The transition between antiferromagnetic order and spin-glass state in layered chalcogenides KFeAgCh2 (Ch = Se, S)

Investigation on the magnetic interaction in Fe-based ThCr 2 Si 2 -type compounds is very important not only for understanding the structure-property relationship in this family but also for exploring the superconducting mechanism in related materials. In this work, we report the synthesis and physical properties of two new Fe-based chalcogenides KFeAgSe 2 and KFeAgS 2 . These two compounds adopt ThCr 2 Si 2 -type structure with I 4/ mmm space group and contain the Fe/Ag mixed occupation in the centre of edge-sharing Fe/AgCh 4 tetrahedron (Ch = Se, Te). The lattice parameters are refined to be a = 4.1866(2) Å, c = 13.7731(4) Å and a = 3.9845(3) Å, c = 13.3610(4) Å for KFeAgSe 2 and KFeAgS 2 respectively. Both two compounds show semiconducting behavior with electrical resistivity increased as the temperature decreased, while the resistivity of KFeAgS 2 is much larger (~61 Ω cm at room temperature) than that of KFeAgSe 2 (~2.5 Ω cm at room temperature). Most interestingly, despite the similar electronic structure of these two compounds, KFeAgSe 2 features a long-range antiferromagnetic order below 26 K while KFeAgS 2 shows a spin-glass state below 19 K. It is indicated that the long-range magnetic ordering can be suppressed in these ThCr 2 Si 2 -type transition metal chalcogenides via compressing the unit cell, that is to say, by chemical pressure. Our work not only gives a new sight to understand the structure-magnetism relationship in ThCr 2 Si 2 -type transition metal chalcogenides , but also provides clue to explore the mechanism of superconductivity in Fe-based family.