Study of the quasi two-dimensional CoxNi1-xTa2O6 compounds by X-ray diffraction and magnetic susceptibility measurements

We report results on the structural and magnetic properties of the CoxNi1−xTa2O6 series of compounds by X-ray powder diffraction, magnetic susceptibility and magnetization measurements. X-ray refinements carried out by the Rietveld method show that these compounds crystallize in a P42/mnm tetragonal structure. Magnetic susceptibility curves show a broadened maximum witnessing that these compounds exhibit two-dimensional antiferromagnetic behaviors. All the CoxNi1−xTa2O6 compounds order below 10K and present a large ion anisotropy. The magnetic properties have been determined in both the paramagnetic and antiferromagnetic state. In the hypothesis of two dimensional AF ordering, the near neighbor exchange constants (J1) and the next near neighbor exchange constants for two different paths (J2 and J'2) were determined. The composition dependence of the magnetic properties including ordering temperature, exchange constants and anisotropy factors are discussed. The drastic reduction of the ordering temperature for x=0.20 for CoxNi1−xTa2O6, suggest the hypothesis of a peculiar magnetic behavior for this composition. ► CoxNi1−xTa2O6 solid solution exhibits two-dimensional antiferromagnetic behavior. ► Intrinsic magnetic properties are determined in both paramagnetic and ordered states. ► Ordering temperature and magnetic frustration are sample composition dependant. ► Cation magnetic anisotropy dominates than the near neighbor exchange interactions. ► A cross-over of the near neighbor exchange interactions is obtained at x=0.2.