1. K. Yvon and M. Francois, Z. Physik, B76, 413 (1989).
2. R.P. Sharma, L.E. Rehn, P.M. Baldo and J.Z. Liu, Phys. Rev., B38, 9287 (1988).
3. R.P. Sharma, L.E. Rehn, P.M. Baldo and J.Z. Liu, Phys. Rev. Lett., 62, 2869 (1989).
4. T. Haga, K. Yamaya, Y. Abe, Y. Tajima and Y. Hidaka, Phys. Rev., B41, 826 (1990).
5. T. Egami, B.H. Toby, W. Dmowski, S. Billinge, P.K. Davies, J.D. Jorgensen, M.A. Subramanian, J. Gopalakrishnan and A.W. Sleight, Physica C, 162–164, 103 (1989).