Magnetic Precursor of the Pressure-Induced Superconductivity in Fe-Ladder Compounds

Abstract

The pressure effects on the antiferromagentic orders in iron-based ladder compounds CsFe2Se3 and BaFe2S3 have been studied using neutron diffraction. With identical crystal structure and similar magnetic structures, the two compounds exhibit highly contrasting magnetic behaviors under moderate external pressures. In CsFe2Se3 the ladders are brought much closer to each other by pressure, but the stripe-type magnetic order shows no observable change. In contrast, the stripe order in BaFe2S3, undergoes a quantum phase transition where an abrupt increase of Néel temperature by more than 50% occurs at about 1 GPa, accompanied by a jump in the ordered moment. With its spin structure unchanged, BaFe2S3 enters an enhanced magnetic phase that bears the characteristics of an orbital selective Mott phase, which is the true neighbor of superconductivity emerging at higher pressures.PACS numbers: 74.25. Ha, The antiferromagnetic (AF) phase adjacent to superconductivity (SC) is so richly faceted that its microscopic origin still eludes a unified description. Significant variation of the ordered magnetic moment and the underlying degree of electron correlations lie at the heart of the heated dispute [1][2][3]. The static AF phase in the parent compounds has roughly two categories: stripe magnetism and block magnetism. The former includes the single stripe in LaFeAsO, BaFe 2 As 2 , NaFeAs, and double stripe in FeTe [4]. Spin block order was found in the vacancy-ordered K 2 Fe 4 Se 5 (245) [5]. These materials all have a plane of Fe square lattice once deemed indispensable for the occurence of SC. The recent successful induction of SC by pressure in the ladder compound BaFe 2 S 3 [6,7] has introduced a quasi-one dimensional structural motif for the studies of iron-based superconductors and a parallel to the quasi-1D cuprates [8]. As if the layers of the superconducting Fe square lattice were sliced up and staggered, the AFe 2 X 3 (A = K, Rb, Cs or Ba and X = Chalcogens) compounds consist of ladders of two-leg Fechains with edge-sharing tetrahedra of anions (Se or S) surrounding each Fe site, as shown in Figure 1(a). The reduced dimensionality leads to modified bandwidth [9], Fermi surface topology, and provides a rare insight into critical open issues such as the nature of the AF order.Both stripe-and block-types of AF orders are hosted by the Fe-ladder compounds. BaFe 2 S 3 and CsFe 2 Se 3 , with the CsCu 2 Cl 3 type structure (Cmcm space group), have the stripe AF order where the ferromagnetic (FM) spin pairs on the same ladder rung correlate antiferromagnetically along the leg direction. The ordered moment lies in the rung-direction in BaFe 2 S 3 (Fig.1(b)) [6] and the leg-direction in CsFe 2 Se 3 (Fig.1(c)) [10]. In BaFe 2 Se 3 , the distorted FeSe 4 tetrahedron lose the Ccentering and result in the lowered symmetry P nma [11]. The magnetic structure consists of blocks of 4 FM spins forming alternating AF pattern along the leg direction [12]. The magnetic excitations in BaFe 2 Se 3 fits the description of localized spins and...

Gradual enhancement of stripe-type antiferromagnetism in the spin-ladder material BaFe2S3 under pressure

“…The NPD and µSR results show a gradual increase in T N with pressure followed by an eventual plateau around the highest pressure measured (2.6 GPa), with no observable change in the magnitude of the ordered moment. This contrasts with the abrupt magnetic enhancement around 1 GPa and subsequent reduction reported earlier [22]. Our density functional theory (DFT) calculations reveal a delicate sensitivity of the magnetism on the Fe-S bond lengths and angles, which may explain the discrepancy with the earlier work.…”

“…The NPD results reported so far provide no indication that a change to the ordered moment or ordering temperature occurs between ambient pressure and 1 GPa, in contrast to the dramatic enhancement at 0.95 GPa reported previously [22]. To verify our NPD findings, we now turn to the µSR measurements, which we performed on a sample taken from the same powder batch as was used for the NPD experiments.…”

“…In both systems, the FeX 4 edge-sharing tetrahedra create well-separated iron ladders [11], distinct from the planar square lattice of other FeSCs. These compounds therefore represent an important new family of materials that has attracted significant theoretical and experimental attention in the quest to understand iron-based superconductivity [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29]. BaFe 2 S 3 belongs to the orthorhombic space group Cmcm and orders antiferromagnetically below ∼100-120 K in a stripe-type spin configuration [8].…”

Strong ferromagnetic exchange interaction under ambient pressure in BaFe2S3

“…It has been suggested that the abrupt increase of the Néel temperature (T N ) as a function of pressure shown in Fig. 1 (a) is associated with a quantum phase transition due to the change of orbital occupancies under pressure 6 . BaFe 2 S 3 is isostructural with the 1D antiferromagnetic (AF) ladder compounds AFe 2 Se 3 (A = K, Rb, and Cs, space group: Cmcm, no.…”

Iron telluride ladder compounds: Predicting the structural and magnetic properties of BaFe2Te3

“…Recently, pressure-induced superconductivity was observed in the two-leg quasi-one-dimensional ladder system BaFe 2 X 3 (X = S, Se) with eletronic density n = 6.0 [9,10], starting a novel field of research for high temperature iron-based superconductors [11][12][13][14][15][16][17][18][19][20][21]. BaFe 2 S 3 displays a stripe-type (CX) AFM order, similar to other 2D iron-based superconductors, below 120 K [9,15]. By applying hydrostatic pressure, this system displayed an insulator-metal transition [16,22] and superconductivity was observed at P ∼ 11 GPa near a first-order magnetic phase transition where the AFM order was suppressed [9,23].…”