X. Li, L. Shen, Y. Bai, J. Wang, X. Zhang, J. Xia, M. Ezawa, O. A. Tretiakov, X. Xu, M. Mruczkiewicz, M. Krawczyk, Y. Xu, R. F. L. Richard, R. W. Chantrell, Y. Zhou
A mgnetic bimeron is an in-plane topological counterpart of a magnetic skyrmion. Despite the topological equivalence, their statics and dynamics could be distinct, making them attractive from the perspectives of both physics and spintronic applications. In this work, we investigate an antiferromagnetic (AFM) thin film with interfacial Dzyaloshinskii-Moriya interaction (DMI), and introduce the AFM bimeron cluster as a new form of topological quasi-particle. Bimerons demonstrate high current-driven mobility as generic AFM solitons, while featuring anisotropic and relativistic dynamics excited by currents with in-plane and out-of-plane polarizations, respectively. Moreover, these spin textures can absorb other bimeron solitons or clusters along the translational direction to acquire a wide range of Néel topological numbers. The clustering involves the rearrangement of topological structures, and gives rise to remarkable changes in static and dynamical properties. The merits of AFM bimeron clusters reveal a potential path to unify multi-bit data creation, transmission, storage and even topology-based computation within the same material system, and may stimulate innovative spintronic devices enabling new paradigms of data manipulations.
A magnetic bimeron is a topologically non-trivial spin texture carrying an integer topological charge, which can be regarded as the counterpart of skyrmion in easy-plane magnets. The controllable creation and manipulation of bimerons are crucial for practical applications based on topological spin textures. Here, we analytically and numerically study the dynamics of an antiferromagnetic bimeron driven by a spin current. Numerical simulations demonstrate that the spin current can create an isolated bimeron in the antiferromagnetic thin film via the damping-like spin torque. The spin current can…
Topological defects embedded in or combined with domain walls have been proposed in various systems, some of which are referred to as domain wall skyrmions or domain wall bimerons. However, the experimental observation of such topological defects remains an ongoing challenge. Here, using Lorentz transmission electron microscopy, we report the experimental discovery of domain wall bimerons in chiral magnet Co-Zn-Mn(110) thin films. By applying a magnetic field, multidomain structures develop, and simultaneously, chained and isolated bimerons arise as the localized state between the domains with…
Skyrmions and bimerons are versatile topological spin textures that can be used as information bits for both classical and quantum computing. The transformation between isolated skyrmions and bimerons is an essential operation for computing architecture based on multiple different topological bits. Here we report the creation of isolated skyrmions and their subsequent transformation to bimerons by harnessing the electric current-induced Oersted field and temperature-induced perpendicular magnetic anisotropy variation. The transformation between skyrmions and bimerons is reversible, which is co…
Skyrmions are topologically protected field configurations with particle-like properties that play important roles in various fields of science. Recently, skyrmions have been directly observed in chiral magnets. Here, we investigate the effects of nonmagnetic impurities (structural point-like defects) on the different initial states (random or helical states) and on the formation of the skyrmion crystal in a discrete lattice. By using first-principle calculations and Monte Carlo techniques, we have shown that even a small percentage of spin vacancies present in the chiral magnetic thin film af…
From Nested Soliton Crystals to Skyrmion Crystals in Chiral Magnets
Institute of Contemporary Mathematics, School of Mathematics and Statistics, Henan University（河南大学数学与统计学院现代数学研究所）；Department of Physics, Chemistry and Pharmacy, University of Southern Denmark（南丹麦大学物理化学药学系）；Department of Physics, Keio University（庆应义塾大学物理学部）；Research and Education Center for Natural Sciences, Keio University（庆应义塾大学自然科学研究与教育中心）；International Institute for Sustainability with Knotted Chiral Meta Matter(SKCM2 ), Hiroshima University（广岛大学缠绕手性超物质可持续发展国际研究所）
In antiferromagnets, the Dzyaloshinskii-Moriya interaction lifts the degeneracy of left- and right-circularly polarized spin waves. This relativistic coupling increases the efficiency of spin-wave-induced domain wall motion and leads to higher drift velocities. We show that in biaxial antiferromagnets, the spin-wave helicity controls both the direction and magnitude of the magnonic force on chiral domain walls. By contrast, in uniaxial antiferromagnets, the magnonic force is propulsive with a helicity dependent strength.
