Frustration and low-dimensional physics in SrR2O4 – Amy Poole, PSI, Switzerland

This presentation will focus on frustrated rare earth materials and, in particular the Ho and Dy members of the recently discovered SrR₂O₄ family of frustrated rare-earth (R) materials. Frustrated magnetic materials in general are systems in which the competi- tion between interactions prevents the system from having a non-degenerate ground state. This competition can either be due to a large number of random interactions, such as those found in a spin glass or, as found in geometrically frustrated materials, a few local equivalent interactions. Often these systems can be described by a simple model of the local interactions, but can give rise to complexity and exotic quasi-particle excitations in the bulk.

Due to the frustrated arrangement of the R ions in SrR₂O₄ three-dimensional magnetic order is suppressed occurring only at T_N = 0.66 K in SrHo₂O₄ and is not observed to 50 mK in SrDy₂O₄. Our neutron powder diffraction measurements indicate that prior to the 3D order in the SrHo₂O₄ compound a 1D magnetically correlated state exists and that a similar state is found at the lowest measured temperatures in SrDy₂O₄. The correlation lengths of the 1D fluctuations have been extracted from neutron powder scattering data and, from fits to the 3D magnetic order found in the Ho analogue, the local correlations can be understood to have an up-up-down-down arrangement (↑↑↓↓) as expected in the ground state of a J₁-J₂ spin chain model. The local Ising anisotropy was determined with an electrostatic point charge model that was used to fit crystal field excitations found with inelastic neutron scattering measurements. The combination of the strong local anisotropy and the low dimensional scattering strongly suggest that these materials are realisations of the Ising J₁-J₂ spin chain model at the classical limit.