Lattice thermal conductivity switching via structural phase transition in ferromagnetic VI ₃

The realization of reversible thermal conductivity through ferromagnetic ordering can improve the heat management and energy efficiency in magnetic materials-based devices. VI ₃, as a new layered ferromagnetic semiconductor, exhibits a structural phase transition from monoclinic ( C2/ m) to rhombohedral ( $R\overline{3}$ ) phase as temperature decreases, making it a suitable platform to investigate thermal switching in magnetic phase transition materials. This work reveals that the thermal switching ratio of VI ₃ can reach 3.9 along the a-axis. Mechanical properties analysis indicates that the C2/ m structure is stiffer than the $R\overline{3}$ one, causing the larger phonon velocity in C2/ m phase. Moreover, due to the fewer phonon branches in C2/ m phase, the number of phonon--phonon scattering channels in C2/ m phase is smaller compared to that of $R\overline{3}$ phase. Both the larger phonon velocity and the longer phonon lifetime lead to larger lattice thermal conductivity in C2/ m phase. This study uncovers the mechanical and thermal properties of VI ₃, which provides useful guides for designing magnetic materials-based devices such as thermal switch.