Crossover in periodic length dependence of thermal conductivity in 5d element substituted Fe_2VAl-based superlattices

摘要

We investigated the 5d element substitution effect on the thermal conductivity in Fe_2VAl-based superlattice thin films epitaxially grown on a MgO (100) substrate. We found unique crossover behavior in the period dependences of thermal conductivity for Ta-free Fe_2VAl and Fe_2(V, Ta)Al-based superlattices. The Fe_2( V, Ta )Al-based superlattices with periods more than 40 nm appeared to have much lower thermal conductivity than Ta-free Fe_2VAl-based superlattices due to the substitution of V by Ta. Unexpectedly, at a shorter periodic length, less than 20 nm, Fe_2(V, Ta)Al-based superlattices appeared to have higher thermal conductivity than Ta-free Fe_2VAl-based superlattices despite such a heavy element substitution by Ta. This surprising experimental fact was well accounted for with theoretical calculations, which predicted the dominant contribution of phonons having a shorter mean free path in the Ta substituted samples.