论文标题
薄膜磁化转换的理论研究
Theoretical studies on switching of magnetisation in thin film
论文作者
论文摘要
在本章中，我们专注于磁化的切换或铁磁系统的亚稳态寿命。在这方面，尤其是ISING模型和Blume-Capel模型，已经在存在基于大都市算法的蒙特卡洛模拟技术的情况下模拟了外部施加的磁场。在存在障碍的情况下，发现磁化切换的速度更快，在这里以淬火的随机场进行建模。观察到随机场的强度与温度发挥的作用相似。贝克 - döring经典成核的理论（最初是针对自旋1/2 ISING系统提出的）已在随机字段ISING模型中进行了验证。然而，更强的随机场影响成核状态。在一个立方体晶格中，发现表面逆转时间与散装逆转时间不同。与散装相反，在这里已经通过引入相对的界面相互作用强度（$ r $）来研究表面的独特行为。根据$ r $，温度和应用场，注意到表面和散装磁化的竞争转换。已经研究了各向异性（$ d $）对亚稳态寿命的影响。我们报告了平均宏观反转时间在适当定义的微观反转时间上的线性依赖性。逆转后，饱和的磁化$ m_f $很大程度上取决于$ d $。 $ m_f $，$ d $和$ h $（字段）遵循拟议的缩放关系。最后，Becker-Döring理论以及Avrami的定律在Spin-$ s $ ising和Blume-Capel模型中得到了验证。切换时间取决于可访问的自旋状态的数量。
In the present chapter, we focus on the switching of magnetisation, or the metastable lifetime of a ferromagnetic system. In this regard, particularly the Ising model and the Blume-Capel model, have been simulated in the presence of an externally applied magnetic field by the Monte-Carlo simulation technique based on the Metropolis algorithm. Magnetisation switching is found to be faster in the presence of disorder, modelled here by a quenched random field. The strength of the random field is observed to play a similar role to that played by temperature. Becker-Döring theory of classical nucleation (originally proposed for the spin-1/2 Ising system) has been verified in the random field Ising model. However, a stronger random field affects the nucleation regime. In a cubic Ising lattice, surface reversal time is found to be different from the bulk reversal time. That distinct behaviour of the surface in contrast to the bulk has been studied here by introducing a relative interfacial interaction strength ($R$). Depending on $R$, temperature, and applied field, a competitive switching of magnetisation of surface and bulk is noticed. The effect of anisotropy ($D$) on the metastable lifetime has been investigated. We report a linear dependency of the mean macroscopic reversal time on a suitably defined microscopic reversal time. The saturated magnetisation $M_f$, after the reversal, is noticed to be strongly dependent on $D$. $M_f$, $D$, and $h$ (field) are found to follow a proposed scaling relation. Finally, Becker-Döring theory as well as Avrami's law are verified in spin-$s$ Ising and Blume-Capel models. The switching time depends on the number of accessible spin states.
