Irreversibility line and critical current studies in κ-(BEDT-TTF)2Cu[N(CN)2]Br organic superconductor: effect of the structural transformation near 80 K

We report systematic magnetic measurements on organic superconductor κ-(BEDT-TTF)2Cu[N(CN)2]-Br. The irreversibility line Hirr(T) and the critical current density Jc were studied. Our results show the strong dependence of Hirr(T) and Jc on the cooling rate. The Hirr(T) data follow power dependence H∝(1-T/Tc)m where m depends on the sample cooling. The structural transformation which occurs at the vicinity of 80 K influences very strongly the physics of vortex lattice and the associated magnetic behavior. This has a pronounced effect on the critical current density and the superconducting transition temperature Tc. Rapid cooling through 80 K will freeze the high temperature magnetic phase to low temperatures and the presence of local magnetic moments suppresses the superconducting Tc. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)