Reliable Paleomagnetic Records From Single-Vortex Iron Particles

Abstract

Dusty olivine containing Fe-rich kamacite grains in chondrules can faithfully record the early solar magnetic fields. To retrieve paleointensity estimates, most experimental protocols are based on the dominance of uniformly magnetized single-domain (SD) particles. However, direct observation shows that most particles adopt a non-uniform magnetic structure. This inconsistency potentially represents a major impediment in reliably reconstructing ancient magnetic fields. Here we present a micromagnetic based model, the State Group Algorithm, that enables efficient simulations of thermoremanence acquisition in magnetic particles with single-vortex (SV) domain states. Our results show that these particles can acquire a thermoremanence that is linear proportional to the external field up to $\sim 100\text{μT}$. They also have cooling rate effects that are generally weaker than those of SD particles. Notably, a small subset of SV particles can exhibit negative cooling rate effects, leading to underestimates in paleointensity. We conclude that SV particles are reliable paleomagnetic recorders.