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arXiv · 2407.12935

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

Ifeanyi John Onuorah·Jonathan Frassineti·Qiaochu Wang·Muhammad Maikudi Isah·Pietro Bonfa·Jeffrey G. Rau·J. A. Rodriguez-Rivera·A. I. Kolesnikov·Vesna F. Mitrovic·Samuele Sanna·Kemp W. Plumb
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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 N\'eel antiferromagnetic order below $T_{\rm N}\! \sim\! 4.9$ K, with a small static magnetic moment $m_{\rm static}\!\leq \! 0.22$~$\mu_{\rm B}/{\rm Pr}$ 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 N\'eel 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 $\delta m^2 = 0.57(22)$ $\mu_{\rm B}^2/{\rm Pr}$ 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 $g_{\rm avg}\approx 1.1$. 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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Ifeanyi John Onuorah, Jonathan Frassineti, Qiaochu Wang, Muhammad Maikudi Isah, Pietro Bonfa, Jeffrey G. Rau, J. A. Rodriguez-Rivera, A. I. Kolesnikov, Vesna F. Mitrovic, Samuele Sanna, Kemp W. Plumb. 2024-07-17. Unraveling the magnetic ground-state in alkali-metal lanthanide oxide Na$_2$PrO$_3$. https://doi.org/10.1103/physrevb.110.064425

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