Unusual magnetic transitions in a new ternary compound: TbCo3Ga2

Two new ternary compounds of the composition RCo3Ga2 (R = Tb, Y) have been prepared and identified by X-ray diffraction. The compounds crystallize in a new hexagonal structure, forming a ‘superlattice’ with lattice vectors, a and b, that are larger by a factor of √3 compared with the unit cell of the related pseudobinary compound RCo5-xGax. Magnetization and Mössbauer measurements reveal two independent magnetic transitions in TbCo3Ga2 occuring around 20 and 200 K. There are strong indications that the lower transition involves the Co sublattice whereas the higher transition is connected with the Tb sublattice.