Mechanically coupled phase field modeling of ferromagnetics unter thermal fluctuation

磁矩对热涨落非常敏感，对磁化翻转动力学、磁畴演化和磁化率有很大影响。此外，机械控制/辅助磁化切换似乎是在新的存储器单元设计中实现确定性180度切换的有吸引力的替代方法。热涨落在机械耦合开关机制中起着重要的作用。在这个项目中，我们将首先发展一个理论框架和数值策略来研究在低于居里温度的有限温度下，热涨落对铁磁材料的开关动力学、畴演化和双磁性的影响，并考虑与力学的耦合。特别是，相场模型将来自一个热力学框架与微力（组态力）理论，其中热涨落引起的随机场将在微力平衡处理。所开发的模型将实施随机有限元法（SFEM），通过使用有效的数值策略。将进行全面的模拟，以评估热波动对磁化翻转动力学，畴结构演变和磁化率的影响。通过理论研究和数值模拟，揭示了磁化与热涨落和机械场的相互作用。该项目将提供一个新的工具包，这不仅有助于下一代基于纳米铁磁体的存储器和逻辑器件的研究和设计，而且有助于揭示高温磁体（如NdFeB）的磁性机制。

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.