Superparamagnetic nickel ferrite colloidal spheres for constructing magnetically responsive photonic crystals

摘要

Well-dispersed nickel ferrite (Ni_xFe_(1-x)Fe_2O_4) colloidal spheres with uniform size and tunable composition were synthesized by a simple hydrothermal method. The changes of diameter, grain size, and magnetic prop-erties of nickel ferrite colloidal spheres with the content of nickel element were investigated. The saturation magnetization of nickel ferrite can be tuned via changing the composition, which affects molecular magnetic moment and diameter of colloidal spheres. All nickel ferrite colloidal spheres prepared in this work show superparamagnetic behavior, and thus can be used to construct magnetically responsive photonic crystals. The color of aqueous solution containing Ni_(0.40)Fe_(0.60)Fe_2O_4 colloidal spheres changed from blue to brown with decreasing external magnetic field.