Hydrothermal synthesis of single crystal CoAs2O4 and NiAs2O4 compounds and their magnetic properties†
The crystal structures of the hydrothermally synthesised trippkeite-related materials, CoAs2O4 and NiAs2O4 were investigated by means of single-crystal X-ray diffraction, Raman and infrared spectroscopy. The obtained compounds crystallise in the tetragonal crystal system (P42/mbc), with unit cell parameters at 293 K of a = 8.34530(10)/8.2277(12) Å, c = 5.62010(10)/5.6120(11) Å, V = 391.406(12)/379.90(13) Å3, Z = 4, for CoAs2O4 and NiAs2O4 respectively. Magnetic measurements show that the resulting single crystal of NiAs2O4 exhibits an antiferromagnetic transition at TN = 53 K in a high magnetic field of 10 kOe, as already reported in the literature. The single crystal of CoAs2O4 reveals an interplay between ferromagnetic and a canted antiferromagnetic interactions resulting in a canted antiferromagnetic state which occurs at 105 K – the highest critical temperature among all similar structures.