Fig. 4: Compilation of the computed magnetic energy barriers for each of the lowest energy LEM states across a minimum energy path to its anti-parallel state, using the Nudged-Elastic-Band method^12,45.

This energy barrier is then applied to the Néel-Arrhenius⁸ equation to calculate the relaxation time (at 20 °C) for the transition τ from one domain state to another. The magenta curve represents the density of the state’s distribution. The vertical dashed (green) lines correspond to τ for 100 seconds, 1 million years, and 4.5 billion years. Most of the states exhibit stabilities that far surpass the age of the Solar System (as seen in the MV states for Grains 19 and 115). However, a minority of them, such as Grain 32, are unstable magnetic recorders, representing the magnetically unstable zone (MUZ) between the transition of the SD to the ESV state. The colours shown for the arrows within the grains (as well as the vortex structures) have the same meaning as the examples shown in Fig. 3 (see colour bar for helicity). Calculations were performed assuming magnetite as the mineral phase.