Aoshima Masayuki, Satoh Akira, Chantrell Roy W
Department of Machine Intelligence and System Engineering, Faculty of System Science and Technology, Akita Prefectural University, 84-4 Ebinokuchi, Tsuchiya-aza, Yurihonjyo, Akita 015-0055, Japan.
J Colloid Interface Sci. 2008 Jul 1;323(1):158-68. doi: 10.1016/j.jcis.2008.04.017. Epub 2008 Apr 12.
We investigated the influences of the magnetic field strength and particle areal density on the microstructure of a quasi-two-dimensional monolayer composed of ferromagnetic particles by means of a Monte Carlo simulation. The magnetic field was applied along a direction perpendicular to the plane of the monolayer. Microstructures of the monolayer obtained in the simulations were analyzed in terms of radial distribution and orientational distribution functions. Formation of the microstructures is discussed from the perspective of particle-particle interaction energy and the perpendicular magnetic susceptibility of the monolayer was calculated from simulated magnetization curves. The obtained results are summarized as follows. For small areal density of particles, formation of chain-like structures is prevented by the repulsive magnetic interaction between particles due to orientations of the magnetic moments in the particles along the magnetic field direction. For intermediate areal density of particles, the chain-like structures remain even when a relatively strong magnetic field is applied, because contributions of the attractive magnetic interactions increase. For large areal density of particles, mixtures of chain-like and locally ordered structures appear due to the anisotropic attractive magnetic interactions in the absence of the magnetic field. However, when a sufficiently strong magnetic field is applied, the magnetic interactions between particles change to isotropic repulsive interactions, which results in the short-range repulsive steric interactions between particles becoming dominant with the appearance of hexagonal close packed structures.
我们通过蒙特卡罗模拟研究了磁场强度和颗粒面密度对由铁磁颗粒组成的准二维单层微观结构的影响。磁场沿垂直于单层平面的方向施加。根据径向分布函数和取向分布函数对模拟中获得的单层微观结构进行了分析。从颗粒间相互作用能的角度讨论了微观结构的形成，并根据模拟的磁化曲线计算了单层的垂直磁化率。所得结果总结如下。对于颗粒面密度较小的情况，由于颗粒中磁矩沿磁场方向的取向，颗粒间的排斥磁相互作用阻止了链状结构的形成。对于颗粒面密度中等的情况，即使施加相对较强的磁场，链状结构仍然存在，因为吸引磁相互作用的贡献增加。对于颗粒面密度较大的情况，在没有磁场时，由于各向异性的吸引磁相互作用，会出现链状结构和局部有序结构的混合物。然而，当施加足够强的磁场时，颗粒间的磁相互作用变为各向同性的排斥相互作用，这导致颗粒间的短程排斥空间相互作用占主导地位，同时出现六方密堆积结构。
