Single Crystal Growth and Effect of Doping on Structural, Transport and Magnetic Properties of A1−x K x Fe2As2 (A = Ba, Sr)

Abstract

We demonstrate the preparation of large, free standing iron pnictide single crystals with a size up to 20 x 10 x 1 mm 3 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 T s ~138 K in BaFe 2 As 2 single crystals from self-flux shifts to T s ~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 T c~3 8.5 K for the single crystal of Ba 0.68 K 0.32 Fe 2 As 2.A nearly 100% shielding fraction and bulk nature of the superconductivity for the single crystal were confirmed by magnetic susceptibility data. A sharp transition T c~2 5 K occurred for the single crystal of Sr 0.85 K 0.15 Fe 2 As 2 . There is direct evidence for a coexistence of the SDW and superconductivity in the low doping regime of Sr 1-x K x Fe 2 As 2 single crystals. Structural implications of the doping effects as well as the coexistence of the two order parameters are discussed.

Spin-density-wave-induced anomalies in the optical conductivity ofAFe2As2, (Charnukha1, Pröpper2, Larkin3 et al. 2013Phys. Rev. BSelf Cite2717531View full textAdd to dashboardCite

“…1) and SrFe 2 As 2 (Ref. 52), respectively. BaFe 2 As 2 single crystals were grown from Asrich self-flux in a glassy carbon crucible using prereacted FeAs 2 powders mixed with Ba and As.…”

“…52 From dc resistivity and magnetization measurements we obtained the Néel temperatures T N = 150 and 200 K for CaFe 2 As 2 (see Fig. 1) and SrFe 2 As 2 (Ref.…”

Superconductivity in iron compounds

“…At about the same time, the first single crystals ( $ 3 Â 3 Â 0:2 mm 3 ) of the 122 superconducting compound Ba 1Àx K x Fe 2 As 2 were grown using Sn flux (Ni et al, 2008a), with an incorporation of $1% Sn [see Su et al (2009) for a report of up to 5% Sn] into the crystals, not just as inclusions but at least partly into the lattice as an impurity. It was clear in the Ni et al work that Sn from the metal flux had an important influence on the properties of crystals of the parent compound, BaFe 2 As 2 , depressing T S =T SDW from the known polycrystalline value of 140 to 85 K. The Sn incorporated in Ba 1Àx K x Fe 2 As 2 also affects the low-energy spin fluctuations in the NMR measurements (Baek et al, 2008;Sun et al, 2011) and causes a large upturn in the low temperature specific heat divided by temperature C=T . Rb doped BaFe 2 As 2 crystals grown in Sn flux have as much as 9% Sn included .…”

Single crystal growth and physical properties of superconducting ferro-pnictides Ba(Fe, Co)2As2 grown using self-flux and Bridgman techniques

“…Initial attempts to grow single crystals of pristine Ba122 and its superconducting variants were made employing the high temperature solution growth techniques using Tin as a flux agent. It was shown that approximately 1 at% of Sn from the flux is incorporated in the structure leaving detrimental effects on the physical properties of the grown crystals [16,17]. For example, the combined structural/magnetic transition in the Sn-grown Ba122 crystals was found to occur at temperatures close to 80 K, which is very different from a value of T $130 K for a polycrystalline sample [18].…”

“…As a result, at the end of the growth experiment, single crystals should be removed mechanically from a solidified flux-matrix [19]. Since these crystals grow in the form of thin layers; exfoliation or even buckling of single crystalline platelets may occur due to stress used in the mechanical extraction [16,19]. Further, strain induced superconductivity in pristine '122' compounds has also been reported [21].…”