Spin-conserving scattering of holes by magnetic ions in semimagnetic quantum wells

Abstract

We have calculated the characteristic time for the direct heating of the Mn spin system by spin-polarized photoexcited holes as well as the relaxation time for a single hole in semimagnetic quantum wells in an external longitudinal magnetic field. This spin-conserving heating process is due to the $p\text{\ensuremath{-}}d$ exchange interaction-induced scattering of the holes with the Mn ions within the first heavy-hole subband. The relaxation time for a single hole determines the maximum relative change of the magnetization in the case of short (femtosecond) pulse excitation. Numerical calculations are given for the example of (Zn,Mn)Se-based quantum wells. Due to the strong spin-orbit and exchange interactions within the valence band, the photoexcited hole gas heats the Mn spin system on a nanosecond time scale. This is much more effective than for an electron gas under similar conditions, for which the corresponding characteristic time lies in microsecond range. For a single hole, the relaxation time is much smaller than the characteristic heating time and, for typical experimental conditions, lies in the picosecond range. In the frame of the developed theoretical model, we analyze the details of the dependence of the Mn heating on the hole concentration and temperature on the Mn content and on magnetic field.