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1

Thermal Decomposition of an Impure (Roxbury) Siderite: Relevance to the Presence of Chemically Pure Magnetite Crystals in ALH84001 Carbonate Disks  

NASA Astrophysics Data System (ADS)

Thermal decomposition of Roxbury siderite resulted in the formation of impure (Mg,Mn)-ferrites. These findings, which are supported by kinetic and thermodynamic equilibrium modeling studies, are in stark contrast to the chemically pure ALH 84001 magnetite.

Thomas-Keprta, K. L.; Clemett, S. J.; McKay, D. S.; Gibson, E. K.; Wentworth, S. J.

2009-03-01

2

Non-chemically Pure Magnetites Produced from Thermal Decomposition of Ankerites  

NASA Astrophysics Data System (ADS)

It has been claimed that chemically pure magnetites (Fe3O4) can be obtained from thermal decomposition of (Fe, Mg, Ca)CO3 (Golden et al., 2004). Such an observation is critical, since it opens the possibility of an inorganic way of formation of the magnetites found on Martian meteorite ALH84001. Such a chemical purity is one of the parameters used, so far, to recognize bacterial origin of natural magnetites (Thomas-Keptra et al., 2001), since it has been demonstrated that biologically-controlled magnetites are chemically pure (Bazylinski and Frankel, 2004) . However, while Golden et al. (2004) obtained pure magnetite from an almost pure precursor, the ankerite cores in ALH84001 in which magnetites are embedded are far from being chemically pure, since they contain considerable amounts of Ca and Mg (Kopp and Humayun, 2003). In this study we have performed several experiments to analyze the chemical purity of magnetites produced by thermal decomposition of four ankerite samples sinthetized in the laboratory, and containing different amounts of Ca, Fe and Mg. Such a thermal decomposition was achieved by two procedures: (1) by heating the samples at 470°C under CO2 pressure and (2) by decomposing the ankerite "in situ" under the TEM (Transmission electron Microscopy) electron beam. Magnetite produced by the first procedure was analyzed by XRD to determine whether or not the resulting solid was a mixture of oxides or rather a solid solution of (Ca, Fe and Mg)oxide. Magnetites formed by the two methods were studied by High Resolution TEM. The chemical composition of about 20 crystals of each experiment was analyzed by EDAX. Under our experimental conditions, ankerites decomposed in magnetite crystals of about 5 nanometers in size. Magentite crystals arranged to keep the morphology of the precursor. Our results confirm that any of these magnetites is chemically pure, but rather, each one of them is a solid solution of Ca and Mg. Therefore, chemically pure magnetites found in the meteorite ALH84001 cannot be obtained, as Golden et al. (2004) proposed, just by the thermal decomposition of the (Fe, Ca, Mg)CO3 precursor in which they were embedded.

Jiménez López, C.; Romanek, C.; Rodríguez-Navarro, A.; Pérez-González, T.; Rodríguez Navarro, C.

2008-12-01

3

Small angle neutron and X-ray scattering from magnetite crystals in magnetotactic bacteria  

Microsoft Academic Search

Small angel neutron and X-ray scattering were used to study the magnetic and structural properties, respectively, of intracellular magnetite crystals (magnetosomes) in the bacterium, Aquaspirillum magnetotacticum, grown in pure culture. An average of twenty magnetite particles of diameter 400-500 Å are arranged in a chain that longitudinally traverses each cell. Behaving like magnetic dipoles, the bacteria orient in the geomagnetic

S. Krueger; G. J. Olson; J. J. Rhyne; R. P. Blakemore; Y. A. Gorby; N. Blakemore

1989-01-01

4

Experimental study of chemical and crystallization remanent magnetizations in magnetite  

Microsoft Academic Search

Crystallization magnetization (KRM) of magnetite is experimentally studied by the oxidation of fine grains of pyrite and by the oxidation (unmixing) of titanomagnetite with Tc = 150-200°C at the temperature of 400-450°C in the magnetic field of 50-100 mkT. Chemical remanence (CRM) of magnetite, which forms by the unmixing of titanomaghemite with Tc = 380-450°C at the temperature of 350°C

T. K. T. Nguyen; D. M. Pechersky

1987-01-01

5

Study of magnetite nanoparticles embedded in lyotropic liquid crystals  

Microsoft Academic Search

A study about the magnetic behaviour of magnetite nanoparticles diluted in lyotropic liquid crystals was carried out. It was corroborated that micellar phases of the liquid crystal suppressed the superparamagnetism of the nanoparticles by rising the blocking temperature beyond the room temperature. Phase transitions in the lyotropic mixtures can be determined from M vs. T curves of the ferrolyotropic. When

F. R. Arantes; A. M. Figueiredo Neto; D. R. Cornejo

2010-01-01

6

Magnetite nanorod thermotropic liquid crystal colloids: synthesis, optics and theory.  

PubMed

We have developed a facile method for preparing magnetic nanoparticles which couple strongly with a liquid crystal (LC) matrix, with the aim of preparing ferronematic liquid crystal colloids for use in magneto-optical devices. Magnetite nanoparticles were prepared by oxidising colloidal Fe(OH)(2) with air in aqueous media, and were then subject to alkaline hydrothermal treatment with 10 mol dm(-3) NaOH at 100°C, transforming them into a polydisperse set of domain magnetite nanorods with maximal length ~500 nm and typical diameter ~20 nm. The nanorods were coated with 4-n-octyloxybiphenyl-4-carboxylic acid (OBPh) and suspended in nematic liquid crystal E7. As compared to the conventional oleic acid coating, this coating stabilizes LC-magnetic nanorod suspensions. The suspension acts as a ferronematic system, using the colloidal particles as intermediaries to amplify magnetic field-LC director interactions. The effective Frederiks magnetic threshold field of the magnetite nanorod-liquid crystal composite is reduced by 20% as compared to the undoped liquid crystal. In contrast with some previous work in this field, the magneto-optical effects are reproducible on time scales of months. Prospects for magnetically switched liquid crystal devices using these materials are good, but a method is required to synthesize single magnetic domain nanorods. PMID:22935749

Podoliak, Nina; Buchnev, Oleksandr; Bavykin, Dmitry V; Kulak, Alexander N; Kaczmarek, Malgosia; Sluckin, Timothy J

2012-08-03

7

Chains of Magnetite Crystals in Allan Hills 84001: Evidence of Biological Origin  

NASA Astrophysics Data System (ADS)

The presence of magnetite crystals in carbonate globules in ALH-84001 was one fact leading to the suggestion that this meteorite may contain relics of martian life. These magnetite crystals are morphologically similar in shape and size to magnetosomes formed by magnetotactic bacteria, but less so to typical inorganically formed magnetite crystals. The size range is significant, as within this range the magnetic moment of the crystals is maximal. Terrestrial magnetobacteria produce magnetosomes, magnetite (Fe3O4), or greigite (Fe3S4) crystals assembled into chains, and the organisms use these chains for aligning themselves along the prevailing magnetic field. No inorganic process is known to produce similar structures.

Friedmann, E. I.; Wierzchos, J.; Ascaso, C.

1998-01-01

8

Elongated prismatic magnetite crystals in ALH84001 carbonate globules: potential Martian magnetofossils.  

PubMed

Using transmission electron microscopy (TEM), we have analyzed magnetite (Fe3O4) crystals acid-extracted from carbonate globules in Martian meteorite ALH84001. We studied 594 magnetites from ALH84001 and grouped them into three populations on the basis of morphology: 389 were irregularly shaped, 164 were elongated prisms, and 41 were whisker-like. As a possible terrestrial analog for the ALH84001 elongated prisms, we compared these magnetites with those produced by the terrestrial magnetotactic bacteria strain MV-1. By TEM again, we examined 206 magnetites recovered from strain MV-1 cells. Natural (Darwinian) selection in terrestrial magnetotactic bacteria appears to have resulted in the formation of intracellular magnetite crystals having the physical and chemical properties that optimize their magnetic moment. In this study, we describe six properties of magnetite produced by biologically controlled mechanisms (e.g., magnetotactic bacteria), properties that, collectively, are not observed in any known population of inorganic magnetites. These criteria can be used to distinguish one of the modes of origin for magnetites from samples with complex or unknown histories. Of the ALH84001 magnetites that we have examined, the elongated prismatic magnetite particles (similar to 27% of the total) are indistinguishable from the MV-1 magnetites in five of these six characteristics observed for biogenically controlled mineralization of magnetite crystals. PMID:11543573

Thomas-Keprta, K L; Bazylinski, D A; Kirschvink, J L; Clemett, S J; McKay, D S; Wentworth, S J; Vali, H; Gibson, E K; Romanek, C S

2000-12-01

9

Properties of intracellular magnetite crystals produced by Desulfovibrio magneticus strain RS1  

Microsoft Academic Search

Desulfovibrio magneticus strain RS-1 is an anaerobic sulfate-reducing bacterium. Cells form intracellular nanocrystals of magnetite but are only weakly magnetotactic. In order to understand the unusual magnetic response of this strain, we studied magnetite crystals within cells grown with fumarate and sulfate. Many cells grown under either condition did not form magnetic crystals while others contained only 1 to 18

Mihály Pósfai; Bruce M. Moskowitz; Balázs Arató; Dirk Schüler; Christine Flies; Dennis A. Bazylinski; Richard B. Frankel

2006-01-01

10

Iron et al.: Incorporation of Manganese in the Crystal Lattice of Magnetosome Magnetite  

NASA Astrophysics Data System (ADS)

Incorporation of foreign metal into the crystal matrix of the magnetotactic bacterial magnetite has been attempted worldwide. Recently, presence of small amounts of cobalt and manganese in magnetosome magnetite crystals in cultured and uncultured magnetotactic bacteria, respectively, was reported. Magnetization of the uncultured cells and their magnetosomes were not determined, while only marginal changes in the magnetic properties of the cultured cobalt-grown cells and their magnetosomes were observed, however no evidence of incorporation of these metals into the crystalline lattice was presented. We grew cells of a magnetotactic bacterium, Magnetospirillum gryphiswaldense strain MSR-1, in the presence of manganese, ruthenium, zinc and vanadium, of which only manganese was incorporated within the magnetosome magnetite crystals. For the first time we demonstrate that the magnetic properties of magnetite crystals of magnetotactic bacteria can be significantly altered by the incorporation of metal ions, other than iron, in the crystal structure, as signaled by a major shift in the Verwey transition.

Prozorov, Tanya; Perez-Gonzalez, Teresa; Jimenez-Lopez, Concepcion; Mallapragada, Surya K.; Howse, Paul; Bazylinski, Dennis A.; Prozorov, Ruslan

2010-03-01

11

Small angle neutron and X-ray scattering from magnetite crystals in magnetotactic bacteria  

NASA Astrophysics Data System (ADS)

Small angel neutron and X-ray scattering were used to study the magnetic and structural properties, respectively, of intracellular magnetite crystals (magnetosomes) in the bacterium, Aquaspirillum magnetotacticum, grown in pure culture. An average of twenty magnetite particles of diameter 400-500 Å are arranged in a chain that longitudinally traverses each cell. Behaving like magnetic dipoles, the bacteria orient in the geomagnetic field. Small angle X-ray scattering measurements revealed that bacteria grown in the presence of large amounts of iron contained magnetosomes with diameters averaging approximately 400 Å. Those grown under iron-starved conditions contained particles with slightly smaller diameters. The contrast variation technique was used for the small angle neutron scattering measurements in order to establish that a 30% D2O/H2O ratio in the solvent resulted in the maximization of the scattering from the bacterium itself, thus enhancing that from the magnetosomes. Measurements in 30% D2O and an applied field of 25 G confirmed that the scattering from the larger magnetic particles is of ferromagnetic character whereas that from the smaller particles is consistent with super-paramagnetic particles. The static spin correlations were found to be of relatively long range, with dynamical fluctuations corresponding to a distance scale of approximately 50 Å.

Krueger, S.; Olson, G. J.; Rhyne, J. J.; Blakemore, R. P.; Gorby, Y. A.; Blakemore, N.

1989-11-01

12

MMS6 protein regulates crystal morphology during nano-sized magnetite biomineralization in vivo.  

PubMed

Biomineralization, the process by which minerals are deposited by organisms, has attracted considerable attention because this mechanism has shown great potential to inspire bottom-up material syntheses. To understand the mechanism for morphological regulation that occurs during biomineralization, many regulatory proteins have been isolated from various biominerals. However, the molecular mechanisms that regulate the morphology of biominerals remain unclear because there is a lack of in vivo evidence. Magnetotactic bacteria synthesize intracellular magnetosomes that comprise membrane-enveloped single crystalline magnetite (Fe(3)O(4)). These nano-sized magnetite crystals (<100 nm) are bacterial species dependent in shape and size. Mms6 is a protein that is tightly associated with magnetite crystals. Based on in vitro experiments, this protein was first implicated in morphological regulation during nano-sized magnetite biomineralization. In this study, we analyzed the mms6 gene deletion mutant (?mms6) of Magnetospirillum magneticum (M. magneticum) AMB-1. Surprisingly, the ?mms6 strain was found to synthesize the smaller magnetite crystals with uncommon crystal faces, while the wild-type and complementation strains synthesized highly ordered cubo-octahedral crystals. Furthermore, deletion of mms6 gene led to drastic changes in the profiles of the proteins tightly bound to magnetite crystals. It was found that Mms6 plays a role in the in vivo regulation of the crystal structure to impart the cubo-octahedral morphology to the crystals during biomineralization in magnetotactic bacteria. Magnetotactic bacteria synthesize magnetite crystals under ambient conditions via a highly controlled morphological regulation system that uses biological molecules. PMID:21169637

Tanaka, Masayoshi; Mazuyama, Eri; Arakaki, Atsushi; Matsunaga, Tadashi

2010-12-18

13

MMS6 Protein Regulates Crystal Morphology during Nano-sized Magnetite Biomineralization in Vivo*  

PubMed Central

Biomineralization, the process by which minerals are deposited by organisms, has attracted considerable attention because this mechanism has shown great potential to inspire bottom-up material syntheses. To understand the mechanism for morphological regulation that occurs during biomineralization, many regulatory proteins have been isolated from various biominerals. However, the molecular mechanisms that regulate the morphology of biominerals remain unclear because there is a lack of in vivo evidence. Magnetotactic bacteria synthesize intracellular magnetosomes that comprise membrane-enveloped single crystalline magnetite (Fe3O4). These nano-sized magnetite crystals (<100 nm) are bacterial species dependent in shape and size. Mms6 is a protein that is tightly associated with magnetite crystals. Based on in vitro experiments, this protein was first implicated in morphological regulation during nano-sized magnetite biomineralization. In this study, we analyzed the mms6 gene deletion mutant (?mms6) of Magnetospirillum magneticum (M. magneticum) AMB-1. Surprisingly, the ?mms6 strain was found to synthesize the smaller magnetite crystals with uncommon crystal faces, while the wild-type and complementation strains synthesized highly ordered cubo-octahedral crystals. Furthermore, deletion of mms6 gene led to drastic changes in the profiles of the proteins tightly bound to magnetite crystals. It was found that Mms6 plays a role in the in vivo regulation of the crystal structure to impart the cubo-octahedral morphology to the crystals during biomineralization in magnetotactic bacteria. Magnetotactic bacteria synthesize magnetite crystals under ambient conditions via a highly controlled morphological regulation system that uses biological molecules.

Tanaka, Masayoshi; Mazuyama, Eri; Arakaki, Atsushi; Matsunaga, Tadashi

2011-01-01

14

Analysis of magnetite crystals and inclusion bodies inside magnetotactic bacteria from different environmental locations  

NASA Astrophysics Data System (ADS)

Biomineralization occurs throughout the living world; a few common examples include iron oxide in chiton teeth, calcium carbonate in mollusk shells, calcium phosphate in animal bones and teeth, silica in diatom shells, and magnetite crystals inside the cells of magnetotactic bacteria. Biologically controlled mineralization is characterized by biominerals that have species-specific properties such as: preferential crystallographic orientation, consistent particle size, highly ordered spatial locations, and well-defined composition and structure. It is well known that magnetotactic bacteria synthesize crystals of magnetite inside of their cells, but how they mineralize the magnetite is poorly understood. Magnetosomes have a species-specific morphology that is due to specific proteins involved in the mineralization process. In addition to magnetite crystals, magnetotactic bacteria also produce inclusion bodies or granules that contain different elements, such as phosphorus, calcium, and sulfur. In this study we used the transmission electron microscope to analyze the structure of magnetite crystals and inclusion bodies from different species of magnetotactic bacteria in order to determine the composition of the inclusion bodies and to ascertain whether or not the magnetite crystals contain elements other than iron and oxygen. Using energy dispersive spectroscopy we found that different bacteria from different environments possess inclusion bodies that contain different elements such as phosphorus, calcium, barium, magnesium, and sulfur. These differences may reflect the conditions of the environment in which the bacteria inhabit.

Oestreicher, Z.; Lower, B.; Lower, S.; Bazylinski, D. A.

2011-12-01

15

Properties of intracellular magnetite crystals produced by Desulfovibrio magneticus strain RS-1  

NASA Astrophysics Data System (ADS)

Desulfovibrio magneticus strain RS-1 is an anaerobic sulfate-reducing bacterium. Cells form intracellular nanocrystals of magnetite but are only weakly magnetotactic. In order to understand the unusual magnetic response of this strain, we studied magnetite crystals within cells grown with fumarate and sulfate. Many cells grown under either condition did not form magnetic crystals while others contained only 1 to 18 small (˜ 40 nm) magnetite-containing magnetosomes. Bulk magnetic measurements of whole cells showed a superparamagnetic-like behavior, indicating that many of the magnetite crystals are too small to have a permanent magnetic moment at ambient temperature. The temperature of the Verwey transition is lower (˜ 86 K) than of magnetite from other magnetotactic strains, likely indicating partial oxidation of magnetite into maghemite. As a result of the small size and small number of magnetite magnetosomes, the magnetic moments of most cells grown anaerobically with fumarate or sulfate are insufficient for magnetotaxis. In addition to intracellular magnetite, in some cultures another iron oxide, hematite, formed on the surfaces of cells. The hematite grains are embedded in an extracellular polymeric material, indicating that the crystals likely resulted from a biologically-induced mineralization process. Although the hematite particles appear to consist of aggregations of many small (5 to 10 nm) grains, the grains have a consensus orientation and thus the whole particle diffracts as a single crystal. The aligned arrangement of nanoparticles within larger clusters may reflect either a templated nucleation of hematite crystallites in an extracellular organic matrix, or result from a self-assembling process during the crystallization of hematite from ferric gels or ferrihydrite.

Pósfai, Mihály; Moskowitz, Bruce M.; Arató, Balázs; Schüler, Dirk; Flies, Christine; Bazylinski, Dennis A.; Frankel, Richard B.

2006-09-01

16

Did an Impact Make the Mysterious Microscopic Magnetite Crystals in ALH 84001?  

NASA Astrophysics Data System (ADS)

Fervent debate swirls around microscopic crystals of magnetite (Fe3O4) in Martian meteorite ALH 84001. Some investigators suggest that the crystals are evidence of past life on Mars, citing magnetite crystals of similar chemical compositions and sizes made by magnetotactic bacteria on Earth. Others cite assorted experiments and observations to argue that the important little crystals formed entirely by non-biological processes, hence say nothing about life on Mars. One of those processes is the decomposition of iron carbonate (the mineral siderite), which occurs in ALH 84001. Researchers argue that heating this mineral causes it to decompose into magnetite and CO2 gas. Experiments showing this were done by heating siderite and observing that it decomposed and formed magnetite, but nobody had shock-heated siderite to see if magnetite crystals formed. (Shock is a rapid, strong rise and fall in pressure. It happens under many circumstances, including meteorite impacts.) The lack of shock experiments has been solved by Mary Sue Bell (University of Houston and Jacobs Engineering). She experimentally shocked samples of siderite at the Experimental Impact Laboratory at the Johnson Space Center. She shows that magnetite crystals of the right size and composition formed when samples were shocked to 49 GPa (about 500,000 times the pressure at the Earth's surface). This is more evidence for a non-biological origin for the magnetite crystals in ALH 84001 and is consistent with what we know about the impact history of the rock. There seems to be growing evidence against a biological origin, but don't expect these results to completely settle the debate!

Taylor, G. J.

2007-10-01

17

Magnetic behavior of 10 nm-magnetite particles diluted in lyotropic liquid crystals  

NASA Astrophysics Data System (ADS)

A magnetic study of 10nm magnetite nanoparticles diluted in lyotropic liquid crystal and common liquids was carried out. In the liquid crystal the ZFC-FC curves showed a clear irreversible behavior, and it was possible to distinguish the nematic from the isotropic phase since the magnetization followed the dependence of the nematic order parameter with the temperature. This behavior could be mimicked by Monte Carlo simulation.

Arantes, F. R.; Figueiredo Neto, A. M.; Cornejo, D. R.

2011-04-01

18

Microstructural characterization of metamorphic magnetite crystals with implications for oxygen isotope distribution  

SciTech Connect

The microstructures of magnetite crystals in three samples from a single outcrop of granulite-facies marble were characterized by transmission electron microscopy (TEM) to determine how exsolution history can affect physical properties and mineral reactivity during retrograde metamorphism. The microstructure of sample 90LP9 consists of dislocation, dislocation arrays (with dislocation spacings of 100 to 500 nm), and linear channels filled with layer silicates. Acid etching and ion milling of polished 90LP9 magnetite grains show dislocation arrays clustered near grain boundaries with rheologically hard magnetite, diopside, and monticellite, but rarely near grain boundaries with softer calcite. Samples LP204-1 magnetite grains contain coherent {l{underscore}brace}100{r{underscore}brace} Al-Mn-Fe-spinel precipitates ({approximately}40 nm diameter, {approximately}1--3 nm thick, {approximately}10{sup 4} platelets/{micro}m{sup 3}) and very few dislocations. Larger, more widely spaced spinel precipitates are present in a third sample, 94AK3. Extremely low dislocation densities in powders of LP204-1 and intermediate dislocation densities in powders of 94AK3, compared with extremely high dislocation densities in powders of 90LP9, are related to strong dislocation pinning effects by precipitates. The different exsolution behavior of the three magnetite samples is attributed to small, but important, differences in Al content. Because dislocations can provide fast pathways for exchange that enhance diffusion, especially in very slowly cooled rocks, these microstructural results may explain previously reported subgrain-scale oxygen isotopic heterogeneity in 90LP9 magnetite compared with relative isotopic homogeneity in LP204-1 magnetite.

Sitzman, S.D.; Banfield, J.F.; Valley, J.W.

2000-01-01

19

Inorganic Magnetite Precipitation at 25?°C: A Low-Cost Inorganic Coprecipitation Method  

Microsoft Academic Search

An easy, low-cost coprecipitation method to inorganically produce magnetite nanoparticles from solutions, in free-drift experiments,\\u000a under anoxic conditions, at 25?°C and 1 atm pressure is here presented. By using this method, pure magnetite is obtained as\\u000a the final solid, which shows the typical magnetic properties and thermal stability behavior of magnetite produced by other\\u000a methods. The size of the magnetite crystals

T. Perez-Gonzalez; A. Rodriguez-Navarro; C. Jimenez-Lopez

2011-01-01

20

Magnetite 3D colloidal crystals formed in the early solar system 4.6 billion years ago.  

PubMed

Three-dimensional colloidal crystals made of ferromagnetic particles, such as magnetite (Fe(3)O(4)), cannot be synthesized in principle because of the strong attractive magnetic interaction. However, we discovered colloidal crystals composed of polyhedral magnetite nanocrystallites of uniform size in the range of a few hundred nanometers in the Tagish Lake meteorite. Those colloidal crystals were formed 4.6 billion years ago and thus are much older than natural colloidal crystals on earth, such as opals, which formed about 100 million years ago. We found that the size of each individual magnetite particle determines its morphology, which in turn plays an important role in deciding the packing structure of the colloidal crystals. We also hypothesize that each particle has a flux-closed magnetic domain structure, which reduces the interparticle magnetic force significantly. PMID:21563777

Nozawa, Jun; Tsukamoto, Katsuo; van Enckevort, Willem; Nakamura, Tomoki; Kimura, Yuki; Miura, Hitoshi; Satoh, Hisao; Nagashima, Ken; Konoto, Makoto

2011-05-18

21

Chains of magnetite crystals in the meteorite ALH84001: evidence of biological origin.  

PubMed

The presence of magnetite crystal chains, considered missing evidence for the biological origin of magnetite in ALH84001 [Thomas-Keprta, K. L., Bazylinski, D. A., Kirschvink, J. L., Clemett, S. J., McKay, D. S., Wentworth, S. J., Vali, H., Gibson, E. K., Jr., & Romanek, C. S. (2000) Geochim. Cosmochim. Acta 64, 4049-4081], is demonstrated by high-power stereo backscattered scanning electron microscopy. Five characteristics of such chains (uniform crystal size and shape within chains, gaps between crystals, orientation of elongated crystals along the chain axis, flexibility of chains, and a halo that is a possible remnant of a membrane around chains), observed or inferred to be present in magnetotactic bacteria but incompatible with a nonbiological origin, are shown to be present. Although it is unlikely that magnetotactic bacteria were ever alive in ALH84001, decomposed remains of such organisms could have been deposited in cracks in the rock while it was still on the surface on Mars. PMID:11226212

Friedmann, E I; Wierzchos, J; Ascaso, C; Winklhofer, M

2001-02-27

22

Polar properties of nominally pure polarized TGS crystals  

NASA Astrophysics Data System (ADS)

Using the method of dynamic pyroeffect, polar properties of surface layers of nominally pure triglycinesulfate (TGS) crystals prepolarized in an electrostatic field are experimentally investigated. The results on the pyrocoefficient distribution over the crystal thickness modeled using the experimental dependences are reported. The model relies on the solution to the first-order integral Fredholm equation by the method of Tikhonov's regularization.

Kushnarev, P. I.; Maslovskaya, A. G.; Baryshnikov, S. V.

2011-06-01

23

Intrinsic response of crystals to pure dilatation.  

National Technical Information Service (NTIS)

The response of an f.c.c. lattice with Lennard-Jones interaction under symmetric lattice extension has been studied by Monte Carlo simulation at several temperatures. The critical strain at which the crystal undergoes a structural change is found to be we...

J. Wang S. Yip S. Phillpot D. Wolf

1991-01-01

24

Thermally populated intrinsic localized modes in pure alkali halide crystals  

NASA Astrophysics Data System (ADS)

The possibility of thermal excitation of intrinsic localized modes (ILMs) arising from anharmonicity in ionic perfect crystals is studied numerically for realistic model systems in one and three dimensions. Implications are discussed for an interesting high-temperature feature seen in earlier inelastic neutron scattering experiments on single crystal NaI. The general conclusion is that ILM formation energies are far too large for thermal excitation of ILMs to account for the observed feature in a pure crystal.

Sievers, A. J.; Sato, M.; Page, J. B.; Rössler, T.

2013-09-01

25

Imaging faces of shadowed magnetite (Fe(3)O(4)) crystals from magnetotactic bacteria with energy-filtering transmission electron microscopy.  

PubMed

We used energy-filtering transmission electron microscopy to image magnetite crystals isolated from uncultured magnetotactic bacteria. These magnetite crystals were shadowed in high vacuum with platinum at 45 degrees. The shadowed crystals were observed in a Zeiss (Thornwood, NY) CEM902 transmission electron microscope. Imaging shadowed crystals with inelastically scattered electrons provided information of the decoration pattern of small platinum particles over crystal surfaces, and thus information on surface characteristics of crystals. Results were comparable to those obtained from scanning electron microscopy using a field emitter gun. Electron energy loss spectra of the crystals as well as of the supporting film were recorded to evaluate variations of image contrast with energy losses. Results indicated that the contrast is attenuated with inelastic imaging and that the effect of contrast tuning caused a contrast inversion at a given point between 100 and 150 eV. We believe this approach can be useful for studying multilayered materials by transmission electron microscopy. PMID:10469468

Lins, U; Kachar, B; Farina, M

26

Intrinsic response of crystals to pure dilatation  

SciTech Connect

The response of an f.c.c. lattice with Lennard-Jones interaction under symmetric lattice extension has been studied by Monte Carlo simulation at several temperatures. The critical strain at which the crystal undergoes a structural change is found to be well predicted by the mechanical stability limit expressed in terms of either the elastic constants or the bulk modulus. At low temperature (reduced temperature T = 0.125), lattice decohesion is observed in the form of cleavage fracture, whereas at higher temperature (T = 0.3) the strained system deforms by cavitation with some degree of local plasticity. At still higher temperature (T = 0.5) the lattice undergoes homogeneous disordering with all the attendant characteristics of melting.

Wang, Jinghan; Yip, S. (Massachusetts Inst. of Tech., Cambridge, MA (United States). Dept. of Nuclear Engineering); Phillpot, S.; Wolf, D. (Argonne National Lab., IL (United States))

1991-01-01

27

Intrinsic response of crystals to pure dilatation  

SciTech Connect

The response of an f.c.c. lattice with Lennard-Jones interaction under symmetric lattice extension has been studied by Monte Carlo simulation at several temperatures. The critical strain at which the crystal undergoes a structural change is found to be well predicted by the mechanical stability limit expressed in terms of either the elastic constants or the bulk modulus. At low temperature (reduced temperature T = 0.125), lattice decohesion is observed in the form of cleavage fracture, whereas at higher temperature (T = 0.3) the strained system deforms by cavitation with some degree of local plasticity. At still higher temperature (T = 0.5) the lattice undergoes homogeneous disordering with all the attendant characteristics of melting.

Wang, Jinghan; Yip, S. [Massachusetts Inst. of Tech., Cambridge, MA (United States). Dept. of Nuclear Engineering; Phillpot, S.; Wolf, D. [Argonne National Lab., IL (United States)

1991-12-31

28

Growth and characterization of pure and doped btzs single crystals  

NASA Astrophysics Data System (ADS)

The growth and characterization of pure and doped BTZS single crystals are discussed. In the present study powder X-Ray diffraction data of the grown crystal were recorded using BRUKER D8 Advance powder crystal X-ray diffractometer with 2.2 KW Cu anode ceramic X-ray tube. The various functional groups present in the grown crystals were identified and confirmed by recording the FTIR spectrum using BRUKER IFS-66V spectrophotometer by KBr Pellet Technique in the region 4000 â?? 400 cm The UV - Vis - NIR optical spectra of the crystals were recorded using the VARIAN CARY 5E model spectrophotometer. The degree of dopant inclusion was estimated by using Atomic Absorption Spectroscopy. The SHG efficiencies of the crystals were studied using Nd:YAG Q - switched laser.

Gunasekaran, Sethu; Venkatesan, Padmapriya

2012-05-01

29

Magnetic susceptibility and remanent coercive force in grown magnetite crystals from 0.1 ?m to 6 mm  

Microsoft Academic Search

Initial susceptibility is frequently used as a palaeoclimatic indicator in sediments, but its grain size dependence is not well established. We measured initial magnetic susceptibility ?0 in grown and natural magnetite crystals ranging from 0.09 ?m to 6 mm in grain size. Over these five decades of grain diameter, the presented initial susceptibilities are essentially independent of grain size with

Franz Heider; Anke Zitzelsberger; Karl Fabian

1996-01-01

30

Dendritic crystal growth in pure /sup 4/He  

SciTech Connect

Dendritic crystal growth of pure hcp and fcc /sup 4/He was observed at pressures between 210 and 6500 bar. Dendrite morphology depends on fluid supercooling and crystal phase. At large supercooling, dendrites with side arms are observed, whereas at low supercooling dendrites grow without side arms. The morpholpogy of hcp /sup 4/He dendrites is strongly influenced by crystalline anisotropy. Comparison with present theories of dendrite growth show good agreement with the power law dependencies of velocity, tip radius, and Peclet number on supercooling. Numerically, theory predicts much larger velocities than are observed. The stability parameter sigma is found to be much smaller than theoretically predicted.

Franck, J.P.; Jung, J.

1986-08-01

31

Closure domains in magnetite  

Microsoft Academic Search

We have observed clear arrays of closure domains at internal and external boundaries, such as crystal edges, cracks, and chemically altered regions, in a single crystal of magnetite, using the Bitter colloid technique with a (110) viewing plane. The common occurrence of closure domains in magnetite confirms the controlling role of magnetostatic energy in determining domain structures in strongly magnetic

Ozden Ozdemir; Song Xu; David J. Dunlop

1995-01-01

32

Liquid crystal-in-water emulsion stabilized by layer-by-layer adsorption of polyelectrolytes and magnetite nanoparticles  

NASA Astrophysics Data System (ADS)

We propose a method for stabilizing and modifying the dispersed phase of a liquid crystal-in-water (LC/water) emulsion using the sequential adsorption of polyelectrolytes and magnetite nanoparticles, which leads to the formation of LC-filled nanocomposite microcapsules. The obtained samples were studied by optical microscopy and Raman spectroscopy. It is established that the LC-filled nanocomposite microcapsules can move under the action of an external magnetic field.

Sadovoy, A. V.; Bratashov, D. N.; Yashchenok, A. M.; Svenskaya, Yu. I.; Sukhorukov, G. B.; Gorin, D. A.

2010-01-01

33

Domain structures in single crystal magnetite below the Verwey Transition as observed with a low-temperature magnetic force microscope  

NASA Astrophysics Data System (ADS)

The magnetic domain structures on the {110} plane of magnetite (Fe3O4) below the Verwey transition (Tv=120K) were studied using a Low-Temperature Magnetic Force Microscope (LTMFM). At 298K, domain structures consisted of arrays of 180°, 109° and 71° walls, typical for magnetite with cubic anisotropy. At 77K (below Tv), the cubic style patterns disappeared and transformed into uniaxial patterns consistent with the uniaxial magnetocrystalline symmetry of the low-temperature monoclinic phase of magnetite. We also observed two distinct styles of domain patterns below Tv: (1) wide domains separated by straight 180° walls along the in-plane [100] easy axis; and (2) intricate wavy walls with reverse spike domains characteristic of out-of-plane easy axes. This intimate mixture of domain styles within adjacent areas of the crystal reflects variations in the direction of the magnetic easy axes in different regions produced by c-axis twinning of the crystal below Tv The thermal dependence of planar and wavy-wall patterns show little change from 77K until 110K, where patterns disappear. Upon cooling back to 77K, domain structures are different from the initial 77K states, indicating that renucleation of different domain states occurs by cycling near Tv.

Moloni, Katerina; Moskowitz, Bruce M.; Dahlberg, E. Dan

34

New Insights into the Origin of Magnetite Crystals in ALH 84001 Carbonate Disks  

NASA Astrophysics Data System (ADS)

Comparison of new TEM results with decomposition studies of sideritic carbonates conducted under a range of heating scenarios suggests that the magnetite nanocrystals in ALH 84001 carbonate disks are not the products of thermal decomposition.

Thomas-Keprta, K. L.; Clemett, S. J.; Wentworth, S. J.; McKay, D. S.; Gibson, E. K.

2010-03-01

35

New Insights into the Origin of Magnetite Crystals in ALH84001 Carbonate Disks  

NASA Astrophysics Data System (ADS)

Comparison of new TEM results with decomposition studies of sideritic carbonates conducted under a range of heating scenarios suggests that the magnetite nanocrystals in ALH 84001 carbonate disks are not the products of thermal decomposition.

Thomas-Keprta, K. L.; Clemett, S. J.; Wentworth, S. J.; McKay, D. S.; Gibson, E. K.

2010-04-01

36

Single-domain-like behavior in a 3-mm natural single crystal of magnetite  

NASA Astrophysics Data System (ADS)

We have observed single-domain (SD) like behavior in a 3-mm natural single crystal of magnetite following low-temperature demagnetization (LTD), which consists of zero-field cycling through the Verwey transition to erase remanence carried by pinned domain walls. We compared stepwise alternating field (AF) and thermal demagnetization curves of 1-mT total thermoremanent magnetization (TRM), 1-mT partial TRM (pTRM) acquired between the Curie point (TC = 575°C) and 565°C, and saturation isothermal remanent magnetization (SIRM) measured with and without prior LTD. AF demagnetization curves of untreated TRM and SIRM decreased exponentially with increasing AF. SIRM was more resistant to demagnetization than was TRM, a multidomain (MD) result of the Lowrie-Fuller test. After LTD the TRM and SIRM memories had AF demagnetization curves with sigmoid shapes and initial plateaus below 8 mT in which little or no demagnetization occurred. Both features are reminiscent of SD behavior. During thermal demagnetization, untreated TRM and SIRM decreased almost linearly with increasing temperature up to ?500°C. Such distributed unblocking temperatures TUB are expected for pinned walls in MD grains. The remaining 60% of TRM and 40% of SIRM were lost over a narrow temperature interval concentrated between 560°C and TC. The TRM memory after LTD was very stable against thermal demagnetization. There was no decrease in remanence below 550°C and very little change until 565°C, only 10°C below TC. This very high TUB fraction of TRM seems to have SD-like character. SIRM has similar behavior. In the case of pTRM, both the untreated remanence and the memory after LTD have almost entirely high TUBs, identical to the range of pTRM blocking temperatures TB, 565°C-TC. TUB = TB is a basic property of SD partial TRM. The pTRM memory fraction is also larger than that of total TRM or SIRM. These observations suggest that pTRM(TC, 565°C) isolates an SD-like fraction of remanence similar to that constituting TRM and SIRM memory. The high AF coercivities of the TRM and SIRM memories indicate that the source of SD-like behavior may be unusually strong domain wall pinning by crystal defects formed at monoclinic twin boundaries as a result of crystal distortion from cubic to monoclinic structure in passing through the Verwey transition.

Özdemir, Özden; Dunlop, David J.

1998-02-01

37

Degeneration of Biogenic Superparamagnetic Magnetite  

SciTech Connect

ABSTRACT. Magnetite crystals precipitated as a consequence of Fe(III) reduction by Shewanella algae BrY after 265 hours incubation and 5-year storage were investigated with transmission electron microscopy, M ssbauer spectroscopy and X-ray diffraction. The magnetite crystals were typically superparamagnetic with an approximate size of 13 nm. The lattice constants of the 265 hour and 5-year crystals are 8.4164 and 8.3774 , respectively. The M ssbauer spectra indicated that the 265 hour magnetite had excess Fe(II) in its crystal-chemistry (Fe3+1.9901Fe2+ 1.0149O4) but the 5-year magnetite was Fe(II)-deficient in stoichiometry (Fe3+2.3875Fe2+0.4188O4). Such crystal-hemical changes may be indicative of the degeneration of superparamagnetic magnetite through the aqueous oxidization of Fe(II) anaerobically, and the concomitant oxidation of the organic phases(fatty acid methyl esters) that were present during the initial formation of the magnetite. The observation of a corona structure on the aged magnetite corroborates the oxidation of Fe(II) on the outer layers of magnetite crystals. These results suggest that there may be a possible link between the enzymatic activity of the bacteria and the stability of Fe(II)-excess magnetite, which may help explain why stable nano-magnetite grains are seldom preserved in natural environments.

Li, Dr. Yi-Liang [University of Tennessee, Knoxville (UTK); Pfiffner, Susan M. [University of Tennessee, Knoxville (UTK); Dyar, Dr. M Darby [Mount Holyoke College; Vali, Dr. Hojatolah [McGill University, Montreal, Quebec; Konhauser, Dr, Kurt [University of Alberta; Cole, David R [ORNL; Rondinone, Adam Justin [ORNL; Phelps, Tommy Joe [ORNL

2009-01-01

38

Origin of magnetite crystals in Martian meteorite ALH84001 carbonate disks  

NASA Astrophysics Data System (ADS)

The Martian meteorite ALH84001 preserves evidence of interaction with aqueous fluids while on Mars in the form of microscopic carbonate disks. These carbonate disks are believed to have precipitated 3.9 Ga ago at beginning of the Noachian epoch on Mars during which both the oldest extant Martian surfaces were formed, and perhaps the earliest global oceans. In-timately associated within and throughout these carbonate disks are nanocrystal magnetites (Fe3O4) with unusual chemical and physical properties, whose origins have become the source of considerable debate [1,2]. One group of hypotheses argues that these magnetites are the product of partial thermal decomposition of the host carbonate [3,4]. Alternatively, the origins of magnetite and carbonate may be unrelated; that is, from the perspective of the carbonate the magnetite is allochthonous. For example, the magnetites might have already been present in the aqueous fluids from which the carbonates were believed to have been deposited. We have sought to resolve between these hypotheses through the detailed characterization of the compositional and structural relationships of the carbonate disks and associated magnetites with the orthopyroxene matrix in which they are embedded. Extensive use of focused ion beam milling techniques has been utilized for sample preparation. We then compared our ob-servations with those from experimental thermal decomposition studies of sideritic carbonates under a range of plausible geological heating scenarios. We conclude that the vast majority of the nanocrystal magnetites present in the carbonate disks could not have formed by any of the currently proposed thermal decomposition scenarios. Instead, we find there is considerable evidence in support of an alternative allochthonous origin for the magnetite unrelated to any shock or thermal processing of the carbonates [5]. [1] McKay et al. (1996) Science 273, 924-930. [2] Thomas-Keprta et al. (2001) Proc. Natl. Acad. Sci. 98, 2164-2169. [3] Treiman (2003) Astrobiology 3, 369-392. [4] Brearley A. J. (2003) Meteorit. Planet. Sci. 38, 849-870. [5] Thomas-Keprta et al. (2009) Geochim. Cosmochim. Acta 73, 6631-6677.

