1. Pirson W.: Crystallochemistry and Physics of Metals and Alloys, part 1, p. 461. Moscow: Mir 1977.
2. Padera K.: Bull. Int. Acad. Czech. Sci.52, 1–16 (1951)
3. Steenberg B.: Ark. Kem. Miner. Geol. A12, 1–15 (1938)
4. Abragam A.: The Principles of Nuclear Magnetism. London: Oxford University Press 1962.
5. Feiock F.D., Johnson W.R.: Phys. Rev.187, 39–50 (1969)