1. Department of Engineering Physics, Air Force Institute of Technology, Wright-Patterson Air Force Base, Ohio 45433, USA
2. Institute of Materials Research, Washington State University, Pullman, Washington 99164-2920, USA
3. Department of Physics and Astronomy, Washington State University, Pullman, Washington 99164-2814, USA
4. Department of Physics and Astronomy, West Virginia University, Morgantown, West Virginia 26506-6315, USA