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Origin of self-reversed thermoremanent magnetization
Richard J Harrison1, Takeshi Kasama, Thomas A White
1Department of Earth Sciences, University of Cambridge, UK.
Physical Review Letters
|February 21, 2006
Summary
Certain magnetic minerals exhibit self-reversed thermoremanent magnetization (SR-TRM), opposing Earth's magnetic field. This study reveals SR-TRM originates from negative exchange coupling at antiphase domain boundaries in ilmenite-hematite.
Area of Science:
- Geophysics
- Materials Science
- Mineral Physics
Background:
- Self-reversed thermoremanent magnetization (SR-TRM) is a phenomenon where magnetic minerals acquire a magnetization opposite to the ambient field.
- The exact origin of SR-TRM, particularly in minerals like ilmenite-hematite, has been a long-standing question in rock magnetism.
Purpose of the Study:
- To elucidate the fundamental mechanism behind self-reversed thermoremanent magnetization (SR-TRM).
- To investigate the role of antiphase domain boundaries (APBs) in ilmenite-hematite in generating SR-TRM.
Main Methods:
- Direct transmission electron microscopy (TEM) to observe microstructures.
- Simulations of chemical and magnetic structures at APBs.
- Analysis of cation ordering transitions in ilmenite-hematite.
Main Results:
- Direct evidence of negative exchange coupling across antiphase domain boundaries (APBs) in ilmenite-hematite was observed.
- Two novel classes of magnetic domain walls at APBs were identified, intrinsically linked to SR-TRM.
- Simulations confirmed SR-TRM arises from coupling between Ti-rich and Fe-rich domains during cation ordering.
Conclusions:
- Negative exchange coupling at APBs is the direct cause of self-reversed thermoremanent magnetization in ilmenite-hematite.
- Understanding this coupling provides insight into the magnetic behavior of minerals and their application in paleomagnetism.
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