Concentration dependent exchange coupling in BaFe12O19/NiFe2O4 nanocomposites

Hard Barium ferrite (BaFe12O19) and soft Nickel ferrite (NiFe2O4) nanoparticles and their nanocomposites with different concentrations, i.e. (BaFe12O19)1−x/(NiFe2O4)x where x = 0, 0.3, 0.5, 0.7 and 1 were successfully synthesized. X-ray diffraction was used to obtain the phase formation and purity of these samples and the average crystallite size was found to be in a narrow range of 27–34 nm. The merging of zero field cooled and field cooled magnetization curves for x = 0.7 was evidence of strong magnetic interactions in these nanocomposites which is due to strong exchange coupling of hard/soft magnetic phase at this particular concentration. The value of coercivity and saturation magnetization of soft ferrite (NiFe2O4) should be linearly increased by the addition of hard ferrite (BaFe12O19), however a sharp increase was found for x = 0.7 and x = 0.5 samples, which is indication for the presence of spring exchange coupling in thesecomposites. The single peak in dM/dH vs H plot indicate the presence of strong exchange coupling for x = 0.5. Bloch’s law fit revealed the smallest value of Bloch’s constant B for x = 0.7, which is also an evidence for the presence of strong magnetic interactions in these nanocomposites. The Kneller’s law fit to the HC versus temperature data revealed the higher value of Kneller’s constant for x = 0.7, which may be due to presence of strong magnetic interactions in these nanocomposites. In summary, hard/soft ferritescomposites with spring exchange mechanism strongly depends on the concentration of hard and soft ferrite phases and may be beneficial for different technological applications.