High energy spin dynamics of La2CuO4 and La1.9Sr0.1CuO4 |
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Authors: | N. Pyka L. Pintschovius A. Yu. Rumiantsev |
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Affiliation: | (1) Institut für Nukleare Festkörperphysik, Kernforschungszentrum Karlsruhe, Postfach 3640, W-7500 Karlsruhe, Federal Republic of Germany;(2) Kurchatov Institute of Atomic Energy, SU-123 182 Moscow, USSR |
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Abstract: | The magnetic excitations in La2CuO4 and La1.9Sr0.1CuO4 were studied by inelastic neutron scattering up to energies of 76 meV. For the pure sample, the results forE15 meV can be well described by conventional spin wave theory with a spin wave velocity c=0.89±0.07 eVÅ. For lower energies, the observed intensities were somewhat higher than expected from spin wave theory and did not follow the Bose-Einstein factor. For the doped sample, the linewidth in constant-E scans at smallE shows a very short correlation length of =7.5 Å only, which is considerably below the value expected from the concentration dependence reported by other authors. An increase of the linewidth for largeE indicates a reduced spin-wave stiffness when compared to the undoped material. However, the use of a spin-wave picture may not be appropriate as the standard expression for damped spin waves in a paramagnetic material is in serious conflict with experiment. |
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