First-principles study of magnetic-field-dependent thermal conductivity in magnetic materials

Measurements of thermal conductivity in magnetic systems have demonstrated large magnetic-field-induced enhancements at low temperatures, for example, in the Kitaev quantum spin liquid candidate α-RuCl₃ [Phys. Rev. Lett. 120, 117204 (2018)] and the cleavable magnet CrCl₃ [Phys. Rev. Res. 2, 013059 (2020)]. Models based on suppression of spin-phonon interactions modulated by magnetic field were used to understand this peculiar thermal transport behavior. However, these models were built from simple isotropic Debye models and a Debye-Callaway formalism with empirical scattering terms based on a variety of fitting parameters to describe intrinsic phonon scattering and magnetic scattering, among others, which hinder the understanding of the complex physics. Here we study phonon transport by solving the Peierls-Boltzmann equation with inputs of harmonic and anharmonic phonon properties calculated from first principles. The phonon scattering mechanisms from boundaries, defects, and three-phonon interactions are explicitly included, and an alternative scattering term for spin-phonon coupling is proposed to replace the previously used resonance scattering. Our work provides physical insights into mechanisms of spin-phonon interactions under magnetic field and field-dependent behaviors of magnetic materials.