Quantification of a propagating spin-wave-packet created by an ultrashort laser pulse in a thin film of magnetic metal

TL;DR

This study demonstrates the generation and propagation of a spin-wave packet in a permalloy thin film induced by ultrashort laser pulses, with detailed measurements and theoretical explanation of its properties.

Contribution

It provides a quantitative analysis of laser-induced spin-wave propagation in a magnetic thin film, highlighting the mechanisms and measurable parameters involved.

Findings

Propagating spin-wave observed perpendicular to magnetization

Propagation length and velocity measured and explained

Spin-wave propagation driven by ultrafast demagnetization field change

Abstract

Coherent spin-wave generation by focused ultrashort laser pulse irradiation was investigated for a permalloy thin film at micrometer scale using an all-optical space and time-resolved magneto-optical Kerr effect. The spin-wave packet propagating perpendicular to magnetization direction was clearly observed, however that propagating parallel to the magnetization direction was not observed. The propagation length, group velocity, center frequency, and packet-width of the observed spin-wave packet were evaluated and quantitatively explained in terms of the propagation of a magneto-static spin-wave driven by ultrafast change of an out-of-plane demagnetization field induced by the focused-pulse laser.