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

Abstract

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 ${\text{CePd}}_{2}{\text{Si}}_{2}$, our analysis confirms the published magnetic structure, but we find that use of the ``exact'' magnetic form factor of ${\text{Ce}}^{3+}$ gives a significantly improved description of the data. For ${\text{NdBa}}_{2}{\text{Cu}}_{3}{\text{O}}_{6+x}$, 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.