Thomas-Keprta, Kathie; Clemett, Simon; McKay, David; Gibson, Everett; Wentworth, Susan

39

Optical, structural and electrical properties of pure and urea doped KDP crystals  

NASA Astrophysics Data System (ADS)

Single crystals of good optical quality, made of potassium dihydrogen phosphate (KDP) doped with urea were grown by slow evaporation solution growth technique at a constant temperature of 35 °C. Optical absorption and dielectric properties were studied for pure and urea doped KDP crystals. Using powder XRD studies, crystalline nature of pure and urea doped KDP crystals was confirmed. AC conductivity was measured for the grown crystals. DC electrical conductivity and photoconductivity studies were carried out for pure and urea doped KDP crystals and the differences caused by the dopant were also discussed.

Babu, B.; Chandrasekaran, J.; Balaprabhakaran, S.; Ilayabarathi, P.

2013-01-01

40

Coloration of Pure and Doped Calcium Fluoride Crystals at 20°C and -190°C  

Microsoft Academic Search

Coloration of pure CaF2 crystals with 2.5-Mev electrons at room-temperature results in bands at 580, 400, 335, and 225 mmu. In YF3-doped crystals the bands are in the same spectral positions as in pure crystals. They are, however, enhanced and their intensity ratios are significantly changed, the 400-mmu band being predominant. NaF-doped crystals show an even more drastic change: Coloration

W. J. Scouler; A. Smakula

1960-01-01

41

Optical and electrical characteristics of pure and doped potassium hydrogen tartrate single crystals  

NASA Astrophysics Data System (ADS)

The optical and electrical characteristics of pure, sodium- and lithium-doped potassium hydrogen tartrate crystals grown by the gel technique are reported. An optical absorption study conducted in the UV-Vis range of 200-800 nm reveals the transparency of these crystals in the entire visible range but not in the ultraviolet range. The optical band gap of pure potassium hydrogen tartrate crystals is found to be dependent on doping by Na or Li ions. The non-linear optical behaviour of these crystals is reported and explained. The electrical properties of pure and doped potassium hydrogen tartrate crystals are studied by measuring electrical resistivity from 80 to 300 K. It is shown that while pure potassium hydrogen tartrate crystal is an insulator at room temperature (300 K), doping by Na or Li ions makes it a semiconductor. The results have been explained in terms of the variable range hopping model.

Quasim, I.; Firdous, A.; Khosa, S. K.; Kotru, P. N.

2009-08-01

42

A dislocation-density-based 3D crystal plasticity model for pure aluminum  

Microsoft Academic Search

A dislocation-density-based crystal plasticity finite-element model (CPFEM) is developed in which different dislocation densities evolve. Based upon the kinematics of crystal deformation and dislocation interaction laws, dislocation generation and annihilation are modeled. The CPFEM model is calibrated for pure aluminum using experimental stress–strain curves of pure aluminum single crystal from the literature. Crystallographic texture predictions in plane-strain compression of aluminum

Alankar Alankar; Ioannis N. Mastorakos; David P. Field

2009-01-01

43

Influence of Growth Conditions on Magnetite Nanoparticles Electro-Crystallized in the Presence of Organic Molecules  

PubMed Central

Magnetite nanoparticles were synthesized by electrocrystallization in the presence of thiourea or sodium butanoate as an organic stabilizer. The synthesis was performed in a thermostatic electrochemical cell containing two iron electrodes with an aqueous solution of sodium sulfate as electrolyte. The effects of organic concentration, applied potential and growth temperature on particle size, morphology, structure and magnetic properties were investigated. The magnetite nanoparticles were characterized by X-ray diffraction, electron microscopy, magnetometry and Mössbauer spectrometry. When the synthesis is performed in the presence of sodium butanoate at 60 °C, a paramagnetic ferric salt is obtained as a second phase; it is possible to avoid formation of this phase, increase the specific magnetization and improve the structure of the oxide particles by tuning the growth conditions. Room-temperature magnetization values range from 45 to 90 Am2kg?1, depending on the particle size, type of surfactant and synthesis conditions. Mössbauer spectra, which were recorded at 290 K for all the samples, are typical of nonstoichiometric Fe3??O4, with a small excess of Fe3+, 0.05 ? ? ? 0.15.

Mosivand, Saba; Monzon, Lorena M. A.; Kazeminezhad, Iraj; Coey, J. Michael D.

2013-01-01

44

Isolation of isoelectrically pure cholera toxin for crystallization  

SciTech Connect

We have determined that the failure of cholera toxin to crystallize well results from its isoelectric heterogeneity, which is probably due to a post-translational process such as deamidation of its B subunit. Every sample of cholera toxin we have examined from commercial or academic suppliers has been heterogeneous; heterogeneous cholera toxin does not crystallize satisfactorily. We have overcome this problem by using ion-exchange fast protein liquid chromatography (FPLC) to obtain an isoelectrically homogeneous species of cholera toxin. Homogeneous cholera toxin crystallizes readily, forming single, nonmosaic crystals suitable for x-ray diffraction studies. For this process, protein was applied to a MonoQ ion-exchange column, then eluted with an isocratic low salt buffer followed by a linear salt gradient (0-100 mM NaCl). Column fractions were analyzed on isoelectric focusing gels, and those fractions containing the desired homogeneous species were pooled and concentrated. Crystals formed within 24 to 48 hours in a MOPS/PEG buffer, which made use of slow isoelectric precipitation to induce crystallization. 23 refs., 6 figs.

Spangler, B.D.; Westbrook, E.M.

1989-01-01

45

Tuning the properties of colloidal magneto-photonic crystals by controlled infiltration with superparamagnetic magnetite nanoparticles  

NASA Astrophysics Data System (ADS)

The performance of magnetic-field sensors and optical isolators is largely determined by the efficiency of the active materials. This efficiency could be dramatically increased by integrating Faraday materials in photonic crystals. For this purpose, monodisperse nanospheres were self-assembled into a colloidal photonic crystal and magnetic functionality was introduced by dipping the photonic crystal in a suspension containing superparamagnetic nanoparticles. Reflection and absorbance measurements of these magneto-photonic crystals revealed clear relationships between the time spent in suspension and the position and strength of the photonic band gap. When additional magnetic material was introduced, the band gap was red shifted and the strength of the band gap was decreased. Using Bragg's law and the Maxwell-Garnet approximation for effective media, the filling fraction of the magneto-photonic crystals was calculated from the observed red shift. While superparamagnetic nanoparticles did confer magneto-optical properties to the photonic crystal, they also increased the absorption, which can be detrimental as the Faraday effect is measured in transmission. Therefore a trade-off exists in the optical regime between the amount of Faraday rotation and the absorption. By carefully controlling the filling fraction, this trade-off was investigated and optimized for photonic crystals with different band gaps. Both polystyrene and silica photonic crystals were filled with superparamagnetic nanoparticles. In case of the polystyrene photonic crystals, it was found that the maximum achievable filling fraction was influenced by the size of the polystyrene nanospheres. Smaller polystyrene nanospheres gave rise to smaller pore diameters and a faster onset of pore blocking when filled with superparamagnetic nanoparticles. As a result, the maximum achievable filling fraction was also lower. Pore blocking was found to be negligible in silica photonic crystals. Together with a higher mechanical strength, this makes silica photonic crystals more suited for the fabrication of colloidal magneto-photonic crystals. In this paper, a nanoscale engineering approach is described to carefully control the filling fraction of magneto-photonic crystals. This allows fine-tuning the absorption and the position and strength of the photonic band gap. By tailoring the properties of magneto-photonic crystals, the means for application-specific designs and a better description of Faraday effects in 3D magneto-photonic crystals are provided.

Demeyer, P. J.; Bloemen, M.; Verbiest, T.; Clays, K.

2012-05-01

46

Thermodynamic Analysis Of Pure And Impurity Doped Pentaerythritol Tetranitrate Crystals Grown At Room Temperature  

SciTech Connect

Pentaerythritol tetranitrate (PETN) powders are used to initiate other explosives. During long-term storage, changes in powder properties can cause changes in the initiation performance. Changes in the morphology and surface area of aging powders are observed due to sublimation and growth of PETN crystals through coarsening mechanisms, (e.g. Ostwald ripening, sintering, etc.). In order to alleviate the sublimation of PETN crystals under service conditions, stabilization methods such as thermal cycling and doping with certain impurities during or after the crystallization of PETN have been proposed. In this report we present our work on the effect of impurities on the morphology and activation energy of the PETN crystals. The pure and impurity doped crystals of PETN were grown from supersaturated acetone solution by solvent evaporation technique at room temperature. The difference in the morphology of the impurity-doped PETN crystal compared to pure crystal was examined by optical microscopy. The changes in the activation energies and the evaporation rates are determined by thermogravimetric (TGA) analyses. Our activation energies of evaporation agree with earlier reported enthalpies of vaporization. The morphology and activation energy of PETN crystals doped with Ca, Na, and Fe cations are similar to that for pure PETN crystal, whereas the Zn-ion-doped PETN crystals have different morphology and decreased activation energy.

Pitchimani, R; Zheng, W; Simon, S; Hope-Weeks, L; Burnham, A K; Weeks, B L

2006-05-25

47

In-situ measurements of iron isotopes by SIMS: MC-ICP-MS intercalibration and application to a magnetite crystal from the Gunflint chert  

Microsoft Academic Search

An analytical procedure is described for in situ measurements of iron isotope compositions of different sulfides and oxides with a spatial resolution of 15–20?m using a Caméca IMS 1270 ion microprobe (SIMS). The 54Fe and 56Fe isotopes were measured on two Faraday cups. The isobaric 54Cr interference on 54Fe was corrected by measuring 53Cr and 52Cr intensities. For magnetite crystals,

Johanna Marin-Carbonne; Claire Rollion-Bard; Béatrice Luais

2011-01-01

48

Signatures in magnetites formed by (Ca,Mg,Fe)CO3 thermal decomposition: Terrestrial and extraterrestrial implications  

NASA Astrophysics Data System (ADS)

It has never been demonstrated whether magnetite synthesized through the heat-dependent decomposition of carbonate precursors retains the chemical and structural features of the carbonates. In this study, synthetic (Ca,Mg,Fe)CO3 was thermally decomposed by heating from 25 to 700 °C under 1 atm CO2, and by in situ exposure under vacuum to the electron beam of a transmission electron microscope. In both cases, the decomposition of the carbonate was topotactic and resulted in porous pseudomorphs composed of oriented aggregates of magnetite nanocrystals. Both calcium and magnesium were incorporated into nanophase magnetite, forming (Ca,Mg)-magnetites and (Ca,Mg)-ferrites when these elements were present in the parent material, thus preserving the chemical signature of the precursor. These results show that magnetites synthesized in this way acquire a chemical and structural inheritance from their carbonate precursor that indicates how they were produced. These results are not only important in the determination of the origin of chemically-impure, oriented nanophase magnetite crystals in general, but they also provide important insights into the origin of the large, euhedral, chemically-pure, [111]-elongated magnetites found within Ca-, Mg- and Fe-rich carbonates of the Martian meteorite ALH84001. Based on our experimental results, the chemically-pure magnetites within ALH84001 cannot be genetically related to the Ca-, Mg- and Fe-rich carbonate matrix within which they are embedded, and an alternative explanation for their occurrence is warranted.

Jimenez-Lopez, Concepcion; Rodriguez-Navarro, Carlos; Rodriguez-Navarro, Alejandro; Perez-Gonzalez, Teresa; Bazylinski, Dennis A.; Lauer, Howard V.; Romanek, Christopher S.

2012-06-01

49

Endcap calorimeter for SuperBelle based on pure CsI crystals  

Microsoft Academic Search

The design of the Belle endcap calorimeter based on pure CsI is presented. The suggested calorimeter consists of pure CsI crystals with readout by vacuum photopentodes followed by the analysis of the shape of the output signal. The results of tests of the counters are presented. Photopentodes provide a gain factor about 150–200 without magnetic field. Tests with magnetic field

A. Kuzmin

2010-01-01

50

Magnetite as a prokaryotic biomarker: A review  

NASA Astrophysics Data System (ADS)

Over the years, nanometer-sized magnetite (Fe3O4) crystals have been recovered from many modern and ancient environments including sediments and soils and even meteorites. In some cases these crystals have been used as "magnetofossils" for evidence of the past presence of specific microbes. Magnetite nanocrystals can be formed by a number of different biological and inorganic mechanisms resulting in crystals with different physical and magnetic characteristics. Prokaryotes (bacteria) biomineralize magnetite through two methods that differ mechanistically, including: biologically induced mineralization (BIM) and biologically controlled mineralization (BCM). Magnetite nanocrystals produced by BIM are known to be synthesized by the dissimilatory iron-reducing bacteria, are deposited external to the cell, and generally are physically indistinguishable from magnetite particles formed inorganically. BCM magnetites, in contrast, are synthesized by the magnetotactic bacteria and some higher organisms and are precipitated intracellularly as membrane-bounded structures called magnetosomes. These magnetites appear to have unique crystal morphologies and a narrow size range leading to their original use as magnetofossils. Because of the discovery of nanometer-sized crystals of magnetite in the Martian meteorite ALH84001, the use of these criteria for the determination of whether magnetite crystals could constitute a prokaryotic biomarker was questioned. Thus, there is currently great debate over what criteria to use in the determination of whether specific magnetite crystals are biogenic or not. In the last decade, additional criteria have been established (e.g., the Magnetite Assay for Biogenicity), and new tools and technologies have been developed to determine the origin of specific types of magnetite crystals.

Jimenez-Lopez, Concepcion; Romanek, Christopher S.; Bazylinski, Dennis A.

2010-06-01

51

Relationship between surface area and crystal size of pure and doped cerium oxides  

Microsoft Academic Search

Pure and Zr, La or Pr-doped cerium oxides were characterised by transmission electron microscopy (TEM), N2 adsorption-desorption at ?196 °C and X-ray diffraction (XRD). For crystal sizes calculation, the Scherrer and Williamson-Hall equations were compared, and the relationship between surface area and crystal size was critically discussed. It was demonstrated that the Williamson-Hall equation must be used instead of the

C. Bueno-Ferrer; S. Parres-Esclapez; D. Lozano-Castelló; A. Bueno-López

2010-01-01

52

Charge transport due to photoelectric interface activation in pure nematic liquid-crystal cells  

Microsoft Academic Search

We report a study of the crucial role of liquid-crystal-polymer interface on photoinduced transport and redistribution of charges in pure nematic liquid-crystal cells that exhibit a photorefractivelike effect. A stationary photocurrent that is 30% of the dark current has been measured for very low power illumination (few mW) and low applied dc electric field (about 0.1 V\\/mum). The experimental results

P. Pagliusi; G. Cipparrone

2002-01-01

53

Growth and characterization of pure and semiorganic nonlinear optical Lithium Sulphate admixtured l-alanine crystal  

NASA Astrophysics Data System (ADS)

Lithium sulphate admixtured l-alanine (LSLA) salt was synthesized and the solubility of the commercially available l-alanine and the synthesized LSLA sample was determined in de-ionized water at various temperatures. In accordance with the solubility data, the saturated aqueous solutions of l-alanine and lithium admixtured l-alanine were prepared separately and the single crystals of the samples were grown by the solution method with a slow evaporation technique. Studying single x-ray diffraction shows that pure and LSLA crystal belong to the orthorhombic system with a non-centrosymmetric space group P212121. Using the powder x-ray diffraction study, the crystallinity of the grown crystals is confirmed and the diffraction peaks are indexed. The various functional groups present in the pure and LSLA crystal are elucidated from Fourier transform infrared spectroscopy study. UV-visible transmittance is recorded to study the optical transmittance range for the grown crystals. The powder second harmonic generation test confirms the nonlinear optical property of the grown crystals. From the microhardness test, the hardness of the grown crystals is estimated. The dielectric behaviour, such as the dielectric constant and the loss of the sample, are measured as a function of temperature and frequency. The ac conductivity of the grown crystals is also studied and the activation energy is calculated.

Vela, T.; Selvarajan, P.; Freeda, T. H.; Balasubramanian, K.

2013-04-01

54

Release of gold-bearing fluids in convergent margin magmas prompted by magnetite crystallization.  

PubMed

A relationship between convergent margin magmas and copper-gold ore mineralization has long been recognized. The nature of the genetic link is controversial, particularly whether the link is due to high-oxygen-fugacity (fO2) melts and fluids released from subducted slabs or to brine exsolution during magmatic evolution. For submarine, subduction-related volcanic glasses from the eastern Manus basin, Papua New Guinea, we here report abrupt decreases in gold and copper abundances, coupled with a switch in the behaviour of titanium and iron from concentration increases to decreases as SiO2 rises. We propose that the abrupt depletion in gold and copper results from concurrent sulphur reduction as a result of fO2 buffering, causing enhanced formation of copper-gold hydrosulphide complexes that become scavenged from crystallizing melts into cogenetic magmatic aqueous fluids. This process is particularly efficient in oxidized arc magmas with substantial sulphate. We infer that subsequent migration and cooling of exsolved aqueous fluids create links between copper-gold mineralization and arc magmatism in the Manus basin, and at convergent margins in general. PMID:15496920

Sun, Weidong; Arculus, Richard J; Kamenetsky, Vadim S; Binns, Raymond A

2004-10-21

55

Additive coloring rate and intensity for pure and doped fluorite crystals  

NASA Astrophysics Data System (ADS)

The mechanism of the additive coloring of calcium fluoride crystals, both pure and doped with I- and III-group elements, has been investigated. The coloring rate and intensity and the dependences of these parameters on the experimental conditions, vapor mixture pressure, and temperature have been experimentally determined. It is shown that the concentration of anion vacancies/electrons that can be introduced into crystals is in the range of 1017-1018 cm-3; in crystals with a high concentration of rare earth ions, the limiting concentration can be an order of magnitude higher.

Shcheulin, A. S.; Semenova, T. S.; Koryakina, L. F.; Petrova, M. A.; Angervaks, A. E.; Ryskin, A. I.

2011-04-01

56

Submicron Magnetite Grains and Carbon Compounds in Martian Meteorite ALH84001: Inorganic, Abiotic Formation by Shock and Thermal Metamorphism  

NASA Astrophysics Data System (ADS)

Purported biogenic features of the ALH84001 Martian meteorite (the carbonate globules, their submicron magnetite grains, and organic matter) have reasonable inorganic origins, and a comprehensive hypothesis is offered here. The carbonate globules were deposited from hydrothermal water, without biological mediation. Thereafter, ALH84001 was affected by an impact shock event, which raised its temperature nearly instantaneously to 500-700K, and induced iron-rich carbonate in the globules to decompose to magnetite and other minerals. The rapidity of the temperature increase caused magnetite grains to nucleate in abundance; hence individual crystals were very small. Nucleation and growth of magnetite crystals were fastest along edges and faces of the precursor carbonate grains, forcing the magnetite grains to be platy or elongated, including the "truncated hexa-octahedra" shape. ALH84001 had formed at some depth within Mars where the lithostatic pressure was significantly above that of Mars' surface. Also, because the rock was at depth, the impact heat dissipated slowly. During this interval, magnetite crystals approached chemical equilibria with surrounding minerals and gas. Their composition, nearly pure Fe3O4, reflects those of equilibria; elements that substitute into magnetite are either absent from iron-rich carbonate (e.g., Ti, Al, Cr), or partitioned into other minerals during magnetite formation (Mg, Mn). Many microstructural imperfections in the magnetite grains would have annealed out as the rock cooled. In this post-shock thermal regime, carbon-bearing gas from the decomposition of iron carbonates reacted with water in the rock (or from its surroundings) to produce organic matter via Fischer-Tropschlike reactions. Formation of such organic compounds like polycyclic aromatic hydrocarbons would have been catalyzed by the magnetite (formation of graphite, the thermochemically stable phase, would be kinetically hindered).

Treiman, Allan H.

2003-06-01

57

Submicron magnetite grains and carbon compounds in Martian meteorite ALH84001: inorganic, abiotic formation by shock and thermal metamorphism.  

PubMed

Purported biogenic features of the ALH84001 Martian meteorite (the carbonate globules, their submicron magnetite grains, and organic matter) have reasonable inorganic origins, and a comprehensive hypothesis is offered here. The carbonate globules were deposited from hydrothermal water, without biological mediation. Thereafter, ALH84001 was affected by an impact shock event, which raised its temperature nearly instantaneously to 500-700K, and induced iron-rich carbonate in the globules to decompose to magnetite and other minerals. The rapidity of the temperature increase caused magnetite grains to nucleate in abundance; hence individual crystals were very small. Nucleation and growth of magnetite crystals were fastest along edges and faces of the precursor carbonate grains, forcing the magnetite grains to be platy or elongated, including the "truncated hexa-octahedra" shape. ALH84001 had formed at some depth within Mars where the lithostatic pressure was significantly above that of Mars' surface. Also, because the rock was at depth, the impact heat dissipated slowly. During this interval, magnetite crystals approached chemical equilibria with surrounding minerals and gas. Their composition, nearly pure Fe(3)O(4), reflects those of equilibria; elements that substitute into magnetite are either absent from iron-rich carbonate (e.g., Ti, Al, Cr), or partitioned into other minerals during magnetite formation (Mg, Mn). Many microstructural imperfections in the magnetite grains would have annealed out as the rock cooled. In this post-shock thermal regime, carbon-bearing gas from the decomposition of iron carbonates reacted with water in the rock (or from its surroundings) to produce organic matter via Fischer-Tropschlike reactions. Formation of such organic compounds like polycyclic aromatic hydrocarbons would have been catalyzed by the magnetite (formation of graphite, the thermochemically stable phase, would be kinetically hindered). PMID:14577885

Treiman, Allan H

2003-01-01

58

Magnetosomes and magnetite crystals produced by magnetotactic bacteria as resolved by atomic force microscopy and transmission electron microscopy.  

PubMed

Atomic force microscopy (AFM) was used in concert with transmission electron microscopy (TEM) to image magnetotactic bacteria (Magnetospirillum gryphiswaldense MSR-1 and Magnetospirillum magneticum AMB-1), magnetosomes, and purified Mms6 proteins. Mms6 is a protein that is associated with magnetosomes in M. magneticum AMB-1 and is believed to control the synthesis of magnetite (Fe(3)O(4)) within the magnetosome. We demonstrated how AFM can be used to capture high-resolution images of live bacteria and achieved nanometer resolution when imaging Mms6 protein molecules on magnetite. We used AFM to acquire simultaneous topography and amplitude images of cells that were combined to provide a three-dimensional reconstructed image of M. gryphiswaldense MSR-1. TEM was used in combination with AFM to image M. gryphiswaldense MSR-1 and magnetite-containing magnetosomes that were isolated from the bacteria. AFM provided information, such as size, location and morphology, which was complementary to the TEM images. PMID:22578947

Oestreicher, Zachery; Valverde-Tercedor, Carmen; Chen, Lijun; Jimenez-Lopez, Concepcion; Bazylinski, Dennis A; Casillas-Ituarte, Nadia N; Lower, Steven K; Lower, Brian H

2012-04-25

59

Microbial preparation of metal-substituted magnetite nanoparticles  

SciTech Connect

A microbial process that exploits the ability of iron-reducing microorganisms to produce copious amounts of extra-cellular metal (M)-substituted magnetite nanoparticles using akaganeite and dopants of dissolved form has previously been reported. The objectives of this study were to develop methods for producing M-substituted magnetite nanoparticles with a high rate of metal substitution by biological processes and to identify factors affecting the production of nano crystals. The thermophilic and psychrotolerant iron-reducing bacteria had the ability to form M substituted magnetite nano-crystals (MyFe3-yO4) from a doped precursor, mixed-M iron oxyhydroxide, (MxFe1-xOOH, x 0.5, M is Mn, Zn, Ni, Co, and Cr). Within the range of 0.01 x 0.3, using the mixed precursor material enabled the microbial synthesis of more heavily substituted magnetite compared to the previous method, in which the precursor was pure akaganeite and the dopants were present as soluble metal salts. The mixed precursor method was especially advantageous in the case of toxic metals such as Cr and Ni. Also this new method increased the production rate and magnetic properties of the product, while improving crystallinity, size control and scalability.

Moon, Ji Won [ORNL; Roh, Yul [Chonnam National University, Gwangju; Lauf, Robert J [ORNL; Vali, Hojatollah [McGill University, Montreal, Quebec; Yeary, Lucas W [ORNL; Phelps, Tommy Joe [ORNL

2007-01-01

60

Effect of non-hydrostatic conditions on the elastic behaviour of magnetite: an in situ single-crystal X-ray diffraction study  

Microsoft Academic Search

The high-pressure elastic behaviour and the pressure-induced structural evolution of synthetic magnetite were investigated\\u000a up to 11.11(5) GPa by means of in situ single-crystal X-ray diffraction with a diamond anvil cell, using the mix methanol:ethanol:water = 16:3:1\\u000a as pressure-transmitting medium and the ruby-fluorescence method for pressure-calibration. The evolution of the ruby R1-fluorescence line with P, with a drastic increase of the full-width-at-half-maximum (FWHM)

G. Diego Gatta; I. Kantor; T. Boffa Ballaran; L. Dubrovinsky; C. McCammon

2007-01-01

61

Metamorphic Origin of Sub-Micron Magnetite Crystals in ALH 84001: Re-Evaluation of Equilibria, Thermochemistry, and Experiments  

NASA Astrophysics Data System (ADS)

Treiman (1993) suggested that magnetite grains in ALH 84001 formed by decomposition of Fe-carbonate after a major impact event. Criticisms of this work (Thomas-Keprta et al.. 2009) lack merit, and demonstrate some pitfalls in the search for signs of extraterrestrial life.

Treiman, A. H.; Essene, E. J.

2010-04-01

62

Metamorphic Origin of Sub-Micron Magnetite Crystals in ALH 84001: Reevaluation of Equilibria, Thermochemistry, and Experiments  

NASA Astrophysics Data System (ADS)

Magnetite grains in ALH 84001, cited as evidence of martian life, could have formed abiotically by thermal decomposition of Fe-rich carbonates. Thomas-Keprta et al. (2009) criticize this abiotic hypothesis; their criticisms lack merit and do not disprove the hypothesis.

Treiman, A. H.; Essene, E. J.

2010-03-01

63

Thermoluminescence of pure and impurity-doped KBr and NaCl crystals  

Microsoft Academic Search

Two thermoluminescence peaks are observed at 90 and 150 °C in highly pure KBr crystals (background divalent cation impurity not greater than 1 p.p.m.). From the growth of F centres with the time of x-irradiation these two peaks have been interpreted in terms of the two types of F centres postulated previously. The presence of Cd impurity in KBr suppresses

P. C. Mehendru; S. Radhakrishna

1969-01-01

64

Design of a broadband highly dispersive pure silica photonic crystal fiber  

Microsoft Academic Search

A highly dispersive dual-concentric-core pure silica photonic crystal fiber is designed with a maximum chromatic dispersion value of about -9500 ps\\/(nm km) around the 1.56 mum wavelength region and a full width at half-maximum (FWHM) of 55 nm. The change in the dispersion-bandwidth product as a function of period is carefully studied by using the plane wave expansion method. The

Harish Subbaraman; Tao Ling; Yongqiang Jiang; Maggie Y. Chen; Peiyan Cao; Ray T. Chen

2007-01-01

65

Electrosynthesis of pure poly(3,4-ethylenedioxythiophene) (PEDOT) in chitosan-based liquid crystal phase  

NASA Astrophysics Data System (ADS)

Ordered poly(3,4-ethylenedioxythiophene) (PEDOT) was successfully prepared by electrochemical polymerization of 3,4-ethylenedioxythiophene in lyotropic liquid crystal phase formed by chitosan in an acetic acid solution. The structure, performance, and morphology of PEDOT were characterized by infrared absorption spectra, cyclic voltammograms, polarizing optical microscopy, and scanning electron microscopy. The ordered pure PEDOT film with good electrochemical behavior exhibited obvious birefringence.

Meng, Xue; Wang, Zhen; Wang, Luyan; Pei, Meishan; Guo, Wenjuan; Tang, Xinde

2013-09-01

66

An experimental study of the mobility of edge dislocations in pure copper single crystals  

Microsoft Academic Search

The velocity of edge dislocations in 99.999% pure copper crystals has been measured as a function of stress at temperatures from 66°K to 373°K by means of a torsion technique. The range of resolved shear stress was 0 to 15 megadynes\\/cm for seven temperatures (66°K, 74°K, 83°K, 123°K, 173°K, 296°K, 373°K).Dislocation mobility is characterized by two distinct features : (a)

K. M. Jassby; T. Vreeland Jr.

1970-01-01

67

Growth and characterization of pure and 1, 10 phenanthraline doped potassium penta borate (KB5) single crystals  

NASA Astrophysics Data System (ADS)

We concentrate on the low temperature slow solvent evaporation method and characterization of pure and 1, 10 phenanthraline doped KB5 and describe its potential as a non-linear optical material. The grown crystal has been subjected to single crystal X-ray diffraction analysis to identify the unit cell parameters and crystal system. The presence of carbon, hydrogen and oxygen content were confirmed by CHN analysis. The Kurtz's-Perry powder SHG efficiency was determined for both pure and 1,10 phenanthraline doped KB5 crystals as 1.6 and 2.2 times than that of pure KDP. Surface morphology of the pure and doped KB5 crystals has been found to be Scanning Electron Microscopic technique (SEM).

Prabha, K.; Babu, M. Ramesh; Sagayaraj, P.

2013-05-01

68

Design of a broadband highly dispersive pure silica photonic crystal fiber.  

PubMed

A highly dispersive dual-concentric-core pure silica photonic crystal fiber is designed with a maximum chromatic dispersion value of about -9500 ps/(nm km) around the 1.56 microm wavelength region and a full width at half-maximum (FWHM) of 55 nm. The change in the dispersion-bandwidth product as a function of period is carefully studied by using the plane wave expansion method. The coupled mode theory matches well with the plane wave expansion method that was used to simulate the chromatic dispersion. This kind of a photonic crystal fiber structure is suitable for high-dispersion application in phased array antenna systems based on photonic crystal fiber arrays. PMID:17514284

Subbaraman, Harish; Ling, Tao; Jiang, YongQiang; Chen, Maggie Y; Cao, Peiyan; Chen, Ray T

2007-06-01

69

Design of a broadband highly dispersive pure silica photonic crystal fiber  

NASA Astrophysics Data System (ADS)

A highly dispersive dual-concentric-core pure silica photonic crystal fiber is designed with a maximum chromatic dispersion value of about -9500 ps/(nm km) around the 1.56 ?m wavelength region and a full width at half-maximum (FWHM) of 55 nm. The change in the dispersion-bandwidth product as a function of period is carefully studied by using the plane wave expansion method. The coupled mode theory matches well with the plane wave expansion method that was used to simulate the chromatic dispersion. This kind of a photonic crystal fiber structure is suitable for high-dispersion application in phased array antenna systems based on photonic crystal fiber arrays.

Subbaraman, Harish; Ling, Tao; Jiang, Yongqiang; Chen, Maggie Y.; Cao, Peiyan; Chen, Ray T.

2007-06-01

70

Comparison of optical properties of pure and doped lithium tetraborate single crystals and glasses  

NASA Astrophysics Data System (ADS)

High optical quality Li2B4O7 (LTB) single crystals and glassy phases of pure, doped (Cu, Ag) and co-doped with Cu+Ag have been grown by Czochralski crystal pulling and melt quenching techniques respectively. They were characterized through photoluminescence (PL), thermoluminescence (TL), and UV-VIS-NIR transmission measurements. The PL of glass phase shows light yield comparable to that of single crystal. 80-85 % optical transmission in the range 350-800 nm revealed good optical quality of the glasses which is comparable to the single crystals though the glasses have higher cut off wavelength (lower energy). TL glow peaks of Cu doped LTB single crystal at 200 °C and for Cu+Ag co-doped LTB single crystals at around 170°C and 240°C are useful for the dosimetry applications and found to be linear in the range from 1mGy to 1kGy. However, in glasses no TL was observed in spite of a good PL yield.

Patra, G. D.; Singh, A. K.; Singh, S. G.; Tyagi, M.; Sen, S.; Tiwari, B.; Gadkari, S. C.

2012-06-01

71

Growth, structural, spectral, mechanical and optical properties of pure and metal ions doped sulphamic acid single crystals.  

PubMed

Bulk single crystals of pure and metal ions (Mn(2+), Cu(2+) and Ni(2+)) doped sulphamic acid (SA) have been grown by conventional and unidirectional solution growth methods. Intensities of powder X-ray diffraction peaks of metal ions doped SA reveal that these dopants enhanced the crystallanity. The peak broadening and intensity variation in some frequency regions in FT-IR spectra show the incorporation of dopants in the SA lattice. Mn(2+) and Cu(2+) doped SA single crystals show high crystalline perfection (FWHM 5.5arcs) compared to pure and Ni(2+) metal ions doped SA crystals. The grown pure and Mn(2+), Cu(2+) and Ni(2+) ions doped SA crystals have transparency in the order SA>Mn:SA>Cu:SA>Ni:SA. The hardness value of Ni(2+) doped crystal is relatively less than that of the pure and other metal ions doped SA crystals. Pure and Ni(2+) ions doped SA crystals possess high dielectric constants than that of Cu(2+) and Mn(2+) ions doped crystals. From the SEM micrograph analyses, it is observed that the doping of these metal ions modify the surface morphology of the grown crystals. PMID:20493763

Ramesh Babu, R; Ramesh, R; Gopalakrishnan, R; Ramamurthi, K; Bhagavannarayana, G

2010-04-24

72

Occurrence of secondary magnetite within biodegraded oil  

SciTech Connect

Samples of solid bitumen from the Thornton Quarry (Illinois) and the Cynthia Quarry (Mississippi) were found to be strongly magnetic and to have rock magnetic properties suggesting that the magnetizable grains present are magnetite. Studies of magnetic isolates revealed that magnetite is present primarily as spherical crystal aggregates that appear identical to magnetite spherules isolated from remagnetized Paleozoic carbonate units from other localities. Organic geochemical analyses of the solid bitumen suggest an origin by microbial attack on what once was liquid crude oil. The occurrence of secondary magnetite as inclusions within solid bitumen suggests a relationship between crude oil biodegradation and development of that mineral in their samples. The authors infer that secondary magnetite in other geologic environments may be related to the presence of hydrocarbons. The discovery of a natural association of secondary magnetite and hydrocarbons has important implications for paleomagnetism and for petroleum exploration.

McCabe, C.; Sassen, R.; Saffer, B.

1987-01-01

73

The Lindemann criterion of melting for pure and mixed ionic crystals  

NASA Astrophysics Data System (ADS)

Generalization of the Lindemann criterion of melting for disordered mixed crystals provides the possibility of predicting the diagram of state for different mixtures. In the present work, this criterion was adapted for pure ionic crystals and was generalized for mixed ionic crystals also. Use of the optical phonon mode instead of the acoustic phonon mode gave the same kind of Lindemann formula as for metals. However, the difference between an ionic crystal and a simple atomic one is that the mass which characterizes the lattice is the reduced mass of the two ions rather than their sum, i.e., M(sub r) = M(sub A)M(sub C)/(M(sub A) + M(sub C)) instead of M(sub s) = M(sub A) + M(sub C) in which M(sub C) and M(sub A) are the masses of the cation and anion, respectively. A melting criterion, equivalent to the Lindemann criterion, was formulated for mixed binary ionic crystals. For many binary and some ternary systems, the calculations gave azeotropic phase boundary lines or surfaces which were confirmed by the experimental data. The criterion for solubility derived from these calculations also agreed well with experimental results. There was a good correlation between the present results and other calculations based on thermochemical considerations. The Debye temperature and Lindemann parameters were calculated for more complex binary solids, having diamond, zinc blend and chalcopyrite structures.

Berrebi, David

1991-11-01

74

Endcap calorimeter for SuperBelle based on pure CsI crystals  

NASA Astrophysics Data System (ADS)

The design of the Belle endcap calorimeter based on pure CsI is presented. The suggested calorimeter consists of pure CsI crystals with readout by vacuum photopentodes followed by the analysis of the shape of the output signal. The results of tests of the counters are presented. Photopentodes provide a gain factor about 150-200 without magnetic field. Tests with magnetic field show that the gain factor drops down about 3.5 times in axial magnetic field of 1.5 T. The preamplifier-shaper has been developed which provides electronics noise of 1000 photoelectrons. The beam test results showed the energy resolution about 2.2% for 100 MeV photons and time resolution better than 2 ns. Radiation hardness tests of the counters have been carried out.

Kuzmin, A.; Belle ECL Team

2010-11-01

75

Microbial synthesis of magnetite and Mn-substituted magnetite nanoparticles: influence of bacteria and incubation temperature.  

PubMed

Microbial synthesis of magnetite and metal (Co, Cr, Ni)-substituted magnetites has only recently been reported. The objective of this study was to examine the influence of Mn ion on the microbial synthesis of magnetite nanoparticles. The reductive biotransformation of an akaganeite (beta-FeOOH) or a Mn-substituted (2-20 mol%) akaganeite (Fe(1-x)Mn(x)OOH) by Shewanella loiha (PV-4, 25 degrees C) and Thermoanaerobacter ethanolicus (TOR-39, 60 degrees C) was investigated under anaerobic conditions at circumneutral pH (pH = 7-8). Both bacteria formed magnetite nanoparticles using akaganeite as a magnetite precursor. By comparison of iron minerals formed by PV-4 and TOR-39 using Mn-mixed akaganeite as the precursor, it was shown that PV-4 formed siderite (FeCO3), green rust [Fe2+Fe3+(OH)16CO3 x 4H2O], and magnetite at 25 degrees C, whereas TOR-39 formed mainly nm-sized magnetite at 60 degrees C. The presence of Mn in the magnetite formed by TOR-39 was revealed by energy dispersive X-ray analysis (EDX) is indicative of Mn substitution into magnetite crystals. EDX analysis of iron minerals formed by PV-4 showed that Mn was preferentially concentrated in the siderite and green rust. These results demonstrate that coprecipitated/sorbed Mn induced microbial formation of siderite and green rust by PV-4 at 25 degrees C, but the synthesis of Mn-substituted magnetite nanoparticles proceeded by TOR-39 at 60 degrees C. These results indicate that the bacteria have the ability to synthesize magnetite and Mn-substituted magnetite nano-crystals. Microbially facilitated synthesis of magnetite and metal-substituted magnetites at near ambient temperatures may expand the possible use of specialized ferromagnetic nano-particles. PMID:18047092

Roh, Yul; Jang, Hee-Dong; Suh, Yongjae

2007-11-01

76

Electrohydrodynamic Pattern Formation in Nematic Liquid Crystals by External Pure Noise  

NASA Astrophysics Data System (ADS)

Pure noise-induced electrohydrodynamic convections (EHCs) in nematic liquid crystals are presented in comparison with ac field-induced ones. There exists a characteristic cutoff frequency fc* of noise dividing EHC patterns qualitatively. Sufficiently colored noise with fc < fc* can induce a variety of well-ordered patterns such as Williams domains, fluctuating Williams domains, and grid patterns. The amplitude of the primary pattern (Williams domains) and its wavelength are investigated with varying intensity VN and/or cutoff frequency fc of noise. The present noise-induced EHCs are discussed on the basis of the conventional (ac-based) Carr-Helfrich mechanism.

Huh, Jong-Hoon

2010-12-01

77

Highly crystalline porous magnetite and vacancy-ordered maghemite microcrystals of rhombohedral habit  

NASA Astrophysics Data System (ADS)

Porous crystals of magnetite and vacancy-ordered maghemite, rhombohedron-shaped, reaching 150 ?m in size, and having remarkably large specific surface area (88.55 m2/g for magnetite, 40.14 m2/g for maghemite) were obtained via topotactical conversion, starting from hydrothermally grown siderite single crystals. The increase in density (from 3.9 g/cm3 for siderite to 5.24 g/cm3 for magnetite and 4.9 g/cm3 for maghemite) caused quasi-ordered internal pores-grains pattern, with mesocrystalline appearance. The X-ray Line-Profile Fitting-based microstructure analysis gave 64±6 nm and 84±8 nm for the average inner grains size in magnetite and maghemite. Structure and phase content analysis indicated high purity and crystallinity. Magnetic measurements indicated saturation magnetization (92.1 emu/g for magnetite and 85.5 emu/g for maghemite) approaching the upper limits reported for the pure bulk oxides.

Ercuta, Aurel; Chirita, Marius

2013-10-01

78

Antimicrobial activity and second harmonic studies on organic non-centrosymmetric pure and doped ninhydrin single crystals.  

