Giant anisotropic magnetoresistance in oxygen-vacancy-ordered epitaxial La_0.5Sr_0.5CoO₃_-δ films

Recent advances in complex oxide heterostructures have realized extraordinary control over oxygen vacancies (V_O), including strain-tuned V_O order, and electric-field-controlled transformations between perovskite and V_O-ordered structures. Perovskite cobaltites such as La_1-xSr_xCoO_3-δ provide a prime example, recent work demonstrating that strain engineering of V_O ordering induces large (~10⁷ erg/cm³) perpendicular magnetic anisotropy. Here we show that V_O-ordered epitaxial La_0.5Sr_0.5CoO_3-δ films exhibit not only strong magnetic anisotropy, but also a giant form of anisotropic magnetoresistance (AMR) [1]. 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 V_O 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.
[1] Walter et al., Phys. Rev. Mater. 4, 091401(R) (2020)