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Applications of CoFe2O4 are limited due to the lack of synthesis technique to produce monodispersed, single domain and high coercivity (Hc) nanoparticles. Here, we describe the growth dominant co-precipitation process to achieve high Hc, with moderate magnetization at room temperature (RT) in CoFe2O4 nanoparticles. It is well known that the particle size is closely related to the relative interdependence between the nucleation and growth steps, which in turn can strongly be affected by the solution chemistry and precipitation conditions. Based on this premise, the effect of 1) reaction temperature, 2) NaOH concentration, and 3) feeding rate of metal ions into the alkali solution were evaluated. The maximum Hc of 2.29 kOe (RT) was observed for the CoFe2O4 prepared at 98°C, 1.13-mol NaOH, and the metal ion feeding rate of 0.00103 M/min. To improve the coercivity, single domain CoFe2O4 nanoparticles were produced by in situ growth of the CoFe2O4 seeds followed by size separation method. A coercivity of 4.3 kOe was achieved at RT for 40-nm single domain CoFe2O4 nanoparticles, which is close to the theoretical value of 5.3 kOe.
Date of Publication: Sep 2002