Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session F40: Novel Topological Spin TexturesFocus Session Live
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Sponsoring Units: GMAG DMP Chair: Jiadong Zang, University of New Hampshire |
Tuesday, March 16, 2021 11:30AM - 11:42AM Live |
F40.00001: Chiral multi-spin multi-site interactions Sascha Brinker, Manuel dos Santos Dias, Samir Lounis The huge progress in the field of magnetic skyrmions and other noncollinear magnetic structures is due in large part to our understanding of the chiral Dzyaloshinskii-Moriya interaction. This illustrates the importance of identifying which magnetic interactions are present in a given material. Here, we discuss our systematic construction of a generalized spin model containing isotropic and chiral multi-site interactions [1,2]. These are motivated by a microscopic model, and their symmetry properties are established. We show that the chiral interactions arise solely from the spin-orbit interaction and that the multi-site interactions do not have to follow Moriya's rules, unlike the Dzyaloshinskii-Moriya and chiral biquadratic interactions. We then illustrate our theoretical considerations with density functional theory calculations for prototypical magnetic systems: triangular trimers made of Cr, Mn, Fe and Co on the Re(0001), Pt(111) and Au(111) surfaces, and Cr and Fe square tetramers on Pt(001). |
Tuesday, March 16, 2021 11:42AM - 11:54AM Live |
F40.00002: Doping effects and higher-order magnetic interactions in skyrmionic B20 compounds Vladislav Borisov, Nikolaos Ntallis, Yaroslav Kvashnin, Danny Thonig, Manuel Pereiro, Anders Bergman, Erik Sjöqvist, Anna Delin, Lars Nordström, Olle Eriksson Skyrmionic B20 compounds based on FeSi and CoSi doped with 3d, 4d and 5d transition metals are studied theoretically using a combination of density functional theory and dynamical mean-field theory. Using the magnetic force theorem, we obtain a detailed picture of magnetic interactions, including Heisenberg, Dzyaloshinskii-Moriya (DM), and symmetric anisotropic exchange. From these calculated interactions, we perform micromagnetic simulations under external field and find non-collinear magnetic phases with a small spatial period. Our results demonstrate that 4d and 5d doping enhances substantially the effect of the DM interaction compared to the 3d-doped case, such as the experimentally studied (Fe1-xCox)Si B20 system. We have also extended the theoretical framework, in order to explore the higher-order multispin interactions, which can contribute significantly to skyrmion stability and dynamics. |
Tuesday, March 16, 2021 11:54AM - 12:06PM Live |
F40.00003: Spin Moiré Engineering of Emergent Electromagnetism Kotaro Shimizu, Shun Okumura, Yasuyuki Kato, Yukitoshi Motome A superposition of waves generates interference fringes called Moiré. It has gained renewed interest in atomic layered materials such as twisted graphene. Here we pursue this idea in magnetism, by regarding a superposition of spin helices as spin Moiré. We find that the manipulation of the Moiré patterns by the angles between the superposed helices and the net magnetization yields successive topological transitions associated with pair annihilation of topological defects called hedgehogs and antihedgehogs. Accordingly, emergent electromagnetic fields arising from the noncoplanar spin textures show systematic evolution. We also show how the system undergoes the topological transitions, in addition to the magnetic phase transitions from the hedgehog lattice to a skyrmion lattice or a conical state associated with spin Moiré modulation. Our results indicate that the spin Moiré is an efficient picture for engineering the topology and the emergent electromagnetism in chiral magnets. |
Tuesday, March 16, 2021 12:06PM - 12:18PM Live |
F40.00004: Chiral magnetism: a geometric perspective Daniel Hill, Oleg Tchernyshyov, Valeriy Slastikov We recast the model of a chiral ferromagnet with the Dzyaloshinski-Moriya interaction as a Heisenberg model with nontrivial spin parallel transport. Within this theoretical framework, the Dzyaloshinskii-Moriya vectors take the role of a background SO(3) gauge field. A combination of analytical and numerical arguments suggests that the ground state of this gauged Heisenberg model in 2 spatial dimensions is a hexagonal skyrmion crystal in a wide range of applied magnetic fields. |
Tuesday, March 16, 2021 12:18PM - 12:54PM Live |
