EFFECT OF SAMPLE SHAPE ON HYSTERESIS LOOPS OF YBA2CU3O7-X SINGLE-CRYSTALS

We have found strong experimental evidence of the dependence of the sh ape of the magnetic hysteresis loops on the thickness d of YBa2Cu3O7-x single crystals when the width over the thickness is much larger than 1. For crystals with similar widths, the full penetration field mu0H( p), defined experimentally as the merging point between the virgin mag netization curve and the external envelope, increases as d increases. Similarly, the magnetic-field variation needed to reverse completely t he magnetization increases with d. Our data are found to support the t heoretical work performed by Clem and Sanchez using the Bean model for thin disks. Reverse legs measured at temperatures up to 70 K and for different reversal fields mu0H(m) up to 10 T are described well by thi s theory.