1. H. HAMADA, H. MOROOKA and H. HIRAI,Oyo Butsuri (Appl. Phys.) 49 (1980) 783 (in Japanese).
2. K. IIJIMA, Y. TOMITA, R. TAKAYAMA and I. UEDA,J. Appl. Phys. 60 (1986) 361.
3. T. NAKAGAWA, J. YAMAGUCHI, M. OKUYAMA and Y. HAMAKAWA,ibid. 21 (1982) L655.
4. H. KIMURA, H. WATANABE, H. KANETANI, H. OHKUMA and E. YAMAKA, in Proceedings of the 33rd Spring Symposium of the Japanese Society of Applied Physics. Tokyo, 1986, p. 267.
5. R. TAKAYAMA, Y. TOMITA, K. IIJIMA and I. UEDA,Jpn. J. Appl. Phys. 61 (1987) 441.