SUPERCONDUCTING AND NORMAL-STATE PROPERTIES OF Y1BA2(CU1-XFEX)3O7 (X-LESS-THAN-0.2)

We have measured the London penetration depth lambda for Y1Ba2(Cu1-xFe x)3O7 (x<0.2) oriented single crystal powders. We observe a rapid init ial increase of lambda in the concentration region where the supercond ucting transition temperature varies weakly. We attribute this increas e to the formation of the dense three-dimensional tweed structure, to which the disappearance of the intrinsic pinning is also related. The divergence of lambda at higher concentrations and the relation to the decrease of the superconducting critical temperature is discussed.