Magnetic study of the new TiNiSi-type TbMnSi, DyMnSi and NdMnGe compounds

Abstract

Investigation made by powder X-ray diffraction, susceptibility measurement and powder neutron diffraction on the new TiNiSi-type (S.G. Pnma) TbMnSi, DyMnSi and NdMnGe compounds in a high-temperature form are reported. All three compounds are antiferromagnetic below T N=410, 400 and 430 K, respectively. Between T N and T t (<150 K), their magnetic structures are collinear antiferromagnetic, with Mn moments aligned along [1 0 0] in the case of TbMnSi and DyMnSi and [0 0 1] in the case of NdMnGe. Below T t, flat spiral structures characterized by a ( q x , 0, 0) wave vector and the Mn and R (Tb, Dy and Nd) moments lying in the (0 0 1) plane take place. At 2 K, the values of the magnetic moments are: μ Mn=3.30 (5) μ B, μ Tb=8.63 (5) μ B; μ Mn=3.2 (1) μ B, μ Dy=9.1 (2) μ B and μ Mn=3.73 (10) μ B, μ Nd=3.30 (8) μ B for TbMnSi, DyMnSi and NdMnGe, respectively. In the whole ordered range, the magnetic structures are characterized by antiferromagnetic Mn–Mn [0 1 0] zig-zag chains. The results are discussed and compared with those previously obtained on the corresponding CeFeSi-type (S.G. P4/nmm) TbMnSi and NdMnGe compounds. The Mn sublattice magnetic behaviour is also examined in the whole TiNiSi-type ternary silicides and germanides series.