[1] Tohoku Univ, Grad Sch Sci, Phys Dept, Sendai, Miyagi 9808578, Japan
[2] Natl Inst Mat Sci, Tsukuba, Ibaraki 3050047, Japan
[3] Tohoku Univ, Inst Mat Res, Sendai, Miyagi 9808578, Japan
[4] Toho Univ, Ctr Low Temp Sci, Sendai, Miyagi 9808578, Japan