Superconductivity, magnetism and crystal chemistry of Ba1-xKxFe2As2

TL;DR

This paper investigates the relationship between superconductivity, magnetism, and crystal structure in Ba1-xKxFe2As2, revealing how doping influences phase transitions, magnetic ordering, and superconducting properties.

Contribution

It provides detailed insights into how potassium doping affects structural, magnetic, and superconducting phases in BaFe2As2, including the suppression of magnetic order and maximization of Tc.

Findings

Superconductivity appears at x >= 0.3 with Tc up to 38 K.

Magnetic order coexists with superconductivity at low doping levels.

Structural distortion and magnetic order are suppressed at optimal doping.

Abstract

BaFe2As2 is the parent compound of the '122' iron arsenide superconductors and crystallizes with the tetragonal ThCr2Si2 type structure, space group I4/mmm. A spin density wave transition at 140 K is accompanied by a symmetry reduction to space group Fmmm and simultaneously by antiferromagnetic ordering. Hole-doping induces superconductivity in Ba1-xKxFe2As2 with a maximum Tc of 38 K at x = 0.4. The upper critical fields approach 75 T with rather small anisotropy of Hc2. At low potassium concentrations (x <= 0.2), superconductivity apparently co-exists with the orthorhombic distorted and magnetically ordered phase. At doping levels x >= 0.3, the structural distortion and antiferromagnetic ordering is completely suppressed and the Tc is maximized. No magnetically ordered domains could be detected in optimally doped Ba1-xKxFe2As2 (x >= 0.3) by 57Fe-Moessbauer spectroscopy in contrast muSR results obtained with single crystals. The magnetic hyperfine interactions investigated by 57Fe Moessbauer spectroscopy are discussed and compared to the ZrCuSiAs-type materials.