Structural investigation of REMgAl11O19 (RE = Ce, Pr, Nd, La) triangular lattice antiferromagnets.

We propose T-dependent NPD measurements on the GEM diffractometer at ISIS to investigate structural disorder in the triangular-lattice hexaaluminates REMgAl₁₁O₁₉ (RE = Ce, Pr, Nd, La). These are promising quantum spin liquid (QSL) candidates, due to their layered rare-earth geometry and effective S = ½ ground states. However, accurate determination of the crystal structure—including site disorder and local symmetry—is critical for interpreting their magnetic properties.

Recent studies suggest structural distortions in PrMgAl₁₁O₁₉ lead to a splitting of its non-Kramers doublet, favoring transverse-field Ising physics over a true QSL. Moreover, multiple members of this series exhibit partial rare-earth site occupancy and dynamic Al site disorder, which may significantly influence the magnetic properties.

Neutron diffraction is essential to resolve these subtle structural features( REO₁₂ cages and Al disorder). GEM’s high flux, resolution, and Q-range make it ideal for capturing temperature-dependent changes in atomic positions and displacement parameters.

We request four days of beamtime to study structural evolution from base temperature to 300 K across all four compositions. Rietveld refinement of these data will support ongoing magnetic characterization and modeling, helping to clarify the role of structure in stabilizing exotic ground states in rare-earth triangular antiferromagnets.