F40.00005: Magnetic textures with particle properties beyond skyrmions: chiral bobbers, globules, and hopfions Invited Speaker: Nikolai S. Kiselev Magnetic crystals with competing interactions allow the existence of localized in space magnetic textures possessing a lot of similarities to ordinary particles meaning that they can move and interact with each other: attract, repel or collide and annihilate. |
Tuesday, March 16, 2021 12:54PM - 1:06PM Live |
F40.00006: Experimental observation of magnetic hopfions in multilayer disks Noah Kent, Neal Reynolds, David Raftrey, Ian T.G. Campbell, Selven Virasawmy, Scott Dhuey, Rajesh V Chopdekar, Aurelio Hierro-Rodriguez, Andrea Sorrentino, Eva Pereiro, Salvador Ferrer, Frances Hellman, Paul M. Sutcliffe, Peter Fischer Topological solitons are currently of high interest to condensed matter physics. Among those, magnetic skyrmions (Sk) are two-dimensional objects with a continuous winding of the magnetization, and magnetic Hopfions are 3D topological solitons that can be formed from a closed loop of a twisted skyrmion string. Whereas intense research with magnetic Sks has already led to a deep understanding and potential applications in advanced storage and logic devices1,2, the experimental validation of magnetic Hopfions has been elusive so far. Theoretical models suggest that Hopfions can be stabilized in frustrated or chiral magnetic systems, and kπ skyrmions, aka target skymions (TSk) can be transformed into Hopfions by adapting their perpendicular magnetic anisotropy3,4. |
Tuesday, March 16, 2021 1:06PM - 1:18PM Live |
F40.00007: Ultrafast spin dynamics in Magnetic Hopfions David Raftrey, Peter Fischer
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Tuesday, March 16, 2021 1:18PM - 1:30PM Live |
F40.00008: Antiferromagnetic Half-skyrmions and Bimerons at room temperature Hariom Jani, Jheng-Cyuan Lin, Jiahao Chen, Jack Harrison, Francesco Maccherozzi, Jonathon Schad, Saurav Prakash, Chang-Beom Eom, Ariando Ariando, Thirumalai Venkatesan, Paolo G. Radaelli In the quest for post-CMOS technologies, ferromagnetic skyrmions and their anti-particles have shown great promise as topologically protected solitonic information carriers in memory-in-logic or neuromorphic devices, and the deleterious skyrmion Hall effect when driven by spin torques have thus far inhibited their practical implementations. Antiferromagnetic analogues, which are predicted to demonstrate relativistic dynamics, fast deflection-free motion and size scaling have recently come into intense focus, but their experimental realizations in natural antiferromagnetic systems are yet to emerge. Here, we demonstrate a family of topological antiferromagnetic spin-textures in α-Fe2O3 – an earth-abundant oxide – capped with a Pt over-layer. By exploiting a first-order analogue of the Kibble-Zurek mechanism, we stabilize exotic merons-antimerons and bimerons, which can be erased by magnetic fields and re-generated by temperature cycling. These structures have sizes in the range ~100 nm that can be chemically controlled via precise tuning of the exchange and anisotropy, with pathway for scaling. Driven by spin torques from the heavy-metal over-layer, some of these AFM textures could emerge as prime candidates for low-energy antiferromagnetic spintronics at room temperature. |
Tuesday, March 16, 2021 1:30PM - 1:42PM Live |
F40.00009: Designing inverse-Heusler antiskyrmion hosts by chemically tailoring the effective magnetic Hamiltonian Daniil Kitchaev, Anton Van der Ven Despite progress in the identification of mechanisms capable of stabilizing magnetic (anti)skyrmions, the number of bulk materials known to host these phases over a wide range of ambient temperatures remains small. Such thermal stability can be guaranteed by designing materials with Cnv, D2d, or S4 symmetry to have low magnetocrystalline anisotropy. An ideal platform for realizing this behavior are the tetragonal inverse Heusler alloys, where several proof-of-concept materials hosting thermally-robust antiskyrmions have been discovered. We report a systematic, first-principles exploration of potential antiskyrmion hosts in this family of materials, from known ordered compounds to hypothetical disordered alloys likely to maintain the tetragonal inverse Heusler structure. We construct a universal model relating mesoscale magnetic phase behavior to atomistic interactions and map out the magnetic behavior of a wide range of candidate chemistries to identify compositions yielding the precise magnetic Hamiltonian necessary for antiskyrmion formation. Our analysis reveals concrete chemical handles for controlling antiskyrmion formation and suggests new chemical spaces likely to host thermally-robust antiskyrmion phases. |
