Magnetic relaxation studied by transient reflectivity inCd1−xMnxTe

We show that the study of transient reflectivity in diluted magnetic semiconductors gives access to magnetic relaxation. Magnetization is carried out of equilibrium by above-band-gap laser pulse and thermalization of the spin system is probed by time-resolved reflectivity in the free exciton energy range. Spin relaxation times have been measured in ${\mathrm{Cd}}_{1-x}{\mathrm{Mn}}_x\mathrm{Te}$ at liquid-helium temperature for $x$ between 0.16% and 5%. It is shown that the relaxation times measured are characteristic of spin-lattice relaxation and that the phonon-bottleneck effect is circumvented in such experiments. No evidence of ${\mathrm{Mn}}^{2+}$ spin relaxation due to exchange interaction with photocarriers could be found in the experimental conditions investigated.