Concentration dependent exchange coupling in BaFe12O19/NiFe2O4 nanocomposites

Hard Barium ferrite (BaFe ₁₂O ₁₉) and soft Nickel ferrite (NiFe ₂O ₄) nanoparticles and their nanocomposites with different concentrations, i.e. (BaFe ₁₂O ₁₉) _1−x/(NiFe ₂O ₄) _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 (NiFe ₂O ₄) should be linearly increased by the addition of hard ferrite (BaFe ₁₂O ₁₉), 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 these nanocomposites. 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 H _C versus temperature data revealed the higher value of Kneller's constant α for x = 0.7, which may be due to presence of strong magnetic interactions in these nanocomposites. In summary, hard/soft ferrites nanocomposites with spring exchange mechanism strongly depends on the concentration of hard and soft ferrite phases and may be beneficial for different technological applications.