Crystallography, magnetism, and band structure of ${\mathrm{Mn}}_5$${\mathrm{Ni}}_2$${\mathrm{Bi}}_4$-type compounds

The crystal structure, magnetic properties, and a schematic band structure have been determined for the new class of magnetic compounds of the type ${\mathrm{Mn}}_5$ ${\mathrm{Ni}}_2$ ${\mathrm{Bi}}_4$. This class includes ${\mathrm{Mn}}_5$ ${\mathrm{Pd}}_2$ ${\mathrm{Bi}}_4$, ${\mathrm{Mn}}_5$ ${\mathrm{Rh}}_2$ ${\mathrm{Bi}}_4$, and ${\mathrm{Mn}}_3$ ${\mathrm{Cu}}_4$ ${\mathrm{Bi}}_4$. The structure has been calculated with the aid of Patterson and difference Patterson analysis of powder x-ray diffraction data. The spontaneous magnetic moment at 4.2 K for these compounds lies in the range 50-64 emu/g and Curie temperatures range between-7 °C and 183 °C. Molar Curie constants have been measured. A schematic band-structure model has been determined. It is based on local-site symmetries and includes both strongly correlated and itinerant $d$ electrons. As in the Heusler and ${\mathrm{Ni}}_3$Mn alloys, antiferromagnetic coupling of a small percentage of Mn-atom moments appears to be associated with atomic disorder. Within the experimental limits of apparent atomic ordering, the magnetization and Curie constants predicted from the band model are in agreement with experiment.