Effect of Cu ion on the formation and magnetic properties of nanocrystalline magnetite prepared in an aqueous solution

We prepared the nanocrystalline magnetite from precipitation in aqueous solution varying the concentration of Cu²⁺ ion. The magnetite powder prepared at the Fe²⁺/Cu²⁺ mole ratio=1:0.5 exhibited that its Cu content was about 5.4 wt% and its particle size was about 20 nm. A Mössbauer study showed that Cu ions were disordered in both the A and B sites. With the higher Fe²⁺/Cu²⁺ mole ratio, the particle size increased. At the Fe²⁺/Cu²⁺ mole ratio below 0.5, superparamagnetic particles of a few nanometer in size appeared and lowered the saturation magnetization as well as the coercivity. These magnetic properties became maximized in the powder prepared at the Fe²⁺/Cu²⁺ mole ratio of 0.5.