Interfacial thermal resistance in epoxy-bonded La-Fe-Co-Si composites

Magnetocaloric composites made from La-Fe-Co-Si particles and an epoxy binder matrix exhibit mechanical stability and good magnetocaloric properties, but also a large characteristic time for thermal transport. In this paper we examine the origin of this large time constant by comparing two measurement techniques - direct and contactless - to finite elements simulations based on a tomographic dataset of the sample. We find that the combination of the low thermal conductivity of the epoxy matrix and a thermal resistance at the interface between epoxy and La-Fe-Co-Si results is in a good agreement between simulation and experiment. Our findings help to disentangle the role of the thermal conductivity and the interfacial thermal resistance for the heat flow in magnetocaloric composites. We show that the low thermal conductivity of the epoxy alone cannot explain the large time constant and lay out possibilities for using the interfacial thermal resistance to tailor anisotropic thermal conductivity for directional heat transfer in magnetocaloric composites.