Site occupancies of Co–Mg–Cr–Fe ions and their impact on the properties of Co0.5Mg0.5CrxFe2−xO4

Co0.5Mg0.5CrxFe2−xO4 spinel ferrite systems (where x = 0.0–1.0 in steps of x = 0.25) were synthesized by sol–gel auto combustion method, aiming to study the correlation between site occupancy and the concentration of the substitution of Cr3+ ions. The properties of the sol–gel synthesized samples were investigated by XRD, TEM, IR, magnetization, resistivity and dielectric measurements. XRD patterns and IR spectra confirm the formation of single phase Co–Mg–Cr ferrite after combustion. Site occupancy of the constituent ions was estimated from XRD data by employing the Bertaut method. The tetrahedral and octahedral site radius permits to calculate the theoretical lattice constant and the oxygen positional parameter. The IR spectra were recorded in the range of 300–800 cm−1. The bands at around 600 cm−1 and around 350 cm−1 were assigned to the tetrahedral and octahedral complexes, respectively. Magnetization decreases continuously with increase of Cr content. For Co0.5Mg0.5CrxFe2−xO4, the Néel model for the two sub-lattice can be used to explain the compositional variation of magnetic moment due to the reduction of the A–B interaction. The dielectric constant as a function of temperature was computed in accordance with Smit and Wijn and explained by the dielectric polarization based on Rabkin and Novikova assumptions. Results are discussed regarding the influence of the site occupancy of the ions.

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► Ct3+ substituted Co–Mg ferrite.
► Site occupancy of Co–Mg–Cr–Fe ions.
► Magnetization and coercivity shows inverse trend to each other.
► Resistivity increased whereas dielectric properties decreased with Cr3+ substitution.