Pressure effects on intermolecular interactions in genuine organic radical crystals

Pressure induced enhancement of magnetic ordering temperature has been found in a quasi-one-dimensional ferromagnetic organic radical crystal, 3-(4-chlorophenyl)-1,5-dimethyl-6-thioxoverdazyl by the measurements of magnetic susceptibility and heat capacity under hydrostatic presures up to 13 kbar (1.3 GPa). This pressure dependence is the opposite direction to the results in the ferromagnetic Beta-phase p-NPNN observed recently, and in the same way as in ordinary antiferromagnets. The effects of pressurization suggest to bring about frustration in kinetic exchange interactions via various charge transfer paths between molecular orbitals.