HYPERFINE FIELD AND ELECTRIC-FIELD GRADIENT AT VARIOUS CATION SITES IN RBA(2)CU(2)NBO(8) AND RSR(2)CU(2)GAO(7)

We have investigated antiferromagnetic nuclear resonance (AFNMR) for C u-site as well as nuclear magnetic (NMR) and quadrupolar (NQR) resonan ces for La, Nh, Ga-sites in antiferromagnetic insulators RBa(2)Cu(2)Nb O(8) (R=La, Pr, Nd) and RSr(2)Cu(2)GaO(7) (R=La, Pr, Nd, Y). Hyperfine magnetic fields at the Cu-site are very close to values published for RBa(2)Cu(3)O(6) analogs. Quadrupolar frequencies for Cu in RSr(2)Cu(2 )GaO(7) are also close to those for RBa(2)Cu(3)O(6) but in RBa(2)Cu(2) NbO(8) these values are about 50% higher. Axially symmetric electric f ield gradient at the La and the Nb-sites in RBa(2)Cu(2)NbO(8) and asym metric one at the La and Ga-sites in RSr(2)Cu(2)GaO(7) are in accord w ith their structures. Split NQR spectrum for Ga in NdSr2Cu2GaO7 eviden ces the different Cu-AF spin stacking sequence in this material. Possi ble cation disorder in RSr(2)Cu(2)GaO(7) is discussed.