Effects of neutron irradiation on superconducting critical temperatures of in situ processed MgB 2 superconductors

Effects of neutron irradiation on the superconducting properties of the undoped MgB2 and the carbon(C)-doped MgB2 bulk superconductors, prepared by an in situ reaction process using Mg and B powder, were investigated. The prepared MgB2 samples were neutron-irradiated at the neutron fluence of 10-10 n/cm in a Hanaro nuclear reactor of KAERI involving both fast and thermal neutron. The magnetic moment-temperature (M-T) and magnetization-magnetic field (M-H) curves before/after irradiation were obtained using magnetic property measurement system (MPMS). The superconducting critical temperature (Tc) and transition width were estimated from the M-T curves and critical current density (Jc) was estimated from the M-H curves using a Bean’s critical model. The Tcs of the undoped MgB2 and C-doped MgB2 before irradiation were 36.9-37.0 K and 36.6-36.8 K, respectively. The Tcs decreased to 33.2 K and 31.6 K, respectively after irradiation at neutron fluence of 7.16×10 n/cm, and decreased to 22.6 K and 24.0 K, respectively, at 3.13×10 n/cm. The Jc cross-over was observed at the high magnetic field of 5.2 T for the undoped MgB2 irradiated at 7.16×10 n/cm. The Tc and Jc variation after the neutron irradiation at various neutron fluences were explained in terms of the defect formation in the superconducting matrix by neutron irradiation.