Comparison of critical properties in MgB2 nanometer films prepared on SiC/Si substrate

Abstract

Critical superconducting properties in 100nm MgB2 film are investigated and examined in comparison with our previous results in 10nm and 50nm films. MgB2 films were prepared by sequential evaporation of boron and magnesium on SiC-buffered Si substrate followed by in situ annealing. The amount of supplied boron was controlled so as to result in the required MgB2 film thickness with excess Mg top layer. The superconducting transition temperature Tc is estimated to be 33.1K from the onset of AC diamagnetic susceptibility. The upper critical field Hc2 is also estimated from the AC susceptibility. Their temperature dependences are almost linear with |dHc2/dT|∼5.6kOe/K for the parallel magnetic field and |dHc2/dT]~3.9kOe/K for the perpendicular field. These values are larger than those in our previous 50nm film (Tc of 34.5K) in spite of a little lower transition temperature. The critical current density Jc and irreversibility field Hirr are estimated from DC magnetization hysteresis. Scaling behavior of Hirr ~ [1 – (T/Tc)2]n is examined in comparision to our previous studies in 10nm and 50nm films with different critical exponents n.