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

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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.