ANOMALOUS MAGNETIC-PROPERTIES IN THE SINGLE-CRYSTAL KAPPA-(BEDT-TTF)(2)CU(NCS)(2) SUPERCONDUCTOR

Magnetization measurements have been performed on single crystals of t he organic superconductor kappa-(BEDT-TTF)(2)Cu(SCN)(2) with the held parallel to the a axis (perpendicular to the conducting plane). At hig h temperatures, the magnetization M displays a power-law dependence on H with M proportional to H-alpha and alpha=-0.45+/-0.05. At low tempe ratures (T less than or equal to 7.5 K), an anomalous field dependence in M(H) is observed. The irreversibility field determined from magnet ic hysteresis loops displays a universal temperature dependence, i.e., from a high-temperature power-law dependence to a low-temperature exp onential dependence. The results are qualitatively similar to the fish tail magnetization reported for the highly anisotropic oxide supercond uctors.