. By extracting the time delays associated with photoemission we show that the lifetime of photoelectrons from the d band of Cu are longer by ∼100 as compared with those from the same band of Ni. We attribute this to the enhanced electron–electron scattering in the unfilled d band of Ni. Using theoretical modeling, we can extract the contributions of electron–electron scattering and screening in different bands of different materials with both simple and complex Fermi surfaces. Our results also show that screening influences high-energy photoelectrons (≈20 eV) significantly less than low-energy photoelectrons. As a result, high-energy photoelectrons can serve as a direct probe of spin-dependent electron–electron scattering by neglecting screening. This can then be applied to quantifying the contribution of electron interactions and screening to low-energy excitations near the Fermi level. The information derived here provides valuable and unique information for a host of quantum materials.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2012

The E3 Ubiquitin Ligase- and Protein Phosphatase 2A (PP2A)-binding Domains of the Alpha4 Protein Are Both Required for Alpha4 to Inhibit PP2A Degradation

Protein phosphatase 2A (PP2A) is regulated through a variety of mechanisms, including post-translational modifications and association with regulatory proteins. Alpha4 is one such regulatory protein that binds the PP2A catalytic subunit (PP2Ac) and protects it from polyubiquitination and degradation. Alpha4 is a multidomain protein with a C-terminal domain that binds Mid1, a putative E3 ubiquitin ligase, and an N-terminal domain containing the PP2Ac-binding site. In this work, we present the structure of the N-terminal domain of mammalian Alpha4 determined by x-ray crystallography and use double electron-electron resonance spectroscopy to show that it is a flexible tetratricopeptide repeat-like protein. Structurally, Alpha4 differs from its yeast homolog, Tap42, in two important ways: (1) the position of the helix containing the PP2Ac-binding residues is in a more open conformation, showing flexibility in this region; and (2) Alpha4 contains a ubiquitin-interacting motif. The effects of wild-type and mutant Alpha4 on PP2Ac ubiquitination and stability were examined in mammalian cells by performing tandem ubiquitin-binding entity precipitations and cycloheximide chase experiments. Our results reveal that both the C-terminal Mid1-binding domain and the PP2Ac-binding determinants are required for Alpha4-mediated protection of PP2Ac from polyubiquitination and degradation.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2018

Beyond electrostatic modification: design and discovery of functional oxide phases via ionic-electronic doping

A new research field of functional materials and device physics is emerging that combines ionic transport with charge carrier modulation to realize emergent physical properties and discovery of metastable phases. The paradigm for enabling function extends far beyond carrier accumulation or depletion in band semiconductors or simply moving ions through an insulating electrolyte. Rather, by careful selection of electronically or structurally fragile materials, one can collapse or open band gaps via extreme ionic dopant concentration, or reconfigure their entire crystal structure to create new phases. Electron-electron and electron-lattice interactions can be coupled or controlled independently in such systems via electric fields without thermal constraints by use of ionic dopants. The unifying theme across these studies is to introduce ions and electrons via electric fields through interfaces with electrochemistry playing a dominant role. In this review, we briefly summarize this nascent field of iontronics and discuss principal results to date with examples from binary and complex oxides as well as selected 2D materials systems. Here, we conclude the review by highlighting gaps in fundamental scientific understanding and prospects for the use of such novel devices in future electronic, photonic and energy technologies.

36 MATERIALS SCIENCE↗
DOE OSTI2013

THE SHOENBERG EFFECT IN A RELATIVISTIC DEGENERATE ELECTRON GAS AND OBSERVATIONAL EVIDENCE IN MAGNETARS

The electron gas inside a neutron star is highly degenerate and relativistic. Due to electron-electron magnetic interactions, the differential susceptibility can equal or exceed one, which causes the magnetic system of the neutron star to become metastable or unstable. The Fermi liquid of nucleons under the crust can be in a metastable state, while the crust is unstable to the formation of layers of alternating magnetization. The change of the magnetic stress acting on adjacent domains can result in a series of shifts or fractures in the crust. The release of magnetic free energy and elastic energy in the crust can cause the bursts observed in magnetars. Simultaneously, a series of shifts or fractures in the deep crust that is close to the Fermi liquid of nucleons can trigger a phase transition of the Fermi liquid of nucleons from a metastable state to a stable state. The magnetic free energy released in the Fermi liquid of nucleons corresponds to the giant flares observed in some magnetars.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Existence of a flat band in highly correlated metal BaCo 2 P 2

