23Na NMR study of sodium order in NaxCoO2 with 22K Neel temperature

Abstract

We report a systematic study of the $c$ lattice parameter in the Na${}_x$CoO${}_2$ phases versus Na content $x>0.5$, in which sodium always displays ordered arrangements. This allows us to single out the first phase which exhibits an AF magnetic order at a Néel temperature $T_N=$22 K which is found to occur for $x\approx 0.77(1)$. Pure samples of this phase have been studied both as aligned powders and single crystals. They exhibit identical ${}^{23}$Na NMR spectra in which three sets of Na sites could be fully resolved, and are found to display $T$ dependencies of their NMR shifts which scale with each other. This allows us to establish that the $T$ variation of the shifts is due to the paramagnetism of the Co sites with formal charge state larger than 3${}^{+}$. The existence of a sodium site with axial charge symmetry and the intensity ratio between the sets of ${}^{23}$Na lines permits us to reveal that the 2D structure of the Na order corresponds to 10 Na sites on top of a 13 Co sites unit cell, that is with $x=10/13\approx 0.77$. This structure fits with that determined from local density calculations and involves triangles of 3 Na sites located on top of Co sites (so called Na1 sites). The associated ordering of the Na vacancies is quite distinct from that found for $x<0.75$.

13 pages, 11 figures, 1 table, with small corrections of v1, accepted in Phys. Rev. B

References in corpus (11)

• Three-Dimensional Spin Fluctuations in Na0.75CoO2
• Evidence of a single nonmagnetic Co3+ state in the Na1CoO2 cobaltate
• Sodium vacancy ordering and the co-existence of localized spins and itinerant charges in NaxCoO2
• Electronic texture of the thermoelectric oxide Na0.75CoO2
• Spin correlations and cobalt charge states: A new phase diagram of sodium cobaltates
• Na ordering imprints a metallic kagome lattice onto the Co planes of Na2/3CoO2
• Direct link between low temperature magnetism and high temperature sodium order in NaxCoO2
• Na atomic order, Co charge disproportionation and magnetism in Na${}_x$CoO${}_2$ for large Na contents
• 59Co NMR evidence for charge and orbital order in the kagome like structure of Na2/3CoO2
• Crystal-to-stripe reordering of sodium ions in NaxCoO2 (x>=0.75)
• Strong correlations enhanced by charge-ordering in highly doped cobaltates

Cited by in corpus (11)

• Magnetism and Ion Diffusion in Honeycomb Layered Oxide K${}_2$Ni${}_2$TeO${}_6$: First Time Study by Muon Spin Rotation & Neutron Scattering
• Na order and Co charge disproportionation in Na${}_x$CoO${}_2$
• Evolution of Co charge disproportionation with Na order in Na${}_x$CoO${}_2$
• Interplay between Magnetism and Na concentration in $N{a}_{x}Co{O}_2$
• Synthesis of sodium cobaltate Na${}_x$CoO${}_2$ single crystals with controlled Na ordering
• Pinball liquid phase from Hund's coupling in frustrated transition metal oxides
• Multiorbital kinetic effects on charge ordering of frustrated electrons on the triangular lattice
• Ferrimagnetic ordering and spin entropy of field-dependent intermediate spins in Na0.82CoO2
• Exploring the possibility of enhancing the figure-of-merit ( $>$ 2) of Na${}_{0.74}$CoO${}_2$: A combined experimental and theoretical study
• Complex magnetic differentiation of cobalts in Na${}_x$CoO${}_2$ with 22K Néel temperature
• Hall effect evidence for an interplay between electronic correlations and Na order induced electronic bands topology in NaxCoO2