1. M.F. Littmann, US patent No. 2,473,156
2. N. Abe, Y. Ushigami, M. Iwasaki, and T. Nozawa, 14th Ann. Conf. on Magnetics in Japan, The Magnetics Society of Japan, Matsuyama C, Japan. 1990, p 402
3. T. Taoka,Tetsu Hagone, Vol 54 (No. 2), 1968, p 22
4. T. Nozawa, T. Nakayama, Y. Ushigami, and T. Yamamoto,J. Magn. Magn. Mater., Vol 58, 1986, p 67–77
5. H. Mogi, M. Yabumoto. Y. Matsuo, and K. Koyanasn, to be published, 1993