Complex antiferromagnetic ordering in Dy3Ag4Sn4

We have studied the complex magnetic ordering of the Dy sublattices in orthorhombic Dy3Ag4Sn4 by high-resolution neutron diffraction and Sn-119 Mossbauer spectroscopy. Magnetic ordering in this compound occurs over two transitions. At 16 K the Dy( 2d) site orders in a doubled commensurate antiferromagnetic structure described by a propagation vector [ 0 1 2 0], with moments aligned along [ 100]. The Dy( 4e) site orders incommensurately with a propagation vector [ 0 0.628( 1) 0] and moments in the ( 001) plane. Below the second transition at 14 K both Dy site ordering modes are commensurate antiferromagnetic with the propagation vector [ 0 1 2 0] and unchanged ordering directions. The Sn-119 Mossbauer spectra comprise three magnetically split sextets in the area ratio 50%: 25%: 25% due to transferred hyperfine fields at the Sn-119 nuclei from the surrounding magnetic Dy neighbours. This spectral decomposition deviates from the area ratio 50%: 50% expected on the basis of the crystal structure and is in perfect agreement with the magnetic structure of Dy3Ag4Sn4 deduced from neutron diffraction data.