Development of Room-Temperature Molecular/Organic Ferromagnets and Estimation of Their Low-Frequency Shielding Materials

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Three years ago we found out room-temperature ferromagnetic behavior in 1 : 2 mixed salts of TCNQ or TCNQF_4 with TCNQF_4 radical anion. The similar behavior was also recognized in 1 : 2 mixed salts of diethyl-substituted TCNQ or tetracyanonaphthoquinodimethane with their radical anions. This observation is quite remarkable, since the highest temperature of spin ordering is 36 K for purely organic ferromagnets and weak ferromagnets obtained so far. However, the saturation magnetization observed in these 1 : 2 mized salts is only 0.1% of the value (5,580 emu.mol^<-1>) obtained by one S=1/2 spin per formula unit.For the 1 : 2 mixed salt of dimethyl-substituted TCNQ with its radical anion, metal-like high electrical conductivity was observed together with room-temperature ferromagnetic behavior. Accordingly, this mixed salt can be regarded as an analogue to a ferromagnetic metal such as iron, cobalt and nickel. Much interest is directed toward the interaction between the interaction between conducting pi electron and localized d spin, while this mixed salt should be noted as a new molecular system involving both conducting pi electron and localized pi spin.In summary, room-temperature ferromagnetic behavior can be in common observed in 1 : 2 mixed salts of TCNQ, substituted TCNQ's and TCNQ analogue, but the mechanism of spin ordering remains to be still not elucidated. Further study is necessary in order to elucidate the mechanism of spin ordering and to search a room-temperature (ferro)magnet with larger saturation magnetization.