Magnetization and critical current density of superconducting granules doped with NiO nanoparticles

A series of bulk superconducting YBa$_2$Cu$_3$O$_{7-\delta}$ (YBCO) samples doped with antiferromagnetic NiO nanoparticles and subjected to 18 h high-temperature annealing have been synthesized. For YBCO samples doped with 8, 12, and 23 nm nanoparticles, the characteristic magnitudes $\Delta M$ of the magnetic hysteresis loops were compared and the optimal size of NiO nanoparticles was determined. The effect of the concentration of NiO nanoparticles with an average size of 8 nm on the magnetic hysteresis loops of YBCO and the critical current density at $T$ = 4.2 K has been studied. An increase in the critical density of intragranular currents is achieved by adding 0.5 wt.% of NiO nanoparticles.