1. Institute of Physics, Johannes Gutenberg-Universität Mainz, 55128 Mainz, Germany
2. Center for Spintronics, Korea Institute of Science and Technology, 34141 Seoul, Republic of Korea
3. Peter Grünberg Institut and Institute for Advanced Simulation, Forschungszentrum Jülich and JARA, 52425 Jülich, Germany
4. Division of Display and Semiconductor Physics, Korea University, 30019 Sejong, Republic of Korea
5. Department of Applied Physics, Institute for Photonic Integration, Eindhoven University of Technology, 5612 AZ Eindhoven, The Netherlands