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2. M. B. Maple, L. E. DeLong, and B. C. Sales, inHandbook on the Physics and Chemistry of Rare Earth's, K. A. Gschneider, ed. (North-Holland, 1978), Vol. 1, p. 798.
3. J. M. Lawrence, P. S. Riseborough, and R. D. Parks,Rep. Prog. Phys. 44, 2 (1981).
4. D. I. Khomskii,Uspekhi Fiz. Nauk 129, 443 (1979).
5. F. N. Mott,Metal-Insulator Transitions (Taylor and Francis, London, 1974).