Exchange spring behaviour in BaFe12O19/CoFe2O4 magnetic nanocomposites

摘要

In this work, nanopowders of BaFe12O19 and CoFe2O4 and nanocomposites of (1-x) BaFe12O19/xCoFe(2)O(4), for x = 0.00, 0.25, 0.50, 0.75 and 1.00, were prepared via co-precipitation and high-speed ball milling techniques, respectively. For structural analysis, the X-ray diffraction revealed the formation of hexagonal BaFe12O19 and spinel CoFe2O4 ferrites, and the average crystallite sizes were about 35 nm and 15 nm, respectively. The transmission electron microscope indicated that the two phases are well distributed and the grain sizes of the composite powders are verified employing the size distribution histograms where two peaks were obtained separately for both ferrites. From EDX spectra, it was shown that all samples exhibit an excellent compositional homogeneity verifying the presence of both phases in the obtained nanocomposite powders. Magnetic measurements were performed via a vibrating sample magnetometer at 300 K and 77 K. The results showed a good single-phase magnetic behavior, proving the good exchange coupling between hard and soft phases. For low CoFe2O4 content, the dipolar interactions were dominated by the exchange-coupling interactions. Additionally, the optimum values of saturation and remanent magnetizations as well as the squareness ratio were obtained for the x = 0.5. This was attributed to the dominance of exchange-coupling interaction. Magnetic properties for nanocomposites were improved as the temperature falls from room temperature down to 77 K. This increase is skilled to the reduction in the thermal fluxes of magnetic moments at the surface. (C) 2021 Elsevier B.V. All rights reserved.