Parametric resonance of spin waves in ferromagnetic nanowires tuned by spin Hall torque

TL;DR

This study investigates how spin wave eigenmodes in ferromagnetic nanowires can be parametrically excited and tuned using spin Hall torque, revealing edge magnetic properties and discrepancies with theoretical models.

Contribution

It provides a combined experimental and theoretical analysis of spin wave resonance in nanowires, highlighting the influence of edge effects on mode ellipticity and resonance thresholds.

Findings

Good agreement between theory and experiment for bulk modes

Discrepancies in edge mode behavior suggest altered edge magnetism

Spin Hall torque effectively tunes parametric resonance thresholds

Abstract

We present a joint experimental and theoretical study of parametric resonance of spin wave eigenmodes in Ni$_{80}$Fe$_{20}$/Pt bilayer nanowires. Using electrically detected magnetic resonance, we measure the spectrum of spin wave eigenmodes in transversely magnetized nanowires and study parametric excitation of these eigenmodes by a microwave magnetic field. We also develop an analytical theory of spin wave eigenmodes and their parametric excitation in the nanowire geometry that takes into account magnetic dilution at the nanowire edges. We measure tuning of the parametric resonance threshold by antidamping spin Hall torque from a direct current for the edge and bulk eigenmodes, which allows us to independently evaluate frequency, damping and ellipticity of the modes. We find good agreement between theory and experiment for parametric resonance of the bulk eigenmodes but significant discrepancies arise for the edge modes. The data reveals that ellipticity of the edge modes is significantly lower than expected, which can be attributed to strong modification of magnetism at the nanowire edges. Our work demonstrates that parametric resonance of spin wave eigenmodes is a sensitive probe of magnetic properties at edges of thin-film nanomagnets.