Study of magnetic flux pinning in granular YBa$_2$Cu$_3$O$_{7-y}$/nanoZrO$_2$ composites

In this work, the effect of ZrO$_2$ nanoparticles prepared in a low-pressure arc discharge plasma on magnetic flux pinning of granular YBa$_2$Cu$_3$O$_{7-y}$ /nanoZrO$_2$ composites has been studied. It has been shown that the ZrO$_2$ nanoparticles do not change the superconducting transition and the microstructure of superconductors. At a temperature of $5$ K, the addition of $0.5$ and $1$ wt $\%$ of ZrO$_2$ nanoparticles may lead to the additional effect of magnetic flux pinning and the increase in the critical current density $J_c$. The $J_c$ value for composites with $1$ wt $\%$ is two times larger than that for the reference sample. The fishtail effect is observed for YBa$_2$Cu$_3$O$_{7-y}$ /nanoZrO$_2$ composites at the temperatures of $20$ and $50$ K. The problems associated with the additional effect of magnetic flux pinning of granular YBa$_2$Cu$_3$O$_{7-y}$ /nanoZrO$_2$ composites and the appearance of the fishtail effect have been discussed.