Transport properties of thin Ba(Fe,Co)2As2 film microbridges

The critical current density of Ba(Fe,Co)2As2 thin film microbridges was evaluated from current-voltage characteristics measured using the standard four-probe technique. The Ba(Fe,Co)2As2 films were deposited by pulsed-laser deposition on heated (La,Sr)(Al,Ta)O3 substrates and patterned by means of photolithography and ion milling. The critical current density at T=4.2 K reaches about 3 MA/cm2. The experimentally obtained temperature dependence of the critical current density is described by (1-T/Tc)1.5 in the unexpectedly wide temperature range 0.4 < T/Tc < 1. The results can be explained in the frame of Ginzburg-Landau theory for the de-pairing critical current. The expulsion of magnetic vortices is considered as a mechanism which is responsible for overcoming Likharev's limit for observation of the de-pairing critical current.