PubMed

In this paper, we report the successful growth of pure, Cu(2+) ions and Cd(2+) ions doped on ninhydrin single crystals by slow solvent evaporation technique. The presence of Cu(2+) and Cd(2+) ions in the specimen of ninhydrin single crystal has been determined by atomic absorption spectroscopy. The powder X-ray diffraction analysis was done to calculate the lattice parameters of the pure and doped crystals. The percentage of transmittance of the crystal was recorded using the UV-Vis Spectrophotometer. Thermal behaviors of the grown crystals have been examined by the thermal gravimetric/differential thermal analysis. The hardness of the grown crystals was assessed and the results show the minor variation in the hardness value for the pure and doped ninhydrin samples. The value of the work hardening coefficient n was found to be 2.0, 1.0 and 1.06 for pure, copper and cadmium doped ninhydrin crystals respectively. The second harmonic generation efficiency of Cd(2+) and Cu(2+) doped ninhydrin is 8.3 and 6.3 times greater than well known nonlinear crystal of potassium dihydrogen phosphate respectively. The antibacterial and antifungal activities of the title compound were performed by disk diffusion method against the standard bacteria Escherichia coli, Xanthomonas oryzae and against the fungus Aspergillis niger and Aspergillus flavus. PMID:23266683

Prasanyaa, T; Jayaramakrishnan, V; Haris, M

2012-11-29

79

Antimicrobial activity and second harmonic studies on organic non-centrosymmetric pure and doped ninhydrin single crystals  

NASA Astrophysics Data System (ADS)

In this paper, we report the successful growth of pure, Cu2+ ions and Cd2+ ions doped on ninhydrin single crystals by slow solvent evaporation technique. The presence of Cu2+ and Cd2+ ions in the specimen of ninhydrin single crystal has been determined by atomic absorption spectroscopy. The powder X-ray diffraction analysis was done to calculate the lattice parameters of the pure and doped crystals. The percentage of transmittance of the crystal was recorded using the UV-Vis Spectrophotometer. Thermal behaviors of the grown crystals have been examined by the thermal gravimetric/differential thermal analysis. The hardness of the grown crystals was assessed and the results show the minor variation in the hardness value for the pure and doped ninhydrin samples. The value of the work hardening coefficient n was found to be 2.0, 1.0 and 1.06 for pure, copper and cadmium doped ninhydrin crystals respectively. The second harmonic generation efficiency of Cd2+ and Cu2+ doped ninhydrin is 8.3 and 6.3 times greater than well known nonlinear crystal of potassium dihydrogen phosphate respectively. The antibacterial and antifungal activities of the title compound were performed by disk diffusion method against the standard bacteria Escherichia coli, Xanthomonas oryzae and against the fungus Aspergillis niger and Aspergillus flavus.

Prasanyaa, T.; Jayaramakrishnan, V.; Haris, M.

2013-03-01

80

Floating zone crystal growth of pure and Si- or Zn-substituted copper germanate CuGeO{sub 3}  

SciTech Connect

Crystal growth of pure and Si- or Zn-substituted copper germanate CuGeO{sub 3} was carried out by the floating zone technique associated with an image furnace and has led to high crystalline quality centimeter-sized crystals. Segregation of Zn and Si in the resulting solid solution crystals has been studied using ICP/AES chemical analysis and has allowed determination of the partition coefficients of these elements in CuGeO{sub 3}.

Dhalenne, G.; Revcolevschi, A. [Univ. Paris-Sud, Orsay (France). Lab. de Chimie des Solides; Rouchaud, J.C.; Fedoroff, M. [CNRS, Vitry-sur-Seine (France). Centre d`Etudes de Chimie Metallurgique

1997-07-01

81

Dielectric and mechanical nonlinearities of lang001rang oriented pure and doped single crystals of PZN-4.5PT  

NASA Astrophysics Data System (ADS)

This paper presents an overview of nonlinear dielectric, electromechanical, piezoelectric relationships in pure and Mn doped single crystals PZN-4.5PT and some modelling. The study of Mn doping on lang001rang oriented PZN-4.5PT single crystals confirms that pure crystals have soft material behaviour, while doped ones have hard material behaviour. This change in structure of the material has an effect on the dielectric, piezoelectric and mechanical properties by decreasing the dielectric constant (5650 to 3500), the dielectric losses (0.39 to 0.33) and the piezoelectric coefficient (-1050 to -650) and increasing the mechanical quality factor (150 to 375) and the velocity (1150 to 1410). It is found that the pure crystals show behaviour, under strong field or stress, that follows the Rayleigh law while the doped crystals show quadratic behaviour. Research has been undertaken to understand the influence of Mn doping on the stability in temperature for the dielectric constant, and d31 and the ageing effect. It appears that Mn neatly stabilizes the crystals compared to the pure ones.

Kobor, Diouma; Albareda, Alfons; Perez, Rafel; Garcia, José; Lebrun, Laurent; Guyomar, Daniel

2005-07-01

82

Structure and Elasticity of Natural Magnetite  

Microsoft Academic Search

Magnetite (Fe3O4) is ubiquitous in the oxidized portion of Earth's crust and upper mantle, where it forms a solid-solution with spinel-hercynite (Mg,Fe)Al2O4. Magnetite forms during secondary alteration and diagenesis, as well as in primary igneous genesis, so it occurs in nearly all rock types and the stony meteorites. We measured the structure, compressibility and elastic constants of a natural single-crystal

H. J. Reichmann; S. D. Jacobsen; T. Boffa-Ballaran

2002-01-01

83

Critical reexamination of resonant soft x-ray Bragg forbidden reflections in magnetite  

NASA Astrophysics Data System (ADS)

Magnetite, Fe3O4 , displays a highly complex low-temperature crystal structure that may be charge and orbitally ordered. Many of the recent experimental claims of such ordering rely on resonant soft x-ray diffraction at the oxygen K and iron L edges. We have reexamined this system and undertaken soft x-ray diffraction experiments on a high-quality single crystal. Contrary to previous claims in the literature, we show that the intensity observed at the Bragg forbidden (00(1)/(2))c reflection can be explained purely in terms of the low-temperature structural displacements around the resonant atoms. This does not necessarily mean that magnetite is not charge or orbitally ordered but rather that the present sensitivity of resonant soft x-ray experiments does not allow conclusive demonstration of such ordering.

Wilkins, S. B.; di Matteo, S.; Beale, T. A. W.; Joly, Y.; Mazzoli, C.; Hatton, P. D.; Bencok, P.; Yakhou, F.; Brabers, V. A. M.

2009-05-01

84

Critical Reexamination of Resonant Soft X-Ray Bragg Forbidden Reflections in Magnetite  

SciTech Connect

Magnetite, Fe{sub 3}O{sub 4}, displays a highly complex low-temperature crystal structure that may be charge and orbitally ordered. Many of the recent experimental claims of such ordering rely on resonant soft x-ray diffraction at the oxygen K and iron L edges. We have reexamined this system and undertaken soft x-ray diffraction experiments on a high-quality single crystal. Contrary to previous claims in the literature, we show that the intensity observed at the Bragg forbidden (001/2){sub c} reflection can be explained purely in terms of the low-temperature structural displacements around the resonant atoms. This does not necessarily mean that magnetite is not charge or orbitally ordered but rather that the present sensitivity of resonant soft x-ray experiments does not allow conclusive demonstration of such ordering.

Wilkins, S.B.; Di Matteo, S.; Beale, T.A.W.; Joly, Y.; Mazzoli, C.; Hatton, P.D.; Bencok, P.; Yakhou, F.; Brabers, V.A.M.

2009-05-01

85

Thermoluminescence in pure LiF crystals: Glow peaks and their connection with color centers  

SciTech Connect

Nominally pure LiF crystals were irradiated with the same dose (0.85 10{sup 6} R) of gamma rays at ambient and low temperatures (-60 deg. C) and the resulting thermoluminescence (TL) is reported. Various optical and thermal treatments were applied in order to change the concentration of color centers (CCs). The effect of such treatments on the glow curves is observed. Knowing the coloration from optical transmission and photoluminescence measurements made on the same samples, we attribute many of the glow peaks (GPs) to the annealing of F center aggregates. For the present conditions of irradiation and dose, TL processes begin with decay of F{sub 3}{sup +} centers that display a GP at 164 deg. C. F{sub 3}(R) centers follow and are responsible for GPs at 193 and 228 deg. C. A GP at 263 deg. C is ascribed to F{sub 2} centers. Several peaks at temperatures in the range of 280-380 deg. C are associated with impurity perturbed F centers. A GP at 410 deg. C is associated with a complex of aggregated F and H centers. These attributions are accomplished by means of TL spectra, optical transmission spectra, and annealing procedures, and are critically discussed. The experimental data confirm the general trend of thermal stability of CCs, which decreases by moving from simple F centers to more complex ones, and the existence of exchange dynamics among CCs.

Baldacchini, G.; Montereali, R. M. [Department of Physical Technologies and New Materials-Frascati Research Center, ENEA, Via E. Fermi 45, Frascati, Roma 00044 (Italy); Nichelatti, E. [Department of Physical Technologies and New Materials-Casaccia Research Center, ENEA, S. Maria di Galeria, Roma 00123 (Italy); Kalinov, V. S.; Voitovich, A. P. [Institute of Physics, Academy of Sciences of Belarus, 70 Nezavisimosti Ave., 220067 Minsk (Belarus); Davidson, A. T.; Kozakiewicz, A. G. [Department of Chemistry, University of Zululand, Kwadlangezwa 3886 (South Africa)

2008-09-15

86

Magnetite morphology and life on Mars  

Microsoft Academic Search

Nanocrystals of magnetite (Fe3O4) in a meteorite from Mars pro- vide the strongest, albeit controversial, evidence for the former presence of extraterrestrial life. The morphological and size re- semblance of the crystals from meteorite ALH84001 to crystals formed by certain terrestrial bacteria has been used in support of the biological origin of the extraterrestrial minerals. By using tomographic and holographic

Peter R. Buseck; Rafal E. Dunin-Borkowski; Bertrand Devouard; Richard B. Frankel; Martha R. McCartney; Paul A. Midgley; Mihaly Posfai; Matthew Weyland

2001-01-01

87

Effect of swift heavy ion beam irradiation on the dielectric and ferroelectric properties of pure and cobalt doped TGS crystals  

NASA Astrophysics Data System (ADS)

Effect of swift heavy ion (100 MeV O7+ ion) beam irradiation on the temperature and frequency dependence of real (&z.epsiv;?) and imaginary (&z.epsiv;?) parts of dielectric permittivity in pure and Co2+ doped TGS crystals are analyzed. Irradiation with swift heavy ion beam changes the dielectric response considerably. Observed dielectric peak in irradiated crystals shifts towards lower temperature and broadens up; the reduction in peak value, shift in temperature and broadening changes systematically with fluence. The most interesting results of SHI irradiation are (i) the dielectric loss peak value (emax?) in all crystals is invariably less in comparison to the value in unirradiated crystals (ii) the minimum value of dielectric loss peak (emax?) occurs at different fluence in different crystals, and (iii) a second loss peak is observed below Tc in CTGS10 especially at higher fluence. It seems that irradiation creates/strengthens internal field in the crystals by orienting the domains through some mechanism that is not clear at present. The observed results could be explained if one presumes that irradiation annihilate the defects already present in the crystals by creating local charges and thermal gradient resulting into internal bias field. Ferroelectric hysteresis loops demonstrate the internal bias field developing in the SHI irradiated crystals. It is argued that SHI irradiation is a better alternate in comparison to cobalt doping in inhibiting dipolar switching in TGS crystal.

Bajpai, P. K.; Shah, Deepak; Kumar, Ravi

2012-01-01

88

Magnetite in carbonaceous chondrites  

NASA Astrophysics Data System (ADS)

Magnetite (Fe3O4) occurs in many carbonaceous chondrites (CCs) and has long attracted the attention of meteorite researchers. However, its origin is unresolved; suggestions range from condensates from the solar nebular to products from aqueous alteration on the meteorite parent body. The report of possible evidence of former life in ancient Martian meteorite ALH84001 suggested an additional and highly intriguing origin for certain meteoritic magnetite, namely as magnetosomes from bacteria. However, a recent publication reports TEM evidence of spiral defects running through some of the the magnetite in ALHA84001, interpreted as evidence for a high temperature origin. These studies provide special interest to the occurrence of magnetite in meteorites. Using SEM, we studied magnetite from the Orgueil, Murchison, and Kaba and Mokoia meteorites, and obtained images at a nm-scale. We also did EMPA measurements to determine the compositions of the magnetite and surrounding minerals.

Hua, Xin; Buseck, Peter R.

1997-03-01

89

Molecular tectonics: design of enantiomerically pure helical tubular crystals with controlled channel size and orientation.  

PubMed

The combination of four enantiomerically pure organic tectons composed of a rigid chiral backbone bearing two terminal pyridyl coordinating sites with ZnSiF(6) behaving as an infinite pillar leads to the formation of tubular 2-D enantiomerically pure helical channels with controlled size and orientation. PMID:21655636

Lin, Mei-Jin; Jouaiti, Abdelaziz; Grosshans, Philippe; Kyritsakas, Nathalie; Hosseini, Mir Wais

2011-06-09

90

Size distribution of magnetite in carbonate globules of ALH84001 Martian meteorite  

NASA Astrophysics Data System (ADS)

The objective of this study was to study the size and shape of magnetite in the carbonate globules of ALH84001 in comparison to terrestrial biogenic magnetite, since the shape and size analysis data of the magnetite in the carbonate globules of Martian meteorite ALH84001 provides an important basis for comparison with terrestrial biogenic magnetite. It is found that the mean particle size and the size distribution of the magnetite crystals in carbonate globules of ALH84001 meteorite are comparable with those of bacterial magnetite from magnetotactic bacteria strain MS-1.

Golden, D. C.; Thomas-Keprta, K. L.; McKay, D. S.; Wentworth, S. J.; Vali, H.; Ming, D. W.

1997-03-01

91

Magnetite biomineralization induced by Shewanella oneidensis  

NASA Astrophysics Data System (ADS)

Shewanella oneidensis is a dissimilatory iron reducing bacterium capable of inducing the extracellular precipitation of magnetite. This precipitation requires a combination of passive and active mechanisms. Precipitation occurs as a consequence of active production of Fe 2+(aq) when bacteria utilize ferrihydrite as a terminal electron acceptor, and the pH rise probably due to the bacterial metabolism of amino acids. As for passive mechanisms, the localized concentration of Fe 2+(aq) and Fe 3+(aq) at the net negatively charged cell wall, cell structures and/or cell debris induces a local rise of supersaturation of the system with respect to magnetite, triggering the precipitation of such a phase. These biologically induced magnetites are morphologically identical to those formed inorganically in free-drift experiments (closed system; 25 °C, 1 atm total pressure), both from aqueous solutions containing Fe(ClO 4) 2, FeCl 3, NaHCO 3, NaCO 3 and NaOH, and also from sterile culture medium added with FeCl 2. However, organic material becomes incorporated in substantial amounts into the crystal structure of S. oneidensis-induced magnetites, modifying such a structure compared to that of inorganic magnetites. This structural change and the presence of organic matter are detected by Raman and FT-IR spectroscopic analyses and may be used as a biomarker to recognize the biogenic origin of natural magnetites.

Perez-Gonzalez, Teresa; Jimenez-Lopez, Concepcion; Neal, Andrew L.; Rull-Perez, Fernando; Rodriguez-Navarro, Alejandro; Fernandez-Vivas, Antonia; Iañez-Pareja, Enrique

2010-02-01

92

Remanence in authigenic magnetite: Testing the hydrocarbon-magnetite hypothesis  

SciTech Connect

Paleomagnetic, rock magnetic, petrographic, and geochemical studies of hydrocarbon-saturated speleothems in southern Oklahoma indicate there is a relation between hydrocarbons and a chemical magnetization that resides in magnetite. The speleothems, which are composed of light and dark calcite bands, occur in caves of karst origin in the Ordovician Kindblade Formation. Vertebrate fossils interbedded with the deposits indicate they are Permian in age. The dark bands contain primary hydrocarbon-filled fluid inclusions. The dark calcites possess over an order of magnitude stronger natural remanent magnetization than the lighter bands which do not yield stable decay during demagnetization. Alternating field (AF) and thermal demagnetization of specimens of the dark bands reveal a Permian direction of magnetization (declination = 160, inclination = 3, k = 17, {alpha}95 = 5, n = 56). The results of rock magnetic experiments, and the fact that most maximum unblocking temperatures are below 580 C, suggest that the dominant component resides in magnetite. In some specimens stable decay to 640 C suggests the presence of a weak component residing in hematite. The presence of authigenic magnetite spheres in magnetic extracts of the dark calcites supports a chemical origin for the magnetization. Shallow burial depths probably eliminate the possibility of a thermoviscous magnetization. The occurrence of primary hydrocarbons seeped into the caves during precipitation of the speleothems and were trapped in the calcite crystals. The relationship between intensity of magnetization and hydrocarbon abundance leads the authors to propose that chemical conditions created by the hydrocarbons caused precipitation of authigenic magnetite and acquisition of the associated chemical remanence.

Elmore, R.D.; Crawford, L. (Univ. of Oklahoma, Norman (United States))

1990-04-10

93

Morphologies and Chemical Composition of Individual Magnetite Grains in CI and CM Chondrites: A Potential Genetic Link to their Origin?  

NASA Astrophysics Data System (ADS)

Magnetite occurs in CI and CM chondrites as plaquettes, framboids, and radially structured spherolites (Jedwab, 1967, 1971). Recent ion microprobe investigations of the O-isotopic compositions of individual magnetite grains in Orgueil, Alais, Ivuna, and Revelstoke revealed enormous variations in delta^18O (-25 to +25) in the same meteorite (Hyman et al., (1991)). A planetary process involving water should lead to formation of grains of similar O-isotopic composition. Individual magnetites in Alais (CI1), Orgueil (CI1), Y-82162 (CI2), Essebi (CM2) and Acfer-207 have been studied in detail by us (e.g., more than 300 electron microprobe analyses). The fact that all morphological types occur together in clusters make an in situ formation not very probable. The stacking morphology of the plaquettes is in fact the strongest argument against epitaxial growth of magnetite along the rhombohedral surfaces of carbonates as suggested by Kerridge et al. (1979). The stacks occur as rounded or oval discs with the top and bottom discs displaying several oblique crystal surfaces and one perpendicular to the axis of the disc stacking. Epitaxial growth should--in contrast to the encountered plaquette morphology--produce three sets of stacks every one parallel to two opposing surfaces of the rhombohedral faces with diminishing disc sizes towards the centre of the rhombohedron. This epitaxial growth would also produce plaquettes with rhombohedral outlines and not circular or oval ones. In none of the studied meteorites were three directional rhombohedral magnetite plaquettes encountered. In Alais a sequence of formation: Magnetite--pyrrhotite--carbonate was found. The magnetites in all C-chondrites studied, are pure Fe3O4 regardless of their morphology and the assemblage in which they occur. Only the magnetites in Y-82162 are enriched in MgO and some of them in MnO. The present investigations, variability of the chemical composition of magnetite in Y-82162 and the oxygen isotopic results of Hyman et al. (1991) cast strong doubt on the meteorite parent body models for the formation of magnetite in C- chondrites proposed by Kerridge et al. (1979). REFERENCES Jedwab J. (1967) Earth and Planet. Sci. Letters 2, 440-444. Jedwab J. (1971) Icarus 15, 319-340. Hyman M., Zinner E.K. and Rowe M.W. (1991) Meteoritics (abstract) 26, 350. Kerridge J.F., Mackay A.L. and Boynton W.V. (1979) Science 205, 395-397.

Lohn, B.; El Goresy, A.

1992-07-01

94

Stoichiometric magnetite grown by infrared nanosecond pulsed laser deposition  

NASA Astrophysics Data System (ADS)

Pulsed laser deposition (PLD) is a versatile technique for the fabrication of nanostructures due to the possibilities it offers to control size and shape of nanostructured deposits by varying the laser parameters. Magnetite nanostructures are currently promising materials to be used in computing, electronic devices and spintronic applications. For all these uses the fabrication of uniform nanostructured pure magnetite thin films is highly advantageous. In PLD of magnetite, the laser irradiation wavelength and substrate temperature crucially affect the composition, crystallinity, surface structure and the magnetic properties of the grown samples. This work shows that the use of nanosecond IR laser at 1064 nm enhances the quality of the resulting magnetite thin films, compared to the extensively used UV wavelengths. Deposition at 1064 nm, upon heating the substrate at 750 K, produces thin films constituted by stoichiometric magnetite nanoparticles with sharp edges and sizes ranging from 80 to 150 nm, with a Verwey transition at 119 K and a coercivity of 232 Oe at room temperature, close to those of pure bulk magnetite. Thus, IR-PLD of self-prepared hematite sintered targets constitutes a low-cost procedure of fabrication of pure magnetite nanostructured thin films.

Sanz, Mikel; Oujja, Mohamed; Rebollar, Esther; Marco, José F.; de la Figuera, Juan; Monti, Matteo; Bollero, Alberto; Camarero, Julio; Pedrosa, Francisco J.; García-Hernández, Mar; Castillejo, Marta

2013-10-01

95

Large magnetorefractive effect in magnetite  

NASA Astrophysics Data System (ADS)

We carried out a magneto-optical spectroscopic study of magnetite (Fe3O4) thin films and single crystals at optical wavelengths. We observed a relevant quadratic magneto-optic contribution that can be notably larger than first-order linear magneto-optics at some range of wavelengths in the visible region. These unusual quadratic effects are particularly strong at the Verwey temperature (100-120 K) and decay slowly away from this transition temperature. We attribute this remarkable magneto-optical response to a magnetorefractive effect associated with the field-dependent polaronic conductivity at optical frequencies, which interestingly enough is already noticeable at room temperature.

Caicedo, J. M.; Arora, S. K.; Ramos, R.; Shvets, I. V.; Fontcuberta, J.; Herranz, G.

2010-10-01

96

Nuclear Magnetic Resonance Studies of Pure and Samarium-Doped CAF2 Crystals.  

National Technical Information Service (NTIS)

The spin-lattice relaxation time T1 of Fluorine-19 was measured over a temperature range of 77 to 1300K in natural and synthetic CaF2 crystals and in CaF2 crystals doped with 0.05% Sm, 0.16% Sm, and 1.20% Sm. Most of the data was taken with the magnetic f...

R. J. Lysiak P. P. Mahendroo

1965-01-01

97

Interferometric investigation of photonic band-structure effects in pure and doped colloidal crystals  

Microsoft Academic Search

A Mach-Zehnder interferometer was developed for accurately measuring relative phase shifts of light propa- gating in photonic colloidal crystals deep into the stop bands. These phase shifts can be used to determine the change in index of refraction and the optical dispersion relation from photonic band structure near the band edges. Phase measurements of colloidal crystals incorporating an impurity peak

Björn T. Rosner; Garrett J. Schneider; George H. Watson

1998-01-01

98

Formation of tabular single-domain magnetite induced by Geobacter metallireducens GS-15  

PubMed Central

Distinct morphological characteristics of magnetite formed intracellularly by magnetic bacteria (magnetosome) are invoked as compelling evidence for biological activity on Earth and possibly on Mars. Crystals of magnetite produced extracellularly by a variety of bacteria including Geobacter metallireducens GS-15, thermophilic bacteria, and psychrotolerant bacteria are, however, traditionally not thought to have nearly as distinct morphologies. The size and shape of extracellular magnetite depend on the culture conditions and type of bacteria. Under typical CO2-rich culture conditions, GS-15 is known to produce superparamagnetic magnetite (crystal diameters of approximately <30 nm). In the current study, we were able to produce a unique form of tabular, single-domain magnetite under nontraditional (low-CO2) culture conditions. This magnetite has a distinct crystal habit and magnetic properties. This magnetite could be used as a biosignature to recognize ancient biological activities in terrestrial and extraterrestrial environments and also may be a major carrier of the magnetization in natural sediments.

Vali, Hojatollah; Weiss, Benjamin; Li, Yi-Liang; Sears, S. Kelly; Kim, Soon Sam; Kirschvink, Joseph L.; Zhang, Chuanlun L.

2004-01-01

99

Formation of tabular single-domain magnetite induced by Geobacter metallireducens GS-15.  

PubMed

Distinct morphological characteristics of magnetite formed intracellularly by magnetic bacteria (magnetosome) are invoked as compelling evidence for biological activity on Earth and possibly on Mars. Crystals of magnetite produced extracellularly by a variety of bacteria including Geobacter metallireducens GS-15, thermophilic bacteria, and psychrotolerant bacteria are, however, traditionally not thought to have nearly as distinct morphologies. The size and shape of extracellular magnetite depend on the culture conditions and type of bacteria. Under typical CO(2)-rich culture conditions, GS-15 is known to produce superparamagnetic magnetite (crystal diameters of approximately <30 nm). In the current study, we were able to produce a unique form of tabular, single-domain magnetite under nontraditional (low-CO(2)) culture conditions. This magnetite has a distinct crystal habit and magnetic properties. This magnetite could be used as a biosignature to recognize ancient biological activities in terrestrial and extraterrestrial environments and also may be a major carrier of the magnetization in natural sediments. PMID:15525704

Vali, Hojatollah; Weiss, Benjamin; Li, Yi-Liang; Sears, S Kelly; Kim, Soon Sam; Kirschvink, Joseph L; Zhang, Chuanlun L

2004-11-03

100

Hot Carrier Velocities in Doped and in Ultra-pure Germanium Crystals at Millikelvin Temperatures  

NASA Astrophysics Data System (ADS)

The velocity laws of electrons and holes in germanium single crystals at millikelvin temperatures are determined as a function of the electric field in the <001> orientation, based on time-of-flight measurements in cryogenic coplanar grid Ge detectors. Results obtained in two n-type crystals (| N a - N d |<1010 cm-3 and doped to 1011 cm-3) are compared with the experimental data from previous investigations, and shown to be consistent with Monte-Carlo simulations of carrier transport.

Domange, J.; Olivieri, E.; Broniatowski, A.

2012-06-01

101

Magnetite-Pentlandite Chondrules in CK Chondrites  

NASA Astrophysics Data System (ADS)

Opaque-mineral-rich chondrules are among the least common chondrule types and have received scant attention since their discovery by Gustav Rose in 1864. This category includes chondrules comprised principally of metallic Fe-Ni (Tschermak, 1885; Gooding and Keil, 1981) or chrome-spinel (Ramdohr, 1967; Krot et al., 1992). Here I report the occurrence of seven magnetite-pentlandite chondrules in Karoonda (CK4), PCA82500 (CK4/5) and EET90007 (CK5). The chondrules range in size from 225x255 micrometers to 440x570 micrometers and have ellipsoidal or spheroidal morphologies. All are concentrically layered: five of the chondrules have 20-60-micrometer-thick magnetite rims surrounding pentlandite-rich cores or mantles; two of the chondrules have thin pentlandite rims surrounding magnetite-rich cores and mantles. One chondrule from Karoonda has four distinct alternating layers of magnetite and pentlandite. Accessory phases, which occur in one or more of the chondrules, include pyrrhotite, chlorapatite, ilmenite, and chalcopyrite. The chondrules have finely to coarsely granular textures; in the center of one chondrule from PCA82500 there is a 25x100 micrometers subhedral crystal of pentlandite. All of the chondrules appear to be recrystallized, presumably due to metamorphism of their host rocks. The magnetite-pentlandite chondrules are very similar to the magnetite-pentlandite-rich nodules within mafic silicate chondrules in CK chondrites. I examined four nodules that range in size from 58x64 micrometers to 400x670 micrometers and have ellipsoidal or spheroidal morphologies. All but one are concentrically layered; one nodule from a Karoonda chondrule has four concentric layers of magnetite+-pentlandite. The nodules probably formed from immiscible sulfide-oxide droplets within their molten silicate chondrule hosts during chondrule formation. Upon cooling, magnetite and monosulfide solid solution (Mss) precipitated during cotectic crystallization; the Mss transformed into pentlandite after cooling below 610 degrees C. Dense immiscible liquid droplets tend to get expelled from the equators of their spinning molten spheroidal hosts if they do not happen to be located in the molten spheroids' centers where the centrifugal forces are minimal. This phenomenon also affected the four magnetite-pentlandite nodules: one nodule is near the margin and three are at the centers of their host silicate chondrules. The similarities in size, shape, mineralogy, and texture between the magnetite-pentlandite chondrules and nodules indicate that these chondrules constitute the set of immiscible nodule droplets that were lost to their mafic silicate chondrule hosts after melting. The occurrence of magnetite-pentlandite chondrules and nodules has important implications for the timing of CK chondrite oxidation. If oxidation had occurred after agglomeration and transformed metallic Fe-Ni into magnetite, the large (factor of 2) increase in molar volume would have disrupted the nodules and chondrules and destroyed the evidence for rhythmic layering. The intactness of the chondrules and nodules implies that the oxidation of fine-grained metallic Fe-Ni into magnetite probably occurred before agglomeration, either during chondrule formation in a region of high fo(sub)2 or within porous chondrule-precursor dust clumps after nebular temperatures cooled below ~130 degrees C. Hence, the pervasive silicate darkening of CK chondrites (Kallemeyn et al., 1991; Rubin, 1992) was caused by the shock mobilization of magnetite and pentlandite, not metallic Fe-Ni and troilite as in shock-darkened ordinary chondrites. References: Gooding J.L. and Keil K. (1981) Meteoritics 16, 17- 43; Kallemeyn G.W., Rubin A.E. and Wasson J.T. (1991) Geochim. Cosmochim. Acta 55, 881-892; Krot A., Ivanova M.A. and Wasson J.T. (1992) Earth Planet. Sci. Lett., submitted; Ramdohr P. (1967) Geochim. Cosmochim. Acta 31, 1961-1967; Rubin A.E. (1992) Geochim. Cosmochim. Acta 56, 1705-1714; Tschermak G. (1885) Die Mikroskopische Beschaffenheit der Meteoriten. Schweizerbart'sche Verlagshandlung, Stuttga

Rubin, A. E.

1992-07-01

102

Electronic structure near cationic defects in magnetite  

NASA Astrophysics Data System (ADS)

We used the DFT + U method to describe the modification of the physical properties induced by cationic point defects in cubic magnetite Fe3O4. We considered the case of Fe vacancies and interstitial atoms in non-stoichiometric magnetite, and of Frenkel defects in a stoichiometric crystal. For each of these defects, we give results on the modification of the magnetic moment of atoms near the defect. We describe the local reorganization of the electric charge which is responsible for changes in the average oxidation degree of Fe atoms. We show that gap states, when they exist, do not destroy the half-metallic character of magnetite. Fe defects, however, change the filling of bands crossing the Fermi level and must be mostly responsible for a decrease in the magnetization.

Arras, R.; Warot-Fonrose, B.; Calmels, L.

2013-06-01

103

Utilization of pure nuclear quadrupole resonance spectroscopy for the study of pharmaceutical crystal forms.  

PubMed

Solid-state physical characterization of a pharmaceutical substance is necessary for successful development and approval of the final product. Different physical analytical techniques are available to do so: X-ray diffraction (XRD), IR, Raman, DSC, TG and NMR. Moreover, all of them detect the presence of excipients perturbing the analysis of the pure substance in low doses. In order to study polymorphism and pseudo polymorphism of drug, this paper introduces possible applications of pure nuclear quadrupole resonance, as a non-destructive technique in qualitative and quantitative approaches. Chlorpropamide and diclofenac sodium were used as examples. Unlike the mentioned techniques, the nuclear quadrupole resonance (NQR) signal of pharmaceutical compounds is not perturbed by the presence of solid excipient or other substances unless they possess resonance frequencies in the same frequency range of the compound studied. PMID:15913931

Pérez, S C; Cerioni, L; Wolfenson, A E; Faudone, S; Cuffini, S L

2005-07-14

104

PREPARATION OF ULTRA-PURE SUCCINONITRILE BY COUNTERCURRENT DISTILLATION FOR CRYSTAL GROWTH  

Microsoft Academic Search

We developed the purification method to produce ultra-pure succinonitrile by multiple countercurrent distillations. The distillation column used was 25?mm in diameter and 110?cm in the packed height with Heli-Pak® packing (0·05” × 0·10” × 0·10”, packing factor+ 960). Typical operational conditions of each stage are as follows: condenser temperature 65 °C, reboiler temperature 160 °C, head pressure 50?m Torr or

YOUN-WOO LEE; RAMAGOPAL ANANTH; WILLIAM N. GILL

1996-01-01

105

Electrooptic characterization and Czochralski growth technique of pure and doped lithium niobate crystals  

NASA Astrophysics Data System (ADS)

Ferroelectric Lithium Niobate (LN) possesses a combination of unique electrooptic, piezoelectric, pyroelectric, and photorefractive properties. These features make it suitable for applications in optical devices-as modulators, switches, and filters in communication systems and holographic recording medium, etc. Here, the growth of lithium Niobate doped with iron and doubly doped with iron and manganese ions will be described. The growth technique will be through Automatic Diameter Control Czochralski Design. From these grown crystals, critical electrooptical coefficients using null detection polarimetry are provided. The results of growth, electrooptic measurements, and some physical properties are compared and presented. Also, the use of doped LN crystals in devices is discussed.

Gebre, Tesfaye; Edwards, Denise E.; Aggarwal, Manmohan D.; Batra, Asok K.; Edwards, Matthew E.; Patel, Darayas; Huey, LaQuieta; Lal, Ravindra B.

2004-10-01

106

Thermophiles as Candidate Iron-Reducing Bacteria For the Putative Biogenetic Magnetite in Banded Iron Formations  

NASA Astrophysics Data System (ADS)

The temperature of the Archaean-Palaeoproterozoic ocean was likely consistent with physiological requirements of thermophilic species being present. In this study, we compared the crystallochemistry and lattice constants of magnetite crystals produced by Thermoanaerobacter sp. TOR39, Geobacter and Shewanella and the slightly altered magnetite from BIF of Hamersley, Western Australia. The lattice constants of TOR39-magnetite and the BIF-magnetite were similar, being 8.3901 and 8.3869 Å respectively. The lattice constant of magnetite produced by Geobacter is more close to perfect stoichiometry (8.4038 Å), however, the magnetite produced by Shewanella experienced oxidization has a much smaller value (8.3522 Å). The stoichiometries of TOR39-magnetite was Fe3+[Fe3+1.1217Fe2+0.8175--0.0608]O4 and that of BIF-magnetite was quite similar being Fe3+[Fe3+0.9963Fe2+1.0056]O4. The stoichiometry, lattice constant and crystal size collectively indicated that TOR39-magnetite was similar to BIF-magnetite. The Mössbauer spectroscopy indicated the existence of a Fe(III)-salt, possibly Fe3+OH(CH3COO)2 in the magnetite lamina of BIF which was widely detected in the magnetite-assemblages of iron-reducing bacterial cultures that contained acetate. This is evidence that supports a potential role for thermophiles such as Thermoanaerobacter in the biogenesis of magnetite in BIF. The magnetite crystals produced by cultures of Shewanella, Geobacter, magnetotactic bacteria and those synthesized from green rust appeared less similar to BIF-magnetite by either their crystallochemistry or their optimized growth temperatures.

Li, Y.; Phelps, T. J.; Cole, D. R.; Vali, H.; Konhauser, K.

2008-12-01

107

Growth and Optical Properties of Li2B4O7 Single Crystals Pure and Doped with Yb, Co and Mn Ions for Nonlinear Applications  

NASA Astrophysics Data System (ADS)

The paper reports on the growth conditions of Li2B4O7 single crystals in both pure and Yb, Co, Mn doped systems. The crystals were grown by the Czochralski method using an intentional concentration of the above-mentioned ions at a level of 0.5 mol.%. The pure and Mn-doped crystals were found to be highly transparent and clear. The crystals doped with Yb2O3 had a lot of precipitations making them opaque. The Co-doped crystals were purple-blue in colour and highly transparent. The growth of Yb and Co doped Li2B4O7 crystals was reported for the first time in this paper. Absorption was measured in the range of 200 to 3200 nm, moreover analysis of changes in the absorption spectrum of ?-irradiated pure and doped Li2B4O7 crystals was performed. Some thermoluminescence properties were measured, e.g. energies and lifetimes of the traps of different charge carriers occurring in the crystals at low temperatures.

Podgórska, D.; Kaczmarek, S. M.; Drozdowski, W.; Berkowski, M.; Worsztynowicz, A.

2005-03-01

108

Raman Study of the Verwey Transition in Magnetite (Fe3O4) at High Pressure and Low Temperature: Effect of Aluminum Doping  

NASA Astrophysics Data System (ADS)

Raman spectra of pure and doped magnetite provide a set of markers allowing one to study how the Verwey transition in magnetite changes with the change of pressure. At ambient pressure Verwey transition temperature, Tv, of the single crystals of magnetite, Fe3O4, is determined to be 123K. High-pressure experiment indicates strong dependence of the change of pressure vs. change in the Verwey transition temperature on the amount of impurities: for pure Fe3O4 the change is -0.2 GPa/K; for doped iron, Fe2.98Al0.02O4, the change is -0.09 GPa/K. Aluminum-doped magnetite (Fe2.98Al0.02O4) where Al substitutes Fe^+2 and Fe^+3 atoms, represents a 2% aluminum doping, which shifts the Verwey transition temperature to Tv=118.5K. The rate with which the Verwey temperature decreases with pressure is further discussed based on the molar specific heat measurements.

Shirshikova, Z.; Gasparov, L.; Struzhkin, V.; Gavriliuk, A.; Berger, H.

2011-03-01

109

Raman Study of the Verwey Transition in Magnetite (Fe3O4) at High Pressure and Low Temperature: Effect of Aluminum Doping  

NASA Astrophysics Data System (ADS)

Raman spectra of pure and doped magnetite provide a set of markers allowing one to study how the Verwey transition in magnetite changes with the change of pressure. At ambient pressure Verwey transition temperature, Tv, of the single crystals of magnetite, Fe3O4, is determined to be 123K. High-pressure experiment indicates strong dependence of the change of pressure vs. change in the Verwey transition temperatureon the amount of impurities: for pure Fe3O4 the change is -0.2 GPa/K; for doped iron, Fe2.98Al0.02O4, the change is -0.09 GPa/K. Aluminum-doped magnetite (Fe2.98Al0.02O4) where Al substitutes Fe^+2 and Fe^+3 atoms, represents a 2% aluminum doping, which shifts the Verwey transition temperature to Tv=118.5K. The rate with which the Verwey temperature decreases with pressure is further discussed based on the molar specific heat measurements.

Shirshikova, Zhanna; Gasparov, Lev; Struzhkin, V.; Gavriliuk, A.; Berger, H.

2011-04-01

110

Weak antiferromagnetic ordering induced by Dzyaloshinskii-Moriya interaction and pure magnetic reflections in MnSi-type crystals.  

PubMed

A symmetry analysis of the Dzyaloshinskii-Moriya (DM) interaction in MnSi-type crystals reveals a nontrivial antiferromagnetic pattern of tilted Mn moments remaining even after an unwinding of the ground-state helix by a strong magnetic field. The remaining tilts are caused by that component of the DM vector which is perpendicular to the component responsible for helical spiraling; both components are evaluated and related to the atomic structure using a simple model. It is shown that the tilting should induce pure magnetic reflections 00?(?=2n+1) in neutron or x-ray magnetic scattering. In addition, the DM-induced antiferromagnetic ordering is important for the core structure of intrinsic defects, for the spectra of magnetic resonances, and generally for a better understanding of spin-orbit interaction in this type of magnetics. PMID:22681111

Dmitrienko, Vladimir E; Chizhikov, Viacheslav A

2012-05-02

111

Smearing of the reconstructive phase transition in pure and mixed LiK1-xRbxSO4 crystals  

NASA Astrophysics Data System (ADS)

The smearing of the reconstructive phase transition in LiK1-xRbxSO4 crystals (x<=0.50), due to the occurrence of different nonuniform local phase transitions, is demonstrated from the temperature dependence of the electrical-conductivity data around the critical region. A model which determines the distribution of critical temperatures is presented and the results are compared with the calorimetric behavior of the system. For the pure compound LiKSO4, the distribution of critical temperatures is fitted by a Gaussian curve, showing that the smearing of the phase transition is uniquely due to its reconstructive character. The multimodal distribution observed for the mixed compounds suggests the appearance of clusters with different concentrations.

Righi, A.; Bourson, P.; Pimenta, M. A.; Moreira, R. L.

1997-11-01

112

Comparison of magnetite nanocrystal formed by biomineralization and chemosynthesis  

NASA Astrophysics Data System (ADS)

Magnetite nanocrystal has been widely used in many fields. Recently, a new magnetite nanocrystal, called magnetosome, has been found in magnetotactic bacteria. In this article, we compared properties of magnetites prepared by co-precipitation with those of magnetosomes isolated from MSR-1 in detail, such as crystalline, morphology, crystal-size distributions, vitro cytotoxicity, and magnetic properties and quantified primary amino groups on the magnetosomes membrane surface by fluorescamine assay for the first time. From the results, it was clear that the magnetosomes might have potential in the biomedical applications in the future.

Han, Lei; Li, Shuangyan; Yang, Yong; Zhao, Fengmei; Huang, Jie; Chang, Jin

2007-06-01

113

Indirect band gap and optical parameters of pure and doped potassium ferrocyanide single crystals  

NASA Astrophysics Data System (ADS)

The optical transmittance for potassium ferrocyanide (KFCT) single crystals were measured as a function of the wavelength at different temperatures in the range 275-320K along the two axes (I01¯) and (010) and hence the absorption coefficient (/?) and optical band gap Eg were deduced. The type of transition was determined and the validity of Urbach's rule was checked. The steepness parameter (/?) and the exciton energy E0 were calculated at different temperatures. The temperature dependence of the energy gap was estimated and the result was confirmed through the calculation of dEg/dT from information about /?. The refractive index, the extinction coefficient and both the real and imaginary parts of the dielectric permittivity were also calculated as a function of photon energy and the results were discussed. The effect of doping KFCT with 2% of sodium nitroproced, cobalt sulphate or potassium dichromate on the same physical parameters was also discussed.

Gaffar, M. A.; Abu-El Fadl, A.

2000-11-01

114

Spectroscopic investigation on the efficient organic nonlinear crystals of pure and diethanolamine added DAST  

NASA Astrophysics Data System (ADS)

4-N,N'-dimethylamino-N-methyl-4-stilbazolium toyslate (DAST) and diethanolamine (DEA) added DAST crystals are grown by slow cooling method. The corresponding powder samples are examined by characterization studies such as XRD, FT-IR, FT-Raman, UV-Vis-NIR and photoluminescence studies. From the powder X-ray diffraction, their lattice parameter values are found out. Since the vibrational spectra of the molecules are considerably contributed to their linear and nonlinear optical effects, Infrared and Raman spectroscopic studies are carried out for the samples. The UV-Vis-NIR absorption spectra of the samples are used to find the nature of transitions occurred in the samples. Using the density functional theory, highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) analyses are done in order to explain the transition and density of states (DOS). The first order hyperpolarizability is calculated by HF and B3LYP/6-311 G(d,p) basis sets for the DAST molecule. From the photoluminescence (PL) spectral studies, the strong excitation emissions are observed.

