Metal-Ordered\nArsenides <i>M</i><sub>2</sub>MnAs<sub>3</sub> (<i>M</i> = Zr, Hf) with a NaCl/NiAs Intergrowth\nStructure

In an attempt to extend the metal-ordered NiAs-type pnictides,\nwe successfully synthesized three ternary arsenides <i>M</i><sub>2</sub>MnAs<sub>3</sub> (<i>M</i> = Zr, Hf) and HfMnAs<sub>2</sub>. HfMnAs<sub>2</sub> adopts the 1:1 metal-ordered NiAs-type\nstructure (space group: <i>P</i>3̅<i>m</i>1), while <i>M</i><sub>2</sub>MnAs<sub>3</sub> crystallizes\nin the metal-ordered intergrowth structure of NaCl- and NiAs-type\nslabs (space group: <i>R</i>3̅<i>m</i>)\nin which Mn layers are separated by double Zr/Hf layers. The appearance\nof the metal-ordered intergrowth structure is found to be induced\nby reducing Coulomb repulsion between high-valent Zr<sup>4+</sup>.\nMagnetization measurements revealed that <i>M</i><sub>2</sub>MnAs<sub>3</sub> undergoes a ferromagnetic transition with considerably\nlower <i>T</i><sub>c</sub> (150 K for Zr<sub>2</sub>MnAs<sub>3</sub> and 85 K for Hf<sub>2</sub>MnAs<sub>3</sub>) in comparison\nto HfMnAs<sub>2</sub> (∼330 K), demonstrating enhanced two-dimensional\ncharacters. This study offers an opportunity to develop pnictides\nhaving various metal-ordered patterns toward interesting magnetic\nproperties.