Neutron scattering from paramagnets

Abstract

Neutron paramagnetic scattering is discussed generally in terms of the relaxation function of the magnetic system. The expansion of the scattering function F(κ, ω) in terms of moments of the energy transfer is evaluated to the fourth moment for the Heisenberg Hamiltonian and for limitingly high temperatures. Consideration of these moments leads to a better approximate form for the cross section at large scattering vector than the usual Gaussian form. The interpretation of experimental data is discussed and it is shown that important inaccuracies may arise from the use of the Gaussian approximation. A procedure for making good use of experimental information is given for data from both single crystals and polycrystals. In the single-crystal case it is possible to determine exchange constants to a large number of different atoms, whilst for the polycrystal it may be difficult experimentally to separate more than two different exchange constants.