It is shown that the decoupling approximation in functional integral method, which has been used by Hasegawa, leads to a generalized Ising model in itinerant-electron systems, and then a new theory to go beyond the single-site aprroximation is proposed. It is based on the Bethe approximation in Ising model. Present theory gives SRO of 0.1 ∼0.2 for Fe, Co and Ni at T ∼ T c .
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Y. Kakehashi (1981) studied this question.
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