PHASE-DIAGRAM FOR THE SPIN PSEUDOGAP IN LABA2CU3OY STUDIED BY NMR

The carrier concentration dependence of the spin pseudogap phenomenon in LaBa2Cu3Oy has been studied by means of the NMR/NQR method. From th e T dependence of 1/T1T of the planar Cu site; it has turned out that the characteristic temperature for the spin pseudogap at the staggered mode is a monotonic function of hole concentration in the lightly dop ed region. However, a spin-gap-like behavior was observed even in the optimally doped sample (y = 6.96), where the maximal superconducting t ransition temperature (T-c) is realized as a function of hole doping. This feature is quite different from that in YBa2Cu3Oy, where the spin pseudogap is restricted to the lightly doped region and is not observ ed in the optimally doped sample (y = 6.98). Together with 1/T-2G and Knight shift data, the nature of the gap is discussed.