Micromagnetic modeling of a multi-layer core-shelled magnetite/maghemite particle and its geological significances

Abstract:

To characterize the magnetic properties of low temperature oxidation of magnetite and solve the discrepancies between modeling and experiments, micromagnetic models of hysteresis parameters and microstructures of a multi-layer core-shelled model were systematically investigated by MERRILL (Micromagnetic Earth Related Rapid Interpreted Language Laboratory). Numerical simulations indicate that the microstructures of single domain (SD) (<80 nm) and larger single vortex (SV) (>140) particles of magnetite remain constant throughout the oxidation process with decreasing coercivities as oxidation proceeds. For fine SV particles (80 nm to 120 nm), the hysteresis parameters initially increases with oxidation but dramatically decreases near complete oxidation. The predicted magnetic properties for the model exhibit significantly improved agreement with experimental data than that of the previously reported single core-shell coupled geometry (a stoichiometric core surrounded by an oxidized shell). Our results indicate that fine SV particle are more sensitive to oxidation, and dominate the dramatic change of experiment observation. Overall, low temperature oxidation of magnetite is better described by a multi-layer (continuously) coupled oxidation process that proceeds from the outside to inside of the grain. The remanence and domain states remain largely unchanged suggesting that paleomagnetic signals should survive the low-temperature oxidation process.