Superexchange interaction and magnetic moment in antiferromagnetic high-Tc cuprate superconductors

We report a Cu-63-NMR study on underdoped Hg-based five-layered (n = 5) compounds HgBa2Ca4Cu5-O12+y (Hg-1245) with T-c = 82 K and 92 K. and review the previous Cu-NMR results on the various multilayered cuprates. On the basis of extensive experiments on n = 5 compounds, we have unraveled that (1) the antiferromagnetic metallic (AFMM) phase is robust up to the carrier-density N-h similar to 0.17, (2) the uniformly mixed state of superconductivity (SC) and AFMM is realized at least in 0.14 < N-h <= 0.17, (3) T-c has a peak close to the quantum critical point (QCP) at which the AFM order collapses, indicating the strong relationship between the high-T-c SC and AFM order. In the four-layered (n = 4) compounds, the QCP of AFM order was at N-h similar to 0.15, which is lower than the case for n = 5 compounds, suggesting that the weaker AFM interlayer coupling makes the carrier-density at QCP decrease. In the light of recent progress in experiments that have unraveled intrinsic phase diagrams in the underdoped regime, we deal with the N5 dependence of the AFM moment and an in-plane superexchange J(in) in order to gain insight into the magnetic characteristics in antiferromagnetic high-T-c superconductors. (C) 2009 Elsevier B.V. All rights reserved.