Magnetic properties of GdBB’Ge4O12; BB’ = FeZn or GdCa

Polycrystalline samples of Gd2CaGe4O12 and GdFeZnGe4O12 have been synthesized via a ceramic route. Both were characterised by X-ray diffraction, magnetometry and Mössbauer spectroscopy; GdFeZnGe4O12 was also studied by neutron diffraction. They adopt the SrNa2P4O12 structure: space group P4/nbm with a = 10.0766(1), c = 5.1043(1) Å for Gd2CaGe4O12; a = 9.7298(1), c = 4.7515(1) Å for GdFeZnGe4O12 at 293 K. Gd2CaGe4O12 is paramagnetic for 2 ≤ T/K ≤ 300 whereas GdFeZnGe4O12 is antiferromagnetic below 13.8(2) K. The six-coordinate Fe3+ and Zn2+ cations are disordered over the pseudo-cubic 4 f sublattice and the Gd3+ cations occupy the eight-coordinate 2b sites. The Fe3+ and Gd3+ cations adopt an A-type, k = [0,0,½] antiferromagnetic arrangement with their ordered moments aligning in the xy plane. The Fe/Zn disorder results in relatively low ordered cation moments (Gd3+ = 6.02(13), Fe3+ = 3.84(15) µB) in the antiferromagnetic phase