The anomalous Hall effect has been indispensable in our understanding of numerous magnetic phenomena. This concerns both ferromagnetic materials, as well as diverse classes of antiferromagnets, where in addition to the anomalous and crystal Hall effects, the topological Hall effect in non-coplanar antiferromagnets has been a subject of intensive research in the past decades. Here, we uncover a new flavour of the anomalous Hall effect in canted spin systems. Using advanced theoretical tools we demonstrate that upon canting, the anomalous Hall effect acquires a contribution which is sensitive to…
We report on the pressure evolution of the giant anomalous Hall effect (AHE) in the chiral antiferromagnet Mn$_3$Ge. The AHE originating from the non-vanishing Berry curvature in Mn$_3$Ge can be continuously tuned by application of hydrostatic pressure. At room temperature, the Hall signal changes sign as a function of pressure and vanishes completely at $p=1.53$ GPa. Even though the Hall conductivity changes sign upon increasing pressure, the room-temperature saturation value of 23 ${\rm Ω^{-1}cm^{-1}}$ at 2.85 GPa is remarkably high and comparable to the saturation value at ambient pressure …
Noncollinear chiral spin textures in ferromagnetic multilayers are at the forefront of recent research in nano-magnetism with the promise for fast and energy-efficient devices. The recently demonstrated possibilities to stabilize such chiral structures in synthetic antiferromagnets (SAF) has raised interests as they are immune to dipolar field, hence favoring the stabilization of ultra small textures, improve mobility and avoid the transverse deflections of moving skyrmions limiting the efficiency in some foreseen applications. However, such systems with zero net magnetization are hence diffic…
The exchange coupling underlies ferroic magnetic coupling and is thus the key element that governs statics and dynamics of magnetic systems. This fundamental interaction comes in two flavors - symmetric and antisymmetric coupling. While symmetric coupling leads to ferro- and antiferromagnetism, antisymmetric coupling has attracted significant interest owing to its major role in promoting topologically non-trivial spin textures that promise high-speed and energy-efficient devices. So far, the antisymmetric exchange coupling rather short-ranged and limited to a single magnetic layer has been dem…
Topological spin textures, like skyrmions, have significant potential for spintronics applications. The main purpose of this work is to study further the topological spin textures on the discrete lattice with magnetic fields. In this work, we study a classical rotated Heisenberg model with Dzyaloshinskii-Moriya interaction, bond-dependent anisotropy and easy-axis anisotropy on the honeycomb lattice via Monte Carlo simulations. We mainly focus on phase diagrams with magnetic fields, especially on the non-trivial phases only existing with fields. The results demonstrate the emergence of field-in…
Magnetic skyrmions are particle-like topological excitations that recently generated much interest as candidates for future spintronic devices based on skyrmion small size, enhanced topological stability, and/or mutual interaction. Here we examine the properties of isolated skyrmions in a frustrated chiral magnet with competing Dzyaloshinskii-Moriya and frustrated exchange interactions. We show that the skyrmion size drastically decreases even for small values of competing stabilization mechanisms. Skyrmion mutual interaction remains attracting as is inherent for frustrated skyrmions, but the …
Temperature gradient in a ferromagnetic conductor may generate a spontaneous transverse voltage drop in the direction perpendicular to both magnetization and heat current. This anomalous Nernst effect (ANE) has been considered to be proportional to the magnetization, and thus observed only in ferromagnets, while recent theories indicate that ANE provides a measure of the Berry curvature at the Fermi energy $E_{\rm F}$. Here we report the observation of a large ANE at zero field in the chiral antiferromagnet Mn$_3$Sn. Despite a very small magnetization $\sim 0.002$ $μ_{\rm B}/$Mn, the transvers…
Non-collinear chiral antiferromagnets like Mn3Sn and Mn3Ge are known to show gigantic anomalous Hall response depending on the orientation of their inverse chiral magnetic order of Mn atoms in Kagome layers. Here we study the stability of such magnetic order in the absence of external magnetic fields on the basis of stochastic Landau-Lifshitz-Gilbert equation for a simplified two-dimensional model of these materials. We find that even without external magnetic fields, the ordered state is, once formed, highly stable against thermal fluctuations. Moreover, we show that if Mn spins are well conf…
As first demonstrated by Tang and Cohen in chiral optics, the asymmetry in the rate of electromagnetic energy absorption between left and right enantiomers is determined by an optical chirality density [1]. Here, we demonstrate that this effect can exist in magnetic spin systems. By constructing a formal analogy with electrodynamics, we show that in antiferromagnets with broken chiral symmetry the asymmetry in local spin-wave energy absorption is proportional to a spin-wave chirality density, which is a direct counterpart of optical zilch. We propose that injection of a pure spin current into …
Institute of Physics, Johannes Gutenberg University Mainz（美因茨约翰内斯·古腾堡大学物理研究所）；Université Grenoble Alpes, CNRS, CEA, SPINTEC（格勒诺布尔阿尔卑斯大学，法国国家科学研究中心，法国原子能和替代能源委员会，SPINTEC）；Laboratory for Nanoelectronics and Spintronics, Research Institute of Electrical Communication, Tohoku University（东北大学电气通信研究所纳米电子与自旋电子学实验室）；Peter Grünberg Institute, Forschungszentrum Jülich and JARA（于利希研究中心和JARA的彼得·格林伯格研究所）；Department of Physics and Astronomy, Uppsala University（乌普萨拉大学物理与天文学系）；Wallenberg Initiative Materials Science, WISE, Uppsala University（乌普萨拉大学瓦伦堡材料科学倡议WISE）；Helmholtz-Zentrum Berlin für Materialien und Energie GmbH（柏林亥姆霍兹材料与能源中心有限公司）
