Crystal and magnetic structures of the R(=Y, Dy-Tm)MnGe compounds

Powder and single-crystal X-ray diffraction, susceptibility measurements and powder neutron diffraction studies on RMnGe compounds (R=Dy-Tm, Y) are reported. The R(=Dy-Er, Y)MnGe compounds crystallize in the TiNiSi-type (S.G. Pnma) while two polytypic forms (H.T.-ZrNiAl and L.T.-TiNiSi) characterize the TmMnGe compound. All compounds exhibit antiferromagnetic ordering of the Mn sublattice above room temperature, while the R sublattice orders antiferromagnetically at 85 (5), 70 (5), 60 (5) and 30 (5) K for R=Dy, Ho, Er and Tm, respectively. At 2 K, DyMnGe is characterized by a cycloid structure (qx∼0.227) whereas HoMnGe exhibits a conical structure (qx∼0.259). YMnGe, ErMnGe and TmMnGe are simple collinear antiferromagnets, and a spin-reorientation process occurs in TmMnGe below 25 (2) K. At 2 K, the values of the magnetic moments are: μMn=3.37(14) μB, μDy=8.87(13) μB; μMn=3.35(9) μB, μHo=8.03(12) μB; μMn=3.25(18) μB, μEr=7.51(39) μB; μMn=3.19(12) μB, μTm=6.40(11) μB; μMn=3.51(15) μB for DyMnGe, HoMnGe, ErMnGe, TmMnGe and YMnGe, respectively. In all cases, the magnetic structures are characterized by antiferromagnetic [0 1 0] Mn chains. The results are discussed in terms of R-R, R-Mn, Mn-Mn interactions and anisotropy effects