1. R.L. Martin, “New Pathways in Inorganic Chemistry,” E.A.V. Ebsworth, A.G. Maddock, and A.G. Sharpe, Eds., Cambridge University Press, London, 1968, Chapter 9.
2. P.W. Anderson, “Magnetism,” (ed., G.T. Rado and H. Suhl), Vol. 1, p. 25, New York, Academic Press, Inc., 1963
3. K.W.H. Stevens, Phys. Reports (Phys. Lett. C) 24C, 1, February, 1976.
4. A. Carrington and A.D. McLachlan, “Introduction to Magnetic Resonance,” Harper and Row, New York, 1967.
5. J.S. Smart, “Magnetism,” (ed. G.T. Rado and Suhl), Vol. III, p. 63, New York: Academic Press, Inc., 1965.