Micromagnetic simulation of taenite particles

The cloudy zone (CZ), an intergrowth structure of Fe-rich and Ni-rich phases that forms during slow cooling of iron meteorites are potential recorders of  their parent body’s thermal and magnetic history. The ability of the cloudy zone’s principal magnetic minerals, taenite and tetrataenite, to reliably record ancient magnetic fields from the early solar system has, however, insufficiently been investigated. In this work we performed a series of micromagnetic simulations in order to assess the magnetic stability of taenite grains. Micromagnetic simulations allow to investigate the changes in the magnetic state in taenite as a function of the grain size: in ellipsoidal grains below 68 nm (equivalent sphere volume diameter, ESVD) a single domain state dominates.  At 68 nm (ESVD) a “flowering” state starts, and further increase in size (> 75 nm) gives rise to a single vortex state. Contrary to common conception, theoretical evaluation of relaxation times for taenite grains based on micromagnetics leads to values that exceed the age of solar system, which makes taenite, not just its ordered equivalent tetrataenite, a reliable paleomagnetic recorder.