Magnesium diboride (MgB2) thin films on r-cut sapphire (r-Al2O3) single crystals were fabricated by a precursor, which was obtained at room temperature via a pulsed laser deposition (PLD) method using a Nd:YAG laser, and an in situ postannealing process. The onset superconducting transition, Tconset, and zero-resistivity transition, Tczero, were observed at 33.6 and 31.7 K, respectively, in the MgB2 thin films prepared by a Mg-rich target with a ratio of Mg:B = 3:2. The critical current density, Jc, calculated from magnetization measurements reached up to 0.9 × 106 A cm−2 at 20 K and 0 T. The broad angular Jc peak was found at 28 K when the magnetic fields were applied in a direction parallel to the film surface (θ = 90°). This could be indicative of the granular structure with randomly oriented grains. Our results demonstrate that this process is a promising candidate for the fabrication of MgB2 superconducting devices.

Synopsis: Magnesium diboride (MgB2) is a promising candidate for superconducting diodes due to its high lower critical field (Hc1). In this study, we fabricate MgB2 thin films by a precursor and in-situ post-annealing process as a candidate material for superconducting diodes. The precursor is obtained by pulsed laser deposition (PLD) method using a Nd:YAG laser. The MgB2 thin films prepared by a high-density Mg-rich target with a ratio of Mg : MgB2 = 2 : 1 show the highest superconducting transition at Tc onset = 33.6 K and Tc zero = 31.7 K. The critical current density Jc(0 T) calculated from magnetization measurements reaches 0.9×10 6 A/cm 2 at 20 K. The X-ray diffraction patterns indicate that the MgB2 phase would be oriented with c-axis perpendicular to the substrate surface and/or would have an extremely fine grain size. These results demonstrate that the precursor and in-situ post-annealing process by Nd:YAG-PLD method is favorable for fabricating superconducting diodes with MgB2 material.