Impact of dynamic Jahn-Teller effect on magnetic excitations, lattice vibration, and thermal conductivity in UxTh1-xO2 system

TL;DR

This study investigates how the dynamic Jahn-Teller effect influences magnetic excitations, lattice vibrations, and thermal conductivity in uranium-thorium dioxide, revealing complex phonon-magnetic interactions affecting low-temperature thermal transport.

Contribution

It provides a comprehensive analysis combining experimental and theoretical approaches to elucidate the role of DJT effect in thermal and magnetic properties of UxTh1-xO2.

Findings

Magnetic effects alter thermophysical properties at room temperature.

Uranium concentration affects magnetic susceptibility and Raman modes.

Phonon-spin resonant scattering explains low-temperature thermal conductivity anomalies.

Abstract

Vibrational and magnetic properties of single-crystal uranium-thorium dioxide (UxTh1-xO2) with a full range of 0<x<1 is investigated. Thorium dioxide is a diamagnet whose thermal properties are governed by lattice vibration. The addition of paramagnetic uranium ion leads to the emergence of magnetic effects that alter the thermophysical properties noticeably even at room temperature. The interaction of phonons with magnetic moments of uranium 5f electrons mediated by magnetoelastic coupling results in an anomalous low-temperature thermal conductivity profile. Analysis of the magnetic susceptibility measurements indicates a uranium-concentration-dependent reduction in effective magnetic moment previously associated with the dynamic Jahn-Teller (DJT) effect. The T2g Raman peak position follows a nonlinear trend as a function of uranium concentration and hints that these Raman active optical modes play a role in either DJT or mediating quadrupole-quadrupole interactions. A first principle-based thermal transport model is implemented to explain the low-temperature transport measurements, where the anomalous reduction is attributed to phonon-spin resonant scattering. The interplay between spins and phonons is also captured using high-resolution inelastic X-ray scattering (IXS) measurements of phonon linewidths. Our results provide new insights into the phonon interactions with the magnetic excitations governing DJT effect and impacting the low-temperature thermal transport processes in this material system. These findings have implications for understanding low-temperature thermal transport and magnetic properties in advanced materials for information processing and energy applications.