Effect of magnetic anisotropy relaxation on laser-induced magnetization precession in thin galfenol films

TL;DR

This study investigates how magnetic anisotropy and magnetization in thin galfenol films relax after femtosecond laser excitation, revealing their recovery dynamics and impact on magnetization precession frequency over nanoseconds.

Contribution

It provides experimental insights into the relaxation pathways of magnetic anisotropy and magnetization, linking these to the evolution of laser-induced magnetization precession.

Findings

Magnetization and anisotropy recover within a nanosecond.

The ratio of anisotropy to magnetization follows a thermal equilibrium power law.

Relaxation times influence the frequency evolution of precession.

Abstract

The rate and pathways of relaxation of a magnetic medium to its equilibrium following excitation with intense and short laser pulses are the key ingredients of ultrafast optical control of spins. Here we study experimentally the evolution of the magnetization and magnetic anisotropy of thin films of a ferromagnetic metal galfenol (Fe$_{0.81}$Ga$_{0.19}$) resulting from excitation with a femtosecond laser pulse. From the temporal evolution of the hysteresis loops we deduce that the magnetization $M_S$ and magnetic anisotropy parameters $K$ recover within a nanosecond, and the ratio between $K$ and $M_S$ satisfies the thermal equilibrium's power law in the whole time range spanning from a few picoseconds to 3 nanoseconds. We further use the experimentally obtained relaxation times of $M_S$ and $K$ to analyze the laser-induced precession and demonstrate how they contribute to its frequency evolution at the nanosecond timescale.