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Spin‐state transitions are an important research topic in complex oxides with the diverse magnetic states involved. In particular, the low‐spin to high‐spin transition in LaCoO₃thin films has drawn a wide range of attention due to the emergent ferromagnetic state. Although various mechanisms (e.g., structural distortion, oxygen‐vacancy formation, spin‐state ordering) have been proposed, an understanding of what really underlies the emergent ferromagnetism remains elusive. Here, the ferromagnetism in LaCoO₃thin films is systematically modulated by varying the oxygen pressure during thin‐film growth. Although the samples show dramatic different magnetization, their cobalt valence state and perovskite crystalline structure remain almost unchanged, ruling out the scenarios of both oxygen‐vacancy and spin‐ordering. This work provides compelling evidence that the tetragonal distortion due to the tensile strain significantly modifies the orbital occupancy, leading to a low‐spin to high‐spin transition with emergent ferromagnetism, while samples grown at reduced pressure demonstrate a pronounced lattice expansion due to cation‐off‐stoichiometry, which suppresses the tetragonal distortion and the consequent magnetization. This result not only provides important insight for the understanding of exotic ferromagnetism in LaCoO₃thin films, but also identifies a promising strategy to design electronic states in complex oxides through cation‐stoichiometry engineering.

Skyrmionic magnetic states are promising in advanced spintronics. This topic is experiencing recent progress in 2D magnets, with, for example, a near 300 K Curie temperature observed in Fe₃GeTe₂. However, despite previous studies reporting skyrmions in Fe₃GeTe₂, such a system remains elusive, since it has been reported to host either Néel‐type or Bloch‐type textures, while a net Dzyaloshinskii–Moriya interaction (DMI) cannot occur in this compound for symmetry reasons. It is thus desirable to develop an accurate model to deeply understand Fe₃GeTe₂. Here, a newly developed method adopting spin invariants is applied to build a first‐principle‐based Hamiltonian, which predicts colorful topological defects assembled from the unit of Bloch lines, and reveals the critical role of specific forms of fourth‐order interactions in Fe₃GeTe₂. Rather than the DMI, it is the multiple fourth‐order interactions, with symmetry and spin–orbit couplings considered, that stabilize both Néel‐type and Bloch‐type skyrmions, as well as antiskyrmions, without any preference for clockwise versus counterclockwise spin rotation. This study also demonstrates that spin invariants can be used as a general approach to study complex magnetic interactions.