1. I. A. Smirnov and V. S. Oskotski, in Handbook on Physics and Chemistry of Rare Earth, Ed. by K. A. Gshneidner, Jr. and L. Eyring (Elsevier, Amsterdam, 1993), Vol. 16, p. 107.
2. B. Battlog, E. Kaldis, A. Schlegel, et al., Solid State Commun. 19, 673 (1976).
3. L. N. Vasil’ev, V. V. Kaminskii, and M. V. Romanova, Fiz. Tverd. Tela (St. Petersburg) 38(7), 2034 (1996) [Phys. Solid State 38, 1122 (1996)].
4. A. V. Golubkov, T. B. Zhukova, and V. M. Sergeeva, Izv. Akad. Nauk SSSR, Neorg. Mater. 2, 77 (1966).
5. E. Kaldis, J. Less-Common Met. 76, 163 (1980).