Crystal Growth, Transport, and the Structural and Magnetic Properties of Ln₄FeGa₁₂ with Ln= Y, Tb, Dy, Ho, and Er

Ln ₄ FeGa ₁₂ , where Ln is Y, Tb, Dy, Ho, and Er, prepared by flux growth, crystallize with the cubic Y ₄ PdGa ₁₂ structure with the Im3m space group and with a ≅ 8.5650(4), 8.5610(4), 8.5350(3), 8.5080(3), and 8.4760(3) Å, respectively. The crystal structure consists of an iron-gallium octahedra and face-sharing rare-earth cuboctahedra of the Au ₃ Cu type. Er ₄ Fe _0.67 Ga ₁₂ is iron-deficient, leading to a distortion of the octahedral and cuboctahedral environments due to the splitting of the Ga2 site into Ga2 and Ga3 sites. Further, interstitial octahedral sites that are unoccupied in Ln ₄ FeGa ₁₂ (Ln = Y, Tb, Dy, and Ho) are partially occupied by Fe2. Y ₄ FeGa ₁₂ exhibits weak itinerant ferromagnetism below 36 K. In contrast, Tb ₄ FeGa ₁₂ , Dy ₄ FeGa ₁₂ , Ho ₄ FeGa ₁₂ , and Er ₄ Fe _0;67 Ga ₁₂ order antiferromagnetically with maxima in the molar magnetic susceptibilities at 26,18.5,9, and 6 K. All of the compounds exhibit metallic electric resistivity, and their iron-57 Mössbauer spectra, obtained between 4.2 and 295 K, exhibit a single-line absorption with a 4.2 K isomer shift of ca. 0.50 mm/s, a shift that is characteristic of iron in an iron-gallium intermetallic compound. A small but significant broadening In the spectral absorption line width is observed for Y ₄ FeGa ₁₂ below 40 K and results from the small hyperfine field arising from its spin-polarized itinerant electrons.