Coherent Magnetization Precession in GaMnAs induced by Ultrafast Optical Excitation

TL;DR

This study demonstrates how femtosecond optical pulses can induce and control coherent magnetization precession in GaMnAs, revealing insights into spin dynamics and damping mechanisms at low temperatures.

Contribution

It provides new understanding of ultrafast optical control of magnetization precession and the dependence of damping on laser intensity in ferromagnetic GaMnAs.

Findings

Coherent oscillations of Mn spins observed below 40 K

Precession amplitude saturates above certain pump intensity

Damping depends on laser intensity, not temperature

Abstract

We use femtosecond optical pulses to induce, control and monitor magnetization precession in ferromagnetic Ga0.965Mn0.035As. At temperatures below ~40 K we observe coherent oscillations of the local Mn spins, triggered by an ultrafast photoinduced reorientation of the in-plane easy axis. The amplitude saturation of the oscillations above a certain pump intensity indicates that the easy axis remains unchanged above ~TC/2. We find that the observed magnetization precession damping (Gilbert damping) is strongly dependent on pump laser intensity, but largely independent on ambient temperature. We provide a physical interpretation of the observed light-induced collective Mn-spin relaxation and precession.