Critical properties of MgB2 thin films on NbN/Si substrate under perpendicular magnetic fields

Critical magnetic properties of MgB2 thin films grown on NbN/Si substrate were investigated under magnetic fields perpendicular to the film surface. Polycrystalline MgB2 films were prepared by sequential evaporation of boron and magnesium on NbN buffered Si substrate followed by an in situ annealing. AC and DC magnetizations were measured by the PPMS system. From the onset of AC diamagnetic susceptibilities, the upper critical fields were estimated resulting in the temperature derivative of about −5 kOe/K at lower temperatures. Critical current densities were evaluated from DC magnetization hystereses to be more than 1 MA/cm2 below 14 K (self field). Critical properties including irreversibility fields were examined in comparison with those under parallel magnetic fields.