1. Center for Materials for Information Technology, The University of Alabama, Tuscaloosa, Alabama 35487, USA
2. Walther-Meissner-Institut, Bayerische Akdademie der Wissenschaften, Garching 85748, Germany
3. Thin Films and Physics of Nanostructures, Department of Physics and Center for Spinelectronic Materials and Devices, Bielefeld University, Bielefeld 33615, Germany