We report on the observation of a flat band situated at the Fermi level E F along with the structural, electrical transport, and magnetic properties of BaCo 2 P 2 that crystallizes in the ThCr 2 Si 2 -type body-center tetragonal structure. This compound has the largest inter-layer pnictide (Pn) distance d Pn–Pn as well as the largest c/a ratio among all the known ACo 2 Pn 2 (A = alkaline earth metal) compounds, where a and c are the tetragonal lattice parameters. Hence, the magnetic and electronic properties of this compound are expected to have a quasi-two-dimensional character. Despite the evidence of the presence of sizable magnetic interactions, magnetic susceptibility χ(T) of BaCo 2 P 2 does not show magnetic ordering down to 1.8 K. The material shows good metallic conduction with a large residual resistivity ratio ρ 300 K /ρ 1.8 K ≈ 70 and a Fermi liquid behavior at low temperature. Kadowaki–Woods ratio R KW of BaCo 2 P 2 suggests the presence of sizable electronic correlations within this system. Additionally, a large many-body enhancement of 2.3 of the experimental density of states D γ (E F ) over the band-structure D band (E F ) is inferred to arise from sizable electron-electron and/or electron-phonon interactions leading to a substantial deviation from the free-electron behavior.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Dimensionality-driven metal to Mott insulator transition in two-dimensional 1T-TaSe2

Abstract Two-dimensional materials represent a major frontier for research into exotic many-body quantum phenomena. In the extreme two-dimensional limit, electron-electron interaction often dominates over other electronic energy scales, leading to strongly correlated effects such as quantum spin liquid and unconventional superconductivity. The dominance is conventionally attributed to the lack of electron screening in the third dimension. Here, we discover an intriguing metal to Mott insulator transition in 1T-TaSe2 that defies conventional wisdom. Specifically, we find that dimensionality crossover, instead of reduced screening, drives the transition in atomically thin 1T-TaSe2. A dispersive band crossing the Fermi level is found to be responsible for the bulk metallicity in the material. Reducing the dimensionality, however, effectively quenches the kinetic energy of these initially itinerant electrons, and drives the material into a Mott insulating state. The dimensionality-driven metal to Mott insulator transition resolves the long-standing dichotomy between metallic bulk and insulating surface of 1T-TaSe2. Our work further reveals a new pathway for modulating two-dimensional materials that enables exploring strongly correlated systems across uncharted parameter space.

1T-TaSe2↗
DOE OSTI2025

Significance of the structural configuration of B2 disorder in Co and Ti based Heusler alloys

We investigate here structural (at local and global levels) and transport properties for 𝑋 2 ⁢MnAl (𝑋= Co and Ti). Additionally, the magnetic properties were also studied for Ti 2 ⁢MnAl. Our x-ray diffraction results show that both the compounds stabilize in B2 disordered phase with cubic structure of 𝑃⁢𝑚⁢$\overline{3}$⁢𝑚 space group. Further, the structural configuration of the above disordered phase for both the compounds was identified using combined studies of x-ray absorption spectroscopy and multiple scattering calculations at the transition metal 𝐾 edges. Upon such identification, in the case of Co 2 ⁢Mn 1−𝑦⁢ Cr 𝑦 ⁢Al (𝑦= 0, 0.05, 0.1, 0.2) with change in 𝑦, we are able to establish a better connection quantitatively between the inverse of Mn-Co bonds and peak in the temperature-dependent resistivity. This highlights the crucial importance of a detailed understanding of the nature of B2 disorder. In the case of 𝑦=0, in the temperature range of study, the resistivity is driven by the functional form associated with (a) three-dimensional enhanced electron-electron Coulomb interaction scattering mechanism and (b) an unconventional one-magnon process. For Ti 2 ⁢MnAl, the transport shows metallic glasslike behavior at high temperature, while at low temperature it follows both the Cote-Meisel's model and quantum correction model. In this compound, the magnetic studies suggest the formation of superparamagnetic clusters in the paramagnetic matrix at low temperatures. Our density functional theory results are in line with the transport and magnetic properties. In literature, the spin polarization percentage (𝑃) for 𝑋= Co in B2 disordered phase is 76%. However, the present results emphasize the fact that in B2 disordered phase, the value of 𝑃 can range from 90% to 71% depending on the structural configuration introduced by swapping of the atomic positions of Mn and Al. For the compound under study, the value of percentage spin polarization obtained ranges between 82% to 85%. In addition, we also identify the origin of the difference in the shape of the Mn 3⁢𝑑 density of states for both the alloys. In conclusion, our results for 𝑋= Co alloy highlights the importance of identifying the specific structural configuration associated with a particular disorder category especially in the estimation of 𝑇 𝑐 and 𝑃 and for 𝑋= Ti, the physical properties can be tuned by varying the position of 𝐸 𝐹 and thereby its utilization in device applications.

36 MATERIALS SCIENCE↗