arXiv subjects

Harish K. Singh

Publications and source records attributed to Harish K. Singh.

14 recordsLinked to original sources

arXiv2026

Frustration-induced multiferroicity in hauerite MnS2

Pyrite-type mineral hauerite MnS$_2$ is a magnetic insulator with localized $S=\frac52$ moments. Below 48 K, it develops a collinear antiferromagnetic order, accompanied by unit-cell doubling and breaking the inversion symmetry. We demonstrate that the latter gives rise to a ferroelectric polarization of up to 360 $μ$C/m$^2$ rendering MnS$_2$ a type-II multiferroic. Microscopically, the electronic polarization originates from S$_2$ dimers that acquire a dipole moment induced by the frustrated magnetic ordering of neighboring Mn sites. We show that time-reversal symmetry leaves ferroelectric domains intact, and that domain switching necessitates overcoming a high energy barrier set by the magnetic exchange energy scale.

cond-mat.str-el↗

arXiv2026

Strain-Tunable Shift Current and Magneto-Optical Kerr Effect in Multiferroic Altermagnet Fe2Mo3O8

Altermagnetism has recently emerged as a compelling frontier in spintronics, seamlessly merging the agile tunability of ferromagnets with the hallmark merits of antiferromagnets. As a prototypical polar multiferroic featuring distinctive altermagnetism, Fe2Mo3O8 hosts an ideal playground for exploring the intricate interplay among ferroelectric polarization, altermagnetic order, and spin-dependent responses. Here, employing first-principles calculations, we systematically investigate the coupling among polarization, spin splitting, shift current, and magneto-optical responses in Fe2Mo3O8. Our findings reveal that switching the ferroelectric polarization not only inverts the sign of the shift current but also comprehensively reshapes the momentum-space spin-splitting texture. Furthermore, the shift current and magneto-optical spectrum exhibits strong tunability under mechanical strain. Remarkably, the application of a-axis uniaxial strain breaks the crystalline symmetry, thereby activating a finite magneto-optical Kerr effect that is otherwise forbidden in the pristine phase.

cond-mat.mtrl-sci↗

arXiv2025

Multiferroicity and 180$^\circ$ domain switching in LaFeO$_3$ via Antisite Defects

Materials with coexisting and coupled ferroelectric and magnetic orders are rare. Here we show, using density functional theory calculations, that inducing Fe$_\mathrm{La}$ antisites into non-ferroelectric and antiferromagnetic LaFeO$_3$ renders the material at the same time ferroelectric and ferrimagnetic. Even more excitingly, we observe a direct coupling between the ferroelectric and ferrimagnetic polarization, the latter being switchable by the former. While on average the magnetic moments of antisites would cancel, we envision that preparing defective LaFeO$_3$ under simultaneous electric and magnetic fields will lead to a net magnetic moment due to magnetic domain reconfiguration. Moreover, ferroelectric switching under a static magnetic field can lead to 180$^\circ$ switching of the antiferromagnetic order in LaFeO$_3$.

cond-mat.mtrl-sci↗

arXiv2022

High-throughput screening of Half-antiperovskites with a stacked kagome lattice

Half-antiperovskites (HAPs) are a class of materials consisting of stacked kagome lattices and thus host exotic magnetic and electronic states. We perform high-throughput calculations based on density functional theory (DFT) and atomistic spin dynamics (ASD) simulations to predict stable magnetic HAPs M$_3$X$_2$Z$_2$ (M = Cr, Mn, Fe, Co, and Ni; X is one of the elements from Li to Bi except noble gases and 4$f$ rare-earth metals; Z = S, Se, and Te), with both thermodynamical and mechanical stabilities evaluated. Additionally, the magnetic ground states are obtained by utilizing DFT calculations combined with the ASD simulations. The existing spin frustration in an AFM kagome lattice manifests as competing behavior of the in-plane FM and AFM couplings. For a total number of 930 HAP compositions considered, we have found 23 compounds that are stabilized at non-collinear antiferromagnetic (AFM) state and 11 compounds that possess ferromagnetic (FM) order.

cond-mat.mtrl-sci↗

arXiv2022

Tunable anomalous Hall and Nernst effects in MM'X compounds

Based on first-principles calculations, the anomalous Hall (AHC) and anomalous Nernst conductivities (ANC) of the XMnP (X=Ti, Zr, Hf) compounds were evaluated, and the possibility to tailor such properties by changing the magnetization directions was also investigated. We observed that nodal lines and small gap areas consist the dominant contributions to AHC and ANC, where the significant variations in AHC and ANC when altering the magnetization direction originate from the whole Brillouin zone. Our studies gave a promising clue on engineering magnetic intermetallic compounds for tunable transverse thermoelectric applications.

