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

Abstract We report a 63 Cu-NMR study on underdoped Hg-based five-layered ( n  = 5) compounds HgBa 2 Ca 4 Cu 5 O 12+ 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 ∼ 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 ∼ 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 N h 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.