Spin-reorientation transition in epitaxial NixPd1-x fims on Cu(001): a microscopic analysis

This thesis deals with the spin-reorientation transition (SRT) usually observed at moderate thicknesses of 35-70ML in Ni and NiPd thin lms on Cu(001) and the connection between domain formation and anisotropy. The intrinsic properties of the magnetic anisotropy in thin lms and native states, characterized by their domain formations, are of high interest in the framework of spintronics. Thin lm epitaxial systems are used to approach a model system behavior, therefore Cu(001) single crystals are prepared in a high surface quality and epitaxial Ni and NiPd lms were grown in-situ by molecular beam epitaxy. The domain formations are studied on demagnetized lms by utilizing the x-ray magnetic circular dichroism on a synchrotron based, energy ltered, and aberration corrected xray photoemission electron microscope. Synchrotron light is used as a multi-purpose tool with element selectivity and high ux, enabling one to determine the magnetization direction by dipole selection rule geometries. A lateral change of the eective anisotropy was achieved by employing a wedged lm geometry, resulting in unique continuous measurements on the perpendicular magnetic anisotropy (PMA) area including the SRT area (0-100 ML) in Ni/Cu(001). A new domain formation of rectangularly ordered domains with domain walls aligning along the -axes was found in the vicinity of the SRT and is attributed to the increasing in uence of planar anisotropies, found to be in a very good agreement with theoretical models and simulations. The domain formation throughout the SRT is observed for the rst time and identied as a canted state transition. Ni-like NiPd lms were grown in order to vary the lm-strain, the major driving parameter for the PMA and SRTs, yielding domain formations of similar characteristics up to Pd-concentrations of 12%. The behavior of NiPd lms exhibiting compressive strain was investigated, verifying theoretical predictions that no SRT or PMA can be found throughout the whole thickness range of 0-60 ML. Osetting the elemental wedges made it possible to observe a composition-driven SRT. While the varied parameter range results in a strongly varied domain formation, in-plane anisotropy in uence and a canted state could be found again. In the framework of the observed domain formations in the microscopic setup, a discussion of the Tc drop at the SRT concludes this thesis. While being frequently reported, we could not nd any hints for its existence in various examined SRTs