Proper dissipative torques in antiferromagnetic dynamics

¹ Department of Physics, Southern University of Science and Technology - Shenzhen 518055, China
² Institute for Quantum Science and Engineering and Department of Physics, Southern University of Science and Technology - Shenzhen, 518055, China
³ The Center for Advanced Quantum Studies and Department of Physics, Beijing Normal University Beijing 100875, China
⁴ Physics Department, The Hong Kong University of Science and Technology - Clear Water Bay, Kowloon, Hong Kong
⁵ HKUST Shenzhen Research Institute - Shenzhen 518057, China

^(a) zyuan@bnu.edu.cn
^(b) phxwan@ust.hk

Received: 24 April 2019
Accepted: 24 June 2019

Abstract

There is little doubt that the magnetization dynamics of ferromagnetic systems is governed by the Landau-Lifshitz-Gilbert equation or its generalization with various spin torques. In contrast, there are several sets of dynamic equations for two-sublattice antiferromagnets (AFMs) in the literature that have different forms of dissipative torques and no proper dynamic equations for multi-sublattice AFMs and ferrimagnets in general. Here we introduce the general Rayleigh dissipation functional into the Lagrange equation and derive the proper form of the dissipative torques in the phenomenological equations for the AFMs with multiple sublattices. A new type of dissipative torque arising from the inter-sublattice drag effect is discovered which has important effects on the magnon lifetime and domain wall motion.