Energy barriers in three-dimensional micromagnetic models and the physics of thermoviscous magnetization
Energy barriers in three-dimensional micromagnetic models and the physics of thermoviscous magnetization
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三维微磁模型中的能垒和热粘磁化物理
DOI：
10.1093/gji/ggy285
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发表时间：
2017
影响因子：
2.8
通讯作者：
V. Shcherbakov
中科院分区：
文献类型：
--
作者：
K. Fabian;V. Shcherbakov
提出了立方磁铁矿伪单畴粒子集合中粘性剩磁（VRM）的第一原理微磁和统计计算。这是通过开发一种快速松弛算法来找到微磁局部能量最小值之间的最佳过渡路径来实现的。它将轻推松紧带技术与动作最小化相结合。初始路径是通过修改能量函数的重复最小化获得的。对于立方伪单域粒子，确定了 60 个不同的局部能量最小值，并在零外场的情况下数值计算了它们之间的所有最佳能垒。结果还可以估计弱外部场中的能量势垒，这是构建描述 VRM 采集和衰减的连续齐次马尔可夫过程的时间相关过渡矩阵所必需的。通过球面平均，计算了所有时间尺度上各向同性 PSD 系综中的剩磁采集。建模的粒子系综在 VRM 采集过程中显示出物理上有意义的超调。结果还解释了为什么 PSD 粒子中 VRM 的获取比 VRM 衰变快得多，因此可以解释一些古地磁研究中极其稳定的 VRM 的发现。
A first principle micromagnetic and statistical calculation of viscous remanent magnetization (VRM) in an ensemble of cubic magnetite pseudo single-domain particles is presented. This is achieved by developing a fast relaxation algorithm for finding optimal transition paths between micromagnetic local energy minima. It combines a nudged elastic band technique with action minimization. Initial paths are obtained by repetitive minimizations of modified energy functions. For a cubic pseudo-single domain particle, 60 different local energy minima are identified and all optimal energy barriers between them are numerically calculated for zero external field. The results allow to estimate also the energy barriers in in weak external fields which are necessary to construct the time dependent transition matrices which describe the continuous homogeneous Markov processes of VRM acquisition and decay. By spherical averaging the remanence acquisition in an isotropic PSD ensemble was calculated over all time scales. The modelled particle ensemble shows a physically meaningful overshooting during VRM acquisition. The results also explain why VRM acquisition in PSD particles can occur much faster than VRM decay and therefore can explain for findings of extremely stable VRM in some paleomagnetic studies.