Giant resonant nonlinear damping in nanoscale ferromagnets

TL;DR

This paper uncovers a giant, frequency-dependent nonlinear damping mechanism in nanoscale ferromagnets caused by three-magnon scattering, significantly impacting magnetic dynamics and spin torque applications.

Contribution

It reveals a previously unknown giant nonlinear damping effect in nanoscale ferromagnets due to geometric confinement and three-magnon scattering, advancing understanding of magnetic dissipation.

Findings

Giant nonlinear damping strongly depends on frequency.

Magnetic damping can be inverted, leading to current-induced damping enhancement.

Three-magnon scattering is enhanced by geometric confinement.

Abstract

Magnetic damping is a key metric for emerging technologies based on magnetic nanoparticles, such as spin torque memory and high-resolution biomagnetic imaging. Despite its importance, understanding of magnetic dissipation in nanoscale ferromagnets remains elusive, and the damping is often treated as a phenomenological constant. Here we report the discovery of a giant frequency-dependent nonlinear damping that strongly alters the response of a nanoscale ferromagnet to spin torque and microwave magnetic field. This novel damping mechanism originates from three-magnon scattering that is strongly enhanced by geometric confinement of magnons in the nanomagnet. We show that the giant nonlinear damping can invert the effect of spin torque on a nanomagnet leading to a surprising current-induced enhancement of damping by an antidamping torque. Our work advances understanding of magnetic dynamics in nanoscale ferromagnets and spin torque devices.