Decoding anomalous thermal transport in magnetic semiconductors

Thermal conductivity in semiconductors typically decreases at high temperatures due to enhanced phonon-phonon interactions. In contrast, certain magnetic semiconductors, such as chromium nitride (CrN), exhibit an increased thermal conductivity above its Néel temperature, predicted to be caused by strong spin-phonon coupling. However, this hypothesis lacks experimental verification and detailed understanding. Here, we present conclusive experimental evidence showing that the enhanced thermal conductivity in CrN arises from anomalous temperature-dependent acoustic phonon lifetimes, driven by a dynamic coupling between spin fluctuations and acoustic phonons in the system. Temperature-dependent inelastic x-ray scattering measurements reveal that acoustic phonon lifetimes in CrN are strongly suppressed near Néel temperature but anomalously increase at higher temperatures. In contrast, the optical phonon lifetime decreases with rising temperature, akin to a nonmagnetic semiconductor, as it remains unaffected by spin-phonon coupling. This finding unveils the microscopic origin of anomalous heat transport behavior in magnetostructurally coupled materials, offering a pathway for effective thermal management in magnetic material-based devices.