F. Wilhelm

Magnetism of (Zn,Co)O thin films probed by x-ray absorption spectroscopies

We report on the electronic and magnetic properties of Co-doped ZnO thin films investigated by x-ray absorption spectroscopies and element selective magnetometry. For a low Co concentration (around 5%), we evidence a paramagnetic phase clearly correlated to Co2+ ions substituted to Zn in the ZnO matrix. For higher Co concentrations (around 25%), we demonstrate the coexistence of both paramagnetic and ferromagnetic phases. The use of advanced element and orbital selective techniques allows us through the distinct spectral signature of Co in ionic or metallic states to assign the ferromagnetic phase to the presence of Co in a metallic state as a consequence of Co metal clustering in our films.

Thermal decomposition of a thin AgOx layer generating optical near-field

Thermal decomposition of AgOx thin layers generating optical near field have been studied by Ag LIII edge x-ray absorption near-edge structure. We found that, different from previous assumptions, the starting layer is a mixture of AgO (∼40%) and Ag2O (∼60%). We further observed that thermal decomposition starts at a temperature as low as 50 °C. The decomposition process exhibits three stages and the oxide layer at intermediate stages consists of a mixture of AgO, Ag2O, and metallic Ag with different fractions of each phase. Activation energies of the decomposition of the thin oxide layer have been determined for different decomposition stages, the obtained values being different from that for powder oxides.

Thermal decomposition of sputtered thin PtOx layers used in super-resolution optical disks

Decomposition of sputtered PtOx layers has been studied by x-ray absorption spectroscopy. X-ray absorption fine structure measurements demonstrated that as-deposited films possess a composition of PtOx (x=1.1–1.7). Upon annealing, the metallic platinum phase is formed. The formation of the metallic Pt phase starts at very early stages of the decomposition process. The decomposition is not monotonic and slows down at the final stage. The structure at intermediate stages of decomposition is a mixture of the starting phase and metallic Pt.

Investigating magnetic proximity effects at ferrite/Pt interfaces

Spintronic devices based on pure spin currents have drawn a lot of attention during the last few years for low energy device design. One approach to generate pure spin currents is to combine a metallic or insulating ferromagnetic layer with a non-magnetic metallic layer with a large spin-orbit coupling. A recent controversy has arisen in the possible role of magnetic proximity effects at ferromagnetic/non-magnetic interfaces, which can hamper the understanding of pure spin current generation mechanisms. While magnetic proximity effects have been frequently observed at ferromagnetic metal/non-magnetic interfaces, there are only a few studies on ferromagnetic insulator/non-magnetic interfaces. Regarding the use of ferromagnetic insulators, the focus has been mainly on yttrium iron garnet (YIG). However, investigation of induced magnetic moments at YIG/Pt interfaces has engendered contradictory results. Here, we propose to study insulating ferrites for which electronic and magnetic properties can be modulate...

Magnetic Circular Dichroism in X‐ray Fluorescence Cascade Processes

The excellent performances of our 35‐element Silicon Drift Diode detector over a very wide energy range (⩾0.5 keV), allowed us to investigate the existence of magnetic circular dichroism in X‐ray fluorescence cascade processes. We report the results of a test experiment performed at the Tb LIII‐edge using an amorphous TbCo2 thin film which was magnetically saturated with an external magnetic field of 0.5 T. In a single energy scan, two XMCD spectra were obtained by monitoring separately the integrated intensities of Lα and Mβ emission lines of the Tb atoms.