Enhanced flux pinning properties in YBa₂Cu₃O_7-δ/(CoFe₂O₄)_0.3(CeO₂)_0.7 multilayer thin films

A combined defect and magnetic pinning effect has been demonstrated in this work for improving critical current density (J_c) of YBa₂Cu₃O_7-δ (YBCO) thin films. Most of the previous work has focused on either defect pinning or magnetic pinning. In this work, we introduced a unique nanocomposite with two phases, e.g., ferrimagnetic CoFe₂O₄ and non-magnetic CeO₂. As a demonstration, the composition of (CoFe₂O₄)_0.3(CeO₂)₀ was chosen for this study. The nanocomposite was incorporated into YBCO films as multilayers, i.e., 1-, 2-, and 4-interlayers. A detailed study on the microstructural and superconducting properties was conducted. The results show that the critical temperature remains at ∼90 K even after introducing interlayers. More importantly, the films with interlayers show enhanced self-field and in-field J_c, especially the 2-interlayer sample with J_c ^sf of 6.36 MA/cm² at 77 K. The enhanced J_c properties are attributed to both magnetic pinning from CoFe₂O₄ and defect pinning from CeO₂, as well as the well-designed pinning landscapes.