Giant Magnetic Coercivity Driven by Spin‐Bag Ferromagnetism in Epitaxial Sr ₃ YCo ₄ O ₁₀ ₊ δ Films with Engineered 2D Oxygen Vacancy Ordering

The physical properties of transition metal oxides are highly sensitive to the concentration and spatial arrangement of oxygen vacancies, which give rise to a rich spectrum of emergent functionalities. Sr 1‐x Y x CoO 3‐𝛿 represents a complex cobaltite system exhibiting tunable oxygen vacancy configurations and magnetic ordering. Here, we report the observation of an anomalously large magnetic coercive field in epitaxial Sr 1‐x Y x CoO 3‐𝛿 thin films grown on (001) ((LaAlO 3 ) 0.3 (Sr 2 TaAlO 6 ) 0.7 ) (LSAT) substrates, exceeding 5 T at 30 K with an estimated value of 11.4 T at 2 K. This giant coercivity originates from a long‐range, 2D oxygen vacancy ordered structure that stabilizes a ferromagnetic spin bag mechanism, in which low‐spin Co 3+ ions interact cooperatively with neighboring intermediate‐spin Co 3+ and high‐spin Co 2+ species, forming robust local magnetic domains. Our work establishes a pathway for engineering oxygen vacancy architectures in transition‐metal oxides and demonstrates a strategy for designing atomically tailored quantum materials with highly tunable magnetic and electronic functionalities.