Temperature-dependent scaling of pinning force data in Bi-based high-Tc superconductors

The scaling of the normalized volume pinning forces, Fp/Fp,max, versus a reduced field h=Ha/Hscale has proven to be a very informative tool to study the origin of the flux pinning in superconductors. Remarkably, on Bi2Sr2Ca2Cu3O10+δ (Bi-2223) and Bi2Sr2CaCu2O8+δ (Bi-2212) data were mostly analyzed only in a narrow temperature range around 77 K. Here, we present a study of the pinning forces in various Bi-2223 samples at temperatures between 18 K and 80 K. The measurements clearly reveal that there is an apparent non-scaling of the pinning force data; instead, two clearly different temperature regimes for the scaling can be recognized, which are found to be in direct relation to a second step observed in the m(T) curves obtained upon field-cooling and -warming.