Two spatially separated phases in semiconductingRb0.8Fe1.5S2

Abstract

We report neutron scattering and transport measurements on semiconducting Rb 0.8 Fe 1.5 S 2 , a compound isostructural and isoelectronic to the well-studied A 0.8 Fe y Se 2 (A = K, Rb, Cs, Tl/K) superconducting systems. Both resistivity and dc susceptibility measurements reveal a magnetic phase transition at T = 275 K. Neutron diffraction studies show that the 275 K transition originates from a phase with rhombic iron vacancy order which exhibits an in-plane stripe antiferromagnetic ordering below 275 K. In addition, the stripe antiferromagnetic phase interdigitates mesoscopically with an ubiquitous phase with √ 5 × √ 5 iron vacancy order. This phase has a magnetic transition at T N = 425 K and an iron vacancy order-disorder transition at T S = 600 K. These two different structural phases are closely similar to those observed in the isomorphous Se materials. Based on the close similarities of the in-plane antiferromagnetic structures, moments sizes, and ordering temperatures in semiconducting Rb 0.8 Fe 1.5 S 2 and K 0.81 Fe 1.58 Se 2 , we argue that the in-plane antiferromagnetic order arises from strong coupling between local moments. Superconductivity, previously observed in the A 0.8 Fe y Se 2−z S z system, is absent in Rb 0.8 Fe 1.5 S 2 , which has a semiconducting ground state. The implied relationship between stripe and block antiferromagnetism and superconductivity in these materials as well as a strategy for further investigation is discussed in this paper.

Elucidating the magnetic and superconducting phases in the alkali metal intercalated iron chalcogenides

“…The 234 and 245 phases are each found in Rb 0.8 Fe 1.5 Se 2 , Rb 0.8 Fe 1.5 SeS, and the previously studied Rb 0.8 Fe 1.5 S 2 (Ref. 30). This implies that the Se:S ratio does not affect the formation of the iron vacancy ordered phases.…”

“…32). In the regime 1.5 < y < 1.6, both the rhombic iron vacancy order and the √ 5 × √ 5 iron vacancy order coexist mesoscopically, while only the ratio of the volume fraction of the two phases varies 30 , suggesting the existence of a miscibility gap. The two phases are both characterized as Mott insulators with large gaps at the Fermi level and localized electrons, promoted by the iron vacancies, as well as a high spin configuration, S = 2 12,39-41 .…”

“…2 for the insulating compound with nominal composition of Rb 0.8 Fe 1.5 Se 2 , in which both the 234 phase and the 245 phase coexist 24,30 . We plot the peak intensities at wave vectors associated with the 234 phase as a function of temperature in Fig.…”

“…Details about the single crystal growth and configurations of neutron scattering experiments have been described elsewhere 30 . The samples used for neutron scattering experiments are 0.5, 0.7 and 0.3 g for Rb 0.8 Fe 1.5 Se 2 , Rb 0.8 Fe 1.5 SeS, and Rb 0.8 Fe 2 S 2 , respectively.…”

Antiferromagnetic order and spin dynamics in iron-based superconductors

“…Lattice and magnetic order in the parent compounds of iron-based superconductors From a crystal structure point of view, the parent compounds of iron-based superconductors can be classified into five different families: RFeAsO (R = La, Ce, Pr, Nd, Sm,..., the 1111 system), AFe 2 As 2 (A = Ba, Sr, Ca, K, the 122 system), AFeAs (A = Li, Na, the 111 system), Fe 1+y Te 1−x Se x (the 11 system), and A x Fe 2−y Se 2 alkali iron selenides (A = K, Rb, Cs, Tl, ..., including the insulating 245 phase A 2 Fe 4 Se 5 and the semiconducting 234 phase A 2 Fe 3 Se 4 ) (Aswathy et al, 2010;Dagotto, 2013;Johnston, 2010;Paglione and Greene, 2010;Sadovskii, 2008;Stewart, 2011;Wang et al, 2014;Zhao et al, 2012), where the 122 and 245 compounds have two FeAs(Se) layers in the unit cell and other systems have single FeAs(Se) layer. A recent development in the field is the synthesis of iron selenide superconductors via intercalation of molecular complexes between layers of FeSe (BurrardLucas et al, 2013;Krzton-Maziopa et al, 2012;Ying et al, 2012).…”