SUPERCONDUCTING AND MIXED-STATE PROPERTIES OF KAPPA-(ET)(2)X

We present dc-magnetization and ac-susceptibility measurements of the organic superconductors kappa-(ET)(2)X with X = I-3, Cu(NCS)(2), and C u[N(CN)(2)]Br. For all investigated materials the lower critical field perpendicular to the highly conducting planes, B-c1(perpendicular to) , tends to zero already 0.5 K below T-c. This might be an indication f or fluctuation effects of single vortices expected for 2D superconduct ors. Pinning effects lead to an apparent increase of B-cl towards lowe r temperatures and they play an important role for the temperature and frequency dependence of the irreversibility field B-irr determined by ac-susceptibility.