Abstract/Details

Magnetic deflagration in the molecular magnet manganese-12-ac


2009 2009

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Abstract (summary)

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.

Indexing (details)


Subject
Condensed matter physics
Classification
0611: Condensed matter physics
Identifier / keyword
Pure sciences; Deflagration; Magnetic deflagration; Manganese; Molecular magnets
Title
Magnetic deflagration in the molecular magnet manganese-12-ac
Author
McHugh, Sean
Number of pages
122
Publication year
2009
Degree date
2009
School code
0046
Source
DAI-B 70/02, Dissertation Abstracts International
Place of publication
Ann Arbor
Country of publication
United States
ISBN
9781109052244
Advisor
Sarachik, Myriam P.
Committee member
Chudnovsky, Eugene; Garanin, Dmitry; Kent, Andrew; Vitkalov, Sergey
University/institution
City University of New York
Department
Physics
University location
United States -- New York
Degree
Ph.D.
Source type
Dissertations & Theses
Language
English
Document type
Dissertation/Thesis
Dissertation/thesis number
3344986
ProQuest document ID
304862363
Copyright
Database copyright ProQuest LLC; ProQuest does not claim copyright in the individual underlying works.
Document URL
http://search.proquest.com/docview/304862363
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