Evidence for SrHo$_2$O$_4$ and SrDy$_2$O$_4$ as model 1D J$_1$-J$_2$ zig-zag chain materials

This presentation will focus on the Ho and Dy members of the recently discovered Sr$R_2$O$_4$ family of frustrated rare-earth ($R$) materials. Despite the $R$ sites forming a honeycomb in the $ab$ plane, we demonstrate that the physics is dominated by 1D correlations in the $c$-direction and that these can be mapped onto the Ising $J_1$-$J_2$ spin chain model. Three-dimensional magnetic order is suppressed from $\theta_w$ = -16.9 K to T$_N$ = 0.66 K in SrHo$_2$O$_4$ and is not observed to 50 mK in SrDy$_2$O$_4$. Our neutron powder diffraction measurements indicate that prior to the 3D order in the SrHo$_2$O$_4$ compound a 1D magnetically correlated state exists and that a similar state is found at the lowest measured temperatures in SrDy$_2$O$_4$. Fits to the diffuse data allow us to identify the 1D nature of the material and the key structural motifs are found from the data collected in the long-range ordered phase of SrHo$_2$O$_4$. Point charge calculations are fitted to the inelastic neutron scattering data and identify a large Ising anisotropy. The combination of neutron scattering and novel modelling techniques has allowed us to unambiguously determine the magnetic structure, identify the key interactions in the system and understand the 1D nature of the system.