Crystal structure magnetic properties and hyperfine interactions in RFe4Al8 (R = rare earth) systems

X-ray, magnetic susceptibility and ⁵⁷Fe, ¹⁵¹Eu, ¹⁵⁵Gd and ¹⁷⁰Yb Mössbauer studies were performed. Detailed analysis of X-ray intensities yields all ion locations and interatomic distances in the body centered tetragonal structure (space group I4/MMM). The unit cell contains two formula units. The rare earth, iron and aluminum occupy the 2(a), 8(f) and 8(i) and 8(j) crystallographic sites, respectively. The susceptibility and Mössbauer studies indicate the existence of two independent magnetic sublattices. The iron sublattice orders into an antiferromagnetic structure at about 120 K, whereas the rare earth sublattice orders (excluding those with La, Ce, Eu, Y and Lu) antiferromagnetically at about 20 K. The ⁵⁷Fe, ¹⁵¹Eu, ¹⁵⁵Gd and ¹⁷⁰Yb Mössbauer studies yield, in addition to the hyperfine interaction parameters, also the direction along which the moments are aligned. In EuFe₄Al₈ the Eu ion is in a mixed valent state.