1. A. Landelli, cited by F. H. Spedding and A. H. Daane, The Rare Earths, New York (1961), p. 237?385, and K. A. Gschneidner, Jr. Rare Earth Alloys, Princeton (1960).
2. E. I. Gladyshevskii, Dopovidi AN Ukr. SSR,3, 294 (1959).
3. A. Landelli, Atti accad. nazl. Lincei,6, 727 (1949).
4. E. I. Gladyshevskii, P. I. Kripyakevich, M. Yu. Teslyuk, O. S. Zarechnyuk, and Yu. B. Kuz'ma, Kristallografiya,6, 267 (1961).
5. E. I. Gladyshevskii, Dopovidi AN Ukr. SSR,2, 209 (1964).