Block-Type Antiferromagnetism in Single Chain Quasi-One-Dimensional K3⁢Fe2⁢Se4

Abstract

One-dimensional (1D) structures provide a unique platform to study the correlated quantum interactions and phase transitions such as unconventional magnetism and superconducting states. Here, we report that iron chalcogenide K3Fe2Se4 with an unusual block-type canted antiferromagnetic (AFM) structure in a clear single chain quasi-1D structure, which is structurally different from the ladder phase BaFe2Se3, through both experimental measurements and Density Matrix Renormalization Group (DMRG) calculations. The narrow gap semiconductor K3Fe2Se4 has a quasi-1D edge-shared FeSe4 tetrahedra chain structure and orders antiferromagnetically below 110 K. The magnetic moments couple antiferromagnetically along the quasi-1D chain direction of the b-axis and form an up-down-down-up (↑-↓-↓-↑) like spin structure with a commensurate propagation vector k = (0, 0, 0), where block-type spin ↑-↑ or ↓-↓ coupling are between the longer Fe-Fe bonds of the quasi-1D chain. DMRG results show that block antiferromagnetic state is stable in K3Fe2Se4 and reveal that the block-ordered arrangement of Fe2.5+ ions spins arise from the competition between ferromagnetic and AFM interaction in the presence of strong electronic correlation. Our research results not only report the discovery of a clear block-type canted antiferromagnetic structure in a real quasi-1D chain material but also provide a theoretical approach to understand the block-type antiferromagnetism in quasi-1D iron chalcogenides.