Field induced flux pinning in Nd_1+xBa_2-xCu₃O_7-δ single crystal

The flux pinning behavior of a Nd_{1 + x}Ba_{2 - x}Cu₃O_{7 - δ} (Nd123) single crystal, which exhibited a peak effect, has been studied by monitoring the time decay of the magnetic moment. The apparent pinning energy (U₀*) was deduced from flux creep data on the basis of the Anderson-Kim model. The magnetic field dependence of U₀* showed maxima at peak fields which depended on the temperatures, in a similar manner to those of critical current densities. In addition, the temperature dependence of U₀* showed several features. To explain the increase in U₀* with the field as well as its temperature and field dependence, we made a numerical calculation by introducing an additional pinning energy which increased with increasing field. The results are in good agreement with the experimental data, especially at temperatures above 60 K, where the contribution of field induced pinning centers is believed to be dominant.