Vortex pinning in artificially layered Ba(Fe,Co) 2 As 2 film

Abstract

Static high critical current densities (J(c)) > 1 MA/cm(2) with magnetic field parallel or perpendicular to c-axis were realized in Co-doped/undoped multilayerd BaFe2As2 films. We made a current bridge by FIB to allow precise measurements, and confirmed that the boundary quality using FIB was considerably better than the quality achieved using a laser. The presence of a high in-plane J(c) suggested the existence of c-axis correlated vortex pinning centers. To clarify the relationship between the J(c) performance and superstructures, we investigated the magnetic flux pinning mechanism using scaling theory of the volume pinning force F-p(H). The J(c)(H) curves, F-p/F-p,F-max vs. h = H/H-irr curves, and parameters p and q depended on the characteristics of the flux pinning mechanism. It was found that the dominant pinning mechanism of Co-doped/undoped multilayerd BaFe2As2 films was Delta l-pinning and the inserted undoped BaFe2As2 layers remained non-superconducting. The dominant pin geometry varied when the magnetic field direction changed. It was concluded that the artificially layered BaFe2As2 film is a 3-D superconductor due to its long correlation length compared to the thickness of the non-superconducting layer.