Vortex Magnetic Domain State Behavior in the Day Plot.

The ability of rocks to hold a reliable record of the ancient geomagnetic field depends on the structure and stability of magnetic domain‐states contained within constituent particles. In paleomagnetic studies, the Day plot is an easily constructed graph of magnetic hysteresis parameters that is frequently used to estimate the likely magnetic recording stability of samples. Often samples plot in the region of the Day plot attributed to so‐called pseudo‐single‐domain particles with little understanding of the implications for domain‐states or recording fidelity. Here we use micromagnetic models to explore the hysteresis parameters of magnetite particles with idealized prolate and oblate truncated‐octahedral geometries containing single domain (SD), single‐vortex and occasionally multi‐vortex states. We show that these domain states exhibit a well‐defined trend in the Day plot that extends from the SD region well into the multi‐domain region, all of which are likely to be stable remanence carriers. We suggest that although the interpretation of the Day plot and its variants might be subject to ambiguities, if the magnetic mineralogy is known, it can still provide some useful insights about paleomagnetic specimens' dominant domain state, average particle sizes and, consequently, their paleomagnetic stability. Plain Language Summary: Ancient magnetic field recordings from rocks, provide information about the early habitability of Earth and formation of the Solar System. Key to understanding the reliability of these magnetic recordings is knowing the particle size and shape of a rock's constituent magnetic minerals. Small magnetite particles (⪅100 nm) are magnetically uniform, but as particle size increases the magnetic structures become non‐uniform and increasingly complex. These different types of structures are termed domain states, and yield different magnetic hysteresis responses, often summarized on a so‐called "Day" diagram—a commonly used diagnostic of domain state (or particle size). The position of particles in the size 100–1,000 nm on the Day plot is poorly quantified. This is a problem, as it has been shown in the last 5 years, that this particle size range carries the most stable magnetic recordings, lasting potentially longer than the age of the universe. These particles contain vortex‐like magnetic structures. Using a numerical micromagnetic algorithm, this is the first comprehensive study to quantify the magnetic response of vortex structures on the Day plot. We show that careful use of the Day plot can provide insight into the ability of a sample to retain recordings of the ancient geomagnetic field. Key Points: Vortex domain states for magnetite predominantly have pseudo‐single‐domain Day plot characteristicsIf the mineralogy is known, the Day plot can provide an estimate on the dominance of stable remanence carriers [ABSTRACT FROM AUTHOR]