Unique thermoremanent magnetization of multidomain sized hematite: Implications for magnetic anomalies

Intense magnetic remanence (100-1000 A/m) associated with MD hematite and/o r titanohematite and associated with high Koenigsberger ratios (40-1000) in dicate that magnetic remanence may dominate the total magnetization if thes e minerals are volumetrically significant. Titanohematite behaves similarly to hematite and, thus, the grain size dependence of TRM acquisition in hem atite is considered as a generalization. The transition between truly MD be havior and tendency towards SD behavior in hematite has been established to be between grain sizes of 0.1 and 0.05 mm. In contrast to magnetite and ti tanomagnetite, hematite exhibits inverse grain size dependence, with MD hem atite acquiring a relatively intense TRM in the geomagnetic field, comparab le to sub-micrometer sized magnetite and only an order of magnitude less th an SD magnetite. Consequently MD hematite (and by analogy titanohematite) r emanence may be of significance as a source of magnetic anomalies at all sc ales. MD hematite exhibits TRM weak field acquisition behavior that is diff erent from all other magnetic minerals, being the only magnetic mineral hav ing an REM (TRM/SIRM) value >> 0.1 for TRM acquisition in the geomagnetic f ield. The very different TRM behavior of MD hematite in contrast to magneti te is due to two factors. The first is the lesser influence of demagnetizin g energy with respect to wall pinning energy, at temperatures almost up to the Curie temperature for hematite. The second is the greater importance of the magnetostatic energy in the applied field, which for hematite dominate s the total energy at high temperatures. (C) 2000 Published by Elsevier Sci ence B.V. All rights reserved.