The effect of hydrostatic pressure up to 1.61 GPa on the Morin transition of hematite‐bearing rocks: Implications for planetary crustal magnetization

We present new experimental data on the dependence of the Morin transition temperature ( T M ) on hydrostatic pressure up to 1.61 GPa, obtained on a well‐characterized multidomain hematite‐bearing sample from a banded iron formation. We used a nonmagnetic high‐pressure cell for pressure application and a Superconducting Quantum Interference Device magnetometer to measure the isothermal remanent magnetization (IRM) under pressure on warming from 243 K to room temperature ( T 0 ). IRM imparted at T 0 under pressure in 270 mT magnetic field (IRM 270mT ) is not recovered after a cooling‐warming cycle. Memory effect under pressure was quantified as IRM recovery decrease of 10%/GPa. T M , determined on warming, reaches T 0 under hydrostatic pressure 1.38–1.61 GPa. The pressure dependence of T M up to 1.61 GPa is positive and essentially linear with a slope d T M /d P  = (25 ± 2) K/GPa. This estimate is more precise than previous ones and allows quantifying the effect of a pressure wave on the upper crust magnetization, with special emphasis on Mars.