Quasiparticle-injection effects in YBa2Cu3O7-δ/La1/3Ca2/3MnO3/La2/3Ca1/3MnO3 heterostructures

We have grown YBa2Cu3O7-delta (40 nm)/La1/3Ca2/3MnO3 (2 nm)/La2/3Ca1/3MnO3 (30 nm) junctions for quasiparticle-injection measurements. Ferromagnetic (F), antiferromagnetic (AF), and superconducting (S) thin films were sequentially grown "in situ" using a dc-sputtering technique at 850 degreesC in pure oxygen at pressures around 3.5 mbar. The temperature dependence of the resistivity of the junction, without any current injection, presented coexistence between magnetism and superconductivity with a metallic insulating transition at 186 K, and zero resistance at 52 K. When current was injected from the F layer into the S layer, superconductivity suppression was obtained at temperatures below 52 K; furthermore, small values of current injection were necessary to change the electrical behavior up to the critical temperature. A negative current gain (G) has been observed and described by the relation Gproportional toalphatau(eff), where tau(eff) is the relaxation time of the quasiparticle. The use of an AF layer as an insulating barrier is also discussed. (C) 2003 American Institute of Physics.