1. See for instance R. Kubo, M. Toda and N. Hashitsume, Statistical Physics II, Nonequilibrium Statistical Mechanics. Springer Verlag, Berlin 1978
2. F. Bloch, Phys.Rev. 70, 460 (1946)
3. See for instance, A. Abragam, Principles of Nuclear Magnetism. Oxford Un. Press London, 1961, or
4. C.P. Slichter, Principles of Magnetic Resonance. Springer Verlag Berlin, 1980.
5. N. Bloembergen, E.M. Purcell and R.V. Pound, Phys.Rev. 73, 679 (1948)