Magnetoresistance at high magnetic fields in superconducting granular Sm1.83Ce0.17CuO4-y compounds

We have performed measurements of electrical resistance, R(T), and magnetor esistance, R(T, H), in applied magnetic fields H up to 18 T in granular sam ples of the electron-doped superconductor Sm1.83Ce0.17CuO4-y. These samples have a small superconducting volume fraction, bellow the percolation thres hold, and can be described by a collection of superconducting islands embed ded in a non-superconducting host. All the investigated samples revealed di amagnetic signal below T-ci similar to 17.5 K. Nevertheless, electrical res istance measurements showed an abrupt increase in the magnitude of R(T) bel ow T-ci. The electrical resistance DeltaR(T, H) exceeding the normal state resistance value extrapolated to low temperatures was found to decrease wit h increasing H. We have also found that DeltaR(T, H) proportional to (T/T-c i)(-4) in the temperature range 0.6 < (T/T-ci) < 1, in agreement with the t wo-fluid theory of superconductivity. However, DeltaR(T,H) shows a crossove r to a (T/T-ci)(-1/4) dependence at lower temperatures (T/T-ci) < 0.6. Such a crossover is discussed within the scenario of high anisotropic layered s uperconductors. (C) 2001 Elsevier Science B.V. All rights reserved.