Neutron irradiation of MgB211: From the enhancement to the suppression of superconducting properties

In this letter, we present the effect of neutron irradiation up to fluences of 1.4×1020cm−2 on the superconducting properties of MgB2. In order to obtain a homogeneously distributed disorder, the experiment was carried out on bulk samples prepared with the B11 isotope. Up to fluences of 1018cm−2, the critical temperature (Tc) is slightly diminished (36K) and the superconducting properties are significantly improved; the upper critical field is increased from 13.5T to 20.3T at 12K and the irreversibility field is doubled at 5K. For the largest neutron fluence, Tc is suppressed down to 9.2K and the superconducting properties come out strongly degraded.