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) grains produce strong dipolar anomalies that attenuate rapidly, limiting reliable detection to observation heights below ∼1μm for 5nT noise or ∼0.5μm for 50nT noise. Larger SV or multivortex grains remain detectable to ∼5-10μm 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 ∼2μm, while multipolar fits can improve near-surface accuracy but add significant uncertainty in noisy data. Because strongly non-dipolar anomalies observed at heights ≥1-2μm may arise from large multidomain grains 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 stand-off distance, and carefully interpret signals for robust micropaleomagnetic measurement.
Bellon et al. (Fri,) studied this question.