Preparation and Magnetic Properties of FeNi/SiO_2 Core-shell Nanosphere

γ-FeNi/SiO2 with core-shell structure nanocomposites was prepared in co-precipitation combined H2 reduction method.The phase structure,morphology and magnetic properties of the nanoparticles were determined and measured by X-ray diffraction(XRD),transmission electron microscopy(TEM) and vibrating samples magnetometer(VSM),respectively.The result has shown that the pH is an important factor for core/shell nanostructure morphology.The TEM images have revealed that the nanoparticles reduced at 700 ℃ have an obvious core-shell structure at about pH 9.The core is γ-FeNi alloy with particles with an average diameter of about 80 nm and the coating shell is amorphous SiO2.It was found that the size of γ-FeNi nanoparticles increases little as the reduction temperature increases.Experiment results have indicated that the value of saturation magnetization decreases with the increase of the SiO2 content.The value of saturation magnetization increases with the increase of reduction temperature,but the coercive force decreases,due to the existence of the exchange coupling interaction interface of FeNi and Fe(Ni)-oxide.