63Cu and 89Y NMR and spin susceptibility of YBa 2Cu 3O 6.9 disordered by neutron irradiation

Abstract

The 63Cu and 89Y Knight shift 63(89)K, spin-lattice 63(89)T 1 −1 and spin-spin 63T 2 −1 relaxation rates were measured in YBa 2Cu 3O 6.9 ( T c,ons = 68 K; <4K), which in structural disorder induced by the neutron irradiation leads to decrease of 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 63T 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.