Phase-resolved imaging of edge-mode spin waves using scanning transmission x-ray microscopy

TL;DR

This study uses time-resolved scanning transmission x-ray microscopy to image and analyze localized spin-wave eigenmodes in nanoscale NiFe ellipses, revealing phase behavior influenced by conductive overlayers and demonstrating STXM's nanoscale imaging capabilities.

Contribution

It introduces a method to image small-amplitude GHz spin waves with high spatial resolution and explores the influence of overlayers on phase behavior.

Findings

Magnetization precession varies from in-phase to out-of-phase with different overlayers.

Strong Oersted fields are generated in the overlayer, affecting phase.

STXM can image GHz magnetization dynamics at the nanoscale.

Abstract

We have imaged the excitation of small-amplitude spin-wave eigenmodes, localized within $\sim$ 100 nm of the vertices of nanoscale Ni$_{81}$Fe$_{19}$ ellipses, using time-resolved scanning transmission x-ray microscopy (STXM) at 2 GHz and resolution of 70 nm. Taking advantage of the buried-layer sensitivity of STXM, we find that the magnetization precession at the two vertices changes from predominantly in-phase to out-of-phase in samples with and without a conductive layer deposited over the ellipses. As a plausible interpretation for the reversal in phase, we propose that unexpectedly strong Oersted fields are generated in the discontinuous overlayer, although effects of edge roughness cannot be fully excluded. The results demonstrate the capabilities of STXM to image small-amplitude, GHz magnetization dynamics with the potential to map rf magnetic fields on the nanoscale.