X-ray and neutron scattering

Abstract:

Lovesey and Staub have argued [S.W. Lovesey and U. Staub, Phys. Rev. B 61, 9130 (2000)] that experimental data on the temperature dependence of the paramagnetic relaxation of lanthanide ions doped into YBa2Cu3O6+x are in agreement with the predictions of a model that describes the relaxation as due to the scattering of phonons via a magnetoelastic interaction. By generalizing their model I show that the level of agreement is strongly dependent on the number of intermediate lanthanide energy levels included in the calculation, and that inclusion of a more complete set of levels leads to very different results that do not necessarily support the phonon damping picture.

Abstract:

The dispersion of the low-energy magnetic excitations of the Pr sublattice in PrBa(2)Cu(3)O(6.2) is determined by inelastic neutron scattering measurements on a single crystal. The dispersion, which shows the effect of interactions with the Cu spin waves, is well described by a model of the coupled Cu-Pr magnetic system. This model enables values for the principal exchange constants to be determined. The results suggest that both Pr-Pr and Cu-Pr interactions are important in producing the anomalously high ordering temperature of the Pr sublattice. Measurements of the Cu optic spin wave mode show that the interlayer Cu-Cu exchange is significantly lower than in YBa(2)Cu(3)O(6.2).