Notable impact of magnetic order and flat phonon mode on the thermal transport properties of 2D magnetic semiconductor CrSBr

Monolayer CrSBr, an air-stable magnetic semiconductor, hosts great potential applications in spintronics, optoelectronics, and magnetic imaging. A deep understanding of its thermal transport behavior, particularly the influence of magnetic order, is essential for revealing the microscopic mechanisms of spin–phonon interactions in two-dimensional magnets. In this study, we systematically investigate the effect of magnetic order on the thermal transport properties of monolayer CrSBr by using machine learning potentials combined with the Boltzmann transport equation. The calculations show that the magnetic order significantly affects the thermal conductivity of monolayer CrSBr. Around the Curie temperature (145 K), the thermal conductivity along the x-axis is 80.79, 89.63, and 58.91 W/mK for ferromagnetic, antiferromagnetic type I, and antiferromagnetic type II phases, respectively. Along the y-axis, the corresponding values are 37.38, 45.77, and 19.20 W/mK. Such substantial variation mainly arises from differences in phonon lifetimes attributable to the distinct anharmonic effects present in CrSBr, influenced by its magnetic order. Meanwhile, it is found that the specific flat phonon modes in monolayer CrSBr could induce strong four-phonon scattering rates. As a result, the lattice thermal conductivity is reduced by up to 36.7% compared to the case where only three-phonon scattering is considered. These findings not only emphasize the critical role of magnetic order and flat phonon modes in governing the thermal transport behavior of monolayer CrSBr but also provide important guidelines for designing thermal management strategies via magnetic order.