Effects of partial substitution by 5d heavy elements on the thermal transport in Fe2VAl thin films

Abstract

The thermal transport properties of $M/\mathrm{F}{\mathrm{e}}_{2}(\mathrm{V},\mathrm{Ta})\mathrm{Al}/M$ ($M=\mathrm{Mo}$, 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 $\mathrm{F}{\mathrm{e}}_{2}\mathrm{VAl}$ 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 $\mathrm{F}{\mathrm{e}}_{2}(\mathrm{V},\mathrm{Ta})\mathrm{Al}$ 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.