Transformational dynamics of BZO and BHO nanorods imposed by Y2O3 nanoparticles for improved isotropic pinning in YBa2Cu3O7-δ thin films

An elastic strain model was applied to evaluate the rigidity of the c-axis aligned one-dimensional artificial pinning centers (1D-APCs) in YBa2Cu3O7-delta matrix films. Higher rigiditywas predicted for BaZrO3 1D-APCs than that of the BaHfO3 1D-APCs. This suggests a secondary APC doping of Y2O3 in the 1D-APC/YBa2Cu3O7-delta nanocomposite films would generate a stronger perturbation to the c-axis alignment of the BaHfO3 1D-APCs and therefore a more isotropic magnetic vortex pinning landscape. In order to experimentally confirm this, we have made a comparative study of the critical current density J(c) (H, theta, T) of 2 vol.% BaZrO3 + 3 vol.% Y2O3 and 2 vol.% BaHfO3 + 3 vol.% Y2O3 double-doped (DD) YBa2Cu3O7-delta films deposited at their optimal growth conditions. A much enhanced isotropic pinning was observed in the BaHfO3 DD samples. For example, at 65 K and 9.0 T, the variation of the J(c) across the entire theta range from theta=0 (H//c) to theta=90 degree (H//ab) is less than 18% for BaHfO3 DDfilms, in contrast to about 100% for the BaZrO3 DDcounterpart. In addition, lower alpha values from the J(c)(H) similar to H-alpha fitting were observed in the BaHfO3 DD films in a large theta range away from the H//c-axis. Since the two samples have comparable J(c) values at H//c-axis, the improved isotropic pinning in BaHfO3 DD films confirms the theoretically predicted higher tunability of the BaHfO3 1D-APCs in APC/YBa2Cu3O7-delta nanocomposite films. (C) 2017 Author(s).