An in-plane hexagonal antiferromagnet in the Cu-Mn-As system, Cu${}_{0.82}$Mn${}_{1.18}$As

Abstract

We report the single-crystal growth and characterization of a new hexagonal phase, Cu${}_{0.82}$Mn${}_{1.18}$As, in the Cu-Mn-As system. This compound contains the same square-pyramidal MnAs${}_5$ units as the tetragonal and orthorhombic polymorphs of CuMnAs. Calorimetry, magnetometry, and neutron diffraction measurements reveal antiferromagnetic ordering at 270 K. The magnetic structure consists of a triangular arrangement of spins in the $ab$ plane. Hexagonal Cu${}_{0.82}$Mn${}_{1.18}$As shows resistivity that varies only weakly from 5 K to 300 K, and is many times higher than tetragonal CuMnAs, indicative of a strongly-scattering metal. First-principles calculations confirm the metallic band structure with a small density of states at the Fermi energy. The neutron-refined magnetic ground state is close to the computationally-determined minimum energy configuration. This compound should serve as a clear control when disentangling the effects of current-driven Néel switching of metallic antiferromagnets since it exhibits in-plane spins but the magnetic ordering does not break degeneracy along the $a$ and $b$ directions, unlike tetragonal CuMnAs.

7 pages, 8 figures; Added Cu-Mn-As phase diagram, updated 1 figure and added some more text