CsMn₄As₃: A Layered Tetragonal Transition-Metal Pnictide Compound with an Antiferromagnetic Ground State

We report the synthesis and properties of a new layered tetragonal ternary compound CsMn₄As₃ (structure type, KCu₄S₃; space group, P4/ mmm, no. 123; and Z = 2). The material is a small band gap semiconductor and exhibits an antiferromagnetic ground state associated with Mn spins. The compound exhibits a signature of a distinct magnetic moment canting event at 150(5) K with a canting angle ≈ 0.3°. Although some features of the magnetic characteristics of this new compound are qualitatively similar to those of the related BaMn₂As₂, the underlying Mn sublattices of the two materials are quite different. While the Mn square-lattice layers in BaMn₂As₂ are equally spaced along the c-direction with the interlayer distance d_L Ba = 6.7341(4) Å, the Mn sublattice forms bilayers in CsMn₄As₃ with the interlayer distance within a bilayer being d_L Cs = 3.1661(6) Å; the distance between the two adjacent bilayers is d_B = 7.290(6) Å. This difference in the Mn sublattice is bound to significantly alter the energy balance among the J₁, J₂, and J _c exchange interactions within the J₁- J₂- J _c model compared to those in BaMn₂As₂ and the other related 122 compounds, including the well-known iron-arsenide superconductor parent compound BaFe₂As₂. Owing to the novelty of its transition-metal sublattice, this new addition to the family of tetragonal materials related to the iron-based superconductors brings prospects for doping and pressure studies in the search of new superconducting phases as well as other exciting correlated electron properties.