MAGNETIC-PROPERTIES OF TB2CO17-XGAX COMPOUNDS STUDIED BY MAGNETIC MEASUREMENTS AND NEUTRON-DIFFRACTION

The magnetic properties of Tb2Co17-xGa4 compounds (x=1,3,5 and 7) were studied by means of neutron diffraction and magnetic measurements. Th e refinement results of the neutron powder diffraction patterns show t hat initially the Ga atoms occupy almost exclusively the 18h site in t he rhombohedral Th2Zn17 structure and presumably are responsible for t he sign reversal of the Co sublattice anisotropy. For x=greater than o r equal to 3 the Ga atoms increasingly occupy the 6c and 18f sites at the cost of the 18h site that shows a decreasing Ga occupancy in this concentration range. The 9d site is completely avoided by the Ga atoms over the whole concentration range. The sign reversal of the Co subla ttice anisotropy is attributed to filling of the 18h site with Ga. Fro m magnetic measurements and neutron diffraction it is derived that the Co moment strongly decreases in size with Ga concentration. There is also a strong decrease of the Curie temperature with Ga concentration. (C) 1998 Elsevier Science S.A.