1. Department of Materials Sciences and Engineering, Cornell University, Ithaca, New York 14853, USA
2. School of Applied and Engineering Physics, Cornell University, Ithaca, New York 14853, USA
3. Peter Grünberg Institute (PGI-9) and JARA-Fundamentals of Future Information Technology, Forschungszentrum Jülich GmbH, 52425 Jülich, Germany
4. Kavli Institute at Cornell for Nanoscale Science, Ithaca, New York 14853, USA
5. Leibniz-Institut für Kristallzüchtung, Max-Born-Str. 2, 12489 Berlin, Germany