Magnetic properties and signatures of ordering in triangular lattice antiferromagnet KCeO₂

The magnetic ground state and the crystalline electric field level scheme of the triangular lattice antiferromagnet ${\text{KCeO}}_2$ are investigated. Below $T_N=300$ mK, ${\text{KCeO}}_2$ develops signatures of magnetic order in specific heat measurements and low energy inelastic neutron scattering data. Trivalent ${\text{Ce}}^{3+}$ ions in the $D_{3d}$ local environment of this compound exhibit large splittings among the lowest three $4f^1$ Kramers doublets defining for the free ion the $J=5\text{/}2$ sextet and a ground state doublet with dipole character, consistent with recent theoretical predictions in M. S. Eldeeb et al. Phys. Rev. Materials 4, 124001 (2020). An unexplained, additional local mode appears, and potential origins of this anomalous mode are discussed.