1. Institute for Advanced Simulation, Jülich Supercomputing Centre, Forschungszentrum Jülich, D-52425 Jülich, Germany
2. Institut Néel, CNRS, 25 Ave. des Martyrs, BP 166, 38 042 Grenoble Cedex 09, France
3. Department of Physics, Graduate School of Science, The University of Tokyo, Bunkyo, Tokyo 113-8656, Japan
4. CREST, JST, Kawaguchi, Saitama 332-0012, Japan
5. Department of Applied Physics, Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, NL-9747 AG Groningen, The Netherlands