NANOPARTICLES IN METERORITES: THE CONTRIBUTION OF SURFACES TO THE MAGNETIC CURIE TEMPERATURE AND MAGNETIC RECORDING FIDELITY

在陨石磁性中，居里温度（矿物依赖的铁磁有序温度）通常被测量以识别磁性矿物。居里温度标志着被称为交换能的短程最近邻有序能的中断，该能量导致铁磁材料中原子的磁矩彼此对齐。对于尺寸大于10-20 nm的晶体，具有较少最近邻原子的晶体表面上的原子的影响相对不重要。然而，对于小于10 nm的磁性矿物，最近邻原子数量的减少导致居里温度的降低。为了确定这种效应，我们数值求解描述原子自旋之间的交换相互作用及其与外场的相互作用的哈密顿量（图1）。交换能的变化理论上也会影响小粒子的记录保真度，这是我们希望研究的问题。该项目将从为金属铁编写的现有三维数值算法开始，为磁铁矿和其他具有地质意义的矿物编写代码，以实现真实的三维几何形状。以前发表的计算只针对一维系统。

In meteoritic magnetism, the Curie temperature (the mineral dependent ferromagnetic ordering temperature) is routinely measured to identify magnetic mineralogy. The Curie temperature marks the break in a short-range nearest-neighbour ordering energy called the exchange energy, which causes the magnetic moments of atoms to align with each other in ferromagnetic materials. For crystals larger than 10-20 nm in size, the effect of atoms on the surface of a crystal that have fewer nearest neighbour atoms is relatively unimportant. However, for magnetic minerals less than 10 nm, the reduction in the number of nearest neighbour atoms leads to a reduction in the Curie temperature. To determine this effect we numerically solve the Hamiltonian describing the exchange interaction between atomic spins and their interaction with an external field (Figure 1). Variations in the exchange energy should theoretically also affect the recording fidelity of small particles; this is some that we wish to investigate. Starting with an existing three-dimensional numerical algorithm written for metallic iron, the project will develop the code for magnetite and other minerals of geological interest, for realistic three-dimensional geometries. Previous published calculations have only been for one-dimensional systems.