Magneto-transport and magnetic susceptibility of SmFeAsO1-xFx (x = 0.0 and 0.20)

Bulk polycrystalline samples, SmFeAsO and the iso-structural superconducting SmFeAsO0.80F0.20 are explored through resistivity with temperature under magnetic field {\rho}(T, H), AC and DC magnetization (M-T), and Specific heat (Cp) measurements. The Resistivity measurement shows superconductivity for x = 0.20 sample with Tc(onset) ~ 51.7K. The upper critical field, [Hc2(0)] is estimated ~3770kOe by Ginzburg-Landau (GL) theory. Broadening of superconducting transition in magneto transport is studied through thermally activated flux flow in applied field up to 130 kOe. The flux flow activation energy (U/kB) is estimated ~1215K for 1kOe field. Magnetic measurements exhibited bulk superconductivity with lower critical field (Hc1) of ~1.2kOe at 2K. In normal state, the paramagnetic nature of compound confirms no trace of magnetic impurity which orders ferromagnetically. AC susceptibility measurements have been carried out for SmFeAsO0.80F0.20 sample at various amplitude and frequencies of applied AC drive field. The inter-granular critical current density (Jc) is estimated. Specific heat [Cp(T)] measurement showed an anomaly at around 140K due to the SDW ordering of Fe, followed by another peak at 5K corresponding to the antiferromagnetic (AFM) ordering of Sm+3 ions in SmFeAsO compound. Interestingly the change in entropy (marked by the Cp transition height) at 5K for Sm+3 AFM ordering is heavily reduced in case of superconducting SmFeAsO0.80F0.20 sample.Comment: 18 pages text + Figs: comments/suggestions welcome ([email protected]

Exchange bias effect in RuSr2GdCu2O8/La0.7Sr0.3MnO3 composites

Reportamos la síntesis y caracterización del compósito magnético superconductor RuSr2GdCu2O8-La0.67Sr0.33MnO3 con 0% to 50% de La0.67Sr0.33MnO3 en el compósito. Se realizaron mediciones sistemáticas de magnetización en función del campo magnético aplicado hasta 5 kOe en los regímenes de temperatura por debajo de la temperatura de Curie (TC) del La0.67Sr0.33MnO3 pero arriba de de la temperatura de Néel (TN) del RuSr2GdCu2O8; abajo de TN del RuSr2GdCu2O8 pero arriba de la temperatura crítica superconductora (TSC) del RuSr2GdCu2O8; y abajo de TSC del RuSr2GdCu2O8. Nuestros resultados muestran la característica ferromagnética de los compósitos en el régimen de temperatura TN 2 kOe) se recuperó el carácter ferromagnético del sistema.We report the synthesis and characterization of RuSr2GdCu2O8-La0.67Sr0.33MnO3 superconductingmagnetic composites with 0 to 50 wt% of La0.67Sr0.33MnO3 in the composites. Systematic measurements of magnetization as a function 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 2 kOe) the ferromagnetic character of the system is recovered