Thermoremanence and Stable Memory of Single Domain Hematites:Implications for Martian Magnetic Anomalies

Details Thermoremanence and Stable Memory of Single Domain Hematites:Implications for Martian Magnetic Anomalies Thermoremanence and Stable Memory of Single Domain Hematites:Implications for Martian Magnetic Anomalies

Dec 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufmgp12b..10o&link_type=abstract

American Geophysical Union, Fall Meeting 2002, abstract #GP12B-10

Mathematics

Logic

1517 Magnetic Anomaly Modeling, 1527 Paleomagnetism Applied To Geologic Processes, 1540 Rock And Mineral Magnetism, 5440 Magnetic Fields And Magnetism

Scientific paper

Single-domain (SD) hematites with grain sizes between 0.12 and 0.42 micrometer carry a strong and stable TRM. The thermoremanence is unaffected by 100 mT alternating field demagnetization and by 600 C thermal demagnetization. Most demagnetization occurs between 625 C and the Neel temperature of 680-690 C. The TRM memory recovered after low-temperature cycling is parallel to the original TRM and equally resistant to thermal demagnetization. TRM and TRM memory of SD hematites are mainly due to the hard spin-canted magnetism intrinsic to the crystal structure above the Morin transition (Tm), and not to the small and softer defect magnetism that survives below Tm. However, the defect magnetism may play a role in renucleating the spin-canted magnetism in a preferred direction during warming through Tm. TRM intensities are well predicted by Neel SD theory and increase in almost exact proportion to grain size. Although smaller than TRM intensities of multidomain hematites, SD TRMs are potent sources of remanent magnetic anomalies, particularly for larger grains (10-15 micrometer), and are likely to be more stable over geological time than multidomain (MD) hematite TRMs. TRM memory after low-temperature cycling is relevant to Mars because surface temperatures in many parts of the planet cycle diurnally or seasonally through Tm in the essentially zero present-day Martian field. Where surface temperatures are lower than the Morin transition (240-260 K), SD and MD hematites will not contribute to Martian magnetic anomalies. Near the equator during Martian summer, the very stable magnetic memory of SD hematite, almost 40% of original TRM, could contribute partially to the Martian magnetic signal.

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