1. Cotton S.A. and Hart F.A., (1975) The Heavy Transition Elements, Chap. 10. J. Wiley & Sons, New York
2. Cotton F.A. and Wilkinson G., (1980) Advanced Inorganic Chemistry, Chap. 23,4th Ed.: J. Wiley & Sons, New York
3. Thompson L.C., (1979) in: Handbook on the Physics and Chemistry of Rare Earths, Vol. 3, Chap. 25 ( Eds. Gschneidner, Jr. K.A. and Eyring L.) North-Holland, Amsterdam
4. Barnes R.G., (1979) in: Ref. 3, Vol. 2, Chap. 18
5. Siddall III T.H., Casey A.T., and Mitra S., (1976) in: Theory and Applications of Molecular Paramagnetism, (Ed.: by Boudreaux E.A. and Mulay L.N.) J. Wiley & Sons, New York