Low-temperature magnetic spectroscopy of a dilute magnetic semiconductor

A newly developed integrated SQUID magnetic spectrometer yields direct high-resolution measurements of the optically induced magnetization in a 10 μm-diam sample of ${\mathrm{Cd}}_{0.8}$ ${\mathrm{Mn}}_{0.2}$Te. Both the magnitude and the picosecond dynamics of the magnetic response have been studied and are seen to be dramatically dependent on the energy and polarization of the optical excitation. The data show that the overall sample magnetization changes upon illumination, and that the perturbed spins equilibrate through spin-lattice relaxation.