Magnetic Properties and Structures of the α- and δ-Phases of ρ-NPNN (Condensed Matter: Electronic Structure, Electrical, Magnetic and Optical Properties)

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We have investigated the crystal structures and magnetic properties of the α- and δ-phases of an organic radical ρ-NPNN (ρ-nitrophenyl α-nitronyl nitroxide), which yielded the first organic bulk ferromagnet, β-ρ-NPNN (the β-phase). The results are compared with those of the β- and γ-phases, which show distinct magnetic ordering due to intermolecular ferromagnetic couplings. Common structural features are found in the four phases. Unlike the other phases, the a-phase exhibits a weak antiferromagnetic interaction. This is attributable to phenyl-phenyl overlapping found only in the α-phase. The crystal structure of δ-ρ-NPNN contains a packing motif similar to that of the γ-phase. Though the δ-phase exhibits ferromagnetic interactions, it shows no magnetic ordering down to 0.46 K. It is suggested that ferromagnetic two-leg spin ladders are formed in the δ-phase, instead of a two-dimensional network as in γ-ρ-NPNN. This low dimensionality explains the absence of a magnetic transition.
社団法人日本物理学会の論文
2003-07-15