Hybrid artificial pinning centers of elongated-nanorods and segmented-nanorods in YBa2Cu3O7 films

To control the anisotropy of critical current density (J(c)), hybrid artificial pinning centers (APCs) of elongated-nanorods and segmented-nanorods were incorporated into YBa2Cu3O7 films. The elongated-nanorods and segmented-nanorods were formed by fabricating multilayer films using YBa2Cu3O7+BaSnO3 targets with a different BaSnO3 content. According to the elastic calculation, the BaSnO3-free YBa2Cu3O7 regions between BaSnO3 segmented-nanorods were highly strained, resulting in their alignment along the c-axis. Pinning of the vortex kinks and straight vortices by the nanorod ends improved J(c) in a wide range around B//ab. The angular dependence of Jc systematically varied with the multilayer structure of layer thickness and BSO content. J(c) depended on the layer thickness even with keeping the constant average BSO content, showing that the BaSnO3 distribution, as well as the average BaSnO3 content, affected the J(c). The hybrid pinning effect of elongated-nanorods and nanorod ends improved the J(c) anisotropy although the effect was not so large in the present films. The control of strain and interface is expected to lead to further improvement of J(c).