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UNIVERSITY OF BUCHAREST
FACULTY OF PHYSICS Guest
2024-11-22 2:18 |
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Conference: Bucharest University Faculty of Physics 2010 Meeting
Section: Atomic and Molecular Physics; Astrophysics
Title:
Study of the Kramers rare earth ions ground multiplet by EPR spectroscopy at multiple frequencies and high fields
Authors:
F. Popescu (1), V. Bercu (1), J.N. Barascu (1)(3), M. Martinelli (2), C.A. Massa (2), L.A. Pardi (2), M. Stefan (3), S.V. Nistor (3), M. Nikl (4)
Affiliation:
(1) University of Bucharest, Magurele, RO-077125, Bucharest, Romania
(2) IPCF-CNR, via G.Moruzzi 1, I-56124 Pisa, Italy
(3) National Institute of Materials Physics, POB MG-7, Bucharest-Magurele, RO-077125, Romania
(4) Institute of Physics AS CR, Cukrovarnicka 10, CZ-16200 Prague 6, Czech Republic
E-mail
vbercu@gmail.com
Keywords:
Rare earth ions; Crystal field splitting; Electron paramagnetic resonance
Abstract:
The recent availability of high magnetic field has prompted the use of higher frequencies. The HF EPR spectra in comparison with the conventional EPR spectra exhibit interesting high field effects that could have important applications. For example, the multifrequency HF − EPR spectroscopy is a suitable method for analyzing the ground multiplet and the local site symmetry in solids of the Kramers rare earths ions (RE 3+) with a large orbital contribution. Usually, the crystal (ligand) field splitting (CFS) of the ground multiplet of the RE 3+ ions is of tens or hundreds cm -1. Up to now, information concerning these CFS could be obtained from the investigation of the infrared (IR) and optical spectra only in an incomplete manner. Moreover, the IR and optical spectra alone cannot usually distinguish clearly between different local site symmetries in solid matrices, associated with the presence of neighboring defects. The great advantage of the EPR spectroscopy resides in the possibility to distinction between these different local site symmetries. For RE 3+ ions at low temperatures, the conventional EPR spectroscopy detects signals attributed to transitions within the lowest-lying doublet of the ground multiplet and the EPR spectra are well described by a fictitious spin one-half. At such low frequency, no information concerning the value of the CFS of the ground multiplet can usually be derived. However, such information can be obtained from HF-EPR spectra. The mixing by the large Zeeman interaction of some of the upper-lying doublets of the ground multiplet into the lowest-lying doublet states makes the diagonal values of the effective g matrix (corresponding to the Zeeman interaction of the lowest doublet of the ground multiple), to be frequency dependent at high fields. In addition, for axial local site symmetries, the HF EPR spectra of the RE 3+ ions exhibit unlike the conventional EPR spectra, an azimuthal angular dependence. This high-field effect makes a clear distinction among different axial local site symmetries.
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