Synthesis and Characterization of Nanocrystalline Magnetic Pigment via Coordinated Precursors

Nanocrystalline cobalt ferrite as a magnetic black pigment was synthesized via coordinated precursors with a significant decrease of the synthesis temperature using citric acid as a coordinating agent. The structure and properties of the cobalt ferrite powder were characterized by X-ray diffraction (XRD), colorimetric analysis (L*a*b* color parameters), diffuse reflectance spectroscopy and vibrating sample magnetometer (VSM). In addition, the structural coordination and morphology of the precursors and cobalt ferrite powder were evaluated by infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). Simultaneous thermal analysis (TG-DTG-DTA) was used to investigate the thermal decomposition of the coordinated precursor. FTIR spectra of the precursors indicated that carboxylate groups of citric acid coordinated to the metal ions to form the coordinated precursors. Diffraction patterns and FTIR spectrum confirmed the formation of a pure organic free single-phase spinel with a cubic system (Fd3m). The crystallite size was in the range of 18-22 nm using Scherrer equation. The SEM micrographs showed changes in the morphology of the precursors and in the sample in which the cobalt ferrite powder had almost spherical morphology. Colorimetric analysis using L*a*b* coordinates and diffuse reflectance spectroscopy revealed nearly full light absorption in the 350-750 nm range which are in agreement with the black color of the cobalt ferrite pigment. Values of the saturation magnetization (Ms), remanent magnetization (Mr) and magnetic coercivity (Hc) corresponding to the cobalt ferrite powder were: 67.72 emu/g, 32.54 emu/g and 1.8 kOe, respectively. They were lower than the bulk values because of the nanoscale of the powder.