63Cu and 89Y NMR and spin susceptibility of YBa2Cu3O6.9 disordered by neutron irradiation

Abstract The 63 Cu and 89 Y Knight shift 63(89) K, spin-lattice 63(89) T 1 −1 and spin-spin 63 T 2 −1 relaxation rates were measured in YBa 2 Cu 3 O 6.9 ( T c,ons = 68 K ; T c . A sharp decrease of K being proportional to the uniform part of spin susceptibility χ s (q=0) is found with increase of disorder. According to the relaxation data of copper a short wave contribution. to χ s (q) around q AF = { π , π }/a if found to be nearly independent of temperature above T c up the room temperature in irradiated material. This evidences that magnetic correlation length ζ of the AF spin fluctuations ceases its change with temperature in disordered YBaCuO. The contribution of indirect spin-spin coupling of Cu in CuO 2 layer 63 T 2g −1 ∝ χ s (q AF )/ ζ holds its magnitude in going through T c both for the unirradiated ( T c,ons =94 K ) and irradiated ( T c,ons =94K cuprates. The behavior of ζ s (q RMAF ) below T c is considered as evidence of stable x 2 -y 2 symmetry of the superconducting energy gap in respect to additionally induced structural disorder.