Influence of NaBH₄ on the size, composition, and magnetic properties of CoFe₂O₄ nanoparticles synthesized by hydrothermal method

Cobalt ferrite nanoparticles are prepared by varying the concentration of reducing agent NaBH₄ by hydrothermal method. Transmission electron microscope observations show that particle size increases from 11.47 to 28.05 nm by increasing the concentration of NaBH₄ from 30 to 70 mM. Williamson–Hall analysis on X-ray diffraction patterns show that strain increases in nanoparticles with increase in quantity of NaBH₄. Energy dispersive X-ray analysis and Inductive coupled plasma atomic emission spectroscopy indicate large amount of oxygen deficiency which increase with amount of NaBH₄. The magnetic hysteresis loops measured at room temperature clearly illustrate the influence of concentration of NaBH₄ on magnetic properties of CoFe₂O₄. Saturation magnetization, coercivity, and anisotropy constant increases with the quantity of NaBH₄ and they reach the maximum values of 93 emu/g, 2210 Oe, and 5.28 × 10⁵ J/m³, respectively, with addition of 70 mM NaBH₄. Estimation of micromagnetic parameters (exchange length, critical single-domain volume, etc.) suggests that prepared nanoparticles of CoFe₂O₄ are in single domain and size lies between superparamagnetic to critical single domain. The enhancement of magnetization is attributed to oxygen deficiency. This technique is useful in tuning the size and magnetic properties of cobalt ferrite nanoparticles.