Phase transition in the mixed state of Bi2Sr2CaCu2Oy observed by local and macroscopic magnetometry

In Bi₂Sr₂CaCu₂O_y under magnetic fields along the c-axis, both the local and the macroscopic magnetization show clear steps indicating the first order phase transition (FOPT) in the vortex lattice (VL). Local measurements have revealed that the FOPT occurs from the center of the sample owing to the field inhomogeneity originated from the geometrical effect. The heights of the steps are strongly suppressed in local measurements by the demagnetization effect. With decreasing temperature, the irreversibility in the magnetization just below the step begins to increase and is smoothly connected to the second peak at low temperatures.