Karthikeyan, C.; Haja Hameed, A. S.; Sagaya Agnes Nisha, J.; Ravi, G.

2013-11-01

115

Morphology and structure of biogenic magnetite particles  

Microsoft Academic Search

Blakemore1 found aquatic bacteria that swim along magnetic lines of force. Such bacteria have small particles of magnetite (magnetosomes) within them2,3 of various shapes3-5. We describe here the morphology and structure of bacterial magnetosomes investigated by high-resolution electron microscopy. From direct observation of various kinds of lattice images, the particles are determined to be single crystals with a hexagonal prism

Tsuyoshi Matsuda; Junji Endo; Nobuyuki Osakabe; Akira Tonomura; Tatsuo Arii

1983-01-01

116

Aqueous immune magnetite nanoparticles for immunoassay  

Microsoft Academic Search

Immune magnetite nanoparticles (MNPs) are prepared by four successive reactions, which are MNPs preparation, silica-coating,\\u000a surface modification with amino group, and conjugation with bio-molecule, respectively. The crystal structure and morphology\\u000a of intermediate products are characterized by XRD, TEM and AFM. Qualitative and quantitative assays for amino group on the\\u000a MNPs’ surface are made by FTIR and Organic Element Assay. Ultraviolet–visible

Guoxin Zhang; Yanbo Liu; Chunfu Zhang; Weiqing Hu; Wanbang Xu; Zheng Li; Sheng Liang; Jinquan Cao; Yongxian Wang

2009-01-01

117

Microbial production of ultrafine-grained magnetite by fermentation processes at room temperature.  

PubMed

A method of producing magnetite nanoparticles was developed through culturing a microorganism designated Haejae-1, Shewanella sp., in the presence of glucose and akaganeite (beta-FeOOH). Haejae-1 isolated from inter-tidal flat sediments was able to produce copious amount of ultrafine magnetite via glucose fermentation extracellularly under anaerobic conditions at room temperature, allowing for easy production, separation, and recovery of the magnetite. TEM observation revealed aggregates of small crystals of ultrafine magnetite which ranged in size from about 2 to 4 nanometers. Magnetic property by SQUID analysis showed the magnetite nanoparticles demonstrate superparamagnetic behavior. As a result, the method of the present study can be used to produce magnetite efficiently using inexpensive means at room temperature. The magnetite is a mineral of a great commercial value in that it is useful, e.g., in magnetic recording devices, drug carriers, and as toner for plain paper copiers. PMID:19198424

Roh, Yul; Kim, Yumi; Lee, Sanghoon; Jang, Heedong; Suh, Yongjae

2008-10-01

118

YBa2Cu3O7-delta single crystals revisited: Scanning probe data on very pure samples grown in BaZrO3 crucibles  

Microsoft Academic Search

We have studied very pure YBa2Cu3O7-delta (YBCO) single crystals grown in BaZrO3 crucibles by scanning and friction force microscopy (SFM, FFM) as well as by scanning tunneling microscopy (STM) and angle resolved X-ray photo-electron spectroscopy (ARXPS). By STM and SFM, clean stepped terraces are observed on as-grown crystals. Friction contrast, however, implies the presence of different materials, presumably traces of

U. Hubler; P. Jess; H. P. Lang; A. Erb; E. Walker; M. Regier; D. Schild; J. Halbritter; H.-J. Güntherodt

1998-01-01

119

YBa 2 Cu 3 O 7-d single crystals revisited: Scanning probe data on very pure samples grown in BaZrO 3 crucibles  

Microsoft Academic Search

We have studied very pure YBa2Cu3O7-? (YBCO) single crystals grown in BaZrO3 crucibles by scanning and friction force microscopy (SFM, FFM) as well as by scanning tunneling microscopy (STM) and angle resolved X-ray photo-electron spectroscopy (ARXPS). By STM and SFM, clean stepped terraces are observed on as-grown crystals. Friction contrast, however, implies the presence of different materials, presumably traces of

U. Hubler; P. Jess; H. P. Lang; A. Erb; E. Walker; M. Regier; D. Schild; J. Halbritter; H.-J. Güntherodt

1998-01-01

120

Magnetosome vesicles are present before magnetite formation, and MamA is required for their activation  

Microsoft Academic Search

Bacterial magnetosomes are intracellular compartments that house highly ordered magnetite crystals. By using Magnetospiril- lum sp. AMB-1 as a model system, we show that magnetosome vesicles exist in the absence of magnetite, biomineralization of magnetite proceeds simultaneously in multiple vesicles, and bi- omineralization proceeds from the same location in each vesicle. The magnetosome-associated protein, MamA, is required for the formation

Arash Komeili; Hojatollah Vali; Terrance J. Beveridge; Dianne K. Newman

2004-01-01

121

Preparation and characterization of pure and Pr(III)-doped lead chloride single crystals grown by modified micro-pulling-down method  

NASA Astrophysics Data System (ADS)

Single crystals of lead chloride pure and doped with Pr(III) were grown for the first time using the modified micro-pulling-down method. Due to hygroscopicity of both lead chloride and doping Pr(III) chloride the standard micro-pulling-down apparatus had to be equipped with a removable protective chamber. Prepared single crystals 25 mm long and 3 mm in diameter were characterized by powder X-ray diffraction and DSC thermal analysis. Optical and luminescence characteristics of lead chloride single crystals, such as absorption, radioluminescence, photoluminescence, and decay curves, were measured as well.

Král, R.; Nitsch, K.; Jarý, V.; Yokota, Y.; Futami, F.; Yoshikawa, A.; Nikl, M.

2013-07-01

122

Oxygen diffusion in magnetite  

NASA Astrophysics Data System (ADS)

The diffusion rate of oxygen in magnetite (Fe3O4) has been measured under hydrothermal conditions between 800° and 500°C at 1000 bars pressure, and yields the Arrhenius relation: D = 3.5 × 10-6 exp(-45,000/RT) kcal/g-atom O. The diffusion rate was found to be the same, within the estimated uncertainty of a factor of 2, for measurements at 100, 1000, and 2000 bars (20-200 MPa) water pressure, and for oxygen fugacities buffered by magnetite-hematite and approximately Ni-NiO. The activation energy and diffusion mechanism probably change to that given by Castle and Surman [10] at temperatures below 460°C. The oxygen diffusion rate in magnetite is between those of quartz and hornblende. Closure temperatures fall in the range 380°C for 0.1 mm radius grains cooling at 1°C/m.y. to 675°C for 1 mm radius and cooling at 1000°C/m.y. if the present data are used, but will be lower for the fine grain sizes and slow cooling rates if the Castle and Surman data are used.

Giletti, B. J.; Hess, K. C.

1988-06-01

123

In situ TEM investigation of Xe ion irradiation induced defects and bubbles in pure molybdenum single crystal  

NASA Astrophysics Data System (ADS)

In order to study irradiation damage and inert gas bubble formation and growth behaviors, and to provide results and insights useful towards the validation of a multi-scale simulation approach based on a newly developed Xe-Mo inter-atomic potential, in situ Transmission Electron Microscopy (TEM) studies of Xe implantations in pure single crystal Molybdenum (Mo) have been conducted. 300 keV and 400 keV Xe+ ion beams were used to implant Xe in pre-thinned TEM Mo specimens. The irradiations were conducted at 300 °C and 600 °C to ion fluence up to 4 × 1016 ions/cm2.In situ TEM characterization allows detailed behaviors of defect clusters to be observed and is very useful in illustrating defect interaction mechanisms and processes. Dislocation loops were found to form at relatively low irradiation fluence levels. The characterization results showed that the free surfaces, formed in the process of producing pre-thinned specimens, play an important role in influencing the behaviors of dislocation loops. Similar characterizations were conducted at high fluence levels where Xe gas bubbles can be clearly observed. Xe gas bubbles were observed to form by a multi-atom nucleation process and they were immobile throughout the irradiation process at both temperatures. Measurements on both the number density and the size of dislocation loops and gas bubbles were taken. The results and implications of the measurements are discussed in this paper.

Yun, Di; Kirk, Marquis A.; Baldo, Peter M.; Rest, Jeffrey; Yacout, Abdellatif M.; Insepov, Zinetula Z.

2013-06-01

124

Effect of Annealing on Coercive Force and Remanent Magnetizations in Magnetite  

Microsoft Academic Search

A series of experiments is described in which single crystals of magnetite were annealed under controlled conditions. Structural changes in the magnetite were followed by changes in the magnitudes of coercive force and saturation isothermal remanent magnetization. The structural changes were identified by comparing their activation energies as estimated from the annealing curves with those of known physical processes. It

W. Lowrie; M. Fuller

1969-01-01

125

Formation of tabular single-domain magnetite induced by Geobacter metallireducens GS15  

Microsoft Academic Search

Distinct morphological characteristics of magnetite formed intracellularly by magnetic bacteria (magnetosome) are invoked as compelling evidence for biological activity on Earth and possibly on Mars. Crystals of magnetite produced extracellularly by a variety of bacteria including Geobacter metallireducens GS-15, thermophilic bacteria, and psychrotolerant bacteria are, however, traditionally not thought to have nearly as distinct morphologies. The size and shape of

Hojatollah Vali; Benjamin Weiss; Yi-Liang Li; S. Kelly Sears; Soon Sam Kim; Joseph L. Kirschvink; Chuanlun L. Zhang

2004-01-01

126

Mineralogical and Isotopic Properties of Biogenic Nanocrystalline Magnetites  

Microsoft Academic Search

Determination of the origin of magnetite nanocrystals is of primary importance because of their significance\\u000a as biomarkers for extraterrestrial life and as environmental indicators. A critical analysis of the\\u000a literature indicates that morphology and magnetic properties of the crystals do not necessarily quantitatively\\u000a allow differentiation of biogenic from abiotic nanomagnetite crystals. Mineralogical properties of magnetosomes\\u000a and of inorganic crystals such as

Damien Faivre; Pierpaolo Zuddas

127

Controllable one-step synthesis of magnetite/carbon nanotubes composite and its electrochemical properties  

NASA Astrophysics Data System (ADS)

Magnetite nanocrystals are deposited on carbon nanotubes by a reflux method in diethylene glycol. The morphological characterization proves that magnetite nanocrystals are decorated on the external surfaces of carbon nanotubes. The crystal size of magnetite nanocrystals can be readily tuned by adjusting the content of sodium acetate, but the content of sodium acetate has little effect on the amount of magnetite. The magnetite/carbon nanotubes composites exhibit an initial capacity as high as 840 mAh g-1 and an excellent cycling performance for lithium storage. The reversible capacity, as high as 390 mAh g-1, can be maintained after 75 charge/discharge cycles. The research has potential implications for the application of magnetite/carbon nanotubes composites as anode materials of lithium ion batteries.

Cheng, J. P.; Yu, J.; Shi, D.; Wang, D. S.; Liu, Y. F.; Liu, F.; Zhang, X. B.; Li, J. G.

2012-03-01

128

Synthesis, characterization and anti-microbial activity of pure, Cu2+ and Cd2+ doped organic NLO l-arginine trifluoroacetate single crystals  

NASA Astrophysics Data System (ADS)

Optically transparent Cu2+ and Cd2+ doped l-arginine trifluoroacetate (LATF) single crystals were grown from its aqueous solution using the slow solvent evaporation technique. The grown crystals were characterized by powder x-ray diffraction to confirm the monoclinic crystal structure. The percentage of transmittance measured using the ultraviolet-visible-near infrared spectrophotometer was found to be more than 80% for doped crystals. The functional group analysis of the grown crystals has been made by Fourier transform infrared spectroscopy. Thermogravimetric/differential thermal analysis was performed for the grown crystals. An atomic absorption study was carried out to determine the presence of Cu2+ and Cd2+. The hardness of the grown crystals was assessed and the results show a significant variation in the hardness value between the pure and doped LATF crystals. The second harmonic generation measurements show that Cu2+ doped LATF is 2.8 times greater and Cd2+ doped is 2.6 times greater than KDP. The anti-bacterial and anti-fungal activities of the title compound were performed using the disc diffusion method against standard bacteria Escherichia coli, Xanthomonas oryzae and against the fungus Aspergillus niger and Aspergillus flavus.

Prasanyaa, T.; Haris, M.; Jayaramakrishnan, V.; Amgalan, M.; Mathivanan, V.

2013-10-01

129

Plagioclase-Hosted Magnetite Inclusions From the Bushveld Complex  

NASA Astrophysics Data System (ADS)

Gabbros from the Main Zone of the 2.064 Ga Bushveld Complex have long been known to possess unusually stable magnetizations due to the presence of high coercivity, exsolved magnetite inclusions in plagioclase and clinopyroxene. The paleomagnetic pole for these rocks has been used to anchor apparent polar wander paths for the Kaapval craton during the Early-Mid Proterozoic. To better understand the rock magnetic properties of silicate-hosted magnetite inclusions, oriented paleomagnetic samples of gabbro were collected from quarries near Belfast and Rustenberg, South Africa, sampling the eastern and western limbs of the Complex, respectively. Plagioclase composition at both sites ranges from An55 (rims) to An65 (cores) based on optical and electron microprobe data. Four kinds of inclusions are present within the plagioclase: elongate magnetite needles, nanometer-scale magnetite particles (responsible for the "cloudy" appearance of some crystals), translucent brown hematite/ilmenite platelets, and colorless euhedral inclusions of pyroxene and/or feldspar. Magnetite inclusions are most abundant at the cores of the plagioclase crystals. Orientations of the needles and the platelets are crystallographically controlled by the silicate host. Although the elongation direction of the magnetite inclusions can occur in any of five possible orientations, only two or three of these directions dominates each plagioclase crystal. Alternating field demagnetization of bulk samples (NRM = 1.5 x 101 A m-1) shows univectorial remanence with average median destructive fields (MDF) of 115 mT (Belfast) and 90 mT (Rustenberg). AF demagnetization of single plagioclase crystals (NRM = 100 A m-1) also shows single component remanence with average MDFs >150 mT. The NRM coercivity spectra of single plagioclase crystals are indistinguishable from that of the bulk samples. When normalized to their abundance in bulk samples the magnetite-bearing plagioclase fully accounts for the NRM of Bushveld gabbros at both sites. Close examination of the inclusions' interiors using magnetic force microscopy shows no ulvöspinel exsolution as observed in other silicate exsolved titanomagnetites with comparably high coercivities. Consequently, we interpret the high coercivities of the inclusions to be a product of their small size and extreme shape anisotropy. Single crystals of plagioclase demonstrate a strong anisotropy of IRM acquisition (see Scott, et al. this conference). Additionally, electron backscatter diffraction (EBSD) orientation indexing shows a strongly preferred orientation for plagioclase and pyroxene (with (010)plag and (100)pyr parallel to subhorizontal layering) consistent with gravitational settling within a magma chamber. Thus, there are two anisotropies (silicate preferred orientation and magnetite inclusion remanence) to consider when describing the ancient magnetic field present during the emplacement of the Bushveld.

Feinberg, J. M.; Scott, G. R.; Renne, P. R.; Wenk, H.

2004-12-01

130

Electrically driven phase transition in magnetite nanostructures  

NASA Astrophysics Data System (ADS)

Magnetite (Fe3O4), an archetypal transition-metal oxide, has been used for thousands of years, from lodestones in primitive compasses to a candidate material for magnetoelectronic devices. In 1939, Verwey found that bulk magnetite undergoes a transition at TV~120K from a high-temperature `bad metal' conducting phase to a low-temperature insulating phase. He suggested that high-temperature conduction is through the fluctuating and correlated valences of the octahedral iron atoms, and that the transition is the onset of charge ordering on cooling. The Verwey transition mechanism and the question of charge ordering remain highly controversial. Here, we show that magnetite nanocrystals and single-crystal thin films exhibit an electrically driven phase transition below the Verwey temperature. The signature of this transition is the onset of sharp conductance switching in high electric fields, hysteretic in voltage. We demonstrate that this transition is not due to local heating, but instead is due to the breakdown of the correlated insulating state when driven out of equilibrium by electrical bias. We anticipate that further studies of this newly observed transition and its low-temperature conducting phase will shed light on how charge ordering and vibrational degrees of freedom determine the ground state of this important compound.

Lee, Sungbae; Fursina, Alexandra; Mayo, John T.; Yavuz, Cafer T.; Colvin, Vicki L.; Sumesh Sofin, R. G.; Shvets, Igor V.; Natelson, Douglas

2008-02-01

131

Pure low-frequency flexural mode of [011]c poled relaxor-PbTiO3 single crystals excited by k32 mode  

PubMed Central

Rhombohedral phase relaxor-PbTiO3 solid solution single crystals poled along [011]c exhibits superior lateral extensional piezoelectric response, which enables the excitation of a pure low frequency flexural mode with a bridge-type electrode configuration. For the ternary 0.24Pb(In1/2Nb1/2) O3-0.46Pb(Mg1/3Nb2/3)O3-0.30PbTiO3 single crystal poled along [011]c, the electromechanical coupling factor of the flexural mode reached as high as 0.66, and the resonance frequency of this mode can be easily made in kHz range, making it possible to fabricate very small size low frequency sensors and actuators. We have delineated theoretically the coupling between flexural mode and other modes and realized a strong pure flexure mode.

Liu, Gang; Jiang, Wenhua; Zhu, Jiaqi; Cao, Wenwu

2012-01-01

132

Magnetite biomineralization in termites  

PubMed Central

Experimental evidence exists for magnetoreception in termites, a major component of the soil macrofauna in many tropical countries. This preliminary study identifies, probably for the first time, the presence of biogenic ferrimagnets (magnetite?) in two species of termite (Nasutitermes exitiosus and Amitermes meridionalis), based on magnetic measurements of whole termite specimens and individual body sections, and analysis by electron microscopy of magnetically extracted grains. The magnetic measurements indicate the presence of very small concentrations of magnetic material, with more magnetic grains in the thorax and abdomen region compared with the head. Magnetic interaction, due to clustering of grains, is also identified by the measurements. Analysis of magnetic extracts by transmission electron microscopy identifies the presence of uniquely ultrafine (10 nm) and unidimensional grains of ferrimagnetic material, unequivocally distinct from any possible extraneous magnetite sources, such as ingested soil. Hence, this provides firm evidence for biogenic formation of this magnetic material by these two termite species. Such ultrafine grains would be superparamagnetic, i.e. incapable of carrying a permanent magnetic moment, unless they were sited in clusters of interacting grains, when some remanence-carrying ability, and hence magnetotaxis, would be possible.

Maher, B. A.

1998-01-01

133

Magnetic response of microbially synthesized transition metal- and lanthanide-substituted nano-sized magnetites  

SciTech Connect

The magnetic susceptibility (?T) and saturation magnetization (MS) of microbially synthesized magnetites were systematically examined. Transition metal (Cr, Mn, Co, Ni, and Zn)- and lanthanide (Nd, Gd, Tb, Ho, and Er)-substituted magnetites were microbially synthesized by the incubation of transition metal (TM)- and lanthanide (L)-mixed magnetite precursors with either thermophilic (TOR-39) or psychrotolerant (PV-4) metal-reducing bacteria (MRB). Zinc incorporated congruently into both the precursor and substituted magnetite, while Ni and Er predominantly did not. Microbially synthesized Mn- and Zn-substituted magnetites had higher ?T than pure biomagnetite depending on bacterial species and they exhibited a maximum ?T at 0.2 cationic mole fraction (CMF). Other TMs?substitution linearly decreased the ?T with increasing substitution amount. Based on the MS values of TM- and L-substituted magnetite at 0.1 and 0.02 CMF, respectively, Zn- (90.7 emu/g for TOR-39 and 93.2 emu/g for PV-4) and Mn- (88.3 emu/g by PV-4) substituted magnetite exhibited higher MS than standard chemical magnetite (84.7 emu/g) or pure biomagnetite without metal substitution (76.6 emu/g for TOR-39 and 80.3 emu/g for PV-4). Lanthanides tended to decrease MS, with Gd- and Hosubstituted magnetites having the highest magnetization. The higher magnetization of microbially synthesized TM-substituted magnetites by the psychrotroph, PV-4 may be explained by the magnetite formation taking place at low temperatures slowing mechanics, which may alter the magnetic properties compared to the thermophile, through suppression of the random distribution of substituted cations.

Moon, Ji Won [ORNL; Yeary, Lucas W [ORNL; Rondinone, Adam Justin [ORNL; Rawn, Claudia J [ORNL; Kirkham, Melanie J [ORNL; Roh, Yul [Chonnam National University, Gwangju; Love, Lonnie J [ORNL; Phelps, Tommy Joe [ORNL

2007-01-01

134

Origin of supposedly biogenic magnetite in the Martian meteorite Allan Hills 84001  

NASA Astrophysics Data System (ADS)

Crystals of magnetite (Fe3O4) and periclase (MgO) in Fe-Mg-Ca carbonate in the Martian meteorite Allan Hills 84001 were studied by using transmission electron microscopy to understand their origin and evaluate claims that the magnetites were made by Martian microorganisms. In magnesian carbonate, periclase occurs as aggregates of crystals (grain size 3 nm) that are preferentially oriented with respect to the carbonate lattice. Larger periclase crystals 50 nm in size are commonly associated with voids of similar size. Periclase clearly formed by precipitation from carbonate as a result of partial decomposition and loss of CO2. Magnetite occurs in more ferroan carbonate, and, like periclase, it is associated with voids and microfractures and the two oxides may be intermixed. Magnetite nanocrystals that are commonly euhedral and entirely embedded in carbonate are topotactically oriented with respect to the carbonate lattice, showing that they formed as solid-state precipitates. Magnetites in Fe-rich carbonate rims are not well oriented. These magnetites are generally more irregular in shape and diverse in size than the euhedral variety. All occurrences of magnetite and periclase are entirely consistent with in situ growth by solid-state diffusion as a result of carbonate decomposition during impact heating. Biogenic sources should not be invoked for any magnetites.

Barber, David J.; Scott, Edward R. D.

2002-05-01

135

Raman study of the Verwey transition in Magnetite at high-pressure and low-temperature; effect of Al doping  

NASA Astrophysics Data System (ADS)

We report high-pressure low-temperature Raman measurements of the Verwey transition in pure and Al --doped magnetite (Fe3O4) Al-doped magnetite Fe2.8Al0.2O4 (TV=116.5K) displays a nearly linear decrease of the transition temperature with an increase of pressure yielding dP/dTV=-0.096±0.013 GPa/K. In contrast pure magnetite displays a significantly steeper slope of the PT equilibrium line with dP/dTV = -0.18±0.013 GPa/K. Contrary to earlier high pressure resistivity reports we do not observe quantum critical point behavior at 8 GPa in the pure magnetite. Our data indicates that Al doping leads to a smaller entropy change and larger volume expansion at the transition. The trends displayed by the data are consistent with the mean field model of the transition that assumes charge ordering in magnetite.

Gasparov, Lev; Shirshikova, Z.; Pekarek, T. M.; Blackburn, J.; Struzhkin, V.; Gavriliuk, A.; Rueckamp, R.; Berger, H.

2012-02-01

136

Spectroscopic Properties of Rare Earth Borohydrides: Er(BH4)3-3THF In Pure and Mixed Crystals.  

National Technical Information Service (NTIS)

The optical spectra of Er(BH4)3-3THF neat crystals and La, Gd, Y(BH4)3-3THF mixed crystals are reported and analyzed. Lanthanum borohydride is found to have a different room temperature crystal structure (triclinic) from Er, Gd, Y(BH4)3-3THF(Pbcn). At low...

E. R. Bernstein K. M. Chen

1975-01-01

137

Iron isotopic fractionation factor between magnetite and hydrous silicic melt  

NASA Astrophysics Data System (ADS)

A "thermal migration" experiment was conducted in the piston cylinder to investigate the changes in composition of a wet andesitic bulk composition in a temperature gradient at 0.5 GPa. A homogeneous andesite powder (AGV-1 containing 4 wt.% H2O was sealed in a AuPd double capsule with the hot end at 950°C and the bottom end 350°C for 66 days. The charge changes from 100% melt at the top to the progressively more crystalline with the sequential appearance of apatite, magnetite, amphibole, biotite, plagioclase, quartz, and K-feldspar. We microdrilled 5 samples along the temperature gradient and analyzed these for Fe isotope ratios by double spike MC-ICP-MS at UIUC. Results show that the 100% melt area is depleted in heavy Fe isotopes relative to all more crystalline portions of the experiment (4 samples) with the offset in {?}^{56/54}FeIRMM of about 1.7‰. This does not appear to reflect Fe loss in the experiment as the Fe content and isotopes mass balance and no detectable Fe was found in the capsule after the experiment. Instead the offset is interpreted to reflect the combination of diffusive fractionation of Fe moving by diffusion and possible equilibrium fractionations between melt and magnetite that occurs throughout the crystalline portion of the experiment. However, both the isotopic fractionation factor between magnetite and melt and the effect of diffusion on Fe isotopes remains unknown. We are currently investigating Fe isotopic fractionation factor between magnetite and melt and effects of melt diffusion on Fe isotopes. To assess diffusion, we will microdrill and analyze melt-melt diffusion couples from Lundstrom(G-Cubed, 2003). To assess magnetite-melt fractionation, we have begun piston cylinder experiments at 0.5 GPa and 800°C using a starting material synthesized based on the melt composition within the thermal migration experiment. Initial experiments produce a layer of 100% melt on top of a 2-phase mush of magnetite-melt. This will allow analysis of pure melt and the magnetite-melt mush with knowledge of the modes providing the ability to back out the fractionation factor. If we can prove attainment of equilibrium, this technique will bypass the difficulty of making pure separates of magnetite and melt. Fe isotopic composition of the melt and melt-magnetite layers will be measured by MC-ICP-MS.

Huang, F.; Lundstrom, C. C.

2006-12-01

138

Magnetite morphology and life on Mars  

NASA Astrophysics Data System (ADS)

Nanocrystals of magnetite (Fe3O4) in a meteorite from Mars provide the strongest, albeit controversial, evidence for the former presence of extraterrestrial life. The morphological and size resemblance of the crystals from meteorite ALH84001 to crystals formed by certain terrestrial bacteria has been used in support of the biological origin of the extraterrestrial minerals. By using tomographic and holographic methods in a transmission electron microscope, we show that the three-dimensional shapes of such nanocrystals can be defined, that the detailed morphologies of individual crystals from three bacterial strains differ, and that none uniquely match those reported from the Martian meteorite. In contrast to previous accounts, we argue that the existing crystallographic and morphological evidence is inadequate to support the inference of former life on Mars.

Buseck, Peter R.; Dunin-Borkowski, Rafal E.; Devouard, Bertrand; Frankel, Richard B.; McCartney, Martha R.; Midgley, Paul A.; Pósfai, Mihály; Weyland, Matthew

2001-11-01

139

Epitaxial growth of nanophase magnetite in Martian meteorite Allan Hills 84001: implications for biogenic mineralization.  

PubMed

Crystallographic relationships between magnetite, sulfides, and carbonate rosettes in fracture zones of the Allan Hills (ALH) 84001 Martian meteorite have been studied using analytical electron microscopy. We have focused on those magnetite grains whose growth mechanisms can be rigorously established from their crystallographic properties. Individual magnetite nanocrystals on the surfaces of carbonates are epitaxially intergrown with one another in "stacks" of single-domain crystals. Other magnetite nanocrystals are epitaxially intergrown with the surfaces of the carbonate substrates. The observed magnetite/carbonate (hkl) Miller indices orientation relationships are (1, 1,3)m ¿¿ (1, 1 ,0)c and (1, 1 ,1)m ¿¿ (0,0, 3)c with lattice mismatches of approximately 13% and approximately 11%, respectively. Epitaxy is a common mode of vapor-phase growth of refractory oxides like magnetite, as is the spiral growth about axial screw dislocations previously observed in other magnetite nanocrystals in ALH 84001. Epitaxy rules out intracellular precipitation of these magnetites by (Martian) organisms, provides further evidence of the high-temperature (> 120 degrees C) inorganic origins of magnetite in ALH 84001, and indicates that the carbonates also have been exposed to elevated temperatures. PMID:11543075

Bradley, J P; McSween, H Y; Harvey, R P

1998-07-01

140

Hydrothermal Preparation of Apatite Composite with Magnetite or Anatase  

SciTech Connect

Microstructure designed porous hydroxyapatite (Ca10(PO4)6(OH)2) composites with magnetite (Fe3O4) particles or anatase (TiO2) dispersion were prepared by hydrothermal treatment. These composites had micro-pores of about 0.1-0.5 {mu}m in size. Magnetite / Hydroxyapatite composites should be suitable for medical treatment of cancer, especially in bones, because HA can bond to bones directly and magnetite can generate heat. They must be used for hyperthermia therapies of cancer in bones. Meanwhile, anatase / Hydroxyapatite composite should be suitable for environmental purification, because HA rod-shape particles expose the specific crystal face, which adsorbs organic contaminants and so on.

Murakami, Setsuaki; Ishida, Emile H.; Ioku, Koji [Graduate School of Environmental Studies, Tohoku University, Sendai, Miyagi 980-8579 (Japan)

2006-05-15

141

The transformation of magnetite to hematite and its influence on the rheology of iron oxide rock  

NASA Astrophysics Data System (ADS)

Phase transformation is an important process for strain localization after the initiation of ductile shear zones. In polyphase aggregates one important aspect to consider is likely to be the interconnectivity of weak phase after the transformation of the load-bearing framework grains. However the physical processes involved in that transition is not well understood, partially because the microstructures of the initial weakening are generally obliterated by subsequent deformation. Iron oxide-quartz rocks from paleoproterozoic Iron Formations in southern Brazil preserve microstructures that allow a good insight into the evolution of the deformation mechanisms and fabrics during the transition from a load-bearing framework (magnetite) to an interconnected weak phase (hematite). We conducted microstructural and textural analyses of aggregates of magnetite and hematite combining observations in an optical microscope and measurements in the electron back-scatter diffraction (EBSD). The samples were cut parallel to the mineral lineation (the X-axis) and perpendicular to the foliation. Our goal was to understand the evolution of fabric and texture of the iron oxide aggregates caused by the change in deformation behavior resulting from the phase transformation. The studied samples consist mainly of aggregates of magnetite and hematite in a varied proportions. Samples that preserve the early microstructures consist in aggregate of magnetite grains of varied sizes. The grains are partially transformed to hematite along {111} planes but no foliation is observed in the samples. Basically the samples consist of grains of irregular shapes and a weak or absent crystallographic preferred orientation. The newly transformed hematite crystals share the (0001) planes and directions <11-20> with planes {111} and directions <110> of magnetite grains. Other samples present relicts of initial magnetite grains surrounded by a matrix of tabular to platy hematite crystals. The matrix show a preferred orientation of hematite grains. Close to the magnetite, hematite crystals show crystallographic relationship similar to those observed inside the magnetite crystals showing a good match in crystallographic planes and directions. However away from the magnetite crystals hematite of the matrix tend to show a more independent crystallographic orientation with respect to the magnetite grains. The poles to the basal planes of hematite distributed in a small circle centered around the Z-axis and the crystallographic directions <11-20> spread in a wide angle along the foliation plane. In samples where no crystal of magnetite grains is observed only platy hematite with a strong shape preferred orientation occur. Their basal planes show a strong concentration around the foliation pole contrasting to the more dispersed distribution around the Z-axis found in the samples with magnetite relicts.The directions <11-20> also distributed along the foliation planes in platy hematite samples but with a narrower angles than those of samples with magnetite relicts. The progressive transformation of magnetite to hematite led to a change in the iron formation rock fabrics from an isotropic distribution of a load-supporting magnetite to an interconnected weak platy hematite forming a strongly anisotropic fabric. The hard magnetite behaves in a brittle manner with a very limited operation of slip along the main crystallographic planes. The microfracturing creates an easy path for oxidation and transformation of magnetite. The newly formed hematite grains behave in a ductile manner and form a matrix of strongly oriented crystals. The deformation mechanisms change from the microfracturing of the harder magnetite phase to a crystal plastic deformation of the softer hematite platy grains through slip along their basal planes.

Lagoeiro, Leonardo; Barbosa, Paola; Goncalves, Fabio; Rodrigues, Carlos

2013-04-01

142

Magentic Properties of Magnetites Produced by Magnetotactic Bacteria  

NASA Astrophysics Data System (ADS)

Magnetotactic bacteria (MTBs) are a diverse group of motile, aquatic bacteria including coccoid, rodshaped, vibrioid, spirilla and multicellular forms that orient and migrate along the geomagnetic field. Their intracellular magnetites (magnetosomes) are characterized by narrow grain-size distributions (30 to 120 nm), distinct species-specific crystal morphology, chemical purity, and arrangement in single or multiple linear chains. The magnetic properties of magnetosome are of great interest for sedimentary magnetism, fine-grain magnetism, magnetic materials, biomineralization in organisms and biomarkers in rocks. We will report magnetic measurements on both air-dried cells containing solely MTBs (wild-type cocci and Magnetobacterium bavaricum), which were directly isolated from the Chiemsee lake sediments, and the whole fresh cells as well as isolated magnetosomes of laboratory cultured strain, Magnetospirillum gryphiswaldense MSR-1. Results show that: (1) the magnetosomes in cells are dominated by single-domain (SD) magnetite; (2) Low-temperature cycling of saturation isothermal remanent magnetization (SIRM) and first-order-reversal-curve (FORC) diagrams of the samples differ significantly from the ones measured on SD-magnetite powder samples; and (3) the Verwey transition temperature (Tv, 100 K) of bacterial magnetites is distinctly lower than that from stoichiometric magnetite (Tv, 120 to 125 K). Moreover, the effects of related low-temperature oxidation and chain arrangement in measured samples will be discussed.

Pan, Y.; Lin, W.; Zhu, R.; Yu, S.; Davila, A. F.; Winklhofer, M.; Petersen, N.

2005-12-01

143

Suppression of photorefractive damage with aid of steady-state temperature gradient in nominally pure LiNbO{sub 3} crystals  

SciTech Connect

Photorefractive damage (PRD) in as-grown, oxidized, and slightly reduced nominally pure LiNbO{sub 3}, and iron-doped crystals with different compositions has been studied with the closed-aperture Z-scan and pseudo-Z-scan techniques at uniform temperature distribution, as well as at a steady-state temperature gradient {nabla}T, created by two external thermoelectric elements in the transverse direction to the light beam trajectory. The most important experimental finding consists of the demonstration of the possibility of a full PRD suppression in nominally pure crystals with the aid of a relatively small temperature gradient (12.5-84 K/cm), if {nabla}T is above a threshold value specific for each crystal studied. The threshold {nabla}T{sub th} decreases significantly with the increase in the so-called bipolaron absorption band (center at 470-500 nm) in the optical spectra, and it is not correlated with the composition of the crystals within the studied range of compositions ([Li]/[Nb]=0.946-0.983). No any partial suppression of PRD was observed in iron-doped ([Fe]{>=}0.01 wt %) lithium niobate crystals, even at the largest temperature gradient (85 K/cm) used in our study. To explain these experimental results, we use theoretical model taking into account local changes of spontaneous polarization (i.e., polarization charge field) at photoionization of intrinsic defects (polarons, bipolarons, and hole polarons). It has been shown that a steady-state temperature gradient may induce a local thermoelectric current of light-induced charge carriers and their instant recombination, resulting in a decrease in the polarization space-charge field and hence, a light-induced refractive index change. The latter mechanism may induce the full PRD suppression, if macroscopic charge separation (space-charge field effect) gives insignificant contribution to the total light-induced electric field, as in as-grown and reduced nominally pure LiNbO{sub 3} crystals.

Kostritskii, S. M. [MPTE Department, Moscow Institute of Electronic Technology, Moscow, 124498 Zelenograd (Russian Federation); Sevostyanov, O. G. [Physics Department, Kemerovo State University, 650043 Kemerovo (Russian Federation); Aillerie, M.; Bourson, P. [Laboratoire Materiaux Optiques, Photonique et Systemes, University Paul Verlaine of Metz and Supelec, UMR CNRS 7132, 2 Rue E. Belin, 57070 Metz (France)

2008-12-01

144

Production of well defined chemically pure single crystals of rare-earth and actinide compounds for solid state reseach  

NASA Astrophysics Data System (ADS)

Today the understanding of delicate problems such as phase transitions or very low temperature phenomena depend on measurements which are very sensitive to the quality of the sample. Since the magnetic moments of rare-earths and actinides are usually anisotropic all experiments on magnetic properties require single crystals. The usual choice for ultrapurification are physical methods such as sublimation, vacuum melting, zone refining and electrotransport. Work has to be done under UHV conditions. Crystal growth is hampered by the high reactivity. For actinides toxicity and radioactivity are a further important handicap. Methods for crystal growth are solution growth, mineralization, Czochralski or Bridgman technique and zone melting. Crucible free methods are always preferable.

Vogt, O.; Spirlet, J. C.

1987-01-01

145

An experimental and theoretical determination of oxygen isotope fractionation in the system magnetite-H 2O from 300 to 800°C  

NASA Astrophysics Data System (ADS)

Oxygen isotope fractionations have been determined between magnetite and water from 300 to 800°C and pressures between 10 and 215MPa. We selected three reaction pathways to investigate fractionation: (a) reaction of fine-grained magnetite with dilute aqueous NaCl solutions; (b) reduction of fine-grained hematite through reaction with dilute acetic acid; and (c) oxidation of fine iron power in either pure water or dilute NaCl solutions. Effective use of acetic acid was limited to temperatures up to about 400°C, whereas oxide-solution isotope exchange experiments were conducted at all temperatures. Equilibrium 18O/ 16O fractionation factors were calculated from the oxide-water experiments by means of the partial isotope exchange method, where generally four isotopically different waters were used at any given temperature. Each run product was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and on a limited basis, high-resolution transmission electron microscopy (HRTEM) and Mössbauer spectroscopy. Results from the microscopic examinations indicate the formation of well-crystallized octahedra and dodecahedra of magnetite where the extent of crystallization, grain size, and grain habit depend on the initial starting material, P, T, solution composition, and duration of the run. The greatest amount of oxygen isotope exchange (˜90% or greater) was observed in experiments where magnetite either recrystallized in the presence of 0.5 m NaCl from 500 to 800°C or formed from hematite reacted with 0.5 m acetic acid at 300, 350 and 400°C. Fractionation factors (10 3 ln ? mt-H2O) determined from these partial exchange experiments exhibit a steep decrease (to more negative values) with decreasing temperature down to about 500°C, followed by shallower slope. A least-squares regression model of these partial exchange data, which accounts for analytical errors and errors generated by mass balance calculations, gives the following expression for fractionation that exhibits no minimum: 1000ln ?lmt-lw=-8.984(±0.3803) x+3.302(±0.377) x2—0.426(±0.092) x3 with an R 2 = 0.99 for 300 ? T? 800°C (x = 10 6/T 2). The Fe oxidation results also exhibit this type of temperature dependence but shifted to slightly more negative 10 3 ln ? values; there is the suggestion that a kinetic isotope effect may contribute to these fractionations. A theoretical assessment of oxygen isotope fractionation using ?-factors derived from heat capacity and Mössbauer temperature (second-order Doppler) shift measurements combined with known ?-factors for pure water yield fractionations that are somewhat more negative compared to those determined experimentally. This deviation may be due to the combined solute effects of dissolved magnetite plus NaCl (aq), as well as an underestimation of ?mt at low temperatures. The new magnetite-water experimental fractionations agree reasonably well with results reported from other experimental studies for temperatures ? 500°C, but differ significantly with estimates based on quasi-theoretical and empirical approaches. Calcite-magnetite and quartz-magnetite fractionation factors estimated from the combination of magnetite ?'s calculated in this study with those for calcite and quartz reported by Clayton and Kieffer (1991) agree very closely with experimentally determined mineral-pair fractionations.

Cole, David R.; Horita, Juske; Polyakov, Veniamin B.; Valley, John W.; Spicuzza, Michael J.; Coffey, Dorothy W.

2004-09-01

146

Magnetic properties of magnetite arrays produced by the method of electron beam lithography  

NASA Astrophysics Data System (ADS)

Arrays of magnetite particles in the submicron range (0.1-4.0 µm) have been produced. A novel method involving the utilisation of Electron Beam Lithography techniques often employed in the engineering design of integrated circuits of microchips was used. The fabrication process involved first producing arrays of iron (Fe) particles and then converting them to magnetite (Fe3O4) by thermal treatment. The fabricated magnetite particles have well controlled parameters including inter-particle spacing, an impossible task to achieve using artificially produced powders often employed in rockmagnetic studies. Two methods of converting Fe to Fe3O4 by annealing were used. One method led to Fe3O4 grains with high coercivities, typical of stressed grains and the other low coercivities in agreement with those for laboratory grown crystals. The crystal unit cell edge. Curie temperature, and saturation isothermal remanent magnetisation (SIRM) intensity observed at the Verwey transition are all consistent with stoichiometric magnetite.

King, James G.; Williams, Wyn; Wilkinson, C. D. W.; McVitie, Stephen; Chapman, John N.

147

Thickness dependence of the resistivity tensor in epitaxial magnetite thin films  

NASA Astrophysics Data System (ADS)

We report a systematic study of the thickness dependence of the resistivity tensor of epitaxial thin films of magnetite (Fe3O4). We find that decreasing film thickness decreases the relative magnitude of the terms related to crystal symmetry but increases their field dependence. We attribute this behavior to the presence of antiphase boundaries in thin films of magnetite and the dependence of their density on the film thickness.

