Collective magnetization dynamics in ferromagnetic (Ga,Mn)As mediated by photo-excited carriers

TL;DR

This study investigates how ultrafast laser pulses influence magnetization precession in ferromagnetic (Ga,Mn)As, revealing a transition from thermal to non-thermal control mechanisms near the band-edge.

Contribution

It demonstrates the dependence of magnetization dynamics on photon energy and distinguishes thermal from non-thermal excitation pathways in ferromagnetic semiconductors.

Findings

Magnetization precession depends strongly on photon energy near the band-edge.

Laser heating and hole-induced effects modulate magnetic anisotropy.

Identification of thermal versus non-thermal mechanisms in ultrafast magnetization control.

Abstract

We present a study of photo-excited magnetization dynamics in ferromagnetic (Ga,Mn)As films observed by time-resolved magneto-optical measurements. The magnetization precession triggered by linearly polarized optical pulses in the absence of an external field shows a strong dependence on photon frequency when the photo-excitation energy approaches the band-edge of (Ga,Mn)As. This can be understood in terms of magnetic anisotropy modulation by both laser heating of the sample and by hole-induced non-thermal paths. Our findings provide a means for identifying the transition of laser-triggered magnetization dynamics from thermal to non-thermal mechanisms, a result that is of importance for ultrafast optical spin manipulation in ferromagnetic materials via non-thermal paths.