Magnetic structure refinement with neutron powder diffraction data using GSAS: A tutorial

Abstract

Neutron diffraction provides a direct probe for the ordering of spins from unpaired electrons in materials with magnetic properties. The ordering of the spins can be modeled in many cases by adding spin directions to standard crystallographic models. This requires, however, that crystallographic space groups be extended by addition of a “color” attribute to symmetry operations, which determines if the operation maintains or flips the direction of a magnetic spin. Rietveld analysis provides a mechanism for fitting magnetic structure models to powder diffraction data. The general structure and analysis system (GSAS) software suite is commonly used for Rietveld analysis and includes the ability to compute magnetic scattering. Different approaches are commonly used within GSAS to create models that include magnetism. Three equivalent but different approaches are presented to provide a tutorial on how magnetic scattering data may be modeled using differing treatment of symmetry. Also discussed is how magnetic models may be visualized. The commands used to run the GSAS programs are summarized within, but are shown in great detail in supplementary web pages.