Preparation and magnetic properties of Zn-doped Fe ₃ O ₄ magnetic colloid

Fe₃O₄ magnentic colloids were produced by co-precipitating a Fe²⁺, Fe³⁺, and Zn²⁺ containing solution with a NaOH solution at 70°C. Analyses results indicated that the Zn content of the Fe₃O₄ colloids was always less than the solution's Zn content. The difference was found to be the smallest when the colloid was precipitated at pH=10. The as values of the Fe₃O₄ colloid significantly improved by adding an appropriate amount of Zn ions and precipitaing it at an optimum pH value, pH=10. The optimum Zn ion content was 6.18 at%, which was corresponded to Zn_{0 · 1054}Fe_{0 · 8145}Fe₂O₄. At this composition the colloid's σ_a value was 94 emu/g, and increased by more than 34% of pure Fe₃O₄ colloid's σ value. By theoretical calculation the σ_s should increase 27.8%.