Volume 49, Number 1, January I 2000
|Page(s)||99 - 104|
|Section||Condensed matter: electronic structure, electrical, magnetic, and optical properties|
|Published online||01 September 2002|
Effect of glassy topological disorder on low-energy magnetic excitations
Dipartimento di Fisica and Istituto Nazionale di Fisica della
Materia Università di Messina -
Contrada Papardo, Salita Sperone 31 I-98166, S. Agata (ME ), Italy
2 Dipartimento di Fisica and Istituto Nazionale di Fisica della Materia Università di Trento - 38050 Povo (TN ), Italy
3 School of Physics, University of Bath - Claverton Down, Bath, UK
Accepted: 25 October 1999
A comparative study of specific-heat and low-frequency Raman scattering at low temperatures of lanthanide metaphosphate glasses and pentaphosphate single crystals has revealed the presence of low-energy magnetic excitations. In an analogous manner to that found for vibrational modes, topological disorder softens the crystal field magnetic excitations, producing a broad band of low-energy states with a low-energy tail. A self-consistent data analysis using a broad Gaussian distribution of singlet-singlet excitations allows a complete interpretation in Pr glass, which exhibits strong magnetic effects in the temperature range explored. This distribution is used to evaluate the magnetic contribution to the specific heat; about one-fifth of the magnetic ions are characterised by singlet-singlet states with very low energies and contribute to the magnetic entropy.
PACS: 75.40.-s – Critical-point effects, specific heats, short-range order / 75.50.-y – Studies of specific magnetic materials / 78.30.-j – Infrared and Raman spectra
© EDP Sciences, 2000
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