Low‐temperature magnetic properties of magnetite

King, James G.; Williams, Wyn

doi:10.1029/2000jb900006

Cited by 43 publications

(47 citation statements)

References 29 publications

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“…3c; Table 1) exhibit increasing loss of remanence upon warming or cooling through the Verwey transition with increasing magnetostatic interactions (decreasing ARM susceptibility), consistent with [42]. In addition, the δ FC /δ ZFC ratio decreases with chain breakdown and only the intact AMB-1 cells pass a Moskowitz test with δ FC /δ ZFC > 2.…”

Section: Lysis Of Magnetotactic Bacteriamentioning

confidence: 54%

Chains, clumps, and strings: Magnetofossil taphonomy with ferromagnetic resonance spectroscopy

Kopp

Weiss

Maloof

et al. 2006

Earth and Planetary Science Letters

182

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Magnetotactic bacteria produce intracellular crystals of magnetite or greigite, the properties of which have been shaped by evolution to maximize the magnetic moment per atom of iron. Intracellular bacterial magnetite therefore possesses traits amenable to detection by physical techniques: typically, narrow size and shape distributions, single-domain size and arrangement in linear chains, and often crystal elongation. Past strategies for searching for bacterial magnetofossils using physical techniques have focused on identifying samples containing significant amounts of single domain magnetite or with narrow coercivity distributions. Searching for additional of traits would, however, increase the likelihood that candidate magnetofossils are truly of biological origin. Ferromagnetic resonance spectroscopy (FMR) is in theory capable of detecting the distinctive magnetic anisotropy produced by chain arrangement and crystal elongation. Here we present analyses of intact and lysed magnetotactic bacteria, dilutions of synthetic magnetite, and sedimentary samples of modern carbonates from the Great Bahama Bank, Oligocene-Miocene deep-sea muds from the South Atlantic, and Pleistocene lacustrine deposits from Mono Basin, California. We demonstrate that FMR can distinguish between intact bacterial magnetite chains, collapsed chains, and linear strings of magnetite formed by physical processes. We also show that sediments in which the magnetization is likely carried by bacterial magnetite have FMR spectra resembling those of intact or altered bacterial magnetite chains.

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Section: Lysis Of Magnetotactic Bacteriamentioning

confidence: 54%

Chains, clumps, and strings: Magnetofossil taphonomy with ferromagnetic resonance spectroscopy

Kopp

Weiss

Maloof

et al. 2006

Earth and Planetary Science Letters

182

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“…Nevertheless, changes of the SIRM lost and magnetic memory (memory refers to recovery of the original direction of remanence or the surviving remanence) after the Verway transition at ~120 K provide clear constraints on magnetite grain size changes against sampling distance of the leaves. Since there is a gradual increase of the SIRM lost with increasing of magnetite grain size in the PSD range [20,21,31] , successive changes of the SIRM lost and magnetic memory against sampling distance (Figs. 2 and 9) imply that magnetite grain size decreases with increasing of sampling distance.…”

Section: Magnetic Composition and Grain Sizementioning

confidence: 97%

“…Low-temperature dependence of SIRM has been repeatedly shown to be one of the most useful methods for identifying the presence of magnetite in rocks and sediments [20,21] . Fig.…”

Section: Low-temperature Propertiesmentioning

confidence: 99%

“…Since the Verway transition at ~120 K of magnetic parameters is a particular characteristic of magnetite [20,21] , low-temperature experiment can availably used to identify the presence of magnetite in tree leaf samples. Together with the IRM acquisition behavior and hysteresis parameters, low-temperature dependence of the SIRM of the tree leaf samples indicates that the entire roadside tree leaf samples are ferromagnetically predominated by PSD magnetite.…”

Section: Magnetic Composition and Grain Sizementioning

confidence: 99%

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Magnetic properties of high-road-side pine tree leaves in Beijing and their environmental significance

Zhang

Huang

et al. 2006

CHINESE SCI BULL

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This is a report on magnetic properties of highroad-side tree (Pinus pumila Regel) leaves collected along an expressway linking Beijing City and the Capital International Airport and further focus on their environmental contributions. A series of rock magnetic experiments show that the primary magnetic mineral of leaf samples was identified to be magnetite, in the pseudo-single domain (PSD) grain size range 0.2-5.0 μm. On the other hand, magnetite concentration and grain size in leaves are ascertained to decrease with increasing of sampling distance to highroad asphalt surface, suggesting that high magnetic response to traffic pollution is localized within a distance of some two meters away from highroad asphalt surface. Although magnetic susceptibility is ordinarily regarded as a simple, rapid and low-cost method for monitoring traffic pollution, saturation isothermal remanent magnetization (SIRM) can be treated as a valid proxy for monitoring air particulate matter (PM) when samples are magnetically weak. It is believed that a synthetic rock magnetic study is an effective method for determining concentration and grain size of ferromagnets in the atmospheric PM, and then it should be a rapid and feasible technique for monitoring atmospheric pollution.

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“…When LTD is done for paleomagnetic purposes, usually only the second memory is measured. King and Williams [9] argue that a more logical de¢nition of memory is the fraction of room-temperature remanence recovered after a complete cycle, i.e. second memory3 ¢rst memory (their Fig.…”

Section: Low-temperature Cycling Of Sirmmentioning

confidence: 99%

Changes in remanence, coercivity and domain state at low temperature in magnetite

Özdemir

Dunlop

Moskowitz

2002

Earth and Planetary Science Letters

161

116

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Submicron magnetite crystals with mean sizes of 0.037, 0.10 and 0.22 Wm undergo major changes in hysteresis properties and domain states in crossing the Verwey transition (T V W120 K). The 0.037 Wm crystals are single-domain (SD) both in the cubic phase at room temperature T 0 and in the monoclinic phase below T V . The 0.10 and 0.22 Wm crystals have a mixture of SD and two-domain (2D) states at room temperature T 0 , but mainly SD structures below T V , in agreement with micromagnetic calculations. Coercive force H c increases on cooling through T V , by a factor 3^5 in the submicron magnetites and 40 in a 1.3 mm single crystal, because of the high crystalline anisotropy and magnetostriction of monoclinic magnetite. As a result, domain walls and SD moments are so effectively pinned below T V that all remanence variations in warming or cooling are reversible. However, between W100 K and T 0 , remanence behavior is variable. Saturation remanence (SIRM) produced in monoclinic magnetite at 5 K drops by 70^100% in warming across T V , with minor recovery in cooling back through T V (ultimate levels at 5 K of 23^37% for the submicron crystals and 3% for the 1.3 mm crystal). In contrast, SIRM produced in the cubic phase at 300 K decreases 5^35% (submicron) or s 95% (1.3 mm) during cooling from 300 to 120 K due to continuous re-equilibration of domain walls, but there is little further change in cooling through T V itself. However, the submicron magnetites lose a further 51 5% of their remanence when reheated through T V . These irreversible changes in cycling across T V , and the amounts of the changes, have potential value in determining submicron magnetite grain sizes. The irreversibility is mainly caused by 2DCSD transformations on cooling through T V , which preserve or enhance remanence, while SDC2D transformations on warming through T V cause remanence to demagnetize. ß

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Low‐temperature magnetic properties of magnetite

Cited by 43 publications

References 29 publications

Chains, clumps, and strings: Magnetofossil taphonomy with ferromagnetic resonance spectroscopy

Chains, clumps, and strings: Magnetofossil taphonomy with ferromagnetic resonance spectroscopy

Magnetic properties of high-road-side pine tree leaves in Beijing and their environmental significance

Changes in remanence, coercivity and domain state at low temperature in magnetite

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