Iron pnictides: Single crystal growth and effect of doping on structural, transport and magnetic properties

TL;DR

This study reports the growth of large iron pnictide single crystals and examines how potassium doping influences their structural, magnetic, and superconducting properties, revealing coexistence of SDW and superconductivity.

Contribution

It presents a method for growing large single crystals and provides new insights into doping effects and coexistence of magnetic and superconducting phases.

Findings

Large single crystals up to 20 x 10 x 1 mm3 were successfully grown.

Potassium doping shifts SDW transition temperature and induces superconductivity.

Evidence of coexistence of SDW and superconductivity in low doping regimes.

Abstract

We demonstrate the preparation of large, free standing iron pnictide single crystals with a size up to 20 x 10 x 1 mm3 using solvents in zirconia crucibles under argon atmosphere. Transport and magnetic properties are investigated to study the effect of potassium doping on the structural and superconducting property of the compounds. The spin density wave (SDW) anomaly at Ts ~138 K in BaFe2As2 single crystals from self-flux shifts to Ts ~85 K due to Sn solvent growth. We show direct evidence for an incorporation of Sn on the Fe site. The electrical resistivity data show a sharp superconducting transition temperature Tc~38.5 K for the single crystal of Ba0.68K0.32Fe2As2. A nearly 100% shielding fraction and bulk nature of the superconductivity for the single crystal were confirmed by magnetic susceptibility data. A sharp transition Tc~25 K occurred for the single crystal of Sr0.85K0.15Fe2As2. There is direct evidence for a coexistence of the SDW and superconductivity in the low doping regime of Sr1-xKxFe2As2 single crystals. Structural implications of the doping effects as well as the coexistence of the two order parameters are discussed.