(Bi13Co11)Co2O40–Co3O4 composites: Synthesis, structural and magnetic properties

Abstract

Nanocrystalline of Co sillenite-Co3O4 composites were prepared by combustion and sol-gel methods. The synthesized materials were further investigated by XRD, FT-IR, Raman spectroscopy, DC magnetometry, FESEM and EDX. The XRD characterization revealed that the sillenite phase is nanostructured with a crystallite size in the range from 48.4 to 64.4 nm. Both syntheses methods yielded between 75 and 80 wt% of sillenite. The FESEM micrographs showed that the particles had sphere like and a nanosheets - sphere like shapes when prepared by combustion and sol-gel methods, respectively. Confirmation of the chemical structure of composites was determined by the FT-IR and Raman spectra through the vibrational modes of bismuth-oxygen and cobalt-oxygen bonds. The M-H and M-T magnetic measurements showed ferromagnetic like behavior at 6 K. An antiferromagnetic transition due to Co3O4 was observed at TN = 36 K. Both samples showed a antiferromagnetic Curie-Weiss behavior with a large -θCW, (θCW » TN) their calculated frustration degrees were of f ≈ 7.5 and 15.1 for samples prepared by sol-gel and combustion methods, respectively. The sample prepared by combustion method showed a blocking temperature at Tb = 148 K, Tb decreased when applied a higher field, it was ascribed to CoO clusters like phase. These results show that the combustion method allows to produce a multiphasic sample with a high degree of geometric magnetic frustration, while, the sol-gel method allows to synthesize a sample with a high crystallinity and purity.