Low-field magnetovoltage measurements in superconducting Y1Ba2Cu3O7−δ

Abstract

We investigated the influences of field orientation with respect to transport current, magnitude of transport current, temperature and field-sweep rate (dH/dt) on the evolution of magnetovoltage (V–H) curves in polycrystalline superconducting bulk sample of Y1Ba2Cu3O7−δ. In well-defined magnetic field and temperature ranges, it was found that a relative decrease in dissipation could be obtained depending on the current as the field-sweep rate decreases, so that it underlines the importance of time spent to plot the whole cycle of V–H curves. This physical observation was correlated to more effective field and less relaxation evolving in the grains and more return flux and less effective field at the grain boundaries. On the other hand, an enhancement in hysteresis effects in V–H curves which manifests itself as an increase in the area enclosed by the hysteresis loop was observed at low currents and at low temperatures. These behaviours were attributed to the increase in effective trapped field originated from the relative increase in the height of pinning barriers due to the low currents, and low-thermal fluctuations together with flux creep appearing at low temperatures. Finally, the strong clockwise hysteresis effects in V–H curves were interpreted within the granularity of sample mainly in terms of flux trapped in the grains returning through the grain boundaries.