Abstract The anisotropy of magnetic susceptibility (AMS) arises from the preferential alignment of minerals within a rock or sediment, which is known as a magnetic fabric. To interpret magnetic fabrics in a geological context, it is essential to understand how the constituent minerals in a rock contribute to the measured fabric. We present a new analysis, employing a micromagnetic approach, to characterize the susceptibility of non-interacting particles of magnetite in the single-domain (SD) or single vortex (SV) domain state. The orientation and magnitudes of the principal susceptibilities can be derived from a susceptibility map. We investigate the combined role of magnetocrystalline and shape anisotropy in rotationally oblate and prolate and triaxial ellipsoidal particles of varying axial ratio, on the orientation and magnitude of the AMS. SD particles exhibit an inverse magnetic fabric, where the smallest susceptibility is along the easy axis of magnetization of the ellipsoid. SV particles, on the other hand, can have either a normal magnetic fabric when the particle elongation is not large, i.e., the largest susceptibility is along easy axis, or an inverse fabric when the particle is more strongly elongated. The underlying explanation for the variation of fabric lies with the relative orientation of the remanence carrying vortex core within a particle with respect to the principal axes of the ellipsoid. Susceptibility maps can also be generated for assemblies of particles with variable orientation, which allows us to examine how orientation influences the total AMS. Although we present a limited number of simple models, the method can be extended to more natural mineral shapes and an array of particles that represent their distribution within a rock or sediment.
Hirt et al. (2026) studied this question.