Skyrmions in anisotropic magnetic fields: strain and defect driven dynamics
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MRS Advances © 2019 Materials Research Society DOI: 10.1557/adv.2019.43
Skyrmions in anisotropic magnetic fields: strain and defect driven dynamics Richard Brearton1,2, Maciej W. Olszewski3, Shilei Zhang1, Morten R. Eskildsen3, Charles Reichhardt4, Cynthia J. O. Reichhardt4, Gerrit van der Laan2, Thorsten Hesjedal1 1
University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, England Magnetic Spectroscopy Group, Diamond Light Source, Fermi Ave, Didcot OX11 0DE, England 3 Department of Physics, University of Notre Dame, Notre Dame, IN 46656, U.S.A. 4 Theoretical Division, Los Alamos National Laboratory, Los Alamos, NM 87545, U.S.A. 2
ABSTRACT Magnetic skyrmions are particle-like, topologically protected magnetization entities that are promising candidates for information carriers in racetrack-memory schemes. The transport of skyrmions in a shift-register-like fashion is crucial for their embodiment in practical devices. Recently, we demonstrated experimentally that chiral skyrmions in Cu2OSeO3 can be effectively manipulated by a magnetic field gradient, leading to a collective rotation of the skyrmion lattice with well-defined dynamics in a radial field gradient. Here, we employ a skyrmion particle model to numerically study the effects of resultant shear forces on the structure of the skyrmion lattice. We demonstrate that anisotropic peak broadening in experimentally observed diffraction patterns can be attributed to extended linear regions in the magnetic field profile. We show that topological (5-7) defects emerge to protect the sixfold symmetry of the lattice under the application of local shear forces, further enhancing the stability of proposed magnetic field driven devices.
INTRODUCTION The encoding of magnetic bits via topologically protected spin configurations presents an interesting route for scaling down magnetic random-access memory, as the scaled magnetic bits remain inherently robust against superparamagnetism [1]. In chiral magnets, individual skyrmion spin swirls assemble into hexagonally closed-packed lattices. Examples of chiral magnets in which skyrmion lattices have been found are MnSi [2], Fe0.5Co0.5Si [3], FeGe [4], Cu2OSeO3 [5], and CoxZnyMnz [6]. The magnetic skyrmion lattice in these materials is in general incommensurate with the atomic lattice. The magnetic skyrmion lattice is highly mobile and can be manipulated via spin-transfer torque (STT) using very low current densities [7-10]. A recognized use of such skyrmion
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systems is racetrack memory, which shows great promise for future memory applications [1,11,12]. Recently, we have demonstrated that skyrmions can be manipulated in a controlled manner with the aid of a magnetic field gradient [13]. First, in a practical skyrmion racetrack device, Oersted fields can be used to create a similar fi
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