X-MCD study of mixed valence manganites

A study of the X-MCD spectra and X-MCD magnetometry, i.e. the X-MCD effect vs. applied field, of the colossal magnetoresistive perovskites La_0.67-yTb_yCa_0.33MnO₃ is reported. The spectra were measured on polycrystalline samples with y = 0.0, 0.1, 0.22 at 10 and 77 K at the K, L₂, L₃ edges of manganese, the L₂, L₃ edges of lanthanum and the L₂, L₃, M₄, M₅ edges of terbium. From the X-MCD signal at the M₄, M₅ edges of terbium a parallel alignment of terbium sublattice magnetisation to the manganese magnetisation and to the applied magnetic field is deduced. The X-MCD magnetometry curves at the Mn K edge and La L edges show a saturation in the applied field, whereas Tb L edge signals do not saturate. The effect is especially pronounced in La_0.45Tb_0.22Ca_0.33MnO₃. The results are discussed in terms of the influence of terbium doping on the magnetic and electronic phase separation and on the strength of the coupling between magnetic moments of Tb and Mn and their relation to the colossal magnetoresistance of the compounds.