arXiv subjects

Kirill D. Belashchenko

Publications and source records attributed to Kirill D. Belashchenko.

At least 19 recordsLinked to original sources

arXiv2026

Reliability of AI/ML Computational Searches for Magnetic Materials: Databases, Validation, and Synthesizability

The rapid growth of AI/ML methods for materials discovery has increased the importance of the quality, physical completeness, and information content of computational databases. We examine these issues for magnetic materials, where incomplete sampling of competing magnetic states, chemical disorder, and finite-temperature properties can lead to apparently accurate but physically unreliable predictions. We propose a hierarchical discovery workflow combining independent ML models with explicit electronic-structure, magnetic, dynamical, thermodynamic, kinetic, and experimental validation. To incorporate kinetic accessibility into high-throughput screening, we introduce a dimensionless synthesis-window descriptor based on the relation between the chemical order-disorder and Tammann temperatures. A cluster-expansion analysis of Fe-Co-B illustrates the importance of this criterion: although ordered Fe3CoB2 is energetically favored at T=0, its small ordering energy produces an order-disorder temperature far below room temperature, making long-range Fe/Co ordering kinetically unachievable. These results demonstrate that reliable AI/ML discovery of magnetic materials requires databases and validation procedures that contain physical information relevant to the target functionality, rather than simply larger numbers of calculated structures.

cond-mat.mtrl-sci↗

arXiv2026

Mapping metallic d-wave altermagnetism across the TiNiSi structural family

The prospect of using altermagnets as switchable sources of perpendicularly polarized spin currents has intensified the search for candidate materials, yet metallic d-wave systems with sizable spin-splitter responses remain scarce. Here, we identify an empirical magnetic motif that supports metallic d-wave altermagnetism in the TiNiSi structural family: ferromagnetically ordered zigzag chains with antiferromagnetic interchain coupling in a relatively low-symmetry crystal environment. The TiNiSi structure type combines this motif with broad chemical flexibility and competing magnetic ground states. By combining first-principles screening of thermodynamic stability and magnetic ground states across 280 ternary systems, we identify 16 metallic d-wave altermagnets. This set recovers four experimentally known members---WFeB, NbMnP, TaMnP, and NbMnAs---and yields 12 new predictions, of which ScMnP, TaMnAs, ScMnAs, MoMnAs, MoMnSi, and WMnSi are the most promising. Noncollinear calculations indicate that the collinear altermagnetic configuration is the ground state across them. Each of the six leading new candidates has a nonzero spin-splitter angle and a finite anomalous Hall conductivity. Notably, ScMnP and TaMnAs exhibit strong spin-splitter responses despite modest altermagnetic band splitting. These results establish TiNiSi-type metallic d-wave altermagnets as a chemically versatile platform for efficient charge-to-spin conversion and provide an empirical magnetic-motif-guided route to identifying further candidates.

cond-mat.mtrl-sci↗

arXiv2026

Magnetoelastic coupling descriptor for high-throughput ab initio search of magnetocaloric materials

We use Landau theory of phase transitions to design a magnetoelastic coupling descriptor that can identify magnetic materials on the brink of a first-order transition, where a strong magnetocaloric effect (MCE) can arise. The descriptor can be computed from electronic structure calculations and requires structural optimization in the paramagnetic state, which we model using special quasi-random collinear spin configurations. We first evaluate the descriptor for a set of known magnetocaloric materials and identify compounds in which the MCE is driven by magnetoelastic coupling. We then apply the descriptor in a high-throughput \emph{ab initio} screening of magnetic L1$_2$ compounds. This search identifies the L1$_2$ cubic phases of Mn$_3$Ge and Mn$_3$Sb as materials with strong magnetoelastic coupling and potential for a large magnetocaloric response.

cond-mat.mtrl-sci↗

arXiv2026

Local multiferroic ordering at room temperature in collinear magnetoelectric antiferromagnets induced by flexo-Zeeman coupling

Spin-driven multiferroicity attracts significant interest due to its tunability and inherently strong magnetoelectric coupling. While this mechanism induces sizeable electric polarization, it typically occurs at low temperatures and in complex materials. In the simple oxide, the magnetoelectric antiferromagnet Cr$_2$O$_3$, we experimentally demonstrate the existence of specific domain walls that act as room-temperature multiferroic regions. This behavior stems from an anisotropic crystal-symmetry-dependent mechanism of exchange origin, which is applicable to a broad class of bipartite antiferromagnets. The key signature is the magnetization occurring at antiferromagnetic textures, driven by the flexo-Zeeman interaction. These findings establish a foundation for exploring high-temperature spin-driven multiferroicity for magnetoelectric spin-orbit memory and logic applications.

