Magnetic ordering in ternary RMn2Ge2 compounds (R=Tb, Ho, Er, Tm, Lu) from neutron diffraction study

The compounds RMn2Ge2 (R=Tb, Ho, Er, Tm, Lu) have been investigated by neutron diffraction. TbMn2Ge2 is a collinear ferrimagnet with the Mn and Tb moment aligned along the c axis (μTb=8.81(59) μB; μMn=2.21(44) μB). HoMn2Ge2 exhibits incommensurate ordering below 2.1 K characterized by two wavevectors at 1.3 K: q1=(0.1543(4), 0.1543(4), 0) and q2=(0.210(1), 0.007(1), 0). The Mn sublattice remains antiferromagnetic down to 1.3 K (μMn=2.38(6) μB). The Er moments order ferromagnetically below 5.5 K in ErMn2Ge2 (μEr=6.81(31) μB). The moments are perpendicular to the c axis. The Mn sublattice remains antiferromagnetic down to 1.8 K (μMn=2.34(18) μB). The magnetic structure of TmMn2Ge2 is characterized by the propagation vector (0,0,1/2), the Tm moments lying in the basal plane. The ordering of the Tm moments yields a canting of the Mn moments (θ=21(3) ; μTm=6.63(18) μB; μMn=2.28(27) μB). The antiferromagnetic structure of LuMn2Ge2 has been determined (μMn=2.32(14) μB). The evolution of the magnetic properties of the heavy rare earth compounds RMn2Ge2 is discussed. (orig.)