Fragile ground state and rigid field-induced structures in the zigzag ladder compound BaDy_2O_4

摘要

We report on a sequence of field-induced transitions in the zigzag ladder compound BaDy_2O_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 k-1 = [1/2 0 1/2] and k-2 = [1/2 1/2 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 k' = [00 1/3] corresponding to an up-up-down (uud) structure as well 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_N of 0.48 K for the zero-field structure. Above 22.5 kOe, the k' peaks disappear while the 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.