Emergent Ferromagnetism in Protonated CaRuO₃

Manipulating the magnetic ground state in complex oxides represents a main stream of research in condensed matter physics and materials science due to their fundamental importance. Here we report the emergence of an itinerant ferromagnetic state from a paramagnetic metallic CaRuO₃ through electrically induced protonation during ionic liquid gating. More importantly, this magnetic transition is accompanied with a structural expansion due to proton intercalation, and both which could be reversibly switched by external voltage. Despite the fact that the ruthenates remains metallic across the magnetic transition, we reveal that the ferromagnetic state is strongly correlated with a non-Fermi liquid toward Fermi liquid transition. The versatile magnetic state in protonated CaRuO₃ therefore strongly suggests that the electrically controllable protonation could sever as a novel pathway to manipulate the electronic and magnetic properties in complex oxides.