1. Harris, A.B., Rastelli, E., Tassi, A.: (to be published)
2. Rastelli, E., Reatto, L., Tassi, A.: J. Phys. C16, L331 (1983)
3. Rastelli, E., Tassi, A., Reatto, L.: Physica97 B, 1 (1979)
4. Rastelli, E., Tassi, A., Oddi, L.: (to be published)
5. See for instance Borsa, F., Tognetti, V.: Magnetic propertien of Matter. p. 197. Singapore, New Jersey, Hong Kong: World Scientific 1988