VORTEX PINNING IN LAYERED ORGANIC SUPERCONDUCTORS - KAPPA-(BEDT-TTF)(2)CU[N(CN)(2)]BR

Magnetization studies on organic single-crystal superconductors of k-( BEDT-TTF)(2)Cu[N(CN)(2)]Br with the field H parallel to the b axis (pe rpendicular to the conducting plane) show anomalous field and temperat ure dependence of vortex pinning in the mixed state. At high temperatu res, the magnetization M decays with increasing field with a power-law dependence. The normalized relaxation rate S=d(ln M)/d(ln t) decrease s monotonically with H. At low temperatures (T<7 K), a change of sign in the curvature of M(H) is observed, accompanied by a corresponding c hange in S as a function of H. Measurement of the irreversibility fiel d H-rev shows a universal power-law dependence of H-rev on (1 - T/T-c) in the temperature range investigated. We suggest that the magnetic a nomaly observed is due to a dimensional crossover in the nature of vor tex pinning. (C) 1996 American Institute of Physics.