Antiferromagnetic System Research Articles

Field-free spin-orbit torque switching via out-of-plane spin-polarization induced by an antiferromagnetic insulator/heavy metal interface

Manipulating spin polarization orientation is challenging but crucial for field-free spintronic devices. Although such manipulation has been demonstrated in a limited number of antiferromagnetic metal-based systems, the inevitable shunting effects from the metallic layer can reduce the overall device efficiency. In this study, we propose an antiferromagnetic insulator-based heterostructure NiO/Ta/Pt/Co/Pt for such spin polarization control without any shunting effect in the antiferromagnetic layer. We show that zero-field magnetization switching can be realized and is related to the out-of-plane component of spin polarization modulated by the NiO/Pt interface. The zero-field magnetization switching ratio can be effectively tuned by the substrates, in which the easy axis of NiO can be manipulated by the tensile or compressive strain from the substrates. Our work demonstrates that the insulating antiferromagnet based heterostructure is a promising platform to enhance the spin-orbital torque efficiency and achieve field-free magnetization switching, thus opening an avenue towards energy-efficient spintronic devices.

Spin wavepackets in the Kagome ferromagnet Fe3Sn2: Propagation and precursors

The propagation of spin waves in magnetically ordered systems has emerged as a potential means to shuttle quantum information over large distances. Conventionally, the arrival time of a spin wavepacket at a distance, d, is assumed to be determined by its group velocity, vg. Here, we report time-resolved optical measurements of wavepacket propagation in the Kagome ferromagnet Fe3Sn2 that demonstrate the arrival of spin information at times significantly less than d/vg. We show that this spin wave "precursor" originates from the interaction of light with the unusual spectrum of magnetostatic modes in Fe3Sn2. Related effects may have far-reaching consequences toward realizing long-range, ultrafast spin wave transport in both ferromagnetic and antiferromagnetic systems.

Photoemission signature of the competition between magnetic order and Kondo effect in CeCoGe3

The competition between magnetic order and Kondo effect is essential for the rich physics of heavy fermion systems. Nevertheless, how such competition is manifested in the quasiparticle bands in a real periodic lattice remains elusive in spectroscopic experiments. Here we report a high-resolution photoemission study of the antiferromagnetic Kondo lattice system CeCoGe3 with a high TN1 of 21K. Our measurements reveal a weakly dispersive 4f band at the Fermi level near the Z point, arisingfrom moderate Kondo effect. The intensity of this heavy 4f band exhibits a logarithmic increase with lowering temperature and begins to deviate from this Kondo-like behavior below 25 K, just above TN1, and eventually ceases to grow below 12 K. Our work provides direct spectroscopic evidence for the competition between magnetic order and the Kondo effect in a Kondo lattice system with local-moment antiferromagnetism, indicating a distinct scenario for the microscopic coexistence and competition of these phenomena, which might be related to the real-space modulation.

Field-induced spin level crossings within a quasi- XY antiferromagnetic state in Ba2FeSi2O7

We present a high-field study of the strongly anisotropic easy-plane square lattice $S=2$ quantum magnet ${\mathrm{Ba}}_{2}{\mathrm{FeSi}}_{2}{\mathrm{O}}_{7}$. This compound is a rare high-spin antiferromagnetic system with very strong easy-plane anisotropy, such that the interplay between spin level crossings and antiferromagnetic order can be studied. We observe a magnetic field-induced spin level crossing occurring within an ordered state. This spin level crossing appears to preserve the magnetic symmetry while producing a nonmonotonic dependence of the order parameter magnitude. The resulting temperature--magnetic field phase diagram exhibits two dome-shaped regions of magnetic order overlapping around 30 T. The ground state of the lower-field dome is predominantly a linear combination of $|{S}^{z}=0\ensuremath{\rangle}$ and $|{S}^{z}=1\ensuremath{\rangle}$ states, while the ground state of the higher-field dome can be approximated by a linear combination of $|{S}^{z}=1\ensuremath{\rangle}$ and $|{S}^{z}=2\ensuremath{\rangle}$ states. At 30 T, where the spin levels cross, the magnetization exhibits a slanted plateau, the magnetocaloric effect shows a broad hump, and the electric polarization shows a weak slope change. We determined the detailed magnetic phase boundaries and the spin level crossings using measurements of magnetization, electric polarization, and the magnetocaloric effect in pulsed magnetic fields to 60 T. We calculate these properties using a mean-field theory based on direct products of SU(5) coherent states and find good agreement. Finally, we measure and calculate the magnetically induced electric polarization that reflects magnetic ordering and spin level crossings. This multiferroic behavior provides another avenue for detecting phase boundaries and symmetry changes.

