Fabrication and Characterization of NdBaCuO-Josephson Junctions on MgO-Substrates Damaged by a Focused Ion Beam

We have fabricated a NdBa2Cu3O7 Josephson junction using a narrow-focused Ga-ion beam to damage MgO(100) substrates prior to film deposition. NdBa2Cu3O7 films with smooth surface morphology and without particulates have been deposited by RF magnetron sputtering under rather low oxygen partial pressures. I c values at 4.2 K of several junctions with the same fabricating conditions vary from several µA to several mA. The junctions with higher I c exhibit flux-flow type I-V curves and Fraunhofer-like diffraction patterns of I c under magnetic field. The junctions with lower I c show RSJ type I-V curves and SQUID-like diffraction patterns of I c under magnetic field.