Going beyond the dipole approximation to improve the refinement of magnetic structures by neutron diffraction

摘要

We have made an analysis of neutron-diffraction data for a number of rare-earth compounds to assess the use of the dipole approximation in magnetic structure refinements. We present two examples. In the case of CePd_2Si_2, our analysis confirms the published magnetic structure, but we find that use of the "exact" magnetic form factor of Ce~(3+) gives a significantly improved description of the data. For NdBa_2Cu_3O_(6+x), however, we find that incorrect conclusions have previously been drawn about the magnetic structure through the use of the dipole approximation. We have extended the magnetic modeling suite MCPHASE to enable a straightforward calculation of the higher-order anisotropic terms in the form factor of rare-earth-based systems.