We report neutron scattering and transport measurements on semiconducting
Rb0.8βFe1.5βS2β, a compound isostructural and isoelectronic to the
well-studied A0.8βFeyβSe2β(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, interdigitated mesoscopically with the rhombic phase is an ubiquitous
phase with 5βΓ5β iron vacancy order. This phase has a
magnetic transition at TNβ=425 K and an iron vacancy order-disorder
transition at TSβ=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 Rb0.8βFe1.5βS2β and
K0.81βFe1.58βSe2β, we argue that the in-plane antiferromagnetic order
arises from strong coupling between local moments. Superconductivity,
previously observed in the A0.8βFeyβSe2βzβSzβ system, is absent
in Rb0.8βFe1.5βS2β, which has a semiconducting ground state. The
implied relationship between stripe/block antiferromagnetism and
superconductivity in these materials as well as a strategy for further
investigation is discussed in this paper.Comment: 7 pages, 5 figure