Stabilizing Metastable Rare-Earth Ferrites on (111) Platinum via an Iron Oxide Interlayer

The metastable P63cm phase of ScFeO3 (h-ScFeO3) is a multiferroic material, but instability on conductive substrates limits the development of next-generation memory and magnetoelectric sensors. Unfortunately, stabilization approaches developed for insulating substrates, such as sapphire, do not translate directly to conductive substrates. In this work, we demonstrate how interlayer design preferentially stabilizes h-ScFeO3 on (111) platinum via molecular beam epitaxy while simultaneously enhancing key figures of merit. We developed a process to deposit a (111) wüstite-like interlayer with a metastable Fe3+ oxidation state to target h-ScFeO3. The films are solely (0001) oriented h-ScFeO3 without any measured secondary phases. Rocking curves of the 0004 h-ScFeO3 peak have a full width at half-maximum of 0.06°, an improvement compared to films deposited without this interlayer approach. A further indication of strain reduction in these films is structural distortion in the first layers of h-ScFeO3, overcoming the critical thickness limit in h-ScFeO3. Designing interlayers to reduce epitaxial strain and target specific phases expands the viable substrates for metastable materials and overcomes the thickness limits for improper ferroelectricity.