The fish-tail effect and the flux pinning induced by the spatial fluctuation of critical temperatures in melt-textured YBa 2 Cu 3 O 7−δ bulk samples

The irreversible magnetization loops and the relaxation of the remnant magnetization were measured for a melt-textured YBa2Cu3O7-delta bulk with two different oxygen states. It is found that introducing the extra oxygen deficiencies into the sample will enhance the critical current density in the low-temperature region and the fish-tail effect in the intermediate-temperature region, but lower the critical current density in the high-temperature region. Further investigation shows that the fish-tail is not due to the crossover between different collective pinning and creep regions, but rather to the presence of the flux pinning induced by the critical temperature fluctuation on the background pinning induced probably, by the mean free path fluctuation.