Antiferromagnetic Materials Research Articles

Predicting intrinsic antiferromagnetic and ferroelastic MnF4 monolayer with controllable magnetization

MnF4 monolayer is predicted to an antiferromagnetic and ferroelastic material with magnetic anisotropy and magneto-elastic coupling, which can be effectively controlled by biaxial strain or carrier doping.

From the transverse field Ising chain to the quantum <i>E</i><sub>8</sub> integrable model

This review reports a series of theoretical and experimental progress on researches of the transverse field Ising chain (TFIC) and the quantum <i>E</i><sub>8</sub> integrable model. For the TFIC, on one hand, a unique exotic quantum critical behavior of Grüneisen ratio (a ratio from magnetic or thermal expansion coefficient to specific heat) is theoretically established; on the other hand microscopic models can accommodate the TFIC universality class are substantially expanded. These progresses successfully promote a series of experiments collaborations to first-time realize the TFIC universality class in quasi one-dimensional anti-ferromagnetic material BaCo<sub>2</sub>V<sub>2</sub>O<sub>8</sub> and SrCo<sub>2</sub>V<sub>2</sub>O<sub>8</sub>. For the quantum <i>E</i><sub>8</sub> integrable model, the low temperature local dynamics and the dynamical structure factor with zero transfer momentum of this system are analytically determined, where a cascade of edge singularities with power-law divergences are obtained in the continuum region of the dynamical structure factor. After combining with detailed quantum critical scaling behaviors analysis and large scale iTEBD calculation, it successfully facilitates a series of experiments, including THz spectrum measurements, inelastic neutron scattering and NMR experiments, to realize the quantum <i>E</i><sub>8</sub> integrable model in BaCo<sub>2</sub>V<sub>2</sub>O<sub>8</sub> for the first time. The experimental realization of the quantum <i>E</i><sub>8</sub> integrable model substantially extends the frontiers of studying quantum integrable models in real materials. The series of progress and developments on the TFIC and the quantum <i>E</i><sub>8</sub> integrable model lay down a concrete ground to go beyond quantum integrability, and can inspire studies in condensed matter systems, cold atom systems, statistical field theory and conformal field theory.

Low temperature magnetic study of α-NiS nanoparticles synthesized via hydrothermal technique

Synthesis of material with nano-order anisotropy has always been a tricky task for the researchers, since there has to be some property-based inhomogeneity present within the homogeneous material. In this report, we discuss the emergence of Exchange Bias (EB), which is itself a case of magnetic property based anisotropy. Here, a thorough low temperature magnetic study of nickel sulfide (NiS) nanoparticles synthesized via solution based hydrothermal technique was performed. To introduce nano-order inhomogeneity we played with different feeding flow rate of the starting materials. The synthesized samples were of highly crystalline mixed phase nature with α-NiS as a dominant phase. Variation in energy bandgap as a function of feeding rate suggests the possibility of the formation different-sized seed cluster. For sample with maximum α-NiS content, presence of strong magnetic coupling at T < Tb arising from uncompensated spins at the surface of the nanoparticles suggest its weak ferromagnetic character with a paramagnetic background. For the first time, an unusual phenomenon of exchange bias (EB) was also observed for the sample with maximum α-NiS content. The presence of EB suggests FM-AFM coupling occurring over the particle surface, which is also prudent from the fact that NiS is intrinsically an antiferromagnetic material. In short the present study opens up the possibility for the use of NiS a possible material spin based device applications.

Domain periodicity in an easy-plane antiferromagnet with Dzyaloshinskii-Moriya interaction

Antiferromagnetic spintronics is a promising emerging paradigm to develop high-performance computing and communications devices. From a theoretical point of view, it is important to implement simulation tools that can support a data-driven development of materials having specific properties for particular applications. Here, we present a study focusing on antiferromagnetic materials having an easy-plane anisotropy and interfacial Dzyaloshinskii-Moriya interaction (IDMI). An analytical theory is developed and benchmarked against full numerical micromagnetic simulations, describing the main properties of the ground state in antiferromagnets and how it is possible to estimate the IDMI from experimental measurements. The effect of the IDMI on the electrical switching dynamics of the antiferromagnetic element is also analyzed. Our theoretical results can be used for the design of multi-terminal heavy metal/antiferromagnet memory devices.

