Enhanced Flux Pinning Properties in  $\hbox{YBa}_{2}\hbox{Cu}_{3}\hbox{O}_{7-\delta}$/  $(\hbox{CoFe}_{2}\hbox{O}_{4})_{0.3}(\hbox{CeO}_{2})_{0.7} $ Multilayer Thin Films
A combined defect and magnetic pinning effect has been demonstrated in this work for improving critical current density <inline-formula> <tex-math notation="TeX">$(J_{c})$</tex-math></inline-formula> of <inline-formula> <tex-math notation="TeX">$\hbox{YBa}_{2}\hbox{Cu}_{3}\hbox{O}_{7-\delta} $</tex-math></inline-formula> (YBCO) thin films. Most of the previous work has focused on either defect pinning or magnetic pinning. In this work, we introduced a unique nanocomposite with two phases, e.g., ferrimagnetic <inline-formula> <tex-math notation="TeX">$\hbox{CoFe}_{2}\hbox{O}_{4}$</tex-math></inline-formula> and non-magnetic <inline-formula> <tex-math notation="TeX">$\hbox{CeO}_{2}$</tex-math></inline-formula>. As a demonstration, the composition of <inline-formula> <tex-math notation="TeX">$(\hbox{CoFe}_{2}\hbox{O}_{4})_{0.3}(\hbox{CeO}_{2})_{0.7} $</tex-math></inline-formula> was chosen for this study. The nanocomposite was incorporated into YBCO films as multilayers, i.e., 1-, 2-, and 4-interlayers. A detailed study on the microstructural and superconducting properties was conducted. The results show that the critical temperature remains at <inline-formula> <tex-math notation="TeX">$\sim$</tex-math></inline-formula>90 K even after introducing interlayers. More importantly, the films with interlayers show enhanced self-field and in-field <inline-formula> <tex-math notation="TeX">$J_{c}$</tex-math></inline-formula>, especially the 2-interlayer sample with <inline-formula> <tex-math notation="TeX">$J_{c}^{sf}$</tex-math></inline-formula> of 6.36 <inline-formula> <tex-math notation="TeX">$\hbox{MA/cm}^{2}$</tex-math></inline-formula> at 77 K. The enhanced <inline-formula> <tex-math notation="TeX">$J_{c}$</tex-math></inline-formula> properties are attributed to both magnetic pinning from <inline-formula> <tex-math notation="TeX">$\hbox{CoFe}_{2}\hbox{O}_{4}$</tex-math></inline-formula> and defect pinning from <inline-formula> <tex-math notation="TeX">$\hbox{CeO}_{2}$</tex-math></inline-formula>, as well as the well-designed pinning landscapes.