T. Hanaguri et al., PHASE-TRANSITION IN THE MIXED-STATE OF BI2SR2CACU2OY OBSERVED BY LOCAL AND MACROSCOPIC MAGNETOMETRY, Czechoslovak journal of Physics, 46, 1996, pp. 1559-1560
In Bi2Sr2CaCu2Oy under magnetic fields along the c-axis, both the loca
l and the macroscopic magnetization show clear steps indicating the fi
rst order phase transition (FOPT) in the vortex lattice (VL). Local me
asurements have revealed that the FOPT occurs from the center of the s
ample owing to the field inhomogeneity originated from the geometrical
effect. The heights of the steps are strongly suppressed in local mea
surements 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 temperat
ures.