Neutron diffraction studies of RSn1+xGe1−x (R=Tb–Er) compounds

The magnetic structures of RSn1+xGe1−x (R=Tb, Dy, Ho and Er, x≈0.1) compounds have been determined by neutron diffraction studies on polycrystalline samples. The data recorded in a paramagnetic state confirmed the orthorhombic crystal structure described by the space group Cmcm. These compounds are antiferromagnets at low temperatures. The magnetic ordering in TbSn1.12Ge0.88 is sine-modulated described by the propagation vector k=(0.4257(2), 0, 0.5880(3)). Tb magnetic moment equals 9.0(1) μB at 1.62 K. It lies in the b–c plane and form an angle θ=17.4(2)° with the c-axis. This structure is stable up to the Nèel temperature equal to 31 K. The magnetic structures of RSn1+xGe1−x, where R are Dy, Ho and Er at low temperatures are described by the propagation vector k=(1/2, 1/2, 0) with the sequence (++−+) of magnetic moments in the crystal unit cell. In DySn1.09Ge0.91 and HoSn1.1Ge0.9 magnetic moments equal 7.25(15) and 8.60(6) μB at 1.55 K, respectively. The moments are parallel to the c-axis. For Ho-compound this ordering is stable up to TN=10.7 K. For ErSn1.08Ge0.92, the Er magnetic moment equals 7.76(7) μB at T=1.5 K and it is parallel to the b-axis. At Tt=3.5 K it tunes into the modulated structure described by the k=(0.496(1), 0.446(4), 0). With the increase of temperature there is a slow decrease of kx component and a quick decrease of ky component. The Er magnetic moment is parallel to the b-axis up to 3.9 K while at 4 K and above it lies in the b–c plane and form an angle 48(3)° with the c-axis. In compounds with R=Tb, Ho and Er the magnetostriction effect at the Nèel temperature is observed.