Naftalis, N.; Shperber, Y.; Moyer, J. A.; Ahn, C. H.; Klein, L.

2013-07-01

148

Magnetite anodes for impressed current cathodic protection  

Microsoft Academic Search

Magnetite anodes for impressed current cathodic protection, when constructed according to the design by Paul Bergsoee and Son A.B., overcome certain inherent disadvantages of magnetite (magnetic iron oxide) to afford low consumption at high current loads. More than 30,000 Bera Magnetite anodes have been put into operation. The anode is cast as an open cylinder with one end closed, approximately

1978-01-01

149

Structural insight into magnetochrome-mediated magnetite biomineralization.  

PubMed

Magnetotactic bacteria align along the Earth's magnetic field using an organelle called the magnetosome, a biomineralized magnetite (Fe(II)Fe(III)2O4) or greigite (Fe(II)Fe(III)2S4) crystal embedded in a lipid vesicle. Although the need for both iron(II) and iron(III) is clear, little is known about the biological mechanisms controlling their ratio. Here we present the structure of the magnetosome-associated protein MamP and find that it is built on a unique arrangement of a self-plugged PDZ domain fused to two magnetochrome domains, defining a new class of c-type cytochrome exclusively found in magnetotactic bacteria. Mutational analysis, enzyme kinetics, co-crystallization with iron(II) and an in vitro MamP-assisted magnetite production assay establish MamP as an iron oxidase that contributes to the formation of iron(III) ferrihydrite eventually required for magnetite crystal growth in vivo. These results demonstrate the molecular mechanisms of iron management taking place inside the magnetosome and highlight the role of magnetochrome in iron biomineralization. PMID:24097349

Siponen, Marina I; Legrand, Pierre; Widdrat, Marc; Jones, Stephanie R; Zhang, Wei-Jia; Chang, Michelle C Y; Faivre, Damien; Arnoux, Pascal; Pignol, David

2013-10-06

150

The effect of oxidation on the Verwey transition in magnetite  

NASA Astrophysics Data System (ADS)

It has long been believed that magnetic remanence and susceptibility would change markedly at T(V) in the case of coarse grains but only slightly or inappreciably in the case of fine grains. We find on the contrary that remanence changes at T(V) by 50-80 percent in both large and small crystals, if they are stoichiometric. However, minor surface oxidation suppresses the transition, and the fact that fine grains oxidize more readily leads to an apparent size dependence. Our experiments used submicron magnetite cubes with mean sizes of 0.037, 0.076, 0.10 and 0.22 micron which were initially nonstoichiometric. A saturation isothermal remanent magnetization (SIRM) given in a 2.5 T field at 5 K decreased steadily during zero-field warming to 300 K with little or no indication of the Verwey transition. After the oxidized surface of each crystal was reduced to stoichiometric magnetite, the SIRM decreased sharply during warming by 50-80 percent around 110 K. The change in SIRM for the 0.22-micron grains was almost identical to that measured for a 1.5 mm natural magnetite crystal. Thus a 10 exp 12 change in particle volume does not materially affect the remanence transition at T(V) but oxidation to z = 0.3 essentially suppresses the transition.

Özdemir, Özden; Dunlop, David J.; Moskowitz, Bruce M.

1993-08-01

151

Metal ion complexes of the optically pure bi(4-phenyl-1,3-oxazoline) ligand. Synthesis, characterization and X-ray crystal structures  

Microsoft Academic Search

Several new complexes of optically pure 2,2?-bis-[(4R)-phenyl-1,3-oxazoline] (L) with Mn(II), Co(II), Cu(II), Zn(II), Cd(II) and Ag(I) metal ions have been synthesized and thoroughly characterized by IR, UV–Vis and 1H NMR spectroscopy, as well as by single-crystal X-ray diffraction. These compounds include [MnL3][MnCl4] (1), [CoL3][Co(NCS)4] (2), [CuL3](ClO4)2 (3), [ZnL3](ClO4)2 (4), [CdL3](ClO4)2 (5) and [AgL](CF3SO3)·1\\/2C6H6 (6). In 1 and 2 the anionic

Goutam Kumar Patra; Israel Goldberg; Amitabha Sarkar; Shubhamoy Chowdhury; Dipankar Datta

2003-01-01

152

Stable remanence and memory of multi-domain materials with special reference to magnetite  

Microsoft Academic Search

The characteristics of memory of remanence across the so-called isotropic point (TK) in single crystals of magnetite are demonstrated experimentally. Memory is shown to be related to the highest microscopic coercivity fraction in the crystal. In order to investigate the nature of the magnetically hard fraction, studies of memory as a function of state of internal stress were undertaken with

Kazuo Kobayashi; M. Fuller

1968-01-01

153

Near-surface Structural Change in Magnetite: An EPR Study  

NASA Astrophysics Data System (ADS)

Magnetite as a lithogenic mineral is widespread in soils. Its bulk magnetic properties have been studied in detail and the grain size distribution has been used as proxy to reconstruct weathering environments. During weathering, oxidation can lead to the formation of ferric oxides at the magnetite surface. Such changes are difficult to detect by classical rock magnetic analysis, because the magnetic data are generally dominated by the bulk properties. In this research we test the use of electron paramagnetic resonance (EPR) spectroscopy in order to get an insight into near-surface properties of magnetite in a soil. The experiments were carried out on untreated and chemically treated soil samples. Chemical treatments included oxalate extraction which dissolves poorly crystallized ferric oxides, as well as citrate-bicarbonate- dithionite (CBD) treatment, which removes ferric oxides (e.g. maghemite, hematite) but also SD magnetite by reductive dissolution. Under the SEM, the magnetite particles showed a particle size of generally more than 10 microns. A minor Ti for Fe substitution was found by EDX analysis. Hysteresis loops of the untreated (KA), oxalate treated (K_ox), and CBD treated (KA_dith) samples at room temperature showed a coercive force (Hc) of 10 ±1 mT and a hysteresis closure between 250-300 mT which is indicative of magnetite. The FORC diagrams of KA, KA_ox and KA_dith were similar and revealed two features : an Hc distribution with maximum at 10 mT and a vertical spread (bias field) with Hc around 2mT. These data suggest that the different chemical treatments had no significant effect on the magnetite in the soil samples. Since CBD treatment is known to dissolve SD magnetite, an assemblage of MD and PSD magnetite particles can be inferred. The EPR spectroscopic parameters (g-value and linewidth ?B) showed different values for the untreated and chemically treated magnetite. For KA, g = 2.12 and ?B = 120 mT were measured. Similar values (g = 2.14 and ?B =120 mT ) were found for Ka_ox. With CBD treatment, both parameters increased to 2.27 and 160 mT, respectively. The significant broadening of the lineshape after CBD treatment is due to an increase of inhomogeneity (e.g. defect structures) caused by the reductive dissolution of Fe^{(III)}. The simultaneous decrease of the resonant field, indicated by higher g-values, points to an enhancement of the internal field. This can be explained by an increase of the magnetic moments due to incongruent dissolution of Fe^{(III)} probably in the vicinity of Ti^{(IV)} sites in the near-surface region of the magnetite grains. In conclusion, EPR spectroscopy is a powerful tool to detect near-surface structural defects and can, therefore, be used to complement classical rock magnetic methods.

Fischer, H.; Luster, J.; Gehring, A. U.

2006-12-01

154

Synthesis and characterization of magnetite nanoparticles from mineral magnetite  

NASA Astrophysics Data System (ADS)

We have synthesized magnetite nanoparticles with sizes that range from 20 to 30 nm from mineral magnetite roughly 45 ?m in size. The procedure consists in the dissolution of the mineral in an acidic medium and subsequent precipitation in a basic medium in the presence of oleic acid. Two experiments were conducted in different gaseous environments. The first was carried out in an environment exposed to air (M1) and the second in an N2 (M2) environment. The x-ray diffraction results showed a slight difference, which corresponds to the surface oxidation of magnetite. The sizes of the modified nanoparticles were determined through the Scherrer equation and transmission electron microscopy. An organic material mass loss corresponding to 18% was observed through a thermogravimetric analysis. The Fourier transform infrared spectroscopic analysis provides information about the type of bond that is formed on the surface of the nanoparticle, which corresponds to a bidentate chelate. The vibrating sample magnetometer results show a superparamagnetic behavior for sample M1.

Morel, Mauricio; Martínez, Francisco; Mosquera, Edgar

2013-10-01

155

Magnetite-Based Magnetoreceptor Cells in the Olfactory Organ of Rainbow Trout and Zebrafish  

NASA Astrophysics Data System (ADS)

Many vertebrate and invertebrate animals have a geomagnetic sensory system, but the biophysics and anatomy of how magnetic stimuli are transduced to the nervous system is a challenging problem. Previous work in our laboratories identified single-domain magnetite chains in olfactory epithelium in cells proximal to the ros V nerve, which, in rainbow trout, responds to magnetic fields. Our objectives are to characterize these magnetite-containing cells and determine whether they form part of the mechanism of magnetic field transduction in teleost fishes, as a model for other Vertebrates. Using a combination of reflection mode confocal microscopy and a Prussian Blue technique modified to stain specifically for magnetite, our Auckland group estimated that both juvenile rainbow trout (ca. 7 cm total length) olfactory rosettes have ~200 magnetite-containing cells. The magnetite present in two types of cells within the olfactory epithelium appears to be arranged in intracellular chains. All of our groups (Munich, Auckland, Cambridge and Caltech) have obtained different types of structural evidence that magnetite chains closely associate with the plasma membrane in the cells, even in disaggregated tissues. In addition, our Cambridge group used Ca2+ imaging to demonstrate a clear response by individual magnetite-containing cells to a step change in the intensity of the external magnetic field and a slow change in Ca2+ activity when the external magnetic field was cancelled. In the teleost, zebrafish (Danio rerio), a small (~4 cm adult length in captivity) genetic and developmental biology model organism, our Caltech group detected ferromagnetic material throughout the body, but concentrated in the rostral trunk, using NRM and IRM scans of whole adults. Our analysis suggests greater than one million, 80-100 nm crystals, with Lowrie-Fuller curves strongly consistent with single-domain magnetite in 100-100,000 magnetocytes. Ferromagentic resonance (FMR) spectra show crystals with narrow particle size distribution concentrated in the trunk, similar to biogenic magnetofossils. In SQUID microscopy images numerous dipole spots are widely distributed throughout the flank, not correlated with skin pigments or the spinal cord and neural arches. We interpret this to indicate a lateral line location for trunk magnetite in zebrafish. In contrast to trout in which rock magnetic experiments and TEM suggest highly interacting bundled ropes of crystals, similar to those in the large magnetotactic bacterium, M. bavaricum, zebrafish magnetic aggregates apparently arrange in clumps or mixed chains and clumps. We report trout olfactory epithelium containing magnetite magnetoreceptors that transduce the external magnetic field, then encode and transmit it to the brain, while zebrafish contain magnetite in the lateral line region.

Kirschvink, J. L.; Cadiou, H.; Dixson, A. D.; Eder, S.; Kobayashi, A.; McNaughton, P. A.; Muhamad, A. N.; Raub, T. D.; Walker, M. M.; Winklhofer, M.; Yuen, B. B.

2011-12-01

156

Electromechanical properties of magnetite transducer  

NASA Astrophysics Data System (ADS)

An oscillographic study was done in Fe3O4 magnetite which gave some light about the generated polarization with the applied electric AC field in playing dielectric hysteresis loop. It was noticed that the dielectric constant increased with enhancing temperature, which was attributed to the rapid hopping of electrons between Fe2+<-->Fe3+at the octahedral sites (B sites) leading to the orientation of domain walls in the direction of the applied AC electric field. The resonant frequency and antiresonance of vibrating tablets have been studied as a function of temperature. The decrease of the resonant frequency with rising temperature was attributed to increase the polarization which facilitate the interaction of domains with the applied AC field at lower frequency. The decrease of the ultrasonic wave velocity with the increase of temperature, was also studied. Magnetite transducers is useful for ultrasonic generation to be used in medical purposes and under water sound transducer.

Tawfik, A.; El-Sharif, A.

2004-07-01

157

Thermoremanent Magnetization in Submicroscopic Magnetite  

Microsoft Academic Search

titano- magnetite particles in igneous rocks. Although hysteresis properties indicate that the magne- tites are above single-domain (SD) size, their weak-field TRM are SD-like. TRM intensity, for a 1-oe inducing field, ranges from 6 to 12 emu\\/cm 8. Median alternating demagnetization fields are between 275 and 400 oe, while blocking temperatures are generally within 50øC of the Curie point. However,

D. J. Dunlop

1973-01-01

158

Lightning-strike fusion of gabbro and formation of magnetite-bearing fulgurite, Cornone di Blumone, Adamello, Western Alps, Italy  

NASA Astrophysics Data System (ADS)

The Adamello gabbro exposed on the summit of Cornone di Blumone, Western Alps, Italy, has been fused by lightning strikes to form magnetite-rich fulgurites produced by melting of magnetite, hornblende, calcic plagioclase and minor clinopyroxene. The composition of quench magnetite in the fulgurite is 44.4 Fe3O4; 27.5 MgFe2O4; 15.1 FeAl2O4; 7.9 Fe2TiO4; 2.5 Fe2SiO4; 1.9 CaFe2O4; 0.8 MnFe2O4 and is inferred to have crystallized from a low-Si, Fe-rich melt under high oxidation conditions of about 1 log unit below the log10ƒO2 of hematite-magnetite. The low Si, Fe-rich melt is considered to have been produced from fusion of magnetite + hornblende-rich areas of the host gabbro and/or possible separation of an immiscible high Fe2O3/FeO Fe-rich, low-Si melt from a more siliceous glass during superheating. Skeletal-dendritic morphologies of magnetite in the fulgurite indicate crystallization under conditions of extreme supercooling. Juxtaposition of areas exhibiting different growth habits and crystal sizes of magnetite may reflect compositionally different local melt domains and/or small differences in the delicate balance between nucleation and growth in domains that had slightly different, although ultrafast, cooling rates.

Grapes, Rodney H.; Müller-Sigmund, Hiltrud

2010-05-01

159

Magnetite fractionation of "chalcophile" elements  

NASA Astrophysics Data System (ADS)

Submarine-quenched glasses provide the clearest record of magmatic evolution available, especially with respect to potentially volatile elements and compounds. A comprehensive suite of arc- and backarc glasses recovered during several research voyages in the SW Pacific are being analysed by a number of research teams in an effort to document genesis and fractionation processes involved in the evolution of subduction- related magma systems. As part of these studies, a suite of basalt to dacite composition glasses recovered from the arc-like Pacmanus Site in the Manus Backarc Basin have been examined in detail. Sun et al. (2004) found trends of increasing enrichments of Re, Cu, and Au with SiO2 in the range from 50 to 60 wt% SiO2. From this stage of magmatic evolution, marked depletions in all these elements are observed in glasses of higher SiO2 contents. The reasons for this trend have been unclear, although a mechanism involving the cessation of olivine and initiation of magnetite saturation was proposed by Sun et al. Our analysis of a larger suite of glasses from the Manus Basin has now confirmed these trends, and found the same behaviour for Zn and Mn. Similarly, analysis of a suite of basalt to dacite glasses recovered from the arc-like Valu Fa Ridge in the Lau Backarc Basin has produced trends for these elements very similar to those of the Pacmanus location. LA-ICP-MS analysis of microphenocrysts in these glasses has shown that magnetite is highly enriched in Re relative to the coexisting melt (Kd up to 7.8 for Re). Magnetite/melt partition coefficients for Re, Mn and Yb can be used to precisely model the liquid line of descent during magnetite (plus clinopyroxene and plagioclase) fractionation using Re vs. Mn/Yb. The variation of Pt abundances with SiO2 for both these suites contrasts with other nominally chalcophile trace elements in showing rapid early depletion from the most Mg-rich basalt through to more SiO2-rich compositions, with no maximum at 60 wt% SiO2. Silver on the other hand is essentially constant at 0.02 to 0.05ppm throughout the basalt to dacite compositional range. Several other compositional features of the Pacmanus and Valu Fa suites are also noteworthy. For example while S has an abundance maximum at 60wt% SiO2 (similar to Fe and Re), and then diminishes in concentration in more silica-rich magmas, Se is initially depleted at 60wt% SiO2 but then increases in abundance as SiO2 increases further. We suggest these features result from sulfide saturation coincidentally with (or shortly after) magnetite saturation. While Se is initially partitioned into the immiscible sulfide phase, moderate incompatibility remains between the overall fractionating assemblage of plagioclase-pyroxene- magnetite and minor sulfide. Pt on the other hand is likely being removed as a native element/alloy. Sun, W, Arculus, RJ, Kamenetsky, VS and Binns, RA, 2004, Release of gold-bearing fluids in convergent margin magmas prompted by magnetite crystallisation. Nature, v. 431, p. 975-978.

Mavrogenes, J. A.; Jenner, F. E.; Arculus, R. J.

2008-12-01

160

Formation of magnetite nanoparticles at low temperature: from superparamagnetic to stable single domain particles.  

PubMed

The room temperature co-precipitation of ferrous and ferric iron under alkaline conditions typically yields superparamagnetic magnetite nanoparticles below a size of 20 nm. We show that at pH ?=? 9 this method can be tuned to grow larger particles with single stable domain magnetic (> 20-30 nm) or even multi-domain behavior (> 80 nm). The crystal growth kinetics resembles surprisingly observations of magnetite crystal formation in magnetotactic bacteria. The physicochemical parameters required for mineralization in these organisms are unknown, therefore this study provides insight into which conditions could possibly prevail in the biomineralizing vesicle compartments (magnetosomes) of these bacteria. PMID:23520462

Baumgartner, Jens; Bertinetti, Luca; Widdrat, Marc; Hirt, Ann M; Faivre, Damien

2013-03-08

161

Immobilization of albumin on magnetite nanoparticles  

Microsoft Academic Search

The magnetite (Fe3O4) nanoparticles were prepared by the co-precipitation of ferrous and ferric salts with NH4OH, and then modified with 3-aminopropyltriethoxysilane (APTES) by silanization reaction and subsequent reaction with glutaraldehyde (GA) to obtain functional groups on their surface. The influence of different terminated groups on protein binding was studied with bare and modified magnetite nanoparticles. Amine terminated magnetite nanoparticles were

Esra Maltas; Mustafa Ozmen; Hasibe Cingilli Vural; Salih Yildiz; Mustafa Ersoz

2011-01-01

162

Synthesis and characterization of Cu2+ substituted magnetite  

NASA Astrophysics Data System (ADS)

Samples of magnetite, both pure and doped with divalent copper, Fe3 - xCuxO4, with x = 0, 0.05, 0.10 and 0.20 atm.%, were synthesized hydrothermally. The samples were characterized by Atomic Absorption Spectroscopy, Mössbauer Spectroscopy, X-ray diffraction, Scanning Electron Microscopy and SQUID magnetometry. The analyses made by the above techniques showed that as the Cu2+ concentration increases, a simultaneous reduction in the magnetic and structural parameters takes place, namely: magnetic hyperfine interactions at octahedral sites, particle size and lattice constant. Degradation in the particles morphology as well as a distribution of their size were also observed. Our study points two important effects of Cu2+ in magnetite, the first one is its incorporation within the structure, replacing Fe2+ ions and decreasing both the magnetic hyperfine interactions at octahedral sites and the bulk magnetization, the second one is the contraction of the crystalline lattice of magnetite, because incorporation of Cu2+ within the structure, generation of vacancies or both simultaneous effects.

Morales, A. L.; Velásquez, A. A.; Urquijo, J. P.; Baggio, E.

2011-11-01

163

Deposition of anatase titania onto carbon encapsulated magnetite nanoparticles.  

PubMed

A novel magnetically separable photocatalyst (titania-coated carbon encapsulated magnetite: TCCEF) was prepared. The prepared composite photocatalyst was characterized with an x-ray diffractometer (XRD), a transmission electron microscope (TEM), a Fourier transform infrared spectrometer (FT-IR) and a vibrating sample magnetometer (VSM). The photocatalytic activity of the samples was determined by degrading model contaminated water, a phenol aqueous solution. The results were compared with single-phase titania (pure titania and Degussa P25) and Fe(3)O(4)/TiO(2), and enhanced photocatalytic activity was obtained. It is suggested that the enhanced photocatalytic activity is ascribed to two major factors. First, the encapsulation of magnetite into the carbon layer may inhibit the direct electrical contact of titania and magnetite, hence preventing the photodissolution of the iron oxide phase. Second, the enhanced hydroxyl groups on TCCEF may inhibit the recombination of electron-hole pairs. On the other hand, the magnetic photocatalyst can be easily recovered from a slurry with the application of an external magnetic field. PMID:21832624

Ao, Yanhui; Xu, Jingjing; Fu, Degang; Ba, Long; Yuan, Chunwei

2008-08-21

164

Fabrication of magnetite nanorods by ultrasound irradiation  

SciTech Connect

Magnetite nanorods have been prepared by the sonication of aqueous iron(II)acetate in the presence of {beta}-cyclodextrin. The properties of the magnetite nanorods were characterized by x-ray diffraction, Mossbauer spectroscopy, transmission electron microscopy, thermogravimetric analysis, and magnetization measurements. The as-prepared magnetite nanorods are ferromagnetic and their magnetization at room temperature is {similar_to}78emu/g. The particle sizes measured from transmission electron micrographs are about 48/14 nm (L/W). A mechanism for the sonochemical formation of magnetite nanorods is discussed. {copyright} 2001 American Institute of Physics.

Kumar, R. Vijaya; Koltypin, Yu; Xu, X. N.; Yeshurun, Y.; Gedanken, A.; Felner, I.

2001-06-01

165

Sonochemical coating of magnetite nanoparticles with silica.  

PubMed

Magnetite nanoparticles were coated with silica through the hydrolysis and condensation of tetraethyl orthosilicate (TEOS) under ultrasonic irradiation. The ultrasonic irradiation was used to prevent the agglomeration of the magnetite particles and accelerate the hydrolysis and condensation of TEOS. TEM, DLS, XRF, VSM, TG and sedimentation test were used to characterize the silica-coated magnetite particles. The dispersibility of silica-coated magnetite particles in aqueous solution was improved significantly and the agglomerate particle size was decreased to 110 nm. It was found that the agglomerate particle size of silica-coated magnetite particles was mainly decided by the coating temperature and the pH value in the silica-coating process. The weight ratio of silica in silica-coated magnetite particles was mainly decided by the pH value in the silica-coating process. The dispersibility of silica-coated magnetite particles was mainly decided by the agglomerate particle size of the suspension. The oxidation of magnetite particles in air was limited through the coated silica. The magnetism of silica-coated magnetite particles decreased slightly after silica-coating. PMID:19502093

Dang, Feng; Enomoto, Naoya; Hojo, Junichi; Enpuku, Keiji

2009-05-21

166

Rock magnetic criteria for the detection of biogenic magnetite  

NASA Astrophysics Data System (ADS)

We report results on the magnetic properties of magnetites produced by magnetotactic and dissimilatory iron-reducing bacteria. Magnetotactic bacterial (MTB) strains MS1, MV1 and MV2 and dissimilatory iron-reducing bacterium strain GS-15, grown in pure cultures, were used in this study. Our results suggest that a combination of room temperature coercivity analysis and low temperature remanence measurements provides a characteristic magnetic signature for intact chains of single domain (SD) particles of magnetite from MTBs. The most useful magnetic property measurements include: (1) acquisition and demagnetization of isothermal remanent magnetization (IRM) using static, pulse and alternating fields; (2) acquisition of anhysteretic remanent magnetization (ARM); and (3) thermal dependence of low temperature (20 K) saturation IRM after cooling in zero field (ZFC) of in a 2.5 T field (FC) from 300 K. However, potentially the most diagnostic magnetic parameter for magnetosome chain identification in bulk sediment samples is related to the difference between low temperature zero-field and field cooled SIRMs on warming through the Verwey transition (T approximately = 100 K). Intact chains of unoxidized magnetite magnetosomes have ratios of delta(sub FC)/delta(sub ZFC) greater than 2, where the parameter delta is a measure of the amount of remanence lost by warming through the Verwey transition. Disruption of the chain structure or conversion of the magnetosomes to maghemite reduces the delta(sub FC)/delta(sub ZFC) ratio to around 1, similar to values observed for some inorganic magnetite, maghemite, greigite and GS-15 particles. Numerical simulations of delta(sub FC)/delta(sub ZFC) ratios for simple binary mixtures of magnetosome chains and inorganic magnetic fractions suggest that the delta(sub FC)/delta(sub ZFC) parameter can be a sensitive indicator of biogenic magnetite in the form of intact chains of magnetite magnetosomes and can be a useful magnetic technique for identifying them in whole-sediment samples. The strength of our approach lies in the comparative ease and rapidity with which magnetic measurements can be made, compared to techniques such as electron microscopy.

Moskowitz, Bruce M.; Frankel, Richard B.; Bazylinski, Dennis A.

1993-12-01

167

Understanding the biological stabilization of ferrihydrite and its transformation to magnetite  

NASA Astrophysics Data System (ADS)

The biosynthesis of magnetite in the chiton tooth begins with the formation of ferrihydrite, which is transformed into magnetite. This strategy, which employs crystallization of a precursor into the desired polymorph, is generalized across a range of organisms. However, the specific biological factors that control the transformation are not known. Our results employing atom probe tomography of chiton tooth magnetite revealed the presence of acidic proteins binding sodium and magnesium ions associated with chitin nanofibers. Using a model system we are investigating the influence of organic and inorganic additives on the stabilization of ferrihydrite and the transformation to magnetite. I will discuss the influence of a range of organic and inorganic additives on the formation and transformation of ferrihydrite within the gel. We have found that acidic polymers stabilize ferrihydrite and prevent the formation of the crystalline polymorphs. Transformation of the ferrihydrite to magnetite upon addition of ferrous iron is observed as early as 30 minutes. Taken together, the contribution of these factors to magnetite biomineralization in the presence of an organic matrix will help to elucidate biological mechanisms for nucleation, stabilization, and transformation of iron oxides.

Gordon, Lyle; Joester, Derk

2013-03-01

168

Vortex magnetic structure in framboidal magnetite reveals existence of water droplets in an ancient asteroid.  

PubMed

The majority of water has vanished from modern meteorites, yet there remain signatures of water on ancient asteroids. How and when water disappeared from the asteroids is important, because the final fluid-concentrated chemical species played critical roles in the early evolution of organics and in the final minerals in meteorites. Here we show evidence of vestigial traces of water based on a nanometre-scale palaeomagnetic method, applying electron holography to the framboids in the Tagish Lake meteorite. The framboids are colloidal crystals composed of three-dimensionally ordered magnetite nanoparticles and therefore are only able to form against the repulsive force induced by the surface charge of the magnetite as a water droplet parches in microgravity. We demonstrate that the magnetites have a flux closure vortex structure, a unique magnetic configuration in nature that permits the formation of colloidal crystals just before exhaustion of water from a local system within a hydrous asteroid. PMID:24149376

Kimura, Yuki; Sato, Takeshi; Nakamura, Norihiro; Nozawa, Jun; Nakamura, Tomoki; Tsukamoto, Katsuo; Yamamoto, Kazuo

2013-10-22

169

Polyhedral magnetite nanocrystals with multiple facets: facile synthesis, structural modelling, magnetic properties and application for high capacity lithium storage.  

PubMed

Polyhedral magnetite nanocrystals with multiple facets were synthesised by a low temperature hydrothermal method. Atomistic simulation and calculations on surface attachment energy successfully predicted the polyhedral structure of magnetite nanocrystals with multiple facets. X-ray diffraction, field emission scanning electron microscopy, and high resolution transmission microscopy confirmed the crystal structure of magnetite, which is consistent with the theoretical modelling. The magnetic property measurements show the superspin glass state of the polyhedral nanocrystals, which could originate from the nanometer size of individual single crystals. When applied as an anode material in lithium ion cells, magnetite nanocrystals demonstrated an outstanding electrochemical performance with a high lithium storage capacity, a satisfactory cyclability, and an excellent high rate capacity. PMID:22147554

Su, Dawei; Horvat, Josip; Munroe, Paul; Ahn, Hyojun; Ranjbartoreh, Ali R; Wang, Guoxiu

2011-12-06

170

Microbial Production of Ultrafine-Grained Magnetite.  

National Technical Information Service (NTIS)

A method of producing magnetite is disclosed which comprises culturing a microorganism designated GS-15 in the presence of organic matter and a ferric iron compound. Unlike prior art production of magnetite using magnetotactic bacteria, GS-15 is able to p...

D. R. Lovley

1988-01-01

171

Bacterial aerobic synthesis of nanocrystalline magnetite.  

PubMed

The synthesis of iron oxide nanoparticles of the predominantly magnetite phase by the reaction of aqueous iron complexes with the bacterium, Actinobacter spp., is described. This reaction occurs at room temperature and under aerobic conditions, resulting in the formation of superparamagnetic magnetite. PMID:15984833

Bharde, Atul; Wani, Aijaz; Shouche, Yogesh; Joy, Pattayil A; Prasad, Bhagavatula L V; Sastry, Murali

2005-07-01

172

Metal-doped magnetite thin films.  

PubMed

This paper investigates magnetite (Fe3O4) thin film containing a small amount of a metal element. The films are prepared by rf sputtering with a composite target of ceramic iron oxide with metal chips. Low-temperature magnetization of magnetite containing 5.3%Ge reveals that the film contains some magnetically weak coupling grains. The metal element Mg reduces both hematite (alpha-Fe2O3) and magnetite, resulting in single-phase wüstite (Fe1-xO). In contrast, adding Ge selectively reduces hematite, while magnetite remains unreactive. According to the free energy of reaction, the element Ge is able to reduce hematite only, whereas the element Mg is capable of reducing both hematite and magnetite. This property is in good agreement with the experiment results. PMID:22905582

Abe, Seishi; Ping, De Hai; Nakamura, Shintaro; Ohnuma, Masato; Ohnuma, Shigehiro

2012-06-01

173

Experimental study of magnetic interactions between individual biogenic magnetite nanocrystals  

NASA Astrophysics Data System (ADS)

We present an electron holographic study of magnetostatic interactions between magnetite nanocrystals from wild-type and mutant magnetotactic bacteria of the Magnetospirillum gryphiswaldense (M. gryph) strain. The results are discussed with reference to their implications for the superparamagnetic limit, magnetic moments of arrays of magnetic nanocrystals, and the threshold of magnetotaxis. The size and spacing of magnetite nanocrystals in M. gryph was carefully adjusted through control of iron provision and growth time. Examination of these cultured cells provided data on the magnetic properties ranging from isolated superparamagnetic crystals to fully assembled magnetosome chains. A magnetic state phase diagram was created showing empirically how the superparamagnetic threshold is influenced by the effect of inter-particle interactions within the chains. This experimental data was compared with analytical models of superparamagnetism which account for size, spacing and crystal shape. Further to this, we also studied two-dimensional arrays of magnetite particles produced by bacteria whose mamJ protein had been removed through genetic modification. In unmodified bacteria this protein is responsible for producing magnetosomes in linear arrangements. The mutant bacteria's non-linear assemblages had much lower magnetic moments per unit volume than bacteria with intact chains, and also displayed more complex magnetic microstructures such as vortex states. These complex magnetic states were metastable, as the states were sensitive to subtle changes in experimental conditions. The magnetic moments of all the samples examined, both wild-type and mutant cells, were compared to that necessary for alignment in the geomagnetic field, showing the threshold at which the crystal sizes, arrangement and numbers led to effective magnetotaxis.

Simpson, E. T.; Kasama, T.; Posfai, M.; Faivre, D.; Scheffel, A.; Schuler, D.; Buseck, P. R.; Harrison, R. J.; Dunin-Borkowski, R. E.

2006-12-01

174

Magnetite Morphology and Life on Mars  

NSDL National Science Digital Library

This National Academy of Sciences scholarly paper discusses the strongest line of evidence for past life on Mars based on NASA's David McKay's original claims of finding nanofossils on the ALH84001 meteorite. This study concentrates on magnetite morphology, comparing morphologies of bacterial and abiotically produced magnetite. The findings are inconclusive, but do not strongly support evidence for biotically produced magnetite. The article features color images of the crystallography. While the abstract is free, this article may require a subscription to access the full text.

2009-06-24

175

Extraterrestrial magnetite studied by Mössbauer spectroscopy  

NASA Astrophysics Data System (ADS)

The meteorite Orgueil is a carbonaceous chondrite of type CI. Carbonaceous chondrites contain Fe(III), Fe(II) and in some cases metallic iron, indicating that they are in a state far from thermodynamic equilibrium. In Orgueil about 40% of the iron is present in magnetite (Fe3O4). In this work a sample of magnetite grains extracted from Orgueil has been studied by Mössbauer spectroscopy. It has been found that the magnetic phase contains about 11% of maghemite and that the remaining magnetite has a vacancy concentration smaller than 0.006, corresponding to the formula Fe2.994O4.

Madsen, M. B.; Mørup, S.; Knudsen, J. M.

1989-06-01

176

Novel magnetite-producing magnetotactic bacteria belonging to the Gammaproteobacteria.  

PubMed

Two novel magnetotactic bacteria (MTB) were isolated from sediment and water collected from the Badwater Basin, Death Valley National Park and southeastern shore of the Salton Sea, respectively, and were designated as strains BW-2 and SS-5, respectively. Both organisms are rod-shaped, biomineralize magnetite, and are motile by means of flagella. The strains grow chemolithoautotrophically oxidizing thiosulfate and sulfide microaerobically as electron donors, with thiosulfate oxidized stoichiometrically to sulfate. They appear to utilize the Calvin-Benson-Bassham cycle for autotrophy based on ribulose-1,5-bisphosphate carboxylase/oxygenase (RubisCO) activity and the presence of partial sequences of RubisCO genes. Strains BW-2 and SS-5 biomineralize chains of octahedral magnetite crystals, although the crystals of SS-5 are elongated. Based on 16S rRNA gene sequences, both strains are phylogenetically affiliated with the Gammaproteobacteria class. Strain SS-5 belongs to the order Chromatiales; the cultured bacterium with the highest 16S rRNA gene sequence identity to SS-5 is Thiohalocapsa marina (93.0%). Strain BW-2 clearly belongs to the Thiotrichales; interestingly, the organism with the highest 16S rRNA gene sequence identity to this strain is Thiohalospira alkaliphila (90.2%), which belongs to the Chromatiales. Each strain represents a new genus. This is the first report of magnetite-producing MTB phylogenetically associated with the Gammaproteobacteria. This finding is important in that it significantly expands the phylogenetic diversity of the MTB. Physiology of these strains is similar to other MTB and continues to demonstrate their potential in nitrogen, iron, carbon and sulfur cycling in natural environments. PMID:21776027

Lefèvre, Christopher T; Viloria, Nathan; Schmidt, Marian L; Pósfai, Mihály; Frankel, Richard B; Bazylinski, Dennis A

2011-07-21

177

Novel magnetite-producing magnetotactic bacteria belonging to the Gammaproteobacteria  

PubMed Central

Two novel magnetotactic bacteria (MTB) were isolated from sediment and water collected from the Badwater Basin, Death Valley National Park and southeastern shore of the Salton Sea, respectively, and were designated as strains BW-2 and SS-5, respectively. Both organisms are rod-shaped, biomineralize magnetite, and are motile by means of flagella. The strains grow chemolithoautotrophically oxidizing thiosulfate and sulfide microaerobically as electron donors, with thiosulfate oxidized stoichiometrically to sulfate. They appear to utilize the Calvin–Benson–Bassham cycle for autotrophy based on ribulose-1,5-bisphosphate carboxylase/oxygenase (RubisCO) activity and the presence of partial sequences of RubisCO genes. Strains BW-2 and SS-5 biomineralize chains of octahedral magnetite crystals, although the crystals of SS-5 are elongated. Based on 16S rRNA gene sequences, both strains are phylogenetically affiliated with the Gammaproteobacteria class. Strain SS-5 belongs to the order Chromatiales; the cultured bacterium with the highest 16S rRNA gene sequence identity to SS-5 is Thiohalocapsa marina (93.0%). Strain BW-2 clearly belongs to the Thiotrichales; interestingly, the organism with the highest 16S rRNA gene sequence identity to this strain is Thiohalospira alkaliphila (90.2%), which belongs to the Chromatiales. Each strain represents a new genus. This is the first report of magnetite-producing MTB phylogenetically associated with the Gammaproteobacteria. This finding is important in that it significantly expands the phylogenetic diversity of the MTB. Physiology of these strains is similar to other MTB and continues to demonstrate their potential in nitrogen, iron, carbon and sulfur cycling in natural environments.

Lefevre, Christopher T; Viloria, Nathan; Schmidt, Marian L; Posfai, Mihaly; Frankel, Richard B; Bazylinski, Dennis A

2012-01-01

178

The verwey phase of magnetite — a long-running mystery in magnetism  

NASA Astrophysics Data System (ADS)

Magnetite (Fe3O4) is the original magnetic material and the parent of ferrite magnets, with modern applications ranging from spintronics to MRI contrast agents. At ambient temperatures magnetite has a cubic spinel-type crystal structure, but it undergoes a complex structural distortion and becomes electrically insulating below the 125 K Verwey transition. The electronic ground state of the Verwey phase has been unclear for over 70 years as the low temperature structure was unknown, but the full superstructure was recently determined by high energy microcrystal x-ray diffraction. An analysis of 168 frozen phonon modes in the acentric (and hence multiferroic) low temperature magnetite structure is presented here. Differences between the amplitudes of centric and acentric branches of, X and W modes all contribute to the significant off-center atomic distortions in the low temperature structure.

Senn, Mark S.; Wright, Jon P.; Attfield, J. Paul

2013-05-01

179

Phase evolution of magnetite nanocrystals on oxide supports via template-free bismuth ferrite precursor approach  

NASA Astrophysics Data System (ADS)

This report investigates the phase evolution pathway of magnetite nanocrystal synthesis on oxide-supported substrates. A template-free phase separation approach, which exploits the thermodynamic instability of ternary perovskite BiFeO3 and inherent volatility of bismuth oxide in low oxygen pressure and high temperature is presented. The formation of an intermediate hematite nanocrystal phase is found as a key step that controls the eventual size and morphology of the magnetite nanocrystals. X-ray absorption spectra measurements and X-ray magnetic circular dichroism confirm that the spectral fingerprints of the magnetite nanocrystals match with that of bulk crystals. Magnetic measurements show that magnetic anisotropy is directly attributed to the nanocrystal morphology.

Cheung, Jeffrey; Bogle, Kashinath; Cheng, Xuan; Sullaphen, Jivika; Kuo, Chang-Yang; Chen, Ying-Jiun; Lin, Hong-Ji; Chen, Chien-Te; Yang, Jan-Chi; Chu, Ying-Hao; Valanoor, Nagarajan

2012-11-01

180

Smart hollow microspheres of chondroitin sulfate conjugates and magnetite nanoparticles for magnetic vector.  

PubMed

Smart hollow microspheres composed of vinyled-chondroitin sulfate conjugates (CS?) and magnetite nanoparticles were obtained by the intermediate of a multiple emulsion in absence of a surfactant, attributable to stabilizing properties of the CS. It was formed an oil-water multiple emulsion in which the CS played a role as an anionic stabilizer for magnetite nanoparticles via complexation. Iron oxides were bonded to the microspheres by the formation of a complex of Fe(3+) ions on the crystalline phase with oxygen atoms at the carboxyl groups without their magnetic properties being affected. The average crystal size of embedded magnetite nanoparticles was approximately 16.5nm, indicative of a good dispersion in microspheres. Furthermore, the introduction of iron oxides resulted in microspheres with a higher diameter and a narrower particle size distribution. PMID:20832809

Guilherme, Marcos R; Reis, Adriano V; Alves, Bruno R V; Kunita, Marcos H; Rubira, Adley F; Tambourgi, Elias B

2010-08-21

181

SEM/STEM observations of magnetite in carbonates of eastern North America: Evidence for chemical remagnettzation during the Alleghenian Orogeny  

NASA Astrophysics Data System (ADS)

Early to middle Paleozoic carbonates of eastern North America have been pervasively remagnetized. In order to determine the process of remagnetization, scanning and scanning transmission electron microscopy have been used to characterize magnetite in thin sections and in concentrated separates. Samples included Ordovician Knox carbonates from east Tennessee, Ordovician Trenton limestone and Devonian Onondaga and Helderberg limestones from New York, and Ordovician Trenton carbonates from Michigan. Inclusions of authigenic minerals within magnetite grains, lack of cations other than iron, and a variety of textural relations all imply that the magnetite is authigenic. These data are consistent with estimates that paleotemperatures never exceeded values that would reset magnetic directions. The remagnetization is thus a chemical remanent magnetization (CRM) rather than viscous remanent magnetization (VRM). As the timing of remagnetization corresponds to the Alleghenian orogeny, the observed relations imply stress-induced crystallization of magnetite that was mediated by fluids, consistent with but not requiring fluid flow on a regional basis.

Suk, Dongwoo; Van der Voo, Rob; Peacor, Donald R.