Skyrmion dynamics induced by surface acoustic waves in antiferromagnetic systems

Skyrmion dynamics induced by surface acoustic waves in antiferromagnetic systems

In-Plane Anomalous Hall Effect in PT-Symmetric Antiferromagnetic Materials.

The anomalous Hall effect (AHE), a protocol of various low-power dissipation quantum phenomena and a fundamental precursor of intriguing topological phases of matter, is usually observed in ferromagnetic materials with an orthogonal configuration between the electric field, magnetization, and the Hall current. Here, based on the symmetry analysis, we find an unconventional AHE induced by the in-plane magnetic field (IPAHE) via the spin-canting effect in PT-symmetric antiferromagnetic (AFM) systems, featuring a linear dependence of magnetic field and 2π angle periodicity with a comparable magnitude to conventional AHE. We demonstrate the key findings in the known AFM Dirac semimetal CuMnAs and a new kind of AFM heterodimensional VS_{2}-VS superlattice with a nodal-line Fermi surface and, also, briefly discuss the experimental detection. Our Letter provides an efficient pathway for searching and/or designing realistic materials for a novel IPAHE that could greatly facilitate their application in AFM spintronic devices. National Science Foundation.

Ab initio prediction of anomalous Hall effect in antiferromagnetic CaCrO3

While the anomalous Hall effect takes place typically in ferromagnets with finite magnetization, large anomalous Hall conductivity in noncollinear antiferromagnetic systems has been recently observed and attracted much attention. In this paper, we predict the anomalous Hall effect in perovskite ${\mathrm{CaCrO}}_{3}$ as a representative of collinear antiferromagnetic materials. Our result shows that the $C$-type antiferromagnetic ordering generates the sizable anomalous Hall conductivity. Based on symmetry analyses, we show that the antiferromagnetic order parameter belongs to the same irreducible representation as the ferromagnetic order parameter in the nonsymmorphic space group, allowing the nonvanishing Berry curvatures in $k$ space. By performing first-principles density-functional theory calculations, we find that the Berry-curvature ``hot spots'' lie along the gapped nodal lines where spin-orbit coupling induces the spin splitting of Cr-$3d$ bands near the Fermi energy and enhances the anomalous Hall effect in ${\mathrm{CaCrO}}_{3}$.

The effect of anisotropic field on magnon dispersion of antiferromagnetic metal fluoride materials

This article investigates the dynamics of spin waves in two sublattice antiferromagnetic (AFM) system spins’ interaction and magnon dispersion relation. The analysis is done starting with a standard model that includes a uniaxial magnetic anisotropy field. Quantum field theory is employed in formulating the problem, and double-time temperature-dependent Green function technique is used to obtain magnon dispersion, whereby random phase approximation is considered to decouple and diagonalize the higher order terms. At low temperatures and long wavelength approximation, dispersion of uniaxial symmetric AFM crystal lattice of metallic fluoride materials, such as MnF2, FeF2, and RbMnF3, is analyzed for illustration. Our findings indicate that as the anisotropic field increases, the magnon dispersion vs wave vector k gradually varies, attempts linearity from being curved, and attains a sinusoidal structure when extended further in the first Brillouin zone. Perhaps, these results are useful to understand the feature of magnon dispersion of stable similar AFM materials for practical application.

Layer-resolved electronic behavior in a Kondo lattice system, CeAgAs2

We investigate the electronic structure of an antiferromagnetic Kondo lattice system CeAgAs2 employing hard x-ray photoemission spectroscopy. CeAgAs2, an orthorhombic variant of HfCuSi2 structure, exhibits antiferromagnetic ground state, Kondo like resistivity upturn and compensation of magnetic moments at low temperatures. The photoemission spectra obtained at different photon energies suggest termination of the cleaved surface at cis-trans-As layers. The depth-resolved data show significant surface-bulk differences in the As and Ce core level spectra. The As 2p bulk spectrum shows distinct two peaks corresponding to two different As layers. The peak at higher binding energy correspond to cis-trans-As layers and is weakly hybridized with the adjacent Ce layers. The As layers between Ce and Ag-layers possess close to trivalent configuration due to strong hybridization with the neighboring atoms and the corresponding feature appear at lower binding energy. Ce 3d core level spectra show multiple features reflecting strong Ce-As hybridization and strong correlation. Intense f 0 peak is observed in the surface spectrum while it is insignificant in the bulk. In addition, we observe a features at binding energy lower than the well-screened feature indicating the presence of additional interactions. This feature becomes more intense in the bulk spectra suggesting it to be a bulk property. Increase in temperature leads to a spectral weight transfer to higher binding energies in the core level spectra and a depletion of spectral intensity at the Fermi level as expected in a Kondo material. These results reveal interesting surface-bulk differences, complex interplay of intra- and inter-layer covalency, and electron correlation in the electronic structure of this novel Kondo lattice system.