cond-mat.mtrl-sci↗

arXiv2026

Metallic d-wave altermagnetism in WFeB: a platform for electrically switchable perpendicular spin-splitter response

We report the synthesis and magnetic characterization of WFeB and identify it as a metallic d-wave altermagnet representative of a broader TiNiSi-type family. Neutron diffraction, Mössbauer spectroscopy, and magnetometry establish a collinear altermagnetic ordering confirmed by first-principles calculations. The electronic structure shows a nonrelativistic spin splitting of approximately 100 meV, but it also supports a strong spin-splitter transport response. This demonstrates that efficient spin-current generation can occur even with such modest band splitting. Symmetry analysis shows that selected film orientations permit deterministic switching of the Néel vector by current-induced staggered torques, enabling electrical control of a perpendicular spin-splitter response. These results establish WFeB and related TiNiSi-type antiferromagnets as a platform for electrically switchable charge-to-spin conversion driven by altermagnetic symmetry.

cond-mat.mtrl-sci↗

arXiv2025

Competing Magnetic Phases in Li-Fe-Ge Kagome Systems

Competing interlayer magnetic interactions in kagome magnets can lead to diverse magnetic phases, which enable various promising topological or quantum material properties. Here, the electronic structure and magnetic properties have been studied using first-principles calculations for the LiFe$_6$Ge$_6$, LiFe$_6$Ge$_4$, and LiFe$_6$Ge$_5$ compounds sharing the kagome Fe$_3$Ge layer motif but with different interlayer arrangements. For LiFe$_6$Ge$_4$ and LiFe$_6$Ge$_5$, the predicted magnetic ground states are collinear antiferromagnetic (AFM) states involving a mix of ferromagnetic (FM) and AFM interlayer orientations. Whereas for LiFe$_6$Ge$_6$, an incommensurate cycloidal spin spiral is stabilized as a ground state, being close to a collinear A-type AFM state. The analysis of magnetic RKKY exchange coupling confirms the results of electronic structure calculations. The values of atomic magnetic moments are in good agreement with existing experimental estimations. Our experiments on LiFe$_6$Ge$_6$ single crystals have observed AFM ordering at ~540 K and transition to another magnetic phase, with a small FM component (possibly with spin canting), below ~270 K. Thus, our theory and experiment suggest the existence and sequence of collinear and noncollinear magnetic states in kagome LiFe$_6$Ge$_6$. Our findings provide a platform for exploring various novel magnetic phases and associated unconventional or topological magnetism.

cond-mat.mtrl-sci↗

arXiv2025

Discovery and Synthesis of a Family of Boride Altermagnets

Borides are a rich material family. To push the boundaries of borides' properties and applications into broader fields, we have conducted systematic theoretical and experimental searches for synthesizable phases in ternary borides TM$_2$B$_2$ (T = 3d, M = 4d/5d transition metals). We find that TM$_2$B$_2$ in the FeMo$_2$B$_2$-type and CoW$_2$B$_2$-type structures form a large family of stable/metastable materials of 120 members. Among them, we identify 40 materials with stable magnetic solutions. Further, we discover 11 altermagnets in the FeMo$_2$B$_2$-type structure. So far, boride altermagnets are rare. In these altermagnets, T = Fe or Mn atoms are arranged in parallel T-chains with strong ferromagnetic intrachain couplings and antiferromagnetic interchain couplings. They simultaneously exhibit electronic band spin splitting, typical of ferromagnetism, and zero net magnetization, typical of antiferromagnetism. They also exhibit magnonic band chiral splitting. Both effects originate from the unique altermagnetic symmetries crucially constrained by the nonmagnetic atoms in the structure. Transport properties of relevance to spintronic applications, including the strain-induced spin-splitter effect and anomalous Hall effect, are predicted. An iodine-assisted synthesis method for TM$_2$B$_2$ is developed, using which 7 of the predicted low-energy phases are experimentally synthesized and characterized, including 4 altermagnets. This work expands the realm of borides by offering new opportunities for studying altermagnetism and altermagnons in borides. It also provides valuable insights into the discovery and design of altermagnets. By demonstrating that altermagnets can exist as families sharing a common motif, this work paves a feasible route for discovering altermagnets by elemental substitutions and high-throughput computations.

