Theoretical studies of spin dynamics in paramagnets.
Item
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Title
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Theoretical studies of spin dynamics in paramagnets.
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Identifier
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AAI3278409
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identifier
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3278409
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Creator
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Calero Borrallo, Carlos.
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Contributor
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Adviser: Eugene M. Chudnovsky
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Date
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2007
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Language
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English
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Publisher
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City University of New York.
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Subject
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Physics, Condensed Matter | Physics, Electricity and Magnetism | Physics, Molecular
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Abstract
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This thesis deals with problems of spin relaxation in solids, mostly in application to quantum dots and molecular magnets.;Spin-phonon effects are investigated by using a symmetry-based approach that is free of fitting parameters. This approach is developed for molecular magnets and for quantum dots. For both systems, two processes are considered: Direct processes, which involve spin transitions accompanied by the emission or absorption of one phonon, and Raman processes, in which the spin transition is accompanied by the absorption of a phonon and the emission of another phonon of different frequency. Relaxation rates are obtained analytically for both mechanisms and evaluated for various temperature ranges.;The effect of acoustic waves on the magnetization dynamics of crystals built of rigid spin clusters is analyzed. Coupled equations of motion for spins and sound are derived and the possibility of strong resonant magneto-acoustic coupling is demonstrated. Dispersion laws for interacting linear sound and spin excitations are obtained for bulk and surface acoustic waves. It is shown that externally excited surface acoustic waves in the GHz range can generate space-time Rabi oscillations between spin states of molecular magnets.;Spin dynamics of crystals of molecular magnets in a time-dependent magnetic field is analyzed along the lines of the Landau-Zener theory. Quantum dynamics of a molecular magnet in a rotating magnetic field is studied. Analytical expressions for the probability of spin transition are derived for fast and slow rotation, and the case of a continuous rotation in the presence of the noise is investigated. The dynamics of the magnetization reversal and the electromagnetic radiation emitted due to collective Landau-Zener relaxation in a crystal of molecular magnets is examined.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
