ANALYSIS OF THE CU-63,CU-65 NMR DATA AS A FUNCTION OF OXYGEN CONCENTRATION IN YBA2CU3O7-DELTA

We compare the 63,65Cu NMR data at δ = 0 and 0 < δ ≤ 0.35 in single crystal samples of YBa2Cu3O7-δ. The lack of δ-dependence in the c component of the magnetic hyperfine shift (MHS) and in the nuclear spin-lattice relaxation rate is associated with the existence of localized Cu (3d) holes. For δ ≠ 0 samples, in addition to the variation of the number of free charge carriers, the system is perturbed by the presence of oxygen vacancies acting as local defects. In the concentration range (0 < δ < 0.1), the 2D character of the oxygen p-holes seems to be reinforced. This may change the coupling between localized Cu (3d) and mobile O (2p) holes, as reflected in the temperature dependence of antiferromagnetic fluctuations of Cu spins. The data on MHS show a strong suppression of its spin component, even for δ = 0.1. © 1990.