Pinning-force measurements in Bi2Sr2CaCu2O8+y

We report on the applied field and temperature dependence of the pinning force in Bi2Sr2CaCu2O8+y single crystals. The pinning force was obtained from the hysteresis curves in magnetization measurements. The field dependence of the pinning force presents a maximum at nonzero applied field. The temperature dependence of the field for maximum pinning force shows three different behaviours: For temperatures between 10 and 25 K it decreases steeply with temperature; this behaviour is changed for a smooth temperature dependence for temperatures in the range 25-40 K and then it approaches to zero above 40 K. This behaviour suggest the existence of different pinning mechanisms for different temperature regions. (C) 1998 Elsevier Science B.V. All rights reserved.