Manipulation of the Ferromagnetism in LaCoO ₃ Thin Films Through Cation‐Stoichiometric Engineering

Spin-state transitions are an important research topic in complex oxides with the diverse magnetic states involved. In particular, low-spin to high-spin transition LaCoO3 thin films has drawn a wide range of attention due emergent ferromagnetic state. Although various mechanisms (e.g., structural distortion, oxygen-vacancy formation, spin-state ordering) have been proposed, understanding what really underlies ferromagnetism remains elusive. Here, is systematically modulated by varying oxygen pressure during thin-film growth. samples show dramatic different magnetization, their cobalt valence state and perovskite crystalline structure remain almost unchanged, ruling out scenarios both spin-ordering. This work provides compelling evidence that tetragonal distortion tensile strain significantly modifies orbital occupancy, leading ferromagnetism, while grown at reduced demonstrate pronounced lattice expansion cation-off-stoichiometry, which suppresses consequent magnetization. result not only insight for exotic films, but also identifies promising strategy design electronic through cation-stoichiometry engineering.