Neutron irradiation of Mg11B2: From the enhancement to the suppression of superconducting properties.

In this letter, we present the effect of neutron irradiation up to fluences of 1.4×10²⁰ cm^-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 ¹¹B isotope. Up to fluences of 10¹⁸ cm^-2, the critical temperature (T_c) is slightly diminished (36 K) and the superconducting properties are significantly improved; the upper critical field is increased from 13.5 T to 20.3 T at 12 K and the irreversibility field is doubled at 5 K. For the largest neutron fluence, T_c is suppressed down to 9.2 K and the superconducting properties come out strongly degraded. [ABSTRACT FROM AUTHOR]