Multi-solitons in the spin-orbit-coupled spin-1 Bose-Einstein condensates

We find a restrictive integrable reduction for the one-dimensional spin-orbit-coupled spin-1 Bose-Einstein condensate system, which allows us to reduce the three-component Gross-Pitaevskii system into the two-component Manakov system or the single cubic Schrödinger equation. Based on the reduction, we obtain the multi-breathers, higher-order rouge waves and multi-dark soliton solutions for ferromagnetic and anti-ferromagnetic system, respectively. Furthermore, the impacts of the spin-orbit coupling to the multi-soliton dynamics, and the stability of these soliton solutions have also been discussed.

Rapid Mixing of Glauber Dynamics up to Uniqueness via Contraction

For general antiferromagnetic 2-spin systems, including the hardcore model on weighted independent sets and the antiferromagnetic Ising model, there is an for the partition function on graphs of maximum degree when the infinite regular tree lies in the uniqueness region by Li, Lu, and Yin [Correlation Decay up to Uniqueness in Spin Systems, preprint, https://arxiv.org/abs/1111.7064, 2021]. Moreover, in the tree nonuniqueness region, Sly in [Computational transition at the uniqueness threshold, in Proceedings of the 51st Annual IEEE Symposium on Foundations of Computer Science, 2010, pp. 287–296] showed that there is no to estimate the partition function unless . The algorithmic results follow from the correlation decay approach due to Weitz [Counting independent sets up to the tree threshold, in Proceedings of the 38th Annual ACM Symposium on Theory of Computing, 2006, pp. 140–149] or the polynomial interpolation approach developed by Barvinok [Combinatorics and Complexity of Partition Functions, Springer, 2016]. However, the running time is only polynomial for constant . For the hardcore model, recent work of Anari, Liu, and Oveis Gharan [Spectral independence in high-dimensional expanders and applications to the hardcore model, in Proceedings of the 61st Annual IEEE Symposium on Foundations of Computer Science, 2020, pp. 1319–1330] establishes rapid mixing of the simple single-site Markov chain, known as the Glauber dynamics, in the tree uniqueness region. Our work simplifies their analysis of the Glauber dynamics by considering the total pairwise influence of a fixed vertex on other vertices, as opposed to the total influence of other vertices on , thereby extending their work to all 2-spin models and improving the mixing time. More important, our proof ties together the three disparate algorithmic approaches: we show that contraction of the so-called tree recursions with a suitable potential function, which is the primary technique for establishing efficiency of Weitz’s correlation decay approach and Barvinok’s polynomial interpolation approach, also establishes rapid mixing of the Glauber dynamics. We emphasize that this connection holds for all 2-spin models (both antiferromagnetic and ferromagnetic), and existing proofs for the correlation decay and polynomial interpolation approaches immediately imply rapid mixing of the Glauber dynamics. Our proof utilizes the fact that the graph partition function is a divisor of the partition function for Weitz’s self-avoiding walk tree. This fact leads to new tools for the analysis of the influence of vertices and may be of independent interest for the study of complex zeros.

Generalized Spin-Wave Theory for the Hubbard Model and D-theory Formulation

It is pointed out that the low energy effective theory of a generalized spin system relates to the more generalized system shown by the Hubbard-like model. When the onsite repulsion is assumed to be provided by hard-core repulsion, a generalized fermion with flavour and colour degrees of freedom is used to define the Hubbard-like Hamiltonian in this case. In the strong coupling limit and at half filling this reduces to an antiferromagnet. The <I>D</I>-theory then helps us to associate the continuum limit of the <i>(4+1)D </i>aniferromagnet to <i>4D </i>principal chiral model. It has been observed that in the strong coupling limit the problem of finding the ground state of lattice QCD is identical to that of solving the generalized antiferromagnet with Neel order playing the role of chiral symmetry breaking. In view of this, now formulate the Hubbard-like model Hamiltonian in terms of the gener- alized fermions with flavor and color degrees of freedom also shall consider the<i> D</i>-theoretical framework to show that the antiferromagnetic system which arises in the strong coupling limit and at half filling corresponds to the principal chiral model in the continuum limit with dimensional reduction. Also pointed out that at strong coupling and half filling the system reduces to a Heisenberg antiferromagnet. This result is analogous to the result obtained in standard Hubbard model.

