NMR Studies of17O in the Normal State of YBa2Cu3O6+x

The temperature dependence of both the Knight shift ( K ) tensor and the nuclear spin-lattice relaxation rate (1/ T 1 ) in the normal state have been studied, by using the magnetically oriented powered samples of YBa 2 Cu 3 O 6+ x with x =0.96, 0.8 and 0.6. From the K -χ plot for the planer oxygen sites (O(2, 3)), we have determined the principal values of the hyperfine field tensor and found that those hardly depend on the hole concentration. The remarkable feature has emerged from the T -dependence of the 1/( T 1 T ) at the O(2, 3) sites; i.e. it reveals almost the same T -dependence of the spin parts of the Knight shift. This observation suggests that the energy width of the spin excitations around q ∼0 is T -independent in the normal state. The Knight shift tensor at the apical oxygen sites has also been measured and is discussed.