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

Abstract

We report on the investigation of CdTe/Cd0.75Mg0.25Te quantum wells grown by molecular-beam epitaxy and containing a digital distribution of magnetic MnTe fractional monolayers in the well. The influence of electronic confinement and of exciton primary localization on the formation of ferromagnetic ordering on the scale of small spin clusters (polarons) has been investigated by performing selective excitation of the exciton luminescence. The calculated temperature dependence of the free magnetic polarons binding energy F is found to qualitatively agree with the photoluminescence excitation data and the ferromagnetic clusters result to be more stable in these magnetic structures of reduced dimensionality, with respect to the three-dimensional case. The magneto-optical Kerr effect is discussed in the case of reflectance difference spectroscopy (RDS) and from the angular dependence of the RDS spectra in magnetic field, signals due to interband Faraday rotation and signals originating from crystal anisotropy could be distinguished. The Faraday rotation in these structures is found to follow the Curie–Weiss law with a transition temperature of −6 K corresponding to the nominal ion spin concentration in the magnetic barriers.