182

Oriented Inclusions of Single Domain Magnetite in Clinopyroxene: Source of Stable Remanent Magnetization in Gabbros of the Early Cretaceous Messum Complex, Namibia  

NASA Astrophysics Data System (ADS)

Oriented magnetite inclusions with two suborthogonal elongation directions in the (010) plane of clinopyroxene (CPX) are the dominant source of highly stable remanent magnetization in gabbros of the Messum Complex, Namibia. The inclusions are subparallel to the X ("X" inclusions) and Z ("Z" inclusions) crystallographic axes in the host CPX crystals. Such inclusions apparently form by exsolution/oxidation upon slow cooling through the range 600-500 oC, and consist of relatively pure magnetite. We term these features "Judd Structures", in homage to the first published account by Judd [1885]. AF and thermal demagnetization, and IRM acquisition experiments on individual grains of CPX from the Messum gabbros are dominated by single-domain magnetite behavior, consistent with observed size and extreme shape anisotropy (up to ca. 0.2 x 125 microns) of the oxide crystals comprising Judd structures. AF demagnetization of oriented crystals reveal minor differences in coercivity between the "X" and "Z" inclusions. VGP's from these rocks (dated by 40Ar/39Ar at 132 Ma) are consistent with poles from the petrogenetically related and well-dated Etendeka volcanics, and coincide with a cusp in the African APWP, thus constraining the age of magnetization at ca. 132 Ma. These observations are consistent with a high-T subsolidus exsolution/oxidation origin, and moreover indicate that despite extreme shape anisotropy at the single pyroxene scale, an apparently random distribution of CPX lattice orientations imposes no bias on bulk-rock magnetization. Of the four sites sampled, two have Normal polarity characteristic magnetization (ChRM) and one has Reverse ChRM. The fourth site has both Normal and Reverse ChRM even in individual bulk (ca. 10 cm3) specimens. Demagnetization of many individual CPX grains from this site reveals dual polarity, restricted to the "X" inclusions. We suggest that remanence acquisition upon cooling of this gabbro spanned a geomagnetic polarity reversal. Improved knowledge of intensive variables (i.e., temperature, cooling rate, reaction stoichiometry) governing Judd structures' paragenesis is needed. Nonetheless, our ongoing work indicates the potential for application to problems requiring exceptionally stable paleomagnetic records, such as paleointensity determinations. Analysis at the single (host) crystal scale is both feasible and desirable for many such applications.

Renne, P. R.; Scott, G. R.; Glen, J. M.; Feinberg, J.

2002-05-01

183

The detection of bacterial magnetite in recent sediments of Lake Chiemsee (southern Germany)  

NASA Astrophysics Data System (ADS)

The sediments of Lake Chiemsee, located in the Alpine foreland in Southern Germany, host a variety of magnetotactic bacteria (MTB), which contain intracellular crystals of magnetite arranged in linear chains. To detect bacterial magnetite in the carbonate-dominated surface sediments and further quantify its contribution to the magnetic signal of the sediments, we conducted detailed rock magnetic measurements as well as complimentary non-magnetic analyses (electron microscopy, powder X-ray diffraction, and sediment pore-water analysis). Our results demonstrate that biogenic single-domain magnetite (characterized by bullet- and truncated hexagonal prismatic shapes) is the dominant ferrimagnetic component in the topmost few centimetres of the sediment. The changes of magnetic properties with depth are due to the occurrence of live MTB and the downward increasing dissolution of biogenic magnetite. Moreover, the ratios of remanence loss on warming through the Verwey transition after field cooling and zero-field cooling of saturation isothermal remanence ( ?FC/ ?ZFC) were determined as 1.47 and 1.25 for freeze-dried and air-dried sediment samples containing MTB, respectively. These low ratios suggest that the bacterial magnetite chains were disrupted to a large extent and/or that the bacterial magnetosomes might have undergone partial low-temperature oxidation. It is proposed that although rock magnetic measurements are suitable for quantifying the contribution of fine-grained particles to the overall magnetic signal of sediments, complementary non-magnetic methods are essential to unambiguously identify its bacterial origin.

Pan, Yongxin; Petersen, Nikolai; Davila, Alfonso F.; Zhang, Liming; Winklhofer, Michael; Liu, Qingsong; Hanzlik, Marianne; Zhu, Rixiang

2005-03-01

184

Complex fringes around magnetite porphyroclasts: Growth and deformation history  

NASA Astrophysics Data System (ADS)

Deformed strain fringes in iron formation rocks show complex quartz fiber patterns that grew alongside magnetite porphyroclasts embedded in a matrix of quartz and iron oxides during coaxial to non-coaxial deformation. These rocks have been deformed by a combination of processes involving microfracturing, pressure solution and dislocation glide at temperatures of approximately 300 °C. Detailed microstructural observation and crystallographic analysis show that quartz fiber growth is not controlled by the crystal faces. Quartz c-axis orientations of fibrous quartz indicate that these grains initially grew with their c-axes parallel to the fiber length. Late solid-state deformation of crystallized fibers comprised dislocation glide along basal plane and subsequent recrystallization. This produces aggregates of recrystallized grains consisting of equant to elongated quartz grains with straight and orthogonal grain boundaries.

Lagoeiro, Leonardo; Barbosa, Paola Ferreira; Fueten, Frank

2011-09-01

185

Synthesis, characterization and applications of magnetite nanoparticles  

NASA Astrophysics Data System (ADS)

In the past few years, the synthesis of magnetic nanoparticles has received considerable attention due to their potential use in clinical applications. Since the properties of these nanoparticles depend strongly on their size, shape and crystallinity, there is a need for a general method to produce these particles with a controlled size, shape and crystal type. Of the many magnetic materials (Co, Ni, and Fe), the magnetite (Fe3O 4) is least toxic and hence most promising for applications in medical diagnostics. Microemulsion-based synthesis utilizes the local aqueous environment within a reverse micelle as a nano-scale reactor and allows synthesizing nanoparticles with a hydrophilic surface for subsequent functionalization. By controlling the water-to-surfactant ratio, the type of surfactants, and the ionic strength of the aqueous core, one can control the size and shape of the resulting particles. We developed such a system that allows the multi-step synthesis of surface-functionalized, magnetic nanoparticles in a one-pot synthesis reaction. By altering the system chemistry, we were further able to produce either spheres or cylinders of controlled dimension in the size range of 5 nm to 30 nm. Using standard bio-conjugation techniques, we successfully immobilized an enzyme onto the nanoparticles. We also developed a theoretical model for the separation and fractionation of nanoparticles based on their size and magnetic properties. Using the multiphysics and finite element modeling capabilities of FEMLAB(TM), we solved the coupled system of PDEs describing the interaction of magnetic particles within a magnetic field for either static (cylindrical beaker) or convective flow (capillary) conditions. A net retention time as high as 310 s is achieved for 200 nm particles at field strength of 1250 kA/m. The model allows the design of a magnetic, field-flow fractionation (MFFF) system to separate nanoparticles by size.

Kanmukhla, Vikram Kumar

186

Crystals  

NSDL National Science Digital Library

In this earth science/math/art activity, learners use simple ingredients to grow crystals and examine the repeating geometric shapes and patterns. Learners compare the growth of crystals from four types of crystal-starters (table salt, Borax, sand, and Epsom salt) to see which starter grows the most crystals in 14 days. Learners report their results online and find out what other learners discovered. Afterward, learners can use the crystals they grew to create works of art.

Science, Lawrence H.

2009-01-01

187

Electrically-driven phase transition in magnetite nanostructures  

NASA Astrophysics Data System (ADS)

In 1939 Verwey found that bulk magnetite undergoes a first-order transition at TV 120 K from a high temperature conducting phase to a low-temperature insulating phase. High-T conduction occurs via the fluctuating valences of the octahedral iron atoms, and the transition comes from the interplay of charge ordering and structural distortion upon cooling. The Verwey transition mechanism and charge ordering remain highly controversial. We will present data on magnetite nanocrystals and single-crystal thin films demonstrating an electrically driven phase transition below the Verwey temperature. We find sharp conductance switching that is hysteretic in source-drain voltage, and show that this transition is not due to local heating, but instead is due to the breakdown of the correlated insulating state when driven out of equilibrium by electrical bias. Scaling of switching voltage with electrode spacing in thin film samples shows that the switching is driven by a critical temperature-dependent electric field. Further studies of this newly observed transition and its low-temperature conducting phase should shed light on how charge ordering and vibrational degrees of freedom determine the ground state of this important compound.

Natelson, D.; Lee, S.; Fursina, A.; Mayo, J. T.; Yavuz, C. T.; Colvin, V. L.; Sofin, R. M. S.; Shvets, I. V.

2008-03-01

188

Neutron diffuse scattering in magnetite due to molecular polarons  

NASA Astrophysics Data System (ADS)

A detailed neutron diffuse scattering study has been carried out in order to verify a model which describes the property of valence fluctuations in magnetite above TV. This model assumes the existence of a complex which is composed of two excess electrons and a local displacement mode of oxygens within the fcc primitive cell. The complex is called a molecular polaron. It is assumed that at sufficiently high temperatures there is a random distribution of molecular polarons, which are fluctuating independently by making hopping motions through the crystal or by dissociating into smaller polarons. The lifetime of each molecular polaron is assumed to be long enough to induce an instantaneous strain field around it. Based on this model, the neutron diffuse scattering cross section due to randomly distributed dressed molecular polarons has been calculated. A precise measurement of the quasielastic scattering of neutrons has been carried out at 150 K. The observed results definitely show the characteristics which are predicted by the model calculation and, thus, give evidence for the existence of the proposed molecular polarons. From this standpoint, the Verwey transition of magnetite may be viewed as the cooperative ordering process of dressed molecular polarons. Possible extensions of the model to describe the ordering and the dynamical behavior of the molecular polarons are discussed.

Yamada, Y.; Wakabayashi, N.; Nicklow, R. M.

1980-05-01

189

Mineral magnetic properties of artificial samples systematically mixed from haematite and magnetite  

NASA Astrophysics Data System (ADS)

Detailed rock magnetic investigations were carried out on a set of samples with defined ratios of haematite and magnetite. The measured parameters provide a reference for interpreting common rock magnetic parameters in investigations of sediments. The contribution of haematite to the magnetic fraction must exceed 95 wt-% of the magnetic fraction when mixed with magnetite in order to visibly influence grain size and coercitivity indicative magnetic parameters. Coercivity of remanence (BCR) and coercive force (BC) do not change in the same way with increasing haematite content, which results in a peak BCR/BC value at around 99.5 wt-% haematite. Variations in haematite content can be ignored when interpreting most rock magnetic parameters, especially grain size indicative parameters for samples where haematite contents range from 0 to 98 wt-%. The S-ratio is still the most sensitive parameter for estimating the relative amount of haematite in magnetite/haematite mixtures. A combination of S-ratio, the saturation isothermal remanent magnetization divided by the low field magnetic susceptibility (SIRM/?LF) and BCR is the most effective way to identify haematite in natural samples. Our results agree with literature data and fill the gap between results obtained either from pure magnetite or haematite with comparable grain sizes.

Frank, Ute; Nowaczyk, Norbert R.

2008-11-01

190

Thermal, Dielectric Studies on Pure and Amino Acid L-Glutamic Acid, L-Histidine L-Valine Doped Potassium Dihydrogen Phosphate Single Crystals  

NASA Astrophysics Data System (ADS)

Amino acids (L-Glutamic acid, L-Histidine, L-Valine) doped potassium dihydrogen phosphate crystals were grown by the solution growth technique. Slow cooling as well as slow evaporation methods were employed to grow these crystals. The concentration of dopants in the mother solution was varied from 0.1 mole % to 10 mole %. The solubility data for all dopant concentrations were determined. The variation in pH and the corresponding habit modification of the grown crystals were characterized with UV - VIS, FT-IR and SHG trace elements, and dielectric studies reveal slight distortion of lattice parameter for the heavily doped KDP crystals. TGA-DTA studies reveal good thermal stability. The dopants increase the hardness value of the material, which also depends on the concentration of the dopants. Amino acids doping improved the NLO properties. The detailed results on the spectral parameters, habit modifications and constant values will be presented.

Kumaresan, P.; Babu, S. Moorthy; Anbarasan, P. M.

191

YBa 2 Cu 3 O 7-? single crystals revisited: Scanning probe data on very pure samples grown in BaZrO 3 crucibles  

Microsoft Academic Search

2  Cu3O7-? (YBCO) single crystals grown in BaZrO3 crucibles by scanning and friction force microscopy (SFM, FFM) as well as by scanning tunneling microscopy (STM) and angle\\u000a resolved X-ray photo-electron spectroscopy (ARXPS). By STM and SFM, clean stepped terraces are observed on as-grown crystals.\\u000a Friction contrast, however, implies the presence of different materials, presumably traces of flux. After oxidation of the

U. Hubler; P. Jess; H. P. Lang; A. Erb; E. Walker; M. Regier; D. Schild; J. Halbritter; H.-J. Güntherodt

1998-01-01

192

The nature of chemical bond of magnetite and consequences  

Microsoft Academic Search

Summary Types of chemical bonding in magnetite are discussed. Magnetite spinel lattice is characterized by tetrahedral covalent bonds and octahedral electrovalent bonds. The consequences for oxidation processes are studied in connection with hitherto existing experimental and theoretical results.

F. Frölich; H. Stiller

1963-01-01

193

Actinide Removal from Aqueous Solution with Activated Magnetite.  

National Technical Information Service (NTIS)

An actinide aqueous waste treatment process using activated magnetite has been developed at Rocky Flats. The use and effectiveness of various magnetites in lowering actinide concentrations in aqueous solution are described. Experiments indicate that magne...

R. L. Kochen R. L. Thomas

1987-01-01

194

Actinide removal from aqueous solution with activated magnetite  

SciTech Connect

An actinide aqueous waste treatment process using activated magnetite has been developed at Rocky Flats. The use and effectiveness of various magnetites in lowering actinide concentrations in aqueous solution are described. Experiments indicate that magnetite particle size and pretreatment (activation of the magnetite surface with hydroxyl ions greatly influence the effective use of magnetite as an actinide adsorbent. With respect to actinide removal, Ba(OH)/sub 2/-activated magnetite was more effective over a broader pH range than was NaOH-activated magnetite. About 50% less Ba(OH)/sub 2/-activated magnetite was required to lower plutonium concentration from 10/sup -4/ to 10/sup -8/ g/l. 7 refs., 8 tabs.

Kochen, R.L.; Thomas, R.L. (ed.)

1987-08-10

195

Immobilization of peroxidase onto magnetite modified polyaniline.  

PubMed

The present study describes the immobilization of horseradish peroxidase (HRP) on magnetite-modified polyaniline (PANImG) activated with glutaraldehyde. After the optimization of the methodology, the immobilization of HRP on PANImG produced the same yield (25%) obtained for PANIG with an efficiency of 100% (active protein). The optimum pH for immobilization was displaced by the effect of the partition of protons produced in the microenvironment by the magnetite. The tests of repeated use have shown that PANImG-HRP can be used for 13 cycles with maintenance of 50% of the initial activity. PMID:22489198

Barbosa, Eduardo Fernandes; Molina, Fernando Javier; Lopes, Flavio Marques; García-Ruíz, Pedro Antonio; Caramori, Samantha Salomão; Fernandes, Kátia Flávia

2012-03-12

196

Rock magnetism linked to human brain magnetite  

NASA Astrophysics Data System (ADS)

Magnetite has a long and distinguished career as one of the most important minerals in geophysics, as it is responsible for most of the remanent magnetization in marine sediments and the oceanic crust. It may come as a surprise to discover that it also ranks as the third or fourth most diverse mineral product formed biochemically by living organisms, and forms naturally in a variety of human tissues [Kirschvink et al., 1992].Magnetite was discovered in teeth of the Polyplacophora mollusks over 30 years ago, in magnetotactic bacteria nearly 20 years ago, in honey bees and homing pigeons nearly 15 years ago, but only recently in human tissue.

Kirschvink, Joseph L.

197

Thermal analysis of two types of dextran-coated magnetite  

Microsoft Academic Search

The thermal stability of two kinds of dextran-coated magnetite (dextran with molecular weight of 40,000 (Dex40) and 70,000\\u000a (Dex70)), obtained by dextran adsorption onto the magnetite surface is investigated in comparison with free dextran in air\\u000a and argon atmosphere. The thermal behavior of the two free dextran types and corresponding coated magnetites is similar, but\\u000a atmosphere dependent. The magnetite catalyzes

Oana Carp; Luminita Patron; Daniela C. Culita; Petru Budrugeac; Marcel Feder; Lucian Diamandescu

2010-01-01

198

Determination of the magnetite-water equilibrium oxygen isotope fractionation factor at 350°C: A comparison of ion microprobe and laser fluorination techniques  

Microsoft Academic Search

A Cameca 4f ion microprobe has been used in conjunction with laser and conventional analytical techniques to measure the oxygen isotope fractionation between magnetite and water at 350°C. A set of experiments in which large (10–200 ?m) magnetite crystals were grown from fine grained (0.2–2 ?m) hematite starting material using four different isotopically labelled waters yields a value of 1000

Steven M. Fortier; David R. Cole; David J. Wesolowski; Lee R. Riciputi; Bruce A. Paterson; John W. Valley; Juske Horita

1995-01-01

199

Determination of the magnetite-water equilibrium oxygen isotope fractionation factor at 350°C: A comparison of ion microprobe and laser fluorination techniques  

Microsoft Academic Search

A Cameca 4f ion microprobe has been used in conjunction with laser and conventional analytical techniques to measure the oxygen isotope fractionation between magnetite and water at 350°C. A set of experiments in which large (10-200 m) magnetite crystals were grown from fine grained (0.2-2 m) hematite starting material using four different isotopically labelled waters yields a value of 1000

Steven M. Fortier; David R. Cole; David J. Wesolowski; Lee R. Riciputi; Bruce A. Paterson; John W. Valley; Juske Horita

1995-01-01

200

Biogenic Magnetite Formation through Anaerobic Biooxidation of Fe(II)  

PubMed Central

The presence of isotopically light carbonates in association with fine-grained magnetite is considered to be primarily due to the reduction of Fe(III) by Fe(III)-reducing bacteria in the environment. Here, we report on magnetite formation by biooxidation of Fe(II) coupled to denitrification. This metabolism offers an alternative environmental source of biogenic magnetite.

Chaudhuri, Swades K.; Lack, Joseph G.; Coates, John D.

2001-01-01

201

Magnetite whiskers and platelets in the ALH84001 Martian meteorite: evidence of vapor phase growth.  

PubMed

Nanometer-sized magnetite crystals associated with carbonates in fracture zones within Martian meteorite ALH84001 have been examined using analytical transmission electron microscopy. Some of the crystals exhibit distinctive morphologies: filamentary rods and ribbon, and platelets. The rods and ribbons are elongated along the crystallographic [100] and [111] directions. Some of the rods contain microstructural defects indicating that they grew by spiral growth about screw dislocations. Platelets are flattened along the [100] and [110] directions. These unique morphologies and microstructures constrain the growth conditions of magnetite. The whiskers and platelets most likely formed in the temperature range 500-800 degrees C by direct condensation from a vapor or precipitation from a supercritical fluid, and their properties are inconsistent with a biogenic origin. PMID:11541129

Bradley, J P; Harvey, R P; McSween, H Y

1996-01-01

202

Surface spin disorder effects in magnetite and poly(thiophene)-coated magnetite nanoparticles  

NASA Astrophysics Data System (ADS)

Chemically synthesized magnetite and poly(thiophene)-coated magnetite nanoparticles and the correlations between their magnetic, structural, and microstructural properties are investigated. A typical superparamagnetic behavior was observed for faceted nanoparticle agglomerates of magnetite and nanocomposite. In nanocomposites, the polymer layer causes a sharp decrease in the spin disorder, which reduces the anisotropy constant significantly. This happens because the intimate contact between magnetite and poly(thiophene) leads to charge transfer from the polymer to the core via polaron interactions, causing a structural rearrangement of the nanoparticles and suppression of the spin movement at the surface. As this dynamic interaction can tune the core dimensions, the magnetic properties of nanocomposites can be tuned by controlling the core size through polymer coating. These characteristics can be exploited to design high-performance magnetically tunable nanodevices and applied in many areas of biomedicine (DNA separation, drug targeting, immune detection, and magnetic nanoparticle hyperthermia in cancer treatment).

Cótica, Luiz F.; Santos, Ivair A.; Girotto, Emerson M.; Ferri, Elidia V.; Coelho, Adelino A.

2010-09-01

203

Formation of magnetite-enriched zones in and offshore of a mesotidal estuarine lagoon: An environmental magnetic study of Tauranga Harbour and Bay of Plenty, New Zealand  

NASA Astrophysics Data System (ADS)

Magnetic iron minerals are widespread and indicative sediment constituents in estuarine, coastal and shelf systems. We combine environmental magnetic, sedimentological and numerical methods to identify magnetite-enriched placer-like zones in a complex coastal system and delineate their formation mechanisms. Magnetic susceptibility and remanence measurements on 245 surficial sediment samples collected in and around Tauranga Harbour, the largest barrier-enclosed tidal estuary of New Zealand, reveal several discrete enrichment zones controlled by local hydrodynamic conditions. Active magnetite enrichment takes place in tidal channels, which feed into two coast-parallel nearshore magnetite-enriched belts centered at water depths of 6-10 m and 10-20 m. A close correlation between magnetite content and magnetic grain size was found, where higher susceptibility values are associated within coarser magnetic crystal sizes. Two key mechanisms for magnetite enrichment are identified. First, tide-induced residual currents primarily enable magnetite enrichment within the estuarine channel network. A coast-parallel, fine sand magnetite enrichment belt in water depths of less than 10 m along the barrier island has a strong decrease in magnetite content away from the southern tidal inlet and is apparently related to active coast-parallel transport combined with mobilizing surf zone processes. A second, less pronounced, but more uniform magnetite enrichment belt at 10-20 m water depth is composed of non-mobile, medium-coarse-grained relict sands, which have been reworked during post-glacial sea level transgression. We demonstrate the potential of magnetic methods to reveal and differentiate coastal magnetite enrichment patterns and investigate their formative mechanisms.

Badesab, Firoz; von Dobeneck, Tilo; Bryan, Karin R.; Müller, Hendrik; Briggs, Roger M.; Frederichs, Thomas; Kwoll, Eva

2012-06-01

204

Synthesis of water dispersible magnetite nanoparticles in the presence of hydrophilic polymers  

Microsoft Academic Search

Water dispersible magnetite nanoparticles (Fe3O4) were synthesized by thermal decomposition of iron (III) acetylacetonate (Fe(acac)3) in the presence of carboxylic acid-terminated poly(ethylene glycol) (mPEG acid), poly(vinyl alcohol) and NH2-containing polyether. Crystal structure was investigated using X-ray diffractometry (XRD) and it showed that the as-synthesized\\u000a particles had high crystallinity with distinct lattices. Particle size of the nanoparticles was investigated using XRD

Thapanapong Theppaleak; Gamolwan Tumcharern; Uthai Wichai; Metha Rutnakornpituk

2009-01-01

205

Frequency and field dependent susceptibility of magnetite at low temperature  

NASA Astrophysics Data System (ADS)

We report the temperature dependence of in-phase and quadrature susceptibilities, k' and k?, between 20 K and 300 K for a stoichiometric natural single crystal of magnetite. Measurements were made for amplitudes of the AC driving field ranging from H = 30 A/m to 2 kA/m and frequencies ranging from f = 40 Hz to 4 kHz. In cubic magnetite above the Verwey transition, Tv = 120 K, k' is limited by self-demagnetization and does not vary greatly with T, H or . As the crystal cools through Tv and transforms to monoclinic structure, k' decreases by about a factor 2, with a further more gradual decrease of 10-20% in cooling from 40 to 20 K. Saturation remanence also drops sharply at Tv but shows no further change in cooling below 40 K. Thus it appears that domain walls remain pinned throughout the 20-40 K range but small segments undergo reversible oscillations in an AC field, the amplitude of oscillation decreasing steadily with cooling below 40 K. In this same range, k? reaches a peak, while the temperature at which k' decreases most rapidly changes with frequency. Both observations indicate that domain wall oscillations lag appreciably behind the driving field at very low temperature. Both k' and k? increase markedly with increasing AC field amplitude below Tv. The field dependence is particularly strong below 40 K. Analysis of the k' (f) data between 20 and 40 K based on an Arrhenius thermal activation equation gives a pre-exponential frequency factor fo ? 2.5 × 108 s-1 and an activation energy ?E = 0.035 eV. The ?E is appropriate for electron hopping but fo suggests an indirect mechanism for wall mobility related to changes in electron ordering within walls.

Özdemir, Ö.; Dunlop, D. J.; Jackson, M.

2009-01-01

206

Charge ordering and ferroelectricity in magnetite  

NASA Astrophysics Data System (ADS)

Magnetite Fe3O4 is one of the most fascinating material in solid state physics. Besides being the first magnetic material known to the mankind, it is also the first example of an insulator-metal transition in transition metal oxides -- the famous Verwey transition [1]. One usually connects this transition with the charge ordering of Fe^2+ and Fe^3+. However the detailed pattern of CO in Fe3O4 is still a matter of debate. Another aspect, which is not so widely known and which did not yet receive sufficient attention, is that below TV, besides being completely spin polarised, magnetite apparently is also ferroelectric (FE) [2]. Thus it seems that magnetite, besides being the first magnetic material and the first transition metal oxide with an insulator-metal transition, is also the first multiferroic material. Using the idea of a coexistence of site-centred and bond-centred charge ordering [3], I suggest a novel type of ordering in magnetite which explains the observed FE in Fe3O4 and which agrees with the structural data. [1] Verwey E.J.W., Nature 144, 327 (1939) [2] Rado G.T. and Ferrari J.M., Phys.Rev.B 12, 5166 (1975); Kato K. and Iida S., J.Phys.Soc.Japan 50, 2844 (1981) [3] Efremov D.V., van den Brink J. and Khomskii D.I., Nature Mater. 3, 853 (2004)

Khomskii, Daniel

2007-03-01

207

Electron-optical characterization of bacterial magnetite  

Microsoft Academic Search

Magnetic grains isolated from magnetococcoid bacterial cells were studied by means of transmission electron microscopy, electron diffraction and electron microprobe analysis. Observed in situ the magnetic grains are each surrounded by an organic membrane and are usually found in a random array although ``chains'' are also seen. Electron diffraction confirms the magnetite mineralogy and provides additional evidence in favor of

K. M. Towe; T. T. Moench

1981-01-01

208

Preparation of magnetite dextran microspheres by ultrasonication  

NASA Astrophysics Data System (ADS)

An improved method of preparing magnetite dextran microspheres by ultrasonication is proposed. Several parameters were evaluated and the characteristics of the microspheres investigated by scanning electron microscope (SEM), atomic force microscope (AFM), particle size analyzer and magnetometer. The results show that the initial Fe/dextran ratio is the most effective parameter for both the size and the magnetic properties.

Xia, Zefeng; Wang, Guobin; Tao, Kaixiong; Li, Jianxing

2005-05-01

209

Magnetite biomineralization induced by Shewanella oneidensis  

Microsoft Academic Search

Shewanella oneidensis is a dissimilatory iron reducing bacterium capable of inducing the extracellular precipitation of magnetite. This precipitation requires a combination of passive and active mechanisms. Precipitation occurs as a consequence of active production of Fe2+(aq) when bacteria utilize ferrihydrite as a terminal electron acceptor, and the pH rise probably due to the bacterial metabolism of amino acids. As for

Teresa Perez-Gonzalez; Concepcion Jimenez-Lopez; Andrew L. Neal; Fernando Rull-Perez; Alejandro Rodriguez-Navarro; Antonia Fernandez-Vivas; Enrique Iañez-Pareja

2010-01-01

210

Magnetite biomineralization and ancient life on Mars  

Microsoft Academic Search

Certain chemical and mineral features of the Martian meteorite ALH84001 were reported in 1996 to be probable evidence of ancient life on Mars. In spite of new observations and interpretations, the question of ancient life on Mars remains unresolved. Putative biogenic, nanometer magnetite has now become a leading focus in the debate.

Richard B Frankel; Peter R Buseck

2000-01-01

211

Experimental Shock Decomposition of Siderite to Magnetite.  

National Technical Information Service (NTIS)

The debate about fossil life on Mars includes the origin of magnetites of specific sizes and habits in the siderite-rich portions of the carbonate spheres in ALH 84001. Specifically were able to demonstrate that inorganic synthesis of these compositionall...

M. S. Bell M. E. Zolensky

2005-01-01

212

Complete sets of elastic constants and photoelastic coefficients of pure and MgO-doped lithium niobate crystals at room temperature  

SciTech Connect

This paper presents the results of ultrasonic measurements of LiNbO{sub 3} and LiNbO{sub 3}:MgO crystals. The tensors of piezoelectric coefficients, elastic stiffness constants, and elastic compliances are determined for both crystals at room temperature. Combining these data with the results of piezo-optical measurements, a complete set of photoelastic tensor coefficients is also calculated. Doping of LiNbO{sub 3} crystals by MgO does not lead to a considerable modification of their elastic and photoelastic properties. However, LiNbO{sub 3}:MgO is characterized by a considerably higher resistance with respect to powerful light radiation, making it promising for future application in acousto-optic devices that deal with superpowerful laser radiation. Presented here are the complete tensor sets of elastic constants and photoelastic coefficients of LiNbO{sub 3} and LiNbO{sub 3}:MgO crystals that may be used for a geometry optimization of acousto-optical interaction providing the best diffraction efficiency of acousto-optical cells made of these materials.

Andrushchak, A. S.; Laba, H. P.; Yurkevych, O. V. [Lviv Polytechnic National University, 12 Stepana Bandera Str., 79013 Lviv (Ukraine); Mytsyk, B. G. [Karpenko Physico-Mechanical Institute, 5 Naukova Str., 79601 Lviv (Ukraine); Solskii, I. M. [Scientific Research Company 'Carat', 202 Stryjska Str., 79031 Lviv (Ukraine); Kityk, A. V. [Department of Electrical Engineering, Institute for Computer Science, Czestochowa University of Technology, Al. Armii Krajowej 17, PL-42200 Czestochowa (Poland); Sahraoui, B. [Laboratoire POMA, FRE CNRS 2988, Universite d'Angers, 2 Boulevard Lavoisier, 49045 Angers Cedex (France)

2009-10-01

213

Synthesis and kinetic shape and size evolution of magnetite nanoparticles  

SciTech Connect

Eleven nanometers of magnetite nanoparticles were synthesized by using 6 nm magnetite nanoparticles as seeds and Fe(acac){sub 3} as precursor at high temperature. Growth kinetics of magnetite nanoparticles was studied during the progress of reaction. Magnetite nanoparticles with different shapes including near-sphere, tetrahedral, truncated tetrahedral and cubic were observed at different reaction time. Transmission electron microscopic results show that the shape and size distributions are time- and temperature-dependent. Hydrodynamic diameter results give the kinetic size distribution changes of magnetite nanoparticles during the reaction, which suggest that this synthesis underwent a 'growth-controlled nucleation'.

Zhang Ling [Institute for Micro and Nano Science and Technology, Shanghai Jiaotong University, 200030 Shanghai (China); He Rong [Institute for Micro and Nano Science and Technology, Shanghai Jiaotong University, 200030 Shanghai (China); Gu Hongchen [Institute for Micro and Nano Science and Technology, Shanghai Jiaotong University, 200030 Shanghai (China)]. E-mail: hcgu@sjtu.edu.cn

2006-02-02

214

Ferromagnetic resonance and low-temperature magnetic tests for biogenic magnetite  

NASA Astrophysics Data System (ADS)

Magnetite is both a common inorganic rock-forming mineral and a biogenic product formed by a diversity of organisms. Magnetotactic bacteria produce intracellular magnetites of high purity and crystallinity (magnetosomes) arranged in linear chains of crystals. Magnetosomes and their fossils (magnetofossils) have been identified using transmission electron microscopy (TEM) in sediments dating back to ˜510-570 Ma, and possibly in 4 Ga carbonates in Martian meteorite ALH84001. We present the results from two rock magnetic analyses—the low-temperature Moskowitz test and ferromagnetic resonance (FMR)—applied to dozens of samples of magnetite and other materials. The magnetites in these samples are of diverse composition, size, shape, and origin: biologically induced (extracellular), biologically controlled (magnetosomes and chiton teeth), magnetofossil, synthetic, and natural inorganic. We confirm that the Moskowitz test is a distinctive indicator for magnetotactic bacteria and provide the first direct experimental evidence that this is accomplished via sensitivity to the magnetosome chain structure. We also demonstrate that the FMR spectra of four different strains of magnetotactic bacteria and a magnetofossil-bearing carbonate have a form distinct from all other samples measured in this study. We suggest that this signature also results from the magnetosomes' unique arrangement in chains. Because FMR can rapidly identify samples with large fractions of intact, isolated magnetosome chains, it could be a powerful tool for identifying magnetofossils in sediments.

Weiss, Benjamin P.; Sam Kim, Soon; Kirschvink, Joseph L.; Kopp, Robert E.; Sankaran, Mohan; Kobayashi, Atsuko; Komeili, Arash

2004-07-01

215

Lanthanide-Substituted Magnetite Nanoparticles Using a New Mixed Precursor Method by Thermoanaerobacter ethanolicus  

NASA Astrophysics Data System (ADS)

A metal reducing bacterium, Thermoanaerobacter ethanolicus successfully converted the precursor of L (lanthanide)-mixed akaganeite (LxFe1-xOOH) phase to L-substituted magnetite (LyFe3-yO4) while avoiding the potentially toxic effects of soluble L-ions. Antibiotic elements, lanthanide (Nd, Gd, Tb, Ho, and Er)-substituted magnetites were produced by microbial fermentation using LxFe1-xOOH, where x was up to 0.02 which is equivalent to 0.72 mM. Combining lanthanides into the akaganeite precursor phase mitigated some of the toxicity when compared to the traditional method by using pure akaganeite and the dissolved L-salt form. This new technique showed that an upper limit of L-concentrations between 0.02 and 0.1 mM might suppress bacterial activity. At the equivalent L-cation mole fraction, the traditional method increased the concentration of soluble toxic L ions in the final media. The precursor method enabled production of microbially synthesized L- substituted magnetite with an L-concentration 36-fold greater than could be obtained when the lanthanides were added as soluble salts. These results were confirmed by protein assay. The increase of L-concentration in the magnetite evidently manipulates its physical properties such as decreasing Curie temperature and decreasing saturation magnetism of L-substituted magnetite. This mixed precursor method can therefore be used to extend the application for nanofermentation and other bacterial synthesis fields where there is a need for economically low-energy consumable microbial production of nanoscale materials that should involve toxic or inhibitory elements to bacterial growth.

Moon, J.; Roh, Y.; Yeary, L. W.; Lauf, R. J.; Phelps, T. J.

2006-12-01

216

Structural purity of magnetite nanoparticles in magnetotactic bacteria.  

PubMed

Magnetosome biomineralization and chain formation in magnetotactic bacteria are two processes that are highly controlled at the cellular level in order to form cellular magnetic dipoles. However, even if the magnetosome chains are well characterized, controversial results about the microstructure of magnetosomes were obtained and its possible influence in the formation of the magnetic dipole is to be specified. For the first time, the microstructure of intracellular magnetosomes was investigated using high-resolution synchrotron X-ray diffraction. Significant differences in the lattice parameter were found between intracellular magnetosomes from cultured magnetotactic bacteria and isolated ones. Through comparison with abiotic control materials of similar size, we show that this difference can be associated with different oxidation states and that the biogenic nanomagnetite is stoichiometric, i.e. structurally pure whereas isolated magnetosomes are slightly oxidized. The hierarchical structuring of the magnetosome chain thus starts with the formation of structurally pure magnetite nanoparticles that in turn might influence the magnetic property of the magnetosome chains. PMID:21247944

Fischer, Anna; Schmitz, Manuel; Aichmayer, Barbara; Fratzl, Peter; Faivre, Damien

2011-01-19

217

Structural purity of magnetite nanoparticles in magnetotactic bacteria  

PubMed Central

Magnetosome biomineralization and chain formation in magnetotactic bacteria are two processes that are highly controlled at the cellular level in order to form cellular magnetic dipoles. However, even if the magnetosome chains are well characterized, controversial results about the microstructure of magnetosomes were obtained and its possible influence in the formation of the magnetic dipole is to be specified. For the first time, the microstructure of intracellular magnetosomes was investigated using high-resolution synchrotron X-ray diffraction. Significant differences in the lattice parameter were found between intracellular magnetosomes from cultured magnetotactic bacteria and isolated ones. Through comparison with abiotic control materials of similar size, we show that this difference can be associated with different oxidation states and that the biogenic nanomagnetite is stoichiometric, i.e. structurally pure whereas isolated magnetosomes are slightly oxidized. The hierarchical structuring of the magnetosome chain thus starts with the formation of structurally pure magnetite nanoparticles that in turn might influence the magnetic property of the magnetosome chains.

Fischer, Anna; Schmitz, Manuel; Aichmayer, Barbara; Fratzl, Peter; Faivre, Damien

2011-01-01

218

Nuclear quadrupole alignment of 176Lum and 177Lu in a lutetium single crystal at low temperatures and systematics of electric field gradients in pure hexagonal transition metals  

Microsoft Academic Search

The quadrupole frequencies for 176Lum and 177Lu nuclei in a Lu single crystal have been determined by nuclear orientation at temperatures down to 6 mK as -128(16) MHz and +294(37) MHz, respectively. From the observed gamma anisotropies several gamma-ray multipole mixing ratios could be derived. With the known ground-state quadrupole moment of Q=3.39(2) b for 177Lu the electric field gradient

H. Ernst; E. Hagn; E. Zech; G. Eska

1979-01-01

219

Occurrence of gigantic biogenic magnetite during the Paleocene-Eocene Thermal Maximum  

NASA Astrophysics Data System (ADS)

The Paleocene-Eocene Thermal Maximum (PETM) is one of the most severe climatic events of the Cenozoic Era. A massive injection of light carbon into the oceans and atmosphere over a few thousand of years triggered drastic perturbation of Earth's climate resulting in abrupt global warming of ~5-9oC [Sluijs et al., 2007] that persisted for ~180,000 years. This episode is marked by the diversification and radiation of terrestrial plants and mammals while in the marine realm numerous deep-sea benthic foraminifera species disappeared and new forms evolved. Sediments deposited during the PETM are clay-rich and contain distinct evidence of these climatic changes. Kopp et al., (2007) and Lippert & Zachos (2007) report an extraordinary magnetofossil ‘Lagerstätte' in lowermost Eocene kaolinite-rich clay sediments deposited at subtropical paleolatitude in the Atlantic Coastal Plain of New Jersey, USA. Magnetofossils are magnetic particles produced most abundantly by magnetotactic bacteria. Kopp et al. (2007) and Lippert & Zachos (2007) used ferromagnetic resonance (FMR) spectroscopy, other rock magnetic methods, and transmission electron microscopy (TEM) of magnetic separates to characterize sediments from boreholes at Ancora (ODP Leg 174AX) and Wilson Lake, NJ, respectively. These sediments contain abundant ~40- to 300-nm cuboidal, elongate-prismatic and bullet-shaped magnetofossils, sometimes arranged in short chains, resembling crystals in living magnetotactic bacteria. Despite the scarcity of intact magnetofossil chains, the asymmetry ratios of the FMR spectra reflects a profusion of elongate single domain (SD) crystals and/or chains. Here we address both conundrums by reporting the discovery from these same sediments of exceptionally large and novel biogenic magnetite crystals unlike any previously reported from living organisms or from sediments. Aside from abundant bacterial magnetofossils, electron microscopy reveals novel spearhead-like and spindle-like magnetite crystals up to 4 ?m long (eight times larger than magnetite produced by magnetotactic bacteria) and elongated hexaoctahedra up to 1.4 ?m long. Similar to magnetite produced by magnetotactic bacteria, these single-crystal particles exhibit chemical composition and lattice perfection consistent with a biogenic origin. The oxygen isotopic composition of indiviual particles supports a low temperature aquatic origin. Electron holography indicates single-domain magnetization despite the large crystal size. In a few cases, we observed apparently intact, tip-outward spherical assemblages of spearhead-like particles that possibly represent the preserved original biological arrangement of these crystals in a hitherto unknown magnetite producing organism. The discovery of these exceptionally large biogenic magnetite crystals that possibly represent the remains of a new microorganism that appeared and disappeared with the PETM sheds some light upon the ecological response to biogeochemical changes that occurred during this warming event. The abundance of fossil magnetotactic bacteria on the Atlantic Coastal Plain during the PETM could be explained by enhanced production, enhanced preservation, or both. The presence of novel magnetofossils, however, argues that changes in growth conditions are a major part of the explanation. Considering that other bacterial magnetofossils are present (although less abundant) and well-preserved in sediments below and above the PETM clay, as well as in a sand lens within the PETM clay [Kopp et al., 2007], suggests that the new magnetofossils are unlikely to be a preservation artefact. We conclude, therefore, that the development of a thick suboxic zone with high iron bioavailability - a product of dramatic changes in weathering and sedimentation patterns driven by severe global warming - resulted in diversification of magnetite-forming organisms, likely including eukaryotes. In this study we extended the search for these new magnetofossils [Schumann et al. 2008] to other PETM locations of the Atlantic margin and to a possible modern

Schumann, D.; Raub, T. D.; Kopp, R. E.; Guerquin-Kern, J. L.; Wu, T. D.; Rouiller, I.; Smirnov, A. V.; Sears, S. K.; Lücken, U.; Tikoo, S. M.; Hesse, R.; Kirschvink, J. L.; Vali, H.

2009-04-01

220

The magnetosome membrane protein, MmsF, is a major regulator of magnetite biomineralization in Magnetospirillum magneticum AMB-1.  