Device geometry dependent deterministic skyrmion generation from a skyrmionium

A magnetic skyrmionium can be perceived as an association of two magnetic skyrmions with opposite topological charges. In this work, we have investigated the transformation of skyrmionium into multi-skyrmionic states via domain wall pairs in three different devices with variable geometric configurations. The same device geometries are considered for single ferromagnetic layer and synthetic antiferromagnetic system. It is observed that by tuning the current density, deterministic generation of skyrmions is possible via the spin transfer torque. The proposed device is efficiently adjustable to change the number of skyrmions also at room temperature. The results may lead to development of skyrmion-based devices for neuromorphic and unconventional computing.

Topological Hall effect driven by short-range magnetic order in EuZn2As2

Short-range (SR) magnetic orders such as magnetic glass orders or fluctuations in a quantum system usually host exotic states or critical behaviors. As the long-range (LR) magnetic orders, SR magnetic orders can also break time-reversal symmetry and drive the non-zero Berry curvature leading to novel transport properties. In this work, we report that in EuZn$_2$As$_2$ compound, besides the LR A-type antiferromagnetic (AF) order, the SR magnetic order is observed in a wide temperature region. The magnetization measurements and electron spin resonance (ESR) measurements reveal the ferromagnetic (FM) correlations for this SR magnetic order which results in an obvious anomalous Hall effect above the AF transition. Moreover the ESR results reveal that this FM SR order coexists with LR AF order exhibiting anisotropic magnetic correlations below the AF transition. The interactions of LR and SR magnetism evolving with temperature and field can host non-zero spin charility and berry curvature leading the additional topological Hall contribution even in a centrosymmetric simple AF system. Our results indicate that EuZn$_2$As$_2$ is a fertile platform to investigate exotic magnetic and electronic states.

Correlation between the magnitude of interlayer exchange coupling and charge-to-spin conversion efficiency in a synthetic antiferromagnetic system

The correlation between the magnitude of interlayer exchange coupling (J ex) and charge-to-spin conversion efficiency (spin Hall angle: θ SH) is investigated in a synthetic antiferromagnetic (AF) system with compensated magnetization. The magnitude of θ SH increases linearly with increasing the magnitude of J ex. We observe the factor of 6.5 increase of spin Hall angle (θ SH = 45.8%) in a low resistive (ρ xx = 41 μΩcm) synthetic AF system by increasing the magnitude of J ex. The low resistive synthetic AF system will be a promising building block for future nonvolatile high-speed memories and logic circuits using the spin Hall effect.

Investigation on magnetic and magnetocaloric properties of Sr0.25Ca0.75Mn0.9Ti0.1O3 perovskite

Interest in magnetic refrigeration, which is based on the magnetocaloric effect (MCE), has greatly increased during the past two decades. As a less-polluting and more effective cooling technology than gas compression, magnetic refrigeration is one of the prominent and possible options. Perovskite Oxides played a major contribution for the development of magnetic refrigeration (MR). Sr0.25Ca0.75Mn1-xTixO3 (x = 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7 and 0.8) polycrystalline samples were synthesized by conventional solid-state reaction. Its cubic perovskite-type crystal structure is discovered to be of the Pm-3m space group. At T = 31.3 K, the alloy experiences antiferromagnetic transition for the composition of Sr0.25Ca0.75Mn0.9Ti0.1O3. It demonstrates that the greatest magnetocaloric reports are 8 J/kg K for a magnetic field of 7 Tesla and 3.2 J/kg K for 1 Tesla. These (ΔSM) value is comparable to the magnetization values of the ferromagnetic Heusler alloys and are very high in these kinds of antiferromagnetic perovskite systems. For the Sr0.25Ca0.75Mn0.9Ti0.1O3 material, this is the first report of substantial magnetic entropy changes brought on by a weak magnetic field.

Structural phase transformation of quantum spin liquid herbertsmithite via pressure induced enhancement of the cooperative Jahn-Teller effect and antisite disorder.

