MAGNETISM AND REENTRANT SUPERCONDUCTIVITY IN K-(BEDT-TTF)2CU[N(CN)I]CL UNDER PRESSURE

Previous resistivity measurements have shown that magnetic fields can enhance or even induce reentrant superconductivity (i.e. existence of SC only in a finite temperature interval between T(c1) and T(c2)) in t he title compound in a rather wide pressure range. By means of d.c. ma gnetization measurements we show that indeed the magnetic field has an effect on the pressure range in which reentrant volume superconductiv ity exists. We also observe that the magnetic/diamagnetic properties o f the samples are influenced by the thermal history. The diamagnetic r eentrance can e.g. be incomplete if the cooling speed is too fast (typ ically faster than 0.1 K min-1). Also, the Meissner signal on warming up from the reentrant state below T(c2) can be about 6 times larger th an the Meissner signal on cooling down from the normal state above T(c 1). These observations together with the previously observed magnetic remanence below T(c2) and the exchange of latent heat at T(c2) lead us to believe that the reentrant transition into a magnetic ground state is of first order and is accompanied by a subtle change in lattice st ructure.