Magnetic deflagration in the molecular magnet manganese-12-ac
Item
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Title
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Magnetic deflagration in the molecular magnet manganese-12-ac
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Identifier
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d_2009_2013:7c71125421b3:10000
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identifier
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10129
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Creator
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McHugh, Sean,
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Contributor
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Myriam P. Sarachik
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Date
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2009
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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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Condensed matter physics | deflagration | molecular magnet
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Abstract
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In 1995, Paulsen and Park [1, 2] observed abrupt spontaneous reversals of the magnetization in crystals of the molecular magnet Mn12-ac, which they dubbed "magnetic avalanches". They suggested that the magnetic avalanches were a thermal runaway process where the reversing spins release heat stimulating further relaxation. Various exotic phenomena were proposed as an alternative explanations [3]. In 2005, Suzuki et al. [4] established that this spontaneous magnetic relaxation occurs as a "front" separating regions of opposing magnetization that propagates at a constant speed through the crystal. They suggested that this propagating front is analogous to a flame in chemical deflagration and introduced the thermal relaxation process, magnetic deflagration. The analysis presented there was limited by lack of data. A more thorough comparison with the theory would require the ability to trigger avalanches in a more controlled way rather than wait for their spontaneous occurrence.;The work presented in this thesis is a continuation of the program initiated by Suzuki [4, 5]. Significant progress experimental progress has been made allowing us to trigger avalanches over a wide range of conditions. The magnetization dynamics and the ignition temperatures are studied in detail using an array of micro-sized Hall sensors and Germanium thermometers. In addition, we report the existence of a new species of avalanches consisting only of the fast-relaxing isomers of Mn12-ac, the so-called "minor species". We explore avalanches of both species, as well as the interaction between them. Finally, a detailed analysis is performed to compare the experiment with the theory of magnetic deflagration [6]. We find the theory of magnetic deflagration to be consistent with the data and extract values for the key physical quantities: the thermal diffusivity and avalanche front temperatures. Agreement between our predicted values and an independent measurement of these quantities would provide compelling verification of the theory.
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Type
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dissertation
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Source
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2009_2013.csv
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degree
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Ph.D.
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Program
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Physics
