Weak ferromagnetism and antiferromagnetic ordering of 2pelectrons in the organic radical compound 2,4,6-triphenylverdazyl

High-quality sizable single crystals of the radical compound 2,4,6-triphenylverdazyl (TPV) have been prepared and their magnetic properties investigated by neutron-diffraction and magnetization measurements. Neutron-diffraction peaks corresponding to long-range antiferromagnetic ordering have been observed below the Néel temperature of 1.78 K. The determined spin structure has intrachain antiferromagnetic coupling extending toward the c axis with the spins aligned to the b axis. Magnetization measurements also reveal that weak ferromagnetism appears below ${\mathit{T}}_{\mathit{N}}$ with the ferromagnetic components in directions parallel and perpendicular to the spin direction. The magnetization curve shows no hysteresis, which is consistent with small anisotropy of 2p electrons in organic magnets.