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arXiv 2009.08342cond-mat.stat-mech
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梯度场阶跃变化的亚稳性与Blume-Capel铁磁体的各向异性

Metastability in graded and step like variation of field and anisotropy of the Blume-Capel ferromagnet

Moumita Naskar, Muktish Acharyya

摘要:

采用Metropolis单自旋翻转算法,用广泛的蒙特卡罗模拟研究了二维各向异性Blume-Capel铁磁体在梯度磁场和阶梯磁场作用下的亚稳行为.从初始的完全有序态出发,研究了磁场存在下的磁化反转。本文研究了均匀各向异性系统在梯度场和阶梯场作用下的亚稳寿命或磁化反转时间。同样,已经探索了在均匀场存在下的{ \it梯度和阶梯各向异性系统}。本文分析了反转时间随场梯度变化的有限尺寸效应,提出了一个$G_h$标度关系。投影状态的密度分布的空间变化(即,+1,0和-1)也已经研究了在磁化反转的时刻。研究了自旋翻转数目的空间变化。运动的界面(或畴壁)的梯度场和梯度的各向异性进行了调查,并发现遵循双曲正切一样的行为在这两种情况下。由于各向异性和外加电场对亚稳态寿命都有显著影响,因此,我们观察到了{ \it梯度各向异性系统在梯度场中}和{ \it阶梯各向异性系统在阶梯场中}的有趣竞争情形.对于场主导反转区和各向异性主导反转区,都发现了一条边缘竞争线。亚稳态体积分数的衰减遵循Avrami定律。观察到的平均反转时间单调减少的铁-对位过渡的相边界。

英文摘要:

The metastable behaviour of two dimensional anisotropic Blume-Capel ferromagnet, under the influence of graded and stepped like variations of magnetic field, has been investigated by extensive Monte Carlo simulation using Metropolis single spin flip algorithm. Starting from the initial perfectly ordered state, reversal of magnetisation has been studied in presence of the field. Metastable lifetime or the reversal time of magnetisation for the system having uniform anisotropy and in the presence of both graded and stepped field has been studied. Also the same has been explored for a {\it graded and stepped anisotropic system} in presence of a uniform field. Finite size effect is analyzed for the variation of reversal time with gradient of field ($G_h$) and a scaling relation $\langle τ\rangle \sim L^{-β} f(G_h L^α)$ is proposed. Spatial variation of density profile for the projection states (i.e., +1, 0 and -1) has also been studied at the moment of reversal of magnetisation. The spatial variation of the number of spin flips per site is studied. Motion of the interface (or domain wall) with the gradient of field and gradient of anisotropy are investigated and are found to follow the hyperbolic tangent like behaviours in both cases. Since, both the anisotropy and the applied field have significant impact on the metastable lifetime, an interesting competitive scenario is observed for a {\it graded anisotropic system in graded field} and a {\it stepped anisotropic system in stepped field}. A line of marginal competition has been found out for both the cases separating the regions of field dominated reversal and anisotropy dominated reversal. The decay of the metastable volume fraction was found to follow the Avrami's law. The mean reversal time was observed to decrease monotonically across the phase boundary of the ferro-para transition.

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