EuAu₃Al₂: Crystal and Electronic Structures and Spectroscopic, Magnetic, and Magnetocaloric Properties

The intermetallic compound EuAu₃Al₂ has been prepared by reaction of the elements in tantalum ampules. The structure was refined from single-crystal data, indicating that the title compound crystallizes in the orthorhombic crystal system (a = 1310.36(4), b = 547.87(1), c = 681.26(2) pm) with space group Pnma (wR₂ = 0.0266, 1038 F² values, 35 parameters) and is isostructural to SrAu₃Al₂ (LT-SrZn₅ type). Full ordering of the gold and aluminum atoms was observed. Theoretical calculations confirm that the title compound can be described as a polar intermetallic phase containing a polyanionic [Au₃Al₂]^δ− network featuring interconnected strands of edge-sharing [AlAu₄] tetrahedra. Magnetic measurements and ¹⁵¹Eu Mössbauer spectroscopic investigations confirmed the divalent character of the europium atoms. Ferromagnetic ordering below T_C = 16.5(1) K was observed. Heat capacity measurements showed a λ-type anomaly at T = 15.7(1) K, in line with the ordering temperature from the susceptibility measurements. The magnetocaloric properties of EuAu₃Al₂ were determined, and a magnetic entropy of ΔS_M = −4.8 J kg^–1 K^–1 for a field change of 0 to 50 kOe was determined. Band structure calculations found that the f-bands of Eu present at the Fermi level of non-spin-polarized calculations are responsible for the ferromagnetic ordering in this phase, whereas COHP chemical bonding coupled with Bader charge analysis confirmed the description of the structure as covalently bonded polyanionic [Au₃Al₂]^δ− network interacting ionically with Eu^δ+.