PINNING-FORCE MEASUREMENTS IN BI2SR2CACU2O8+Y

We report on the applied field and temperature dependence of the pinni ng force in Bi2Sr2CaCu2O8+y single crystals. The pinning force was obt ained from the hysteresis curves in magnetization measurements. The fi eld dependence of the pinning force presents a maximum at nonzero appl ied field. The temperature dependence of the field for maximum pinning force shows three different behaviours: For temperatures between 10 a nd 25 K it decreases steeply with temperature; this behaviour is chang ed for a smooth temperature dependence for temperatures in the range 2 5-40 K and then it approaches to zero above 40 K. This behaviour sugge st the existence of different pinning mechanisms for different tempera ture regions. (C) 1998 Elsevier Science B.V. All rights reserved.