cond-mat.mtrl-sci↗

arXiv2022

Thermodynamical and topological properties of metastable Fe3Sn

Combining experimental data, first-principles calculations, and Calphad assessment, thermodynamic and topological transport properties of the Fe-Sn system were investigated. Density functional theory (DFT) calculations were performed to evaluate the intermetallics' finite-temperature heat capacity (Cp). A consistent thermodynamic assessment of the Fe-Sn phase diagram was achieved by using the experimental and DFT results, together with all available data from previous publications. Hence, the metastable phase Fe3Sn was firstly introduced into the current metastable phase diagram, and corrected phase locations of Fe5Sn3 and Fe3Sn2 under the newly measured corrected temperature ranges. Furthermore, the anomalous Hall conductivity and anomalous Nernst conductivity of Fe3Sn were calculated, with magnetization directions and doping considered as perturbations to tune such transport properties. It was observed that the enhanced anomalous Hall and Nernst conductivities originate from the combination of nodal lines and small gap areas that can be tuned by doping Mn at Fe sites and varying magnetization direction

cond-mat.mtrl-sci↗

arXiv2021

Giant anomalous Hall and anomalous Nernst Conductivities in Antiperovskites and their Tunability via Magnetic Fields

The anomalous Hall conductivity (AHC) and anomalous Nernst conductivity (ANC) are two prominent transport phenomena in ferromagnetic materials of a topological nature. Based on first-principles calculations, we evaluated the AHC and ANC of 35 cubic ferromagnetic antiperovskites (APVs) and observed giant AHC and ANC as large as 1128 S/cm and 6.27 AK-1m-1 for Co3LiN and Co3PtN, respectively. Detailed analysis reveals that the origin of giant ANC can be attributed to the occurrence of Weyl nodes near the Fermi energy, as demonstrated for Co3PtN. Interestingly, both the magnitude and sign of AHC and ANC can be tuned by changing the magnetization (M) directions, which could be applied to realize spin-caloritronics devices.

cond-mat.mtrl-sci↗

arXiv2021

Anomalously low thermal conductivity of two-dimensional GaP monolayers: A comparative study of the group GaX (X = N, P, As)

With the successful synthesis of the two-dimensional (2D) gallium nitride (GaN) in a planar honeycomb structure, the phonon transport properties of 2D GaN have been reported. However, it remains unclear for the thermal transport in Ga-based materials by substituting N to other elements in the same main group, which is of more broad applications. In this paper, based on first-principles calculations, we performed a comprehensive study on the phonon transport properties of 2D GaX (X = N, P, and As) with planar or buckled honeycomb structures. The thermal conductivity of GaP (1.52 Wm-1K-1) is found unexpectedly ultra-low, which is in sharp contrast to GaN and GaAs despite their similar honeycomb geometry structure. Based on PJTE theory, GaP and GaAs stabilize in buckling structure, different from the planar structure of GaN. Compared to GaN and GaAs, strong phonon-phonon scattering is found in GaP due to the strongest phonon anharmonicity. Given electronic structures, deep insight is gained into the phonon transport that the delocalization of electrons in GaP is restricted due to the buckling structure. Thus, non-bonding lone pair electrons of P atoms induce nonlinear electrostatic forces upon thermal agitation, leading to increased phonon anharmonicity in the lattice, thus reducing thermal conductivity. Our study offers a fundamental understanding of phonon transport in GaX monolayers with honeycomb structure, which will enrich future studies of nanoscale phonon transport in 2D materials

cond-mat.mtrl-sci↗

arXiv2021

Enhanced anomalous Nernst effects in ferromagnetic materials driven by Weyl nodes

Based on high-throughput first-principles calculations, we evaluated the anomalous Hall and anomalous Nernst conductivities of 266 transition-metal-based ferromagnetic compounds. Detailed analysis based on the symmetries and Berry curvatures reveals that the origin of singular-like behaviour of anomalous Hall/Nernst conductivities can be mostly attributed to the appearance of Weyl nodes or nodal lines located in the proximity of the Fermi energy, which can be further tailored by external stimuli such as biaxial strains and magnetic fields. Moreover, such calculations are enabled by the automated construction of Wannier functions with a success rate of 92%, which paves the way to perform accurate high-throughput evaluation of the physical properties such as the transport properties using the Wannier interpolation

cond-mat.mtrl-sci↗

arXiv2020

Designing of Magnetic MAB Phases for Energy Applications

Based on high-throughput density functional theory calculations, we performed screening for stable magnetic MAB compounds and predicted potential strong magnets for permanent magnet and magnetocaloric applications. The thermodynamical, mechanical, and dynamical stabilities are systematically evaluated, resulting in 21 unreported compounds on the convex hull, and 434 materials being metastable considering convex hull tolerance to be 100 meV/atom. Analysis based on the Hume-Rothery rules revealed that the valence electron concentration and size factor difference are of significant importance in determining the stability, with good correspondence with the local atomic bonding. We found 71 compounds with the absolute value of magneto-crystalline anisotropy energy above 1.0 MJ/m$^3$ and 23 compounds with a uniaxial anisotropy greater than 0.4 MJ/m$^3$, which are potential gap magnets. Based on the magnetic deformation proxy, 99 compounds were identified as potential materials with interesting magnetocaloric performance.

