Enhancement of critical current density in CaKFe4As4 single crystals through 3 MeV proton irradiation

Abstract

We study the influence of random point disorder on the vortex dynamics and critical current densities J c of CaKFe4As4 single crystals by performing magnetization measurements. Different samples were irradiated with a proton (p) beam at constant energy of 3 MeV to fluencies from 2 × 1015 p cm-2 to 4 1016 p cm-2. The results show the addition of extrinsic random point disorder enhances the J c values at low and intermediate temperatures over the entire range of magnetic fields applied. The optimum pinning enhancement is achieved with a proton fluence of 3 × 1016 p cm-2, increasing J c at 5 K by factors ≈5 and 14 at self-field and μ 0 H = 3 T, respectively. We analyze the vortex dynamics using the collective creep theory. The enhancement in J c matches with a systematic reduction in the flux creep relaxation rates as a consequence of a gradual increase in the collective pinning energy U 0. The substantial increment in J c produced by random point disorder, reaching values of 9 MA cm-2 at 5 K and self-field, makes CaKFe4As4 a promising material for applications based on current carrying capacity at high magnetic fields.