A NEUTRON POWDER DIFFRACTION STUDY OF THE STRUCTURE OF HO2FE17-XGAXC2(X=4.0 AND 5.5)

The crystallographic and magnetic structures of Ho2Fe17-xGaxC2 (x = 4. 0 and 5.5) at room temperature were refined by the Rietveld analysis o f neutron powder diffraction data. The analysis indicates that Ho2Fe17 -xGaxC2 has a Th2Zn17-type structure space group, (R3mBAR); the galliu m atoms occupy only 18h sites with an occupancy of 0.66 for x = 4.0, t hey occupy both 18h and 6c sites with occupancies of 0.66 and 0.75, re spectively, for x = 5.5 and they are absent from the 9d and 18f sites at all gallium concentrations. The carbon atoms occupy 9e sites. For t he x = 4.0 compound, the magnetic moments of all atoms lie in a plane perpendicular to the sixfold axes and have a parallel arrangement. The magnetic moments of all Fe atoms display ferromagnetic coupling, but the magnetic moments of Ho and Fe are antiferromagnetically oriented. The x = 5.5 compound is paramagnetic at room temperature.