Abstract
The antiferromagnetic ordering temperatures of the rare earth (RE) moments in RE Ba2 Cu3O7-gd, obtained from specific heat measurements, are roughly in agreement with the de Gennes factors, i.e., the ordering mechanism can be mainly seen as an indirect spin-spin exchange. However, the oxygen dependence of T N is found to be reversed for the light rare earths compared to the heavy rare earths. As origin for this systematic observation an indirect interaction between the 3d-moments of copper and the 4f-moments of rare earths is discussed as a second order effect. Such an interaction is supported by measurements of the 4f relaxation behavior on the Nd 1: 2: 3 cuprates by inelastic magnetic neutron scattering. Here, the usual thermally driven increase of the magnetic relaxation rate is suppressed up to about 80 K. This correlates with the appearance of a spin gap found by Rossat- Mignod in YBa2Cu3O7 and therefore the 3d-4f coupling can be understood as an interaction of the 4f moments with a spin-fluctuation exchange in the CuO2 planes. Furthermore, the quasielastic magnetic response has a Gaussian contribution at temperatures below 100 K, i.e., much above the long ranged ordering temperatures T N. Magnon-like excitations appear already at slightly larger temperatures than T N. In addition the paramagnetic inelastic spectra show only little dependence of the crystal field scheme on the oxygen concentration.
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Drößler, H., Jostarndt, HD., Harnischmacher, J. et al. Magnetic interactions between Copper and RE in RE Ba2Cu3O7-δ . Z. Phys. B - Condensed Matter 100, 1–11 (1996). https://doi.org/10.1007/s002570050086
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DOI: https://doi.org/10.1007/s002570050086