Giant thermal switching in ferromagnetic VSe with programmable switching temperature.

Active and reversible modulation of thermal conductivity can realize efficient heat energy management in many applications such as thermoelectrics. Using first-principles calculations, this study reports a giant thermal switching ratio of 12, much higher than previously reported values, in monolayer 2H-VSe above room temperature. Detailed analysis indicates that the high thermal switching ratio is dominated by the ferromagnetic ordering induced phonon bandgap, which significantly suppresses the phonon-phonon scattering phase space across the entire vibration spectrum. The thermal switching in bulk 2H-VSe is also investigated and the thermal switching ratio reaches 9.2 at the magnetic transition temperature. Both the phonon-phonon scattering space phase and phonon anharmonicity are responsible for the 9.2-fold thermal switching. This study advances the understanding of heat energy transport in two-dimensional ferromagnets, and also provides new insight into heat energy control and conversion.