Boris computational spintronics—High performance multi-mesh magnetic and spin transport modeling software

This work discusses the design and testing of a new computational spintronics research software. Boris is a comprehensive multi-physics open-source software, combining micromagnetics modeling capabilities with drift-diffusion spin transport modeling and a heat flow solver in multi-material structures. A multi-mesh paradigm is employed, allowing modeling of complex multi-layered structures with independent discretization and arbitrary relative positioning between different computational meshes. Implemented micromagnetics models include not only ferromagnetic materials modeling, but also two-sublattice models, allowing simulations of antiferromagnetic and ferrimagnetic materials, fully integrated into the multi-mesh and multi-material design approach. High computational performance is an important design consideration in Boris, and all computational routines can be executed on graphical processing units (GPUs), in addition to central processing units. In particular, a modified 3D convolution algorithm is used to compute the demagnetizing field on the GPU, termed pipelined convolution, and benchmark comparisons with existing GPU-accelerated software Mumax3 have shown performance improvements up to twice faster.

Ferroelectric control of electron half-metallicity in A -type antiferromagnets and its application to nonvolatile memory devices

Two-dimensional (2D) $A$-type antiferromagnetic van der Waals (vdW) materials with either intralayer ferromagnetic and/or intralayer antiferromagnetic coupling have sparked great interest due to their potential applications in spintronics. By first-principles design we predict that a heterostructure formed by sandwiching the 2D $A$-type antiferromagnet, $2\mathrm{H}\text{\ensuremath{-}}\mathrm{V}{\mathrm{Se}}_{2}$, between the 2D out-of-plane ferroelectric, ${\mathrm{Sc}}_{2}{\mathrm{CO}}_{2}$, presents a semimetal band structure with a half-metallic conduction band. The mechanism giving rise to this peculiar structure cooperatively originates from the strong built-in electric field of the double-layer ferroelectric ${\mathrm{Sc}}_{2}{\mathrm{CO}}_{2}$, and from the charge transfer selectively occurring only at one interface. Based on the so-designed ${\mathrm{Sc}}_{2}{\mathrm{CO}}_{2}\text{/}\mathrm{V}{\mathrm{Se}}_{2}$ multiferroic heterostructure, two concepts for nonvolatile memory devices are proposed, in which two states (``1'' and ``0'') are realized by switching the polarization direction of the ferroelectric layers. These results demonstrate that the combination of 2D ferroelectrics and $A$-type antiferromagnetic vdW materials provides not only a fascinating way to achieve half-metallicity in 2D materials, but also a route to the design of new types of nonvolatile ferroelectric memory devices.

Long-distance spin-transport across the Morin phase transition up to room temperature in ultra-low damping single crystals of the antiferromagnet \u03b1-Fe2O3

Antiferromagnetic materials can host spin-waves with polarizations ranging from circular to linear depending on their magnetic anisotropies. Until now, only easy-axis anisotropy antiferromagnets with circularly polarized spin-waves were reported to carry spin-information over long distances of micrometers. In this article, we report long-distance spin-transport in the easy-plane canted antiferromagnetic phase of hematite and at room temperature, where the linearly polarized magnons are not intuitively expected to carry spin. We demonstrate that the spin-transport signal decreases continuously through the easy-axis to easy-plane Morin transition, and persists in the easy-plane phase through current induced pairs of linearly polarized magnons with dephasing lengths in the micrometer range. We explain the long transport distance as a result of the low magnetic damping, which we measure to be ≤ 10−5 as in the best ferromagnets. All of this together demonstrates that long-distance transport can be achieved across a range of anisotropies and temperatures, up to room temperature, highlighting the promising potential of this insulating antiferromagnet for magnon-based devices.

