KxFe2-ySe2 single crystals: Floating-zone growth, Transport and Structural properties

TL;DR

This study reports the successful growth of high-quality KxFe2-ySe2 single crystals using the floating-zone method, analyzing their structural, magnetic, and superconducting properties, and revealing coexistence of superconductivity with magnetic order.

Contribution

It introduces a novel floating-zone growth process for KxFe2-ySe2 crystals and characterizes their superconducting and magnetic properties in detail.

Findings

High-quality crystals (~6 mm diameter) were grown successfully.

Superconducting transition at Tc = 31.6 K with full magnetic expulsion.

Superconductivity coexists with iron-vacancy order and antiferromagnetic order.

Abstract

Single crystals of superconducting KxFe2-ySe2 have been grown with the optical floating-zone technique under application of 8 bar of argon pressure. We found that large and high quality single crystals with dimensions of ~\varnothing6 \times 10 mm could be obtained at the termination of the grown ingot through quenching, while the remaining part of the ingot decomposed. As-grown single crystals commonly represent an intergrowth of two sets of the c-axis characterized by slightly different lattice constants. Single crystal of K0.80Fe1.81Se2 shows a superconducting transition at Tc = 31.6 K, leading to a near 100% expulsion of the external magnetic field in magnetization measurements. On the other hand, neutron-diffraction data indicate that superconductivity in the sample coexists with a iron-vacancy superstructure and static antiferromagnetic order. The anisotropic ratio of the upper critical field Hc2 for both H//c and H//ab configurations is \sim3.46.