Coherent Magnetization Precession in GaMnAs induced by Ultrafast Optical Excitation

摘要

We use femtosecond optical pulses to induce, control and monitormagnetization precession in ferromagnetic Ga0.965Mn0.035As. At temperaturesbelow ~40 K we observe coherent oscillations of the local Mn spins, triggeredby an ultrafast photoinduced reorientation of the in-plane easy axis. Theamplitude saturation of the oscillations above a certain pump intensityindicates that the easy axis remains unchanged above ~TC/2. We find that theobserved magnetization precession damping (Gilbert damping) is stronglydependent on pump laser intensity, but largely independent on ambienttemperature. We provide a physical interpretation of the observed light-inducedcollective Mn-spin relaxation and precession.