Recent progress in antiferromagnetic dynamics

Spintronics, since its inception, has mainly focused on ferromagnetic materials for manipulating the spin degree of freedom in addition to the charge degree of freedom, whereas much less attention has been paid to antiferromagnetic materials. Thanks to the advances of micro-nano-fabrication techniques and the electrical control of the Néel order parameter, antiferromagnetic spintronics is booming as a result of abundant room temperature materials, robustness against external fields and dipolar coupling, and rapid dynamics in the terahertz regime. For the purpose of applications of antiferromagnets, it is essential to have a comprehensive understanding of the antiferromagnetic dynamics at the microscopic level. Here, we first review the general form of equations that govern both antiferromagnetic and ferrimagnetic dynamics. This general form unifies the previous theories in the literature. We also provide a survey for the recent progress related to antiferromagnetic dynamics, including the motion of antiferromagnetic domain walls and skyrmions, the spin pumping and quantum antiferromagnetic spintronics. In particular, open problems in several topics are outlined. Furthermore, we discuss the development of antiferromagnetic quantum magnonics and its potential integration with modern information science and technology.

An antiferromagnetic two-dimensional material: Chromium diiodides monolayer

The two-dimensional (2D) ferromagnetic materials and the related van der Waals homostructures have attracted considerable interest, while the 2D antiferromagnetic material has not yet been reported. Based on first-principles calculations, we investigate both electronic structures and magnetic orderings of bulk and monolayer of chromium diiodides (CrI2). We demonstrate a counter-intuitive fact that the ground state of the free-standing monolayer of CrI2 is antiferromagnetic though the bulk possesses macroscopic ferromagnetic ordering. The interlayer interaction remains antiferromagnetic up to few-layer scenarios. The unique feature of CrI2 makes it an ideal workbench to investigate the relation between magnetic couplings and interlayer van der Waals interactions, and may offer an opportunity to 2D antiferromagnetic spintronic devices.

Inverse spin Hall effect and spin pumping in the polycrystalline noncollinear antiferromagnetic Mn3Ga

Noncollinear antiferromagnetic (AFM) materials have drawn research interest because they exhibit large anomalous Hall effect at room temperature (RT) due to large Berry curvature. ${\mathrm{Mn}}_{3}\mathrm{Ga}$ is a noncollinear AFM in which the order of Mn magnetic moments is arranged in inverse triangular configuration on a kagome lattice. It makes ${\mathrm{Mn}}_{3}\mathrm{Ga}$ a promising candidate for inverse spin Hall effect (ISHE) study which has not been studied before. In this work, investigation of ISHE and spin pumping in polycrystalline ${\mathrm{Mn}}_{3}\mathrm{Ga}$/CoFeB heterostructures at RT has been performed. Angle-dependent measurements of ISHE have been performed in order to disentangle various spin-rectification effects. Spin-mixing conductance (${g}_{\mathrm{eff}}^{\ensuremath{\uparrow}\ensuremath{\downarrow}})$, spin Hall angle $({\ensuremath{\theta}}_{SH})$, and spin Hall conductivity (${\ensuremath{\sigma}}_{SH}$) are evaluated to be $(5.0\ifmmode\pm\else\textpm\fi{}1.8)\ifmmode\times\else\texttimes\fi{}{10}^{18}\phantom{\rule{0.16em}{0ex}}{\mathrm{m}}^{\ensuremath{-}2}, 0.31\ifmmode\pm\else\textpm\fi{}0.01$, and $7.5\ifmmode\times\else\texttimes\fi{}{10}^{5}\phantom{\rule{0.28em}{0ex}}(\ensuremath{\hbar}/2e)\phantom{\rule{0.16em}{0ex}}{\mathrm{\ensuremath{\Omega}}}^{\ensuremath{-}1\phantom{\rule{4pt}{0ex}}}\phantom{\rule{0.16em}{0ex}}{\mathrm{m}}^{\ensuremath{-}1}$, respectively. The observed value of ${\ensuremath{\theta}}_{SH}$ is higher than ${\mathrm{Mn}}_{3}\mathrm{Sn}$ and comparable to the ${\mathrm{IrMn}}_{3}$, which is also a noncollinear AFM. Large spin Hall angle makes ${\mathrm{Mn}}_{3}\mathrm{Ga}$ a promising candidate for future spintronics devices.

