4F-5D EXCHANGE INTERACTION AND MAGNETIC CIRCULAR-DICHROISM IN L2,3 ABSORPTION FOR FERROMAGNETIC RARE-EARTHS

We give an interpretation for the observed systematic trend of magnetic circular dichroism (MCD) in L2,3 photoabsorption of rare-earth (RE) atoms from Ce to Tm in ferro- or ferrimagnetic RE2Co17 assuming the 2p-->5d electric dipole transition. We assume that the 4f state of trivalent RE ions is in the polarized Hund-ground-state. We then take into account the spin and orbital magnetic moments induced in the RE 5d state through the intraatomic 4f-5d exchange interaction approximated by a molecular field with assuming a band width of several eV and one tenth filling of the 5d band. The integrated MCD intensity calculated with a naive one-electron picture is shown to correspond well to the observed trend. The 5d orbital moment estimated both from the present model and from a MCD sum rule applied to the experiment is of the order of -0.1 mu(B), which is comparable to the 5d spin moment.