Growth dominant co-precipitation process to achieve high coercivity at room temperature in CoFe/sub 2/O/sub 4/ nanoparticles

Abstract

Applications of CoFe/sub 2/O/sub 4/ are limited due to the lack of synthesis technique to produce monodispersed, single domain and high coercivity (H/sub c/) nanoparticles. Here, we describe the growth dominant co-precipitation process to achieve high H/sub c/, with moderate magnetization at room temperature (RT) in CoFe/sub 2/O/sub 4/ 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 H/sub c/ of 2.29 kOe (RT) was observed for the CoFe/sub 2/O/sub 4/ prepared at 98/spl deg/C, 1.13-mol NaOH, and the metal ion feeding rate of 0.00103 M/min. To improve the coercivity, single domain CoFe/sub 2/O/sub 4/ nanoparticles were produced by in situ growth of the CoFe/sub 2/O/sub 4/ seeds followed by size separation method. A coercivity of 4.3 kOe was achieved at RT for 40-nm single domain CoFe/sub 2/O/sub 4/ nanoparticles, which is close to the theoretical value of 5.3 kOe.