Fragile ground state and rigid field-induced structures in the zigzag ladder compound BaDy2O4

We report on a sequence of field-induced transitions in the zigzag ladder compound ${\mathrm{BaDy}}₂{\mathrm{O}}₄$ studied with powder neutron diffraction and magnetization measurements. In agreement with the previously published results, the low-temperature zero-field structure is characterized by two half-integer propagation vectors ${\mathbf{k}}₁=[\frac{1}{2}\phantom{\rule{0.16em}{0ex}}0\phantom{\rule{0.16em}{0ex}}\frac{1}{2}]$ and ${\mathbf{k}}₂=[\frac{1}{2}\phantom{\rule{0.16em}{0ex}}\frac{1}{2}\phantom{\rule{0.16em}{0ex}}\frac{1}{2}]$. However, on application of an external magnetic field, the Bragg peaks corresponding to the zero-field structure lose their intensity rather rapidly and disappear completely in a field of 2.5 kOe. In the intermediate fields, 2.5 to 22.5 kOe, new peaks are observed characterized by the propagation vector ${\mathbf{k}}^{\ensuremath{'}}=[0\phantom{\rule{0.16em}{0ex}}0\phantom{\rule{0.16em}{0ex}}\frac{1}{3}]$ corresponding to an up-up-down (uud) structure as well $\mathbf{k}=0$ ferromagnetic peaks. This regime of fields corresponds to a pronounced plateau in the magnetization curve. Remarkably, the uud structure survives heating to at least 1.4 K, three times higher temperature than the ${T}_{\mathrm{N}}$ of 0.48 K for the zero-field structure. Above 22.5 kOe, the ${\mathbf{k}}^{\ensuremath{'}}$ peaks disappear while the $\mathbf{k}=0$ peaks gain significant intensity indicating an increase in the polarization of the system. The analysis of the intensities of the field-induced reflections allows for a clear identification of the magnetic structures in both the intermediate- and high-field regimes.