Notable effect of magnetic order on the phonon transport in semi-hydrogenated graphene

Abstract

Semi-hydrogenated graphene (SHG) is a ferromagnetic semiconductor with a large Curie temperature. Using this simple structure as a platform, we investigate how the coupling between magnetic order and lattice vibration affects the thermal transport by using first-principles calculations and the phonon Boltzmann transport equation. The results show that both paramagnetic and ferromagnetic phases are stable in SHG. The frequency features of the Raman-active phonon modes of the two phases clearly differ, which could serve as a fingerprint by which to identify the different magnetic orders. In addition, the coupling effect plays a critical role in the lattice thermal conductivity. At room temperature, SHG in its paramagnetic phase has a lattice thermal conductivity of about 24.5 W/mK, whereas, in its ferromagnetic phase, it is about 55.7 W/mK, almost twice as large as the paramagnetic case. An analysis of the phonon modes reveals that the enhanced thermal conductivity of ferromagnetic SHG is mainly due to the greater group velocity of the flexural acoustic mode and the attenuation of the anharmonicity of the transverse and longitudinal acoustic modes. These results reveal how magnetic order affects phonon transport in SHG and open the way for potential applications of magnetic monolayer materials as thermal switching devices.