Giant Polar Displacements via Strain Relaxation in Itinerant Ferromagnet SrRuO ₃ Freestanding Films

Abstract Polar displacements are conventionally seen as incompatible with metallicity due to charge screening. However, in perovskite oxide heterostructures, cation off‐centring distortions can be achieved through interface engineering strategies—such as ferroelectric proximity and substrate strain—even in centrosymmetric metallic systems. It remains unexplored whether such off‐centring displacements can be stabilized in freestanding oxide films, where substrate‐induced strain is intentionally eliminated. Here, the discovery of substantial Ru off‐centre displacements exceeding 30 pm in freestanding SrRuO ₃ films is reported, achieved by properly controlling the strain relaxation process to engineer an expanded lattice. It is further demonstrated that these Ru off‐centre displacements effectively tune the electronic structure and consequently modify the magnetic properties of SrRuO ₃ thin films. This work shows that tailored strain relaxation strategies can be used to design magnetic polar metals with desired electronic states in otherwise centrosymmetric perovskite oxides.