Complex magnetic differentiation of cobalts in Na x CoO2 with 22 K Néel temperature

Mukhamedshin, I. R.; Gilmutdinov, I. F.; Salosin, M. A.; Alloul, H.

doi:10.1134/s0021364014080116

Cited by 8 publications

(18 citation statements)

References 15 publications

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“…The existence of such a T 2 differentiation in the T N = 22 K phase has already been demonstrated in Ref. 15 and can be seen in Appendix A (Fig. 5 and Fig.…”

Section: IIImentioning

confidence: 67%

“…15 In all studied samples at least six sets of Co quadrupolar satellite lines could be distinguished by their ν Q values. For each Co site the largest splitting between satellites is observed when H c, which evidences that the principal axis Z of the EFG tensor is close to the crystallographic c axis for all cobalts.…”

Section: Co1mentioning

confidence: 99%

“…From the 23 Na NMR study we could characterize the Na in plane order and could as well evidence by 59 Co NMR the existence of at least six Co sites, three of them with quite distinct magnetic properties. 15 This large number of sites opens a quite interesting situation permitting to search for the correlation of the Co charge order with the magnetic properties. For that we need to get accurate determinations of the quadrupole data on each of the Co sites in order to try to distinguish the contributions to the EFG of the static and mobile charges.…”

Section: 11mentioning

confidence: 99%

“…Using an electrochemical Na de-intercalation method we reduced the sodium content in the as-grown crystals down to that of the pure phase with 22 K Néel temperature and x ≈ 0.77. 15 One of them was used in this studybelow we quote it as single crystal SC4. The 59 Co NMR measurements were done using homebuilt coherent pulsed NMR spectrometers.…”

Section: Samples and Experimental Techniquesmentioning

confidence: 99%

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Evolution of Co charge disproportionation with Na order inNaxCoO2

et al. 2014

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59Co NMR experiments have been performed on single crystals of the layered cobaltate NaxCoO2 with x=0.77 which is an antiferromagnet with Néel temperature TN = 22 K. In this metallic phase six Co sites are resolved in the NMR spectra, with distinct quadrupole frequencies νQ, magnetic shifts KZZ and nuclear spin lattice relaxation rates 1/T1. Contrary to the x = 1/2 or x = 2/3 phases the 3D stacking of the Na planes is not perfect for x = 0.77 but this does not influence markedly the electronic properties. We evidence that the magnetic and charge properties of the Co sites are highly correlated with each other as KZZ and (1/T1) 1/2 scale linearly with νQ. The data analysis allows us to separate the contribution ν latt Q of the ionic charges to νQ from that ν el Q due to the hole orbitals on the Co sites. We could extend coherently this analysis to all the known phases in the Na cobaltate phase diagram. The variation with x of ν latt Q is found to fit rather well numerical computations done in a point charge model. The second term ν el Q allowed us to deduce the hole concentration on the cobalts. These detailed experimental results should stimulate theoretical calculations of the electronic structure involving both the Co orbital configurations and DMFT approaches to take into account the electronic correlations.

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“…The existence of such a T 2 differentiation in the T N = 22 K phase has already been demonstrated in Ref. 15 and can be seen in Appendix A (Fig. 5 and Fig.…”

Section: IIImentioning

confidence: 67%

Section: Co1mentioning

confidence: 99%

Section: 11mentioning

confidence: 99%

Section: Samples and Experimental Techniquesmentioning

confidence: 99%

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Evolution of Co charge disproportionation with Na order inNaxCoO2

et al. 2014

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“…39 Using an electrochemical Na de-intercalation method, we reduced the sodium content in the as-grown crystals down to that of the pure phase with x = 2/3. In the inset of Fig.…”

Section: Methodsmentioning

confidence: 99%

Origin of electron disproportionation in metallic sodium cobaltates

et al. 2016

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Recently the unusual metallic state with a substantially non-uniform distribution of a charge and magnetic density in CoO2 planes was found experimentally in the NaxCoO2 compound with x > 0.6. We have investigated an origin of such electron disproportionation in the lamellar sodium cobaltates by calculating the ion states as a function of a strength of the electron correlations in the d(Co)-shells within the GGA+U approximation for the system with a realistic crystal structure. It was found that the nonuniformity of spin and charge densities are induced by an ordering of the sodium cations and enhanced correlations. Two important magnetic states of cobalt lattice competing with each other at realistic values of the correlation parameter were found -low spin hexagons (LS) and higher spin kagome lattice (HS-KSL). In the heterogeneous metallic HS-KSL phase magnetic Co ions form a kagomé structure. In LS phase the kagomé pattern is decomposed into hexagons and Co ions possess minimal values of their spin. Coexistence of these states could explain the emergence of the disproportionation with the peculiar kagomé structure experimentally revealed in previous studies of the cobaltates.

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Synthesis of sodium cobaltate NaxCoO2 single crystals with controlled Na ordering

Gilmutdinov

Mukhamedshin

Rullier‐Albenque

et al. 2018

Journal of Physics and Chemistry of Solids

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In this study, we synthesized single crystals of Na x CoO 2 with x ~ 0.8 using the optical floating zone technique. A thorough electrochemical treatment of the samples permitted us to control the de-intercalation of Na to obtain single crystal samples of stable Na ordered phases with x = 0.5-0.8. Comparisons of the bulk magnetic properties with those observed in the Na ordered powder samples confirmed the high quality of these single crystal phases. The ab plane resistivity was measured for the Na ordered samples and it was quite reproducible for different sample batches. The data were analogous to those found in previous initial experimental studies on single crystals, but the lower residual resistivity and sharper anti-ferromagnetic transitions determined for our samples confirmed their higher quality.

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Complex magnetic differentiation of cobalts in Na x CoO2 with 22 K Néel temperature

Cited by 8 publications

References 15 publications

Evolution of Co charge disproportionation with Na order inNaxCoO2

Evolution of Co charge disproportionation with Na order inNaxCoO2

Origin of electron disproportionation in metallic sodium cobaltates

Synthesis of sodium cobaltate NaxCoO2 single crystals with controlled Na ordering

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