Effect of NaOH and precursor concentration on size and magnetic properties of FeCo nanoparticles synthesized using the polyol method

In this study, the effects of NaOH and precursor concentration on the particle size and magnetic properties of FeCo nanoparticles are investigated. Results suggest that an optimized ratio of NaOH molar concentration [OH] to precursor molar concentration [M] is required to obtain a small particle size, high saturation magnetization, and low coercivity. When the [OH]/[M] ratio was greater than 40, the FeCo nanoparticles aggregated, whereas when the [OH]/[M] ratio was less than 20, FeCo + CoFe2O4 nanoparticles were obtained due to unstable reduction reactions. When [OH]/[M] was 40, the 387 nm FeCo nanoparticles showed the highest saturation magnetization and lowest coercivity, which are the best conditions for achieving high permeability. In contrast, the complex permeability of the 173 nm FeCo nanoparticles was higher than that of the 387 nm FeCo nanoparticles owing to the decrease in the demagnetization effect in the high frequency band. This confirmed that the particle size had a greater effect on the complex permeability than that on the saturation magnetization and coercivity in GHz ranges.