Probing single magnetic nanoparticles by polarization-dependent soft x-ray absorption spectromicroscopy

Using photoemission electron microscopy, we have measured x-ray absorption (XAS) and x-ray magnetic circular dichroism (XMCD) spectra of single, three-dimensional iron nanoparticles in the size range 6-25 nm. We discuss the feasibility and limits of single-particle XAS and XMCD spectroscopy, in particular the influence of the experimental conditions such as nanofocusing effects, and analytical methods on the resulting spectra. While care must be taken in interpreting peak intensities, the overall line shape is less affected, which allows relative comparisons between different single particles in the ensemble and with reference spectra. Our work reveals that the spectral shape of both the isotropic absorption and the XMCD of single particles is retained for particles down to 6 nm and is in reasonable agreement with that of metallic bulk iron.