  Magnetic diffuse scattering -- the broad magnetic scattering features
observed in neutron-diffraction data above a material's magnetic ordering
temperature -- provides a rich source of information about the material's
magnetic Hamiltonian. However, this information has often remained
under-utilised due to a lack of available computer software that can fit values
of magnetic interaction parameters to such data. Here, an open-source computer
program, Spinteract, is presented, which enables straightforward refinement of
magnetic interaction parameters to powder and single-crystal magnetic diffuse
scattering data. The theory and implementation of this approach are summarised.
Examples are presented of refinements to published experimental
diffuse-scattering data sets for the canonical antiferromagnet MnO and the
highly-frustrated classical spin liquid Gd3Ga5O12. Guidelines for data
collection and refinement are outlined, and possible developments of the
approach are discussed.
