LOCAL MAGNETIC-PROPERTIES OF PRBA2CU3O6- NMR AND NQR IN CRYSTALS(X )

NQR spectra of Cu-chain sites in PrBa2Cu3O6 crystals show below the Ne el temperature of Pr the presence of a transferred hyperfine field of approximate to 0.12 T from the Pr sublattice. The fields at the Cu-pla ne sites observed below 4.2 K are an order of magnitude larger. In con trast no field could be detected at the Cu chains in PrBazCu(3)O(7). T he spectrum at the Cu-plane sites for high oxygen concentration indica tes the existence of a transferred field similar to the one in the red uced sample. The large transferred fields are in direct contradiction to the antiferromagnetic structure generally assumed for the Pr moment s. They strongly support the model of a broken Pr point symmetry at le ast in PrBa2Cu3O6 The most simple distortion of the tetragonal PrO8 co mplex (D-4h), which may give rise to the fields, is not to orthorhombi c (D-2h) as is usually assumed, but to C-4v. The results indicate that the Pr moments are perpendicular to the c axis and that the antiferro magnetic coupling along the c axis is distorted for the reduced sample .