Three-dimensional spin fluctuations in Na0.75CoO2 |
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Authors: | Helme L M Boothroyd A T Coldea R Prabhakaran D Tennant D A Hiess A Kulda J |
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Affiliation: | Department of Physics, University of Oxford, Oxford OX1 3PU, United Kingdom. |
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Abstract: | We report polarized- and unpolarized-neutron scattering measurements of magnetic excitations in single-crystal Na0.75CoO2. The data confirm ferromagnetic correlations within the cobalt layers and reveal antiferromagnetic correlations perpendicular to the layers, consistent with an A-type antiferromagnetic ordering. The magnetic modes propagating perpendicular to the layers are sharp, and reach a maximum energy of approximately 12 meV. From a minimal spin-wave model, containing only nearest-neighbor Heisenberg exchange interactions, we estimate the interlayer and intralayer exchange constants to be 12.2+/-0.5 meV and -6+/-2 meV, respectively. We conclude that the magnetic fluctuations in Na0.75CoO2 are highly three dimensional. |
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