Effects of partial substitution by 5 d heavy elements on the thermal transport in F e2VAl thin films

The thermal transport properties of M /F e₂(V ,Ta ) Al /M (M =Mo , W) multilayer thin films, which were epitaxially grown on the [100] MgO single-crystal substrates by means of a radio-frequency magnetron sputtering system, were systematically investigated using a picosecond pulsed laser heating time-domain thermoreflectance method. Not only the thermal diffusivity but also the boundary thermal resistance was strongly affected by both the Ta substitution for V in F e₂VAl and the elements in the metallic layer of top and bottom sides. From the first-principles density-functional theory calculations, we found that such changes in heat transport properties were directly related to the intrinsic phonon dispersion. In the F e₂(V ,Ta ) Al layer thickness region of less than 14 nm, the boundary thermal resistances of all thin-film series abruptly decreased with decreasing the thickness, which was due to the coherently ordered interfacial structure.