NEUTRON-DIFFRACTION AND MAGNETIZATION INVESTIGATION OF TB2CO17-XGAX INTERMETALLICS

The crystallographic and magnetic structures of Tb2Co17-xGax (x = 1, 3 , 5 and 7) intermetallics have been investigated by time-of-flight neu tron powder diffraction at 293 and 4.2 K. All four compounds crystalli ze in the rhombohedral Th2Zn17 structure (R (3) over bar m) with Co at oms fully occupying the 9d site whilst Co and Ga atoms are found to di stribute themselves in a non-random manner on the remaining 6c, 18f an d 18h sites. These observed site occupations can be correlated with th e sign reversal of the Co sublattice magneto-crystalline anisotropy fo r Ga concentrations x > 3. The magnetic structures of the Tb and Co su blattices have also been refined from the neutron-diffraction data and indicate a complex ferrimagnetic behaviour with Ga composition. The C o moment decreases in size with Ga concentration, as does the Curie te mperature. (C) 1998 Elsevier Science B.V. All rights reserved.