Modification of intergrain connectivity, upper critical field anisotropy and critical current density in ion irradiated MgB2 films

We compare the effect of isotropic point defects vis á vis extended defects on the inter and intra grain properties of superconducting MgB2 thin films. In a recent paper Gandikota et al. [Appl. Phys. Lett. 86 (2005) 012508] reported that after 200 MeV α particle irradiation intergrain connectivity remains unaffected. Our results on the contrary indicate that connectivity does depend on irradiation dose and type of ions used. We ascertain that extended defects alter the σ band properties of this two-band superconductor more effectively than the point defects. The improvement in upper critical field and critical current density is intricately related to the type and density of defects created.