The critical current density, irreversibility line, and flux pinning properties of $Ba2CaCu2O4(O,F)2$ high-$Tc$ superconductor

The high-$Tc$ superconductor of $Ba2CaCu2O4(O,F)2$ (F-0212) is an appealing material for application as it has a simple crystal structure with a highest $Tc$ of 108 K. We have derived the intragrain critical current density $(Jc)$⁠, irreversibility field $(Birr)$⁠, flux pinning properties, etc., for the polycrystalline samples from under doping $(Tc=82K)$ to slightly-over doping $(Tc=106K)$ from the dc magnetization hysteresis loops. The $Jc$ and $Birr$ properties were found to improve rapidly as the doping state changes from under doping to slightly-over doping. Here we show that property of the spacing is crucial to enhance $Birr$ as well as its thickness. An anisotropy factor for under doped $Ba2CaCu2O4F2$ was reckoned to 118 from a three-dimensional-two-dimensional crossover field of about 0.28 T. The double logarithmic plot of irreversibility field versus $[1−(T/Tc)]$ analysis hints that the flux line melting model is adopted. Analysis of the normalized pinning force reveals that a surface pinning mechanism is dominant and reduced magnetic field $bmax=0.2$ agree with surface pinning mechanism with closely spaced pins.