Micromagnetic Modeling of a Magnetically Unstable Zone and Its Geological Significances

Abstract

Recent micromagnetic simulations have found that particles in the transitional zone between the single domain (SD) and single vortex (SV) zone are prone to thermal and external magnetic field instabilities 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 behavior of 68–104 nm truncated octahedral magnetite particles using the MERRILL modeling software. We found that: (a) The size region of the “MU zone” for grains of truncated octahedron shape is different from cubic octahedrons and spheres, indicating that the zone may be controlled by the geometry and shape of particles; (b) The MU zone has a range of 79–97 nm region, which is dominated by a hard‐axis aligned single vortex (HSV); and (c) MU particles are unstable as a function of temperature and have low coercive fields. Finally, the numerical fitting of hysteresis parameters for experimental data suggests that the influence of such MU particles in samples should not be ignored, especially for samples with fine‐grained magnetic minerals as the primary magnetic recording carriers. This research has extended our understanding of the behavior of the “MU zone” and its significance on paleomagnetic records.

Clay minerals and continental-scale remagnetisation: a case study of South American Neoproterozoic carbonates

“…Although the ESV magnetic structure can yield stabilities exceeding that of SD (Nagy, Williams, Tauxe, Muxworthy, & Ferreira, 2019), HSV states are often unstable, even at room temperature (Nagy, 2017). For equidimensional octahedral grains of magnetite, the UMZ occurs for grains sizes of 84-100 nm, but this range will vary with both mineralogy and morphology (Wang, 2022;Nagy, Williams, Tauxe, Muxworthy, & Ferreira, 2019).…”

“…Particles within the UMZ will suffer not only a decrease in thermal stability, but other magnetic properties will change as well. For instance, coercivity is largely reduced and the magnetic susceptibility can be as high as those of SP particles (Wang, 2022;Nagy, Williams, Tauxe, Muxworthy, & Ferreira, 2019). These results might have a profound implication for the interpretation of bulk magnetic properties of remagnetised carbonates since the effects of distorted hysteresis loops and the frequency-dependent susceptibility of grains within the UMZ could be erroneously interpreted as the result of SP grains.…”