Vortex avalanches in the vortex lattice phase of Bi₂Sr₂CaCu₂O_8+y

Local magnetization and local permeability in the mixed state of Bi2Sr2CaCu2O8+y, single crystals have been measured by using a micro-Hall-probe. When temperature is decreased in the vortex lattice phase, local magnetic induction shows step-like decrease, indicating that vortices are expelled from the sample discontinuously. This behavior suddenly disappears at the so-called depinning temperature. In addition to this, broad band low-frequency noise in the local permeability is observed in the region where the discontinuous vortex expulsion occurs. The noise spectrum shows a power-law behavior. Magnetic field dependence of the local permeability suggests that these phenomena are related to the bulk pinning. The discontinuous vortex expulsion and the power-law behavior of the local permeability noise are consistently explained by the vortex avalanches in the vortex lattice phase. © 2000 Elsevier Science B.V. All rights reserved.