Giant anisotropic magnetoresistance in oxygen-vacancy-ordered epitaxial La0.5Sr0.5Co O3-δ films

Recent advances in complex oxide heterostructures have realized extraordinary control over oxygen vacancies (VO), including strain-tuned VO order, and electric-field-controlled transformations between perovskite and VO-ordered structures. Perovskite cobaltites such as La1-xSrxCoO3-δ provide a prime example, recent work demonstrating that strain engineering of VO ordering induces large (∼107erg/cm3) perpendicular magnetic anisotropy. Here we show that VO-ordered epitaxial La0.5Sr0.5CoO3-δ films exhibit not only strong magnetic anisotropy, but also a giant form of anisotropic magnetoresistance (AMR). This has magnetic field, temperature, and angular dependencies in quantitative accord with conventional AMR, but with AMR ratios up to an extraordinary 40.3%, 20 times enhanced over bulk cobaltites, and ∼10-100 times larger than typical transition metals. This giant AMR has no strong dependence on heteroepitaxial strain (between -2.1% and +1.8%) or thickness, and is instead ascribed to symmetry lowering associated with VO ordering. The AMR ratios thus obtained are among the largest reported in the over 160-year history of this phenomenon, despite the absence of heavy elements.