1. Institute of Solid State Physics, Vienna University of Technology, 1040 Vienna, Austria
2. Christian Doppler Laboratory for Advanced Magnetic Sensing and Materials, 1040 Vienna, Austria
3. Magnetfabrik Bonn GmbH, 53119 Bonn, Germany
4. Department of Polymer Engineering and Science, Montanuniversitaet Leoben, 8700 Leoben, Austria