Very thin magnets : X-rays, lasers and spectroscopy

Detta är en avhandling från Uppsala : Acta Universitatis Upsaliensis

Sammanfattning: The magnetic properties of transition metal films are investigated using synchrotron based x-ray absorption and x-ray photoelectron spectroscopy. These techniques are elementally selective and may therefore be used, either to probe a specific element in a multicomponent system or, as very sensitive magnetometers. These are complemented by magneto-optic measurements using laser light. Based on x-ray absorption spectroscopy, a new technique for the accurate measurement of critical properties ofthin films is presented. In the present work the emphasis has been on high quality, ultra thin thin films prepared and measured in ultra high vacuum. These films have been stabilised in different crystallographic structures than those normally found for bulk samples by deposition on the (100) surface of copper.The systematic study of these films has facilitated the observation of novel phenomena related to their unique character. The orbital moment of the surface layer is enhanced. Such effects are supported by theory. Energy shifts in x-ray absorption features are quantified and linked to the magnetic character of the spectra.In an attempt to better understand the absorption spectrum, of thin films, a series of Ni films were oxidised. These data are interpreted in terms of the charge transfer between the Ni and O in the resulting oxide which is correlated with the redistribution of intensity in the resulting absorption spectra.Using x-ray photoelectron spectroscop the Fe/Cu(100) system was investigated. Magnetic contrast was discovered for an experimental geometry where such effects are forbidden from symmetry considerations. In combination with theory, we address the reorientation of the remnant magnetisation for this system upon the addition of sub monolayers of cobalt. Adding magnetic contrast to L edge extended x-ray absorption fine structure measurements of 3d ferromagnets, highlights the subtle interplay between magnetism and local crystal structure via the spin polarisation dependence of the scattered electron wave.Evidence is presented that demonstrates how the degree of spatial coherence of the x-ray source effects the relative intensity of spectral features in x-ray absorption spectroscopy.

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