Effects of heat treatment on the structural, dielectric and magnetic properties of ZnO@CoFe2O4 nanocomposites

Pure ferrite (CoFe2O4), semiconductor oxide (ZnO), and their nanocomposites (<= 5 wt% CoFe2O4) were calcined at 750 degrees C/4 h and were successfully prepared using co-precipitation and sol -gel methods. The structural results showed cubic and hexagonal crystallization phases of CoFe2O4 and ZnO, respectively. While mixed crystallization phases of cubic and hexagonal were detected in nanocomposites. The crystallite size decreased from 43.82 to 37.72 nm with the incorporation of CoFe2O4, as detected by the XRD results. Whereas particle sizes obtained from HR-TEM are 10 nm and 93 nm for ZnO and CoFe2O4, respectively. While nanocomposites showed an accumulated nanoparticle with a circular grain size <= 150 nm. A blue shift was observed in the optical band gap (from 3.22 to 3 eV) as a result of an increase in CoFe2O4 content. The enhancement in magnetic properties was presented after adding a small percent (up to 5 wt%) of ferrite to ZnO since the diamagnetic behavior of ZnO transformed to that of soft ferromagnets in their nanocomposites. All magnetic parameters were enhanced by the incorporation of CoFe2O4 wt.%. Broadband dielectric spectroscopy is employed to study the electrical conductivity and dielectric properties of the investigated samples. It is noticed that the calcination temperature at 750 degrees C/4 h enhances the dc-conductivity of nanocomposites by about 5 times. Also, increasing the percentage of CoFe2O4 gradually increases the conductivity of the nanocomposite. The activation plot of the investigated samples shows strange behavior. However, ferrite follows an Arrhenius relation, and all considered nanocomposites as well as ZnO deviated from both the Arrhenius and VFT equations.