Current-induced rotational torques in the skyrmion lattice phase of chiral magnets

Abstract

In chiral magnets without inversion symmetry, the magnetic structure can form a lattice of magnetic whirl lines, a two-dimensional skyrmion lattice, stabilized by spin-orbit interactions in a small range of temperatures and magnetic fields. The twist of the magnetization within this phase gives rise to an efficient coupling of macroscopic magnetic domains to spin currents. We analyze the resulting spin-transfer effects, and, in particular, focus on the current-induced rotation of the magnetic texture by an angle. Such a rotation can arise from macroscopic temperature gradients in the system as has recently been shown experimentally and theoretically. Here we investigate an alternative mechanism, where small distortions of the skyrmion lattice and the transfer of angular momentum to the underlying atomic lattice play the key role. We employ the Landau-Lifshitz-Gilbert equation and adapt the Thiele method to derive an effective equation of motion for the rotational degree of freedom. We discuss the dependence of the rotation angle on the orientation of the applied magnetic field and the distance to the phase transition.

Scattering of high-energy magnons off a magnetic skyrmion

“…(19) so that the scattering has a purely magnetic character. In particular, in this limit one can neglect the anomalous potential V x , and the BdG equation (14) reduces to a Schrödinger equation for the magnon wavefunction…”

“…In turn, a finite winding number W translates to a gyrocoupling vector G in the Thiele equation of motion of the skyrmion, 38 and the resulting gyrotropic spin-Magnus force governs its dynamics. 39 As a consequence, in the presence of an applied electronic spin current, the skyrmions will acquire a velocity 14,15,17 that remains finite in the limit of adiabatic spin-transfer torques and small Gilbert damping α, giving rise to a universal current-velocity relation. 18 In order to address the interaction of magnon currents with magnetic textures, a corresponding adiabatic approximation has been recently invoked on the level of the Landau-Lifshitz-Gilbert equation by Kovalev and Tserkovnyak.…”

Breathing modes of confined skyrmions in ultrathin magnetic dots

“…Their topological nature has important consequences on electron and heat transport, 15,16 which lead to novel features involving current-driven dynamics of skyrmion lattices. [17][18][19] A recent demonstration of the controlled nucleation and annihilation of isolated skyrmions 20 is promising for future applications exploiting these objects for information storage and processing.…”

Charged skyrmions on the surface of a topological insulator

“…Electric fields as low as 10 2 V/m can induce drift velocities v H ∼ 0.1 mm/s, comparable to skyrmions driven by conduction electrons in metallic systems 42 , according to the STT mechanism (Ref. 26,27,32,43,44 and references therein). In the system under consideration the skyrmionic material is insulating and the the surface spectrum of TI is gapped away from the skyrmion, which makes the STT mechanism unimportant.…”