cond-mat.mtrl-sci↗

arXiv2025

Inverse Lieb Materials: Altermagnetism and More

The Lieb lattice, originally proposed for cuprate superconductors, has gained new attention in the emerging field of altermagnetism as a minimal analytical model for the latter. While initially the so-called inverse Lieb lattice (ILL) was deemed only a theoretical model, recently several real materials with this crystallographic motif have been found. The unique geometry of ILL can accommodate complex magnetic orderings arising from competing exchange interactions and geometric frustration, offering great tunability for magnetic properties. In this work, we provide comprehensive insights into magnetic phases in ILL materials and establish guidelines for efficient identification of altermagnetic materials within this family. We begin by constructing phase diagrams using a simple Heisenberg model to elucidate the fundamental mechanisms underlying altermagnetism and other complex magnetic phases observed experimentally. To bridge theory with experiment, we systematically investigate a series of existing ILL compounds using density functional theory (DFT) calculations to determine their magnetic ground states. Our computational results are in good agreement with experimental observations. Importantly, we identify a trend linking magnetic ordering to the $d$-shell filling of transition metal ions, with $d^{2-3}$ and $d^{5}$ configurations showing propensity for altermagnetic behavior. Additionally, we identify a promising metallic compound Sr$_{2}$CrO$_{2}$Cr$_{2}$OAs$_{2}$ as an altermagnet that is highly anisotropic in its $J_2$ exchange couplings with large Néel temperature ($\sim 600$ K). Using exchange coupling parameters extracted from DFT calculations, we compute the magnon spectra for altermagnetic systems. As expected, chiral splittings in the magnon dispersion are directly correlated with anisotropy between crystallographically inequivalent $J_{2}$ exchange interactions.

cond-mat.mtrl-sci↗

arXiv2025

High-Throughput Studies of Novel Magnetic Materials in Borides

Borides are a versatile material family with various properties for valuable applications. Conventional magnetism, such as ferromagnetism and antiferromagnetism in borides, have been extensively studied. However, research on unconventional magnetism in borides where quantum effects are dominant is scarce. Here, we implement a high-throughput workflow combining first-principles calculations, materials prediction, and magnetic properties calculations to discover novel magnetism and magnetic materials in borides. Successfully applying the workflow, we report three families of novel magnetic borides, including two families of borides exhibiting quantum magnetism. One is a family of dimerized quantum magnets among YCrB$_4$-type borides, which provides a rare platform for studying the spin-gap quantum critical point. The other is a family of altermagnets among FeMo$_2$B$_2$-type borides, extending the magnetic orderings exhibited by borides beyond conventional ferromagnetism and antiferromagnetism. We also predict a family of magnetic laminate transition metal borides, known as the MAB phases, in the AlFe$_2$B$_2$-type family, which provide pure-phase or alloying candidates for studying magnetocaloric materials and the associated magnetic transitions. The workflow is expected to be used in further studies of novel magnetism and magnetic materials.

cond-mat.mtrl-sci↗

arXiv2024

Prediction of polarization vortices, charge modulation, flat bands, and moiré magnetism in twisted oxide bilayers

The recent surge of interest in moiré superlattices of twisted van der Waals compounds has spotlighted the emergence of unconventional superconductivity and novel electronic phases. However, the range of moiré phenomena can be dramatically expanded by incorporating complex oxide materials into twisted heterostructures. In this study, motivated by the recent breakthroughs in synthesis of free-standing oxide membranes, we explore the emergent structural and electronic properties of twisted oxide bilayers. We focus on the classic perovskite oxide, SrTiO3, and design SrTiO3 bilayers with a relative twist between the individual layers. Using density functional theory calculations, we predict the appearance of vortex-antivortex polarization patterns at the interface of the SrTiO3 bilayers driven by twist. We also predict charge modulation of the interfacial Ti ions induced by varying local coordination which follow the moiré pattern. Furthermore, we forecast the emergence of flat bands at large twist angles and the associated localized electronic states with moiré-periodic charge density, originating from the interlayer bonding effects resulting in the formation of dangling bonds. Finally, we predict that hole doping induces unconventional d0 magnetism in otherwise nonmagnetic SrTiO3, driven by the exchange splitting of the high-density O-p bands and producing the spin density with moiré periodicity. These results demonstrate a broad landscape of emergent phenomena which may occur in moiré-engineered oxide heterostructures showing far-reaching perspectives of these material systems for further fundamental studies and potential applications.

