Three-dimensional spin fluctuations in Na0.75CoO2.
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.
Helme
L M
LM
Department of Physics, University of Oxford, Oxford OX1 3PU, United Kingdom.
Boothroyd
A T
AT
Coldea
R
R
Prabhakaran
D
D
Tennant
D A
DA
Hiess
A
A
Kulda
J
J