Indirect excitation of self-oscillation in perpendicular ferromagnet by spin Hall effect

TL;DR

This paper theoretically explores how adding a pinned layer enables stable self-oscillation in a perpendicular ferromagnet via the spin Hall effect, which was previously unachievable with direct spin torque alone.

Contribution

It introduces a novel method of inducing stable self-oscillation by combining spin Hall effect with an additional pinned layer providing reflected spin torque.

Findings

Stable self-oscillation achieved with tilted pinned layer

Reflection of spin current enhances oscillation stability

Self-oscillation not possible with direct spin torque alone

Abstract

A possibility to excite a stable self-oscillation in a perpendicularly magnetized ferromagnet by the spin Hall effect is investigated theoretically. It had been shown that such self-oscillation cannot be stabilized solely by the direct spin torque by the spin Hall effect. Here, we consider adding another ferromagnet, referred to as pinned layer, on the free layer. The pinned layer provides another spin torque through the reflection of the spin current. The study shows that the stable self-oscillation is excited by the additional spin torque when the magnetization in the pinned layer is tilted from the film plane.