Anomalies in the Temperature Dependence of the Local Magnetization in YBa₂Cu₃O_7-δ and Nd_1.85Ce_0.15CuO_4-δ Crystals

Local magnetic measurements as a function of temperature (m_H(T)) in Nd_1.85Ce_0.15CuO_4-d (NCCO) and untwinned YBa₂Cu₃O_7-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.