Pulsed-neutron-diffraction studies of two-dimensional magnetic ordering in DyRu2Si2

We have investigated magnetic orderings of DyRu2Si2 by pulsed-neutron diffraction. Below TN the magnetic ordering is confirmed to be one-dimensional with Q=(2/9 0 0) and its odd harmonics. However, at 2.6 K below Tt=3.5 K a number of magnetic satellites have been observed not only on high-symmetry lines, but also on low-symmetry lines with the modulation of Q=(τ τ 0) and (mτ nτ 0), where τ=0.222(=2/9) and m,n= odd, in the a*–b* reciprocal plane. These magnetic satellites show that in this region the magnetic structure is not one-dimensional as previously reported, but two-dimensional with a 9a×9a×c magnetic unit cell. This unit cell contains two frustrated Dy ions, one at the corner site and the other at body-centered tetragonal site.