Property and cation valence engineering in entropy-stabilized oxide thin films

We present data for epitaxial thin films of the prototypical rocksalt entropy-stabilized oxide (ESO) Mg${}_{0.2}$Ni${}_{0.2}$Co${}_{0.2}$Cu${}_{0.2}$Zn${}_{0.2}$O that reveals a remarkably large property dependence on growth temperature. Variable net Co valence strongly influences the unit cell volume, optical response, and magnetic response. ESO solid solutions are well known for their compositional flexibility and corresponding property tunability. However, the present observations illustrate that even at constant metallic element proportions, synthesis conditions alone can strongly influence the physical properties of ESO crystals without significant changes in microstructure.