Magnetic properties of CoFe2O4 nanoparticles prepared by thermal treatment of ball-milled precursors

Abstract We developed a simple synthesis method for production of CoFe 2 O 4 nanoparticles. The method is based on the solid state ball-milling and calcinations of acetate precursors and citric acid. The samples were characterized using X-ray diffraction, transmission electron microscope, Fourier transform infrared and energy-dispersive X-ray spectroscopy. Magnetic properties of the samples were studied using vibrating sample magnetometer and ac susceptibility measurements. The results show that the products mainly consist of CoFe 2 O 4 nanoparticles. Magnetization measurements demonstrate the effect of calcination temperature on particle size and hence, on the magnetic properties of the CoFe 2 O 4 nanoparticles. By increasing the particle size from 3.5 to 7.2 nm, the room temperature coercivity and magnetization increase from 0 to 152 Oe and from 8 to 30 emu/g respectively. Also, the low temperature calcinated samples, C250 and C30 are superparamagnetic in nature due to it’s near-zero coercivity and remanence. We estimated the mean value of the effective anisotropy constant, K eff  = 9.2 × 10 6  erg/cm 3 . This value is much larger than the bulk value, due to the surface effects.