Anomalies in the Temperature Dependence of the Local Magnetization in YBa2Cu3O7−δ and Nd1.85Ce0.15CuO4−δ Crystals.

Local magnetic measurements as a function of temperature (m_H( T) ) in Nd_1.85 Ce_0.15 CuO_{4− 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 (m_T( H) ) curves. However, while in YBCO the anomalies in m_T( H) and m_H( 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 m_T( H) are identified as signifying vortex solid-solid disorder induced transition. However, we show that the anomalies in m_H( T), although associated with the vortex solid-solid transition, do not necessarily indicate the location of the transition. [ABSTRACT FROM AUTHOR]