1. J. Inoue is in the Department of Applied Physics, Graduate School of Engineering, Nagoya University, Chikusa-ku, Nagoya 464-8603, Japan.
2. H. Ohno is at the Laboratory for Nanoelectronics and Spintronics, Research Institute of Electrical Communication, Tohoku University, Aoba-ku, Sendai 980-8577, Japan, and the ERATO Semiconductor Spintronics Project, Japan Science and Technology Agency, Kitame-machi 1-18, Aoba-ku, Sendai 980-0023, Japan.