1. Zhdanov, V.G.; Kolomiets, B.T., Lyubin, V.M., and Malinovsky, V.K. (1979) Phys. Stat. Sol. (1) 52, 621.
2. Hajto, J. and Janossy, I. (1982) J. Phys. C: Solid State Phys. 15, 6293.
3. Dembovsky, S.A., Chechetkina, E.A. and Kozyukhin, S.A. (1985) JETP Lett. 41, 88.
4. Dembovsky, S.A., Chechetkina, E.A. and Kozyukhin, S.A. (1982) Solid State Comm. 44, 1561.
5. Kozyukhin, S.A. (1986) Thesis, Inst. Gen. & Inorg. Chem.,, Moscow.