Mechanically coupled phase field modeling of ferromagnetics unter thermal fluctuation

磁矩对温度涨落很敏感，这对磁化转变动力学、磁畴演化和矫直力有很大的影响。此外，在新的存储单元设计中，机械控制/辅助磁化切换似乎是实现确定性180度切换的一种有吸引力的替代方法。热涨落在机械耦合开关机构中起着重要的作用。在这个项目中，我们将首先建立一个理论框架和数值策略，研究在居里温度以下的有限温度下，热涨落对铁磁性中的开关动力学、磁畴演化和矫顽力的影响，并考虑到与力学的耦合。特别是，相场模型将从微力(构造力)理论的热力学框架中导出，其中热涨落引起的随机场将在微力平衡中处理。所开发的模型将通过使用有效的数值策略，用随机有限元方法(SFEM)实现。为了评估热涨落对磁化转变动力学、磁畴结构演化和矫顽力的影响，将进行全面的模拟。通过所提出的理论研究和数值模拟，将揭示磁化强度与热涨落和机械场的相互作用。本项目将为下一代纳米铁磁存储器和逻辑器件的研究和设计提供一种新的工具包，并将有助于揭示NdFeB等高温磁体的矫顽力机制。

Magnetic moment is sensitive to thermal fluctuation, which leads to strongly effect on magnetization switching dynamics, domain evolution and coercivity. Moreover, mechanically controlled/assisted magnetization switching appears as an attractive alternative method to achieve a deterministic 180 degree switching in new memory cell designs. Thermal fluctuation plays an important role in the mechanically-coupled switching mechanism. In this project we will first develop a theoretical framework and numerical strategies to study the influence of thermal fluctuation on switching dynamics, domain evolution and coercivity in ferromagnetics at finite temperature below the Curie temperature, with the consideration of coupling with mechanics. Particularly, a phase field model will be derived from a thermodynamic framework with the microforce (configurational force) theory, in which thermal fluctuation induced random fields will be treated in the microforce balance. The developed model will be implemented with the stochastic finite element method (SFEM), by using efficient numerical strategies. Comprehensive simulations will be carried out in order to evaluate the effect of thermal fluctuations on the magnetization switching dynamics, domain structure evolution and coercivity. Through the proposed theoretical study and numerical simulations, the interaction of magnetization with thermal fluctuations and mechanical field will be disclosed. This project should provide a novel toolkit, which is useful not only for the study and design of next generation of nanoferromagnet-based memory and logic devices, but also for revealing the coercivity mechanism of high temperature magnets such as NdFeB.