1. Slater, J. C., Phys. Rev., 36, 57 (1930).
2. Wallace, W. E., J. Chem. Phys., 23, 2281 (1955).
3. Zener, C., Phys. Rev., 81, 440 (1951).
4. Shull, C. G., and Wollan, E. O., in Solid State Physics, Advances in Research and Applications, edit. by Seitz, F. and Turnbull, D., 2, 137 (Academic Press, Inc., New York, 1956).