纳米CoPt/Co双层膜和三层膜中长程磁极子相互作用引起的skyrmion与vortex现象

Skyrmion and vortex states induced by long-ranged magnetic dipolar interactions in nanoscaled CoPt/Co bilayer and trilayer systems

本文通过三维微磁学数值模拟,系统地计算了CoPt/Co磁性双层膜与CoPt/Co/CoPt三层膜结构中的自旋分布.计算结果表明,当三层膜的硬磁相和软磁相厚度分别为8nm和16nm左右时,在三层膜的每一层均会出现斯格明子(Skyrmion)结构.特别是,我们首次发现,当双层膜的硬软磁层厚度均在8nm左右时,在硬磁相和软磁相中均会出现斯格明子结构,即双斯格明子态.双层膜软磁相出现斯格明子的厚度要比三层膜小很多,其对应的斯格明子数只比三层膜小约8%.斯格明子数对硬磁相和软磁相的磁晶各向异性常数K和交换作用常数A都比较敏感,随着K和A的变化,体系硬磁相和软磁相的自旋分布会在涡旋(Vortex)态和斯格明子态之间相互转化,而界面耦合常数对斯格明子数影响不大.

Spin distributions for exchange-coupled CoPt/Co bilayers and CoPt/Co/Co Pt trilayers have been systematically simulated by a three-dimensional（3D） micromagnetic model. It is found that skyrmion structures can occur in all three layers for the trilayer systems when the hard and soft layer thicknesses are about 8 nm and 16 nm respectively. Especially, it is found for the first time that skyrmion states can occur in both the hard and soft phases when both the two layer thicknesses are about 8 nm, i.e., the double skyrmion states will occur. The soft layer thickness（ts）, at which the skyrmion structure occurs in the bilayers, is much smaller than that of trilayers. On the other hand, the corresponding skyrmion numbers obtained in bilayers are only about 8% smaller than those for the trilayers. The exchange constant A and crystalline anisotropy constant K have important influences on the skyrmion numbers and spin distributions, whereas the exchange coupling between the soft and hard layers has negligible effects on them. As A and K change, the spin distributions can transform from vortex into skyrmion as A and K vary.