cond-mat.mtrl-sci↗

arXiv2024

Unconventional Field-Like Spin-Torques in CrPt$_3$

The topological semimetal CrPt$_3$ has potential for generating unconventional spin torques due to its ferrimagnetic ordering, topological band structure, and high anomalous Hall effect. CrPt$_3$ exhibits ferrimagnetic behavior only in its chemically ordered phase and is paramagnetic in its chemically disordered phase. By controlling the growth and annealing temperatures, epitaxial films of both chemically ordered and disordered phases of CrPt$_3$ are prepared allowing us to investigate the role of magnetic ordering on unconventional torque generation. We use angle dependent spin-torque ferromagnetic resonance and second harmonic Hall measurements to probe the spin torques generated from epitaxial CrPt$_3$ in CrPt$_3$/Cu/Ni$_{81}$Fe$_{19}$ heterostructures. With current applied along specific directions with respect to the crystal order we reveal unconventional spin torques in both ordered and disordered films. When current flows parallel to the $[1\overline{1}1]$ and $[\overline{1}11]$ directions we observe an unconventional field-like torque that is opposite in sign for the two directions. Our calculations reveal that this unconventional torque originates from an indirect nonlocal spin-orbit torque due to spin scattering at the CrPt$_3$/Cu interface, in addition to symmetry breaking at this interface.

cond-mat.mtrl-sci↗

arXiv2024

Unveiling a Family of Dimerized Quantum Magnets in Ternary Metal Borides

Dimerized quantum magnets are exotic crystalline materials where Bose-Einstein condensation of magnetic excitations can happen. However, known dimerized quantum magnets are limited to only a few oxides and halides. Here, we unveil 9 dimerized quantum magnets and 11 conventional antiferromagnets in ternary metal borides MTB$_4$ (M = Sc, Y, La, Ce, Lu, Mg, Ca, Al; T = V, Cr, Mn, Fe, Co, Ni). In this type of structure, 3d transition-metal atoms T are arranged in dimers. Quantum magnetism in these compounds is dominated by strong antiferromagnetic interactions between Cr (both Cr and Mn for M = Mg and Ca) atoms within the structural dimers, with much weaker interactions between the dimers. These systems are proposed to be close to a quantum critical point between a disordered singlet spin-dimer phase, with a spin gap, and the ordered conventional Néel antiferromagnetic phase. This new family of dimerized quantum magnets greatly enriches the materials inventory that allows investigations of the spin-gap phase. All the quantum-, conventionally-, and non-magnetic systems identified, together with experimental synthesis methods of a phase suitable for characterization, provide a platform with abundant possibilities to tune the magnetic exchange coupling by doping and study this unconventional type of quantum phase transition. This work opens up new avenues for studying the quantum magnetism of spin dimers in borides and establishes a theoretical workflow for future searches for dimerized quantum magnets in other families or types of materials.

cond-mat.mtrl-sci↗

arXiv2023

Large and tunable magnetoresistance in van der Waals Ferromagnet/Semiconductor junctions

Magnetic tunnel junctions (MTJs) with conventional bulk ferromagnets separated by a nonmagnetic insulating layer are key building blocks in spintronics for magnetic sensors and memory. A radically different approach of using atomically-thin van der Waals (vdW) materials in MTJs is expected to boost their figure of merit, the tunneling magnetoresistance (TMR), while relaxing the lattice-matching requirements from the epitaxial growth and supporting high-quality integration of dissimilar materials with atomically-sharp interfaces. We report TMR up to 192% at 10 K in all-vdW Fe3GeTe2/GaSe/Fe3GeTe2 MTJs. Remarkably, instead of the usual insulating spacer, this large TMR is realized with a vdW semiconductor GaSe. Integration of two-dimensional ferromagnets in semiconductor-based vdW junctions offers gate-tunability, bias dependence, magnetic proximity effects, and spin-dependent optical-selection rules. We demonstrate that not just the magnitude, but also the TMR sign is tuned by the applied bias or the semiconductor thickness, enabling modulation of highly spin-polarized carriers in vdW semiconductors.

