A theoretical investigation on the magneto-optical spectra of Ce-substituted yttrium aluminium garnet

Abstract

Calculations of the Faraday rotation and ellipticity spectra at photon energies between 1.6 and 4.0 eV (wavelengths between 775 and 310 nm) resulting from Ce3+ ions in Ce-substituted yttrium aluminium garnets (YAG:Ce) based on the quantum theory are presented. The Faraday effect contributed by the Ce3+ ions is caused mainly by the intra-ionic electrical dipole transitions between the 4f and 5d configurations. The Faraday effect of the Ce3+ ions in both the diamagnetic YAG and the ferrimagnetic yttrium iron garnet (YIG) crystals has a paramagnetic spectral shape but the resonance frequencies of YAG:Ce are at 2.76 and 3.7 eV, which are obviously higher than those of YIG:Ce. This difference can be explained by the fact that the crystal field acting upon the rare-earth ions in garnets depends strongly on the nature of the next-nearest neighbours. The differences between the transition intensities for the right- and left-handed circularly polarized light from both the lowest and the second crystal-field (CF)-split 5d levels to the ground state are negative. Therefore the Faraday rotation spectrum contributed by the Ce3+ ions in YAG has a wave-like shape in the energy region considered. However, for YIG:Ce, the difference between the transition intensities for the right- and left-handed circularly polarized light from the second CF-split 5d level to the ground state is positive. So the corresponding spectrum for YIG:Ce has a different shape. The calculated results are in good agreement with experiment.