1. Department of Electrical and Computer Engineering, Iowa State University, Ames, Iowa 50011, USA
2. Division of Materials Science & Engineering, Ames Laboratory, U.S. Department of Energy, Ames, Iowa 50011, USA
3. Wolfson Center for Magnetics, Cardiff University, Cardiff CF24 3AA, United Kingdom
4. Institute of Physics, Polish Academy of Science, Warsaw 02-668, Poland
5. Department of Materials Science & Engineering, Iowa State University, Ames, Iowa 50011, USA