中文摘要：

磁铁矿是在 paleomagnetism 的最重要的磁性的矿物质。它的磁性被许多因素控制，例如谷物尺寸分发，形状和相互作用。传统的岩石然而，磁性的实验在去耦有大困难这些参数的效果。在这研究，我们试图由使用一个 micromagnetic 方法在磁铁矿粉末的磁性上调查谷物尺寸分发的效果。在 micromagnetic 模型使用的粒子几何学基于在合成磁铁矿粉末观察的谷物尺寸分发。模仿的磁滞现象参数与试验性的大小同意很好并且提供磁性的顽磁的清楚的微观结构。我们的结果证明那种谷物尺寸在在相互作用的效果下面比形状影响磁铁矿集合的磁滞现象参数起一个更重要的作用。制服或旋涡超级国在二形成了或更多的粒子被发现并且显示在集合的磁性的记录的不同稳定性。一些领域结构单个域(SD ) 当应用领域减少到零，粒子被颠倒。小 pseudo-single-domain 粒子作为 SD 结构表现并且可以统治磁性的记录。总共， micromagnetic 当模特儿分布提供一更好由 nanoscale 粒子组成的磁性的集合理解的谷物尺寸。

英文摘要：

Magnetite is the most important magnetic mineral in paleomagnetism. Its magnetic properties are controlled by many factors, such as grain size distribution, shape and interactions. Traditional rock magnetic experiments, however, have great difficulty in decoupling the effects of these parameters. In this study, we attempted to investigate the effects of grain size distribution on magnetic properties of magnetite powders by using a micromagnetic method. The particle geometries used in the micromagnetic model were based on the grain size distribution observed in a synthetic magnetite powder. The simulated hysteresis parameters agree well with the experimental measurements and provide clear microstructures of the magnetic remanence. Our results show that grain size plays a more important role in affecting hysteresis parameters of magnetite assemblages than shape under effects of interactions. Uniform or vortex superstates formed by two or more particles are found and display different stabilities of magnetic recording in assemblages. Some domain structures of single-domain （SD） particles are reversed as the applied field decreases to zero. Small pseudo-single-domain particles behave as SD structures and may dominate the magnetic recordings. In all, micromagnetic modeling of grain size distributions provide a better understanding of magnetic assemblages consisting of nanoscale particles.