SYNTHESIS, STRUCTURAL CHARACTERIZATION AND MAGNETIC BEHAVIOR OF RuSr_2GdCu_2O_8/La_(0.67)Sr_(0.33)MnO_3 COMPOSITES

摘要

In this work we report the synthesis of RuSr_2GdCu_2O_8/La_(0.67) Sr_(0.33)MnO_3 superconducting-magnetic composites with 50 vol.% of both RuSr_2GdCu_2O_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 ex_periments confirmed chemical stability between RuSr_2GdCu_2O_8 and La_(0.67)Sr_(0.33)MnO_3 compounds in the composites. Resistivity measurements provided evidence of supercon_ducting transition for the RuSr_2GdCu_2O_8 material, with T_(SC)= 39.2 K. Results of magnetization as a function of temperature corroborated the superconducting transi_tion and showed the expected antiferromagnetic character of the Ru perovskite, with a Néel temperature T_N = 132.7 K. Systematic measurements of applied magnetic field up to 5 kOe were performed at these temperature regimes: T_N < T < T_C (with T_C being the Curie temperature of the La_(0.67)Sr_(0.33)MnO_3 compound); T_(SC) < T < T_N; and T < T_(SC). Our results reveal the ferromagnetic character of the composites at the temperature regime T_N < T < T_C. The exchange bias effect was observed for weak applied fields (H < 1.5 kOe) at temperatures between T_SC < T < T_N. At the super_conducting regime (T < T_SC) 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.