Reversible topotactic reduction induced metal–insulator transformations in La2/3Sr1/3MnO3 thin films

The topochemical reduction process has been demonstrated to generate a range of metastable and structurally distinct phases in transition metal oxides, thereby providing an expansive parameter space for engineering correlated electron systems. Among these systems, La2/3Sr1/3MnO3 (LSMO), a prototypical semi-metallic ferromagnet, has attracted significant attention as a promising candidate for memory and spintronic applications. Here, we demonstrate that utilizing topotactic reduction under compressive stress modulation enables a reversible structural transition from the pristine perovskite phase to a hydrogenated brownmillerite (HBM) phase. Density functional theory calculations reveal that the incorporated H atoms are most likely to occupy oxygen vacancies, preferentially occupying two oxygen vacancies and forming MnO4H2-like octahedral structures. This unique hydrogenation process significantly alters the electronic structure, inducing a transformation from a ferromagnetic metallic state to a weakly ferromagnetic insulating state, accompanied by a decrease in the saturation magnetic moment from 2.87 to 0.59 μB at 10 K. The temperature-dependent resistivity curve of the HBM phase can be effectively fitted using the thermal activation model. After re-oxidation, both the magnetic properties and resistivity are restored to their original states. Unlike conventional control methods, this reversible phase transition provides a unique platform for investigating emergent properties arising from hydrogen-mediated chains and networks, opening new avenues for functional material design.