1. Department of Quantum Matter, ADSM, Hiroshima University, Higashihiroshima, Hiroshima 739-8530, Japan
2. Department of Applied Physics, National Defense Academy, Yokosuka, Kanagawa 239-8686, Japan
3. Institute for Advanced Materials Research, Hiroshima University, Higashihiroshima, Hiroshima 739-8530, Japan
4. Cryogenics and Instrumental Analysis Division, N-BARD, Hiroshima University, Higashihiroshima, Hiroshima 739-8526, Japan