The Antiferromagnetic Correlations in the Half—Filled Double—Exchange Model at Finite Temperature

We extend a previous result of ours [G.S.Tian,Phys.Rev.B63 (2001) 224413] on the antiferromagnetic spin correlations in the half-filled Hubbard model at finite temperature to the double-exchange model.To overcome the mathematical difficulty cused by the S=3/2 localized spin freedom in this model,we apply both Zener‘s argument and the finite-temperature spin-reflection-positivity method to show rigorously that,at any temperature T,the spin correlations in the half-filled double-exchange model are predominantly antiferromagnetic.This conclusion is completely consistent with the experimental observations and the previous theoretical results by approximate methods.

The Antiferromagnetic Correlations in the Half-Filled Double-Exchange Model at Finite Temperature

We extend a previous result of ours [G.S. Tian, Phys. Rev. B63 (2001) 224413] on the antiferromagneticspin correlations in the half-filled Hubbard model at finite temperature to the double-exchange model. To overcome themathematical difficulty caused by the S = 3/2 localized spin freedom in this model, we apply both Zener's argumentand the finite-temperature spin-reflection-positivity method to show rigorously that, at any temperature T, the spincorrelations in the half-filled double-exchange model are predominantly antiferromagnetic. This conclusion is completelyconsistent with the experimental observations and the previous theoretical results by approximate methods.