Synthesis, Crystal and Electronic Structure of the Quaternary Magnetic EuTAl₄Si₂ (T = Rh and Ir) Compounds

Single crystals of the quaternary europium compounds EuRhAl₄Si₂ and EuIrAl₄Si₂ were synthesized by using the Al–Si binary eutectic as a flux. The structure of the two quaternary compounds has been refined by single crystal X-ray diffraction. Both compounds are stoichiometric and adopt an ordered derivative of the ternary KCu₄S₃ structure type (tetragonal tP8, P4/mmm). The two compounds reported here represent the first example of a quaternary and truly stoichiometric 1:1:4:2 phase crystallizing with this structure type. In light of our present results, the structure of the BaMg₄Si₃ compound given in literature as representing a new prototype is actually isotypic with the KCu₄S₃ structure. Local spin density approximation including the Hubbard U parameter (LSDA + U) calculations show that Eu ions are in the divalent state, with a significant hybridization between the Eu 5d, Rh (Ir) 4d (5d), Si 3p and Al 3p states. Magnetic susceptibility measured along the [001] direction confirms the divalent nature of the Eu ions in EuRhAl₄Si₂ and EuIrAl₄Si₂, which order magnetically near ∼11 and ∼15 K, respectively.