Resonant magnetization tunneling in high-spin molecules.
Item
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Title
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Resonant magnetization tunneling in high-spin molecules.
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Identifier
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AAI9707091
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identifier
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9707091
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Creator
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Friedman, Jonathan R.
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Contributor
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Adviser: Myriam P. Sarachik
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Date
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1996
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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 | Chemistry, Physical
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Abstract
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I present experimental data indicating that {dollar}\rm Mn\sb{12}O \sb{12}(CH\sb3COO)\sb{16}(H\sb2O)\sb4,{dollar} a system of high-spin molecules, exhibits thermally assisted field-tuned resonant tunneling. I also develop a theoretical framework to explain much of the data. The evidence for tunneling is that, in oriented samples of this material, one finds steps in the hysteresis loops at regular intervals of magnetic field, dips in the superparamagnetic blocking temperature and concomitant increases in the magnetic relaxation rate at the same fields. This data is explained in terms of a simple model that makes quantitative predictions that are in reasonable agreement with the experimental data. In Chapter I, I review some of the theory of macroscopic quantum tunneling of magnetization and provide some background information about this molecular magnet. Chapter II covers experimental techniques: sample preparation, measuring devices and data-taking procedures. In Chapter III, I present the experimental data obtained from samples of Mn{dollar}\sb{12}{dollar}, showing the aforementioned steps in the hysteresis loops and related phenomena. A section of that chapter will be devoted to a detailed study of the effect of a transverse magnetic field on the magnetic relaxation. The theory of tunneling in a large spin is developed in Chapter IV, where a simple Hamiltonian is shown to predict some very interesting effects and a phenomenological model of spin relaxation is analyzed. Chapter V consists of discussion and interpretation of the experimental data and comparison of the data with the theory developed in Chapter IV. The chapter ends with some detailed discussion of the data that so far eludes explanation. In Chapter V, I conclude by discussing possible future experiments and other systems that show magnetization steps.
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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.
