γ-Fe_2O_3微粉的磁各向异性和磁粘滞性的研究

Study on the Magnetic Anisotropy and Magnetic Viscosity of γ Fe 2O 3 Powders

制备了粒状γ－Ｆｅ２Ｏ３微粉和针状γ－Ｆｅ２Ｏ３以及ＣｏＦｅ－γ－Ｆｅ２Ｏ３磁片样品．利用透射电子显微镜观察了样品颗粒的形貌，并用Ｘ射线衍射确定了样品的相组成．利用振动样品磁强计测量了样品在不同温度下的磁化曲线和磁滞回线，用“趋近饱和定律”方法求出了在不同温度下粒状γ－Ｆｅ２Ｏ３微粉的有效磁各向异性常数，而用磁转矩方法测量针状γ－Ｆｅ２Ｏ３和ＣｏＦｅ－γ－Ｆｅ２Ｏ３样品的有效磁各向异性常数，结果首次显示粒状γ－Ｆｅ２Ｏ３微粉的有效磁各向异性常数ＫＥ随温度的变化趋势与其形状各向异性常数随温度的变化趋势相同．还测量了不同温度下样品的涨落场和有效激活体积，推导了有效激活体积的理论表达式，并和实验结果进行了比较．粒状样品在不同温度下的实验结果皆与理论计算基本符合，但针状样品的实验结果与理论计算则有明显差别．首次得出粒状γＦｅ２Ｏ３微粉在不同温度下的反磁化机制与均匀反磁化较为符合的结果．

The granular γ Fe 2O 3 powders, the acicular γ Fe 2O 3 and CoFe γ Fe 2O 3 powders are prepared. The particle shapes and mean particle sizes of the samples are determined by transmission electron microscopy. The phases are determined by X ray diffraction. By using vibrating sample magnetometer, the magnetic parameters are measured at different temperatures. By the law of approach to saturation, the effective magnetic anisotropy constants of granular γ Fe 2O 3 powders at different temperatures are obtained. By using magnetotorquemeter, the effective magnetic anisotropy constants of acicular γ Fe 2O 3 and CoFe γ Fe 2O 3 powders are measured. It is found for the first time that variation tendency of effective magnetic anisotropy of granular γ Fe 2O 3 with the temperature is about the same as that of the magnetic anisotropy with the temperature. The fluctuation field H f and the activation volume of the samples at different temperatures are measured. The theoretical expression of activation volume is derived, For the granular γ Fe 2O 3 powders, the calculated activation volumes at different temperatures are consistent with the experimental ones. But for acicular γ Fe 2O 3 powders, the calculated activation volumes at different tempera tures is different from the experimental ones. It is found experimentally, for the first time, that magnetization reversal of granular γ Fe 2O 3 at different temperatures is close to the uniform rotation.