Materials Science Forum, Vol.378-3, 414-419, 2001
Neutron powder diffraction of iron-rich rare earth-iron-aluminium intermetallics RFe7Al5 (R = Tb, Dy, Ho, Er)
Iron-rich rare earth-iron -aluminium intermetallics (R = heavy rare earth) have been synthesized by arc melting the metallic constituents. The specimens have been investigated by neutron powder diffraction in the temperature range from 4.2 K to 400 K. The compounds crystallize in the ThMn12-type structure (space group 14/mmm) with R, Fe and Al on 2a, 8f and 8i sites, respectively, and remaining Fe and Al on 8j as analysed from Rietveld refinements. The HoFe7Al5 and ErFe7Al5 patterns show several minor reflection lines which are attributed to cubic Fe(3)AL The Th and Dy compounds are severely contaminated by other impurity phases. Magnetic order occurs around 320 K. The basic spin configurations of RFe7Al5 are ferrimagnetic with antiparallel orientations of R and 8f-site Fe spins within the tetragonal basis planes. In HoFe7Al5 and, less developed in ErFe7Al5, the Fe spins on the mixedly occupied 8j sites form an antiferromagnetic superstructure with propagation vector [0,0,(1)/(2)]and spin orientations along the tetragonal c-axis. Moment values and temperature dependencies of the magnetization are presented. The magnetic data obtained from the Th and Dy specimens are considered not representative because of the unknown phase contaminations. Structural details and the magnetic behaviour of the compounds are discussed in the context of previous findings on ThMn12-type R(FexAl1-x)(12) with x less than or equal to 0.5.
Keywords:4f-3d-intermetallics;magnetic ordering;neutron diffraction;phase contaminations;ThMn12 structure