Perpendicular magnetic anisotropy and the reorientation transition of the magnetization in CeH2/Fe multilayers probed by x-ray magnetic circular dichroism

The transition of the magnetization of multilayers [CeH2(x Angstrom)/Fe(16 Angstrom)] x n, x = 10, 16, 25, from planar to perpendicular orientation at low temperatures is explained on a microscopic basis by performing angle- and temperature-dependent measurements of x-ray magnetic circular dichroism at the 2p absorption edge of Fe and at the 2p and 3d absorption edges of Ce. The 3d orbital magnetic moment in the Fe sublayers is considerably enhanced with respect to bulk bce Fe and distinctly larger parallel to the layer normal than perpendicular to it. The Ce 4f states in these structures are well localized. The 4f magnetic moment is oriented along the layer normal due to a strong single-ion anisotropy resulting from crystal-field effects. The spin-split 3d states of Fe induce magnetic order on the Ce 5d states via hybridization and spin-orbit coupling, even on ions more distant from the interface. By intra-atomic 5d-4f exchange coupling the 4f states become magnetically polarized, with increasing strength toward low temperature. Together with the Sd-mediated 4f-3d coupling and the crystal-field induced single-ion 4f anisotropy this leads to a perpendicular orientation of the Fe 3d moment at low temperature. Hence the: Ce 4f states are the motor of the reorientation transition of the multilayer magnetization. The 4f-5d exchange interaction in the hydnided Ce sublayers affects dramatically the spectral shape of the dichroic Ce 5d spectra and, at low temperature, the ratio of the integrated signals at the L-2 and L-3 edges. [S0163-1829(99)00305-7].