Au₄Mn: A localized ferromagnet with strong spin-orbit coupling, long-range ferromagnetic exchange, and high Curie temperature

Metallic Mn-based alloys with a nearest-neighbor Mn-Mn distance greater than 0.4 nm exhibit large, welllocalized magnetic moments. Here we investigate the magnetism of tetragonal Au₄Mn with a Curie temperature of 385 K, where manganese has a spin moment of 4.1 μ_B and its orbital moment is quenched. Since 80% of the atoms are gold, the spin-orbit interaction is strong and Au₄Mn exhibits uniaxial magnetocrystalline anisotropy with surface maze domains at room temperature. The magnetic hardness parameter of 1.0 is sufficient to maintain the magnetization along the c axis for a sample of any shape. Au also reduces the spin moment of Mn through 5d-3d orbital hybridization. An induced moment of 0.05 μ_B was found on Au under a pulsed field of 40 T. Density functional theory calculations indicate that the Mn-Mn exchange is mediated by spin-polarized gold 5d and 6p electrons. The distance dependence shows that it is ferromagnetic or zero for the first ten shells of Mn neighbors out to 1.041 nm (64 atoms), and very weak and oscillatory thereafter.