Magnetic behavior of magnesium diboride superconducting thin films

We report the experimental results of the field H and temperature T dependent magnetization M measurements of MgB2 superconducting thin films deposited by pulsed laser deposition. MgB2 thin films were obtained from a precursor layer deposited in UHV at room temperature from stoichiometric target, then an annealing treatment in Mg atmosphere allowed to crystallize the superconducting phase. From the hysteresis loops at each temperature of measurement the critical current density J(c)(H) has been extracted according to Brandt's model for a transverse geometry. At low temperatures an anomalous behavior has been observed in the hysteresis loops: as the external magnetic field approaches the zero field region on the upper and lower branches, a double peak of the magnetization occurs. This magnetic flux jumping can be explained within an adiabatic critical state model, and can be ascribed to thermomagnetic instabilities as in bulk samples.