Enhancement of critical current density in helium ion irradiated Ba(Fe, Co)2As2 thin films

Abstract

The effect of 600 keV He+ ion irradiation on the temperature and magnetic field dependence of the critical current density JC in high quality BaFe1.84Co0.16As2 (Co-doped Ba122 type) thin films is investigated. The films are prepared by pulsed-laser-deposition (PLD) on CaF2 (00 ) substrates. The irradiation dosages are varied between 1 × 1013 and 1 × 1016 cm−2. Upon irradiation, the superconducting transition temperature TC drops slightly from 25 K for the unirradiated sample to about 20 K for the sample with the highest irradiation level. The JC values of the thin film samples are calculated by using the Bean critical state model. The results showed that JC could be enhanced substantially. The maximum JC value at 4.5 K temperature is enhanced up to 2.4 MA cm−2 under 1 T field. The analysis of pinning force dependence on magnetic field shows that the pinning behavior is not changed in the irradiated samples, suggesting more pinning centers of similar nature to those of presented in the unirradiated samples are introduced by the irradiation process. The results indicate that the irradiation of light element ions He+ with relatively low energy could increase the critical current density in iron based superconductors.