Core-level magnetic circular dichroism in 3d and 4f magnetic systems (invited) (abstract)

Abstract

With the recent availability of circulary polarized synchrotron radiation over a wide photon energy range from VUV to hard X rays, the magnetic circular dichroism (MCD) in core-level photoabsorption has rapidly attracted growing interest, both experimentally and theoretically. This novel technique can provide element-specific and site-selective information about the magnetic and the electronic states in various magnetic substances because the core-level MCD process involves optical transitions in which the one-electron initial states are well localized and have well-defined angular momenta. In order to get insight into the local magnetic states in 3d and 4f magnetic systems, we have studied MCD of ferrites, Fe1−xPtx alloys, and mixed-valence CeRh3B2 at the core-absorption edges in the VUV∼soft x-ray region. The experiments were performed by utilizing directly characterized, circularly polarized undulator radiation and off-plane synchrotron radiation1 in conjunction with an ultrahigh vacuum compatible superconducting magnet of special design.2 Clear MCD signals were observed for CeRh3B2 in the prethreshold region of the Ce 4d→4f (N4,5) edges. A comparison of the experimental MCD spectrum with theoretical ones3 for uniaxial crystal fields of Δc=0 and 0.2 eV shows that the experimental spectrum qualitatively agrees with the theoretical one for Δc=0 eV. Theory predicts that the MCD pattern for Δc<0.14 eV will be essentially the same as that for Δc=0 eV. Considering a Δc value of 0.1–0.2 eV, which was determined from the linear dichroism measurement,4 the present result leads to the conclusion that Δc∼0.1 eV. With a model based on the strong hybridization between the neighboring Ce 4f0(lz=0) and Ce 5d0(lz=0) orbitals together with the value of Δc∼0.1 eV, we can successfully explain many of the extraordinary magnetic properties of CeRh3B2. We will also present the MCD data in the M2,3 core-absorption region for ferrites (Fe3O4 and CoFe2O4) and Fe1−xPtx alloys, discussing the results.