Magnetic properties of hydrothermally synthesized greigite (Fe3S4)--II. High- and low-temperature characteristics

Abstract

SUMMARYThe magnetic behaviour of hydrothermally synthesized greigite was analysed in the temperature range from 4 K to 700°C. Below room temperature, hysteresis parameters were determined as a function of temperature, with emphasis on the temperature range below 50 K. Saturation magnetization and initial susceptibility were studied above room temperature, along with X-ray diffraction analysis of material heated to various temperatures. The magnetic behaviour of synthetic greigite on heating is determined by chemical alteration rather than by magnetic unblocking. Heating in air yields more discriminative behaviour than heating in argon. When heated in air, the amount of oxygen available for reaction with greigite determines the products and magnetic behaviour. In systems open to contact with air, haematite is the final reaction product. When the contact with air is restricted, magnetite is the final reaction product. When air is excluded, pyrrhotite and magnetite are the final reaction products; the amount of magnetite formed is determined by the purity of the starting greigite and the degree of its surficial oxidation. The saturation magnetization of synthetic greigite is virtually independent of temperature from room temperature down to 4 K. The saturation remanent magnetization increases slowly by 20-30 per cent on cooling from room temperature to 4 K. A broad maximum is observed at~10 K which may be diagnostic of greigite. The coercive and remanent coercive force both increase smoothly with decreasing temperature to 4 K. The coercive force increases from~50 mT at room temperature to approximately 100-120 mT at 4 K, and the remanent coercive force increases from approximately 50-80 mT at room temperature to approximately 110-180 mT at 4 K.

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

“…5a) indicate no magnetic transition in the range of 2 K to 300 K, which is consistent with prior low-temperature measurements of greigite [20,21]. Our data did not show the 10 K remanence peak reported by ref [21].…”

“…5a) indicate no magnetic transition in the range of 2 K to 300 K, which is consistent with prior low-temperature measurements of greigite [20,21]. Our data did not show the 10 K remanence peak reported by ref [21]. The absence of transitions specifically excludes the presence of significant magnetite (which has a transition between 80 and 120 K), monoclinic pyrrhotite (which has a transition at 30-35 K), and hematite (which becomes a true antiferromagnet below 260 K).…”

Petrography and shock‐related remagnetization of pyrrhotite in drill cores from the Bosumtwi Impact Crater Drilling Project, Ghana

“…T C s higher than 590 °C probably indicate maghemitization of magnetite during further heating. Pure magnetite can be produced during heating of pyrrhotite (e.g., Dekkers et al 2000), but not from nickel. During the cooling run, additional T C s between 420 and 500 °C probably indicate the formation of an intermediate ferrimagnetic spinel phase during the heating experiment.…”

Paleomagnetic and geochemical record from cores from the Sea of Marmara, Turkey: Age constraints and implications of sapropelic deposition on early diagenesis

“…The sharp magnetic susceptibility increase, starting in all samples at 280°C, indicates the onset of a phase thermal alteration. This temperature is compatible with irreversible greigite decomposition upon heating (Dekkers et al, 2000;Roberts et al, 2011). High-temperature magnetic susceptibility variations undergo another inflection at 320°C and a maximum at 450°C (Fig.…”