CRYSTALLOGRAPHIC ANALYSIS OF MAGNETIC STRUCTURES. A. Santoro and Q. Huang, Reactor Division, National Institute of Standards and Technology, Gaithersburg, MD 20899.

The nature of the spin ordering in a significant number of simple magnetic structures can be clarified by using the expression of the magnetic structure factor and by making use of simple crystallographic principles. The method used in our study of magnetic materials is based on a careful analysis of the diffraction patterns to determine the reflections with zero or near zero intensities. A judicious application of the procedure also allows one to find out if structural ambiguities are possible, i.e. to discover if two ore more spin orderings are consistent with the same distribution of powder or single crystal intensities, and to determine all the magnetic structures generating the ambiguity. This analysis does not make assumptions about the symmetry of the structure, which may be derived a posteriori. Applications to the derivation of the magnetic structures of HoNiBC, YBa₂Fe₃O₈ and other compounds will be illustrated in detail.