ABSTRACT

We investigate the formation and stabilisation of magnetic skyrmions defined on a ferromagnetic square lattice Heisenberg model in the presence of single ion anisotropy. By means of Monte Carlo simulations, we show in the absence of magnetic anisotropy that for the ground state and finite temperature region, the present model exhibits spiral, skyrmion lattice and field polarised phases in the presence of Dzyaloshinskii–Moriya interaction and magnetic field. For this particular case, our simulation results suggest that in the low magnetic field region, there exists a critical value of DM interaction above which formation of skyrmions takes place. Besides, density and size of skyrmions emerging in the system depends on the competition between local energies due to DM interaction and magnetic field. We also focus on the influence of non-zero magnetic anisotropy energy on the emergence of skyrmions with a special emphasis on disordered anisotropy configurations represented by a certain probability distribution. In order to model a disordered magnetic anisotropy effect, we consider a model with a diluted single ion anisotropy distribution, as well as a disordered model mimicked by a Gaussian distribution of magnetic anisotropy constants accompanied to each lattice site. Our results show that when the antisymmetric exchange (DM) interaction and the magnetic field are kept fixed, skyrmion phase disappears with increasing magnetic anisotropy, however it can be recovered by properly tuning the relevant probability distribution parameters.

摘要

我们研究了在存在单离子各向异性的情况下，在铁磁方格海森堡模型上定义的磁性斯格明子的形成和稳定。通过蒙特卡罗模拟，我们表明在没有磁各向异性的情况下，对于基态和有限温度区域，本模型在存在 Dzyaloshinskii-Moriya 相互作用和磁场的情况下表现出螺旋、斯格明子晶格和场极化相。对于这种特殊情况，我们的模拟结果表明，在低磁场区域，存在 DM 相互作用的临界值，高于该临界值会发生斯格明子的形成。此外，系统中出现的斯格明子的密度和大小取决于 DM 相互作用和磁场引起的局部能量之间的竞争。我们还关注非零磁各向异性能量对斯格明子出现的影响，特别强调由一定概率分布表示的无序各向异性配置。为了模拟无序磁各向异性效应，我们考虑了一个具有稀释单离子各向异性分布的模型，以及一个由伴随每个晶格位点的磁各向异性常数的高斯分布模拟的无序模型。我们的结果表明，当反对称交换（DM）相互作用和磁场保持固定时，斯格明子相位随着磁各向异性的增加而消失，但可以通过适当调整相关概率分布参数来恢复。