Collective spin dynamics under dissipative spin Hall torque

TL;DR

This paper develops a general theoretical framework to analyze how dissipative spin Hall torques influence the collective spin dynamics across various magnetic materials, revealing different behaviors like switching and limit cycles.

Contribution

It introduces a Lagrangian-Rayleigh approach to study dissipative torques in diverse magnetic systems, highlighting their effects on stability and dynamic regimes.

Findings

Dissipative torques can induce dynamic instabilities in magnetic systems.

The behavior depends on the magnetic order, with unipolar switching in ferromagnets.

Limit cycles with chirality emerge in magnetically compensated materials.

Abstract

Current-induced spin torques in layered magnetic heterostructures have many commonalities across broad classes of magnetic materials. These include not only collinear ferromagnets, ferrimagnets, and antiferromagnets, but also more complex noncollinear spin systems. We develop a general Lagrangian-Rayleigh approach for studying the role of dissipative torques, which can pump energy into long-wavelength magnetic dynamics, causing dynamic instabilities. While the Rayleigh structure of such torques is similar for different magnetic materials, their consequences depend sensitively on the nature of the order and, in particular, on whether there is a net magnetic moment. The latter endows the system with a unipolar switching capability, while magnetically compensated materials tend to evolve towards limit cycles, at large torques, with chirality dependent on the torque sign. Apart from the ferromagnetic and antiferromagnetic cases, we discuss ferrimagnets, which display an intricate competition between switching and limit cycles. As a simple case for compensated noncollinear order, we consider isotropic spin glasses, as well as a scenario of their coexistence with a collinear magnetic order.