Antiferromagnetism and crystalline-electric field excitations in tetragonal NaCeO2.

We investigate the crystal structure, magnetic properties, and crystalline electric field of tetragonal, $I{4}_{1}/amd, \mathrm{Na}\mathrm{Ce}{\mathrm{O}}_{2}$. In this compound, ${\mathrm{Ce}}^{3+}$ ions form a tetragonally elongated diamond lattice coupled by antiferromagnetic interactions (${\mathrm{\ensuremath{\Theta}}}_{\mathrm{CW}}=\ensuremath{-}7.69$ K) that magnetically order below ${T}_{N}=3.18$ K. The ${\mathrm{Ce}}^{3+}\phantom{\rule{4pt}{0ex}}J=5/2$ crystalline electric field-split multiplet is studied via inelastic neutron scattering to parametrize a ${J}_{\mathrm{eff}}=1/2$ ground state doublet composed of states possessing mixed $|{m}_{z}\ensuremath{\rangle}$ character. Neutron powder diffraction data reveal the onset of $A$-type antiferromagnetism with $\ensuremath{\mu}=0.57(2){\ensuremath{\mu}}_{B}$ moments aligned along the $c$ axis. The magnetic structure is consistent with the expectations of a frustrated Heisenberg ${J}_{1}\ensuremath{-}{J}_{2}$ model on the elongated diamond lattice with effective exchange values ${J}_{1}g4{J}_{2}$ and ${J}_{1}g0$.