Physics
Scientific paper
Jan 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002pepi..129..173k&link_type=abstract
Physics of the Earth and Planetary Interiors, Volume 129, Issue 1-2, p. 173-179.
Physics
14
Scientific paper
Grain sizes in the range (10-4 to 10-1mm) are common in some rocks. Because thermal and/or chemical remanent magnetization of hematite in this range approaches intensities of single domain (SD) magnetite, careful exploration of this transition, may serve to develop new applications in rock magnetism that relate to magnetic anomaly source identification, and various paleomagnetic and grain size-dependent investigations. Grain size-dependent magnetic behavior of hematite reveals a SD-multidomain (MD) transition at 0.1mm. This transition is recognized by variation in magnetic coercivity and susceptibility and is related to an anomaly in remanence recovery when cycling through the Morin transition. The coercivity decrease with increasing grain size occurs much more gradually above 0.1mm than below this value. Magnetic susceptibility of the grains smaller than 0.1mm has negligible dependence on the amplitude of the applied alternating magnetic field. For the larger grains a new amplitude-dependent susceptibility component is observed. The grain size of 0.1mm is also associated with loss of most of the remanence when cycling through the Morin transition. This behavior is ascribed to a transition from the metastable SD to the MD magnetic state. The increase in magnetized volume causes the demagnetizing energy to destabilize the SD state, resulting in a transition where the demagnetizing energy is reduced by nucleation of the domain wall for grains larger than 0.1mm. The 0.1mm transition has no significant effect on shape of the temperature-dependent coercivity and saturation magnetization.
Kletetschka Gunther
Wasilewski Peter J.
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