Magnetic properties of RMn6Sn6 (R = Gd-Er) compounds from neutron diffraction and Mossbauer measurements

The magnetic structures of the HfFe6Ge6-type structure RMn6Sn6 (R = Gd-Er) compounds have been investigated by neutron diffraction and Gd-155 and Er-1 66 Mossbauer spectroscopy. Strong Mn-R antiferromagnetic coupling causes th e rare earth and manganese sublattices to order simultaneously, yielding co llinear ferrimagnetic arrangements in the whole ordered state for R = Gd, T b, Dy, Ho compounds and below 75 K in ErMn6Sn6. Neutron diffraction studies of Tb- and DyMn6Sn6 above room temperature and in the whole ordered state of GdMn6Sn6 prove the planar anisotropy of the Mn sublattice whereas the ra re-earth anisotropy for R elements with negative alpha(2). Stevens factor y ields total (Tb) or partial (Dy, Ho) spin reorientation processes of both R and Mn sublattices at low temperature. Mossbauer spectroscopy shows that t he rare earth single ion anisotropy is related to an interplay of the secon d- and fourth-order crystal electric field coefficients. (C) 1999 Elsevier Science B.V. All rights reserved.