Nonlocal feedback in ferromagnetic resonance

TL;DR

This paper investigates how nonlocal spatiotemporal feedback influences ferromagnetic resonance in thin films, deriving an analytical linewidth expression that accounts for damping and retardation effects, revealing nonlinear frequency dependence.

Contribution

It introduces a comprehensive model incorporating nonlocal feedback effects into ferromagnetic resonance analysis, extending traditional theories with new damping and retardation considerations.

Findings

Derived an analytical linewidth expression including retardation effects.

Identified nonlinear frequency dependence of linewidth due to feedback.

Showed relevance of the model to experimental ferromagnetic resonance data.

Abstract

Ferromagnetic resonance in thin films is analyzed under the influence of spatiotemporal feedback effects. The equation of motion for the magnetization dynamics is nonlocal in both space and time and includes isotropic, anisotropic and dipolar energy contributions as well as the conserved Gilbert- and the non-conserved Bloch-damping. We derive an analytical expression for the peak-to-peak linewidth. It consists of four separate parts originated by Gilbert damping, Bloch-damping, a mixed Gilbert-Bloch component and a contribution arising from retardation. In an intermediate frequency regime the results are comparable with the commonly used Landau-Lifshitz-Gilbert theory combined with two-magnon processes. Retardation effects together with Gilbert damping lead to a linewidth the frequency dependence of which becomes strongly nonlinear. The relevance and the applicability of our approach to ferromagnetic resonance experiments is discussed.