Eddy-current effects on ferromagnetic resonance: Spin wave excitations and microwave screening effects

TL;DR

This paper explores how eddy currents in thin ferromagnetic-normal metal structures can be used to manipulate local microwave fields, enabling selective screening and excitation of non-zero wave vector spin wave modes in ferromagnetic resonance experiments.

Contribution

It demonstrates that eddy currents can be controlled to tailor microwave fields and excite specific spin wave modes, offering new ways to manipulate magnetic resonance phenomena.

Findings

Eddy currents can partially screen the applied microwave field.

Localized eddy-current fields enable excitation of non-zero wave vector spin waves.

Orientation of the microwave field significantly affects eddy-current effects.

Abstract

We investigate how controlling induced eddy currents in thin film ferromagnet-normal metal (FM/NM) structures can be used to tailor the local microwave (MW) fields in ferromagnetic resonance (FMR) experiments. The MW fields produced by eddy currents will in general have a relative phase shift with respect to the applied MW field which depends on the sample geometry. The induced fields can thus partially compensate the applied MW field, effectively screening the FM in selected parts of the sample. The highly localized fields produced by eddy currents enable the excitation of spin wave modes with non-zero wave vectors, in contrast to the uniform k = 0 mode normally excited in FMR experiments. We find that the orientation of the applied MW field is one of the key parameters controlling the eddy-current effects. The induced currents are maximized when the applied MW field is oriented perpendicular to the sample plane. Increasing the magnitude of the eddy currents results in a stronger induced MW field, enabling a more effective screening of the applied MW field as well as an enhanced excitation of spin wave modes. This investigation underlines that eddy currents can be used to control the magnitude and phase of the local MW fields in thin film structures.