/spl mu/SR studies of nitronyl nitroxide organic magnets

Summary form only given. The field of organic magnetism has opened up recently following the discovery of bulk ferromagnet Ism in a nitronyl nitroxide compound at -0.6 K. A whole series of magnetic compounds may be synthesised based on the nitronyl nitroxide radical group with its single unpaired spin, thus allowing a study of the interplay between the molecular and the crystal properties. We have studied three members of this series of compounds using /spl mu/SR and magnetic susceptibility to characterise the spontaneous magnetic-ordering. We report here /spl mu/SR measurements on the following nitronyl nitroxides: /spl beta/ phase p-nitrophenyl (p NPNN), 3-quinolyl (3-QNNN) and p-pyridyl (p-PYNN). The magnetic transition has rather different character in each system. Our data for p-NPNN is consistent with previous reports suggesting a 3D Heisenberg ferromagnet (T/sub c/-670mK). In contrast, p-PYNN shows behaviour indicative of a spin-glass transition around 110mK. In 3-QNNN there is also a strongly defined transition to a state of magnetic order at 210mK, but the complex /spl mu/SR signal indicates that this is not simply ferromagnetic nor spin-glass like and suggests that some form of mixed behaviour occurs in 3-QNNN below 210mK.