Multidomain hematite: A source of planetary magnetic anomalies?

Thermoremanent magnetization (TRM) in hematite is larger than TRM in magnetite for grain sizes ≥ 10 μm. 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 proportional 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 (0.3 Am 2 /kg) outweighs TRM and induced magnetization of MD magnetite ( 0.01-0.02 Am 2 /kg) and rivals TRM of single-domain and PSD magnetite as a source of magnetic anomalies on Earth and perhaps on Mars.