Revisiting the A -type antiferromagnet NaNiO2 with muon spin rotation measurements and density functional theory calculations

An $A$-type antiferromagnet, ${\mathrm{NaNiO}}_2$, was examined by means of positive muon spin rotation and relaxation (${\mu }^{+}\mathrm{SR}$) measurements and first-principles calculations based on a density functional theory (DFT). Below $T_{\mathrm{N}}=20$ K, a clear muon spin precession signal was observed in the ${\mu }^{+}\mathrm{SR}$ time spectrum recorded under zero field, due to the formation of a static internal magnetic field. The microscopic origin of such an internal field was computed as a sum of dipolar and hyperfine contact fields at the site (0.624, 0, 0.854), where both the muon site and the local spin density at such a site were predicted with DFT calculations. While the computed values were consistent with experimentally obtained ones, in both the antiferromagnetic and the paramagnetic states, the contribution of the hyperfine contact field was shown to be insignificant even below $T_{\mathrm{N}}$. Finally, measurements at higher temperatures signified thermally activated Na-ion diffusion with $E_{\mathrm{a}}=50\left(20\right)$ meV and $D_{\mathrm{Na}}\left(300\mathrm{K}\right)=8.8\times {10}^{-11}{\mathrm{cm}}^2$/s, commonly observed in layered-type compounds.