Micromagnetic Calculations of the Effect of Magnetostatic Interactions on Isothermal Remanent Magnetization Curves: Implications for Magnetic Mineral Identification

Isothermal remanent magnetization (IRM) curves are used widely in rock magnetic and environmental magnetic studies to characterize magnetic properties of natural samples. Previous theoretical and experimental investigations indicate that magnetostatic interactions can strongly affect the IRM behavior. In order to quantitatively investigate this effect, we modeled IRM curves and hysteresis properties for magnetite assemblages with variable morphologies (grain size, elongation, and shape) using the finite-element micromagnetic modeling code MERRILL. We also conducted an analytical study of IRM behavior for noninteracting single domain grains utilizing the Stoner–Wohlfarth model. It is found that multiple Gaussian components do not necessarily reflect multiple magnetic mineral populations. For example, magnetostatic interactions can produce coercivity distributions that resemble results of some samples containing a detrital and extracellular (D + EX) and a biogenic soft or hard (BS/BH) coercivity components. Simulated IRM curves for different morphologies of interacting flattened grains are similar, indicating that the effect of interactions can overshadow the effect of grain morphologies. Moreover, our micromagnetic and analytical calculations consistently indicate that the IRM curves for noninteracting fine-grained assemblages are mostly determined by grain shape (elongated or flattened) and elongation distributions of the magnetic mineral assemblages. Our simulations present possible outcome of IRM curves for magnetic mineral assemblages with controlled grain size, shape and microstructures, which provides important theoretical constraints on characterizing complex magnetic mineral components in natural samples through IRM curves and hysteresis.