Structural, magnetocaloric and magnetodielectric properties of chromium substituted cobalt ferrites

Abstract

Structural, mechanical, magnetic, magnetocaloric, dielectric, and magnetodielectric properties of Cr3+ substituted stoichiometric and non-stoichiometric cobalt ferrite with a general formula of Co1-xCrxFe2O4 and Co1+xCrxFe2-xO4 have been studied. The samples were synthesized using a standard solid-state reaction technique, with sintering temperatures of 1200, 1250, and 1300 °C. X-ray diffraction studies confirm the formation of a single-phase cubic spinel structure with a space group of Fd-3m for both series. The ferrite formation has also been confirmed by FTIR spectra and Raman spectra. Rietveld refined result shows that Cr occupies both the tetrahedral and octahedral sites. The lattice parameters show increasing trends wherein crystallite size shows a decreasing value with increasing Cr3+ content for both series. The cation-anion vacancies, chemical bonding, and oxygen displacement have been evaluated to understand the effect of Cr3+ substitution on the physical and chemical properties. As estimated from scanning electron microscopic images, the average grain size shows a decreasing trend with an increase of Cr3+ for both series. The elastic properties analysis reveals that the synthesized samples for both series are ductile. The tunability of Cr3+ on the magnetic moment, exchange interaction, magnetocrystalline anisotropy constant, and microwave frequency has been found. The nature of magnetic phase transitions for all the Cr3+ concentrations exhibit second order, confirmed by the analysis of critical scaling, universal curve scaling, and scaling analysis of the magnetocaloric effect. The Cr3+ led to tuning the magnetic moment, exchange interaction, magnetocrystalline anisotropy constant, and microwave frequency. The second-order magnetic phase transition has been confirmed from the Arrot and Arrot-Noakes plots for all the samples. The Cr3+ tuned the magnetocaloric (MCE) properties, showing the maximum relative cooling power of 156 Jkg-1 for 50% of Cr3+ for non-stoichiometric series by decreasing the Curie temperature toward room temperature. The reliability of MCE and the nature of the magnetic phase transition of the investigated samples are confirmed by analyzing the critical exponent analysis, universal curve scaling, and scaling analysis of MCE. A significant impact of grain size on dielectric nature has been observed. The temperature-dependent dielectric constant confirms the ferroelectric nature of the samples. At around relaxation frequency, remarkable magnetodielectric responses have been found for all samples.