Structure, Microstructure and Magneto-Dielectric Properties of Barium Titanate-Ferrite Based Composites

Abstract

Magneto-dielectric composites materials are those which perform both magnetic and dielectric properties in one single component. Due to the coupling between the ferroelectric and ferromagnetic, the magnetization can be controlled by an applied electric field, while the electric polarization can be controlled by applying a magnetic field. The phase connectivity and phase morphology plays an important role in the modifying the magneto-dielectric properties of the composites. Synthesis method is great tool to explore the microstructure and magneto-dielectric properties of the composites.
In present work three synthesis methods were adopted to prepare magneto-dielectric composites. They are combustion derived solid-state mixing, combustion derived in-situ synthesis method. BaTiO3 selected for the ferroelectric phase which is having moderate properties of permittivity, loss, piezoelectric constant. CoFe2O4, ZnFe2O4 and Co0.5Zn0.5Fe2O4 are selected for ferrite phase, which are hard, soft and non-magnetic in nature respectively. Ferrite weight percentage was used in magneto-dielectric composites at 20%, 30%, 40%. Structure, microstructure and magneto-dielectric properties of composites were studied and analyzed. Dielectric, magnetic and magneto-dielctric properties of composites varied significantly by varying synthesis method. Traces hexagonal BaTiO3 has been detected when tetragonal BaTiO3 sintered along with ferrites. Plate like morphology of BaTiO3 was evolved along with nearly spherical morphology of BaTiO3 in solid-state derived composites, but no evidence of plate like BaTiO3 in in-situ composites. Cobalt ferrite based composite shows negative magneto-capacitance response in both solid state and in-situ synthesis, which not in other ferrite systems of solid-state and in-situ derived composites.
Along with the solid-state and in-situ synthesis methods, ex-situ synthesis method was also adopted to explore in present magneto dielectric composites. Typical 30 wt% ferrite (CoFe2O4, ZnFe2O4 and Co0.5Zn0.5Fe2O4) composites were made in this method. Microstructural study shows large no of plate like BaTiO3 exists in ferrite@BT composites than BT@ferrite composites. Cobalt and zinc ferrite based ex-situ composites show both positive and negative magneto capacitances in 7BT@3(CF/ZF) and 3(CF/ZF)@7BT composites respectively. Cobalt zinc ferrite based ex-situ composite show the positive magneto-capacitance in both 7BT@3CZF and 3CZF@7BT. Magneto-capacitance responses are dependent on both magnetostriction and magnetoresistance. Magneto-capacitance values of about -1.48%, -1.08%, 19.9% and -2.1% were observed in 7BT$3CZF, 7BT#3CZF, 7BT@3CZF and 3CZF@7BT composites respectively. Similarly 9.91%, 19.76% and 19.9% were observe in 7BT@3CF, 7BT@3ZF and 7BT@3CZF composites respectively. [math mode missing closing $]