A study on the extent of exchange coupling between (Ba0.5Sr0.5Fe12O19)1-x(CoFe2O4)x magnetic nanocomposites synthesized by solgel combustion method

One step citrate gel combustion method followed by high temperature annealing was employed for preparing (Ba0.5Sr0.5Fe12O19)(1-x)(CoFe2O4) (x=0.1, 0.2, and 0.3) composite ferrite powders. The powders were subjected to annealing at 800 degrees C in order to decisively study the phase evolution of the combined hard and soft ferrites. Thermogravitry (TGA)/differential scanning calorimetry (DSC) analysis exhibited three stages of decomposition in the precursor gels combined with an exothermic peak at 210 degrees C. X-ray diffraction (XRD) analysis confirmed that the diffraction peaks were perfectly indexed to the hexagonal magneto-plumbite structure of Ba0.5Sr0.5Fe12O19 and the cubic spinel structure of CoFe2O4. Fourier transform infrared spectroscopy (FT-IR) analysis for the samples showed a Co-O stretching vibration accompanied with Co-O-Co or Fe-O-Fe bands at 1220 cm(-1). The morphology of the samples were examined by field emission scanning electron microscope (FE-SEM) and transmission electron microscope (TEM). The crystallinity of a selected sample was evaluated by using the high resolution transmission electron microscope (HR-TEM) and selected area electron diffraction (SAED) pattern. It confirmed the presence of planes comprising the hard and soft phases in the synthesized nanocomposites. The magnetic parameters like saturation magnetization M-S, remanent magnetization M-R, squareness ratio S-R, coercivity H-C and magnetic moment mu(B) were evaluated using hysteresis by employing vibrating sample magnetometer (VSM). Maximum He of 4.7 kOe and M-S of 60.4 emu/g were obtained for (Ba0.5Sr0.5Fe12O19)(0.9)(CoFe2O4)(0.1). Switching field distribution curves were analysed by using the demagnetization curve. The exchange coupling between the hard and soft phases were analysed by the dM/dH plots and it indicated the exchange coupling first increased with the increase in the concentration of spinels and then decreased. The possible comparison of exchange coupling between the hard and soft phases has been discussed in detail. (C) 2016 Elsevier B.V. All rights reserved.