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Record Id 29635
Title A Magneto-Elastic Model for the Relaxation of Lanthanide Ions in YBa(2)Cu(3)O(7-delta) Observed by Neutron Scattering
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Abstract The 4f eletrons attached to a lanthanide ion substituting Y in YBa(2)Cu(3)O(7-delta) are described with a crystal-field potential (symmetry D(2h)) and a magneto-elastic interaction, linear in the normal modes of vibration of the paramagnetic ion and anions. The most significant matrix elements of the interaction are determined using selection rules and wavefunctions for the crystal-field states. Applied to Tb(3+), Ho(3+) and Tm(3+), calculations for the ground state and the first excited state indicate that the dynamic properties of the lanthanide ions are adequately described by the simple addition of one crystal-field state, leading to a three-state model similar to the one introduced by Orbach for the interpretation of electron paramagnetic resonance signals from lanthanide ion in dilute concentration in a salt. The cross-section for inelastic scattering of neutrons by an ion is derived by constructing a pseudo-spin model (spin = 1) and treating the magneto-elastic interaction as a perturbation on the three crystal-field states. In the case of Tb(3+), the energy of the first excited state relative to the ground state is found to be very much smaller than the energy of any other state, the scattering of neutrons is thus a quasi-elastic process and the width in energy or, alternatively, the relaxation state is proportional to {exp (alpha/k(B)T) - 1} to the -1, where T is the temperature and alpha is the energy of the third, intermediate crystal-field state at which the density of phonon states is very significant. The value of alpha suggested by the calculation and the law predicted for the temperature dependence of the relaxation rate are in accord with measurements, on metallic and non metallic samples. An equally impressive account is given of data published on the relaxation rate of Ho(3+) in metallic YBa(2)Cu(3)O(7-delta), and the relaxation rate is predicted to be different from zero at zero temperature. The relaxation rate and cross-section for Tm(3+) are predicted to be significantly different from those for Tb(3+) and Ho(3+).
Organisation CCLRC
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Language English (EN)
Type Details URI(s) Local file(s) Year
Report RAL Technical Reports RAL-TR-1999-034. 1999. raltr-1999034.pdf 1999
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