Crystal Structure and Magnetic Properties of the Verdazyl Biradical m-Ph-V2 Forming a Ferromagnetic Alternating Double Chain

We have succeeded in synthesizing organic biradical crystals of m-Ph-V-2 [= 1,3-bis-(1,5-diphenylverdazyl-3-yl)benzene]. The intra and intermolecular interactions, which are deduced from the molecular packing in the crystal, are considered to form an alternating double chain. We evaluated the intramolecular ferromagnetic ( FM) interaction from an analysis of the magnetic susceptibility of isolated m-Ph-V-2 molecules. We analyzed the magnetic susceptibility and magnetization curves of the crystals by the quantum Monte Carlo method and successfully explained these properties using an S = 1/2 FM alternating double chain model, which consists of antiferromagnetically coupled FM alternating chains. In addition, the magnetic susceptibility and specific heat showed anomalous behavior at T-N = 1.9 K, which indicates the magnetic phase transition to an antiferromagnetically ordered state.