Skyrmion flow near room temperature in an ultralow current density

Abstract

The manipulation of spin textures with electric currents is an important challenge in the field of spintronics. many attempts have been made to electrically drive magnetic domain walls in ferromagnets, yet the necessary current density remains quite high (~10 7 A cm − 2 ). A recent neutron study combining Hall effect measurements has shown that an ultralow current density of J~10 2 A cm − 2 can trigger the rotational and translational motion of the skyrmion lattice in mnsi, a helimagnet, within a narrow temperature range. Raising the temperature range in which skyrmions are stable and reducing the current required to drive them are therefore desirable objectives. Here we demonstrate near-room-temperature motion of skyrmions driven by electrical currents in a microdevice composed of the helimagnet FeGe, by using in-situ Lorentz transmission electron microscopy. The rotational and translational motions of skyrmion crystal begin under critical current densities far below 100 A cm − 2 .

Universal current-velocity relation of skyrmion motion in chiral magnets

“…This value is an order of magnitude smaller than that for the HL as estimated in Fig. 2 and also as seen experimentally 19 . Fig.…”

Quantized transport for a skyrmion moving on a two-dimensional periodic substrate

“…As an external magnetic field is increased, skyrmions emerge from a spiral state and their density initially increases and then decreases with field until the sample enters a uniform ferromagnetic state 2,3,9 . In bulk samples, skyrmions form three-dimensional (3D) line objects and occur in a limited range of fields and temperatures 2,16 , while for thin samples the skyrmions exhibit two-dimensional (2D) properties and are stable over a much larger range of fields and temperatures extending close to room temperature [4][5][6][7] . Skyrmions can be set into motion through the application of an external current 7,10,[18][19][20] , and it has been shown that there is a critical current above which the skyrmions depin into a sliding state [19][20][21][22][23][24][25][26] .…”

“…In bulk samples, skyrmions form three-dimensional (3D) line objects and occur in a limited range of fields and temperatures 2,16 , while for thin samples the skyrmions exhibit two-dimensional (2D) properties and are stable over a much larger range of fields and temperatures extending close to room temperature [4][5][6][7] . Skyrmions can be set into motion through the application of an external current 7,10,[18][19][20] , and it has been shown that there is a critical current above which the skyrmions depin into a sliding state [19][20][21][22][23][24][25][26] . Skyrmion motion can be directly observed with Lorentz microscopy 7,10 or deduced from changes in the transport properties, permitting the construction of effective skyrmion velocity versus applied force curves that show that the skyrmion velocity increases with increasing current 20 .…”

“…Since this initial discovery there has been tremendous growth in the field as an increasing number of materials have been found that can support a skyrmion phase [3][4][5][6][7][8][9][10] . There are also numerous proposals on how to stabilize skyrmion states by utilizing different materials properties or bilayers [11][12][13][14] .…”

“…There are also numerous proposals on how to stabilize skyrmion states by utilizing different materials properties or bilayers [11][12][13][14] . Direct imaging of skyrmions with Lorentz microscopy [3][4][5]7,10 and other techniques 8,15,16 show that the skyrmions form a triangular lattice and have particle-like properties similar to vortices in type-II superconductors 17 . As an external magnetic field is increased, skyrmions emerge from a spiral state and their density initially increases and then decreases with field until the sample enters a uniform ferromagnetic state 2,3,9 .…”