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

在陨石磁性中，通常测量居里温度(矿物相关的铁磁有序温度)来识别磁性矿物学。居里温度标志着一种被称为交换能的短程最近邻有序能的断裂，这种交换能导致铁磁材料中原子的磁矩彼此对准。对于尺寸大于10-20 nm的晶体，近邻原子较少的晶体表面原子的影响相对较小。然而，对于小于10 nm的磁性矿物，最近邻原子数目的减少导致居里温度的降低。为了确定这种影响，我们数值求解描述原子自旋之间的交换相互作用以及它们与外场相互作用的哈密顿量(图1)。理论上，交换能量的变化也应该影响小粒子的记录保真度；这是我们想要研究的一些问题。从为金属铁编写的现有三维数值算法开始，该项目将开发用于磁铁矿和其他地质兴趣矿物的代码，用于逼真的三维几何图形。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.