Exchange narrowing in correlated spin systems: local field contributions

Abstract

The theory of exchange narrowing is extended to include spin correlations, arising from the isotropic exchange J0, which are particularly important in low-dimensional spin systems. Exact corrections are found in s = 1/2 lattices for the second moment M2(J0/kT) of a general nearest-neighbor perturbation H′. The different temperature dependence of spin symmetric and antisymmetric contributions to H′ is pointed out and illustrated for the square-planar ferromagnet.