Micropaleomagnetic analysis offers a path to high-precision reconstructions of ancient magnetic fields from terrestrial and space-returned samples by inverting the vertical stray field of individual particles to recover their magnetic moments through the use of magnetic microscopes. Constraining such inversions requires a detailed understanding of how domain state influences the dipolar and non-dipolar components of the stray field with distance. Here, we use micromagnetic solutions of remanent states in real, irregular sub-to near-micron magnetite particle morphologies to calculate vertical stray fields at various heights, evaluating how dipolar and non-dipolar signals can be recovered with both simple Cartesian dipole and multidipolar models in the presence and absence of noise. Our results show that single-domain and single-vortex state (SV) particles produce strong dipolar anomalies that attenuate rapidly, limiting reliable detection to observation heights below ∼1 μm for 5 nT noise or ∼0.5 μm for 50 nT noise. Larger SV or multivortex particles remain detectable to ∼5−10 μm but with reduced moment fidelity. Multipolar components decay orders of magnitude faster than the dipole and are quickly lost in noise at practical distances. Dipole-only inversions yield stable, accurate results beyond ∼2 μm, while multipolar fits can improve near-surface accuracy but add significant uncertainty in noisy data. Because strongly non-dipolar anomalies observed at heights μm may arise from large multidomain particles or from the combined response of short- and long-wave signals of clusters of particles, they should be interpreted with caution. We highlight the need to minimize sensor noise, optimize standoff distance, and carefully interpret signals for robust micropaleomagnetic measurements.
Bellon et al. (Tue,) studied this question.