We have grown YBa2Cu3O7-δ (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 °C 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 G∝ατeff, where τeff is the relaxation time of the quasiparticle. The use of an AF layer as an insulating barrier is also discussed.