Microstructural and Pinning Properties of ${\rm YBa}_{2}{\rm Cu}_{3}{\rm O}_{7-\delta}$ Thin Films Doped With Magnetic Nanoparticles

In this paper, we report a strong enhancement in the in-field transport properties of the ${\rm YBa}_{2}{\rm Cu}_{3}{\rm O}_{7-\delta}$ (YBCO) thin films doped with magnetic ${\rm Fe}_{2}{\rm O}_{3}$ nanoparticles. We incorporated magnetic ${\rm Fe}_{2}{\rm O}_{3}$ nanoparticles with two different architectures by laser ablation of the YBCO and dopant targets. YBCO film thickness was controlled at around 1 $\mu{\rm m}$ for all the samples. We conducted a detailed microstructural characterization on all the doped samples by X-ray diffraction (XRD) and cross-sectional transmission electron microscopy (TEM) and compared with the pure YBCO films. A systematic study on the superconducting properties has been conducted on all the thin film samples. The critical current densities at both self-field and in-field ( $J_{c}^{sf}$ and $J_{c}^{in-field}\ ({\rm H}//c)$) and the critical transition temperature $(T_{c})$ of the doped and un-doped YBCO sample were measured by a Superconducting Quantum Interference Device (SQUID). The $T_{c}$ of the doped YBCO films varies from 84 K–90 K and the $J_{c}$ is in the range of 1.2–3.9 ${\rm MA/cm}^{2}$ (at 65 K) depending on the doping approach. The pinning properties of these doped YBCO films were explored at different temperatures (5 K, 40 K, and 65 K) and correlated with their microstructural characteristics.