Neutron-diffraction studies of two-dimensional magnetic ordering in TbRu2Si2

by neutron diffraction. Below TN, the order is confirmed to be one-dimensional, with a propagation vector Q=(3/1300). At Tt∼5 K and Tt′∼4 K there are additional phase transitions giving rise to a number of magnetic satellites, not only on high-symmetry lines, but also on low-symmetry lines in the a*–b* reciprocal lattice plane. The satellites on high-symmetry lines are described by the fundamental modulation vector Q=(3/1300) and its odd harmonics, while the satellites on low-symmetry lines are given by Q=(mτnτ0), where m and n are odd. The diffraction patterns show that, below Tt, the magnetic structures are never one-dimensional as previously reported, but the order is consistent with a two-dimensional model having a 13a×13a×c magnetic unit cell, containing two frustrated Tb sites, one at the corner and the other at the body-centered position. Below Tt′, the order is more complex.