CRYSTAL-STRUCTURE, MAGNETISM AND FE-57 MOSSBAUER-SPECTRA OF TERNARY RE6FE11AL3 AND RE6FE13GE COMPOUNDS

From room-temperature X-ray powder analysis, alloys with composition RE6Fe11Al3 (RE = La, Ce, Pr, Nd, Sm, mischmetal) and RE6Fe13Ge (RE= Pr, Nd)were observed to crystallize with the tetragonal La6Co11Ga3-type structure and the Nd6Fe13Si-type structure, respectively. The alloys were arc-melted, annealed in silica tubes at 600 to 800-degrees-C for up to 120 h and quenched. The compounds of RE = La, Pr, Nd and MM with aluminium order magnetically at 281-285 K, whereas the compounds with germanium order at 303 K for RE = Pr and at 352 K for RE = Nd. All have a small net magnetization (2-13 J T-1 kg-1), which is ascribed to a ferrimagnetic spin structure of the iron sublattices (4d down, 16k up, 16l1 down, 16l2 up or 4d up, 16k up, 16l1 down, 16l2 down). The compounds with Al, including RE = La, exhibit a sharp increase in magnetization in an applied field of 3-5 T at 6 K, and a similar effect is seen in the compounds with Ge, which is attributed to a ferrimagnetic --> ferromagnetic transition of the iron sublattices. The rare-earth sublattices are antiferromagnetic and noncollinear. The average iron moment, deduced from the average Fe-57 hyperfine field, is 1.5mu(B) for the Al compounds, and 2.0mu(B) for the Ge compounds. The largest iron moments (2.4mu(B)) are on 4d sites, while the smallest (1.2mu(B))are on 16l2 sites.