Strain-Induced High Coercivity in La_0.7Sr_0.3CoO₃ Films

Here, we report strain-induced high coercivity in La_0.7Sr_0.3CoO₃ (LSCO) films, which suffer in-plane tensile strains due to the positive lattice mismatch between the substrate and the LSCO bulk. The films on (011)-0.7Pb(Mg_1/3Nb_2/3)O₃-0.3PbTiO₃ exhibit large uniaxial anisotropy, large coercivity, and high saturation magnetization at low temperature in contrast to the well soft magnetic behaviors in LSCO bulk. It is found that the coercivity of the 40 nm (001)-LSCO/SrTiO₃ film can be as high as 1.45 T at 10 K and the observed coercivity decreases rapidly as the thickness increases, though the Curie temperature is below room temperature. The large coercivity and anisotropy should be closely related to the strain-induced structural changes and the different orbital ordering of Co³⁺ and Co⁴⁺ ions. Meanwhile, the enhanced domain wall pinning by the tensile strain may also contribute to the observed high coercivity.