Effects of spin-dependent spectral weight on magnetic circular X-ray dichroism: Application to R(Ni_xCo_1-x)₅ intermetallic compounds

Systematic study of the RE(Ni_xCo_1-x)₅ compounds (RE=La, Gd and Tb) has allowed to investigate the combined effects of the 3d-Sd hybridization and 4f-5d exchange on the RE L2,3-edge MCXD signal. In La(Ni_xCo_1-x)₅ compounds, where the 5d polarization results only from the hybridization between the 5d and 3d bands, the MCXD signal scales with the 5d moment and can be explained by a one-particle model for the absorption process [1-3]. When only the 4f-5d exchange intervenes, like in the GdNi₅ and TbNi₅ compounds, its effects on the MCXD sign and amplitude are very important, they are understood in term of spin-dependence of the radial matrix elements. When both the 3d-5d hybridization and the 4f-Sd exchange are present like in the Tb(Ni_xCo_1-x)₅ compounds, the amplitude variations of the L_2,3-edge MCXD spectra may be qualitatively descripted by a balanced contribution of both effects.