Element-selective magnetic imaging in exchange-coupled systems by magnetic photoemission microscopy

We have used a photoemission microscope to obtain element-resolved magnetic contrast in stacked magnetic thin film systems. Magnetic information is thereby provided by X-ray magnetic circular dichroism. Elemental sensitivity, which is crucial for studying magnetic coupling phenomena in systems with several different layers, is achieved by tuning the energy of the illuminating photons to atomic absorption edges. We present measurements of a Ni-coated Co micropattern on Cu(001), and a wedged Co/Cr/Fe(001) sample. In the former sample the Ni magnetization is seen to follow the magnetization of the Co pattern, thereby changing from an out-of-plane easy axis in areas without underlying Co to in-plane on top of the Co microstructures. In the latter a reversal of the exchange coupling of the Co layer to the Fe magnetization is observed when the Cr layer thickness exceeds approximately two monolayers. A small net magnetic moment is also observed in the Cr spacer layer, which follows in sign the Co magnetization at the reversal of the exchange coupling. This finding is discussed in terms of interface roughness or interdiffusion.