Ultralow thermal conductance across the [FePt/h-BN/FePt] interface

Heat transfer in nanocomposite materials has attracted great interest for various applications. Multilayer structures provide an important platform to study interfacial thermal transport and to engineer materials with ultralow thermal conductivity. Here we report on the fabrication and thermal characterization of [h-BN/$L1_0$-FePt]xN multilayers, where hexagonal boron nitride (h-BN) nanosheets (2.5 nm thick) and $L1_0$-FePt layers (6.5 nm thick) alternate periodically. Differential three-omega($3ω$) measurements reveal an ultralow effective thermal conductivity of $ 0.60 \pm 0.05 W \cdot m^{-1}K^{-1}$ across the multilayer films, and a low thermal boundary conductance (TBC) of $ 67.9 \pm 6.6 MW \cdot m^{-2}K^{-1}$ for the [FePt/h-BN(2.5nm)/FePt] interface at room temperature. We attribute the ultralow thermal conductivity to the weak van der Waals bonding at h-BN/FePt interfaces, which dominates the thermal resistance of the multilayer structure. These findings provide insights into the thermal transport in 2D-material/metal multilayer nanostructures and suggest the [h-BN/FePt] superlattice as a promising material for nanoscale thermal barrier coating. Furthermore, the obtained TBC lays the foundation for analyzing heat transfer in FePt-(h-BN) nanogranular films, a promising magnetic recording media which can potentially provide high thermal gradient for heat-assisted magnetic recording (HAMR). This work advances the understanding of thermal transport in 2D-material/metal nanocomposites and demonstrates interface engineering as an effective approach to achieve materials with ultralow thermal conductivity.