Spin-Torque Ferromagnetic Resonance Measurements of Damping in Nanomagnets

TL;DR

This study measures the magnetic damping parameter in nanomagnets using ferromagnetic resonance driven by spin-transfer torque, revealing lower damping values than previous large-angle excitation studies, attributed to nonlinear mode excitation.

Contribution

It provides direct measurements of damping in nanomagnets using a novel ferromagnetic resonance method driven by spin-transfer torque, offering insights into damping behavior at nanoscale.

Findings

Measured damping parameters for CoFeB and Py nanomagnets.

Damping values are comparable to extended thin films.

Greater damping in large-angle dynamics due to nonlinear modes.

Abstract

We measure the magnetic damping parameter a in thin film CoFeB and permalloy (Py) nanomagnets at room temperature using ferromagnetic resonance driven by microwave frequency spin-transfer torque. We obtain $\alpha_{CoFeB} = 0.014 \pm 0.003$ and $\alpha_{Py}=0.010 \pm 0.002$, values comparable to measurements for extended thin films, but significantly less than the effective damping determined previously for similar nanomagnets by fits to time-domain studies of large-angle magnetic excitations and magnetic reversal. The greater damping found for the large amplitude nanomagnet dynamics is attributed to the nonlinear excitation of non-uniform magnetic modes.