Controlled growth of large-area arrays of gadolinium-substituted cobalt ferrite nanorods by hydrothermal processing without use of any template

Abstract

CoFe2−xGdxO4 nanorods were synthesized by a hydrothermal process without use of any template and surfactant. X-ray diffraction, field-emission scanning electron microscope, energy dispersive X-ray microanalyzer, and vibrating sample magnetometer were employed to evaluate structural and magnetic properties of synthesized nanorods. The X-ray diffraction analysis indicated that single phase spinel ferrites were obtained. The XRD data were processed for Rietveld refinement of structure by Reflex program. The FE-SEM micrographs of the synthesized samples showed the presence of large-area arrays of ferrite nanorods . The possible formation mechanism for the synthesis of ferrites nanorods has been preliminarily explained. Based on the EDS analysis, it was suggested that the applied process for preparation of CoFe2−xGdxO4 nanorods is a suitable method for the synthesis of spinel ferrites with homogeneity in composition. It was observed from the magnetic hysteresis loop at a room temperature that with substitutions of gadolinium cations, the coercive field increased from 590.35Oe for x=0–826.10Oe for x=0.05. It was also found that with an increase in gadolinium content, the values of saturation magnetization decreased from 72.36emu/g for x=0–53.61emu/g for x=0.05. Likewise, the demagnetizing factors of ferrite nanorods is calculated. Based on the FE-SEM micrographs, it was observed that with an increase in gadolinium content, the axial ratio c/a of nanorods decrease from 21 for x=0–13 for x=0.05. Therefore, with the substitutions of gadolinium cations, the values of demagnetizing factor along c increased from 0.006 for x=0–0.013 for x=0.05. We can say that at a maximum axial ratio of about 20, the shape-anisotropy constant Ks is lower than the first crystal-anisotropy constant K1 (neglecting K2). Consequently, we proposed that with an increase in gadolinium content, the intrinsic magnetocrystalline anisotropy dominates over the shape anisotropy and thus dictates the magnetic behavior of the system in the present work.