Synthesis and characterization of CoFe2O4 magnetic particles prepared by co-precipitation method: Effect of mixture procedures of initial solution

CoFe₂O₄ magnetic particles were prepared by co-precipitation method in 60 °C homogeneous aqueous solution without any subsequent heat treatment. It was found that the mixing procedure and Fe²⁺/Fe³⁺ ratio of initial solution were critical in the preparation of CoFe₂O₄ particles in particle size, magnetization characters, uniformity in particle size and even cation distribution in spinel structure. Two different procedures were used to precipitate CoFe₂O₄ magnetic particles. Evidenced by XRD, Mossbauer analyses and magnetization determination, particles in comparative uniformity average size were obtained in procedure A, denoted as normal pH regulation procedure, in which NaOH solution was dropped into the mixture solution of iron ions, and with the decreasing in Fe²⁺/Fe³⁺ ratio of initial solution, the particle size decreased, which followed the same rule of diversification in saturation magnetization. Uniformity in particle size lowered when procedure B, referred to as reverse pH regulation procedure, where ferrous and cobalt ions were dropped into alkaline solution, was used to precipitate CoFe₂O₄. In both procedures, with the decreasing in Fe²⁺/Fe³⁺ ratio of initial solution, the saturation magnetization decreased, while the magnetic coercivity decreased but increased sharply when Fe²⁺/Fe³⁺ ratio of initial solution was 0.