Characteristics of as-grown MgB2 thin films made by sputtering

We describe the characteristics of MgB₂ thin films, which were deposited by sputtering. Under optimized conditions, the critical temperature was 29 K and the surface roughness of the films was 10 nm. The 1-micrometer-wide, 47.3-centimeter-long meander lines fabricated using the films had almost the same critical temperature and resistivity as of the MgB₂ films. However, magnetic susceptibility data showed that there was a relatively broad (approximately 8 K) superconductivity transition, which indicates that the films had nonuniformity in the thickness direction. From the magnetic-field dependence of the resistivity- temperature curve, H_C2(0) was estimated to be 12 T in the ab-axis direction and 10 T in the c-axis direction. We also estimated that the coherent length was 4.8 nm in the c-axis direction and 5.7 nm in the ab-axis direction. The anisotropy value was 1.2, which is smaller than the values reported elsewhere. From the magnetic susceptibility measurements, the critical current density was estimated to be 1.7×10⁶ A/cm².