Magnetic properties of high-Tc superconductive materials in low fields

Magnetic hysteresis loops in low fields at 77 K were measured by vibrating sample magnetometer for sintered and melt-textured high-Tc superconductors. The characteristics of loops for different samples were compared and analyzed, and the difference between transport and magnetic critical current density of these granular materials is discussed. For studying the vortex pinning mechanism of grain interfaces, critical state models were used to derive critical current density jcm(b) by fitting model-calculated magnetic hysteresis to experimental results. The field dependence of intergranular currents determined by intergranular weak links was found to correspond very well to the exponential model. (orig.)