Improved multiferroic in EuTiO₃ films by interphase strain engineering

Interphase strain engineering provides a unique methodology to significantly modify the lattice structure across a single film, enabling the emergence and manipulation of novel functionalities that are inaccessible in the context of traditional strain engineering methods. In this work, by using the interphase strain, we achieve a ferromagnetic state with enhanced Curie temperature and a room-temperature polar state in EuO secondary phase-tunned EuTiO₃ thin films. A combination of atomic-scale electron microscopy and synchrotron X-ray spectroscopy unravels the underlying mechanisms of the ferroelectric and ferromagnetic properties enhancement. Wherein, the EuO secondary phase is found to be able to dramatically distort the TiO₆ octahedra, which favors the non-centrosymmetric polar state, weakens antiferromagnetic Eu-Ti-Eu interactions, and enhances ferromagnetic Eu-O-Eu interactions. Our work demonstrates the feasibility and effectiveness of interphase strain engineering in simultaneously promoting ferroelectric and ferromagnetic performance, which would provide new thinking on the property regulation of numerous strongly correlated functional materials.