Structural and critical current properties in polycrystalline SmO1-xFxFeAs

TL;DR

This study investigates the structural, magnetic, and superconducting properties of polycrystalline SmO1-xFxFeAs with varying fluorine content, revealing how composition influences critical temperature and current densities.

Contribution

It introduces a characterization method for inter-grain current density and analyzes the effects of composition gradients on superconducting properties.

Findings

Critical temperature Tc increases with fluorine content, reaching 53 K at x=0.4.

Critical current density in the pure sample is 1.1x10^4 A/cm^2 at 5 K.

Inter-grain Jc is significantly lower than intra-grain Jc, at 3.6x10^3 A/cm^2 versus 10^6 A/cm^2.

Abstract

A series of polycrystalline SmO1-xFxFeAs bulks (x=0.15, 0.2, 0.3 and 0.4) were prepared by the conventional solid state reaction. Resistivity, susceptibility, magnetic hysteresis, critical current density and microstructure of these samples have been investigated. It is found that critical transition temperature Tc increases steadily with increasing fluorine content, with the highest onset Tc=53 K at x=0.4. On the other hand, the superconductivity seems correlated with lattice constants; that is, Tc rises with the shrinkage of a-axis while resistivity increases with the enlargement of c-axis. A global critical current density of 1.1x10^4 A/cm^2 at 5 K in self field was achieved in the purest sample. A method of characterization of inter-grain current density is proposed. This method gives an inter-grain Jc of 3.6x10^3 A/cm^2 at 5 K in self field, in contrast to the intra-grain Jc of 10^6 A/cm^2. The effect of composition gradients on the inter-grain Jc in SmO1-xFxFeAs is also discussed.