Effect of digestion time on size and magnetic properties of spinel CoFe₂O₄ nanoparticles

Abstract

We investigate the effect of digestion time on size, distribution, and magnetic properties of CoFe₂O₄ nanoparticles prepared by the precipitation approach. The average crystalline size increases from 14 to 19 nm as the digestion time is increased from 1 to 120 min. The observed dependence of average particle size with digestion time is in good agreement with Lifshitz, Slyozov, and Wagner theory. Our results suggest that the dissolution of Co²⁺-Fe³⁺ complexes form the surface followed by crystallization of spinel oxide through Oswald ripening process. This observation is in sharp contrast to the growth process in Fe₃O₄ nanoparticles where Oswald ripening is insignificant beyond 5 min due to the electron hopping between Fe²⁺ and Fe³⁺ ions. Magnetization measurements show that the saturation magnetization value decreases from 60 to 49 emu/g as the digestion time is increased from 1 to 120 min. Raman and Mossbauer spectroscopic investigations reveal that reduction of magnetization with increasing particle size is due to the formation of nonmagnetic ferrihydrite at higher digestion times.