Magnetic and impedance properties of magnetoelectric Co ₄ Nb ₂ O ₉

The compound Co ₄ Nb ₂ O ₉ (CNO) exhibits interesting magnetoelectric coupling across its antiferromagnetic transition temperature (T _N ). Here, we report the structural, magnetic and complex dielectric properties of polycrystalline CNO within a wide temperature range (120–360 K), well above its T _N . The temperature dependent dc magnetization reveals that T _N ∼27.2 K. The isothermal magnetization results infer the magnetic field induced transition around 11 kOe at 5 K. The temperature dependent real part of complex dielectric behavior shows sharp increase around 160 K with frequency dispersion and a clear frequency dependent peak is observed in tanδ across the same temperature region. This feature corroborates the dielectric relaxation in CNO well above the long range magnetic ordering. Interestingly; the Curie-Weiss behavior of magnetization results deviate from linearity around the same temperature regime (∼160 K) which suggests the presence of short range magnetic correlation well above T _N . The details impedance spectroscopy results are also analyzed to comprehend the grain and grain boundary contributions.