Degree Type


Date of Award


Degree Name

Doctor of Philosophy


Physics and Astronomy


Over the past several years there have been considerable interest in materials exhibiting a nonintegral valence. As a result, the properties of cerium metal and its compounds have been the subject of many theoretical and experimental studies. In the present work the electronic and lattice dynamical properties of CeSn(,3) were investigated using the powerful techniques of neutron spectroscopy. The electronic properties of this compound were studied using polarized neutrons and its dynamical properties were investigated by inelastic neutron scattering techniques;In the polarized neutron study the field induced magnetization in CeSn(,3) was found to be of 4f electronic character in the 40-300K temperature range. On the other hand, below 40K the experimental results could be explained by assuming a 4f-5d mixed electronic character for the induced magnetization of this compound. Therefore, the polarized neutron experiments provided directed evidence for the mixed-valent character of this compound. The 5d component of the magnetization density was found to be of e(,g) symmetry and it could account, at least partly, for the increase in the magnetic susceptibility of CeSn(,3) at low temperatures. In a simple model advanced by S. Liu and collaborators, the 4f level is positioned slightly above the Fermi energy and is hybridized with the conduction band. This model gives rise to a magnetic susceptibility of CeSn(,3) exhibiting roughly the main characteristics of the measured susceptibility. Moreover, it predicts a nearly equal mixture of the 4f and conduction band wavefunctions at the Fermi level in quite good agreement with the polarized neutron experiment;In the inelastic neutron scattering experiment the phonon dispersion curves of CeSn(,3) and LaSn(,3) along the 100, 110 and 111 symmetry directions were measured. Anomalously soft modes of CeSn(,3), as compared with the dispersion curves of LaSn(,3), were observed close to the zone boundary in the 111 symmetry direction. These anomalies can be understood qualitatively as a result of the Ce 4f () 5d electronic transitions in CeSn(,3) induced by the nuclear motion in the phonon modes. Recently phonon anomalies have also been observed in another mixed valence system Sm(,.75)Y(,.25)S. Thus, the inelastic neutron experimental results show that the electron-phonon coupling in these systems is quite significant. In addition, from the comparison of the lattice specific heat of CeSn(,3) obtained in the present measurements with total specific heat measurements, it is clear that the electronic contribution is very large ((gamma) (DBLTURN) 84 mJ/mole-K('2)). This implies a large density of states at the Fermi level, as expected if the 4f level is close to the Fermi level.



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Chun-Keung Loong



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227 pages