Tunable flux pinning landscapes achieved by functional ferromagnetic Fe₂O₃:CeO₂ vertically aligned nanocomposites in YBa₂Cu₃O_7-δ thin films

Functional ferromagnetic (Fe₂O₃)_x:(CeO₂)_1-x vertically aligned nanocomposite (VAN) layers were deposited as either buffer or cap layers for YBa₂Cu₃O_7-δ (YBCO) thin films. The composition of Fe₂O₃ dopants in the VAN nanolayers is controlled at 10%, 30% and 50% in order to create different arrangements of Fe₂O₃ and CeO₂ nanopillars and therefore to tune the flux pining landscapes. The composition variation provides tunable and ordered arrangements of magnetic nanodopants and interfacial defects as pinning centers in the YBCO thin films. The superconducting property measurements show that most doped samples obtain a T_c above 90 K and the J_c^sf measured at 75 K and 65 K maximized at 3.07 MA/cm² and 9.2 MA/cm² for 30% Fe₂O₃ VAN doped sample. As the temperature decreased to 5 K, the sample with 50% Fe₂O₃ VAN doped sample show the best pinning effect due to pronounced magnetic pinning effects. This work demonstrates the tunable density of magnetic pinning centers can be achieved by VAN to meet the specific pinning requirement.