1. M. Gasgnier,Phys. Status Solidi (a) 57 (1980) 11.
2. Idem, ibid. 114 (1989) 11.
3. G. Brauer, in ?Progress in the Science and Technology of the Rare Earths?, Vol. 2 edited by L. Eyring (Pergamon Press, Oxford, 1966) p. 312.
4. L. Eyring, in ?Handbook Physics and Chemistry of Rare Earths?, Vol. 3, edited by K. A. Gschneider Jr and L. Eyring (North-Holland, Amsterdam, 1979) Ch. 27, p. 337.
5. P. Kunzmann andL. Eyring,J. Solid State Chem. 14 (1975) 229.