Enhanced Critical Current Density in the Carbon-Ion Irradiated MgB2 Thin Films

Abstract

We report large improvement of the critical current density (J(c)) of 400-nm-thick MgB2 thin films through carbon (C) ion irradiation. When 350 keV C ions with various dose levels ranging from 1 x 10(13)-1 x 10(15)C atoms/cm(2) are irradiated into the films, the c-axis lattice constant gradually expands with increase in the number of irradiated C ions and superconducting transition temperature (T-c) of the MgB2 films is suppressed. On the other hand, the field performance of J(c) for the MgB2 films remarkably improves after irradiations, which is accompanied by the crossover of the pinning mechanism from weak collective to strong pinning. In addition, scaling behavior of flux pinning force for irradiated MgB2 films shows a dominance of normal point pinning, indicating that the improved field performance of J(c) mainly originates from the point defects, such as vacancies and interstitials, created by C-ion irradiation. Our results suggest that carbon acts as an effective irradiating source as well as a doping source to improve J(c) in high magnetic fields.