1. Catalan Institute of Nanoscience and Nanotechnology (ICN2), CSIC, and The Barcelona Institute of Science and Technology (BIST), Campus UAB, Bellaterra, 08193 Barcelona, Spain
2. Graduate School of Engineering Science and Center for Spintronics Research Network (CSRN), Osaka University, Toyonaka, Osaka 560-8531, Japan
3. Institució Catalana de Recerca i Estudis Avançats (ICREA), 08070 Barcelona, Spain