PUB - Publikationen an der Universität Bielefeld

This thesis adresses investigations of the static and the non-equilibrium magnetic proximity effect (MPE) in different bilayer structures consisting of Pt in contact to a ferromagnetic insulator (FMI) or a ferromagnetic metal (FMM). In particular, the ferromagnetic insulator NiFe2O4 (NFO) is studied in this regard. The first experimental chapter of the thesis focusses on the preparation of NFO thin films with different techniques for the application in spintronic and spin caloric devices. The film properties are studied in detail to obtain the optimum fabrication conditions and gain high quality samples. The fabricated films have already been successfully utilized in various investigations on the longitudinal spin Seebeck effect and the spin Hall magnetoresistance (SMR). In order to rule out static MPE induced parasitic effects in these experiments, the interfacial magnetic properties of the Pt/NFO double layers are adressed in the next chapter. In particular, x-ray resonant magnetic reflectivity (XRMR) is introduced as a powerful alternative to the commonly used x-ray magnetic circular dichroism when investigating interfacial spin polarizations, as it is highly interface sensitive and independent of the film thickness. Therefore, XRMR is well suited for studies on the static MPE. In addition to the XRMR measurements on Pt/NFO bilayers, auxiliary studies on YIG based heterostructures are out for a more comprehensive analysis of the static MPE in Pt/FMI systems. Furthermore, the technique of XRMR is explored in more detail and tested for its suitability for the observation of MPEs in different Pt/FMM reference samples. Especially, thickness independence as well as challenges in the quantitative analysis of experimental data are evaluated. The influence of the ferromagnet (FM) thickness and composition on the magnitude of the induced spin polarization is also monitored in different Pt/FM bilayer systems. In the last chapter the Pt/NFO heterostructures are tested for their magnetoresistive properties thus, their suitability for spintronic devices. In particular, the layers are checked for the occurence of an SMR.