Ultrafast magneto-optical spectroscopy of GaMnAs

摘要

Spin dynamics in the III-V dilute magnetic semiconductor GaMnAs is investigated by photo-induceddemagnetization. Experimental results obtained from two different time-dependent characterization techniques – “twocolor-probe” magneto-optical Kerr effect (TR-MOKE) and mid-infrared differential transmittance – are compared.Upon photo-excitation with a 100 fs, 3.1 eV light pulse, a long demagnetization time in the hundreds of picosecondstimescale is found by TR-MOKE, indicating a spin-dependent band structure in this material. In mid-infraredmeasurements, a positive increase of the differential transmittance is observed in the same time interval when the sampleis cooled below its Currie temperature. It is shown that this mid-infrared absorption feature is directly related toferromagnetism in this material. The magnetism-related component of the broad DC mid-infrared absorption peakcharacteristic of this p-type material could be observed with this time-resolved measurement. Experimental results weresimulated with a model describing the interaction between three thermal reservoirs (hole, spin and lattice) and takingthermal diffusion into account.