Micromagnetic simulations of first-order reversal curve (FORC) diagrams of framboidal greigite

Abstract

SUMMARY Greigite is a sensitive environmental indicator and occurs commonly in nature as magnetostatically interacting framboids. Until now only the magnetic response of isolated non-interacting greigite particles have been modelled micromagnetically. We present here hysteresis and first-order reversal curve (FORC) simulations for framboidal greigite (Fe3S4), and compare results to those for isolated particles of a similar size. We demonstrate that these magnetostatic interactions alter significantly the framboid FORC response compared to isolated particles, which makes the magnetic response similar to that of much larger (multidomain) grains. We also demonstrate that framboidal signals plot in different regions of a FORC diagram, which facilitates differentiation between framboidal and isolated grain signals. Given that large greigite crystals are rarely observed in microscopy studies of natural samples, we suggest that identification of multidomain-like FORC signals in samples known to contain abundant greigite could be interpreted as evidence for framboidal greigite.

Matuyama-brunhes Geomagnetic Reversal Record and Associated Key Tephra Layers in Boso Peninsula: Extraction of Primary Magnetization of Geomagnetic Fields From Mixed Magnetic Minerals of Depositional, Diagenesis, and Weathering Processes

“…The measured values also fall within the area of greigite-baring marine sediments with diagenesis (colored area in Figure 5b; Roberts et al, 2011). The measured values were also compared with those calculated using micromagnetic simulations for greigite (Figure 5c;Valdez-Grijalva et al, 2020). It is suggested that the measured values are also consistent with those for non-interacting greigite of 80-90 nm grain size.…”

Diagenesis of Magnetic Minerals in Active/Relict Methane Seep: Constraints From Rock Magnetism and Mineralogical Records From Bay of Bengal

“…In natural system, greigite can commonly occur as magnetostatically interacting framboids. A micromagnetic modelling study involving hysteresis and FORC simulations demonstrated that magnetostatic interactions could remarkably alter the FORC response of greigite framboids and can form patterns similar to vortex and MD (Rodelli et al, 2018;Valdez-Grijalva et al, 2020). It is quite possible that greigite clusters observed in SPC-02 ( Figures 7E,F) and SPC-04 ( Figure 7J) might be contributing significantly towards the observed FORC (vortex to multi-domain) distributions.…”

Magnetic Biosignatures of Magnetosomal Greigite From Micromagnetic Calculation

“…In addition, numerical calculations were implemented to calculate magnetic energy and magnetic moments of MMP (Acosta‐Avalos et al., 2012) and critical single domain (SD) threshold sizes in greigite magnetosome chains (Muxworthy et al., 2013). Yet, the magnetic properties of greigite magnetosomes are much less known compared to the extensively investigated magnetite counterparts (e.g., Li et al., 2010; Moskowitz et al., 1993, 1989; Pan et al., 2005) and abiotic greigite crystals (e.g., Chang et al., 2007, 2008; Roberts, Chang, et al., 2011; Snowball, 1991, 1997a, 1997b; Valdez‐Grijalva et al., 2018, 2020), because of the difficulties in isolating and culturing greigite MTB (Bazylinski & Frankel, 2004; Lefèvre et al., 2011) to obtain pure biogenic greigite samples. Moreover, greigite magnetosome chains often appear to be disordered and the magnetic consequences of this remain unclear.…”