Abstract
Here, we describe the growth assisted (a) co-precipitation and (b) oxidation methods to achieve CoFe2O4 nanoparticles with high coercivity (Hc) and moderate magnetization (Ms) at room temperature (RT). The particle size is closely related to the relative interdependence between the nucleation and growth steps, which can be manipulated by the solution chemistry and precipitation conditions. Based on this premise, the particles synthesized by optimizing reaction parameters such as, reaction temperature, NaOH concentration and feed rate of metal ion supply source into the alkali solution, was used as seed to prepare particles as large as 40 nm in diameter. On the other hand, by optimizing the reaction parameters such as, concentrations of NaOH and oxidizing agent KNO3, and the ratio of Fe3+/ (Fe3+Fe2+), particles ranging from 15 to 110 nm were synthesized using the oxidation method. The He was enhanced from 0.56 kOe to 2.29 kOe at RT for particles synthesized via growth-assisted coprecipitation method using 1.13 mol of NaOH, metal ion feed rate of 0.06 mollh at 98°C. Using the above single domain CoFe2O4 nanoparticles as seed during in-situ growth improved the He further to 2.9 kOe. On the other hand, among the particles synthesized with the growth assisted oxidation method, particles with diameter around 35 nm recorded the highest He of 2.02 kOe. The relation between He and particle diameter of CoFe2O4 synthesized using the above two methods was studied. The results suggested that size classified particles with 40 nm diameter obtained from the seeded particles showed the highest He of 4.3 kOe.
