Metal-Ordered Arsenides M₂MnAs₃ (M = Zr, Hf) with a NaCl/NiAs Intergrowth Structure

In an attempt to extend the metal-ordered NiAs-type pnictides, we successfully synthesized three ternary arsenides M 2 MnAs 3 ( M = Zr, Hf) and HfMnAs 2 . HfMnAs 2 adopts the 1:1 metal-ordered NiAs-type structure (space group: P 3̅ m 1), while M 2 MnAs 3 crystallizes in the metal-ordered intergrowth structure of NaCl- and NiAs-type slabs (space group: R 3̅ m ) in which Mn layers are separated by double Zr/Hf layers. The appearance of the metal-ordered intergrowth structure is found to be induced by reducing Coulomb repulsion between high-valent Zr 4+ . Magnetization measurements revealed that M 2 MnAs 3 undergoes a ferromagnetic transition with considerably lower T c (150 K for Zr 2 MnAs 3 and 85 K for Hf 2 MnAs 3 ) in comparison to HfMnAs 2 (∼330 K), demonstrating enhanced two-dimensional characters. This study offers an opportunity to develop pnictides having various metal-ordered patterns toward interesting magnetic properties.