CAREER: Anisotropic Suppression of Lattice Thermal Conductivity through the Interaction between Phonons and Thermal Magnetic Excitations

更好地了解磁性如何影响热传递可以影响从计算机芯片设计到航天器的关键应用。该项目的总体目标是设计一种创新的热开关，它可以通过磁力控制热流。由于不存在完美的热导体或绝缘体，因此设计具有理想热传输性能的系统一直具有挑战性。因此，能够控制能量的产生、传递和消耗中的热流是一个非常重要的问题。这个CAREER项目将结合国家设施的创新实验研究和热流的高性能计算模型。首席研究员将与当地高中合作，为学生提供接触大型数据集的机会，并通过设计的课外活动学习使用软件工具进行分析。其他举措包括在社区活动中进行科学演示，目标是南加州内陆帝国的多元化社区，并从附近的社区大学招募成绩优异的学生，让他们在暑期参与该项目。这个职业项目利用创新的实验技术，在计算模拟的支持下，提供了核结构（声子）和磁结构（磁振子）中热激发之间相互作用的第一组直接测量。这些结果有望阐明这些相互作用对晶格热输运的各向异性抑制，从而使设计和控制新一代具有增强热输运性质的多功能晶格结构成为可能。本项目以中子散射技术的最新进展为基础，利用几台非弹性中子能谱仪在温度从10到1300 K和外部磁场高达5 t的情况下对声子和热磁激发进行补充测量。测量结果提供了各种声子模式的色散关系、群速度和寿命数据；基于第一性原理密度泛函理论的分子动力学模拟被用来解释所测量的声子动力学，并理解由于声子散射引起的磁激发对晶格热输运的影响。该项目的成功有望显著提高对热磁激励如何影响负责晶格输运的声子的基本理解；量化相互作用对各向异性热输运性质的贡献；并提供了使用磁性结构作为额外自由度来调整晶格热输运的指导方针。该项目还扩展了非弹性中子散射作为理解热输运过程的科学工具的使用。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。

A better understanding of how magnetism affects heat transfer can impact key applications ranging from the design of computer chips to spacecraft. The overarching goal of this project is to design an innovative thermal switch, which allows the control of heat flow by magnetism. It has been challenging to design systems with desired thermal transport properties as no perfect thermal conductor or insulator exists. Therefore, being able to control heat flow in the generation, transfer, and consumption of energy represents a very important issue. This CAREER project will use a combination of innovative experimental research at national facilities and high-performance computing modeling of heat flow. The principal investigator will collaborate with local high schools to provide an opportunity for students to get exposure to large data sets and learn to use software tools for their analysis through designed extracurricular activities. Other initiatives include science demonstrations at community events targeted to the diverse community in Southern California's Inland Empire and recruitment of high-achieving students from nearby community colleges to spend their summer working on the project. This Career project utilizes innovative experimental techniques, supported by computational simulations, to provide the first set of direct measurements of the interactions between the thermal excitations in nuclear structure (phonons) and the thermal excitations in magnetic structure (magnons). The results are expected to illuminate the anisotropic suppression of lattice thermal transport by these interactions, which enables the design and control of a new generation of multifunctional lattice structures with enhanced thermal transport properties. This project builds upon recent advances in neutron scattering techniques by leveraging several inelastic neutron spectrometers to make complementary measurements of phonons and thermal magnetic excitations at temperatures from 10 to 1300 K and under external magnetic fields up to 5 T. The measurements provide dispersion relation, group velocities, and lifetime data for various phonon modes; molecular dynamics simulations based on first principles density functional theory is used to interpret the measured phonon dynamics and to understand the effects of magnetic excitations on lattice thermal transport due to phonon scattering. The success of the project is expected to significantly improve fundamental understanding of how thermal magnetic excitations affect the phonons responsible for the lattice transport; quantify the contribution of the interactions to the anisotropic thermal transport properties; and provide guidelines to tailor the lattice thermal transport using magnetic structure as an additional degree of freedom. The project also extends the use of inelastic neutron scattering as a scientific tool to understand thermal transport process.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.