Wave-vector-dependent magnetic susceptibility of classical Heisenberg rings
Abstract
We first extend previous results of G S Joyce so as to derive the exact wave-vector-dependent susceptibility N.q; T / for a ring of N classical Heisenberg spins with isotropic
nearest-neighbour interactions. Our major result however is a simple, highly accurate, analytic approximation for N.q; T / which nevertheless preserves an associated sum rule over the
Brillouin zone.