EFFECTS OF TETRAHEDRAL Co3+ ON INFRARED FARADAY ROTATION IN MAGNETIC GARNETS

Effects of the trivalent Co ion on the tetrahedral site of magnetic garnets on the Faraday rotation spectra (FRS) in the infrared region were investigated in the scheme of the crystal field theory (strong crystal field approximation), and the calculated FRS were compared with the experimentally obtained FRS in (YGd)3(CoxFe5-x)O12 films grown by the conventional liquid phase epitaxy (LPE) method. The experimental FRS of Co doped magnetic garnets, having a dispersion-type shape, were well explained by the crystal field transition 5E → 5T2 taking into account the spin-orbit interaction (S.O.) and the tetragonally distorted field (S4). From the calculations of the energy level splittings of 5T2 excited state and ones of the FRS for Co3+, on the tetrahedral site, we found that the sign of S.O. and the magnitude of the low symmetry field (S4) give a strong influence on the shape of FRS; only when S.O. is negative and a', a measure of the low symmetry field (S4), is larger than about 1000 cm-1, the shape of FRS is of dispersive type as observed experimentally.