Micromagnetic Modeling of Magnetite/Maghemite Particles with a Multi-Layer Core-Shelled Structure

Abstract

Low temperature oxidized core-shelled magnetite is paramount important in recording geomagnetic field. To characterize the effects of transition zone between the core-shell on the magnetic properties of low temperature oxidation of magnetite, 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 SD particles (<70 nm) remain highly uniform magnetization, but show decreasing coercivities as oxidation preceeds. For fine SV particles (80 nm to 120 nm), the hysteresis parameters respectively increase and dramatic decrease at the early and late stage of oxidation, and the micromagnetic behaviors vary significantly. Finally the hysteresis parameters of larger SV (>130) particles remain nearly unchanged during oxidation. It indicates that fine SV particles are more sensitive to oxidation, and dominate the dramatic change of experiment observation. Overall, low temperature oxidation of magnetite preferring a multi-layer coupled oxidation process from outside to interior and is capable of recording paleomagnetic signals.