Magnon-mediated Dzyaloshinskii-Moriya torque in homogeneous ferromagnets

Abstract

In thin magnetic layers with structural inversion asymmetry and spin-orbit coupling, the DzyaloshinskiiMoriya interaction arises at the interface. When a spin-wave current j(m) flows in a system with a homogeneous magnetization m, this interaction produces an effective fieldlike torque of the form T-FL alpha m x (z x j(m)) as well as a dampinglike torque, T-DL alpha m x [(z x j(m)) x m], the latter only in the presence of spin-wave relaxation (z is normal to the interface). These torques mediated by the magnon flow can reorient the time-averaged magnetization direction and display a number of similarities with the torques arising from the electron flow in a magnetic two-dimensional electron gas with Rashba spin-orbit coupling. This magnon-mediated spin-orbit torque can be efficient in the case of magnons driven by a thermal gradient.