Showing papers by "Markus Münzenberg published in 2003"

Isolating the interface magnetocrystalline anisotropy contributions in magnetic multilayers.

Abstract: The interface magnetocrystalline anisotropy energy (MAE) in Fe/CeH(2) multilayers has been site and element-specifically isolated by combining soft x-ray resonant magnetic scattering (SXRMS) with soft x-ray standing waves. Using the different temperature evolutions of the Fe and Ce SXRMS contributions, following an in-plane to out-of-plane spin reorientation, the interface Fe 3d MAE and Ce 4f single-ion anisotropy have been separated. The results demonstrate that the transition metal interface MAE dominates the spin reorientation while the rare-earth contribution becomes significant only at much lower temperatures.

Magnetic polarization of the La and Ce 5 d states near the interfaces of F e / L a H x and F e / C e H x multilayers across the metal-insulator transition in the hydrides: An x-ray magnetic circular dichroism study

Abstract: Rare-earth hydrides $R{\mathrm{H}}_{x}$ show a metal-to-insulator transition for x between 2 and 3. In an ionic picture strong Coulomb interactions between the electrons on H sites are responsible for opening up a gap of \ensuremath{\sim}2 eV between the valence bands derived from $R\mathrm{H}$ and H-H hybridization and a set of bands of predominantly R-metal d character. We have studied the magnetic polarization near the interfaces of $\mathrm{Fe}/R{\mathrm{H}}_{x}$ multilayers $(R=\mathrm{La},$ Ce) across the metal-to-insulator transition in the hydrides by measurements of x-ray magnetic circular dichroism (XMCD) at the $R{L}_{2,3}$ edges. The mean Fe-induced magnetic polarization of the R $5d$ states is considerably reduced in the insulating phase but remains finite. We attribute this to the presence of $5d$ states induced into the energy gap of the insulator sublayers by Fe, as they result from recent calculations of the electronic structure of ferromagnet/insulator interfaces. Variation of the $R{\mathrm{H}}_{x}$ sublayer thickness reveals that the $5d$ polarization decays exponentially away from the interface, on a length scale of about 10 \AA{} into the volume of the $R{\mathrm{H}}_{x}$ sublayers, both in the metallic and insulating phase. To our knowledge this is the first experimental observation that metal-induced gap states evanescent into the interior of an insulator may be spin polarized. The identical decay length in both $R{\mathrm{H}}_{x}$ phases, independent of the R element, is remarkable. The $R{L}_{2,3}$ XMCD spectra themselves reveal the complex interplay between the magnetic polarization by Fe $3d$ and R $5d$ hybridizations, and the R $4f$ magnetic moment. In fact, they are not only related to the magnetic $5d$ polarization in the ground state, but are largely controlled by the exchange interaction between the $2p$ core level and the spin polarized $5d$ band and, in the case of Ce, by the difference between the radial parts of the $2p$-to-$5d$ matrix element for the $5d$ majority and minority spin channels, resulting from the $4f\ensuremath{-}5d$ exchange interaction. It induces a drastic modification of the line shape and even a change in sign when the samples are cooled to low temperature or oriented under different angles with respect to the beam. We present a detailed discussion within a simple phenomenological model.