High critical current density over 1 MA cm^-2 at 13 T in BaZrO₃ incorporated Ba(Fe,Co)₂As₂ thin film

Achieving high critical current density (J _c) under a high magnetic field in Fe based superconductors is indispensable for practical applications. Here we report that high critical current density over 1 MA cm^-2 in high field (13 T) can be achieved in BaZrO₃ (BZO) incorporated Ba(Fe,Co)₂As₂ (Co-Ba122) thin film grown on CaF₂ substrate using pulsed laser deposition. The magnetization J _c of Co-Ba122 thin film incorporated with 2 mol.% BZO reaches 1.3 MA cm^-2 (Hc, 13 T and 4.2 K), 14 times higher than that of pure Co-Ba122 thin film. Transmission electron microscopy observation revealed that BZO forms nanorods of ∼4 nm in average diameter with mean separation of 10-11 nm which corresponds to a matching field of about 17-20 T. Incorporating BZO in Co-Ba122 thin films led to a strong vortex pinning effect and a significant enhancement of J _c because a high density of BZO nanorods could form in the superconducting matrix without significant degradation of T _c, and the diameter of BZO nanorods is approximately twice the coherence length of Co-Ba122 (ξ_ab(0) ∼ 2.5 nm) which is the optimal size as pinning centers.