Unusual spin-wave population in nickel after femtosecond laser pulse excitation

TL;DR

This study investigates the unusual behavior of spin-wave populations in nickel after femtosecond laser excitation, revealing a non-linear mode discontinuity and energy redistribution in the spin-wave spectrum.

Contribution

It uncovers a non-linear process causing a mode discontinuity and energy redistribution in nickel's spin-wave spectrum post laser excitation.

Findings

Identification of uniform precession, Damon-Eshbach modes, and standing spin waves

Observation of a mode discontinuity deviating from expected dispersion

Detection of energy redistribution within the spin-wave spectrum

Abstract

The spin-wave relaxation mechanisms after intense laser excitation in ferromagnetic nickel films are investigated with all-optical pump-probe experiments. Uniform precession (Kittel mode), Damon-Eshbach surface modes and perpendicular standing spin waves can be identified by their dispersion f(H). However, different to other ferromagnets f(H) deviates from the expected behavior. Namely, a mode discontinuity is observed, that can be attributed to a non-linear process. Above a critical field the power spectrum reveals a redistribution of the energy within the spin-wave spectrum populated.