1. H. Alloul, preprint and APS March Meeting, St Louis USA (1989)
2. M. Takigawa, preprint and APS March Meeting, St Louis USA (1989)
3. Y. Tokura, IT. Takigi and S. Uchida, Nature 337, 345 (1989)
4. II. Takagi, Y. Tokura, S. Uchida, Phys. Rev. Lett. 62, 1197 (1989)
5. V.J. Emery, Nature 337, 306 (1989)