1. School of Materials Science, Japan Advanced Institute of Science and Technology, Nomi 923-1211, Japan
2. Physics Department, Faculty of Science, Minia University, 11432 Main Road-Shalaby Land, Minia 61519, Egypt
3. TAIYO YUDEN CO., LTD. R&D Center, 5607-2, Nakamuroda-machi, Takasaki-shi, Gunma 370-3347, Japan
4. Hitachi Cambridge Laboratory, Hitachi Europe Ltd., J.J. Thomson Avenue, Cambridge CB3 0HE, U.K.