PubMed

Magnetotactic bacteria (MTB) use magnetosomes, membrane-bound crystals of magnetite or greigite, for navigation along geomagnetic fields. In Magnetospirillum magneticum sp. AMB-1, and other MTB, a magnetosome gene island (MAI) is essential for every step of magnetosome formation. An 8-gene region of the MAI encodes several factors implicated in control of crystal size and morphology in previous genetic and proteomic studies. We show that these factors play a minor role in magnetite biomineralization in vivo. In contrast, MmsF, a previously uncharacterized magnetosome membrane protein encoded within the same region plays a dominant role in defining crystal size and morphology and is sufficient for restoring magnetite synthesis in the absence of the other major biomineralization candidates. In addition, we show that the 18 genes of the mamAB gene cluster of the MAI are sufficient for the formation of an immature magnetosome organelle. Addition of MmsF to these 18 genes leads to a significant enhancement of magnetite biomineralization and an increase in the cellular magnetic response. These results define a new biomineralization protein and lay down the foundation for the design of autonomous gene cassettes for the transfer of the magnetic phenotype in other bacteria. PMID:22716969

Murat, Dorothée; Falahati, Veesta; Bertinetti, Luca; Csencsits, Roseann; Körnig, André; Downing, Kenneth; Faivre, Damien; Komeili, Arash

2012-07-10

221

The magnetosome membrane protein, MmsF, is a major regulator of magnetite biomineralization in Magnetospirillum magneticum AMB-1  

PubMed Central

Summary Magnetotactic bacteria (MTB) use magnetosomes, membrane bound crystals of magnetite or greigite, for navigation along geomagnetic fields. In Magnetospirillum magneticum sp. AMB-1, and other MTB, a magnetosome gene island (MAI) is essential for every step of magnetosome formation. An 8-gene region of the MAI encodes several factors implicated in control of crystal size and morphology in previous genetic and proteomic studies. We show that these factors play a minor role in magnetite biomineralization in vivo. In contrast, MmsF, a previously uncharacterized magnetosome membrane protein encoded within the same region plays a dominant role in defining crystal size and morphology and is sufficient for restoring magnetite synthesis in the absence of the other major biomineralization candidates. In addition, we show that the 18 genes of the mamAB gene cluster of the MAI are sufficient for the formation of an immature magnetosome organelle. Addition of MmsF to these 18 genes leads to a significant enhancement of magnetite biomineralization and an increase in the cellular magnetic response. These results define a new biomineralization protein and lay down the foundation for the design of autonomous gene cassettes for the transfer of the magnetic phenotype in other bacteria.

Murat, Dorothee; Falahati, Veesta; Bertinetti, Luca; Csencsits, Roseann; Kornig, Andre; Downing, Kenneth; Faivre, Damien; Komeili, Arash

2013-01-01

222

The HtrA/DegP family protease MamE is a bifunctional protein with roles in magnetosome protein localization and magnetite biomineralization.  

PubMed

Magnetotactic bacteria contain nanometre-sized, membrane-bound organelles, called magnetosomes, which are tasked with the biomineralization of small crystals of the iron oxide magnetite allowing the organism to use geomagnetic field lines for navigation. A key player in this process is the HtrA/DegP family protease MamE. In its absence, Magnetospirillum magneticum str AMB-1 is able to form magnetosome membranes but not magnetite crystals, a defect previously linked to the mislocalization of magnetosome proteins. In this work we use a directed genetic approach to find that MamE, and another predicted magnetosome-associated protease, MamO, likely function as proteases in vivo. However, as opposed to the complete loss of mamE where no biomineralization is observed, the protease-deficient variant of this protein still supports the initiation and formation of small, 20 nm-sized crystals of magnetite, too small to hold a permanent magnetic dipole moment. This analysis also reveals that MamE is a bifunctional protein with a protease-independent role in magnetosome protein localization and a protease-dependent role in maturation of small magnetite crystals. Together, these results imply the existence of a previously unrecognized 'checkpoint' in biomineralization where MamE moderates the completion of magnetite formation and thus committal to magneto-aerotaxis as the organism's dominant mode of navigating the environment. PMID:21414040

Quinlan, Anna; Murat, Dorothée; Vali, Hojatollah; Komeili, Arash

2011-03-30

223

The HtrA/DegP family protease MamE is a bifunctional protein with roles in magnetosome protein localization and magnetite biomineralization  

PubMed Central

Summary Magnetotactic bacteria contain nanometer-sized, membrane-bound organelles, called magnetosomes, which are tasked with the biomineralization of small crystals of the iron oxide magnetite allowing the organism to use geomagnetic field lines for navigation. A key player in this process is the HtrA/DegP family protease MamE. In its absence, Magnetospirillum magneticum str AMB-1 is able to form magnetosome membranes but not magnetite crystals, a defect previously linked to the mislocalization of magnetosome proteins. In this work we use a directed genetic approach to find that MamE, and another predicted magnetosome-associated protease, MamO, likely function as proteases in vivo. However, as opposed to the complete loss of mamE where no biomineralization is observed, the protease-deficient variant of this protein still supports the initiation and formation of small, 20 nm-sized crystals of magnetite, too small to hold a permanent magnetic dipole moment. This analysis also reveals that MamE is a bifunctional protein with a protease-independent role in magnetosome protein localization and a protease-dependent role in maturation of small magnetite crystals. Together these results imply the existence of a previously unrecognized “checkpoint” in biomineralization where MamE moderates the completion of magnetite formation and thus committal to magneto-aerotaxis as the organism’s dominant mode of navigating the environment.

Quinlan, Anna; Murat, Dorothee; Vali, Hojatollah; Komeili, Arash

2011-01-01

224

Extracellular biosynthesis of magnetite using fungi.  

PubMed

The development of synthetic processes for oxide nanomaterials is an issue of considerable topical interest. While a number of chemical methods are available and are extensively used, the collaborations are often energy intensive and employ toxic chemicals. On the other hand, the synthesis of inorganic materials by biological systems is characterized by processes that occur at close to ambient temperatures and pressures, and at neutral pH (examples include magnetotactic bacteria, diatoms, and S-layer bacteria). Here we show that nanoparticulate magnetite may be produced at room temperature extracellularly by challenging the fungi, Fusarium oxysporum and Verticillium sp., with mixtures of ferric and ferrous salts. Extracellular hydrolysis of the anionic iron complexes by cationic proteins secreted by the fungi results in the room-temperature synthesis of crystalline magnetite particles that exhibit a signature of a ferrimagnetic transition with a negligible amount of spontaneous magnetization at low temperature. PMID:17193569

Bharde, Atul; Rautaray, Debabrata; Bansal, Vipul; Ahmad, Absar; Sarkar, Indranil; Yusuf, Seikh Mohammad; Sanyal, Milan; Sastry, Murali

2006-01-01

225

Quantifying magnetite magnetofossil contributions to sedimentary magnetizations  

NASA Astrophysics Data System (ADS)

Under suitable conditions, magnetofossils (the inorganic remains of magnetotactic bacteria) can contribute to the natural remanent magnetization (NRM) of sediments. In recent years, magnetofossils have been shown to be preserved commonly in marine sediments, which makes it essential to quantify their importance in palaeomagnetic recording. In this study, we examine a deep-sea sediment core from offshore of northwestern Western Australia. The magnetic mineral assemblage is dominated by continental detritus and magnetite magnetofossils. By separating magnetofossil and detrital components based on their different demagnetization characteristics, it is possible to quantify their respective contributions to the sedimentary NRM throughout the Brunhes chron. In the studied core, the contribution of magnetofossils to the NRM is controlled by large-scale climate changes, with their relative importance increasing during glacial periods when detrital inputs were low. Our results demonstrate that magnetite magnetofossils can dominate sedimentary NRMs in settings where they are preserved in significant abundances.

Heslop, David; Roberts, Andrew P.; Chang, Liao; Davies, Maureen; Abrajevitch, Alexandra; De Deckker, Patrick

2013-11-01

226

EBSD analysis of electroplated magnetite thin films  

NASA Astrophysics Data System (ADS)

By means of electron backscatter diffraction (EBSD), we analyse the crystallographic orientation of electroplated magnetite thin films on Si/copper substrates. Varying the voltage during the electroplating procedure, the resulting surface properties are differing considerably. While a high voltage produces larger but individual grains on the surface, the surfaces become smoother on decreasing voltage. Good quality Kikuchi patterns could be obtained from all samples; even on individual grains, where the surface and the edges could be measured. The spatial resolution of the EBSD measurement could be increased to about 10 nm; thus enabling a detailed analysis of single magnetite grains. The thin film samples are polycrystalline and do not exhibit a preferred orientation. EBSD reveals that the grain size changes depending on the processing conditions, while the detected misorientation angles stay similar.

Koblischka-Veneva, A.; Koblischka, M. R.; Teng, C. L.; Ryan, M. P.; Hartmann, U.; Mücklich, F.

2010-05-01

227

Pressure-induced magnetoresistivity reversal in magnetite  

NASA Astrophysics Data System (ADS)

The magnetoresistivity (MR) of nano-powdered magnetite has been measured under pressures up to 19.0 GPa and magnetic fields up to 15 kG. An unexpected quasi-linear positive MR below 6.0 GPa and an MR transition from positive to negative around 6.0 GPa have been found. The abnormal positive MR below 6.0 GPa originates from the confinement effect caused by nano-scale heterogeneity at the contact surface between Mo and Fe3O4 sample and the high negative spin polarization of magnetite. The MR transition at about 6.0 GPa comes from a phase transition from half-metal to metal induced by pressure.

Su, Ningning; Han, Yonghao; Ma, Yanzhang; Liu, Hongwu; Ma, Boheng; Gao, Chunxiao

2011-11-01

228

Interaction of fibrinogen with magnetite nanoparticles  

Microsoft Academic Search

The interaction between fibrinogen and magnetite nanoparticles in solution has been studied by the methods of spin labeling,\\u000a ferromagnetic resonance, dynamic and Rayleigh light scattering. It is shown that protein molecules adsorb on the surface of\\u000a nanoparticles to form multilayer protein covers. The number of molecules adsorbed on one nanoparticle amounts to ?65 and the\\u000a thickness of the adsorption layer

A. V. Bychkova; O. N. Sorokina; A. L. Kovarski; A. B. Shapiro; V. B. Leonova; M. A. Rozenfel’d

2010-01-01

229

Strong adsorption of chlorotetracycline on magnetite nanoparticles  

Microsoft Academic Search

In this work, environmentally friendly magnetite nanoparticles (Fe3O4 MNPs) were used to adsorb chlorotetracycline (CTC) from aqueous media. Fe3O4 MNPs exhibit ultrahigh adsorption ability to this widely used antibiotic. The adsorption behavior of CTC on Fe3O4 MNPs fitted the pseudo-second-order kinetics model, and the adsorption equilibrium was achieved within 10h. The maximum Langmuir adsorption capacity of CTC on Fe3O4 (476mgg?1)

Di Zhang; Hongyun Niu; Xiaole Zhang; Zhaofu Meng; Yaqi Cai

2011-01-01

230

An experimental and theoretical determination of oxygen isotope fractionation in the system magnetite-H 2O from 300 to 800°C 1 1 Associate editor: E. M. Ripley  

Microsoft Academic Search

Oxygen isotope fractionations have been determined between magnetite and water from 300 to 800°C and pressures between 10 and 215MPa. We selected three reaction pathways to investigate fractionation: (a) reaction of fine-grained magnetite with dilute aqueous NaCl solutions; (b) reduction of fine-grained hematite through reaction with dilute acetic acid; and (c) oxidation of fine iron power in either pure water

David R. Cole; Juske Horita; Veniamin B. Polyakov; John W. Valley; Michael J. Spicuzza; Dorothy W. Coffey

2004-01-01

231

Mechanisms in the First Stage of Oxidation of Magnetites  

Microsoft Academic Search

THE oxidation of magnetite is a two-stage process. The final product of the second stage of oxidation is always alpha-Fe2O3 formed from residual magnetite, and\\/or from the product of the first stage of oxidation. During the first stage, several reactions are possible, according to the mode of formation and the characteristics of the magnetite1-3.

U. Colombo; G. Fagherazzi; F. Gazzarrini; G. Lanzavecchia; G. Sironi

1964-01-01

232

Preparation and characterization of magnetite nanoparticles coated by amino silane  

Microsoft Academic Search

Magnetite nanoparticles were prepared by coprecipitation of Fe2+ and Fe3+ with NH4OH, and then, amino silane was coated onto the surface of the magnetite nanoparticles. Transmission electronic microscopy shows the average size of 7.5 nm in diameter. Powder X-ray diffraction and electronic diffraction measurements show the spinel structure for the magnetite nanoparticles. FT–IR spectra indicate that amino silane molecules have

Ming Ma; Yu Zhang; Wei Yu; Hao-ying Shen; Hai-qian Zhang; Ning Gu

2003-01-01

233

Crystals  

NSDL National Science Digital Library

This page contains four documents explaining crystals. The topic is covered at an advanced level in relation to nanotechnology and requires background knowledge in eight grade science. A powerpoint with illustrations and instructor guide containing activities are included to aid in teaching this subject. Additionally, links to related videos, a lab handout, and discussion questions are available.

2012-10-16

234

A Magnetite-Dolomite-rich Clast in Orgueil: Differentiation on the CI Parent Body  

NASA Astrophysics Data System (ADS)

In a thin section of CI Orgueil a 4x5 mm clast was found with an unusual composition. It consists mainly of magnetite (63 wt%) and dolomite (12 wt%) in the usual fine matrix. The magnetite occurs in rounded grains of 5 to 20 micron, occasionally also as framboidal spherules composed of many tiny grains. The dolomite grains have about the same size and rounded shape as the magnetites. The magnetite is chemically very pure, with no element except iron detectable by microprobe (as usual in Orgueil). Dolomite contains, besides Ca and Mg, variable amounts of Mn and Fe. In a Mn vs. Fe diagram they plot in the same area as reported for Orgueil [1], but they show an Fe/Mn anticorrelation, which has not been found before. Mn varies over a wider range than Fe (Fig. 1), so there is not a simple replacement of Mn by Fe, or vice versa. Many dolomite grains show fan-shaped overgrowth towards the matrix; these areas plot at the low-Mn/high-Fe end of the Fe/Mn anticorrelation (Fig. 1). Dolomites sometimes contain tiny spherules of magnetite, often arranged in strings close to their outer margins. The bulk composition of this clast shows more than twice as much Fe and three times as much Ca as Orgueil, and is correspondingly poorer in Mg and Si (Table 1). The matrix composition in the clast is generally similar to that in Orgueil proper, but it is significantly higher in Fe, S, and Ni. The similar compositions of magnetite and dolomite in the clast and in Orgueil proper show that they formed under similar conditions, that is on the parent body [1, 2]. The high enrichment of these minerals must have formed by differentiation on the parent body. This differentiation was no longer isochemical, as so far assumed for all processes on the Orgueil parent body. References: [1] Fredriksson K. and Kerridge J. F. (1988) Meteoritics, 23, 35-44. [2] Johnson C. A. and Prinz M. (1993) GCA, 57, 2843-2852. Table 1: Bulk composition of clast and Orgueil proper Clast^1 Orgueil^2 MgO 11 22 Al2O3 0.5 2.3 SiO2 10 31 S 2.0 7.6 CaO 6.1 1.9 FeO* 69 33 NiO 1.3 1.8 100 100 1 Calculated from mineral compostion and mode. 2 Recalculated from chemical analysis by E. Jarosewich in [1]. * All Fe as FeO.

Wlotzka, F.; Thacker, R.; Fredriksson, K.

1995-09-01

235

Functional Analysis of the Magnetosome Island in Magnetospirillum gryphiswaldense: The mamAB Operon Is Sufficient for Magnetite Biomineralization  

PubMed Central

Bacterial magnetosomes are membrane-enveloped, nanometer-sized crystals of magnetite, which serve for magnetotactic navigation. All genes implicated in the synthesis of these organelles are located in a conserved genomic magnetosome island (MAI). We performed a comprehensive bioinformatic, proteomic and genetic analysis of the MAI in Magnetospirillum gryphiswaldense. By the construction of large deletion mutants we demonstrate that the entire region is dispensable for growth, and the majority of MAI genes have no detectable function in magnetosome formation and could be eliminated without any effect. Only <25% of the region comprising four major operons could be associated with magnetite biomineralization, which correlated with high expression of these genes and their conservation among magnetotactic bacteria. Whereas only deletion of the mamAB operon resulted in the complete loss of magnetic particles, deletion of the conserved mms6, mamGFDC, and mamXY operons led to severe defects in morphology, size and organization of magnetite crystals. However, strains in which these operons were eliminated together retained the ability to synthesize small irregular crystallites, and weakly aligned in magnetic fields. This demonstrates that whereas the mamGFDC, mms6 and mamXY operons have crucial and partially overlapping functions for the formation of functional magnetosomes, the mamAB operon is the only region of the MAI, which is necessary and sufficient for magnetite biomineralization. Our data further reduce the known minimal gene set required for magnetosome formation and will be useful for future genome engineering approaches.

Lohsse, Anna; Ullrich, Susanne; Katzmann, Emanuel; Borg, Sarah; Wanner, Gerd; Richter, Michael; Voigt, Birgit; Schweder, Thomas; Schuler, Dirk

2011-01-01

236

Study of the surface chemistry and morphology of single walled carbon nanotube-magnetite composites  

SciTech Connect

The study of the morphologies of the single walled carbon nanotube (SWCNT), magnetite nanoparticles (MNP), and the composite based on them was carried with combined X-ray diffraction (XRD), Raman spectroscopy (RS), scanning electron microscopy (SEM), field emission scanning electron microscopy (FESEM) and high resolution transmission electron microscopy (HRTEM). These techniques together with thermogravimetric analyses (TGA) and diffuse reflectance infrared transform spectroscopy (DRIFTS) confirmed the production of pure single phases, and that the composite material consisted of MNP attached to the outer surface of the SWCNT. The Moessbauer spectroscopy (MS) research showed the presence of a large quantity of Lewis acid sites in the highly dispersed magnetite particles supported on the SWCNT outer surface. The DRIFTS carbon dioxide adsorption study of the composites revealed significant adsorption of carbon dioxide, fundamentally in the Lewis acid sites. Then, the Lewis acid sites were observed to be catalytically active. Further, the electron exchange between the Lewis acid sites and the basic or amphoteric adsorbed molecules could influence the magnetic properties of the magnetite. Consequently, together with this first ever use of MS in the study of Lewis acid sites, this investigation revealed the potential of the composites for catalytic and sensors applications. -- Graphical abstract: A large amount of Lewis acid sites were found in the highly dispersed magnetite which is supported on the SWCNT outer surface. Display Omitted Research highlights: {yields} The obtained materials were completely characterized with XRD, Raman and SEM-TEM. {yields} DRIFT, TGA and adsorption of the composites allowed understand the material formation. {yields} This is the first report of a study of Lewis sites by Moessbauer spectroscopy.

Marquez-Linares, F. [Institute for Physical Chemical Applied Research, School of Science, University of Turabo, PO Box 3030, Gurabo, PR 00778-3030 (Puerto Rico); Uwakweh, O.N.C. [Engineering Science and Materials Department, College of Engineering, University of Puerto Rico-Mayagueez Campus, Mayaguez, PR 00681-9044 (Puerto Rico); Lopez, N. [Chemical Engineering Department, College of Engineering, University of Puerto Rico-Mayagueez Campus, Mayaguez, PR 00681-9000 (Puerto Rico); Chavez, E. [Physics Department, University of Puerto Rico-Mayagueez Campus, Mayaguez, PR 00681-9000 (Puerto Rico); Polanco, R. [Institute for Physical Chemical Applied Research, School of Science, University of Turabo, PO Box 3030, Gurabo, PR 00778-3030 (Puerto Rico); Morant, C.; Sanz, J.M.; Elizalde, E. [Department of Applied Physics, C-XII, Universidad Autonoma de Madrid, Cantoblanco, 28049-Madrid (Spain); Neira, C.; Nieto, S. [Institute for Physical Chemical Applied Research, School of Science, University of Turabo, PO Box 3030, Gurabo, PR 00778-3030 (Puerto Rico); Roque-Malherbe, R., E-mail: RRoque@suagm.ed [Institute for Physical Chemical Applied Research, School of Science, University of Turabo, PO Box 3030, Gurabo, PR 00778-3030 (Puerto Rico)

2011-03-15

237

Genes Necessary for Bacterial Magnetite Biomineralization Identified by Transposon Mutagenesis  

NASA Astrophysics Data System (ADS)

Magnetic bacteria synthesize nanoscale crystals of magnetite in intracellular, membrane-bounded organelles (magnetosomes). These crystals are preserved in the fossil record at least as far back as the late Neoproterozoic and have been tentatively identified in much older rocks (1). This fossil record may provide deep time calibration points for molecular evolution studies once the genes involved in biologically controlled magnetic mineralization (BCMM) are known. Further, a genetic and biochemical understanding of BCMM will give insight into the depositional environment and biogeochemical cycles in which magnetic bacteria play a role. The BCMM process is not well understood, though proteins have been identified from the magnetosome membrane and genetic manipulation and biochemical characterization of these proteins are underway. Most of the proteins currently thought to be involved are encoded within the mam cluster, a large cluster of genes whose products localize to the magnetosome membrane and are conserved among magnetic bacteria (2). In an effort to identify all of the genes necessary for bacterial BCMM, we undertook a transposon mutagenesis of Magnetospirillum magneticum AMB-1. Non-magnetic mutants (MNMs) were identified by growth in liquid culture followed by a magnetic assay. The insertion site of the transposon was identified two ways. First MNMs were screened with a PCR assay to determine if the transposon had inserted into the mam cluster. Second, the transposon was rescued from the mutant DNA and cloned for sequencing. The majority insertion sites are located within the mam cluster. Insertion sites also occur in operons which have not previously been suspected to be involved in magnetite biomineralization. None of the insertion sites have occurred within genes reported from previous transposon mutagenesis studies of AMB-1 (3, 4). Two of the non-mam cluster insertion sites occur in operons containing genes conserved particularly between MS-1 and MC-1. We are undertaking a complementation strategy to demonstrate the necessity of these novel genes in BCMM as well as characterizing the phenotypes of the mutants. 1. S. B. R. Chang, J. F. Stolz, J. L. Kirschvink, S. M. Awramik, Precambrian Res. 43, 305-315 (1989). 2. K. Grünberg, C. Wawer, B. M. Tebo, D. Schüler, Appl. Environ. Microbiol. 67, 4573-4582 (2001). 3. A. T. Wahyudi, H. Takeyama, T. Matsunaga, Appl. Biochem. Biotechnol. 91-3, 147-154 (2001). 4. T. Matsunaga, C. Nakamura, J. G. Burgess, K. Sode, J. Bacteriol. 174, 2748-2753 (1992).

Nash, C. Z.; Komeili, A.; Newman, D. K.; Kirschvink, J. L.

2004-12-01

238

Habits of Magnetosome Crystals in Coccoid Magnetotactic Bacteria  

Microsoft Academic Search

High-resolution transmission electron microscopy and electron holography were used to study the habits of exceptionally large magnetite crystals in coccoid magnetotactic bacteria. In addition to the crystal habits, the crystallographic positioning of successive crystals in the magnetosome chain appears to be under strict biological control. Magnetotactic bacteria (MB) contain magnetosomes com- prising nanoscale magnetic iron mineral crystals in membrane vesicles

Ulysses Lins; Martha R. McCartney; Marcos Farina; Richard B. Frankel; Peter R. Buseck

2005-01-01

239

Polyaspartate coated magnetite nanoparticles for biomedical applications  

NASA Astrophysics Data System (ADS)

The use of magnetic nanoparticles (MNP) in biomedical applications is subject to specific conditions. Special demands such as non-toxic core material and a biocompatible shell are prerequisites. These are fulfilled with magnetite cores and amino acid shell material, which provide different functional groups for coupling biomolecules as presented here. In this study the biocompatibility was tested by using breast cancer cell lines and leukocytes from peripheral blood. Functionalization with antibodies and the binding experiments detected by magneto-optical relaxation measurements confirm the bonding capacity and demonstrate the application of the presented MNP in magnetic immunoassays or magnetic drug targeting.

Aurich, Konstanze; Schwalbe, Manuela; Clement, Joachim H.; Weitschies, Werner; Buske, Norbert

2007-04-01

240

Magnetic anisotropy modulation of magnetite in Fe{sub 3}O{sub 4}/BaTiO{sub 3}(100) epitaxial structures  

SciTech Connect

Temperature dependent magnetometry and transport measurements on epitaxial Fe{sub 3}O{sub 4} films grown on BaTiO{sub 3}(100) single crystals by molecular beam epitaxy show a series of discontinuities, due to changes in the magnetic anisotropy induced by strain from the different crystal phases of BaTiO{sub 3}. The magnetite film is under tensile strain at room temperature, which is ascribed to the lattice expansion of BaTiO{sub 3} at the cubic to tetragonal transition, indicating that the magnetite film is relaxed at the growth temperature. From the magnetization versus temperature curves, the variation in the magnetic anisotropy is determined and compared with the magnetoelastic anisotropies. These results demonstrate the possibility of using the piezoelectric response of BaTiO{sub 3} to modulate the magnetic anisotropy of magnetite films.

Vaz, C. A. F.; Hoffman, J.; Posadas, A.-B.; Ahn, C. H. [Department of Applied Physics and CRISP, Yale University, New Haven, Connecticut 06520 (United States)

2009-01-12

241

Biogeochemical role of magnetite in urban soils (Review of publications)  

NASA Astrophysics Data System (ADS)

The surface horizons of urban soils are enriched in technogenic magnetite Fe3O4 accumulated from emissions. Its content there reaches 3-4% and more, whereas it does not exceed 0.1% in the back-ground soils. In urban soils, large spherical magnetite particles of pseudo-single-domain and multidomain fabric predominate; the cavities in magnetic spherules decrease their chemical stability and increase their reactivity. Magnetite is most often destroyed in urban soils due to complexing; its destruction may be initiated by mineral salts entering the soil with deicing mixtures and by organic acids excreted by roots (e.g., by oxalic acid). The high solubility of magnetite with ammonium oxalate should be taken into account when using Tamm's reagent for the analysis of urban soils. Magnetite is a mineral carrier of some heavy metals. Therefore, its content (as determined from the magnetic susceptibility) serves as an indirect index of soil pollution. In addition, magnetite may affect many soil properties as a reducer and sorbent. It adsorbs phosphorus thus preventing the penetration of this nutrient into rivers and lakes. Magnetite also oxidizes Cl-containing aliphatic hydrocarbons and purifies the soil. Although magnetite enters urban soils as a pollutant, its influence on the soil properties cannot be unambiguously judged as only negative.

Vodyanitskii, Yu. N.

2013-03-01

242

Preparation and application of magnetic fluid with magnetite (I).  

National Technical Information Service (NTIS)

Magnetite should be larger than 1 mm in order to supply as the raw materials of iron making industries. In Synemi mine, more than 40 % of the magnetite has not been utilized too fine as iron source. The objects of this study are preparing the magnetic flu...

H. S. Lee D. J. Kim Y. Hwang

1996-01-01

243

Evidence for a relationship between hydrocarbons and authigenic magnetite  

Microsoft Academic Search

Establishing a relationship between hydrocarbon migration and the precipitation of authigenic magnetite in sedimentary rocks is of significant interest with respect to (1) elucidating mechanisms for remagnetization and establishing the origin of secondary magnetizations residing in magnetite, (2) developing a method to date hydrocarbon migration events by determining the time of remanence acquisition by palaeomagnetic methods, and (3) evaluating whether

R. D. Elmore; M. H. Engel; L. Crawford; K. Nick; S. Imbus; Z. Sofer

1987-01-01

244

A comparison of ARM and TRM in magnetite  

Microsoft Academic Search

Experiments comparing anhysteretic remanence (ARM) and thermoremanence (TRM) in samples containing natural and synthetic magnetite, whose mean particle sizes range from single domain to multidomain, show that ARM and TRM are very similar (but not identical) in their stabilities with respect to alternating field (AF) demagnetization, temperature cycles in zero field to below magnetite's isotropic temperature near 130°K, and stability

Shaul Levi; Ronald T. Merrill

1976-01-01

245

Magnetic Process for Removing Heavy Metals from Water Employing Magnetites.  

National Technical Information Service (NTIS)

A process for removing heavy metals from water is provided. The process includes the steps of introducing magnetite to a quantity of water containing heavy metal. The magnetite is mixed with the water such that at least a portion of, and preferably the ma...

F. C. Prenger D. D. Hill

2003-01-01

246

EPR evidence for maghemitization of magnetite in a tropical soil  

Microsoft Academic Search

SUMMARY Electron paramagnetic spectroscopy (EPR) was used in combination with standard rock mag- netic methods to study magnetic minerals in a tropical soil. The susceptibility and hysteresis measurements showed magnetite grains with a Curie temperature near 850 K as the domi- nant magnetic remanence carriers in the soil. A minor Ti content in the magnetite was found by energy dispersive

H. Fischer; J. Luster; A. U. Gehring

2007-01-01

247

Lymphatic mapping and sentinel node location with magnetite nanoparticles  

NASA Astrophysics Data System (ADS)

Subcutaneously administered magnetite nanoparticles were used to locate sentinel lymph nodes in normal rats. Nanoparticles sequestered in brachial and axillary lymph nodes produced magnetic susceptibility artifacts in gradient recall echo magnetic resonance images. The artifact sizes enabled the determination of nanoparticle nodal uptake rates and lymphatic drainage patterns. These studies were confirmed by use of 59Fe labeled magnetite nanoparticles.

Jung, Chu W.; Rogers, James M.; Groman, Ernest V.

1999-04-01

248

Porphyrin-magnetite nanoconjugates for biological imaging  

PubMed Central

Background The use of silica coated magnetic nanoparticles as contrast agents has resulted in the production of highly stable, non-toxic solutions that can be manipulated via an external magnetic field. As a result, the interaction of these nanocomposites with cells is of vital importance in understanding their behaviour and biocompatibility. Here we report the preparation, characterisation and potential application of new "two-in-one" magnetic fluorescent nanocomposites composed of silica-coated magnetite nanoparticles covalently linked to a porphyrin moiety. Method The experiments were performed by administering porphyrin functionalised silica-coated magnetite nanoparticles to THP-1 cells, a human acute monocytic leukaemia cell line. Cells were cultured in RPMI 1640 medium with 25 mM HEPES supplemented with heat-inactivated foetal bovine serum (FBS). Results We have synthesised, characterised and analysed in vitro, a new multimodal (magnetic and fluorescent) porphyrin magnetic nanoparticle composite (PMNC). Initial co-incubation experiments performed with THP-1 macrophage cells were promising; however the PMNC photobleached under confocal microscopy study. ?-mercaptoethanol (?-ME) was employed to counteract this problem and resulted not only in enhanced fluorescence emission, but also allowed for elongated imaging and increased exposure times of the PMNC in a cellular environment. Conclusion Our experiments have demonstrated that ?-ME visibly enhances the emission intensity. No deleterious effects to the cells were witnessed upon co-incubation with ?-ME alone and no increases in background fluorescence were recorded. These results should present an interest for further development of in vitro biological imaging techniques.

2011-01-01

249

Coating agents affected toward magnetite nanoparticles properties  

NASA Astrophysics Data System (ADS)

Magnetite nanoparticles --MNPs-- are innovative materials used in biological and medical applications. They respond to magnetic field through the superparamagnetic behavior at room temperature. In this study, the MNPs were synthesized via the chemical co-precipitation method using various coating agents. Fatty acids, found naturally in the animal fats, can be used as a coating agent. Oleic acid and hexanoic acid were chosen as the surface modification agents to study the improvement in the suspension of MNPs in water and the magnetite properties. Suspension stability, particle size, and electrical conductivity of MNPs are critically affected by the modification process. The well-dispersed MNPs in water can be improved by the surface modification and the oleic acid coated MNPs possess excellent suspension stability over 1 week. The particle size of MNPs increases up to 40 nm using oleic acid coated MNPs. The electrical conductivity of the smallest particle size is 1.3x10-3 S/cm, which is 5 times higher than that of the largest particle, suggesting potential applications as a biomedical material under both of the electrical and magnetic fields.

Petcharoen, Karat; Sirivat, Anuvat

2012-02-01

250

Spin-Dependent Transport For Magnetite (Fe3O4) Thin Films On SiO2-Glass, MgO And MgAl2O4 Substrates  

NASA Astrophysics Data System (ADS)

Spin-dependent-transport was studied for magnetite (Fe3O4) thin films on SiO2-glass, MgO (100) and MgAl2O4 (100) single crystal substrates prepared by RF-magnetron sputtering. The magnetite thin film was found to be composed of nano-sized grains. The magnetoresistance is mainly dominated by the crystallinity of the thin film rather than the grain-size.

Kobori, H.; Shimizu, D.; Yamasaki, A.; Sugimura, A.; Taniguchi, T.; Kawanaka, H.; Ando, A.; Shimizu, T.

2008-04-01

251

Spin-Dependent Transport For Magnetite (Fe3O4) Thin Films On SiO2Glass, MgO And MgAl2O4 Substrates  

Microsoft Academic Search

Spin-dependent-transport was studied for magnetite (Fe3O4) thin films on SiO2-glass, MgO (100) and MgAl2O4 (100) single crystal substrates prepared by RF-magnetron sputtering. The magnetite thin film was found to be composed of nano-sized grains. The magnetoresistance is mainly dominated by the crystallinity of the thin film rather than the grain-size.

H. Kobori; D. Shimizu; A. Yamasaki; A. Sugimura; T. Taniguchi; H. Kawanaka; A. Ando; T. Shimizu

2008-01-01

252

Spin moment over 10-300 K and the delocalization of magnetic electrons above the Verwey transition in magnetite  

Microsoft Academic Search

In order to probe the magnetic ground state, we have carried out temperature dependent magnetic Compton scattering experiments on an oriented single crystal of magnetite (Fe3O4), together with the corresponding first-principles band theory computations to gain insight into the measurements. An accurate value of the magnetic moment muS associated with unpaired spins is obtained directly for the first time over

P. A. Montano; Yinwan Li; B. Barbiellini; P. E. Mijnarends; S. Kaprzyk; A. Bansil

2006-01-01

253

The magnetosome proteins MamX, MamZ and MamH are involved in redox control of magnetite biomineralization in Magnetospirillum gryphiswaldense.  

PubMed

Magnetospirillum gryphiswaldense uses intracellular chains of membrane-enveloped magnetite crystals, the magnetosomes, to navigate within magnetic fields. The biomineralization of magnetite nanocrystals requires several magnetosome-associated proteins, whose precise functions so far have remained mostly unknown. Here, we analysed the functions of MamX and the Major Facilitator Superfamily (MFS) proteins MamZ and MamH. Deletion of either the entire mamX gene or elimination of its putative haem c-binding magnetochrome domains, and deletion of either mamZ or its C-terminal ferric reductase-like component resulted in an identical phenotype. All mutants displayed WT-like magnetite crystals, flanked within the magnetosome chains by poorly crystalline flake-like particles partly consisting of haematite. Double deletions of both mamZ and its homologue mamH further impaired magnetite crystallization in an additive manner, indicating that the two MFS proteins have partially redundant functions. Deprivation of ?mamX and ?mamZ cells from nitrate, or additional loss of the respiratory nitrate reductase Nap from ?mamX severely exacerbated the magnetosome defects and entirely inhibited the formation of regular crystals, suggesting that MamXZ and Nap have similar, but independent roles in redox control of biomineralization. We propose a model in which MamX, MamZ and MamH functionally interact to balance the redox state of iron within the magnetosome compartment. PMID:23889511

Raschdorf, Oliver; Müller, Frank D; Pósfai, Mihály; Plitzko, Jürgen M; Schüler, Dirk

2013-07-25

254

Experimental evidence for non-redox transformations between magnetite and hematite under H2-rich hydrothermal conditions  

NASA Astrophysics Data System (ADS)

Transformations of magnetite (FeIIFe2IIIO4) to hematite (Fe2IIIO3) (and vice versa) have been thought by many scientists and engineers to require molecular O2 and/or H2. Thus, the presence of magnetite and/or hematite in rocks has been linked to a specific oxidation environment. However, the availability of reductants or oxidants in many geologic and industrial environments appears to have been too low to account for the transformations of iron oxides through redox reactions. Here, we report the results of hydrothermal experiments in mildly acidic and H2-rich aqueous solutions at 150 °C, which demonstrate that transformations of magnetite to hematite, and hematite to magnetite, occur rapidly without involving molecular O2 or H2: Fe3O4(Mt) + 2H(aq)+ ? Fe2O3(Hm) + Fe(aq)2+ + H2O The transformation products are chemically and structurally homogeneous, and typically occur as euhedral single crystals much larger than the precursor minerals. This suggests that, in addition to the expected release of aqueous ferrous species to solution, the transformations involve release of aqueous ferric species from the precursor oxides to the solution, which reprecipitate without being reduced by H2. These redox-independent transformations may have been responsible for the formation of some iron oxides in natural systems, such as high-grade hematite ores that developed from Banded Iron Formations (BIFs), hematite-rich deposits formed on Mars, corrosion products in power plants and other industrial systems.

Otake, Tsubasa; Wesolowski, David J.; Anovitz, Lawrence M.; Allard, Lawrence F.; Ohmoto, Hiroshi

2007-05-01

255

Studies of magnetite nanoparticles synthesized by thermal decomposition of iron (III) acetylacetonate in tri(ethylene glycol)  

NASA Astrophysics Data System (ADS)

In this paper, water-soluble magnetite nanoparticles have been directly synthesized by thermal decomposition of iron (III) acetylacetonate, Fe(acac)3 in tri(ethyleneglycol). Size and morphology of the nanoparticles are determined by transmission electron microscopy (TEM) and dynamic light scattering (DLS) measurements while the crystal structure is identified using X-ray diffraction (XRD). Surface charge and surface coating of the nanoparticles are recognized using Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectra (XPS) and zeta potential measurements. Magnetic properties are determined using vibrating sample magnetometer (VSM) and superconducting quantum interference device (SQUID) measurements. The results show that as-prepared magnetite nanoparticles are relatively monodisperse, single crystalline and superparamagnetic in nature with the blocking temperature at around 100 K. The magnetite nanoparticles are found to be highly soluble in water due to steric and electrostatic interactions between the particles arising by the surface adsorbed tri(ethyleneglycol) molecules and associated positive charges, respectively. Cytotoxicity studies on human cervical (SiHa), mouse melanoma (B16F10) and mouse primary fibroblast cells demonstrate that up to a dose of 80 ?g/ml, the magnetic nanoparticles are nontoxic to the cells. Specific absorption rate (SAR) value has been calculated to be 885 and 539 W/gm for samples with the iron concentration of 1 and 0.5 mg/ml, respectively. The high SAR value upon exposure to 20 MHz radiofrequency signifies the applicability of as-prepared magnetite nanoparticles for a feasible magnetic hyperthermia treatment.

Maity, Dipak; Kale, S. N.; Kaul-Ghanekar, Ruchika; Xue, Jun-Min; Ding, Jun

2009-10-01

256

Magnetite reveals ambient field strength at low temperatures  

NASA Astrophysics Data System (ADS)

Magnetite (Fe3O4) is the most important and oldest known magnetic mineral on Earth (Figure l). We have come a long way from the magnetite loadstone compasses of ancient China; magnetite and titanomagnetite have been established as the principal carriers of geologically important remanent magnetizations in rocks, the study of which led to the plate tectonic paradigm. We now recognize that magnetite plays an important role in the biosphere. Some organisms contain intra-cellular particles of Fe3O4 that they use for spatial orientation and navigation. When preserved in rocks, these particles—called "magnetofossils"— can provide important insight into the origin and development of life here, and perhaps, on other planets [e.g., Thomas-Keprta et al., 2000]. Magnetite is now used in the medical field and in nanotechnology research. Nanoparticles of magnetite are used as a contrasting agent in magnetic resonance imaging and are being developed to deliver site-specific drugs for the treatment of cancer [Alexiou et al., 2000]. Such applications add to a long list of industrial uses of magnetite that range from magnetic ink to magnetic recording media.

Smirnov, Alexei V.; Tarduno, John A.

257

Reduction of Hg(II) to Hg(0) by Magnetite  

SciTech Connect

Mercury (Hg) is a highly toxic element, and its contamination of groundwater presents a significant threat to terrestrial ecosystems. Understanding the geochemical processes that mediate mercury transformations in the subsurface is necessary to predict its fate and transport. In this study, we investigated the redox transformation of mercuric Hg (Hg[II]) in the presence of the Fe(II)/Fe(III) mixed valence iron oxide mineral magnetite. Kinetic and spectroscopic experiments were performed to elucidate reaction rates and mechanisms. The experimental data demonstrated that reaction of Hg(II) with magnetite results in the loss of Hg(II) and the formation of volatile elemental Hg (Hg[0]). Kinetic experiments showed that Hg(II) reduction occurred within minutes, with reaction rates increasing with increasing magnetite suspension density (0.05 to 0.2 g/L) and solution pH (4.8 to 6.7), and decreasing with increasing chloride concentration (10-6 to 10-2 mol/L). Mössbauer spectroscopic analysis of reacted magnetite samples revealed a decrease in Fe(II) content, corresponding the oxidation of Fe(II) to Fe(III) in the magnetite structure. X-ray photoelectron spectroscopy detected the presence of Hg(II) on magnetite surfaces, suggesting that adsorption is involved in the electron transfer process. These results suggest that Hg(II) reaction with solid-phase Fe(II) is a kinetically favorable pathway for Hg(II) reduction in magnetite-bearing environmental systems.

