Structural, magnetic and dielectric properties of nickel- magnesium substituted cobalt ferrites nanoparticles and core-shell nanocomposites

Abstract

Cobalt ferrite has gained great scientist interest because of its important applications in various fields of science and technology. However, the magnetic character of the particles used for many applications depends crucially on the size, shape and purity of these nanoparticles. Hence the need for developing fabrication processes that are relatively simple and yield controlled particle sizes is desired. This work involves the study of structural, magnetic, dielectric properties and morphology of Co0.5Ni0.5-xMgxFe2O4 ferrite nanoparticles (x = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5), which are synthesized by chemical co-precipitation method. In addition, the core-shell nanocomposites of Co0.5Ni0.5-xMgxFe2O4/Polyaniline were successfully synthesized via chemical polymerization method. The ferrite samples were then sintered at selected temperatures of 700 °C, 800 °C, 900 °C and 1000°C for 8 hours. X-ray powder diffraction indicated that the core material is having a single phase of spinel cubic structure. The crystallite size of Co0.5Ni0.5-xMgxFe2O4 nanoparticles was found in the range of 25-40 nm. The infrared spectra of the synthesized samples displayed two absorption bands characteristic of the spinel ferrites at 585–595 cm-1 and 390–400 cm-1, which correspond to vibrations of tetrahedral and octahedral bonds, respectively. The Field Emission Scanning Electron Microscope and Transmission Electron Microscope images of ferrite nanoparticles show different aggregations at different sintering temperatures and concentrations. The combination of both Ni-, Mg- substituted cobalt ferrites showed that the substitution of Mg2+ ions for Fe made more pronounced effects on magnetic and dielectric properties at room temperature. The values of saturation magnetization (Ms) and coercivity (Hc) are enhanced by increasing of Mg concentration up to x = 0.1. By increasing Mg2+ substitution, the Ms and Hc increase from 57.35 emu/g (x = 0.0) to 61.49 emu/g (x = 0.1) and 603.26 Oe (x = 0.0) to 684.11 Oe (x = 0.1), respectively. In contrast, the Ms decreases from a maximum value 12.00 emu/g (x = 0.1) to a minimum value 5.39 emu/g (x = 0.4) when ferrites are encapsulated with Polyaniline. However, the Hc increases from a maximum value 766.94 Oe (x = 0.1) to a minimum value 646.17 Oe (x = 0.0). At 1 kHz, dielectric constant e' shows a maximum value at 86.22 for x = 0.1 and minimum value at 56.67 for x = 0.3. In addition, the dielectric loss e" shows a maximum value of 10.98 for x = 0.2 and minimum value of 9.45 for x = 0.0. For nanocomposites, e' reaches a maximum value of 68.32 (x = 0.1) and minimum value of 46.73 (x = 0.3) at 1 kHz. In addition, e" shows a maximum value of 49.42 (x = 0.2) and a minimum value of 36.33 (x = 0.3).