H-1-NMR RELAXATION ANOMALY AT THE METAL-METAL TRANSITION IN THE SLOWLY-COOLED (BEDT-TTF)2CLO4(C2H3CL3)0.5

H-1-NMR relaxation Tate, T1(-1), was measured in a two-dimensional org anic conductor, (BEDT-TTF)2ClO4(C2H3Cl3)0.5, in order to investigate t he nature of unusual transition dependent on the cooling rate of the s ample. When the sample is cooled rapidly, H-1-T1(-1) follows a Korring a-like behavior down to 1.4K, in agreement with the metallic behavior of resistivity. On the other hand, in a slow cooling condition, a larg e enhancement of H-1-T1(-1) is observed below 50 K. A maximum of T1(-1 ) appearing around 10K is two orders of magnitude larger than the valu e in a rapid cooling condition. This seems to suggest a magnetic natur e of the transition in the slowly-cooled sample, but an excess line br oadening, expected in the standard magnetic transition, is not observe d as far as the FID signal is concerned.