Synthesis, structural and complex impedance spectroscopy studies of Ni_0.4Co_0.4Mg_0.2Fe₂O₄ spinel ferrite

Spinel ferrite having composition Ni_0.4Co_0.4Mg_0.2Fe₂O₄ was prepared by sol-gel method. X-ray diffraction result indicates that the ferrite sample has a cubic spinel type structure. FT-IR showed two absorption bands (ν₁ and ν₂) that are attributed to the stretching vibration of tetrahedral and octahedral sites. Complex impedance properties have been investigated in 200–420 K temperature range with varying frequency between 40 and 10⁷ Hz. Frequency and temperature dependency of imaginary part of permittivity (ϵ″) and dielectric loss (tanδ) has been discussed in terms of hopping of charge carriers between Fe²⁺ and Fe³⁺ ions. Activation energy has been estimated from both temperature dependency of dc conductivity and relaxation time data, which indicates that the relaxation process and conductivity have the same origin. Nyquist plots of impedance show semicircle arcs for sample and an electrical equivalent circuit has been proposed to explain the impedance results.