Fish-tail effect and its evolution under neutron irradiation in Li-doped YBa2Cu3O7-x

The evolution of the critical current density of Li-doped YBa2Cu3O7-x polyc rystalline samples submitted to neutron irradiation is investigated as func tion of magnetic field (0 less than or equal to B less than or equal to 6 T ) temperature (5 less than or equal to T less than or equal to 85 K) and ne utron fluence (0 less than or equal to Phi less than or equal to 9.98 x 10( 17) cm(-2)). At fluences lower than 10(17) cm(-2), a second peak in j(s) vs . B dependence is present (fish-tail effect). Its magnitude decreases with increasing the fluence. Above 10(17) cm(-2), the second peak of current den sity completely disappears; instead, the logarithmic susceptibility shows a second peak at a certain field B-infi. A dependence of B-infi on fluence i s proposed.