Designing ferroic domain states and coupling through low-energy He-irradiation

The physical properties of ferroic thin films are typically dominated by their domain configurations and the response of domain walls to external fields. Domain engineering has thus developed as a powerful tool to tailor functionalities of oxide thin films. A particularly successful approach has been the use of strain fields through heteroepitaxy.

As an alternative approach we deploy low-energy He implantation to induce out-of-plane strain in epitaxial ferroelectric thin films, while the in-plane strain due to coherent growth on single-crystal substrates remains fixed. We show that this kind of uniaxial strain engineering effectively alters the ratio of ferroelectric and ferroelastic domains in BaTiO₃ and BiFeO₃ films. We also demonstrate that controlling domains by strain doping can provide a direct handle on ferromagnetic metal films magnetoelastically coupled to the interfaced ferroelectric films.