GOALI/Collaborative Research: Effect of Stress and Heat on Magnetic Properties of Thin Films

磁性材料的性能受应力和热的影响。当铁磁材料经历表面接触时，它可能会降低或改变其原始的磁性。随着材料中微观磁畴尺寸的减小，磁稳定性降低。为了提高铁磁器件的性能，需要减小磁畴的物理尺寸。GOALI计划合作研究奖支持基础研究，以研究铁磁薄膜在应力、热和摩擦条件下磁退化的科学机制。随着大学和产业合作伙伴的合作，基础研究活动将转化为实际产品，即硬盘驱动器(HDD)中的磁记录介质，以实现更稳定可靠的设计。这项多学科协作研究的成果不仅将为提高磁机械应用(例如磁存储设备、磁性传感器和执行器、磁性MEMS/NEMS谐振器等)的能效、精度和可靠性提供直接的解决方案。而且还提供了下一代铁磁器件的关键设计规则。针对材料的磁化设计参数，如磁畴尺寸和磁各向异性能量密度，系统地、定量地研究了绝热/摩擦生热引起的微观应力和热搅拌的耦合效应。首先，在理论建模中，将接触力学和传热学理论融入到磁特性中，其中微观应力张量和空间温度分布改变了磁场和磁化强度。其次，在计算模拟中，从从头计算得到的原子能级无序将扩展到宏观磁化过程，在宏观磁化过程中将采用蒙特卡罗模拟来最小化系统能量。最后，通过动态表面接触实验和仪器材料表征对理论和计算模拟的科学结果进行了验证。

The properties of magnetic materials are affected by stress and heat. When a ferromagnetic material experiences surface contact, it can degrade or change its original magnetic properties. The magnetic stability decreases as the size of the microscopic magnetic domain in the material decreases. In order to improve the performance of ferromagnetic devices, the physical size of magnetic domains needs to be reduced. This Grant Opportunity for Academic Liaison with Industry (GOALI) Program collaborative research award supports fundamental research to investigate the scientific mechanism of magnetic degradation for ferromagnetic thin films under stress, heat, and friction. With the collaboration between universities and industrial partner, the fundamental research activities will be brought into actual product, i.e., magnetic recording media in a hard disk drive (HDD), to achieve more stable and reliable design. The outcomes from this multi-disciplinary and collaborative research will not only provide immediate solutions to improve energy efficiency, accuracy and reliability of magneto-mechanical applications (e.g., magnetic storage devices, magnetic sensors and actuators, magnetic MEMS/NEMS resonator, etc.) but also deliver key design rules for the next-generation ferromagnetic devices. The coupled effects of micro-stress and thermal agitation by adiabatic/frictional heat generation will be systematically and quantitatively examined with respect to magnetic design parameters of materials such as magnetic domain size and magnetic anisotropy energy density. First, in theoretical modeling, the theories of contact mechanics and heat transfer will be incorporated into magnetic properties, where the micro-stress tensor and spatial temperature distribution change magnetic field and magnetization. Second, in computational simulation, atomic level disorders obtained from the ab-initio calculation will be extended to the macroscopic magnetization process, where Monte Carlo simulation will be applied to minimize the system energy. Lastly, the scientific findings from the theoretical and computational simulations will be verified through dynamic surface contact experiment and instrumental material characterization.