Ferromagnetic insulating ground states in oxygen deficient La0.8Sr0.2CoO3 − δ films induced by ionic liquid gating

Ferromagnetic (FM) insulators are regarded as promising candidates for next-generation electronic and spintronic devices due to their low power consumption and high processing efficiency. However, achieving FM insulators with high Curie temperatures (Tc) remains a challenge. Here, we report high-Tc FM insulating La0.8Sr0.2CoO3 (LSCO) thin films with oxygen deficiencies, in which the concentration of oxygen vacancy (Vo) is modulated through ionic liquid gating (ILG). An abrupt metal–insulator transition has been observed in LSCO films even at low Vo concentration, which can be attributed to the disorder-dominant electric transport behavior. At high Vo concentrations, the transition from original Co–O octahedral (Oh) to tetrahedral (Td) symmetry opens a bandgap with well-defined band edges, stabilizing the insulating state. These findings provide important insights into the manipulation and design of robust FM insulating ground states in complex oxides via topotactic ILG regulation, offering a viable pathway toward advanced spintronics applications.