Atomic Magnetic State and Theory of X-Ray Spectroscopy in d and f Electron Systems

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By using sum rules to relate the integrated intensity of magnetic circular dichroism (MCD) spectrum in core-to-valence x-ray absorption and the atomic spin and orbital magnetic moments, the atomic orbital moment (MィイD20ィエD2) has been measured extensively in many transition metal multilayers and has been compared with that for bulk systems. We discuss the atomic environment dependence of MィイD20ィエD2 of various Co superlattices in Pd and Cu matixes on the basis of the tight-binding model including the d-d multipole interaction within the Hartree-Fock approximation In Pd matrix due to a large lattice constant, MィイD20ィエD2 of Co is increased to twice or so of the bulk value and it is rather insensitive to the atomic environment. In Cu matrix, on the other hand, since the effective Co-Cu 3d hybridization is much smaller than the Co-Co one, MィイD20ィエD2 of Co is found to be strongly dependent on the atomic environment and can be comparable to its spin counterpart.We discussed the relation between the "antiferromagnetic" Mn 3d orbital ordering in LaMnOィイD23ィエD2 and the linear dichroism in MnLィイD22,3ィエD2, absorption on the basis of the single-ion model taking into account the crystal field and the intraatomic multipole interaction. Although the recent resonant x-ray scattering at Mn K edge is expected as a method of directly observing the orbital ordering there have been controversies that it only observe the distortion of MnOィイD26ィエD2 cluster. The present study shows that the multiplet structure in x-ray absorption spectrum can play a role as a fingerprint to identify the type of orbital ordering.