Pressure induced enhancement of Tc in weak-ferromagnetic radical crystal 1,3,5-triphenyl-6-oxoverdazyl

Study of pressure effect of organic weak-ferromagnet 1,3,5-triphenyl-6-oxov erdazyl (TOV) with the transition temperature T-c(P-0) = 5.0 K (P-0; ambien t pressure) has been motivated by the experimental finding that slight dilu tion of TOV with the non-magnetic derivative changed the Weiss temperature (Theta) from negative to positive, i.e, from antiferromagnetic (AF) to ferr omagnetic (F). We understood that above change of Theta would originate fro m the slight change of the crystal structure by an internal stress. Expecti ng the pressurization would bring about the same result as the dilution eff ect, we measured the ac magnetic susceptibility of pure TOV under the press ure up to P = 10.9 kbar. The pressure effect of pure TOV, however, revealed no transition from AF to F, but did the enhancement of T-c(P). The pressur e dependence of T-c(P) is characterized with T-c(P) = T-c(P-0) (1 + 0.086 P ), and T-c(P) exceeds 10.0 K at P = 10.9 kbar.