中文摘要：

采用溶胶-凝胶法制备了CoFe2O4／SiO2纳米复合材料，利用x射线衍射，透射电镜以及傅立叶变换红外吸收光谱分析了该复合材料的结构、形貌及形成机理，并在室温下用振动样品磁强计测量了复合材料的磁滞回线．实验结果表明：当煅烧温度不超过1250℃时，复合材料中的球型CoFe2O4纳米晶镶嵌在非晶SiO2基体中，纳米晶的平均尺寸从煅烧温度850℃时的5nm缓慢增大到1250℃时的35nm；当煅烧温度升高到1300℃时，SiO2的晶化导致了CoFe2O4纳米晶的严重团聚，CoFe2O4纳米颗粒的平均尺寸迅速增大到83nm，CoFe2O4的晶体结构有所改变，饱和磁化强度急剧增大，矫顽力和剩磁比则显著下降．并且在1250℃时，复合材料的矫顽力和剩磁比均达到最大值，分别为1．61kOe和0．91．在850℃时，复合材料表现超顺磁性．

英文摘要：

CoFe2O4/SiO2 nano-composites were prepared by sol-gel method. The crystal structure, morphologies, and formation mechanism of the composites were studied through X-ray diffraction （XRD）, Fourier transform infrared （FT-IR） spectrum, and transmission electron microscope （TEM）. The magnetic hysteresis loops were collected using a vibrating sample magnetometer （VSM） at room temperature. The results show that as the calcining temperature is below 1 250 ℃, the composites compose of CoFe2 04 nano-crystallite dispersed in the amorphous SiO2 matrix, and the crystallite size increases slowly from 5 nm to 35 nm as the calcining temperature increases from 850 ℃ to 1 250 ℃. As the calcining temperature in- creases to 1 300 ℃, the crystallization of SiO2 results in a serious agglomeration of CoFe204 nanoparticles, and induces the crystal structure change from the normal spinel to mixing of normal spinel and inverse spinel, the drastic increase of Ms, and the considerable decrease of Hc and remanence ratio, at 1 250 ℃, both Hc and remanence ratio reach their maximum values of 1.61 kOe and 0.91 respectively. Furthermore, superparamagnetic behavior is observed in the nano-composites calcined at 850℃.