Pressure induced enhancement of ordering temperature of a ferromagnetic organic radical crystal: P-CDTV

The magnetic susceptibility of 3-(4-chlorophenyl)-1,5-dimethyl-6-thioxoverdazyl (p-CDTV) has been measured down to 0.2 K under hydrostatic pressures. The ordering temperature of T_c = 0.65K at the ambient pressure is found to increase under pressure up to T_c = 0.80 K at 6.0 kbar, giving the demonstrative temperature independent susceptibility of a ferromagnetic state at low temperatures. This pressure dependence is the opposite direction to that observered in the other organic ferromagnet β-phase p-NPNN, and is interpreted in terms of the virtual charge transfer mechanism rather than pressure effects on the dipolar interactions.