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Detailed Reference Information |
Yu, Y. and Tauxe, L. (2005). On the use of magnetic transient hysteresis in paleomagnetism for granulometry. Geochemistry Geophysics Geosystems 6. doi: 10.1029/2004GC000839. issn: 1525-2027. |
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Parameters derived from magnetic hysteresis experiments have been used as granulometric indicators in paleomagnetism. In practice, discriminating the superparamagnetic (SP) fraction from the coarse grain magnetites in parameter ratio plots is often inconclusive. To overcome this ambiguity, transient hysteresis (TH) has been recently proposed. We have carried out micromagnetic simulations to provide a fundamental rationale for the use of TH for granulometry. We found that magnetic TH results from the difference of magnetization configuration between ascending and descending hysteresis loops as a result of self-demagnetization. The descending branch has a tendency to keep a more uniform (e.g., flower-like) configuration, while the ascending branch prefers a less uniform (e.g., vortex-like) structure. According to our simulations, TH increases as the grain size increases and as the aspect ratio decreases. We also carried out TH measurements for well-defined synthetic and natural samples. It is notable that TH from the simulation for samples with aspect ratio q = 1.5 agrees well with the experimental observations for annealed magnetites of smaller sizes. In general, small TH is a clear indication for the absence of complex magnetized structures. Adding TH analysis to the hysteresis loop measurements requires a minor effort yet provides strong constraint on grain size. Parameters derived from magnetic hysteresis experiments have been used as granulometric indicators in paleomagnetism. In practice, discriminating the superparamagnetic (SP) fraction from the coarse grain magnetites in parameter ratio plots is often inconclusive. To overcome this ambiguity, transient hysteresis (TH) has been recently proposed. We have carried out micromagnetic simulations to provide a fundamental rationale for the use of TH for granulometry. We found that magnetic TH results from the difference of magnetization configuration between ascending and descending hysteresis loops as a result of self-demagnetization. The descending branch has a tendency to keep a more uniform (e.g., flower-like) configuration, while the ascending branch prefers a less uniform (e.g., vortex-like) structure. According to our simulations, TH increases as the grain size increases and as the aspect ratio decreases. We also carried out TH measurements for well-defined synthetic and natural samples. It is notable that TH from the simulation for samples with aspect ratio q = 1.5 agrees well with the experimental observations for annealed magnetites of smaller sizes. In general, small TH is a clear indication for the absence of complex magnetized structures. Adding TH analysis to the hysteresis loop measurements requires a minor effort yet provides strong constraint on grain size. |
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BACKGROUND DATA FILES |
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Abstract |
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Abstract |
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Table 1 |
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Table 2 |
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Preliminaries to Micromagnetic Modeling |
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Micromagnetic Simulation |
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Angular Dependance of Magnetic Hysteresis |
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Experimental Observations |
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Samples & Experiments |
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Synthetic Samples |
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Natural Samples |
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Keywords
Geomagnetism and Paleomagnetism, Rock and mineral magnetism, Geomagnetism and Paleomagnetism, Instruments and techniques, Geomagnetism and Paleomagnetism, General or miscellaneous, FORC, granulometry, hysteresis, magnetite, transient hysteresis |
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Journal
Geochemistry Geophysics Geosystems |
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Publisher
American Geophysical Union 2000 Florida Avenue N.W. Washington, D.C. 20009-1277 USA 1-202-462-6900 1-202-328-0566 service@agu.org |
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