G. Ceballos

X-ray magnetic circular dichroic magnetometry on Ni/Pt multilayers

X-ray magnetic circular dichroism measurements have been performed on Ni/Pt multilayers at a temperature of 10 K. The element specificity and shell selectivity of the technique allows us to probe Ni and Pt magnetic moments and to separate them into their constituent spin (μS) and orbital (μL) magnetic moments. The Ni magnetic moment at the interface is found to be reduced. However, magnetically “dead” Ni layers are unambiguously ruled out. Induced Pt magnetic moments up to about 0.3 μB/atom are reported. The results are compared to ab initio calculations and to previous experiments performed on NiPt alloys. The role of intermixing in the reduction of the Ni magnetic moments is also discussed.

Thickness dependence of the V induced magnetic moment in Fe/V/Fe(110) trilayers

We report on in situ x-ray magnetic circular dichroism experiments at the Fe and V L edges on Fe/V/Fe(110) trilayers. Our results show that the induced V magnetic moment, which couples antiparallel to the Fe one, decreases rapidly away from the interface indicating a short-range polarization in the V layers. This finding confirms recent ab initio calculations.

Shape resonances of oriented molecules

Abstract We report ab initio calculations of the X-ray absorption cross section for the near edge X-ray absorption fine structure of C 2 H 6 , C 2 H 4 and C 2 H 2 , at the carbon K-edge, based on a full multiple scattering formalism. We find that shape resonances dominate the photoabsorption carbon K-edge spectra close to the edge, leading to a spectacular enhancement in cross section of order 3–4 Mbarn. Our analysis highlights the strong influence of the molecular vibrations on the intensity, asymmetric profile and energy of this spectral feature. Calculations with and without hydrogen atoms, allow to estimate the amount of C–H character of this feature. A quantitative comparison between theory and experiment, using spectra of oriented molecules on surfaces is performed. Molecular orientation in the experiment is obtained by means of physisorption which has the advantage of obtaining molecules very close to their gas phase state.

Quadrupolar and dipolar contributions to x-ray magnetic circular dichroism at the Tb L3,2 edges: Experiment versus theory

We investigate the x-ray magnetic circular dichroism (XMCD) at the L3,2 edges using a single crystal of Tb as a prototype system for a one-element magnet in order to ascertain the multipolar nature of the features in the dichroic spectra. The high resolution of the experimental data allows for a clear identification of the dipolar (E1: 2p→5d) and quadrupolar (E2: 2p→4f) transitions. On the basis of ab initio calculations we developed a simple procedure to extract the quadrupolar part by subtracting the derivative of the spin-averaged absorption spectra from the experimental XMCD data. The deconvolution has to be carried out before applying sum rules to determine 4f and 5d moments.

Surface EXAFS study of the p4g(2 x 2) reconstruction of C on Ni(100)and C on Ni films

We report temperature- and angular-dependent surface extended X-ray absorption fine structure spectroscopy (SEXAFS) measurements of the p4g(2 x 2)C/Ni(100) system. Both a Ni(100) single crystal and ...

Vibrational fine structure in the N 1s→π∗ resonance of the N2 molecule physisorbed on the Cu(100) surface

Abstract High-resolution photoabsorption spectra at the N 1s→π∗ resonance of N2 physisorbed on the Cu(100) surface are reported. The vibrational fine structure of this resonance could be resolved, allowing the determination of the vibrational constants, the lifetime and intramolecular distances of the core-excited states of the physisorbed molecules. The obtained fundamental vibrational constants are compared with the corresponding vibrational parameters for the gas phase.

Influence of exchange coupling on the Ni magnetization in Co/Cu/Ni trilayers.

Abstract The X-ray magnetic circular dichroism has been used to study trilayers consisting of two ferromagnets (Ni, Co) separated by a non-magnetic spacer (Cu). The coupling of Ni and Co layers was found to be both ferromagnetic and anti-ferromagnetic depending on spacer thickness. Two magnetization curves vanishing at two different temperatures were recorded for Ni and Co in a coupled trilayer. For Ni, this temperature is larger than the Curie temperature ( T C ) of the Cu-capped Ni layer, due to the effect of interlayer exchange coupling.