Electronic structure of the high-mobility two-dimensional antiferromagnetic metal GdTe3

The newfound two-dimensional antiferromagnetic $\mathrm{Gd}{\mathrm{Te}}_{3}$ has great potential in novel magnetic twistronic and spintronic devices because it has the highest carrier mobility among all known layered magnetic materials. Here, we used high-resolution angle-resolved photoemission spectroscopy to investigate its Fermi-surface topology and low-lying electronic band structure. The Fermi surface is partially gapped by charge-density waves below the transition temperature. Very steep and nearly linear band dispersion near the Fermi energy contributes to the high carrier mobility in $\mathrm{Gd}{\mathrm{Te}}_{3}$. We find that the scattering rate of the quasiparticle increases linearly as a function of binding energy within a wide energy range, indicating that $\mathrm{Gd}{\mathrm{Te}}_{3}$ is a non-Fermi-liquid metal. Our results in this paper provide a fundamental understanding of this layered antiferromagnetic material to guide future studies on it.

Spin-orbit torque switching of an antiferromagnetic metallic heterostructure

The ability to represent information using an antiferromagnetic material is attractive for future antiferromagnetic spintronic devices. Previous studies have focussed on the utilization of antiferromagnetic materials with biaxial magnetic anisotropy for electrical manipulation. A practical realization of these antiferromagnetic devices is limited by the requirement of material-specific constraints. Here, we demonstrate current-induced switching in a polycrystalline PtMn/Pt metallic heterostructure. A comparison of electrical transport measurements in PtMn with and without the Pt layer, corroborated by x-ray imaging, reveals reversible switching of the thermally-stable antiferromagnetic Néel vector by spin-orbit torques. The presented results demonstrate the potential of polycrystalline metals for antiferromagnetic spintronics.

Vector potential and surface magnetic field in magnetoelectric antiferromagnetic materials

A general formula for the average vector potential of bulk periodic systems is proposed and shown to set the boundary conditions at magnetic interfaces. For antiferromagnetic materials, the study reveals a unique relation between the macroscopic potential and the orientation-dependent magnetic quadrupole, as a result of the different crystalline and magnetic symmetries. In particular, at surfaces and interfaces of a truncated bulk without inversion and time-reversal symmetries, the average vector potential exhibits a discontinuity, which results in an interfacial magnetic field. In general, however, due to the surface and interface electronic and atomic relaxations, additional magnetization may result. For the experimentally-observed magnetoelectric antiferromagnets, in particular, our symmetry analysis suggest that the relaxation effects could well be a system response to the presence of such a potential discontinuity.

High-throughput computational screening for two-dimensional magnetic materials based on experimental databases of three-dimensional compounds

We perform a computational screening for two-dimensional (2D) magnetic materials based on experimental bulk compounds present in the Inorganic Crystal Structure Database and Crystallography Open Database. A recently proposed geometric descriptor is used to extract materials that are exfoliable into 2D derivatives and we find 85 ferromagnetic and 61 antiferromagnetic materials for which we obtain magnetic exchange and anisotropy parameters using density functional theory. For the easy-axis ferromagnetic insulators we calculate the Curie temperature based on a fit to classical Monte Carlo simulations of anisotropic Heisenberg models. We find good agreement with the experimentally reported Curie temperatures of known 2D ferromagnets and identify 10 potentially exfoliable 2D ferromagnets that have not been reported previously. In addition, we find 18 easy-axis antiferromagnetic insulators with several compounds exhibiting very strong exchange coupling and magnetic anisotropy.

