Abstract
A comprehensive set of muon spin spectroscopy and neutron scattering measurements supported by ab initio and model Hamiltonian simulations have been used to investigate the magnetic ground state of Na2PrO3. 𝜇SR reveals a Néel antiferromagnetic order below 𝑇𝑁∼4.9K, with a small static magnetic moment 𝑚static≤0.22𝜇B/Pr collinearly aligned along the 𝑐 axis. Inelastic neutron measurements reveal the full spectrum of crystal field excitations and confirm that the Pr4+ ground-state wave function deviates significantly from the Γ7 limit that is relevant to the Kitaev model. Single- and two-magnon excitations are observed in the ordered state below 𝑇𝑁=4.6K and are well described by nonlinear spin wave theory from the Néel state using a magnetic Hamiltonian with Heisenberg exchange 𝐽=1meV and symmetric anisotropic exchange Γ/𝐽=0.1, corresponding to an 𝑋𝑌 model. Intense two magnon excitations are accounted for by 𝑔-factor anisotropy 𝑔z/𝑔±=1.29. A fluctuating moment 𝛿𝑚2=0.57(22)𝜇2B/Pr extracted from the energy and momentum integrated inelastic neutron signal is reduced from expectations for a local 𝐽=1/2 moment with average 𝑔 factor 𝑔avg≈1.1. Together, the results demonstrate that the small moment in Na2PrO3 arises from crystal field and covalency effects and the material does not exhibit significant quantum fluctuations.
