Paleointensity observations from meteorites provide insights into planetary formation and evolution. Meteoritic samples are usually dominated by Fe-rich kamacite, which is capable of faithfully recording the ancient dynamo activity of meteorites’ parent body. To retrieve paleointensity estimates, experimental protocols assume that samples are dominated by uniformly magnetized particles. However, most magnetic carriers observed in extraterrestrial samples are non-uniformly magnetized. This inconsistency represents a major impediment in reliably reconstructing paleointensities from meteorites. Here we present the State Group Algorithm (SGA); a micromagnetic based model capable of efficiently simulating thermoremance acquisition of magnetic particles with a single-vortex domain state. The results show that iron particles can acquire thermoremance that is linear with the external field up to ∼100 µT. Single-vortex cooling rate effects are generally weaker than those of single-domain particles, providing more accurate paleointensity estimates. A small number of particles exhibit inverse cooling rate effects, leading to underestimates in paleointensity.

Iron meteorites are believed to be fragments of mantle-stripped planetary cores ejected during catastrophic collisions. They are, therefore, a unique class of material, as they constitute the only available samples from planetary cores. An increasing amount of evidence suggests that the tetrataenite-bearing cloudy zones (CZ) in iron and stony-iron meteorites can preserve magnetic records of ancient magnetic activity of their parent bodies over solar system timescales. Tetrataenite islands in the CZ are nanometer-sized ($<$ 200 nm) crystals that form through ordering from precursor taenite islands upon extremely slow cooling through 320 \textsuperscript{o}C. Recent micromagnetic models have shown that such precursor taenite islands form highly thermally stable single-domain (SD) or single-vortex states (SV). In this work we employ a 3D finite-element multi-phase micromagnetic modeling to show that tetratenite inherits the magnetic remanence of taenite precursor when it forms over underlying SD states. When taenite form SV states, nevertheless, tetrataenite reset the precursor magnetization and record a new remanence through chemical ordering at 320 \textsuperscript{o}C. We further assess the thermal stability of tetrataenite islands. We show that in cases where tetrataenite inherits the domain states of its precursor taenite, the origin of the remanence is in fact 10\textsuperscript{5} years older than in cases where tetrataenite resets the precursor SV magnetization, corresponding to records of two very different stages of planetary formation.