Two-component vortex phase diagram inBi2Sr2CaCu2O8+yunder tilted fields studied by a micro-Hall probe

Abstract

Angular dependence measurements of local magnetization in ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{CaCu}}_{2}{\mathrm{O}}_{8+y}$ revealed the existence of multiple peak effects peculiar to the hysteresis loops in tilted fields. We discuss the origins of these peak effects in relation to changes of underlying vortex states, and propose a phase diagram for two-component vortex matter composed of pancake and Josephson vortices. Furthermore, systematic studies with changing temperature and oxygen concentration clarified the nature of the breakpoint of linear suppression of the first-order vortex-lattice melting transition, and the second peak field at low temperatures. It is also demonstrated that the two-component vortex matter shows two kinds of penetration field for pancake vortices.