1. O. V. Stal’gorova and E. L. Gromitskaya, Fiz. Tverd. Tela (St. Petersburg) 37, 1671 (1995) [Phys. Solid State 37, 908 (1995)].
2. E. L. Gromitskaya and O. V. Stal’gorovka, Zh. Éksp. Teor. Fiz. 106, 1453 (1994) [JETP 79, 785 (1994)].
3. J. Gallaway, X. Zou, and D. Bagayoko, Phys. Rev. B 27, 631 (1983).
4. A. A. Lysykh and I. K. Yanson, Fiz. Tverd. Tela (Leningrad) 21, 117 (1979) [Sov. Phys. Solid State 21, 68 (1979)].
5. H. Stachowiak, Phys. Status Solidi 41,2, 599 (1970).