# Optical excitation of propagating magnetostatic waves in an epitaxial Galfenol film by an ultrafast magnetic anisotropy change

## TL;DR

This study demonstrates laser-driven excitation and propagation of spin waves in epitaxial Galfenol films via ultrafast magnetic anisotropy changes, highlighting their potential for magnonic device applications.

## Contribution

It introduces a novel all-optical method using thermal anisotropy changes to excite and control spin waves in epitaxial Galfenol films, expanding material options for magnonics.

## Key findings

- Spin waves are excited and propagate up to 10 μm in Galfenol films.
- Laser pulses induce magnetostatic surface waves with a 3.4 μm propagation length.
- Magnetic field orientation controls wave frequency, amplitude, and length.

## Abstract

Using a time-resolved optically-pumped scanning optical microscopy technique we demonstrate the laser-driven excitation and propagation of spin waves in a 20-nm film of a ferromagnetic metallic alloy Galfenol epitaxially grown on a GaAs substrate. In contrast to previous all-optical studies of spin waves we employ laser-induced thermal changes of magnetocrystalline anisotropy as an excitation mechanism. A tightly focused 70-fs laser pulse excites packets of magnetostatic surface waves with a $e^{-1}$ propagation length of 3.4 $\mu$m, which is comparable with that of permalloy. As a result, laser-driven magnetostatic spin waves are clearly detectable at distances up to 10 $\mu$m, which promotes epitaxial Galfenol films to the limited family of materials suitable for magnonic devices. A pronounced in-plane magnetocrystalline anisotropy of the Galfenol film offers an additional degree of freedom for manipulating the spin waves' parameters. Reorientation of an in-plane external magnetic field relative to the crystallographic axes of the sample tunes the frequency, amplitude and propagation length of the excited waves.