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Yu, YJ, Gee JS.  2005.  Spinel in Martian meteorite SaU 008: implications for Martian magnetism. Earth and Planetary Science Letters. 232:287-294.   10.1016/j.epsl.2004.12.015   AbstractWebsite

Shergotty-Nakhla-Chassigny (SNC) meteorites provide the only available samples of Martian material. The stable permanent magnetization of SNC meteorites has been traditionally attributed to magnetite (Fe3O4) or pyrrhotite (Fe7S8). On the basis of rock magnetic, microscopic, and electron microprobe analyses on rock chips and mineral separates, we suggest that a new material (Fe-Cr-Ti spinel) is responsible for the stable paleomagnetic record of Martian meteorite SaU 008. It is possible that SaU 008 acquired a primary remanence of thermal origin from the Martian crustal field. However, this proposition requires further testing because the effect of shock events on Fe-Cr-Ti spinel is unknown. (c) 2004 Elsevier B.V. All rights reserved.

Yu, YJ, Tauxe L, Gee JS.  2007.  A linear field dependence of thermoremanence in low magnetic fields. Physics of the Earth and Planetary Interiors. 162:244-248.   10.1016/j.pepi.2007.04.008   AbstractWebsite

We tested a linear field-dependence of thermoremanent magnetization (TRM) to saturation isothermal remanent magnetization (SIRM) ratio for magnetite-containing natural samples. The TRM/SIRM shows a linear field-dependence to very low field ranges (<1 mu T). This observation is at odds with a claim of limited sensitivity at low fields in TRM acquisition documented in previous studies. We attribute the difference to poor field control in the ovens used in previous studies. The TRM/SIRM ratio shows a grain-size dependence. For magnetite-containing samples with insignificant anisotropy, the TRM/SIRM is most efficient in pseudo-single-domain magnetites. These results suggest that while the TRM/SIRM ratio is linear at low field strengths, the ratio provides only a crude estimation on the actual paleo-field within two orders of magnitude, suggesting that a careful sample characterization is necessary in applying the TRM/SIRM as a paleointensity proxy. (c) 2007 Elsevier B.V. All rights reserved.