Nonlinear sub-switching regime of magnetization dynamics in photo-magnetic garnets

TL;DR

This study investigates the nonlinear behavior of photo-induced magnetization dynamics in garnet films, revealing how laser fluence and magnetic field influence spin precession through anharmonic energy landscapes.

Contribution

It provides a combined experimental and numerical analysis of nonlinear spin dynamics, emphasizing the role of magnetic symmetry and energy landscape anharmonicity.

Findings

Nonlinear spin response increases with laser fluence.

Magnetic energy landscape anharmonicity causes nonlinearity.

Numerical mapping of spin dynamics below switching threshold.

Abstract

We analyze, both experimentally and numerically, the nonlinear regime of the photo-induced coherent magnetization dynamics in cobalt-doped yttrium iron garnet films. Photo-magnetic excitation with femtosecond laser pulses reveals a strongly nonlinear response of the spin subsystem with a significant increase of the effective Gilbert damping. By varying both laser fluence and the external magnetic field, we show that this nonlinearity originates in the anharmonicity of the magnetic energy landscape. We numerically map the parameter workspace for the nonlinear photo-induced spin dynamics below the photo-magnetic switching threshold. Corroborated by numerical simulations of the Landau-Lifshitz-Gilbert equation, our results highlight the key role of the cubic symmetry of the magnetic subsystem in reaching the nonlinear spin precession regime. These findings expand the fundamental understanding of laser-induced nonlinear spin dynamics as well as facilitate the development of applied photo-magnetism.