1. Department of Mechanical Engineering Kobe University 1‐1 Rokkodai‐cho, Nada‐ku Kobe 657‐8501 Japan
2. Department of Materials Science and Engineering Korea University 145 Anam‐ro, Seongbuk‐gu Seoul 02841 South Korea
3. Division of Physics Faculty of Liberal Arts Sciences and Global Education Osaka Metropolitan University 1‐1 Gakuen‐cho, Naka‐ku Sakai Osaka 599‐8531 Japan