High-Temperature Wavelength-Dependent Properties of a Heisenberg Paramagnet

The first four terms of the high-temperature expansion of the wavelength-dependent susceptibility χ (k) and the spin correlation function S (k) are calculated. Nearest-neighbor exchange interactions are assumed with general spin values and a Bravais lattice. From these results the first four terms in the high-temperature expansion of the effective range of the spin correlation are obtained for both ferromagnets and anti-ferromagnets. The terms are slightly different according to whether the range is defined from χ (k) or from S (k), though they become identical limitingly close to the critical ordering temperature. The calculated properties can all be measured by current neutron scattering techniques.