Vortex matter transition in Bi₂Sr₂CaCu₂O_8+y under tilted fields

Vortex phase diagram under tilted fields from the c axis in Bi2Sr2CaCu2O8+y is studied by local magnetization hysteresis measurements using Hall probes. When the field is applied at large angles from the c axis, an anomaly (Hp) other than the well-known peak effect (Hp) is found at fields below Hp is nonmonotonic and clearly different from that of Hp and depends on the oxygen content of the crystal. The results suggest existence of a vortex matter transition under tilted fields. Possible mechanisms of the transition are discussed. © 2001 American Physical Society.