Micromagnetic modeling of a magnetic unstable zone and its geological significances

Abstract

Recent micromagnetic simulations have found that particles in the size region of the single domain (SD) to single vortex (SV) transition zone are prone to poor thermal and field stabilities that could adversely affect the accuracy of interpretations of paleomagnetic recordings. In this study, we attempt to evaluate the internal magnetization characteristics of these magnetically unstable (MU) particles and the influence on paleomagnetic observations by simulating the magnetic behaviour of 68-104 nm truncated octahedral magnetite particles via the MERRILL modelling software. We found that: (i) The size region of the "MU zone" for grains of cubic octahedral shape is different with cubic octahedrons and spheres, indicating the zone may be controlled by the geometry and shape of particles; (ii) The MU zone has a range of 79-91 nm region, which is dominated by a hard-axis aligned single vortex (HSV); (iii) MU particles are unstable as a function of temperature. Finally, the numerical fitting of hysteresis parameters for experimental data suggests that the influence of such MU particles in samples cannot be ignored, especially for samples with fine-grained magnetic minerals as the primary magnetic recording carriers. This research has extended our understanding of the behaviour of the "MU zone" and its significance on paleomagnetic records.