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Local magnetic measurements as a function of temperature (mH( T) ) in Nd1.85 Ce0.15 CuO4− d (NCCO) and untwinned YBa2 Cu3 O7−δ (YBCO) crystals reveal an abrupt increase in the local magnetization at a field dependent temperature, in a certain field range. Both crystals also exhibit a pronounced kink in their local magnetization vs field (mT( H) ) curves. However, while in YBCO the anomalies in mT( H) and mH( T) curves occur along the same line in the field-temperature plane, in NCCO the ( B,T) locations of the anomalies do not coincide. In both crystals the anomalies in mT( H) are identified as signifying vortex solid-solid disorder induced transition. However, we show that the anomalies in mH( T), although associated with the vortex solid-solid transition, do not necessarily indicate the location of the transition. [ABSTRACT FROM AUTHOR]

An array of miniature Hall sensors has been utilized to measure the spatial distribution and time evolution of the local induction in a thin YBa2 Cu3 O7−x film at the remanent state, before and after the application of a dc transport current. As a result of transport current the induction peak is shifted from the center of the sample, indicating an inhomogeneous current distribution. Transport current markedly changes the spatial distribution of the electric field and the relaxation rate, creating a “dynamic neutral line” where the electric field is maximum, and the relaxation rate is zero. [ABSTRACT FROM AUTHOR]