Nonlinear analysis of magnetization dynamics excited by spin Hall effect

TL;DR

This paper analyzes whether spin Hall effect can induce self-oscillation in perpendicular ferromagnets, concluding that it cannot due to the failure to meet specific energy and current conditions based on nonlinear LLG equation analysis.

Contribution

It provides a nonlinear analytical investigation showing that spin Hall torque alone cannot excite self-oscillation in perpendicular ferromagnets, clarifying limitations of spin Hall effect-driven dynamics.

Findings

Self-oscillation cannot be excited solely by spin Hall torque.

Analytical solutions show the second condition for self-oscillation is not satisfied.

The study clarifies the limitations of spin Hall effect in magnetization dynamics.

Abstract

We investigate the possibility of exciting self-oscillation in a perpendicular ferromagnet by the spin Hall effect on the basis of a nonlinear analysis of the Landau-Lifshitz-Gilbert (LLG) equation. In the self-oscillation state, the energy supplied by the spin torque during a precession on a constant energy curve should equal the dissipation due to damping. Also, the current to balance the spin torque and the damping torque in the self-oscillation state should be larger than the critical current to destabilize the initial state. We find that the second condition in the spin Hall system is not satisfied by deriving analytical solutions of the energy supplied by the spin transfer effect and the dissipation due to the damping from the nonlinear LLG equation. This indicates that the self-oscillation of a perpendicular ferromagnet cannot be excited solely by the spin Hall torque.