Magnetic order in R2Ni17 intermetallics: a neutron-diffraction investigation

The crystal and magnetic structures of hexagonal intermetallic compounds of the type R2Ni17 with R=Y, Tb, Dy, Ho and Er have been investigated by neutron powder diffraction at 20 and 200 K. The crystal structures at 200 K, which is above the magnetic ordering temperature for these compounds, have been refined and show that they crystallize in the hexagonal Th2Ni17 structure (space group P63/mmc). The magnetic structure at 20 K has a magnetic propagation vector k → =0 and consists of a ferrimagnetic alignment of R and Ni moments. At 20 K, compounds with R=Tb, Dy and Ho are collinear ferrimagnets with moments aligned in the basal plane of the hexagonal unit cell, whilst the compound with R=Er is an axial collinear ferrimagnet. The low-temperature magnitudes of the R moments at 2b and 2d sites are markedly different, with an almost free ion value at the 2b site, whilst the 2d site moment is substantially reduced from its free ion value.