Flux-pinning energy and critical current densit detwinned single crystals

Abstract

We have measured the magnetic relaxation of four detwinned single crystals of Pr-doped (Formula presented)(Formula presented)(Formula presented)(Formula presented)(Formula presented) with x=0, 0.1, 0.2, and 0.3, in a magnetic field of 0.5 T applied parallel to the c axis of each sample. We have calculated the effective flux-pinning energy U for each sample using the Anderson-Kim (AK) model of thermally activated flux creep, Maley’s procedure, collective-pinning theory, and the pinning energy distribution model of Hagen and Griessen. Analysis in terms of the AK model, shows that for T/(Formula presented)0.45, U shows a clear maximum at x=0.2. Maley’s procedure indicates that the J dependence of U is highly nonlinear, and therefore the results from the AK model should be interpreted with caution. However, Maley’s procedure also suggests that the pinning energy is optimally enhanced for approximately 10% Pr doping. In addition, we have measured magnetic hysteresis loops for each sample at T/(Formula presented)=0.1, 0.5, and 0.8. We find that the samples exhibit a strong “fishtail” effect, and, of particular interest, the sample with x=0.1 shows two magnetization peaks in addition to the zero-field peak. © 1996 The American Physical Society.