Flux Pinning Properties of Multilayered MgB₂/Ni Thin Film Prepared by EBE Method

Abstract

Flux pinning properties of multilayered MgB₂/Ni thin film prepared by an electron beam evaporation method were investigated. The MgB₂/Ni thin film shows the peak around the matching magnetic field in the magnetic field dependence of J_c when the magnetic field is applied in the direction parallel to the surface of the thin film. The strong peak also appears at the B // surface in the field angular dependence of J_c. These results indicate that Ni layers work as two-dimensional pinning centers. Electric field vs. current density characteristics were measured in various magnetic fields and temperatures to obtain the vortex glass-liquid transition temperature T_g and the m-value. The value of T_g at the B // surface was much larger than that of T_g at the B ⊥ surface. The magnetic field dependence of m-value changes drastically at the matching magnetic field when the magnetic field is applied in the direction parallel to the thin-film surface.