Magnetic properties of 1,5-dimethyl-6-oxoverdazyl radical crystals observation of a spin-peierls transition in 3-(4- cyanophenyl)-1,5-dimethyl-6-oxoverdazyl radical, p-CyDOV

Magnetic susceptibilities of 5 kinds of 3-(4-R-phenyl)-1,5-dimethyl-6-oxoverdazyl radicals (PDOV (R=H), p-MDOV (R=CH₃O), p-MeDOV (R=CH₃), p-CyDOV (R=CN), and p-NDOV (R=NO₂)) have been measured in the temperature range of 4.2-300 K. The susceptibilities of PDOV, p-MDOV, and p-MeDOV can be explained by an antiferromagnetic Heisenberg alternating chain model. The susceptibility of p-CyDOV shows a broad maximum at 54 K, and decreases abruptly at 15 K, suggesting a spin-Peierls transition. High-field magnetization data (H = 0 to 35 T) which provide a clear evidence for a spin-Peierls transition were reported The magnetic susceptibilities of diluted crystal, (p-CyDOV)_1-x(p-CyDOV- H)_x (x = 0 - 0.10), were measured to study the effects of nonmagnetic impurities, p-CyDOV-H (amine precursor of p-CyDOV), on the spin-Peierls transition. The transition temperature reduced rapidly upon p-CyDOV-H substitution and the spin-Peierls state disappeared around x = 0.07.