Pressure effects on an organic radical ferromagnet: 2,5-difluorophenyl-a-nitronyl nitroxide
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Raising a transition temperature (Tc) in organic radical ferromagnets is a desire for material scientists. We investigated the pressure effects on an organic radical ferromagnet 2,5-difluorophenyl-ﾎｱ-nitronyl nitroxide (2,5-DFPNN), which has a ferromagnetic transition at 0.45 K. The hydrostatic pressure effects were investigated through measurements of ac magnetic susceptibility (ﾏ・ up to P=1.7 GPa, heat capacity (Cp) up to P=1.5 GPa, and powder x-ray diffraction up to P=4.7 GPa. Furthermore, ac magnetic susceptibility under nonhydrostatic pressure was also measured in the pressure region up to 10.0 GPa. As for 2,5-DFPNN, we observed the pressure-induced enhancement of Tc as dTc/dP=7.9ﾃ・0-2 K/GPa [Tc(P=1.5 GPa)=0.57 K], while other prototypes, the ﾎｲ phase of p-NPNN and p-Cl-C6H4-CH=N-TEMPO show the negative pressure effects. The results for the Cp and the crystal structural analysis suggest that the magnetic dimension of the short-range order developing above Tc transforms from one dimension (a axis) to two dimensions (ac plane) under high pressure. This increase of the magnetic dimension probably promotes to increase Tc. The ferromagnetic signal of ﾏ・ however, decreases with increasing pressure, and finally disappears for P>~5.0 GPa. The decrease seems to originate from the decrease of the ferromagnetic interaction along the b axis. Similar instability of organic ferromagnetic long range order against pressure has been observed for the ﾎｲ phase of p-NPNN and p-Cl-C6H4-CH=N-TEMPO.
論文 | ランダム
- 都市経済と都市圏 (フォーラム論文 特集 都市経済の視角)
- 業務資料 「軌道を構成する材料と構造」まくらぎ(その3)
- 地方都市に建つ「レストラン付中規模事務所」--昭和54年度・一級建築士/設計製図課題の検討(特集)
- 白のコスチュ-ム (幻の設計プラン)
- 増田歯科医院--東京都・目黒区〔設計・平山建築設計事務所〕