Effect of Ga substitution on the structure and magnetic properties of Ho2Fe17−xGax (x=0–8) compounds

The Rietveld analysis of x-ray diffraction data shows that Ho2Fe17−xGax (x=0–8) solid solutions crystallize with the Th2Ni17 structure for x⩽2, the Th2Zn17 structure for x⩾4, and the two coexisting phases for x=3. The unit-cell volume increases linearly with a slope of 8.7 A3 per Ga atom. At lower gallium concentrations, Ga atoms occupy the 18f, 18h sites in the Th2Zn17 structure (or 12j, 12k sites in the Th2Ni17 structure) and avoid the 6c, 9d sites. For higher Ga content (x⩾6) Ga atoms still avoid the 9d site, but preferentially occupy 6c and 18f sites for x=6–8 while the occupancy factor of the 18h site decreases. Gallium substitution decreases the saturation magnetization linearly with a slope of 2.5μB. The compounds Ho2Fe17−xGax (x=7,8) possess uniaxial magnetocrystalline anisotropy at room temperature. Doping first increases, then decreases the Curie temperature until this finally rebounds for x>6. The “anomalous” enhancement of the Curie temperature for x=7, 8 may be correlated with the variation o...