Non-reciprocal spin wave can facilitate the realization of spin wave logic devices. It has been demonstrated that the non-reciprocity can emerge when an external magnetic field is applied to chiral magnets, of which spin structures depend crucially on an asymmetric exchange interaction, that is, the Dzyaloshinskii-Moriya interaction (DMI). Here we demonstrate that the non-reciprocity can arise even without the DMI. We demonstrate this idea for the chiral antiferromagnet Ba$_2$NbFe$_3$Si$_2$O$_{14}$, of which DMI is very small and chiral spin structure arises mainly from the competition between…
We study inter-skyrmion interactions and stable spin configurations in a 2D chiral magnet with in-plane anisotropies of a tilted magnetic field and the magneto-crystalline anisotropy on a (011) thin film. We find that in both cases a small deformation of a skyrmion shape makes the inter-skyrmion interaction anisotropic, and that the skyrmions are weakly bounded along a certain direction due to an emergent attractive interaction. Furthermore, when the magneto-crystalline anisotropy is comparable to the Zeeman energy, skyrmions embedded in a uniform magnetization are tightly bound by creating a …
Optical generation of complex spin textures is one of the most exciting challenges of modern spintronics. Here, we uncover a distinct physical mechanism for imprinting spin chirality into collinear magnets with short laser pulses. By simultaneously treating the laser-ignited evolution of electronic structure and magnetic order, we show that their intertwined dynamics can result in an emergence of quasi-stable chiral states. We find that laser-driven chirality does not require any auxiliary external fields or intrinsic spin-orbit interaction to exist, and it can survive on the time scale of nan…
Breathing oscillations of skyrmions in chiral antiferromagnets can be excited by a temporal modification of the Dzyaloshinskii-Moriya interaction or magnetocrystalline anisotropy strength. We employ an adiabatic approximation and derive a formula for the potential that directly implies breathing oscillations. We study the nonlinear regime and the features of larger amplitude oscillations. We show that there is a maximum amplitude supported by the potential. As a consequence, we predict theoretically and observe numerically skyrmion annihilation events due to excitation of large amplitude breat…
Combination of proximity-induced superconductivity and ferromagnetic exchange field in a two-dimensional square-lattice antiferromagnet with spin-orbit coupling and nonsymmorphic symmetry can induce a topological superconductor phase with chiral Majorana edge states. The lattice model of the Bogoliubov-de Gennes (BdG) Hamiltonian was applied to study the phase diagram of bulks and chiral Majorana edge states in nanoribbons. By numerically studying the phase diagram, we found that the non-uniformity of either the superconducting pairing parameters or the exchange field at the two sublattices is…
Exotic spin textures viz. chiral domain wall, vortices, skyrmion, skyrmionium, etc. have recently emerged as active field of research because of their potential applications in high density data storage technology and logic gate computing. Magnetic skyrmionium is a skyrmion like soliton, which carries zero topological quantum number. Skyrmioniums are superior to conventional skyrmions in ferromagnets due to their negligible skyrmion hall effect and higher velocity. The physical properties of both skyrmion and skyrmionium have been investigated rigorously in ferromagnetic systems. Recent observ…
We study positions of chiral hinge states in higher-order topological insulators (HOTIs) with inversion symmetry. First, we exhaust all possible configurations of the hinge states in the HOTIs in all type-I magnetic space groups with inversion symmetry by studying dependence of the sign of the surface Dirac mass on surface orientations. In particular, in the presence of glide symmetry, for particular surface orientations, the surface Dirac mass changes sign by changing the surface terminations. By applying this result to a layered antiferromagnet (AFM), we find a difference in the hinge states…
The magnetic interfacial Dzyaloshinskii-Moriya interaction (DMI) in multi-layered thin films can lead to exotic chiral spin states, of paramount importance for future spintronic technologies. Interfacial DMI is normally manifested as an intralayer interaction, mediated via a paramagnetic heavy metal in systems lacking inversion symmetry. Here we show how, by designing synthetic antiferromagnets with canted magnetization states, it is also possible to observe interfacial interlayer-DMI at room temperature. The interlayer-DMI breaks the symmetry of the magnetic reversal process via the emergence…
The existence of the magnetostatic surface spin waves in ferromagnets, known as Damon-Eshbach mode, was recently demonstrated to originate from the topology of the dipole-dipole interaction. In this work, we study the topological characteristics of magnons in easy-axis antiferromagnets with uniaxial anisotropy. The dipolar spin waves are found to be, driven by the dipole-dipole interaction, in a topological nodal-line semimetal phase, which hosts Damon-Eshbach-type surface modes due to the bulk-edge correspondence. The long wavelength character of dipolar spin waves makes our proposal valid fo…
Skyrmions in antiferromagnetic (AFM) materials with the Dzyaloshinskii-Moriya (DM) interaction are expected to exist for essentially the same reasons as in DM ferromagnets (FM). It is shown that skyrmions in antiferromagnets with the DM interaction can be traveling as solitary waves with velocities up to a maximum value that depends on the DM parameter. Their configuration is found numerically. The energy and the linear momentum of an AFM skyrmion lead to a proper definition of its mass. We give the details of the energy-momentum dispersion of traveling skyrmions and explore their particle-lik…
