DC superconducting quantum interference devices fabricated using bicrystal grain boundary junctions in Co-doped BaFe₂As₂ epitaxial films

DC superconducting quantum interference devices (dc-SQUIDs) were fabricated in Co-doped BaFe₂As₂ epitaxial films on (La, Sr)(Al, Ta)O₃ bicrystal substrates with 30° misorientation angles. The 18 × 8 µm² SQUID loop with an estimated inductance of 13 pH contained two 3  µm wide grain boundary junctions. The voltage–flux characteristics clearly exhibited periodic modulations with ΔV = 1.4 µV at 14 K, while the intrinsic flux noise of dc-SQUIDs was 7.8 × 10 ^{− 5} Φ₀ Hz ^{− 1/2} above 20 Hz. The rather high flux noise is mainly attributed to the small voltage modulation depth which results from the superconductor–normal-metal–superconductor junction nature of the bicrystal grain boundary.