抄録
Magnetic properties have been examined for zinc ferrite nanocrystals synthesized via hydrothermal reaction. The hydrothermal reaction has been carried out at 200°C using an aqueous suspension containing zinc hydroxide and iron hydroxide. X-ray diffraction analysis indicates that the resultant specimens are composed of single phase of ZnFe2O4 independent of the reaction time. The size of crystal, which is smaller than 10 nm, is apt to increase as the reaction time is increased, as revealed from transmission electron micrographs as well as linewidth at half maximum of X-ray diffraction lines. A single phase of ZnFe2O4 is still observed in X-ray diffraction patterns after heat treatment at 300°C in air. The present ZnFe2O4 nanocrystals exhibit high magnetization even at room temperature. The temperature dependence of magnetization manifests superparamagnetic behavior with a blocking temperature of several tens K under external magnetic field of 500 Oe. The magnetization is apt to decrease with a decrease in temperature below the blocking temperature even when field cooling is carried out, suggesting that there is strong magnetic interaction among nanocrystals so that the magnetization of nanocrystals is oriented randomly with each other.
