Low Sr doping effects on critical current density and pinning mechanism of YBa2Cu3O7-x single crystals

Abstract

We report on isotherm dc magnetization hysteresis loops, M(H) to 70K ¿ T ¿ 82.5K of YBa2-xSrxCu3O7-x (x = 0, 0.02 and 0.1) single crystals with the purpose to study the influence of the low Sr doping effects on the YBa2Cu3O7-¿ critical current density, JC(H) and normalized flux pinning force density, f(h). The M(H) measurements were performed in a commercial SQUID magnetometer with H ¿ 50kOe applied parallel to the c axis of the samples. The extended Bean critical state model was applied to JC(H) determination. The magnetic irreversibility fields, Hirr(T) were obtained from M(H) loops. The f(h) behavior was determined from FP/FP,max versus H/Hirr plots where FP is the pinning force density (FP = J ¿ ¿0H). The results show that the low Sr doped samples transport higher JC(H) than the pure one. The application of the Dew-Hughes scaling functions to the f(h) plots designates the core normal punctual type as majority pinning mechanism of samples. We suggest that the core normal punctual pinning mechanism, responsible to the enhancement of the JC(H) transported by YBa2-xSrxCu3O7-x samples, is possibly connected to the segregation of Sr atoms precipitates at the crystalline structure of these samples.