Controlling BCC-FCC Phase Selection in Cantor Thin Films Grown by Molecular Beam Epitaxy

High entropy alloys (HEAs) constitute a new class of materials with promising physicochemical properties which remain largely unexplored experimentally. The overall objective of this study is to prepare single-crystalline Cantor films (CrMnFeCoNi) grown by Molecular Beam Epitaxy. Film growth was monitored in real time via electron diffraction, while their structure and morphology were characterized using x-ray diffraction and transmission electron microscopy. The use of metallic buffer layers such as Ni, Rh, or RhNi₂ enabled the growth of epitaxial Cantor alloy layers with an FCC structure, consistent with existing literature. Surprisingly, the use of Fe, Cr, or Pd buffer layers resulted in the formation of Cantor alloy films with a BCC structure-a phase never previously reported. This phase is also obtained by depositing the Cantor by magnetron sputtering on a Cr buffer layer. Using ab initio calculations, we demonstrate that the selection of the FCC or BCC phases is governed by the commensurability with buffer layer thanks to strong adsorption energies. Finally, structural relaxation during calculations yields the same energy gain for both structures. Unlike FCC films, this BCC Cantor phase is observed to be ferromagnetic with a moment around 1000 kA/m at 300K, confirming reported ab initio calculations.