LOW-ENERGY MAGNETIC EXCITATIONS IN THE PR METAPHOSPHATE GLASS

Large magnetic contributions to the low-temperature specific heats of rare-earth metaphosphate (R2O3)(0.25)(P2O5)(0.75) glasses have been ob served. These effects result from electronic transitions between 4f le vels multiply split due to local disorder, which also give rise to a s trong electronic contribution to the low-frequency Raman scattering at low temperatures in the Pr metaphosphate glass. By contrast Sm and Gd metaphosphate glasses show the usual spectral features for a glass: t he quasielastic scattering and the boson peak. Both the thermal and op tical characteristics in the Pr glass are associated with a very large density of low-lying magnetic excitations, induced by the topological disorder. Using the electronic low-frequency Raman scattering at 1.5 K, which reflects this high density of low-energy states, it has prove d possible to fit the magnetic contribution to the low-temperature spe cific heat in the Pr glass.