Magnetoresistance of La2CuO4+y single crystals with different oxygen content

Measurements of the magnetoresistance of La2CuO4+y single crystals in magnetic fields up to 35 T are reported. The behaviour of ρ(T, H) remarkably depends on the heat treatment of the crystals in various chemical O2 potentials. The thoroughly oxidized crystal shows a superconducting transition at 38 K, with a small value ΔT = 2 K. The upper critical field Hc2 for HparallelCuO-planes is 35 T (T = 10 K, 0.5ρn value). For the thoroughly reduced La2CuO4 crystal the resistivity increases strongly with decreasing temperature. For magnetic fields applied parallel to the CuO-planes, a magnetic transition is observed between 5 T and 6 T for La2CuO4+y crystals with different oxygen content. The temperature dependence of the spin-flop transition is observed in insulating La2CuO4+y. (orig.)