High-quality sizable single crystals of the radical compound 2,4,6-tri
phenylverdazyl (TPV) have been prepared and their magnetic properties
investigated by neutron-diffraction and magnetization measurements. Ne
utron-diffraction peaks corresponding to long-range antiferromagnetic
ordering have been observed below the Neel temperature of 1.78 K. The
determined spin structure has intrachain antiferromagnetic coupling ex
tending toward the c axis with the spins aligned to the b axis. Magnet
ization measurements also reveal that weak ferromagnetism appears belo
w T(N) with the ferromagnetic components in directions parallel and pe
rpendicular to the spin direction. The magnetization curve shows no hy
steresis, which is consistent with small anisotropy of 2p electrons in
organic magnets.