A stable skyrmion, representing the smallest realizable magnetic texture, could be an ideal element for ultra-dense magnetic memories. Here, we review recent progress in the field of skyrmionics, which is concerned with studies of tiny whirls of magnetic configurations for novel memory and logic applications, with a particular emphasis on antiskyrmions. Magnetic antiskyrmions represent analogs of skyrmions with opposite topological charge. Just like skyrmions, antiskyrmions can be stabilized by the Dzyaloshinskii-Moriya interaction, as has been demonstrated in a recent experiment. Here, we emphasize differences between skyrmions and antiskyrmions, e.g., in the context of the topological Hall effect, skyrmion Hall effect, as well as nucleation and stability. Recent progress suggests that anitskyrmions can be potentially useful for many device applications. Antiskyrmions offer advantages over skyrmions as they can be driven without the Hall-like motion, offer increased stability due to dipolar interactions, and can be realized above room temperature.
We show that elongated magnetic skyrmions can host Majorana bound states in a proximitycoupled two-dimensional electron gas sandwiched between a chiral magnet and an s-wave superconductor. Our proposal requires stable skyrmions with unit topological charge, which can be realized in a wide range of multilayer magnets, and allows quantum information transfer by using standard methods in spintronics via skyrmion motion. We also show how braiding operations can be realized in our proposal.
We investigate the intrinsic magnon spin current in a noncollinear antiferromagnetic insulator. The spin current is in general found to be non-conserved, but for certain symmetries and spin polarizations, the averaged effect of non-conserving terms can vanish. We formulate a general linear response theory for magnons in noncollinear antiferromagnets subject to a temperature gradient and analyze the effect of symmetries on the response tensor. We apply this theory to single-layer potassium iron jarosite KFe3(OH)6(SO4)2 and predict a measurable spin current response. arXiv:1907.10567v2 [cond-mat.mes-hall]
Topological antiferromagnetic (AFM) spintronics is an emerging field of research, which involves the topological electronic states coupled to the AFM order parameter known as the Néel vector. The control of these states is envisioned through manipulation of the Néel vector by spin-orbit torques driven by electric currents. Here we propose a different approach favorable for low-power AFM spintronics, where the control of the topological states in a two-dimensional material, such as graphene, is performed via the proximity effect by the voltage induced switching of the Néel vector in an adjacent magnetoelectric AFM insulator, such as chromia. Mediated by the symmetry protected boundary magnetization and the induced Rashba-type spin-orbit coupling at the interface between graphene and chromia, the emergent topological phases in graphene can be controlled by the Néel vector. Using density functional theory and tightbinding Hamiltonian approaches, we model a graphene/Cr2O3 (0001) interface and demonstrate non-trivial band gap openings in the graphene Dirac bands asymmetric between the K and K′ valleys. This gives rise to an unconventional quantum anomalous Hall effect (QAHE) with a quantized value of 2e 2 /h and an additional step-like feature at a value close to e 2 /2h, and the emergence of the spin-polarized valley Hall effect (VHE). Furthermore, depending on the Néel vector orientation, we predict the appearance and transformation of different topological phases in graphene across the 180° AFM domain wall, involving the QAHE, the valley-polarized QAHE and the quantum VHE (QVHE), and the emergence of the chiral edge state along the domain wall. These topological properties are controlled by voltage through magnetoelectric switching of the AFM insulator with no need for spin-orbit torques. A. Optimization of the graphene/Cr 2 O 3 (0001) interface structureThe in-plane position of graphene on the Cr2O3 (0001) surface was optimized by considering three different interface structures: (1) a graphene C atom is atop the Cr atom of the Cr2O3 surface (Figures 1a,b in the main text), (2) a graphene C atom is atop the O atom in the first O monolayer from the Cr2O3 surface ( Figure S1a), and (3) the Cr surface atom is below the center of a hexagonal ring of graphene ( Figure S1b). Starting from these initial configurations, the atomic structure of the whole supercell is relaxed. We find that the lowest total energy structure forms C located atop Cr (Figures 1a,b in the main text). The structure with C atop O atom ( Figure S1a) and the structure with Cr under the graphene hollow site, respectively, have the total energy 36 meV and 55 meV higher. In the main text, we focus on the most stable atomic structure to investigate the electric, magnetic, and spin transport of the on the Cr2O3 (0001) interface.
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