1. a Department of Electrical and Electronic Engineering , Gifu University , Gifu , 501-1193 , Japan
2. b Faculty of Science , Naruto University of Education , Naruto , 772-8502 , Japan
3. c Department of Physics and Astronomy , University of Sheffield , Sheffield , S3 7RH , UK
4. d Institute for Materials Research , Tohoku University , Sendai , 980-8577 , Japan