1. Department of Physics and Astronomy, University of California, Irvine, California 92697, United States
2. Institute of Magnetism, Kyiv 03142, Ukraine
3. HGST, San Jose, California 95135, United States
4. Department of Physics, Oakland University, Rochester, Michigan 48309, United States
5. Department of Physics and Astronomy, University of Delaware, Newark, Delaware 19716, United States