Where are the iron atoms and iron moments in RFE<i>m</i>Al12−<i>n</i>? A Wigner-Seitz analysis

Abstract

The ternary compounds RFenAl12−n (n=4,5,6; ThMn12 structure) form an extensive family of alloys having complicated magnetic structures, with the rare earths (R) and Fe ordering at different temperatures. This magnetic ordering has been inferred from magnetization, Mössbauer and neutron diffraction measurements. X-ray results are in disagreement with the magnetic measurements as to which sites are occuped by the Fe, and it is not clear at which of the sites iron has the largest magnetic moment. Recently, we have suggested that the occurrence of a substantial magnetic moment at an atomic site in certain magnetic systems can be related to the occurrence of −72° disclination lines connection atoms on this site. These disclinations are bond lines joining two near-neighbor atoms which have six nearest neighbors and can be recognized by a sixfold face appearing on the Wigner-Seitz polyhedra of the two atoms. The Wigner-Seitz construction and its use in the analysis of this and related problems is presented.