Hierarchy of relaxation times in the system of Mn-ion spins in photoexcited semimagnetic quantum wells

Energy and spin relaxation in a Mn-ion system has been investigated in (Cd,Mn) Te/(Cd,Mg) Te semimagnetic quantum wells photoexcited by 70-ps laser pulses at the magnetic field $B=14\mathrm{}$ T with the use of a pump-probe technique. An effective (within characteristic time of 0.5 ns) energy transfer from photoexcited carriers to the Mn-ion spin system has been established. It leads to the formation of spatial microdomains with an elevated Mn-ion spin temperature. Two strongly different relaxation times ${\tau }_1=4\mathrm{}$ ns and ${\tau }_2=270\mathrm{}$ ns were found from the exciton emission line shift. The short one appears in the measurements during the decay of the excitons generated with the strong pump pulse and reflects the exciton diffusion from hot microdomains. The long time corresponds to the Mn-spin-lattice relaxation: it has been found from the time dependence of the energy of the excitons generated with weak probe laser pulses.