Effects of lateral device size and material properties on the ferromagnetic resonance response of spinwave eigen-modes in magnetic devices

TL;DR

This study investigates how the size and material properties of magnetic devices influence their ferromagnetic resonance responses, revealing significant size-dependent variations and mode evolutions that impact magnetic parameter measurements.

Contribution

It demonstrates the size-dependent effects on FMR responses and explains the underlying eigen-mode evolutions, providing insights for accurate magnetic parameter extraction in nanostructured devices.

Findings

FMR response varies significantly with device size and material properties.

Eigen-mode evolution explains size-dependent trends in damping.

Device size can cause up to 40% apparent increase in damping.

Abstract

We analyze the effects of lateral device size and magnetic material parameters on the ferromagnetic resonance (FMR) response. Results presented are directly relevant to widely used FMR experimental techniques for extracting magnetic parameters from thin films, the results of which are often assumed to carry over to corresponding nanometer-sized patterned devices. We show that there can be significant variation in the FMR response with device size, and that the extent of the variation depends on the magnetic material properties. This explains, for example, why different experiments along these lines have yielded different size-dependent trends from damping measurements. Observed trends with increasing size and different material parameters are explained through the evolution of three distinct eigen-modes, demonstrating the respective roles of demagnetization and exchange. It is also shown that there is a crossover of dominant eigen-modes in the response signal, accompanied by conjugating edge-type modes, leading to evident effects in measured linewidth and damping. Among the sizes considered, in higher saturation magnetization, we observe as much as a 40% increase in apparent damping, due solely to device size variation.