Synthesis and Characterization of Nanocrystalline Magnetic Pigment via ‎Coordinated Precursors

N anocrystalline 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. ‎