Magnetocrystalline anisotropy imprinting of an antiferromagnet on an amorphous ferromagnet in FeRh/CoFeB heterostructures

Magnetic anisotropy is a fundamental key parameter of magnetic materials that determines their applications. For ferromagnetic materials, the magnetic anisotropy can be easily detected by using conventional magnetic characterization techniques. However, due to the magnetic compensated structure in antiferromagnetic materials, synchrotron measurements, such as X-ray magnetic linear dichroism, are often needed to probe their magnetic properties. In this work, we observed an imprinted fourfold magnetic anisotropy in the amorphous ferromagnetic layer of FeRh/CoFeB heterostructures. The MOKE and ferromagnetic resonance measurements show that the easy magnetization axes of the CoFeB layer are along the FeRh〈110〉 and FeRh〈100〉 directions for the epitaxially grown FeRh layer in the antiferromagnetic and ferromagnetic states, respectively. The combined Monte Carlo simulation and first-principles calculation indicate that the fourfold magnetic anisotropy of the amorphous CoFeB layer is imprinted due to the interfacial exchange coupling between the CoFeB and FeRh moments from the magnetocrystalline anisotropy of the epitaxial FeRh layer. This observation of imprinting the magnetocrystalline anisotropy of antiferromagnetic materials on easily detected ferromagnetic materials may be applied to probe the magnetic structures of antiferromagnetic materials without using synchrotron methods.

Tunable magnetism in layered CoPS3 by pressure and carrier doping

Despite extensive research on recently discovered layered ferromagnetic (FM) materials, their further development is hampered by the limited number of candidate materials with desired properties. As a much bigger family, layered antiferromagnetic (AFM) materials represent excellent platforms to not only deepen our understanding of fundamental physics but also push forward high-performance spintronics applications. Here, by systematic first-principles calculations, we demonstrate pressure and carrier doping control of magnetic properties in layered AFM CoPS3, a representative of transition metal phosphorus trichalcogenides. In particular, pressure can drive isostructural Mott transition, in sharp contrast to other transition metal thiophosphates. Intriguingly, both pressure and carrier doping can realize the long-sought FM half-metallic states with 100% spin polarization percentage, which is good for improving the injection and detection efficiency of spin currents among others. Moreover, the Mott transition is accompanied by instantaneous spin-crossover (SCO) in CoPS3, and such cooperative SCO facilitates the implementation of fast-response reversible devices, such as data storage devices, optical displays and sensors. We further provide an in-depth analysis for the mechanisms of FM half-metallicity and SCO. Tunable magnetism in layered AFM materials opens vast opportunities for purposeful device design with various functionalities.

Longitudinal Spin Dynamics in the Heisenberg Antiferromagnet: Two-Magnon Excitations

Understanding the ultrafast spin dynamics in magnetically ordered materials is important for the comprehenssion of fundamental limits in spin-based magnetic electronics – magnonics. We have studied a microscopic model of magnetization dynamics in a two-sublattice antiferromagnet with the emphasis on longitudinal spin excitations. The diagrammatic technique for spin operators has been used to overcome limitations typical of phenomenological approaches. The graphical representations of spin wave propagators allow us to summing up the infinite series of distinctive diagrams. Its sum is transformed into an analytic expression for the longitudinal spin susceptibility xzz (q, w) applicable in all regions of the frequency w and wave vector q spaces beyond the hydrodynamical and critical regimes. It is found that the longitudinal magnetization dynamics consists of two types of excitations, which have different dependences on the temperature and wave vector q. The obtained result could be important for understanding the physics of nonequilibrium magnetic dynamics under the effect of ultrafast laser pulses in antiferromagnetic materials.

