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 neutron powder diffraction at 293 and 4.2 K. All four compounds crystallize in the rhombohedral Th2Zn17 structure (R (3) over bar m) with Co atoms fully occupying the 9d site whilst Co and Ga atoms are found to distribute themselves in a non-random manner on the remaining 6c, 18f and 18h sites. These observed site occupations can be correlated with the sign reversal of the Co sublattice magneto-crystalline anisotropy for Ga concentrations x > 3. The magnetic structures of the Tb and Co sublattices have also been refined from the neutron-diffraction data and indicate a complex ferrimagnetic behaviour with Ga composition. The Co moment decreases in size with Ga concentration, as does the Curie temperature. (C) 1998 Elsevier Science B.V. All rights reserved.