Coexistence of magnetic fluctuations and long-range order in the one-dimensional J1-J2 zigzag chain materials BaDy2 O4 and BaHo2 O4

Abstract

The compounds BaDy2O4 and BaHo2O4 are part of a family of frustrated systems exhibiting interesting properties, including spin-liquid-type ground states, magnetic-field-induced phases, and the coexistence of short- and long-range magnetic order, with dominant one-dimensional correlations, which can be described as Ising J1-J2 zigzag chains along the c axis. We have investigated polycrystalline samples of BaDy2O4 and BaHo2O4 with both neutron diffraction and neutron spectroscopy, coupled to detailed crystalline electric field calculations. The latter points to site-dependent anisotropic magnetism in both materials, which is corroborated by the magnetic structures we determined. The two systems show the coexistence of two different long-range orders: two double Néel ↑↑↓↓ orders in the ab plane with propagation vectors k1=(12,0,12) and k2=(12,12,12) for BaDy2O4, and two distinct arrangements of simple Néel ↑↓↑↓ orders along the c axis, both with the propagation vector k0=(0,0,0) for BaHo2O4. The order for both wave vectors in BaDy2O4 occurs at TN=0.48K, while in BaHo2O4 the first order sets in at TN∼1.3K and the second one has a lower ordering temperature of 0.84 K. Both compounds show extensive diffuse scattering which we successfully modeled with a one-dimensional axial next-nearest neighbor Ising (ANNNI) model. In both materials, strong diffusive scattering persists to temperatures well below where the magnetic order is fully saturated.