SYNTHESIS, STRUCTURAL CHARACTERIZATION AND MAGNETIC BEHAVIOR OF RuSr₂GdCu₂O₈/La_0.67Sr_0.33MnO₃ COMPOSITES

Abstract

In this work we report the synthesis of RuSr 2 GdCu 2 O 8/ La 0.67 Sr 0.33 MnO 3 superconducting-magnetic composites with 50 vol.% of both RuSr 2 GdCu 2 O 8 and La 0.67 Sr 0.33 MnO 3 compounds. Structural characterization was performed by X-ray diffraction, which permitted us 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 the grains. Energy dispersive X-ray experiments confirmed chemical stability between RuSr 2 GdCu 2 O 8 and La 0.67 Sr 0.33 MnO 3 compounds in the composites. Resistivity measurements provided evidence of superconducting transition for the RuSr 2 GdCu 2 O 8 material, with TSC=39.2 K. Results of magnetization as a function of temperature corroborated the superconducting transition and showed the expected antiferromagnetic character of the Ru perovskite, with a Néel temperature TN=132.7 K. Systematic measurements of applied magnetic field up to 5 kOe were performed at these temperature regimes: TN < T < TC (with TC being the Curie temperature of the La 0.67 Sr 0.33 MnO 3 compound); TSC < T < TN; and T < TSC. Our results reveal the ferromagnetic character of the composites at the temperature regime TN < T < TC. The exchange bias effect was observed for weak applied fields (H < 1.5 kOe) at temperatures between TSC < T < TN. At the superconducting regime (T < TSC) weaker exchange bias is observed for low magnetic fields (H < 1 kOe). For strong magnetic fields (H > 2 kOe) the ferromagnetic character of the system is recovered.

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