1. Department of Science and Technology, Campus Norrköping, Linköping University, S-60174 Norrköping, Sweden, Department of Physics and Measurement Technology, Linköping University, S-58183 Linköping, Sweden, Division of Molecular and NanoMaterials, Katholieke Universiteit Leuven, Celestijnenlaan 200F, B-3001 Leuven, Belgium, and Laboratory of Solid State Physics and Magnetism, Katholieke Universiteit Leuven, Celestijnenlaan 200D, B-3001 Heverlee, Belgium