1. For a review of the physical properties of Van Vleck compounds see: Fulde, P.: Crystal Fields. In: Handbook on the Physics and Chemistry of Rare Earth. ed. Gschneider, K.A., Eyring, L. (eds.), Chap. 17. Amsterdam, Oxford, New York: North-Holland Publ. Co. 1978
2. Holden, T.M., Buyers, W.J.L., Svensson, E.C.: In: Crystal Field Effects in Metals and Alloys. Furrer, A. (ed.), p. 189. New York: Plenum Press 1977
3. Kjems, J.K., Nielsen, M., Buyers, W.L.J., Crow, J.E.: J. Phys. (Paris) Collq. C5-132 (1979)
4. Elliott, R.J.: In: Crystal Field Effects in Metals and Alloys. Furrer, A. (ed.), p. 76. New York: Plenum Press 1977
5. Smith, S.R.P.: J. Phys. C.5, L 157 (1972)