MAGNETOOPTICAL INVESTIGATIONS OF EU-BASED DILUTED MAGNETIC LEAD CHALCOGENIDES

MBE grown Pb1-xEuxTe and Pb1-xEuxSe films with Eu contents up to 7% we re investigated by various magneto-optical methods as interband absorp tion, photomodulated reflectivity, photoluminescence, and coherent ant i-Stokes Raman scattering (CARS) in the midinfrared. The observed inte rband and intraband transition energies were interpreted in the framew ork of the Mitchell and Wallis band-structure model with the exchange interaction taken into account in mean-field approximation. The interb and matrix elements of the selenide are independent of the Eu concentr ation up to x=0.07, whenas in the telluride they are reduced by about a factor of 2 between x=0 and 0.05. The signs and the magnitudes of th e exchange parameters for the exchange interaction between the free ca rriers in the conduction and valence band, respectively, and the local ized magnetic moments of the Eu2+ ions are similar in Pb1-xEuxTe and P b1-xEuxSe. This implies that in Pb1-xEuxTe the exchange interaction de creases the spin splitting of the valence band as it is known from Pb1 -xEuxSe. The sign and magnitude of the exchange parameters are differe nt from the Mn-based compounds indicating that the effect is dominated by the hybridization of the band states with the localized wave funct ions of the 4f or 3d electrons, respectively. The minima of the magnet oabsorption spectra exhibit a strong line broadening with increasing E u concentration. Weaker transitions are no longer observable. Thus for higher Eu contents CARS turned out to be important not only for the d etermination of exchange parameters but also for the precise determina tion of the anisotropy of the interband matrix elements. With increasi ng x a strong decrease of the matrix elements is observed in the tellu ride, whereas the matrix elements in the selenide are less influenced.