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

ABSTRACT 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.