EFFECT OF GA SUBSTITUTION ON THE STRUCTURE AND MAGNETIC-PROPERTIES OFHO2FE17-XGAX (X=0-8) COMPOUNDS

The Rietveld analysis of x-ray diffraction data shows that Ho2Fe17-xGa x (x=0-8) solid solutions crystallize with the Th2Ni17 structure for x less than or equal to 2, the Th2Zn17 structure for x greater than or equal to 4, and the two coexisting phases for x=3. The unit-cell volum e increases linearly with a slope of 8.7 Angstrom(3) per Ga atom. At l ower gallium concentrations, Ga atoms occupy the 18f, 18h sites in the Th2Zn17 structure (or 12j, 12k sites in the Th2Ni17 structure) and av oid the 6c, 9d sites. For higher Ga content (x greater than or equal t o 6) Ga atoms still avoid the 9d site, but preferentially occupy 6c an d 18f sites for x=6-8 while the occupancy factor of the 18h site decre ases. Gallium substitution decreases the saturation magnetization line arly with a slope of 2.5 mu(B). The compounds Ho2Fe17-xGax (x=7,8) pos sess uniaxial magnetocrystalline anisotropy at room temperature. Dopin g first increases, then decreases the Curie temperature until this fin ally rebounds for x>6. The ''anomalous'' enhancement of the Curie temp erature for x=7, 8 may be correlated with the variation of the Fe-Fe b ond lengths. (C) 1998 American Institute of Physics.