Magnetic hysteresis ofp+and3He++irradiated melt‐textured YBa2Cu3O7−δ

We have measured the magnetic hysteresis loops and temperature dependent trapped fields in melt‐textured YBa2Cu3O7−δ samples before and after p + and 3He++ irradiation using a Hall effect magnetometer (HEM) as well as a commercial vibrating sample magnetometer (VSM). For proper 3He++ fluence, the critical current density may be enhanced by a factor of 10. Calculations based on various critical state models show that before the irradiation, the hysteresis loops can be well accounted for by a critical current density of a modified power law field dependence J c (T,B)=J 0(T)/(1+B/B 0) n with n=1/2; after the irradiation, the best fit has been achieved by using an exponential form such as J c (T,B)=J 0(T)exp(−B/B 0), where B 0 is a model dependent parameter. J c and its field dependence deduced from HEM hysteresis loops are in good agreement with those deduced from the VSM loops, suggesting that the Hall effect magnetometer can be conveniently used to characterize bulk high T c oxide superconductors.