Size selected synthesis of CoFe_2O_4 nanoparticles prepared in a chitosan matrix

摘要

In this paper we report the synthesis and magnetic properties of CoFe_2O_4 nanoparticles. The nanoparticles with sizes ranging from 6 to 20 nm were prepared in a chitosan matrix. Size selection was achieved by introducing a nonionic surfactant Tween-X, where X={20, 60, 80, and 85}. Aqueous dispersions of Tween-X show micelles with increasing hydrodynamic sizes as X increases. Mossbauer spectroscopy measurements at 300 K show superparamagnetic behavior for the small particles, changing gradually to a blocked magnetic regime as the particle size increases. Magnetization measurements at 300 K show increasing values for the ratio M_r/M_(Hmax) and coercive fields (H_c).