Tuesday, March 16, 2021 1:42PM - 1:54PM Live |
F40.00010: Magnetic vortex-antivortex pairs in the magnetic stripe domain pattern: magnetization reversal and topology. Maria Velez, Aurelio Hierro-Rodriguez, Victoria Vega Fernandez, Javier Hermosa, Carlos Quiros, Andrea Sorrentino, Luis Manuel Alvarez Prado, Jose I. Martín, Eva Pereiro, Salvador Ferrer Bloch points and magnetic vortex-antivortex pairs are key actors in the magnetization reversal process of weak perpendicular anisotropy magnetic multilayers [1]. Bifurcations within the parallel stripe domain pattern act as nucleation sites for Bloch points at the onset of magnetization reversal and serve as guided paths for the subsequent propagation of vortex-antivortex pairs within the sample. In this work, we will present the analysis of topological charge transformations during the nucleation/propagation process based on micromagnetic simulations of NiFe/NdCo/NiFe multilayers and experimental 3D magnetization maps obtained from X-ray vector magnetic tomography of NiFe/NdCo/NiFe trilayers [2,3]. The signature of vortex-antivortex propagation in magnetotransport measurements taken during the magnetization reversal of NdCo and NiFe/NdCo/NiFe trilayers will also be discussed. |
Tuesday, March 16, 2021 1:54PM - 2:06PM Live |
F40.00011: Topological transport of deconfined hedgehogs in magnets Ji Zou, Shu Zhang, Yaroslav Tserkovnyak We theoretically investigate the dynamics of magnetic hedgehogs, which are three-dimensional topological spin textures that exist in common magnets, focusing on their transport properties and connections to spintronics. We show that fictitious magnetic monopoles carried by hedgehog textures obey a topological conservation law, based on which a hydrodynamic theory is developed. In the high-temperature (paramagnet) regime, the topological stability of the hedgehog flows results in an algebraically decaying drag signal in nonlocal transport measurements. The bulk-edge correspondence between hedgehog number and skyrmion number, the fictitious electric charges arising from magnetic dynamics, and the analogy between the low-temperature bound states of hedgehogs and the quark confinement in quantum chromodynamics are also discussed. Our study points to a practical potential in utilizing hedgehog flows for long-range neutral signal propagation or manipulation of skyrmion textures in three-dimensional magnetic materials. |
Tuesday, March 16, 2021 2:06PM - 2:18PM Live |
F40.00012: Deformation of spin-hedgehog lattice in MnGe Aki Kitaori, Naoya Kanazawa, Jonathan S White, Victor Ukleev, Henrik M Ronnow, Atsushi Tsukazaki, Masakazu Ichikawa, Masashi Kawasaki, Yoshinori Tokura In a chiral magnet MnGe, there appears a spin hedgehog crystal, which is a lattice of spin hedgehogs and antihedgehogs formed from a superposition of three orthogonal helical spin structures [1]. The three-dimensional topological spin arrangements of hedgehogs and antihedgehogs serve as quantized sources and sinks of emergent magnetic fields, i.e., emergent magnetic monopoles, resulting in unconventional transport properties [2]. |
Tuesday, March 16, 2021 2:18PM - 2:30PM Live |
F40.00013: Magneto-transport and magnetic ordering in the intercalated transition metal dichalcogenides. Daniel Mayoh, Amelia Hall, Sam Holt, Martin Lees, Geetha Balakrishnan Noncentrosymmetric magnetic systems have been found to host a variety of exotic, and in some cases topologically protected, magnetic states such as skyrmion lattices, bimerons, chiral solitons and helimagnetism to list a few examples. One such class of material that has faced increased scrutiny in recent years for their magnetism are two-dimensional (2D) materials. The intercalated transition metal dichalcogenides (TMDCs) are an interesting class of materials exhibiting ferromagnetic or antiferromagnetic ordering. Cr1/3NbS2 is an example of a 2D TMDC where the structure consists predominately of layers of Nb and S where the Cr atoms have been intercalated between the layers. Cr1/3NbS2 exhibits chiral helimagnetic ordering as well as a chiral soliton lattice. We present our recent studies of the magneto-transport properties and magnetic state in these TMDCs where several different magnetic atoms (Cr, Mn, V) have been intercalated. |
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