Discovery of a novel 112-type iron-pnictide and La-doping induced superconductivity in Eu 1− x La x FeAs 2 ( x = 0–0.15)

Abstract

Abstract:We report the discovery and characterization of a novel 112-type iron pnictide

Magnetic and superconducting phase diagram of Eu(Fe$_{1-x}$Ni$_{x}$)As$_{2}$

“…Similar phenomena were observed in other groups [21] or in other 112 materials [23,24,35], reflecting the inherent instability of 112 iron pnictides [36]. Nevertheless, most of the XRD reflections can be indexed with a monoclinic 112-type unit cell with a ∼ 3.99 Å, b ∼ 3.90 Å, c ∼ 10.6 Å, and β ∼ 89.9 • [21,34]. Tiny secondary phases of Eu 2 O 3 and FeAs 2 are discernable, yet no 122-type phase of Eu(Fe 1−x Ni x ) 2 As 2 can be detected.…”

“…Overall, the reflections are weak with a small signal-to-noise ratio, suggesting relatively poor crystallinity. Similar phenomena were observed in other groups [21] or in other 112 materials [23,24,35], reflecting the inherent instability of 112 iron pnictides [36]. Nevertheless, most of the XRD reflections can be indexed with a monoclinic 112-type unit cell with a ∼ 3.99 Å, b ∼ 3.90 Å, c ∼ 10.6 Å, and β ∼ 89.9 • [21,34].…”

“…The Mössbauer measurement demonstrated that the 110-K transition was due to a spin-density-wave (SDW) ordering in the Fe sublattice, and the 40-K transition was associated with a magnetic ordering in the Eu sublattice [33]. With the specific-heat and magnetization measurements, the present authors [34] confirmed the dominant antiferromagnetic ordering of Eu spins at T m , and found a reentrant spin-glass transition at T SG ∼ 15 K and a spin reorientation at T SR ∼ 7 K. SC was realized with La doping [21] or with Ni doping [34], and the T c values achieve 11 K and 17.5 K in Eu 0.85 La 0.15 FeAs 2 and Eu(Fe 0.96 Ni 0.04 )As 2 , respectively. In the case of Ni doping, a weak spontaneous magnetization coexisting with SC was observed at low temperatures.…”

“…EuFeAs 2 is so far the unique 112 iron-pnictide parent compound that can be stabilized by itself. Measurements of electrical resistivity and magnetic susceptibility show two distinct anomalies at T SDW ∼ 110 K and T m ∼ 40 K, respectively [21]. The Mössbauer measurement demonstrated that the 110-K transition was due to a spin-density-wave (SDW) ordering in the Fe sublattice, and the 40-K transition was associated with a magnetic ordering in the Eu sublattice [33].…”

“…Recently, a new type of Eu-containing iron pnictide EuFeAs 2 was discovered [21]. It is structurally analogous to the 112-type superconductors AFeAs 2 (A = (Ca,La) [22] or (Ca,Pr) [23]) which can be stabilized only by the partial substitution with rareearth elements [24].…”