1. O. K. Kultashev and S. E. Rozhkov, in Rare-Earth Metals and Alloys, Ed. by E. M. Savitskii and V. F. Terekhov (Nauka, Moscow, 1971), p. 57.
2. B. K. Medvedev, N. I. Ionov, and Yu. I. Belyakov, Fiz. Tverd. Tela (Leningrad) 15(9), 2620 (1973) [Sov. Phys. Solid State 15, 1743 (1973)].
3. M. A. Shevchenko and S. A. Shakirova, Fiz. Tverd. Tela (Leningrad) 31(11), 29 (1989) [Sov. Phys. Solid State 31, 1854 (1989)].
4. V. A. Pleshkov, S. A. Shakirova, and G. A. Rump, Poverkhnost, No. 10, 16 (1990).
5. V. K. Medvedev, T. P. Smereka, S. I. Stepanovskii, et al., Fiz. Tverd. Tela (Leningrad) 33(12), 3603 (1991) [Sov. Phys. Solid State 33, 2028 (1991)].