Low-temperature magnetic structures in the DySi FeB-type compound 27.03.09

The low-temperature magnetic ordering of the dimorphic DySi compound has been studied at 1.5 K by neutron diffraction on two polycrystalline samples. The samples comprise various amounts of the two orthorhombic modifications: CrB-type (Cmcm Nr. 63, all atoms at 4c site: (0, y  , 14)) and FeB-type (Pnma Nr. 62, all atoms at 4c site: (x  , 14, z)), both order antiferromagnetically (TN≈38 K). The CrB-type phase orders with a uniaxial structure with the wave vector q1=(0, 0, 12) requiring a doubling of the c-axis. The Dy moments point along the linear chain with the shortest distance c. At 1.5 K, the ordered moment value is 8.57(1) μB/Dy atom.Two symmetry independent wave vectors describe the 1.5 K magnetic ordering of the FeB-type phase: q2=(0, 12, 16) and q3=(0, 0.484(1), 0.0892(1)), coexisting in form of domains. In both structures the magnetic moments are confined to the (0 0 1) plane at an angle of 2(2)° and 22(3)° from the shortest axis b, respectively. Both structures correspond to sine wave modulations. The amplitude of the q2 wave is mo=7.5(1) μB/Dy atom and that of q3 8.2(1) μB/Dy atom. The wave vector q2 when referring to the (a, 2b, c) cell and the wave vector q=(0, 0, 16) corresponds to a transversal modulation, which by a proper origin choice can be also described as an antiphase domain structure with two amplitudes. The moments point to the b-axis and are stacked in the sequence (+mo/2, −mo/2, −mo, −mo/2, +mo/2, +mo, …) along the c-direction, while tb acts as an antitranslation. For the q3 phase, the local moment value depends on the atom position in the wave. We also discuss the case where q3 and q2 act simultaneously in physical space.