MAGNETIC EXCITATIONS IN RARE-EARTH-BASED HIGH-TEMPERATURE SUPERCONDUCTORS

The unique character of inelastic neutron scattering in the study of m agnetic excitations of rare-earth-containing high-temperature supercon ductors is summarized. It is exemplified for single-ion, cluster and c ollective magnetic excitations which are directly related to the funda mental interactions associated with the rare-earth sublattice. Crystal line-electric-field and cluster excitations are discussed for HoxY1-xB a2Cu3O7 which provide information on the electrostatic potential and t he magnetic pair coupling at the rare-earth site, respectively. The st udy of collective magnetic excitations in both grain-aligned samples ( HoBa2Cu3O7) and single crystals (Nd2-xCexCuO4) yields more detailed in formation on the exchange coupling. In particular, we show how Ce dopi ng affects the spin-wave dispersion of Nd2CuO4, i.e., a strong softeni ng of the excitation spectra is observed which explains the huge Somme rfeld coefficients in Nd2-xCexCuO4 (x > 0.1).