Coherent Raman spectroscopy of CdTe/MnTe short-period superlattices

Short-period (CdTe)(m)/(MnTe)(n) superlattices. were investigated by coherent Stokes Raman scattering (CSRS) in backscattering geometry. Temperatures ranged between 1.6 and about 120 K, and magnetic fields up to 7 T were applied in Voigt configuration. The method allows the observation of spin splittings of delocalized band carriers as well as of electrons localized to magnetic ions. The magnetic properties are probed by measuring the paramagnetic (PMR) and antiferromagnetic resonances (AFMR) of the Mn2+ d electrons and the spin splittings of photoexcited free electrons [conduction-electron spin flip (CSF)I in the CdTe wells, the wave functions of which are extended more or less into the MnTe barriers. Since resonant CSRS is particularly sensitive to Mn ions located in regions with high expectation probabilities for electrons, the investigations yield some spatial resolution in growth direction. A simultaneous observation of AFMR and PMR shows that, besides the antiferromagnetically coupled Mn2+ ions, uncoupled ones exist. The CSF data are analyzed in the framework of a mean-field model. The Neel temperatures are substantially decreased with respect to bulklike MnTe due to the reduced dimensionality, but on the other hand are increased by a magnetic coupling of the MnTe layers across the diamagnetic CdTe. We prove that the probability of finding electrons close to the CdTe/MnTe interface is enhanced as compared to results from superlattice hand-structure calculations. Furthermore the experimental data show the existence of two-dimensional bound magnetic polarons.