Preparation and Properties of MgB2 Thin Films

The superconducting transition temperature of 140 nm +/- 10 nm thin films on sapphire substrates, which were deposited by magnetron sputtering, was around 36 K. Using a magnetization technique, the film's critical current density was estimated as J(c) = 1.8 x 10(7)A/cm(2 )at 10 K, J(c) = 8 x 10(6) A/m(2) at 20 K in a zero magnetic field B,and J(c)= 3 x 10(6) A/m(2) at 10 K and B = 5 T. The values of the upper critical magnetic field Bc(2 )and the irreversibility field B-irr estimated using the four-probe technique were Bc(2) (22 K) = 15 T when H parallel to film surface, 11 T when H perpendicular to film surface, and B-irr (22 K) = 11 T when H parallel to film surface. The X-ray study showed that the microstructure of the film contains only MgB2 and MgO (in minority). The SEM and EPXMA study and quantitative Auger spectroscopy analysis revealed periodical variations of the film composition on the nanolevel and the presence of (mainly) two intercalated Mg-B-O-C phases of slightly different, especially in oxygen content, and thus with different conductivity and, possibly, with different T-C. The characteristics of superconducting magnesium diboride films make them promising for application in electronic devices, e.g., as high-pass filters.