Metal-Ordered Arsenides <i>M</i>₂MnAs₃ (<i>M</i> = 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 M2MnAs3 (M = Zr, Hf) and HfMnAs2. HfMnAs2 adopts the 1:1 metal-ordered NiAs-type structure (space group: P3̅m1), while M2MnAs3 crystallizes in the metal-ordered intergrowth structure of NaCl- and NiAs-type slabs (space group: R3̅m) 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 Zr4+. Magnetization measurements revealed that M2MnAs3 undergoes a ferromagnetic transition with considerably lower Tc (150 K for Zr2MnAs3 and 85 K for Hf2MnAs3) in comparison to HfMnAs2 (∼330 K), demonstrating enhanced two-dimensional characters. This study offers an opportunity to develop pnictides having various metal-ordered patterns toward interesting magnetic properties.