Fl. Pratt et al., ORGANIC FERROMAGNETISM IN THE NITRONYL NITROXIDES P-NPNN AND 3-QNNN -MUSR, EPR AND AC SUSCEPTIBILITY STUDIES, Synthetic metals, 61(1-2), 1993, pp. 171-175
Following the discovery of organic ferromagnetism in p-NPNN, we report
the observation of ferromagnetic ordering in a second nitronyl nitrox
ide radical system, 3-quinolyl nitronyl nitroxide (3-QNNN), using the
muon spin rotation (MUSR) technique. The onset of ferromagnetic order
is indicated in the MUSR experiment by the appearance of a rotation si
gnal in zero applied field for temperatures below approximately 0.2 K.
This signal corresponds to the precession of the muon spin in the int
ernal field of the ferromagnetic state. We have measured the muon spin
rotation and relaxation signals as a function of temperature, giving
a measure of the magnetization and spin dynamical properties. The temp
erature dependence of the internal field is consistent with the S = 1/
2 Weiss molecular field model with a Curie temperature of 0.21 K and a
saturation internal field of 60 G. We also report additional studies
of the magnetic properties of 3-QNNN and p-NPNN using EPR and a.c. sus
ceptibility techniques. We find evidence for a canted ferromagnetic sp
in structure in 3-QNNN and a simpler uniform magnetic lattice in p-NPN
N.