Modeling spin waves in noncollinear antiferromagnets: Spin-flop states, spin spirals, skyrmions, and antiskyrmions

Spin waves in antiferromagnetic materials have great potential for next-generation magnonic technologies. However, their properties and their dependence on the type of ground-state antiferromagnetic structure are still open questions. Here, we investigate theoretically spin waves in one- and two-dimensional model systems with a focus on noncollinear antiferromagnetic textures such as spin spirals and skyrmions of opposite topological charges. We address in particular the nonreciprocal spin excitations recently measured in bulk antiferromagnet $\alpha$--$\text{Cu}_2\text{V}_2\text{O}_7$ utilizing inelastic neutron scattering experiments [Phys.\ Rev.\ Lett.\ \textbf{119}, 047201 (2017)], where we help to characterize the nature of the detected spin-wave modes. Furthermore, we discuss how the Dzyaloshinskii-Moriya interaction can lift the degeneracy of the spin-wave modes in antiferromagnets, resembling the electronic Rashba splitting. We consider the spin-wave excitations in antiferromagnetic spin-spiral and skyrmion systems and discuss the features of their inelastic scattering spectra. We demonstrate that antiskyrmions can be obtained with an isotropic Dzyaloshinskii-Moriya interaction in certain antiferromagnets.

Can a sample having zero net magnetization produce polarized spin current?

Antiferromagnetic materials can be the suitable functional elements for designing of future spin based electronic devices, circumventing the use of conventional ferromagnetic materials and spin–orbit coupled systems. In the present work first time we put forward the underlying physical mechanism, to the best of our knowledge, to generate polarized spin current through a magnetic material having zero net magnetization. Our proposal is substantiated by considering a 2D geometry which is composed of several concentric 1D rings where neighboring rings are mutually connected with each other. The misalignment of up and down spin bands, which is the primary requirement to have finite spin polarization, is described analytically and then several aspects of spin polarization are studied numerically. Finally, we discuss experimental realization of the proposed magnetic quantum system. Our analysis can be utilized to any other complicated magnetic geometries, and may open up a new platform for future spintronic applications.

Dirac fermions in the antiferromagnetic spintronics material CuMnAs

Dirac semimetals (DSMs) are the focus of study as new candidates for topological superconductivity and spintronics. Although the Dirac points are not necessarily associated with crystalline symmetries, the experimentally realized robust DSMs such as $\mathrm{C}{\mathrm{d}}_{3}\mathrm{A}{\mathrm{s}}_{2}$ have fourfold-degenerate Dirac points at generic wave vectors on high symmetry line enabled by a fourfold crystalline symmetry. The magnetic counterpart of these robust DSMs remains unknown. On the other hand, the theoretically proposed magnetic DSMs in potential antiferromagnetic (AFM) spintronics materials where both time-reversal $(\mathcal{T})$ and inversion $(\mathcal{P})$ symmetry are broken but their combination $\mathcal{P}\mathcal{T}$ is preserved have Dirac points on the boundary of the Brillouin zone protected by a low-order twofold crystalline symmetry. Here, combined with first-principles calculations and symmetry analysis, we find the Dirac fermion at generic wave vector on high symmetry line with associated nontrivial surface states in $\mathcal{P}\mathcal{T}$-symmetric tetragonal CuMnAs, which is the prototype AFM spintronics material observed in experiments. Furthermore, we reveal the hidden spin textures in this $\mathcal{P}\mathcal{T}$-symmetric magnetic system, demonstrating interesting vortex-like spin textures. Our study opens the way for designing robust magnetic DSMs that can serve as an ideal platform to study the interplay of magnetism, Dirac fermions, and spin-orbit interactions, and could stimulate a series of research in the field of topological antiferromagnetic spintronics.