Manipulation of skyrmion motion by magnetic field gradients

S L Zhang,A Bauer,C Pfleiderer,T Hesjedal,H Peng,G Van Der Laan,W W Wang,D M Burn,H Berger

doi:10.1038/s41467-018-04563-4

Abstract

Magnetic skyrmions are particle-like, topologically protected magnetisation entities that are promising candidates as information carriers in racetrack memory. The transport of skyrmions in a shift-register-like fashion is crucial for their embodiment in practical devices. Here, we demonstrate that chiral skyrmions in Cu2OSeO3 can be effectively manipulated under the influence of a magnetic field gradient. In a radial field gradient, skyrmions were found to rotate collectively, following a given velocity–radius relationship. As a result of this relationship, and in competition with the elastic properties of the skyrmion lattice, the rotating ensemble disintegrates into a shell-like structure of discrete circular racetracks. Upon reversing the field direction, the rotation sense reverses. Field gradients therefore offer an effective handle for the fine control of skyrmion motion, which is inherently driven by magnon currents. In this scheme, no local electric currents are needed, thus presenting a different approach to shift-register-type operations based on spin transfer torque.

Highlights

Magnetic skyrmions are particle-like, topologically protected magnetisation entities that are promising candidates as information carriers in racetrack memory
The skyrmion dynamics is well-described in the Landau–Lifshitz–Gilbert micromagnetic framework[1], and the centre of mass motion of a skyrmion was further generalised by Thiele[26]
The circular motion of the skyrmions is governed by the magnetic field gradient, the inherent source of energy of the skyrmion motion is, in the absence of other energy sources such as electric currents, the momentum carried by magnons due to temperature inhomogeneities across the sample surface[23,24]

Summary

Results

Concentric contour lines will lead to rotational motion of the skyrmions (see Supplementary Methods 1), allowing for a circular skyrmion racetrack memory scheme based on patterned rings (Fig. 1c). At 57 K and 0 mT, the multidomain helical phase is stabilised as the ground state, characterised by two sets of magnetic satellites around the structural (001) peak The skyrmion lattice state is stable in an uniform magnetic field, where one pair of the magnetic peaks is locking along h100i Once this phase is formed, the diffraction pattern only undergoes slight drifts within ±2° over time due to thermal fluctuation-induced motion

57 K 25 mT

Discussion

Methods