Paramagnetic and diamagnetic centers in YBa2 CU3 O7-x crystals induced by neutron irradiation

Irradiation with high-energy particles produces defects of structure: point defects (vacancies and interstitials) and disordered areas (clusters and cascades of displaced atoms:). In high temperature super conducting materials this leads to decrease in the critical temperature, Tc, increase in the normal state resistivity and, if a fluence is high enough, to total degradation of superconductivity, so as the material becomes insulator. However after a moderate fluence the radiation induced defect structure becomes beneficial for effective pinning of high magnetic field, which implies enhancement of magnetization critical current density. So such an irradiated structure should consist of both super conducting (diamagnetic) and non-conducting (para-or ferromagnetic) domains. The available literature data report about observation of dimensional defects in TEM giving rise the magnetic hysteresis in high fields (>1 Tesla) measured with SQUID-magnetometer. Also there has been found the paramagnetic Meissner effect (or Wohlleben effect) of incomplete expelling magnetic field by the over doped HTSC with the degraded super conducting transition. We think there should be some correlation between the two phenomena in the defective superconductors