Pressure Dependence of Exchange Interactions in Diluted Magnetic Semiconductors Studied by High-Field Magnetophotoluminescence(Research in High Magnetic Fields)

Effects of hydrostatic pressure on the magnetophotoluminescence due to the A-exciton have been investigated in Cd_Co_Se, Cd_Mn_Se and Cd_Mn_Se at 1.4 K and 4.2 K. In all the substances pressure strengthens the exchange interaction between the exciton and transition-metal ions substituted for Cd of the host CdSe lattice. The stepwise magnetization of paired Mn ions has been successfully observed in Cd_Mn_Se under hydrostatic pressures up to 1.9 GPa at 1.4 K. The stepwise anomalies are found to shift toward higher magnetic fields with increasing pressure, indicating that the Mn-Mn superexchange coupling is strengthened also by pressure. It emerges from an analysis of these findings based on the Mott-Hubbard model that the effective on-site Coulomb energy is significantly reduced by pressure