Universal current-velocity relation of skyrmion motion in chiral magnets

Abstract

Current-driven motion of the magnetic domain wall in ferromagnets is attracting intense attention because of potential applications such as racetrack memory. There, the critical current density to drive the motion is B10 9 -10 12 A m À 2 . The skyrmions recently discovered in chiral magnets have much smaller critical current density of B10 5 -10 6 A m À 2 , but the microscopic mechanism is not yet explored. Here we present a numerical simulation of Landau-Lifshitz-Gilbert equation, which reveals a remarkably robust and universal currentvelocity relation of the skyrmion motion driven by the spin-transfer-torque unaffected by either impurities or nonadiabatic effect in sharp contrast to the case of domain wall or spin helix. Simulation results are analysed using a theory based on Thiele's equation, and it is concluded that this behaviour is due to the Magnus force and flexible shape-deformation of individual skyrmions and skyrmion crystal, which enable them to avoid pinning centres.

Tailoring magnetic skyrmions in ultra-thin transition metal films

“…Figure 3d shows that for fcc Pd stacking the exchange interaction favours the skyrmion over the ferromagnetic state (Eo0). This is in contradiction to the predictions from the micromagnetic model that assumes a ferromagnetic exchange stiffness [1][2][3][4]13,14,[21][22][23]32 . In Pd/Fe/Ir(111), however, we need to consider a ferromagnetic NN exchange that competes with antiferromagnetic interactions beyond the NNs.…”

“…Skyrmions can also be moved by an electric current due to spin-transfer torque at current densities that are five orders of magnitude smaller than those required for domain wall motion 18,19 . This discovery makes skyrmions potentially interesting for future applications in racetrack-like memories 15 and sparked great interest in exploring current-induced skyrmion motion [20][21][22][23] .…”

Skyrmions in square-lattice antiferromagnets

“…Secondly, skyrmions in an antiferromagnet are less sensitive to magnetic fields. Thirdly, they move faster, and in the direction of the charge current (while skyrmions in ferromagnets experience a Magnus force with a significant component perpendicular to their trajectory [19]), which makes it easier to control them [20]. For these reasons, skyrmions have been investigated in many different antiferromagnetic systems, ranging from doped bulk materials [21], Bose-Einstein condensates [22], and various triangular lattice antiferromagnets [23,24] to nanodisks [25].…”

Creation of skyrmions and antiskyrmions by local heating

“…This fact enables richer skyrmion structures in the latter case compared with the former case 11 . The equilibrium properties of skyrmions as well as the current-driven dynamics of skyrmions have been recently studied intensively [12][13][14][15][16][17][18] . Time-dependent nonequilibrium dynamics is an issue of great interest; however, the experimental approach has been rather limited: A Lorentz microscope can map the in-plane components of the magnetization, but the time resolution is of the order of a second, and one cannot follow the rapid dynamics 4 .…”