Observation of the spin-charge thermal isolation of ferromagnetic Ga 0.94 Mn 0.06 As by time-resolved magneto-optical measurements

The dynamics of magnetization under femtosecond optical excitation is studied in a ferromagnetic semiconductor ${\mathrm{Ga}}_{0.94}{\mathrm{Mn}}_{0.06}\mathrm{As}$ with a time-resolved magneto-optical Kerr effect measurement with two-color probe beams. The transient reflectivity change indicates the rapid rise of the carrier temperature and relaxation to a quasithermal equilibrium within a few ps, while a very slow rise of the spin temperature of the order of 500 ps is observed. This anomalous behavior originates from the thermal isolation between the charge and spin systems due to the spin polarization of carriers (holes) contributing to ferromagnetism. This constitutes experimental proof of the half-metallic nature of ferromagnetic ${\mathrm{Ga}}_{0.94}{\mathrm{Mn}}_{0.06}\mathrm{As}$ arising from the large exchange energy of carriers compared to Fermi energy.