cond-mat.mtrl-sci↗

arXiv2021

Spirals and skyrmions in antiferromagnetic triangular lattices

We study realizations of spirals and skyrmions in two-dimensional antiferromagnets with a triangular lattice on an inversion-symmetry-breaking substrate. As a possible material realization, we investigate the adsorption of transition-metal atoms (Cr, Mn, Fe, or Co) on a monolayer of MoS$_2$, WS$_2$, or WSe$_2$ and obtain the exchange, anisotropy, and Dzyaloshinskii-Moriya interaction parameters using first-principles calculations. Using energy minimization and parallel-tempering Monte-Carlo simulations, we determine the magnetic phase diagrams for a wide range of interaction parameters. We find that skyrmion lattices can appear even with weak Dzyaloshinskii-Moriya interactions, but their stability is hindered by magnetic anisotropy. However, a weak easy plane magnetic anisotropy can be beneficial for stabilizing the skyrmion phase. Our results suggest that Cr$/$MoS$_2$, Fe$/$MoS$_2$, and Fe$/$WSe$_2$ interfaces can host spin spirals formed from the 120$^{\circ}$ antiferromagnetic states. Our results further suggests that for other interfaces, such as Fe$/$MoS$_2$, the Dzyaloshinskii-Moriya interaction is strong enough to drive the system into a three-sublattice skyrmion lattice in the presence of experimentally feasible external magnetic field.

cond-mat.mes-hall↗

arXiv2020

Reinvestigation of the intrinsic magnetic properties of (Fe$_{1-x}$Co$_x$)$_2$B alloys and crystallization behavior of ribbons

New determination of the magnetic anisotropy from single crystals of (Fe$_{1-x}$Co$_x$)$_2$B alloys are presented. The anomalous temperature dependence of the anisotropy constant is discussed using the standard Callen-Callen theory, which is shown to be insufficient to explain the experimental results. A more material specific study using first-principles calculations with disordered moments approach gives a much more consistent interpretation of the experimental data. Since the intrinsic properties of the alloys with $x=0.3-0.35$ are promising for permanent magnets applications, initial investigation of the extrinsic properties are described, in particular the crystallization of melt spun ribbons with Cu, Al, and Ti additions. Previous attempts at developing a significant hysteresis have been unsuccessful in this system. Our melt-spinning experiment indicates that this system shows rapid crystallization.

cond-mat.mtrl-sci↗

arXiv2019

Questaal: a package of electronic structure methods based on the linear muffin-tin orbital technique

This paper summarises the theory and functionality behind Questaal, an open-source suite of codes for calculating the electronic structure and related properties of materials from first principles. The formalism of the linearised muffin-tin orbital (LMTO) method is revisited in detail and developed further by the introduction of short-ranged tight-binding basis functions for full-potential calculations. The LMTO method is presented in both Green's function and wave function formulations for bulk and layered systems. The suite's full-potential LMTO code uses a sophisticated basis and augmentation method that allows an efficient and precise solution to the band problem at different levels of theory, most importantly density functional theory, LDA+U, quasi-particle self-consistent GW and combinations of these with dynamical mean field theory. This paper details the technical and theoretical bases of these methods, their implementation in Questaal, and provides an overview of the code's design and capabilities.

cond-mat.mtrl-sci↗

arXiv2015

Spin-fluctuation mechanism of anomalous temperature dependence of magnetocrystalline anisotropy in itinerant magnets

The origins of the anomalous temperature dependence of magnetocrystalline anisotropy in (Fe$_{1-x}$Co$_{x}$)$_{2}$B alloys are elucidated using first-principles calculations within the disordered local moment model. Excellent agreement with experimental data is obtained. The anomalies are associated with the changes in band occupations due to Stoner-like band shifts and with the selective suppression of spin-orbit "hot spots" by thermal spin fluctuations. Under certain conditions, the anisotropy can increase, rather than decrease, with decreasing magnetization due to these peculiar electronic mechanisms, which contrast starkly with those assumed in existing models.

cond-mat.mtrl-sci↗

arXiv2015

What Makes Effective Gating Possible in Two-Dimensional Heterostructures?

Electrostatic gating provides a way to obtain key functionalities in modern electronic devices and to qualitatively alter materials properties. While electrostatic description of such gating gives guidance for related doping effects, inherent quantum properties of gating provide opportunities for intriguing modification of materials and unexplored devices. Using first-principles calculations for Co/bilayer graphene, Co/BN, and Co/benzene, as well as a simple physical model, we show that magnetic heterostructures with two-dimensional layered materials can manifest tunable magnetic proximity effects. van der Waals bonding is identified as a requirement for large electronic structure changes by gating. In particular, the magnitude and sign of spin polarization in physisorbed graphene can be controlled by gating, which is important for spintronic devices.

cond-mat.mtrl-sci↗