1. Correlated Electron Research Center (CERC), National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8562
2. Tokura Spin Superstructure Project (SSS), ERATO, JST, c/o AIST, Tsukuba, Ibaraki 305-8562
3. Department of Applied Physics, The University of Tokyo, Tokyo 113-8656