磁铁矿颗粒指前频率因子的精确测定

The pre-exponential frequency factor is the intrinsic spin frequency of magnetic particle, which is a very important basic parameter in Néel theory for determining the values of relaxation times. However, its value is still not accurately determined, due to no appropriate sample with no interaction, narrow size distribution and uniform shape for magnetic characterization. Ferrimagnetic human ferritin is a novel magnetite material synthesized in a biomimetic way. The cage-like structure renders each magnetite core encapsulated by a protein shell, which makes magnetite nanoparticles non-interacting, narrow-size distributed, shape uniform and ramdomly oriented. Due to its special properties, it serves as a perfect model for understanding basic magnetic properties of magnetite particles. The purpose of this project is to determine accurately the value of pre-exponential frequency factor through studying the ferrimagnetic human ferritin combining with different magnetic measurement techniques such as alternating current susceptibility, thermal relaxation under low temperature and M?ssbauer spectroscopy measurements. Furthermore, we use ferrimagnetic human ferritin as a model to investigate the effect of size distribution and quantity on magnetic properties of superparamagnetic magnetite particles.

指前频率因子是磁性颗粒固有的自旋弛豫频率，它是尼尔理论的一个基本磁学参数，对于磁性颗粒的弛豫时间的确定至关重要。但是由于极难获得无磁相互作用、粒径均一、形状相似的磁铁矿样品，难以通过实验测定指前频率因子值。人源磁性铁蛋白是通过生物矿化仿生合成的具有磁铁矿内核和铁蛋白外壳的核-壳型复合体,具有无磁相互作用、粒径均一、形状相似和矿物相单一的独特优势。本项目拟以人源磁性铁蛋白为研究对象，利用低温交流磁化率、热剩磁弛豫过程、低温穆斯堡尔谱测量等多种手段分析，结合磁学理论模拟，精确测定磁铁矿的指前频率因子值。此外，把磁性铁蛋白作为超顺磁磁铁矿颗粒模型，研究粒径和含量变化对其磁学参数的影响。

为了精确测定磁铁矿颗粒的尼尔指前频率因子，本项目以仿生矿化合成的人源磁性铁蛋白为研究对象，综合利用透射电子显微镜、电子能量损失谱、交流磁化率和热剩磁弛豫过程测量等多种手段分析，结合磁学理论模拟，精确测定磁铁矿的指前频率因子值值约为 (1.3 ± 0.67) ×1010 Hz。此外，通过不同铁原子添加量的控制，分别合成不同核粒径的磁性铁蛋白，作为超顺磁磁铁矿颗粒模型，研究粒径对其磁学参数的影响。磁性铁蛋白的饱和磁化强度、驰豫率都随着其磁铁矿核粒径的增大而显著地升高，磁性铁蛋白的横向驰豫率可升高高达321 mM-1 s-1。另外发现磁性铁蛋白具有天然的肿瘤靶向性，拓展了该材料在肿瘤核磁共振成像中的应用研究。这些研究成果不仅为研究环境和生物样品中所含有的超顺磁磁铁矿颗粒的磁学性质提供基础数据，而且为通过仿生方法开发新型磁性纳米材料的应用奠定了基础。