MAGNETOOPTIC SPECTROSCOPY OF PEROVSKITE-TYPE LA-1-X(BA,SR)(X)MNO3

Epitaxial thin films of ferromagnetic perovskite-type La-1-x(Ba, Sr)(x )MnO3 have been studied at room temperature by means of polar Kerr rot ation and ellipsometric measurements over a wide photon energy range. The Kerr-rotation spectra show two prominent features, one at 2 eV and a second, larger one around 3.2 eV but the spectra do not differ much with Sr or Ba substitution, This indicates that exclusively electroni c transitions involving Mn-3d and O-2p electrons are magnetooptically active, The Kerr rotation reaches a maximum value of -0.23 degrees in La0.7Sr0.3MnO3 at a photon energy of 3.2 eV. The structure at 2 eV is tentatively assigned to a dipole-forbidden, spin-allowed intra-Mn tran sition between crystal-field split 3d levels. The feature at 3.2 eV ar ises from a charge-transfer transition from occupied O-2p into empty M n-3d levels, At low Sr doping (x = 0.1), a narrow peak appears in the Kerr spectra at 4.6 eV. The full width at half maximum is estimated to be 0.25 eV. This is a factor of three smaller than the width of the t wo structures at lower energies, From the narrow width it is concluded that well localized electronic states are involved. Yet, the origin o f this structure remains unclear.