Magnetic Properties of Hydrothermally Recrystallized Magnetite Crystals

Abstract

The discrepancy between the magnetic hysteresis properties of magnetite crystals that are precipitated from solution (<0.3 micrometer) and of crushed sifted grains (>0.3 micrometer) is not an inherent property of magnetite but is caused by the highly stressed state of crushed material and by adhering finer fragments. The size trends of magnetic properties exhibited by submicrometer-size precipitated grains continue in the size range from 1 micrometer to 1 millimeter in a set of hydrothermally recrystallized magnetite crystals. Coercive forces of these narrowly sized crystals follow a power law over a wide size range (0.1 micrometer to 1 millimeter) as predicted by theory. Dislocation etch pits show similar dislocation densities for hydrothermally grown (3 x 10(10) meter (-2)) and natural (1 x 10(10) meter(-2)) magnetite crystals. Hysteresis parameters of hydrothermally grown crystals are similar to those of natural crystals but are about one-fifth of those for crushed grains.

High Southern Latitude Magnetostratigraphy and Rock Magnetic Properties of Sediments from Sites 747, 749, and 751

“…The two samples from the Pliocene diatom ooze have softer magnetic remanence carriers than the two samples from the diatom nannofossil ooze of early Miocene age. Despite this difference, all four samples from Site 751 have SD-or PSD-like demagnetization curves (MDF > 25 mT) distinctly different from the much softer multidomain (MD) AF demagnetization behavior of magnetite (MDF < 10 mT) (Heider, 1988). Similar groupings to the ones in Figures 8A and 8B were found for the AF demagnetization curves of ARMs in the 11 samples.…”

“…The results from all samples lie in the field, which is characteristic for small PSD particles close to the SD region. Multidomain grains of magnetite above 10 µm in diameter have IJI S <0.006 and HJH C ratios around 25 (Heider et al, 1987). We will show with the low-temperature experiments below that some of the samples contain particles in the SP (superparamagnetic) size range.…”

“…These two samples probably contain an additional magnetic phase with high coercivity values. A Lowrie-Fuller test (Lowrie and Fuller, 1971;Bailey and Dunlop, 1983;Heider, 1988) was performed to determine the domain state of the magnetic minerals. All samples were given anhysteretic remanent magnetization with a 160-mT peak alternating field and a 0.1-or 2-mT bias field.…”

Rock-Magnetic Properties of Pleistocene Passive Margin sediments: Environmental Change and Diagenesis offshore New Jersey

“…Both hysteresis properties H c (coercive force) and M rs /M s (remanent saturation magnetization/saturation magnetization) are strongly grain-size dependent for hydrothermally grown magnetite (Heider et al, 1987 properties of the New Jersey slope samples are comparable to hydrothermally grown magnetite, the two power laws were linked by way of grain-size d in a linear equation, using the proportionality factors 3.83 (H c ) and 0.039 for M rs /M s (cf. Karlin, 1990aKarlin, , 1990b IRM-acquisition curves representative of the sampled section at Hole 904A indicate magnetite ( Fig.…”

Paleomagnetic and Rock Magnetic Properties of Hole 896A

“…We do not think that this is appropriate for this data set because we have not measured the degree of maghematization and because this model is appropriate only for a narrow range of compositions. The grain size of the magnetites has been related to the hysteresis properties, particularly the coercive force, H c (Heider et al, 1987). This relationship is not entirely suitable for titanomagnetites (see, e.g., fig.…”