Deformation of the moving magnetic skyrmion lattice in MnSi under electric current flow

Daisuke Okuyama ,Y Tokura,J S White,Y Taguchi,Jeffery R Krzywon ,Shintaro Hoshino ,Z Q Im,Gergely Nagy ,Markus Bleuel ,M Bartkowiak,Johannes Reim ,Naoto Nagaosa ,Akiko Kikkawa ,Daiki Higashi ,Jun Iwasaki ,Henrik M Rønnow ,Q Ye,Yusuke Nambu ,Ivica Živković ,Taku Sato

doi:10.1038/s42005-019-0175-z

Abstract

Topological defects are found ubiquitously in various kinds of matter, such as vortices in type-II superconductors, and magnetic skyrmions in chiral ferromagnets. While knowledge on the static behavior of magnetic skyrmions is accumulating steadily, their dynamics under forced flow is still a widely open issue. Here, we report the deformation of the moving magnetic skyrmion lattice in MnSi under electric current flow observed using small-angle neutron scattering. A spatially inhomogeneous rotation of the skyrmion lattice, with an inverse rotation sense for opposite sample edges, is observed for current densities greater than a threshold value jt ~ 1 MA m−2 (106 A m−2). Our result show that skyrmion lattices under current flow experience significant friction near the sample edges due to pinning, this being a critical effect that must be considered for anticipated skyrmion-based applications at the nanoscale.

Highlights

Topological defects are found ubiquitously in various kinds of matter, such as vortices in type-II superconductors, and magnetic skyrmions in chiral ferromagnets
Topological defects, i.e., defects that cannot be annihilated by continuous deformation, are found ubiquitously in various kinds of matter, such as screw dislocation in crystals[1,2,3], defect in nematic liquid crystal[4,5,6], and quantum vortices in superfluid and type-II superconductor[7,8,9,10,11,12,13]
Triangular skyrmion-lattice structures are widely confirmed in various magnets ranging from metallic to insulating compounds[18,19,20,21,22,23], and by various techniques such as Lorentz transmission electron microscopy (TEM) and magnetic force microscopy[24,25]

Summary

Introduction

Topological defects are found ubiquitously in various kinds of matter, such as vortices in type-II superconductors, and magnetic skyrmions in chiral ferromagnets. We report the deformation of the moving magnetic skyrmion lattice in MnSi under electric current flow observed using small-angle neutron scattering. In the pioneering study of Jonietz et al using SANS, a rotation of the skyrmion lattice in MnSi was detected for an electric current density greater than the threshold value jt ~ 1 MA m−2 31. From a Lorentz TEM study of FeGe, the skyrmion lattice was observed to ‘disappear’ as the electric current exceeded a threshold value, indicating the skyrmion lattice to move much faster than the Lorentz TEM time frame[34]. Important microscopic information, such as the skyrmion-lattice deformation, under thermally homogeneous conditions remains largely unexplored

Methods

Results

Conclusion