Glassy Ferromagnetic Shape Memory Alloys: Interplay Between Disorder, Phase Transitions, and Multi-Physics Couplings

非技术综述：形状记忆合金(SMA)是一种特殊类型的晶体金属，由于可逆的固-固结构相变，即马氏体相变，加热后可以恢复其变形的形状。最近发现的几个SMA也是磁性的，并显示出同时发生的马氏体相变和磁性转变。主要研究人员最近表明，仔细操纵这些合金中的缺陷可以产生新颖的类似玻璃的行为，即根据磁自旋和/或应变来定义“非晶态”结构。这种多功能耦合、各种类型固态的出现以及由此产生的性质可以提供全新的功能，例如磁驱动、高效的磁制冷、热管理、收集废弃的机械能、以及通过远程驱动的活性组织支架促进细胞生长。该奖项支持基础实验和理论研究以及教育，以了解不同类型的固体到固体相转变、玻璃度和晶体缺陷如何在磁性SMA中相互作用并影响其功能特性。这一新的理解有望对未来多功能智能材料的设计和开发产生积极影响。该奖项支持对本科生和研究生进行最先进的实验和计算材料技术方面的培训。该项目的一个完整方面是通过基于国家标准和技术研究所的材料数据管理系统的材料数据库公开传播研究成果。技术摘要：基于NiMnIn的磁性形状记忆合金(MSMA)表现出一系列复杂的现象，这些现象是由于构型无序和不同类型的相变(有序、磁性、结构)之间的相互作用而产生的，包括自旋玻璃相变和应变玻璃相变。这些相变导致了包括热、磁和机械热力学共轭对在内的多种耦合模式。反过来，合金表现出丰富的响应，导致独特的行为，如磁交换偏置，可定制的热膨胀，巨大的磁热和弹性热效应。主要研究人员已经证明，有序度以及点缺陷和反相界的存在在控制多个竞争相的稳定性方面起着基础性的作用，但关于构型无序对MSMA的磁热机械性质的具体影响尚不清楚。在这个项目中，计算-实验相结合的方法的目的是阐明决定不同竞争阶段的稳定性、相变的开始及其耦合的机制和微观结构特征。重点是使用最先进的多物理表征和建模来研究NiMnIn MSMA中磁热机械耦合的性质作为构型顺序和各种外部刺激(温度、应力和磁场或它们的组合)的函数。结合中子衍射测量、第一性原理计算和蒙特卡罗模拟，研究了位形无序对磁结构相变和玻璃化行为的影响。该项目的主要科学影响预计将是为调整磁性SMA的磁性和结构响应制定健全的、基于多种物理的合金化和热处理准则。

NON-TECHNICAL SUMMARY:Shape Memory Alloys (SMAs) are a special type of crystalline metals that can recover their deformed shape upon heating, as a result of the reversible solid to solid structural phase transformations, i.e. martensitic transformations. Few recently discovered SMAs are also magnetic, and demonstrate simultaneous martensitic and magnetic transitions. The principal investigators have recently shown that careful manipulation of defects in these alloys can bring about novel glass-like behavior in which the 'amorphous' structure is defined in terms of magnetic spin and/or strain. Such multi-functional coupling, the appearance of various types of solid states, and the resulting properties may provide completely new functionalities such as magnetic actuation, efficient magnetic refrigeration, thermal management, harvesting of waste mechanical energy, and cell growth stimulation via remotely actuated active tissue scaffolds. This award supports fundamental experimental and theoretical research and education to understand how different types of solid to solid phase transformations, glassiness, and crystal defects interact in magnetic SMAs and influence their functional properties. The new understanding is expected to positively impact future design and development of multifunctional smart materials. The award supports the training of undergraduate and graduate students in state-of-the-art experimental and computational materials techniques. An integral aspect of this project is the open dissemination of research results through a Materials Data Repository based on the National Institute of Standards and Technology's Materials Data Curation System.TECHNICAL SUMMARY:NiMnIn-based Magnetic Shape Memory Alloys (MSMAs) exhibit a wide range of complex phenomena resulting from the interplay between configurational disorder and different types of phase transitions (ordering, magnetic, structural) including spin glass and strain glass transitions. These phase transitions result in multiple coupling modes involving thermal, magnetic and mechanical thermodynamic conjugate pairs. In turn, the alloys demonstrate rich responses that result in unique behavior such as magnetic exchange bias, tailorable thermal expansion, giant magneto-caloric and elasto-caloric effects. The principal investigators have shown that the degree of order and the presence of point defects and anti-phase boundaries play a fundamental role in controlling the stability of multiple competing phases but much remains unknown regarding the specific effect of configurational disorder on the magneto-thermo-mechanical properties of MSMAs. The goal of the combined computational-experimental approach in this project is to elucidate the mechanisms and microstructural features that determine the stability of the different competing phases, the onset of the phase transitions and their couplings. The focus is to use state-of-the-art multi-physics characterization and modeling to investigate the nature of magneto-thermo-mechanical couplings in NiMnIn MSMAs as a function of configurational order and various external stimuli (temperature, stress, and magnetic field or their combinations). In-situ investigation of micro and magneto structure coupled with neutron diffraction measurements in combination with first-principles calculations and Monte Carlo simulations are used to examine the effect of configurational disorder on the magneto-structural phase transitions and the onset of glassy behavior. The major scientific impact of this project is expected to be the development of sound, multi-physics-based alloying and heat treatment guidelines for tuning magnetic and structural responses in magnetic SMAs.