Unraveling the magnetic ground-state in alkali-metal lanthanide oxide Na${}_2$PrO${}_3$

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 Na${}_2$PrO${}_3$. $\mu$SR reveals Néel antiferromagnetic order below $T_{\mathrm{N}}\sim 4.9$ K, with a small static magnetic moment $m_{\mathrm{static}}\le 0.22$~${\mu }_{\mathrm{B}}/\mathrm{Pr}$ collinearly aligned along the $c-$axis. Inelastic neutron measurements reveal the full spectrum of crystal field excitations and confirm that the Pr${}^{4+}$ ground state wave function deviates significantly from the ${\Gamma }_7$ limit relevant to the Kitaev model. Single and two magnon excitations are observed in the ordered state below $T_N=4.6$ K and are well described by non-linear spin wave theory from the Néel state using a magnetic Hamiltonian with Heisenberg exchange $J=1$ meV and symmetric anisotropic exchange $\Gamma /J=0.1$, corresponding to an XY model. Intense two magnon excitations are accounted for by $g$-factor anisotropy $g_{\mathrm{z}}/g_{\pm }=1.29$. A fluctuating moment $\delta m^2=0.57(22)$ ${\mu }_{\mathrm{B}}^2/\mathrm{Pr}$ 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 $g_{\mathrm{avg}}\approx 1.1$. Together, the results demonstrate that the small moment in Na${}_2$PrO${}_3$ arises from crystal field and covalency effects and that the material does not exhibit significant quantum fluctuations..

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Cited by in corpus (3)

• Exploring rare-earth Kitaev magnets by massive-scale computational analysis
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• Magnetic behavior of the $5d^1$ Re-based double perovskite Sr${}_2$ZnReO${}_6$