CU-63 AND Y-89 NMR AND SPIN SUSCEPTIBILITY OF YBA2CU3O6.9 DISORDERED BY NEUTRON-IRRADIATION

The (CU)-C-63 and Y-89 Knight shift (63(89))K, spin-lattice (63(89))T- 1(-1) and spin-spin T-63(2)-1 relaxation rates were measured in YBa2Cu 3O6.9 (T-c,T-ons=68K;<4K), which in structural disorder induced by the neutron irradiation leads to decrease of T-c. A sharp decrease of K b eing proportional to the uniform part of spin susceptibility chi(s)(q= 0) is found with increase of disorder. According to the relaxation dat a of copper a short wave contribution to chi(s)(q) around q(AF)={pi,pi }/a is found to be nearly independent of temperature above T-c up to t he room temperature in irradiated material. This evidences that magnet ic correlation length xi of the AF spin fluctuations ceases its change with temperature in disordered YBaCuO. The contribution of indirect s pin-spin coupling of Cu in CuO2 layer T-63(2g)-1 proportional to chi(s )(q(AF))/xi holds its magnitude in going through T-c both for the unir radiated (T-c,T-ons=94K) and irradiated (T-c,T-ons=68K) cuprates. The behavior of chi(s)(g(AF)) below T-c is considered as evidence of stabl e x(2)-y(2) symmetry of the superconducting energy gap in respect to a dditionally induced structural disorder.