EPR and Magnetometry of Mixed Phases in FeVO ₄ –Co ₃ V ₂ O ₈ System

Magnetic properties of five samples obtained in reactions between nFeVO ₄ and (1 − n)Co ₃ V ₂ O ₈ (with the composition index n = 0.54, 0.50, 0.40, 0.30 and 0.20) have been investigated by dc magnetometry and electron paramagnetic resonance (EPR). The investigated samples contained two phases: one having lyonsite-type structure and the other Co ₃ V ₂ O ₈ . Temperature dependence of dc magnetic susceptibility showed the Curie–Weiss paramagnetic behaviour with a strong antiferromagnetic (AFM) interaction in the high-temperature range leading to magnetic transitions at 6 and 12 K. For all samples, the magnetic hysteresis loop in isothermal magnetisation was registered at T = 5 K indicating the existence of a ferromagnetic component. Samples n = 0.54 and 0.50 displayed a large coercive field and remanent magnetisation in contrast to the other three samples due to higher content of the lyonsite-type structure. EPR spectra of the studied samples showed a broad asymmetric line that was decomposed on lorentzian or gaussian components. Temperature dependence of the spectral parameters (resonance field, linewidth, integrated intensity) of these components was studied in high-temperature range (T > 90 K). The observed spectra were attributed to different types of magnetic spin clusters.