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

Abstract Polycrystalline samples of Gd 2 CaGe 4 O 12 and GdFeZnGe 4 O 12 have been synthesised via a ceramic route. Both were characterised by X-ray diffraction, magnetometry and Mossbauer spectroscopy; GdFeZnGe 4 O 12 was also studied by neutron diffraction. They adopt the SrNa 2 P 4 O 12 structure: space group P 4/ nbm with a  = 10.0766(1), c  = 5.1043(1) A for Gd 2 CaGe 4 O 12 ; a  = 9.7298(1), c  = 4.7515(1) A for GdFeZnGe 4 O 12 at 293 K. Gd 2 CaGe 4 O 12 is paramagnetic for 2 ≤ T/K ≤ 300 whereas GdFeZnGe 4 O 12 is antiferromagnetic below 13.8(2) K. The six-coordinate Fe 3+ and Zn 2+ cations are disordered over the pseudo-cubic 4 f sublattice and the Gd 3+ cations occupy the eight-coordinate 2 b sites. The Fe 3+ and Gd 3+ 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 (Gd 3+ = 6.02(13), Fe 3+ = 3.84(15) µ B ) in the antiferromagnetic phase.