Enhancement of the critical current density by increasing the collective pinning energy in heavy ion irradiated Co-doped BaFe2As2 single crystals

Abstract

We investigate the effect of heavy ion irradiation (1.4-GeV Pb) on the vortex matter in Ba(Fe0.92Co0.08)2As2 single crystals by SQUID magnetometry. The defects created by the irradiation are discontinuous amorphous tracks, resulting in an effective track density smaller than 25% of the nominal doses. We observe large increases in the critical current density (Jc), ranging from a factor of ~ 3 at low magnetic fields to a factor of ~ 10 at fields close to 1 T after irradiation with a nominal fluence of B= 3.5 T. From the normalized flux creep rates (S) and the Maley analysis, we determine that the Jc increase can be mainly attributed to a large increment in the pinning energy, from < 50 K to approx. 500 K, while the glassy exponent u changes from ~ 1.5 to < 1. Although the enhancement of Jc is substantial in the entire temperature range and S is strongly suppressed, the artificial pinning landscape induced by the irradiation does not modify significantly the crossover to fast creep in the field-temperature vortex phase diagram.