A lot of theoretical and experimental results are examined to obtain a unified picture of magnetism and superconductivity in strongly correlated electron systems. First principle computational results reported recently have been used to elucidate electronic structures of strongly correlated electron systems. In this series of articles theoretical efforts for the systems such as transition metal oxides have been extended to search high-Tc superconductors (HTSC) other than cuprates in relation to possible mechanism(s) of high-Tc superconductivity. Very recently, Kamihara et al. have found that quaternary oxypictides LaOMPn (M = V, Cr, Mn, Fe, Co, Ni, and Pn = P, As) are a new family of high-Tc superconductors, exhibiting high-transition temperature Tc = 26 K for the case of M = Fe and Pn = As. Since iron has been believed to be magnetic in many systems, their finding raises extremely interesting question concerning with relationships between magnetism and superconductivity. Moreover, coexistence of antiferromagnetism (AF) and superconductivity (SC) is also discovered in the recently synthesized cuprates with five CuO2 planes. This may indicate the uniformly mixed phase of AF and SC in cuprates without disorder corresponds to spin glass, instead of other complex phases resulting from random potentials in disordered cuprates. Coexistence of AF and SC phases and multiband effects are also suggested for quaternary oxypictides LaOMPn. Here, comparison between quaternary oxypictides LaOMPn and cuprates is carried out from both theoretical and experimental grounds, leading to an extension of our magnetic (J) model for LaOMPn. Implications of these analyses are discussed in relation to possible candidates of HTSC with multi (N)-layers consisted of iso-electronic π-d, π-R, and σ-R systems, for which similar electronic phases are expected from the theoretical grounds. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008
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