Magnetic properties of CeM1.5M'0.5Ge4O12 (M = Mn, Co; M' = Ni, Cu)

A study of the solid solutions CeM2-xM'xGe4O12 (M = Mn, Co; M' = Ni, Cu) by X-ray diffraction and magnetometry is described. For M = Co the introduction of Ni and Cu was possible for x <= 0.5; for M = Mn attempts to introduce Cu were unsuccessful but CeMn1.5Ni0.5GeO4 was obtained as a single phase. These compositions crystallise in the space group P4/nbm with a similar to 9.76, c similar to 4.85 angstrom. They all order antiferromagnetically with T-N < 10 K. The magnetic structures adopted by CeMn1.5Ni1.5GeO4O12 and CeCo1.5Cu0.5Ge4O12 were shown by neutron diffraction to be the same as those adopted by CeMn2Ge4O12 and CeCo2Ge4O12, respectively. The in-field metamagnetic transition of the latter to a weakly ferromagnetic phase was shown to persist in the Cu-doped composition. The available data suggest that the anisotropy associated with the Co2+ cation plays a dominant role in determining the magnetic behaviour of these compounds.