1. For a good review of the experimental work in this field, see,e.g.,P. A. Fleury:Intern. Journ. Magnetism,1, 75 (1970);S. R. Chinn, R. W. Davies andH. J. Zeiger:A.I.P. Conf. Proc.,5, 317 (1972).
2. P. A. Fleury:Phys. Rev.,180, 591 (1969).
3. P. A. Fleury, S. P. S. Porto, L. E. Cheesman andH. J. Guggenheim:Phys. Rev. Lett.,17, 84 (1966);P. A. Fleury, S. P. S. Porto andR. Loudon:Phys. Rev. Lett.,18, 658 (1967).
4. M. T. Hutchings:Solid State Physics, edited byF. Seitz andD. Turnbull, Vol.16 (New York, N. Y., 1964), p. 227.
5. A. Abragam andB. Bleaney:Electron Paramagnetic Resonance of Transition Ions (Oxford, 1970).