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Abstract

We have performed magnetisation measurements on Bi2Sr2CaCu2Os+y and obtained the pinning force Fp=Jc.B at different temperatures as a function of field for sintered pellets and for single crystals. Using the flux creep model we have fitted theoretical curves to the data and obtained the pinning activation energy U and the pinned volume 8,. We have performed relaxation measurements and obtained U(B,T), which we have put explicitly into the model.The behaviour of the vortex state in Bi2Sr2CaCU20gfy remains controversial, with many theories being proposed to explain experimentally observed results. These include, amongst others, the ideas of collective pinning [l], a vortex glass [2], and flux lattice melting 131, as well as the more conventional flux creep theories [4]. The latter are well developed and so we proposed to use the predictions of the flux creep model to describe experimentally determined pinning force curves Fp(B), then to examine the parameters involved for any signs of dramatic change that might, for example, accompany a sudden softening or melting of the vortex state.he pinning force curves are shown in figure i. Hysteresis loops up to IZT were performed on an Oxford Instruments VSM system, with a field sweep rate of ImT/s. The sintered material was pressed into a pellet, in order to prevent grains moving due to the vibration. The pellet was not subsequently