X-ray magnetic circular dichroism at rare-earth L-absorption edges in Laves-phase compounds, RFe ₂ (R = rare-earth)

Recent progress of the theoretical interpretation for the X-ray magnetic circular dichroism (XMCD) at the rare-earth (RE) L_2,3 absorption edges is reviewed. We discuss the XMCD spectra of RFe₂ (R = RE) in the Laves phase based on the tight-binding approximation for RE 5d and Fe 3d conducting states. A variety of the XMCD spectra can be attributed to (i) the electric dipole and (ii) the electric quadrupole transitions. For (i), the polarization of the RE 5d electrons, being indispensable for XMCD, is dominated by the RE intra-atomic exchange interaction, which also yields the enhancement of the 2p-5d dipole matrix element. In addition, the hybridization with the spin-polarized Fe 3d states plays a distinctive role. For (ii), the multiplet couplings among the 4f electrons and the 2p core hole determine the XMCD spectra. We also consider XMCD in the mixed valence compound CeFe₂, taking many-body interactions into account based on the impurity Anderson model combined with a cluster approximation.