We report the synthesis of RuSr2GdCu2O8-La0.67Sr0.33MnO3 superconducting-magnetic composites with 50 vol.% of both RuSr2GdCu2O8 and La0.67Sr0.33MnO3 compounds. Structural characterization was performed by x-ray diffraction, which permitted to establish the absence of other crystallographic phases and the non reactive character of the compounds into the composite. Scanning electron microscopy showed the sub-micrometric size of grains of the system. Resistivity measurements evidenced the superconducting transition for the RuSr2GdCu2O8 material, which has the value Tsc=39.2 K. Results of magnetization as a function of temperature corroborated the superconducting transition and showed the expected antiferromagnetic character of the RuSr2GdCu2O8 perovskite, with a Néel temperature of TN=132.7 K. Systematic measurements of applied magnetic field at up 5 kOe were performed at temperature regimes below the Curie temperature (TC) of La0.67Sr0.33MnO3 but above the Néel temperature (TN) of RuSr2GdCu2O8; below TN of RuSr2GdCu2O8 but above the superconducting critical temperature (TSC) of RuSr2GdCu2O8; and below TSC of RuSr2GdCu2O8. Our results reveal the ferromagnetic character of the composites at the temperature regime TN < T < TC. Exchange bias effect was observed for weak applied fields (H < 1.5 kOe) at the temperature regime TSC < T < TN. At the superconducting temperature regime (T<TSC) weaker exchange bias is observed for low magnetic fields (H < 0.6 kOe). For strong magnetic fields (H > 2 kOe) the ferromagnetic character of the system is recovered. |
