Observation of the crystal-electric-field excitations in the frustrated triangular metal RNiAl4Ge2 (R = Tb, Dy, Ho, Er).

Geometrical frustration suppresses conventional order and yields large ground-state degeneracy, enabling exotic magnetism. Metallic frustrated systems remain relatively unexplored: here long-range, oscillatory RKKY exchange combined with geometrical frustration can stabilize topological spin textures without DMI. We have grown high-quality layered triangular-lattice intermetallics RNiAl4Ge2 (R = Tb, Dy, Ho, Er), which exhibit multiple field/temperature-driven transitions and strong anisotropy, pointing to distinct crystal-electric-field (CEF) ground states across the series. We aim to use inelastic neutron scattering (INS) performed on MERLIN or MARI to map CEF excitations of rare earth ions and determine these materials single-ion Hamiltonians, thereby quantitatively linking single-ion anisotropy to the observed phase behavior