Influence of carbon-ion irradiation on the superconducting critical properties of MgB2 thin films

Abstract

We investigate the influence of carbon-ion irradiation on the superconducting (SC) critical properties of MgB2 thin films. MgB2 films of two thicknesses, 400 nm (MB400nm) and 800 nm (MB800nm), were irradiated by 350 keV C ions having a wide range of fluence, 1 × 1013–1 × 1015 C atoms cm−2. The mean projected range (R p) of 350 keV C ions in MgB2 is 560 nm, thus the energetic C ions will pass through the MB400nm, whereas the ions will remain into the MB800nm. The SC transition temperature (T c), upper critical field (H c2), c-axis lattice parameter, and corrected residual resistivity (ρ corr) of both the films showed similar trends with the variation of fluence. However, a disparate behavior in the SC phase transition was observed in the MB800nm when the fluence was larger than 1 × 1014 C atoms cm−2 because of the different T cs between the irradiated and non-irradiated parts of the film. Interestingly, the SC critical properties, such as T c, H c2, and critical current density (J c), of the irradiated MgB2 films, as well as the lattice parameter, were almost restored to those in the pristine state after a thermal annealing procedure. These results demonstrate that the atomic lattice distortion induced by C-ion irradiation is the main reason for the change in the SC properties of MgB2 films.