Multidomain hematite: A source of planetary magnetic anomalies?

Thermoremanent magnetization (TRM) in hematite is larger than TRM in magnet ite for grain sizes greater than or equal to 10 mum. We show that hematite' s weak spontaneous magnetization M-s causes its strong TRM, since the self- demagnetizing field H-d opposing large domain wall displacements is proport ional to M-s. In hematite, H-d is comparable to the Earth's magnetic field but in magnetite, H-d is 1000 times larger. As a result, Earth's field TRM of MD hematite (approximate to0.3 Am-2/kg) outweighs TRM and induced magnet ization of MD magnetite (approximate to0.01-0.02 Am-2/kg) and rivals TRM of single-domain and PSD magnetite as a source of magnetic anomalies on Earth and perhaps on Mars.