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 B and Mg on NbN buffered Si substrate followed by in situ annealing. Alternating-current and direct-current magnetizations were measured by the PPMS system. From the onset of alternating-current diamagnetic susceptibilities, the upper critical fields were estimated resulting in the temperature derivative of about −5kOe/K at lower temperatures. Critical current densities were evaluated from direct-current magnetization hysteresis to be more than 1MA/cm2 below 14K (self field). Critical properties including irreversibility fields were examined in comparison with those under parallel magnetic fields

Critical Properties of MgB2 Thin Films on NbN/Si Substrate under Perpendicular Magnetic Fields. A.Nishida, C.Taka, S.Chromik, R.Durny: Physica C, 2005, 426-431[1], 340-4