Abstract
The ternary compound UFe 7Al 5 was synthesized by arc melting, followed by annealing at 850°C. The crystal structure was determined by single-crystal X-ray diffraction and refined to a residual value of R=0.039 ( S=1.030), with lattice parameters a=8.581(2) Å and c=4.946(1) Å. This compound is a new extreme composition in the family of intermetallics with general formula UFe x Al 12− x crystallizing in the tetragonal ThMn 12-type structure, space group I4 /mmm. In contrast to UFe x Al 12− x within the composition range 4⩽ x⩽6, in UFe 7Al 5 the additional iron atom is found in the 8 i equipositions. Magnetization measurements versus temperature show two magnetic transitions at 363 and 275 K, respectively, with a ferromagnetic behavior below the highest temperature transition. 57Fe Mössbauer data indicate that the high-temperature transition is related to the ordering of the iron atoms. The dependence of the isomer shifts and magnetic hyperfine fields on the crystallographic site and on the number of the iron nearest neighbors is similar to that observed in the other UFe x Al 12− x and rare-earth analogues. The magnetic hyperfine field values of iron atoms on 8 i sites is larger than in the other sites, in agreement with previous data obtained for other ThMn 12-type compounds.
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