Local magnetization anomalies and inhomogeneous vortex penetration in the crossing-lattices state of Bi2Sr2CaCu2O8+y

Nature of vortices in a highly anisotropic superconductor Bi2Sr2CaCu2O8+y is investigated in the presence of largely tilted magnetic fields. Direct visualizations of vortex distributions were performed under large in-plane fields up to 4000Oe by magneto-optical imaging technique. Our visualization clearly revealed inhomogeneous evolutions of the vortex penetration forming one-dimensional stripes. Comparative studies on the local magnetization revealed the existence of novel multiple peak structures in hysteresis loops. These peaks appear only in the increasing branch of the hysteresis curves when a magnetic field is applied nearly parallel to the superconducting plane. The origin of the novel anomalies is discussed on the basis of inhomogeneous vortex distribution.