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Master's Dissertation
DOI
10.11606/D.54.1983.tde-18042007-120859
Document
Author
Full name
Alberto Tannus
Institute/School/College
Knowledge Area
Date of Defense
Published
São Carlos, 1983
Supervisor
Committee
Carvalho, Rene Ayres (President)
Barberis, Gaston Eduardo
Oliveira, Luiz Nunes de
Title in Portuguese
Medidas de tempos de relaxação spin-rede em cristais mistos de halogenetos alcalinos.
Keywords in Portuguese
Dicroismo circular
Magneto óptica
Relaxação
Abstract in Portuguese
Neste trabalho, utilizando técnicas magneto-ópticas, estudamos tempos de relaxação spin-rede (T1) do estado fundamental de centros 'F' e, cristais de halogenetos alcalinos (KCl-KBr). Descrevemos um sistema semi-automático para medidas ópticas de T1, capaz de medir tempos de relação curtos (~1mS), baseado na medida do Dicroísmo Circular magnético (DCM) que apresentam aqueles sais quando portadores de centros paramagnéticos. Obtivemos a dependência de T1 com o campo magnético H (até 65 Kgauss), bem como os espectros de DCM para diferentes concentrações nas matrizes mistas. Uma teoria desenvolvida por Panepucci e Mollenauer (1) para matrizes puras, foi adaptadas para explicar a relaxação spin-rede nos cristais mistos. Os resultados obtidos para o processo direto (T~2.0 K), confrontados com auqela teoria, mostram que o mecanismo de relaxação dominante até 25 KGauss continua sendo a modulação por fônons da interação hiperfins entre o elétron 'F' e os núcleos vizinhos.
Title in English
Spin-lattice relaxation measurements on mixed crystals of alkali halides.
Keywords in English
Circular dichroism
Magneto-optics
Relaxation
Abstract in English
Using magneto-optic techniques we have studied the ground state spin- lattice relaxation times (T1) of 'F' centers in mixed Alkali Halide cristals (KCl-KBr). We describe a computer assisted system to optically measure short relaxation times (~1mS). The technique is based on the measurement of the Magnetic Circular Dicroism (MCD) presented by F centers. We obtained the T1 magnetic field dependency at 2 K up to 65 kGauss), as well as the MCD spectra for different relative concentration at the mixed matrices. The theory developed by Panepucci and Mollenauer for F centers spin-lattice relaxation in pure matrices was modified to explain the behavior of T1 in mixed cristais. The Direct Process results (T~2.0 K) compared against that theory shows that the main relaxation mecanism, Up to 25 kGauss, continues to be phonon modulation of the hyperfine interaction between 'F' electrons and surrounding nuclei.
 
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Tannus.pdf (3.78 Mbytes)
Publishing Date
2007-04-19
 
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