Herbertsmithite, Cu3Zn(OH)6Cl2, serves as one of the most promising candidates for quantum spin liquids with a perfect quantum kagome Heisenberg antiferromagnetic system. It can comprise an ideal model system for studying the compression response of the unique structure as well as exotic properties of kagome quantum spin liquid materials, which is of fundamental importance from both scientific and technological viewpoints. In this work, the structural evolution of herbertsmithite was investigated via in situ X-ray diffraction and Raman scattering techniques up to 30 GPa. The trigonal herbertsmithite structure transformed into a monoclinic clinoatacamite-like structure at 12.6 GPa. High pressure seems to act in a reverse way as Zn-doping for herbertsmithite, with the distortion degree of the system changing continuously. The occurrence of the displacive and reversible phase transition between the polymorphs is a consequence of the interplay between the external pressure and cooperative Jahn-Teller (JT) effect, aided by the presence of antisite mutual substitution of magnetic Cu2+ ions and nonmagnetic Zn2+ ions between the kagome layer and interlayer sites.

Symmetry-enforced two-dimensional Dirac node-line semimetals

Based on symmetry analysis and lattice model calculations, we demonstrate that Dirac nodal line (DNL) can stably exist in two-dimensional (2D) nonmagnetic as well as antiferromagnetic systems. We focus on the situations where the DNLs are enforced by certain symmetries and the degeneracies on the DNLs are inevitable even if spin–orbit coupling is strong. After thorough analysis, we find that five space groups, namely 51, 54, 55, 57 and 127, can enforce the DNLs in 2D nonmagnetic semimetals, and four type-III magnetic space groups (51.293, 54.341, 55.355, 57.380) plus eight type-IV magnetic space groups (51.299, 51.300, 51.302, 54.348, 55.360, 55.361, 57.387 and 127.396) can enforce the DNLs in 2D antiferromagnetic semimetals. By breaking these symmetries, the different 2D topological phases can be obtained. Furthermore, by the first-principles electronic structure calculations, we predict that monolayer YB4C4 is a good material platform for studying the exotic properties of 2D symmetry-enforced Dirac node-line semimetals.

Electric-Field-Tunable Spin Polarization and Carrier-Transport Anisotropy in an A-Type Antiferromagnetic van der Waals Bilayer

Two-dimensional (2D) magnetic semiconductor materials with the electric-field-tunable spin polarization and carrier-transport anisotropy are of great significance for the fundamental physics and device application. Here we propose a general strategy to tune the spin polarization and anisotropic effective mass in a 2D A-type antiferromagnetic (AFM) bilayer system. We take the A-type AFM bilayer $\mathrm{CrSBr}$ (with the intralayer ferromagnetic and interlayer AFM coupling) as an example to confirm this design principle. Firstly, a vertical electric field can lift the spin degeneracy in the A-type AFM bilayer $\mathrm{CrSBr}$. By flipping the direction of electric field, the spin polarization direction can be reversed. Secondly, in the A-type AFM bilayer $\mathrm{CrSBr}$ with an interlayer twist angle of 90\ifmmode^\circ\else\textdegree\fi{}, both the spin direction and the carrier-transport anisotropy can be tuned simultaneously by applying a vertical electric field due to the in-plane anisotropic carrier effective mass in each $\mathrm{CrSBr}$ monolayer. This opens an opportunity for controlling the spin polarization as well as carrier-transport anisotropy in the 2D magnetic van der Waals layered materials by interlayer twist and electric field, and provides an idea for utilizing A-type AFM semiconductors to design spintronic devices.

Tunable magnon-magnon coupling mediated by in-plane magnetic anisotropy in synthetic antiferromagnets

The magnon–magnon coupling is the key issue to exchange information in hybrid magnonic systems. We investigate the magnon–magnon coupling in a synthetic antiferromagnet (SAF) system with the presence of an in-plane uniaxial magnetic anisotropy via micromagnetic simulations. The magnon–magnon coupling arises, and its strength is field-direction dependent. The maximum magnon–magnon coupling occurs when the in-plane magnetic field along 45° deviates from the easy axis. The magnon–magnon coupling can be regulated by the in-plane magnetic anisotropy field. The dynamical phase between two magnetic layers is neither 0° nor 180°, which indicates the magnon in a hybrid mode. This study provides a simple method for a tunable magnon–magnon coupling in SAFs to realize a practical hybrid quantum system based on magnonics.