Investigation of critical behaviour of MgB2 thin films on SiC/Si substrate

Abstract

Critical magnetic behaviour of MgB2 thin films grown on SiC-buffered Si substrate was investigated in comparison with MgB2 films on NbN-buffered Si substrate. MgB2 films were prepared by sequential evaporation of boron and excess magnesium followed by in situ annealing in an Ar atmosphere. The upper critical field Hc2 estimated from the onset of AC diamagnetic susceptibility was larger in films with SiC buffer than those with NbN buffer. The temperature dependence was almost linear with |dHc2/dT| up to 8 kOe/K, especially under parallel magnetic field to the film surface. Although the critical current density evaluated from DC magnetization hysteresis approached 1 MA/cm2 at the lowest temperatures, the maximum value was smaller than that in MgB2/NbN/Si. The irreversibility field also inferred effects of weak links, possibly due to some impurity phases.