cond-mat.mtrl-sci↗

arXiv2020

Multifunctional Antiperovskites driven by Strong Magnetostructural Coupling

Based on density functional theory calculations, we elucidated the origin of multifunctional properties for cubic antiperovskites with noncollinear magnetic ground states, which can be attributed to strong isotropic and anisotropic magnetostructural coupling. 16 out of 54 stable magnetic antiperovskites M$_3$XZ (M = Cr, Mn, Fe, Co, and Ni; X = selected elements from Li to Bi except for noble gases and 4f rare-earth metals; and Z = C and N) are found to exhibit the $Γ_{4g}$/$Γ_{5g}$ (i.e., characterized by irreducible representations) antiferromagnetic magnetic configurations driven by frustrated exchange coupling and strong magnetocrystalline anisotropy. Using the magnetic deformation as an effective proxy, the isotropic magnetostructural coupling is characterized, and it is observed that the paramagnetic state is critical to understand the experimentally observed negative thermal expansion and to predict the magnetocaloric performance. Moreover, the piezomagnetic and piezospintronic effects induced by biaxial strain are investigated. It is revealed that there is not a strong correlation between the induced magnetization and anomalous Hall conductivities by the imposed strain. Interestingly, the anomalous Hall/Nernst conductivities can be significantly tailored by the applied strain due to the fine-tuning of the Weyl points energies, leading to promising spintronic applications.

cond-mat.mtrl-sci↗

arXiv2020

Effect of N, C and B interstitials on the structural and magnetic properties of alloys with Cu$_3$Au-structure

High-throughput density functional calculations are used to investigate the effect of interstitial B, C and N atoms on 21 alloys reported to crystallize in the cubic Cu$_3$Au structure. It is shown that the interstitials can have a significant impact on the magneto-crystalline anisotropy energy (MAE), the thermodynamic stability and the magnetic ground state structure, making these alloys interesting for hard magnetic, magnetocaloric and other applications. For 29 alloy/interstitial combinations the formation of stable alloys with interstitial concentrations above 5\% is expected. In Ni$_3$Mn interstitial N induces a tetragonal distortion with substantial uniaxial MAE for realistic N concentrations. Mn$_3X$N$_x$ ($X$=Rh, Ir, Pt and Sb) are identified as alloys with strong magneto-crystalline anisotropy. For Mn$_3$Ir we find a strong enhancement of the MAE upon N alloying in the most stable collinear ferrimagnetic state as well as in the non-collinear magnetic ground state. Mn$_3$Ir and Mn$_3$IrN show also interesting topological transport properties. The effect of N concentration and strain on the magnetic properties are discussed. Further, the huge impact of N on the MAE of Mn$_3$Ir and a possible impact of interstitial N on amorphous Mn$_3$Ir, a material that is indispensable in today's data storage devices, are discussed at hand of the electronic structure. For Mn$_3$Sb, non-collinear, ferrimagnetic and ferromagnetic states are very close in energy, making this material potentially interesting for magnetocaloric applications. For the investigated Mn alloys and competing phases, the determination of the magnetic ground state is essential for a reliable prediction of the phase stability.

cond-mat.mtrl-sci↗

arXiv2018

Polytypism at its best: improved thermoelectric performance in Li based Nowotony-Juza phases

In principle thermoelectricity is a viable route of converting waste heat into electricity, but the commercialization of the technology is limited by its present efficiency. In quest of improved materials, utilizing an \textit{ab initio} approach, we report polytypism induced improved thermoelectric performance in Li based Nowotny-Juza phases LiZn\textit{X} (\textit{X} = N, P, As, Sb, and Bi). In addition to LiZnSb, we find that cubic LiZnBi is energetically more favorable than the hitherto explored hexagonal phase whereas the hexagonal polytypes of cubic LiZnP, and LiZnAs are likely to be stabilized by pressure -- hydrostatic pressure can be aided by internal pressure to facilitate the phase transition. We find a pronounced impact of the polytypism on thermoelectric properties. We determine conservative estimates of the figure of merit and find that while power factor and figure of merit values are improved in hexagonal phases, the values in cubic phases are still excellent. The \textit{ZT} values of cubic and hexagonal LiZnSb at 700 K are 1.27 and 1.95, respectively. Other promising \textit{ZT} values at 700 K are 1.96 and 1.49 of hexagonal LiZnP and LiZnAs, respectively, for \textit{n}-type doping. Overall, our findings proffers that the Nowotny-Juza phases are a new potential class of thermoelectric materials.

cond-mat.mtrl-sci↗

arXiv2017

Ab-initio design of new Heusler materials for thermoelectric applications

In search of new prospects for thermoelectric materials, using ab-initio calculations and semi-classical Boltzmann theory, we have systematically investigated the electronic structure and transport properties of 18-valence electron count cobalt based half-Heusler alloys with prime focus on CoVSn, CoNbSn, CoTaSn, CoMoIn, and CoWIn. The effect of doping on transport properties has been studied under the rigid band approximation. The maximum power factor, S$^2σ$, for all systems is obtained on hole doping and is comparable to the existing thermoelectric material CoTiSb. The stability of all the systems is verified by phonon calculations. Based on our calculations, we suggest that CoVSn, CoNbSn, CoTaSn, CoMoIn and CoWIn could be potential candidates for high temperature thermoelectric materials.

physics.comp-ph↗