Orbital-selective magnetism in the spin-ladder iron selenides Ba1−xKxFe2<

Abstract

Here we show that the 2.80(8) µ B Fe -1 block antiferromagnetic order of BaFe 2 Se 3 transforms into stripe antiferromagnetic order in KFe 2 Se 3 with a decrease in moment to 2.1(1) µ B Fe -1 . This reduction is larger than expected from the change in electron count from Ba 2+ to K + , and occurs with the loss of the displacements of Fe atoms from ideal positions in the ladders, as found by neutron pair distribution function analysis. Intermediate compositions remain insulating, and magnetic susceptibility measurements show a suppression of magnetic order and probable formation of a spin-glass. Together, these results imply an orbital-dependent selection of magnetic versus bonded behavior, driven by relative bandwidths and fillings.

Colloquium: The unexpected properties of alkali metal iron selenide superconductors

“…22, upper panel). Moreover, the other phase of ladders that was recently reported in neutron experiments (Caron et al, 2012), denoted as CX in the figure, is also part of the phase diagram. In addition, several other phases not yet observed experimentally are also stable varying the couplings, suggesting that many states are close in energy and likely competing.…”

“…When the Ba atoms of BaFe 2 Se 3 are replaced by K, eventually arriving to KFe 2 Se 3 , the magnetic order changes to that in Fig. 20 (upper panel), with spins along the rungs coupled ferromagnetically, and with an AFM coupling along the legs (Caron et al, 2012).…”

“…In this subsection, recent experimental efforts (Caron et al, 2011;Saparov et al, 2011;Lei et al, 2011d;Caron et al, 2012;Nambu et al, 2012) in the study of selenides with the geometry of two-leg ladders (sometimes also referred to as double chains) will be reviewed, while a description of the status of the theoretical work will be presented in the next subsection. A typical compound in this context is BaFe 2 Se 3 that contains building blocks made of [Fe 2 Se 3 ] 2− that when assembled along a particular direction leads to an array of two-leg ladder structures, as sketched in Fig.…”

Temperature and composition phase diagram in the iron-based ladder compoundsBa1−xCsxFe2Se3

“…Unlike the most ironbased SCs, iron-based ladder compounds are insulators. KFe 2 Se 3 26 and CsFe 2 Se 3 25 have stripe magnetism; magnetic moments are arranged to form ferromagnetic units along the rung direction, and the units stack antiferromagnetically along the leg direction. BaFe 2 Se 3 20,23 has block magnetism; magnetic moments are arranged to form Fe 4 ferromagnetic units, and each units stack antiferromagnetically along the leg direction.…”

“…Recently, iron-based ladder compounds AFe 2 X 3 (A = K, Rb, Cs or Ba, and X = chalcogen) [17][18][19] have been under intensive investigation [20][21][22][23][24][25][26][27][28][29] . The AFe 2 X 3 compounds consist of FeX 4 tetrahedra, which are similar to the 2D iron-based SCs, but Fe atoms form two-leg ladder lattice giving rise to the quasi-one dimensionality.…”