Ternary R4Mn3–xAu10+x (R = Gd or Y; 0.2 ≤ x ≤ 1) compounds have been synthesized and characterized using single-crystal X-ray diffraction. The structure is a ternary variant of orthorhombic Zr7Ni10 (oC68, space group Cmca) and is isostructural with Ca4In3Au10. The structure contains layers of Mn-centered rectangular prisms of gold (Mn@Au8), interbonded via Au atoms in the b-c plane, and stacked in a hexagonal close packed arrangement along the a direction. These layers are bonded via additional Mn atoms along the a direction. The rare-earth metals formally act as cations and fill the rest of the space. The structure could also be described as sinusoidal layers of gold atoms, which are interconnected through Au–Au bonds. The magnetic characteristics of both compounds reveal the presence of nearly localized Mn magnetic moments. Magnetization M measurements of Y4Mn2.8Au10.2 versus temperature T and applied magnetic field H demonstrate the dominance of antiferromagnetic (AFM) interactions in this compound and indicate the occurrence of noncollinear AFM ordering at TN1 = 70 K and a spin reorientation transition at TN2 = 48 K. For the Gd analogue Gd4Mn2.8Au10.2, the M(H,T) data instead indicate the dominance of ferromagnetic interactions and suggest a ferrimagnetic transition at TC ≈ 70 K for which two potential ferrimagnetic structures are suggested. Linear muffin-tin orbital calculations on the stoichiometric composition “Y4Mn3Au10” using the local spin density approximation indicate a ∼1 eV splitting of the Mn 3d states with nearly filled majority spin states and partially filled minority spin states at the Fermi level resulting in approximately four unpaired electrons per Mn atom in the metallic ground state. The crystal orbital Hamilton population analyses demonstrate that ∼94% of the total Hamilton populations originate from Au–Au and polar Mn–Au and Y–Au bonding.
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