Open Access Version

Abstract:
This thesis deals with the application of soft x-ray Fourier-transform holography (FTH) for imaging magnetic samples with nanometer structure size. FTH can be set up as a lensless method by exploiting the coherence properties of the illumination. An image of the sample is obtained by first recording a hologram which is the interference pattern of the light scattered at the sample with light originating from a reference structure. The hologram is then digitally reconstructed by a Fourier transform. The used x-ray probe facilitates nanometer spatial resolution of the images due to the small wavelength of the radiation and delivers magnetic contrast via the x-ray magnetic circular dichroism effect. The first part of the thesis contains a theoretical investigation of the function and properties of soft x-ray FTH. The fundamental image formation process with focus on achieving magnetic contrast is deduced. Furthermore, the impact of the experimental apparatus on the image is studied in a formal way. In particular, the influence of the reference structure, the area detector, and the coherence of the radiation delivered by the x-ray source on the point spread function of the imaging system is considered. Finally, the conclusions of the findings for the actual FTH experiment are discussed. In the second part of the thesis, an experimental application of FTH in the field of magnetic research on the nanometer scale is presented. The switching behavior of magnetic islands of a bit-patterned media (BPM) sample is studied via direct imaging of the islands’ magnetic state under an applied magnetic field. The data analysis focuses on the switching field distribution of the island ensemble. The origins for the broadening of this distribution are found in an intrinsic variation, the magnetostatic interaction between the islands and thermal fluctuations. For the latter two effects, models describing the experimental findings were developed. The intrinsic variations were further investigated by structural analysis using transmission electron microscopy.