Block-type and canted-type antiferromagnetism in ternary quasi-1D iron chalcogenides with single chain structure

One-dimensional (1D) and quasi-1D systems with correlated quantum interactions have attracted significant attention due to the intricate interplay among charge, orbital, spin and lattice degrees of freedom in low-dimensional phase space, and thus is a rich platform to study the exotic and competing electronic and magnetic orders In this talk, we will present the synthesis and magnetic studies of a class of ternary iron chalcogenides, namely BaFe₂Se₄, K₃Fe₂Se₄ and Ba₂FeSe_3, with clear one-dimensional single chain structures. The quasi-1D structures in these chalcogenides are built upon the tetragonally-coordinated FeSe₄ building motifs, similar as Fe-based superconductors, but are connected differently.  Both canted AFM and block-type AFM magnetic structures are discovered through experimental measurements and theoretical calculations. It is worthwhile to note that this is the first report block-type AFM structure in a clear single chain quasi-1D structure, which is structurally different from the two-leg ladder phase BaFe₂Se₃. The detailed results and outlook will be presented and discussed.