Magnetische Neutronenstreuexperimente zum Relaxationsverhalten von Zwischenvalenten Seltene- Erd-Verbindungen

Neutron scattering measurements with energy analysis were performed on the intermediate valence(IV) compounds CePd$_{3}$, CeSn$_{3}$, CeBe$_{13}$, CeCu$_{2}$Si$_{2}$, TmSe, and YbCu$_{2}$Si$_{2}$ for different scattering angles. The isostructural diamagnetic compounds with Lanthanum or Yttrium, instead of the rare earth, were used as reference samples with no 4f-shell. The paramagnetic compounds with Terbium or Holmium were measured as reference systems with a stable 4f-shell. The experimental results are: (a) Magnetic scattering which was consistent with a 4f-formfactor could clearly be detected for an IV-system. (b) The quasielastic magnetic scattering has an anomalously large line width (e.g. 20 meV for CePd$_{3}$ and 6 meV for YbCu$_{2}$Si$_{2}$) , which is nearly temperature independent. Below a certain temperature Tsp the line width r/2 becomes largerthan the thermal energy k$_{B}$T. Therefore it is now a fact that the anomalies in the static susceptibility of an IV-compound do not depend on some complicated magnetic structures or crystal-field singuletts. Because of the anomalously large line width these anomalies must be due to a very fast relaxation process. (c) The quasielastic line width of the paramagnetic reference compound is about two orders of magnetude smaller than those of the IV-compounds. (d) The scattering intensities are in accordance with a broken valence. These results are interpreted by a temperature independent quantummechanical valence-fluctuation