1. N. Bloembergen, Physica 15, 386 (1949)
2. M. Goldman, Spin Temperature and Nuclear Magnetic Resonance in Solids (Claredon Press, Oxford, 1970)
3. G.R. Khutsishvili, Sov. Phys. Usp. 8, 743 (1965)
4. A. Abragam, M. Goldman, Nuclear Magnetism: Order and Disorder (Claredon Press, Oxford, 1982)
5. PYu. Efitsenko, V.M. Mikushev, E.V. Charnaya, JETP Lett. 54, 587 (1991)