Magnetic study of phases in FeVO₄-Co₃V₂O₈ system

Magnetic properties of four nFeVO₄/(1-n)Co₃V₂O₈ samples obtained in reactions between FeVO₄ and Co₃V₂O₈ (n = 0:96, 0.86, 0.84 and 0.83, samples designated S1, S3, S4, S5, respectively) have been investigated by DC magnetisation in field cooling and zero-field-cooling modes and EPR. DC magnetic susceptibility showed paramagnetic behavior of all samples in high-temperature range (T > 20 K) and transition to antiferromagnetic state at 16-18 K (depending on sample iron content). Additional magnetic freezing at 8 K was registered for S3-S5 samples containing larger amount of cobalt. The Curie-Weiss law in 100-300 K temperature range indicates that Co²⁺ is in the high-spin state (S = 3=2). From the parameters of the hysteresis loop observed for the samples it was calculated that 0.58% of all magnetic (Fe³⁺, Co²⁺) ions were involved in the ferromagnetic states. EPR spectra of the samples were recorded in high temperature range (T > 90 K). The temperature dependence of the spectral parameters (resonance field, linewidth, integrated intensity) suggested the Fe³⁺ high-spin ions coupled by antiferromagnetic interaction and clusters of ions play major role in EPR spectra.