Magnetic structures of TbTX compounds

Complete text of publication follows. The results of neutron diffraction measurements for some TbTX (T = 4d or 5d metal and X = Si, Ge, Ga) compounds are presented. All the compounds crystallize in the orthorhombic TiNiSi-type of crystal structure and except for TbRuGe they are antiferromagnets. The TbRuGe compound below Tc = 70 K is a noncollinear ferromagnetic of the FxCz type. For TbTGe (T = Rh, Ir, Pt) compounds in the temperature range 1.5 - K Neel temperature (equal to 23 K for T = Rh, 24 K for T = Ir and 15 K for T = Pt) the sine modulated magnetic ordering with the propagation vector k = (0, ky, 0) is observed. They y-component of the propagation vector is 0.450 for T = Rh, 0.409 for T = Ir and 0.385 for T = Pt. The Tb magnetic moment is parallel to the a-axis in TbRhGe and to the c-axis in TbIrGe and TbPtGe. in TbPtSi a complex magnetic ordering is observed, while in TbPtGa at T = 1.5 K magnetic order of rare-earth moments is collinear and described by the propagation vector k = (0, 1/2, 0). With increasing temperature above Tt = 18 K a change into a sine modulated structure was observed. The obtained results are analyzed in the terms of exchange interaction of the RKKY type and crystal-electric field effect. (author)