Magnetic-field dependence of electron-spin relaxation in a diluted magnetic semiconductor quantum well studied by pump-probe absorption spectroscopy

We study the spin dynamics of photo-excited carriers in a diluted magnetic Cd0.95Mn0.05Te quantum well by means of pump-probe absorption spectroscopy. Transient differential absorption intensities, which are discriminated with left/right circular polarizations, indicate the spin-relaxation dynamics after pumping. Time constants of 0.5 and 7 ps are obtained for the heavy-hole (hh)- and electron-spin relaxations at 0 T, where the electron-spin relaxation is mainly caused by the s-d exchange mechanism involving Mn-spins. We observe a systematic increase in the electron-spin relaxation time up to 19 ps with an increase in the magnetic field up to 2.5 T. We attribute this to suppression of the electron-spin relaxation via the s-d exchange mechanism, where the spin transfer from the electron to the Mn-spin requires energy compensation due to the Zeeman splitting of the Mn-spin under magnetic fields. Above 3 T, the electron-spin relaxation time decreases with increasing magnetic field, possibly resulting from LO-phonon scattering involving acoustic phonons and Mn-spins. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim