Spin pumping in noncollinear antiferromagnets

The spin pumping and spin-transfer torque (STT) mechanisms in antiferromagnets have been theoretically and experimentally investigated in recent years. However, most of these works have concentrated on collinear antiferromagnets, leaving the spin dynamics of the more complex noncollinear antiferromagnets largely unexplored. In this talk, I will present our latest work [1] on ac spin pumping in non-collinear antiferromagnets. Starting from an effective theory of the spin system, we derive the Onsager coefficients connecting the spin pumping and STT associated with the dynamics of the SO(3)-valued antiferromagnetic order parameter. Our theory is applied to a kagome AFM resonantly driven by a uniform external magnetic field. We demonstrate that the reactive (dissipative) STT parameter can be extracted from the pumped ac spin-current in phase (in quadrature) with the driving field. Furthermore, we find that the three spin-wave bands of the kagome AFM generate spin currents with mutually orthogonal polarization directions. This offers a unique way of controlling the spin orientation of the pumped spin current by exciting different spin-wave modes.



[1] M. A. Lund, A. Salimath, K. M. D. Hals, Phys. Rev. B 104, 174424 (2021).