SPIN RELAXATION OF MN IONS IN (CDMN)TE (CDMG)TE QUANTUM-WELLS UNDER PICOSECOND OPTICAL-PUMPING/

Spin relaxation of Mn ions in a Cd0.97Mn0.03Te/Cd0.75Mg0.25Te quantum well with photogenerated quasi-two-dimensional electron-hole plasma at liquid helium temperatures in an external magnetic field has been inv estigated. Heating of Mn ions by photogenerated carriers due to spin a nd energy exchange between the hot electron-hole plasma and Mn ions th rough direct sd-interaction between electron and Mn spins has been det ected. This process has a short characteristic time of about 4 ns, whi ch leads ttl appreciable heating of the Mn spin subsystem in about 0.5 ns. Even under uniform excitation of a dense electron-hole plasma, th e Mn heating is spatially nonuniform, and leads to formation of spin d omains in the quantum well magnetic subsystem. The relaxation time of spin domains after pulsed excitation is measured to be about 70 ns. En ergy relaxation of excitons in the random exchange potential due to sp in domains results from exciton diffusion in magnetic field B = 14 T w ith a characteristic time of I to 4 ns. The relaxation time decreases with decreasing optical pump power, which indicates smaller dimensions of spin domains, In weak magnetic fields (B = 2 T) a slow down in the exciton diffusion to 15 ms has been detected. This slow down is due t o exciton binding to neutral donors (formation of bound excitons) and smaller spin domain amplitudes in low magnetic fields. The optically d etermined spin-lattice relaxation time of Mn ions in a magnetic field of 14 T is 270 +/- 10 and 16 +/- 7 ns for Mn concentrations of 3% and 12%, respectively. (C) 1997 American Institute of Physics.