Reflectance difference spectroscopy and magneto-optical analysis of digital magnetic heterostructures

We report on the investigation of CdTe/Cd0.75Mg0.25Te quantum wells grown b y molecular-beam epitaxy and containing a digital distribution of magnetic MnTe fractional monolayers in the well. The influence of electronic confine ment and of exciton primary localization on the formation of ferromagnetic ordering on the scale of small spin clusters (polarons) has been investigat ed by performing selective excitation of the exciton luminescence. The calc ulated temperature dependence of the free magnetic polarons binding energy F is found to qualitatively agree with the photoluminescence excitation dat a and the ferromagnetic clusters result to be more stable in these magnetic structures of reduced dimensionality, with respect to the three-dimensiona l case. The magneto-optical Kerr effect is discussed in the case of reflect ance difference spectroscopy (RDS) and from the angular dependence of the R DS spectra in magnetic field, signals due to interband Faraday rotation and signals originating from crystal anisotropy could be distinguished. The Fa raday rotation in these structures is found to follow the Curie-Weiss law w ith a transition temperature of -6 K corresponding to the nominal ion spin concentration in the magnetic barriers. (C) 1999 American Vacuum Society. [ S0734-211X(99)07304-7].