The benefit of Ca in improving pinning of BaZrO3-Y2O3 doubly-doped YBa2Cu3O7-x/Ca0.3Y0.7Ba2Cu3O7-x multilayer nanocomposite films

Abstract

This work examines the pinning enhancement in BaZrO₃ (BZO) +Y₂O₃ doubly-doped (DD) YBa₂Cu₃O₇ (YBCO) nanocomposite multilayer (DD-ML) films. The film consists of two 10 nm thin Ca_0.3Y_0.7Ba₂Cu₃O_7-x (CaY-123) spacers stacking alternatively with three BZO + Y₂O₃/YBCO layers of 50 nm each in thickness that contain 3 vol% of Y₂O₃ and BZO doping in the range of 2–6 vol%. Enhanced magnetic vortex pinning and improved pinning isotropy with respect to the orientation of magnetic field (B) have been achieved in the DD-ML samples at lower BZO doping as compared to that in the single-layer counterparts (DD-SL) without the CaY-123 spacers. For example, the pinning force density (F_p) of ∼58 GNm⁻³ in 2 vol.% of DD-ML film is ∼110% higher than in 2 vol% of DD-SL at 65 K and B//c-axis, which is attributed to the improved pinning efficiency by c-axis aligned BZO nanorods through diffusion of Calcium (Ca) along the tensile-strained channels at BZO nanorods/YBCO interface for improvement of the interface microstructure and hence pinning efficiency of BZO nanorods. An additional benefit is in the considerably improved J_c(θ) and reduced J_c anisotropy in the former over the entire range of the B orientations. However, at higher BZO doping, the BZO nanorods become segmented and misoriented, which may change the Ca diffusion pathways and reduce the benefit of Ca in improving the pinning efficiency of BZO nanorods.