Irreversibility line and critical current studies in κ-(BEDT-TTF)_2CuN(CN)_2Br organic superconductor: effect of the structural transformation near 80 K

摘要

We report systematic magnetic measurements on organic superconductor k-(BEDT-TTF)_2Cu[N(CN)_2]-Br. The irreversibility line H_(irr)(T) and the critical current density J_c were studied. Our results show the strong dependence of H_(irr)(T) and J_c on the cooling rate. The H_(irr)(T) data follow power dependence H ∝ (1 -^sT/T_C)~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 T_c. 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 T_c.