Lattice Modulation Induced by Magnetic Order in DyZn₂

DyZn₂ has an orthorhombic CeCu₂-type structure. Between 29 K and the Néel temperature of 35 K, the magnetic structure is that of sinusoidal modulation characterized by a wavevector q_m=ζ_mc*, where ζm is approximately 0.45 (MAF). The magnetic moments are parallel to the b-axis and, hence, the modulation is transverse. Below 29 K, the wavevector is 0.5c* and the compound is a simple antiferro magnet. On this study, X-ray diffraction measurements were carried out on a single crystal of DyZn₂. There is an anomaly in the thermal expansion at the Néel temperature, and satellite peaks were observed at 2q_m in the MAF phase. The amplitude of the lattice modulation u was observed to depend on ζ_m. The fact that the lattice modulation has wavevector 2q_m has been examined on the basis of a model which takes into account modifications of the exchange interactions due to atomic displacements. Furthermore, the same model can explain the change of the thermal expansion. Measurements in magnetic fields up to 1.4 T were also performed. A new satellite peak was observed at (0 0 6+ζ_m) in fields. The appearance of the new satellite peak is expected by the model. The magnetic phase diagram was determined by measurements of satellite peaks at various temperatures and magnetic fields.