Ab initio Boltzmann approach to coupled magnon-phonon thermal transport in ferromagnetic crystals

We propose an ab initio Boltzmann transport approach taking into account magnon-phonon scattering (MPS) and three-phonon scattering simultaneously to accurately evaluate the thermal transport properties of ferromagnetic crystals. Using this approach, we studied the nonelectronic thermal transport properties of the body-centered cubic iron as a case. The reasonable agreement between our calculation results and the available experimental data suggests that phonons dominate the nonelectronic thermal conduction at high temperatures, and magnons may contribute to the thermal conductivity only at low temperatures. Remarkably, the abnormal increase in the magnon thermal conductivity at high temperatures implies that other magnon-involved scattering events instead of MPS should dominate the magnon thermal conductivity. Moreover, analyses of average scatter-ing rates and heat propagation lengths suggest that hydrodynamic heat transport may occur at low temperatures. This new approach fills the gap in the first-principles evaluation of the coupled magnon-phonon thermal transport properties in magnetic crystals. Our results will provide valuable references for further investigations of the interplay between magnons and phonons and broaden relevant research prospects about heat management and energy manipulation.

Automated summary

We present a new ab initio Boltzmann transport approach that considers both magnon-phonon scattering (MPS) and three-phonon scattering to accurately analyze the thermal transport properties of ferromagnetic crystals. By applying this approach to the body-centered cubic iron, we find that phonons dominate the thermal conduction at high temperatures, while magnons play a role only at low temperatures. Additionally, the abnormal increase in magnon thermal conductivity at high temperatures suggests the dominance of other magnon-involved scattering events instead of MPS. Furthermore, our analysis reveals the possibility of hydrodynamic heat transport at low temperatures.