No abstract

No abstract

As-grown MgB2 thin films were prepared by a MBE method under the conditions of low temperature, low deposition rate and high vacuum for applications in electric devices. The MgB2 thin films deposited on MgO and Ti buffered ZnO substrates have considerably higher Jc under magnetic fields among MgB2 thin films reported before. The value of Jc for the MgB2 thin film deposited on Ti buffered ZnO has been 5.8 × 105 A cm−2 at 10 K, 5 T in the magnetic field applied parallel to the c axis. In the angular dependence of Jc, the peak of Jc attributable to c-axis-correlated pinning centres has been observed when the magnetic field was applied parallel to the c axis.

We present experimental results of the upper critical fields Hc2 of various MgB2 thin films prepared by the molecular beam epitaxy, multiple-targets sputtering, and co-evaporation deposition apparatus. Experimental data of the Hc2(T ) are successfully analyzed by applying the Gurevich theory of dirty two-band superconductivity in the case of Dπ/Dσ > 1, where Dπ and Dσ are the intraband electron diffusivities for π and σ bands, respectively. We find that the parameters obtained from the analysis are strongly correlated to the superconducting transition temperature Tc of the films. We also discuss the anormalous narrowing of the transition width at intermediate temperatures confirmed by the magnetoresistance measurements.

As-grown superconducting MgB 2 thin films have been grown on SrTiO 3 (001), MgO(001), and Al 2 O 3 (0001) substrates by a molecular beam epitaxy (MBE) method with novel co-evaporation conditions of low deposition rate in ultra-high vacuum. The structural and physical properties of the films were studied by RHEED, XRD, electrical resistivity measurements, and SQUID magnetometer. The RHEED patterns indicate three-dimensional growth for MgB 2 . The highest T c determined by resistivity measurement was about 36K in these samples. And a clear Meissner effect below T c was observed using magnetic susceptibility measurement. We will discuss the influence of B buffer layer on the structural and physical properties