Elucidating Pressure- and Field-Tuned Phases and Multifunctionality in Magnetic Spinels

“磁响应”材料具有随压力和磁场调节的特性。这些材料表现出一系列科学上有趣和技术上有用的特性。了解这些奇特性质的物理机制不仅在科学上很重要，而且是优化这些材料用于技术应用的必要先决条件。该项目结合了高压、高磁场和可见激光的使用，以识别和控制在一组选定的材料中负责磁响应行为的潜在机制。本研究中采用的各种技术，包括使用金刚石砧细胞技术的高压技术、高磁场和低温方法、光学和激光技术以及材料生长方法，为研究生研究人员提供了在学术界、工业界或国家实验室从事各种职业的优秀培训。该项目还致力于通过科学公开讲座、中学科学演示和实验室参观，向公众和K-12学生传授科学素养和对科学的热情，这些活动突出了研究材料的兴奋性，以及项目中使用的科学技术。该项目还包括努力增加STEM领域代表性不足的博士的数量和指导；提高博士生的科学沟通能力；并为在读博士生的职业道路提供指导。技术摘要磁性受挫材料，如磁性尖晶石（化学式AB2X4），表现出一系列不同的基态相和现象，可以随压力和磁场敏感地调谐，包括自旋螺旋相、电荷有序相、多铁性相和自旋/轨道液相。尖晶石和其他磁响应材料的特殊可调性使它们成为极好的科学实验室，可以灵敏地控制和研究无数的相和现象。然而，对于导致这些材料表现出重要的压力和场调谐行为的微观磁结构效应的微观理解有限，这主要是由于缺乏光谱信息来阐明磁受挫材料的自旋和晶格动力学如何随着磁场和压力的变化而变化。本研究的目的是通过使用非弹性光散射技术来研究选择的磁受挫材料在不同相位进行场和压力调谐时的自旋和晶格激发，从而填补我们在理解上的这一重要空白。本研究的目标是澄清在不同相区观察到的竞争相之间的关系，研究尚未探索的磁受挫材料中的相制度和现象，作为温度，压力和磁场的函数，并实现具有科学或技术重要性的奇异物质的新相。该研究还揭示了有利于增强磁受挫材料磁响应磁化率的一般条件；这些信息是控制这些材料用于有用技术应用的必要先决条件。除了为一些研究生提供不同的技术培训外，这项研究还将通过实验室之旅影响更广泛的社区，旨在使K - 12学生和教师接触到材料研究的兴奋，并向中学生展示光学相关的演示；通过努力提高被低估的博士生的数量和指导；通过科学的沟通技巧训练博士生。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Non-technical abstract"Magnetically responsive" materials have properties that can be tuned with pressure and magnetic field. Such materials exhibit a range of scientifically interesting and technologically useful properties. Understanding the physical mechanisms responsible for these exotic properties is not only important scientifically, but is an essential prerequisite to optimizing these materials for use in technological applications. This project combines the use of high pressures, high magnetic fields, and visible laser light to identify and control the underlying mechanisms responsible for magnetically responsive behavior in a select group of materials. The diverse techniques employed in this research, including high-pressure techniques using diamond anvil cell technology, high-magnetic-field and low-temperature methods, optical and laser techniques, and materials growth methods, provide the graduate student researchers outstanding training for a diverse range of careers in academia, industry, or national laboratories. This project is also dedicated to imparting scientific literacy and enthusiasm for science in both the general public and K-12 students, through public lectures on science, middle-school scientific demonstrations, and lab tours that highlight the excitement of the materials studied, and the scientific techniques used in this project. This project also includes efforts to increase the number and mentoring of underrepresented PhDs in STEM fields; to improve scientific communication skills of PhD students; and to provide guidance to current PhD students concerning their career paths.Technical abstractMagnetically frustrated materials, such as the magnetic spinels (chemical formula AB2X4), exhibit a range of diverse ground state phases and phenomena that can be sensitively tuned with pressure and magnetic field, including spin-spiral, charge-ordered, multiferroic, and spin/orbital-liquid phases. The exceptional tunability of the spinels and other magnetically responsive materials make them excellent scientific laboratories in which myriad phases and phenomena can be sensitively controlled and studied. Yet, there is limited microscopic understanding of the microscopic magnetostructural effects that lead to the important pressure- and field-tuned behaviors these materials exhibit, due largely to the absence of spectroscopic information that elucidates how the spin- and lattice-dynamics of magnetically frustrated materials change as functions of magnetic field and pressure. The purpose of this research is to fill this important gap in our understanding by using inelastic light scattering techniques to study the spin- and lattice-excitations of select magnetically frustrated materials while field- and pressure-tuning through their diverse phases. The goals of this research are to clarify the relationship between competing phases observed in different phase regions, to study as-yet-unexplored phase regimes and phenomena in magnetically frustrated materials as functions of temperature, pressure-, and magnetic-field, and to realize exotic new phases of matter that are of scientific or technological importance. This research also sheds light on the general conditions that are conducive to enhancing magnetoresponsive susceptibilities in magnetically frustrated materials; such information is an essential prerequisite to controlling these materials for useful technological applications. In addition to providing diverse technical training to several graduate students, this research will impact the broader community through laboratory tours aimed at exposing K 12 students and teachers to the excitement of materials research and optics-related demonstrations to middle schools students; through efforts to improve the numbers and mentoring of underrepresented PhD students; and through scientific communication skills training of PhD students.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.