Structural and magnetic properties of a BaFe12O19/NiFe2O4 nanostructured composite depending on different particle size ratios

Abstract

A nanostructured magnetic composite based on hexagonal ferrite BaFe12O19 (magnetically hard) and cubic ferrite NiFe2O4 (magnetically soft) is synthesized. The hexagonal ferrite precursor is obtained by the Sol-Gel method using citric acid as a coordinating agent. The precursor obtained is heated at different temperatures to get nanoparticles with different sizes. Cubic ferrite is obtained by chemical co-precipitation, method and the nanoparticle growth process is controlled with different heat treatments. The hexagonal and cubic ferrite nanoparticles are mixed providing low energy. Three samples of this kind of composite are obtained with a different ratio of particle size. The composites are a mixture where there are clusters of the minority phase NiFe2O4 distributed in a matrix of the main phase BaFe12O19. Both ferrite phases are composed of nanoparticles with an average size less than 50 nm without tensions in the crystal lattice. These structural parameters were compared between the composites and their precursor ferrites. The relationship between the composite microstructures and their magnetic properties is analyzed. A weak exchange coupling was detected between the component magnetic phases of the composites. Depending on the synthesis conditions, some samples exhibit monodomain or a multidomain regime. The higher BH product appears for composites from ferrites with a nanoparticle size ratio approximately equal to one. The structural characterization is carried out by X-ray diffraction. The homogeneity of the composition in the volume of the nanostructured composites is analyzed with a field emission scanning electron microscope equipped with energy dispersive spectroscopy for the analysis of the element mapping. The magnetic study is carried out through measurements of magnetization as a function of the applied field (M vs. H) at 300 K.