Magnetic domain state and coercivity predictions for biogenic greigite (Fe₃S₄): A comparison of theory with magnetosome observations

Abstract

The discovery of bacteria that precipitate greigite within intracellular organelles (magnetosomes) offers new evidence about the origin of greigite in natural environments. Unlike magnetite, only scarce information is available abo~t the. magnetic challl~ristics of greigite. For this reason, and the present inability to grow these microorg~~s ~ pure ~re, It u ~ot known .whether ~r not the magnetosomes in the newly discovered greigiteprea~tatmg bactena ~re of smgle-d~ (SD) sJZe, as are the magnetosomes from magnetite-precipitating bactena. The hypotheSls of natural selection for magnetotactic behavior predicts that the greigite-bearing magnetos~es should also be s~~e magnetic domains. Using previously reported magnetic properties and crystalloglllphic featul7s for gre1g1te, we have calculated the size and shape boundaries expected for SD and superpa~gnetlc (SP~ behavior~ this m!neral. For further characterization ofthe greigite crystals, we analyzed the ~am state at vanous length/Width ratios assuming crystal shapes of parallelepipeds and prolate spheroids. Mag~etlte was used as control for the current theories supporting these calculations. We also present a simple alg~~thm to cal~te the upper size ~t of single-domain glllins. Our resuhs show that the crystals of bacterial greigite characte~ so far are l~ted m the region close to the single-domain superparamagnetic boundary and should have relatlv_ely lo~ .coerCJ.Vlty. If these crystals contribute to the magnetization ci sediments, remanence ~rodu~ by bacterial gre1g1te could be mistaken for large, multidomain magnetite in alternating field demagnetization studies.

Sclerite formation in the hydrothermal-vent “scaly-foot” gastropod—possible control of iron sulfide biomineralization by the animal

“…Previous calculations of the single-domain field for greigite [23] suggest that the greigite rods observed by TEM should lie near the single-domain/superparamagnetic domain boundary, with a maximum coercivity of about 30 mT. Low-temperature measurements indicate a 45% loss of remanence upon warming from 2 K to 300 K, which is consistent with the presence of a significant superparamagnetic fraction (Fig.…”

Comparison of Pedogenic and Sedimentary Greigite by X-ray Diffraction and Mössbauer Spectroscopy

“…The most interesting feature, however, is the fact that the soil and sedimentary greigite show magnetic order at room temperature, although their particle sizes lie within the region that is characteristic for SP behavior (Figure 3; Ricci and Kirschvink, 1992). This discrepancy has also been described for the macroscopic single-domain behavior (Stanjek et aL, 1994).…”

“…Single-domain stability diagram for different shapes of prolate spheroid grains of greigite (redrawn from Figure 1 of Ricci and Kirschvink, 1992). Boundaries between the superparamagnetic and the single-domain region are indicated for relaxation times of 100 s (upper curve) and of 10 -8 s (broken line).…”

“…Boundaries between the superparamagnetic and the single-domain region are indicated for relaxation times of 100 s (upper curve) and of 10 -8 s (broken line). The approximate ratio of width/length has been inferred from the saturation magnetization values, which are given in Figure 1 of Ricci and Kirschvink, 1992. s for macroscopic measurements to 10 -8 s for Mtssbauer spectroscopy (dashed curve in Figure 3), both greigites still lie within the SP region. This behavior is similar to that of a ferrihydrite--organic matter association, in which Schwertmann and Murad (1988) observed an enhancement of magnetic coupling across the ferrihydrite crystallites after removal of the organic matter.…”

Collection and Enrichment of Magnetotactic Bacteria from the Environment

“…Three common crystal morphologies have been described in all MTB based on electron microscopy of the crystal structures: (i) cuboctahedral [1,31,44], (ii) elongated prismatic [8,31,47], and (iii) bullet-shaped [6,10,17,36,37,63]. The size of magnetosome crystals range from about 35 to 120 nm in diameter, and appears to be under strict biological control as all magnetosome crystals, regardless of whether they consist of magnetite or greigite, are single-domain magnets [10,21,30,56]. Each species or strain exhibits a particular arrangement of magnetosomes within the [4,10,45,61].…”