Wiatrowski, Heather A.; Das, Soumya; Kukkadapu, Ravi K.; Ilton, Eugene S.; Barkay, Tamar; Yee, Nathan

2009-06-12

258

LA-ICP-MS of magnetite: Methods and reference materials  

USGS Publications Warehouse

Magnetite (Fe3O4) is a common accessory mineral in many geologic settings. Its variable geochemistry makes it a powerful petrogenetic indicator. Electron microprobe (EMPA) analyses are commonly used to examine major and minor element contents in magnetite. Laser ablation ICP-MS (LA-ICP-MS) is applicable to trace element analyses of magnetite but has not been widely employed to examine compositional variations. We tested the applicability of the NIST SRM 610, the USGS GSE-1G, and the NIST SRM 2782 reference materials (RMs) as external standards and developed a reliable method for LA-ICP-MS analysis of magnetite. LA-ICP-MS analyses were carried out on well characterized magnetite samples with a 193 nm, Excimer, ArF LA system. Although matrix-matched RMs are sometimes important for calibration and normalization of LA-ICP-MS data, we demonstrate that glass RMs can produce accurate results for LA-ICP-MS analyses of magnetite. Cross-comparison between the NIST SRM 610 and USGS GSE-1G indicates good agreement for magnetite minor and trace element data calibrated with either of these RMs. Many elements show a sufficiently good match between the LA-ICP-MS and the EMPA data; for example, Ti and V show a close to linear relationship with correlation coefficients, R2 of 0.79 and 0.85 respectively. ?? 2011 The Royal Society of Chemistry.

Nadoll, P.; Koenig, A. E.

2011-01-01

259

Electric field driven transition in magnetite  

NASA Astrophysics Data System (ADS)

Magnetite, Fe3O4, is a strongly electronically correlated system and thus exhibits remarkable electrical and magnetic properties, including the Verwey transition at TV˜122 K, which has attracted much attention since its 1939 discovery. Fe3O4 has recently revealed a new effect. By performing experiments at the nanoscale, we have discovered a novel electric-field driven transition (EFT) in magnetite below TV, from high- to low-resistance states driven by high electric field. The EFT is detected both in Fe3O4 nanoparticles and thin films, is hysteretic in voltage under continuous biasing, and is not caused by self- heating (S. Lee et. al., Nature Mater. 7, 130 (2008)). In this work we report on a thorough investigation of this new EFT. First, we unveil the origin of hysteresis observed in I-V curves. By applying voltage in a pulsed manner with controlled parameters we unambiguously demonstrate that while the transition is field-driven, hysteresis results from Joule heating in the low-resistance state. A simple relaxation-time thermal model captures the essentials of the hysteresis mechanism (A. Fursina et al., Phys. Rev. B 79, 245131 (2009)). Second, by doing multilead electrical measurements, we quantitatively separate the contributions of the Fe3O4 channel and each electrode interfaces and explore the contact effects upon testing several different contact metals. On the onset of the transition, contact resistances at both source and drain electrodes and the resistance of Fe3O4 channel decrease abruptly. This behavior is consistent with a theoretically predicted transition mechanism of charge gap closure by electric field. Finally, we report recent measurements of the distribution of switching voltages and its evolution with temperature. These studies demonstrate that nanoscale, nonequilibrium probes can reveal much about the underlying physics of strongly correlated materials.

Lee, Sungbae

2010-03-01

260

Superparamagnetic magnetite nanocrystals-graphene oxide nanocomposites: facile synthesis and their enhanced electric double-layer capacitor performance.  

PubMed

Superparamagnetic magnetite nanocrystals-graphene oxide (FGO) nanocomposites were successfully synthesized through a simple yet versatile one-step solution-processed approach at ambient conditions. Magnetite (Fe3O4) nanocrystals (NCs) with a size of 10-50 nm were uniformly deposited on the surfaces of graphene oxide (GO) sheets, which were confirmed by transmission electron microscopy (TEM) and high-angle annular dark field scanning transmission election microscopy (HAADF-STEM) studies. FGO with different Fe3O4 loadings could be controlled by simply manipulating the initial weight ratio of the precursors. The M-H measurements suggested that the as-prepared FGO nanocomposites have a large saturation magnetizations that made them can move regularly under an external magnetic field. Significantly, FGO nanocomposites also exhibit enhanced electric double-layer capacitor (EDLC) activity compared with pure Fe3O4 NCs and GO in terms of specific capacitance and high-rate charge-discharge. PMID:22905504

Wang, Qihua; Wang, Dewei; Li, Yuqi; Wang, Tingmei

2012-06-01

261

Permittivity of nanocomposites based on magnetite nanoparticles and polymer matrices (collagen and polystyrene)  

NASA Astrophysics Data System (ADS)

The kinetics of polarization of nanocomposites based on magnetite nanoparticles and polymer matrices (collagen and polystyrene) in an electric field was studied. The polarization and depolarization times of magnetite nanoparticles were determined. The dependence of the maximum electric dipole moment of magnetite nanoparticles on their size was studied. The permittivity of nanocomposites, magnetite nanoparticles and collagen and polystyrene polymer matrices, was determined.

Ali-Zade, R. A.

2010-09-01

262

Habits of Magnetosome Crystals in Coccoid Magnetotactic Bacteria  

PubMed Central

High-resolution transmission electron microscopy and electron holography were used to study the habits of exceptionally large magnetite crystals in coccoid magnetotactic bacteria. In addition to the crystal habits, the crystallographic positioning of successive crystals in the magnetosome chain appears to be under strict biological control.

Lins, Ulysses; McCartney, Martha R.; Farina, Marcos; Frankel, Richard B.; Buseck, Peter R.

2005-01-01

263

Saturation of copper-iron mattes with solid magnetite  

NASA Astrophysics Data System (ADS)

Conditions which lead to the saturation of simple copper-iron mattes with solid magnetite have been evaluated in this study. Diagrams have been developed which illustrate quantitatively the surface of saturation of matte with magnetite in the phase and stability diagrams for the Cu-Fe-S-0 system at 1468 K and 1 atm total pressure. Conditions fo. simultaneous saturation of matte with magnetite and gas ( P so2 + P s2= 1 atm) have also been estimated by extrapolation of the data on magnetitesaturated mattes. Comparison of the results with compositions of mattes from oxygen-enriched smelters indicates that these smelters operate at magnetite saturation under conditions close to equilibrium. Conditions during oxygen-enriched smelting can be predicted from the diagrams given in this paper and correlation equations for the oxygen and sulfur concentrations in magnetitesaturated matte which were previously developed from the experimental data.

Kaiser, D. L.; Elliott, J. F.

1988-12-01

264

Novel high pressure magnetic measurements with application to magnetite  

NASA Astrophysics Data System (ADS)

We report a novel system designed to measure reversible magnetic susceptibility of micron-sized samples under high pressures in a diamond anvil cell. We find that magnetite reversible hysteresis parameters vary <15% below 0.6 to 1.0 GPa, while at higher pressures significant increases occur in (1) bulk coercivity (Hc) and (2) the ratio of saturation remanent magnetization (Mrs) to saturation magnetization (Ms). The net effect of pressure is to displace magnetite toward a truer single domain state with both higher Mrs/Ms and Hc. Our data, together with the fact that magnetite Curie temperature increases with pressure, suggest that magnetite can account for geomagnetic anomalies related to some subduction zones and potentially to meteorite impact sites on Earth, as well as magnetic signatures observed on some planetary bodies like Mars.

Gilder, Stuart A.; LeGoff, Maxime; Peyronneau, Jean; Chervin, Jean-Claude

2002-05-01

265

Magnetic Properties of Bio-Synthesized Magnetite Nanoparticles  

SciTech Connect

Magnetic nanoparticles, which are unique because of both structural and functional elements, have various novel applications. The popularity and practicality of nanoparticle materials create a need for a synthesis method that produces quality particles in sizable quantities. This paper describes such a method, one that uses bacterial synthesis to create nanoparticles of magnetite. The thermophilic bacterial strain Thermoanaerobacter ethanolicus TOR-39 was incubated under anaerobic conditions at 65 C for two weeks in aqueous solution containing Fe ions from a magnetite precursor (akaganeite). Magnetite particles formed outside of bacterial cells. We verified particle size and morphology by using dynamic light scattering, X-ray diffraction, and transmission electron microscopy. Average crystallite size was 45 nm. We characterized the magnetic properties by using a superconducting quantum interference device magnetometer; a saturation magnetization of 77 emu/g was observed at 5 K. These results are comparable to those for chemically synthesized magnetite nanoparticles.

Rawn, Claudia J [ORNL; Yeary, Lucas W [ORNL; Moon, Ji Won [ORNL; Love, Lonnie J [ORNL; Thompson, James R [ORNL; Phelps, Tommy Joe [ORNL

2005-01-01

266

Preparation and magnetisation of a silica-magnetite inverse ferrofluid  

NASA Astrophysics Data System (ADS)

We introduce an `inverse ferrofluid' comprising sterically stabilized, colloidal silica spheres and oleic acid stabilized magnetite particles. The preparation is described as well as magnetisation measurements which turns out to be a linear function of the silica volume fraction.

de Gans, B. J.; Blom, C.; Mellema, J.; Philipse, A. P.

1999-07-01

267

Magnetic properties of bacterial magnetosomes and chemosynthesized magnetite nanoparticles  

NASA Astrophysics Data System (ADS)

In this work, the magnetic properties of biologically produced magnetite (magnetosomes) by a mineralization process of magnetotactic bacteria {Magnetospirillum sp.} AMB-1 were compared to those of chemically synthesized magnetite nanoparticles and nanorods. X-ray diffraction data reveal that for all samples the peaks come from magnetite. A sharp magnetic transition (Verwey transition) is clearly observed in magnetosomes at 105 K (magnetite nanocrystals obtained by mineralization) and nanorodes at 112 K, in opposite, this transition is significantly smeared in Fe_{3}O_{4} powder, where the magnetic nanoparticles are separated and the magnetic fluctuations are strong to overcome magnetic anisotropy and randomize magnetic moment. The existence of coercivity of 71 Oe at room temperature is related to the fact that the mean diameter (34 nm) is larger than the critical size for the transition from superparamagnetic to ferromagnetic behaviour. Figs 6, Refs 14.

Timko, M.; Dzarova, A.; Zavisova, V.; Koneracka, M.; Sprincova, A.; Kopcansky, P.; Kovac, J.; Vavra, I.; Szlaferek, A.

2008-06-01

268

Origins of magnetite nanocrystals in Martian meteorite ALH84001  

NASA Astrophysics Data System (ADS)

The Martian meteorite ALH84001 preserves evidence of interaction with aqueous fluids while on Mars in the form of microscopic carbonate disks. These carbonate disks are believed to have precipitated 3.9 Ga ago at beginning of the Noachian epoch on Mars during which both the oldest extant Martian surfaces were formed, and perhaps the earliest global oceans. Intimately associated within and throughout these carbonate disks are nanocrystal magnetites (Fe 3O 4) with unusual chemical and physical properties, whose origins have become the source of considerable debate. One group of hypotheses argues that these magnetites are the product of partial thermal decomposition of the host carbonate. Alternatively, the origins of magnetite and carbonate may be unrelated; that is, from the perspective of the carbonate the magnetite is allochthonous. For example, the magnetites might have already been present in the aqueous fluids from which the carbonates were believed to have been deposited. We have sought to resolve between these hypotheses through the detailed characterization of the compositional and structural relationships of the carbonate disks and associated magnetites with the orthopyroxene matrix in which they are embedded. Extensive use of focused ion beam milling techniques has been utilized for sample preparation. We then compared our observations with those from experimental thermal decomposition studies of sideritic carbonates under a range of plausible geological heating scenarios. We conclude that the vast majority of the nanocrystal magnetites present in the carbonate disks could not have formed by any of the currently proposed thermal decomposition scenarios. Instead, we find there is considerable evidence in support of an alternative allochthonous origin for the magnetite unrelated to any shock or thermal processing of the carbonates.

Thomas-Keprta, K. L.; Clemett, S. J.; McKay, D. S.; Gibson, E. K.; Wentworth, S. J.

2009-11-01

269

Functionalized Magnetite Nanoparticles—Synthesis, Properties, and Bio-Applications  

Microsoft Academic Search

Nanotechnology has generated tremendous hopes in recent years toward the design of advanced functional materials, especially in the bio-medical field. Nano-sized-materials such as magnetite nanoparticles display indeed fascinating physico-chemical properties that, if tuned properly, can be exploited to design new bio-diagnostic and therapeutic strategies as well as innovative biotechnology methodologies. Owing to their biocompatibility and excellent magnetic properties, magnetite nanocrystals

Peter Majewski; Benjamin Thierry

2007-01-01

270

Activity of magnetite-immobilized catalase in hydrogen peroxide decomposition  

Microsoft Academic Search

The present work analyzes the activity in decomposition of H2O2 using magnetite-immobilized catalase. The support of catalase is a glutaraldehyde-treated magnetite (Fe3O4). The data obtained in the H2O2 decomposition are analyzed. The fitting of the initial rate of the H2O2 decomposition versus hydrogen peroxide concentration data is discussed using a specific program for enzyme kinetics modeling (Leonora). The free catalase

F. Horst; E. H. Rueda; M. L. Ferreira

2006-01-01

271

High voltage microscopy of the reduction of hematite to magnetite  

Microsoft Academic Search

The microstructural changes associated with the formation of magnetite in hematite have been studied in specimens which have\\u000a been partially reduced outside the microscope, thinned until electron transparent, and then examined in the normal way. Three\\u000a types of structure have been observed in varying proportions which depend on the reduction temperature. At low temperatures,\\u000a magnetite grows by the propagation of

P. R. Swann; N. J. Tighe

1977-01-01

272

Magnetite formation by a sulphate-reducing bacterium  

Microsoft Academic Search

BACTERIAL production of magnetite (Fe3O4)1 makes an important contribution to iron biomineralization and rcmanent magnetization of sediments2,3. Accurate magnetostratigraphy, reconstruction of the Earth's past magnetic-field behaviour and extraction of environmental information from the geomagnetic record depend on an understanding of the conditions under which bacterial magnetite is formed. In aquatic sediments, the process is thought to be restricted to a

Toshifumi Sakaguchi; J. Grant Burgess; Tadashi Matsunaga

1993-01-01

273

Mountain building, regional diagenesis, and magnetite authigenesis in Alleghenian foredeep  

SciTech Connect

In recent years a number of diagenetic features have been linked to regional events, possibly resulting from large-scale migration of fluids driven by orogenesis. These features include, but are not limited to, authigenic feldspar development, clay mineral transformations, and the formation of diagenetic hematite and magnetite. This presentation will focus on magnetite authigenesis and its implications for the nature, origin, and timing of regional diagenetic events in the foreland basin setting.

McCabe, C.

1988-02-01

274

Magnetite authigenesis and diagenetic paleotemperatures across the northern Appalachian basin  

SciTech Connect

The concentration of magnetite in the Lower and Middle Devonian Helderberg and Onondaga carbonate formations varies in a distinct pattern along an east-west profile across New York State. Magnetite concentrations are uniformly low in the western half of the profile, increase sharply eastward to a peak value near Syracuse, and decrease farther east. The pattern strongly resembles previously reported variations in the extent of clay mineral diagenesis that reflect differences in paleotemperatures along the profile. Previous paleomagnetic studies have documented that the magnetite carries a well-defined magnetization of Pennsylvanian-Permian age, and magnetite authigenesis is therefore no younger than late Paleozoic. The authors attribute the correlation between high magnetite concentration and high illite content to temperature-dependent diagenesis triggered by orogenic fluids. The large proportion of secondary magnetite indicates that over most of the area, the mechanism of late Paleozoic remagnetization was principally chemical. Thermal effects played a less direct role in the remagnetization of the strata by controlling the extent of the chemical processes that resulted in overprinting of the original remanence.

Jackson, M.; McCabe, C.; Ballard, M.M.; Van der Voo, R.

1988-07-01

275

The Periplasmic Nitrate Reductase Nap Is Required for Anaerobic Growth and Involved in Redox Control of Magnetite Biomineralization in Magnetospirillum gryphiswaldense  

PubMed Central

The magnetosomes of many magnetotactic bacteria consist of membrane-enveloped magnetite crystals, whose synthesis is favored by a low redox potential. However, the cellular redox processes governing the biomineralization of the mixed-valence iron oxide have remained unknown. Here, we show that in the alphaproteobacterium Magnetospirillum gryphiswaldense, magnetite biomineralization is linked to dissimilatory nitrate reduction. A complete denitrification pathway, including gene functions for nitrate (nap), nitrite (nir), nitric oxide (nor), and nitrous oxide reduction (nos), was identified. Transcriptional gusA fusions as reporters revealed that except for nap, the highest expression of the denitrification genes coincided with conditions permitting maximum magnetite synthesis. Whereas microaerobic denitrification overlapped with oxygen respiration, nitrate was the only electron acceptor supporting growth in the entire absence of oxygen, and only the deletion of nap genes, encoding a periplasmic nitrate reductase, and not deletion of nor or nos genes, abolished anaerobic growth and also delayed aerobic growth in both nitrate and ammonium media. While loss of nosZ or norCB had no or relatively weak effects on magnetosome synthesis, deletion of nap severely impaired magnetite biomineralization and resulted in fewer, smaller, and irregular crystals during denitrification and also microaerobic respiration, probably by disturbing the proper redox balance required for magnetite synthesis. In contrast to the case for the wild type, biomineralization in ?nap cells was independent of the oxidation state of carbon substrates. Altogether, our data demonstrate that in addition to its essential role in anaerobic respiration, the periplasmic nitrate reductase Nap has a further key function by participating in redox reactions required for magnetite biomineralization.

Li, Yingjie; Katzmann, Emanuel; Borg, Sarah

2012-01-01

276

The periplasmic nitrate reductase nap is required for anaerobic growth and involved in redox control of magnetite biomineralization in Magnetospirillum gryphiswaldense.  

PubMed

The magnetosomes of many magnetotactic bacteria consist of membrane-enveloped magnetite crystals, whose synthesis is favored by a low redox potential. However, the cellular redox processes governing the biomineralization of the mixed-valence iron oxide have remained unknown. Here, we show that in the alphaproteobacterium Magnetospirillum gryphiswaldense, magnetite biomineralization is linked to dissimilatory nitrate reduction. A complete denitrification pathway, including gene functions for nitrate (nap), nitrite (nir), nitric oxide (nor), and nitrous oxide reduction (nos), was identified. Transcriptional gusA fusions as reporters revealed that except for nap, the highest expression of the denitrification genes coincided with conditions permitting maximum magnetite synthesis. Whereas microaerobic denitrification overlapped with oxygen respiration, nitrate was the only electron acceptor supporting growth in the entire absence of oxygen, and only the deletion of nap genes, encoding a periplasmic nitrate reductase, and not deletion of nor or nos genes, abolished anaerobic growth and also delayed aerobic growth in both nitrate and ammonium media. While loss of nosZ or norCB had no or relatively weak effects on magnetosome synthesis, deletion of nap severely impaired magnetite biomineralization and resulted in fewer, smaller, and irregular crystals during denitrification and also microaerobic respiration, probably by disturbing the proper redox balance required for magnetite synthesis. In contrast to the case for the wild type, biomineralization in ?nap cells was independent of the oxidation state of carbon substrates. Altogether, our data demonstrate that in addition to its essential role in anaerobic respiration, the periplasmic nitrate reductase Nap has a further key function by participating in redox reactions required for magnetite biomineralization. PMID:22730130

Li, Yingjie; Katzmann, Emanuel; Borg, Sarah; Schüler, Dirk

2012-06-22

277

Purely lytic osteosarcoma  

SciTech Connect

The radiographic features of 42 purely lytic osteosarcomas are presented. Purely lytic osteosarcoma is identified as a lytic lesion of bone with no demonstrable osteoid matrix by conventional radiographic modalities. Purely lytic osteosarcoma represented 13.7% of a group of 305 osteosarcomas. The most common presentation was that of a lytic illdefined lesion with a moderate to large extraosseous mass component. Nine lesions presented with benign radiographic features. The differential diagnosis is outlined. The need for awareness of this type of presentation of osteosarcoma is stressed.

De Santos, L.A.; Eideken, B.

1982-11-01

278

Strong adsorption of chlorotetracycline on magnetite nanoparticles.  

PubMed

In this work, environmentally friendly magnetite nanoparticles (Fe(3)O(4) MNPs) were used to adsorb chlorotetracycline (CTC) from aqueous media. Fe(3)O(4) MNPs exhibit ultrahigh adsorption ability to this widely used antibiotic. The adsorption behavior of CTC on Fe(3)O(4) MNPs fitted the pseudo-second-order kinetics model, and the adsorption equilibrium was achieved within 10h. The maximum Langmuir adsorption capacity of CTC on Fe(3)O(4) (476 mg g(-1)) was obtained at pH 6.5. Thermodynamic parameters calculated from the adsorption data at different temperature showed that the adsorption reaction was endothermic and spontaneous. Low concentration of NaCl and foreign divalent cations hardly affected the adsorption. Negative effect of coexisting humic acid (HA) on CTC adsorption was also observed when the concentration of HA was lower than 20 mg L(-1). But high concentration of HA (>20 mg L(-1)) increased the CTC adsorption on Fe(3)O(4) MNPs. The matrix effect of several environmental water samples on CTC adsorption was not evident. Fe(3)O(4) MNPs were regenerated by treatment with H(2)O(2) or calcination at 400°C in N(2) atmosphere after separation from water solution by an external magnet. This research provided a high efficient and reusable adsorbent to remove CTC selectively from aqueous media. PMID:21724321

Zhang, Di; Niu, Hongyun; Zhang, Xiaole; Meng, Zhaofu; Cai, Yaqi

2011-06-12

279

Geomorphology: Pure and applied  

SciTech Connect

The book summarizes the history of intellectual debate in geomorphology and describes modern developments both ''pure'' and ''applied.'' The history begins well before W.M. Davis and follows through to such debates as those concerned with the Pleistocene. Modern developments in pure geomorphology are cast in terms of chapters on form, process, materials, and methods analysis. The applied chapters concentrate on environmental hazards and resources, and their management.

Hart, M.G.

1986-01-01

280

Low Temperature Cycling of Partially Oxidized Submicron Magnetites  

NASA Astrophysics Data System (ADS)

In nature, the oxidation of magnetite to maghemite is the most common oxide mineral alteration. Small deviations from stoichiometry, such as surface oxidation in magnetite, have a considerable effect on the Verwey transition. The present work studies the effect of partial oxidation on the Verwey transition temperature Tv of submicron magnetites with mean particle sizes of 40 nm to 210 nm. Samples were heated in air at 100, 150 and 200 C. Saturation isothermal remanent magnetization (SIRM) given to the oxidized nanoparticles by a 2.5 T field at 10 K decreased steadily during zero-field warming to 300 K, with little or no indication of the Verwey transition. After completing the thermal cycle by cooling in zero field to 10 K the stoichiometric magnetites, which had lost 70-90 percent of their SIRM in warming through Tv, recovered very little of their initial remanence. However, the partially oxidized magnetites, which had lost 30-60 percent of their SIRM in the warming half-cycle, recovered 50-90 percent of the initial remanence after cooling to 10 K. A complete set of zero-field cooling-warming cycles of SIRM produced at 300 K was also carried out. These curves have more structure in both cooling and warming and are more diagnostic of degree of oxidation than the usually measured warming curve of SIRM produced below Tv. The 300 K SIRM of stoichiometric magnetites decreases steadily with cooling to the isotropic point, with variable amounts of recovery in cooling through Tv. The oxidized magnetites behave quite differently: the SIRM at first increases in zero-field cooling from 300 K, then decreases as Tv is approached. The hump-like form of the zero-field warming curve above Tv is even more pronounced. With complete oxidation to maghemite and the disappearance of the Verwey transition, the 300 K SIRM increases monotonically throughout zero-field cooling from 300 to 10 K.

Ozdemir, O.

2009-05-01

281

Liquid crystal inorganic hybrid photorefractives  

Microsoft Academic Search

We report on the photorefractive properties of liquid crystals sandwiched between windows of cerium doped strontium barium niobate (Ce:SBN). This adaptable design has been used to create devices using pure nematic liquid crystals, ferroelectric nanoparticle doped liquid crystals, and cholesteric liquid crystals. In all these systems, modulation of the liquid crystal molecules is driven by the surface space-charge field from

G. Cook; A. V. Glushchenko; V. Yu. Reshetnyak; E. R. Beckel; M. A. Saleh; D. R. Evans

2008-01-01

282

Biogeochemical Conditions Favoring Magnetite Formation during Anaerobic Iron Reduction  

PubMed Central

Several anaerobic bacteria isolated from the sediments of Contrary Creek, an iron-rich environment, produced magnetite when cultured in combinations but not when cultured alone in synthetic iron oxyhydroxide medium. When glucose was added as a carbon source, the pH of the medium decreased (to 5.5) and no magnetite was formed. When the same growth medium without glucose was used, the pH increased (to 8.5) and magnetite was formed. In both cases, Fe2+ was released into the growth medium. Geochemical equilibrium equations with Eh and pH as master variables were solved for the concentrations of iron and inorganic carbon that were observed in the system. Magnetite was predicted to be the dominant iron oxide formed at high pHs, while free Fe2+ or siderite were the dominant forms of iron expected at low pHs. Thus, magnetite formation occurs because of microbial alteration of the local Eh and pH conditions, along with concurrent reduction of ferric iron (direct biological reduction or abiological oxidation-reduction reactions).

Bell, P. E.; Mills, A. L.; Herman, J. S.

1987-01-01

283

Observations of magnetite dissolution in poorly drained soils  

USGS Publications Warehouse

Dissolution of strongly magnetic minerals is a common and relatively rapid phenomenon in poorly drained soils of the central United States, resulting in low magnetic susceptibility (MS). Low Eh reducing conditions are primarily responsible for magnetic mineral dissolution; a process likely mediated by iron-reducing bacteria in the presence of soil organic matter. Based on transects across drainage sequences from nine sites, natural magnetic minerals (>5 ??m) extracted from surface soil consist of 54% ?? 18% magnetite, 21% ?? 11% titanomagnetite, and 17% ?? 14% ilmenite. Magnetite and titanomagnetite dissolution, assessed by scanning electron microscopy on a 0-to-3 scale, inversely correlates with surface soil MS (r = 0.53), a proxy for soil drainage at studied transects. Altered magnetite typically displays etch pits 5 ??m) include 26% ?? 18% anthropogenic fly ash that also exhibits greater dissolution in low MS soils (r = 0.38), indicating detectable alteration can occur within 150 years in low Eh soils. Laboratory induced reduction of magnetite, titanomagnetite, and magnetic fly ash, with a citrate-bicarbonate- dithionite solution, resulted in dissolution textures similar to those of in situ soil particles. Although experiments indicate that reductive dissolution of magnetite can occur abiotically under extreme conditions, bacteria likely play an important role in the natural environment. ?? 2007 Lippincott Williams & Wilkins, Inc.

Grimley, D. A.; Arruda, N. K.

2007-01-01

284

Magnetic Separations with Magnetite: Theory, Operation, and Limitations  

SciTech Connect

This dissertation documents the theory development and experimental plan followed to describe how a magnetite-based column under the influence of an external magnetic field functions as a magnetic separator. Theoretical simulations predict that weekly paramagnetic particles in the sub-micron range can be magnetically separated while diamagnetic particles as large as 2 microns in diameter may pass. Magnetite-based columns were evaluated as magnetically-controllable enhanced filtration devices. There was no evidence of enhanced filtration for diamagnetic particles by the magnetite-based bed. Magnetite-based magnetic separators have proven to be effective in specific laboratory experiments, indicating a potential feasibility for scale-up operations. Column media-filter type filtration effects indicate a magnetite-based column would not be suitable for treatment of a waste stream with a high diamagnetic solids content or high volume throughput requirements. Specific applications requiring removal of sub-micron para- or ferromagnetic particles under batch or Stokes flow conditions would be most applicable.

G. B. Cotten

2000-08-01

285

Reduction of iron by decarboxylation in the formation of magnetite nanoparticles.  

PubMed

The process of formation of magnetite nanoparticles has been investigated by liquid chromatography and mass spectroscopy in the liquid phase decomposition of either Fe(III) acetylacetonate with decanoic acid or Fe(III) decanoate. In both cases, the dissociation into radicals of the iron carboxylate bonds provides the reduction of the Fe(III) cations and the oxygen atoms required for the formation of the mixed-valence inverse spinel magnetite structure. A reaction mechanism is proposed. It is also shown that the reaction of free decanoic acid with the Fe(III) cations in solution promotes the growth of faceted particles at the reflux temperature of the solvent (ca. 280 °C), while, under the same conditions, the stepwise decomposition of the Fe(III) decanoate generates smaller and pseudo-spherical particles. The latter also yields faceted particles when the temperature is increased above that of the total decomposition of the salt. Magnetic measurements make evident that the reaction starting from Fe(III) acetylacetonate yields nanoparticles with higher magnetization and lower spin disorder, due to the improved regularity of the surface crystal structure. The starting conditions for the decarboxylation process thus affect the morphology and magnetic properties of the resulting nanoparticles. PMID:21960123

Pérez, Nicolás; López-Calahorra, Francisco; Labarta, Amílcar; Batlle, Xavier

2011-09-29

286

The MagA protein of Magnetospirilla is not involved in bacterial magnetite biomineralization.  

PubMed

Magnetotactic bacteria have the ability to orient along geomagnetic field lines based on the formation of magnetosomes, which are intracellular nanometer-sized, membrane-enclosed magnetic iron minerals. The formation of these unique bacterial organelles involves several processes, such as cytoplasmic membrane invagination and magnetosome vesicle formation, the accumulation of iron in the vesicles, and the crystallization of magnetite. Previous studies suggested that the magA gene encodes a magnetosome-directed ferrous iron transporter with a supposedly essential function for magnetosome formation in Magnetospirillum magneticum AMB-1 that may cause magnetite biomineralization if expressed in mammalian cells. However, more recent studies failed to detect the MagA protein among polypeptides associated with the magnetosome membrane and did not identify magA within the magnetosome island, a conserved genomic region that is essential for magnetosome formation in magnetotactic bacteria. This raised increasing doubts about the presumptive role of magA in bacterial magnetosome formation, which prompted us to reassess MagA function by targeted deletion in Magnetospirillum magneticum AMB-1 and Magnetospirillum gryphiswaldense MSR-1. Contrary to previous reports, magA mutants of both strains still were able to form wild-type-like magnetosomes and had no obvious growth defects. This unambiguously shows that magA is not involved in magnetosome formation in magnetotactic bacteria. PMID:22194451

Uebe, René; Henn, Verena; Schüler, Dirk

2011-12-22

287

The MagA Protein of Magnetospirilla Is Not Involved in Bacterial Magnetite Biomineralization  

PubMed Central

Magnetotactic bacteria have the ability to orient along geomagnetic field lines based on the formation of magnetosomes, which are intracellular nanometer-sized, membrane-enclosed magnetic iron minerals. The formation of these unique bacterial organelles involves several processes, such as cytoplasmic membrane invagination and magnetosome vesicle formation, the accumulation of iron in the vesicles, and the crystallization of magnetite. Previous studies suggested that the magA gene encodes a magnetosome-directed ferrous iron transporter with a supposedly essential function for magnetosome formation in Magnetospirillum magneticum AMB-1 that may cause magnetite biomineralization if expressed in mammalian cells. However, more recent studies failed to detect the MagA protein among polypeptides associated with the magnetosome membrane and did not identify magA within the magnetosome island, a conserved genomic region that is essential for magnetosome formation in magnetotactic bacteria. This raised increasing doubts about the presumptive role of magA in bacterial magnetosome formation, which prompted us to reassess MagA function by targeted deletion in Magnetospirillum magneticum AMB-1 and Magnetospirillum gryphiswaldense MSR-1. Contrary to previous reports, magA mutants of both strains still were able to form wild-type-like magnetosomes and had no obvious growth defects. This unambiguously shows that magA is not involved in magnetosome formation in magnetotactic bacteria.

Uebe, Rene; Henn, Verena

2012-01-01

288

Study of cerium doped magnetite (Fe3O4:Ce)/PMMA nanocomposites  

NASA Astrophysics Data System (ADS)

The paper presents the synthesis and properties of polymer nanocomposite material based on cerium doped magnetite (Fe3O4) as filler material and poly methyl methacrylate (PMMA) as host matrix. The magnetite (Fe3O4) particles were synthesized by co-precipitation route using stable ferrous and ferric salts with ammonium hydroxide as precipitating agent. Further, they doped by cerium oxide (CeO2) non-stoichiometrically. The composite material was fabricated by solvent evaporation method. Here 2.4 GHz microwaves were used to study the effect of microwaves heating on polymerization. The phase and crystal structure is determined by X-ray diffraction (XRD). The average crystallite size of the composites varies from 28 to 35 nm. The chemical structure is confirmed by Fourier transform infrared (FTIR) spectroscopy. The magnetic and thermal properties are investigated by vibrating sample magnetometer (VSM) and differential scanning calorimetry (DSC). The thermal study shows that the microwave heated samples possess higher glass transition temperature (Tg). The magnetic results suggest that coercivity (HC) and squareness (Mr/Ms) of the loop increases with increasing doping percent of cerium.

Padalia, Diwakar; Johri, U. C.; Zaidi, M. G. H.

2012-03-01

289

Magnetite-orthopyroxene symplectites in gabbros of the Urals: A structural track of olivine oxidation  

NASA Astrophysics Data System (ADS)

The chemical compositions of magnetite-orthopyroxene symplectites (MOS) and rock-forming minerals—olivine (Ol), clinopyroxene (Cpx), and magnetite(Mt)—have been studied in 20 samples of olivine-bearing rocks in the Urals, including troctolite, olivine gabbro, and gabbronorite. MOS are orthopyroxene (Opx) monocrystals up to 500 ?m in size containing myrmekite-like magnetite intergrowths up to 20-30 ?m in width. According to the microprobe examination, the dark-colored minerals are characterized by a high Fe mole fraction F = Fe/(Fe + Mg) = 0.20-0.50, whereas F = 0.33-0.65 is typical of the bulk rock compositions. The plagioclase varies in composition from An90 to An50. No significant compositional difference has been established between the MOS and rock-forming minerals. The F opx and F Ol are closely correlated (linear trend, r = 0.97); F Ol/ F Opx is ˜1.2. Similarly, a positive correlation between F Opx and F Cpx is noted (linear trend, r = 0.90); F Opx/ F Cpx is ˜1.2. The crystallization temperature of the Ol-Opx-Cpx assemblage is roughly estimated at 700-800°C. A high positive correlation ( r = 0.95) is established between the TiO2 contents in the magnetites from the MOS (Mt1) and host rock (Mt2). The Mt1/Mt2 ratio reaches ˜0.8, implying that Mt1 contains somewhat less TiO2 than Mt2. Hence, the rock-forming and MOS minerals make up an equilibrium assemblage. As follows from the structural pattern, symplectites were formed as products of the reaction between olivine and oxygen in the solid state with the entire volume of the rock involved in the oxidation; i.e., the distance of the diffusion was significant. Free oxygen appeared as a product of the dissociation of the water penetrating into the hot gabbro and ultramafic rocks at the initial stage of the tectonic extension and high-temperature hydration. According to the redox state of dunite coexisting with gabbro, the oxygen fugacity is estimated at +2.7 log units of fO2 relative to the QFM buffer. The structure and products of the olivine oxidation were eventually obliterated in the course of the hydration.

Efimov, A. A.; Malitch, K. N.

2012-12-01

290

Size selected synthesis of magnetite nanoparticles in chitosan matrix  

NASA Astrophysics Data System (ADS)

We report a new method to prepare magnetite nanoparticles with narrow size distribution and controlled particle size. Magnetite nanoparticles were prepared in the pores of the biopolymer chitosan. To develop pores with different sizes, chitosan was gelificated with several concentrations of the crosslinker glutaraldehyde. X-ray diffraction studies showed pattern characteristic for magnetite particles with diameters varying from 4 to 12.7 nm. Mössbauer spectra at room temperature showed only paramagnetic component for the smaller particles, and magnetic and paramagnetic components for the bigger particles, indicating the transition from superparamagnetic to blocked magnetic regime as the particle size increases. The zero field cooling (ZFC) magnetization measurements showed peak temperatures varying from 55 to 151.4 K. The ZFC peak temperatures showed a trend in agreement with the size of the particles. Considering the different experimental time window between Mössbauer spectroscopy and magnetometry, the results obtained from both techniques are in agreement.

Morales, Marco A.; de Souza Rodrigues, Eloise C.; de Amorim, Artur S. C. M.; Soares, João M.; Galembeck, Fernando

2013-06-01

291

Investigation of Electrically Driven Phase Transition in Magnetite Thin Films  

NASA Astrophysics Data System (ADS)

Magnetite, Fe3O4, is an example of strongly electronically correlated system. It undergoes so called Verwey transition at TV˜122 K accompanied both by structural distortion and drastic decrease in electrical conductivity, i.e. metal-insulator transition. Recently, we discovered a new electrically driven phase transition in magnetite nanoparticles and thin films. We observed that a low-temperature (T below TV) insulating state is broken upon applying an electric field, resulting in a sharp transition to the state with much higher conductivity. We report on further electrical characterization of this newly discovered state. There is a question whether this state is the same as high-temperature phase above TV or this is a new state of magnetite. In standard two-terminal measurement dominant contribution of contact resistance impedes intrinsic electrical properties. Thus, four-terminal configuration is necessary. Electrical and magnetoresistance properties are measured in challenging four-terminal geometry at nanoscale.

Fursina, Alexandra A.; Sumesh Sofin, R. G.; Shvets, Igor V.; Natelson, Douglas

2009-03-01

292

Novel High Pressure Magnetic Measurements With Application to Magnetite  

NASA Astrophysics Data System (ADS)

We report a novel system designed to measure reversible magnetic susceptibility of micron-sized samples under high pressures (in excess of 30 GPa) in a diamond anvil cell. We find that magnetite reversible hysteresis parameters vary <15% below 0.6 to 1.0 GPa, while at higher pressures significant increases occur in (1) bulk coercivity (Hc) and (2) the ratio of saturation remanent magnetization (Mrs) to saturation magnetization (Ms). The net effect of pressure is to displace magnetite toward a truer single domain state with both higher Mrs/Ms and Hc. Our data, together with the fact that the Curie temperature increases with pressure, suggest that magnetite can account for geomagnetic anomalies related to some subduction zones and potentially to meteorite impact sites on Earth, as well as magnetic signatures observed on some planetary bodies like Mars.

Gilder, S.; Legoff, M.; Peyronneau, J.; Chervin, J.

2002-12-01

293

Effects of ELF magnetic fields on biological magnetite  

SciTech Connect

The effects of 60 Hz magnetic fields of 5 [mu]T (50 mG) or less on biological structures holding magnetite (Fe[sub 3]0[sub 4]) are shown to be much smaller than that from thermal agitation; hence such interactions cannot be expected to be biologically significant. Various species have been shown to manufacture magnetite, which is used in some cases in conjunction with the earth's magnetic field to determine direction ([Frankel, 1986; Kirschvink and Kobayashi-Kirschvink, 1991].) This magnetite is usually found in sets of single domain grains, about 500[angstrom] in diameter, where all grains are magnetized in the same direction. Typically, such grains are enclosed by a membrane and are called magnetosomes. Hence, the possibility that weak ELF magnetic fields may cause biological effects in humans by the interaction of the field with magnetosomes must be considered.

Adair, R.K. (Yale Univ., New Haven, CT (United States))

1993-03-01

294

Simple and Rapid Synthesis of Magnetite/Hydroxyapatite Composites for Hyperthermia Treatments via a Mechanochemical Route.  

PubMed

This paper presents a simple method for the rapid synthesis of magnetite/hydroxyapatite composite particles. In this method, superparamagnetic magnetite nanoparticles are first synthesized by coprecipitation using ferrous chloride and ferric chloride. Immediately following the synthesis, carbonate-substituted (B-type) hydroxyapatite particles are mechanochemically synthesized by wet milling dicalcium phosphate dihydrate and calcium carbonate in a dispersed suspension of magnetite nanoparticles, during which the magnetite nanoparticles are incorporated into the hydroxyapatite matrix. We observed that the resultant magnetite/hydroxyapatite composites possessed a homogeneous dispersion of magnetite nanoparticles, characterized by an absence of large aggregates. When this material was subjected to an alternating magnetic field, the heat generated increased with increasing magnetite concentration. For a magnetite concentration of 30 mass%, a temperature increase greater than 20 K was achieved in less than 50 s. These results suggest that our composites exhibit good hyperthermia properties and are promising candidates for hyperthermia treatments. PMID:23629669

Iwasaki, Tomohiro; Nakatsuka, Ryo; Murase, Kenya; Takata, Hiroshige; Nakamura, Hideya; Watano, Satoru

2013-04-29

295

Simple and Rapid Synthesis of Magnetite/Hydroxyapatite Composites for Hyperthermia Treatments via a Mechanochemical Route  

PubMed Central

This paper presents a simple method for the rapid synthesis of magnetite/hydroxyapatite composite particles. In this method, superparamagnetic magnetite nanoparticles are first synthesized by coprecipitation using ferrous chloride and ferric chloride. Immediately following the synthesis, carbonate-substituted (B-type) hydroxyapatite particles are mechanochemically synthesized by wet milling dicalcium phosphate dihydrate and calcium carbonate in a dispersed suspension of magnetite nanoparticles, during which the magnetite nanoparticles are incorporated into the hydroxyapatite matrix. We observed that the resultant magnetite/hydroxyapatite composites possessed a homogeneous dispersion of magnetite nanoparticles, characterized by an absence of large aggregates. When this material was subjected to an alternating magnetic field, the heat generated increased with increasing magnetite concentration. For a magnetite concentration of 30 mass%, a temperature increase greater than 20 K was achieved in less than 50 s. These results suggest that our composites exhibit good hyperthermia properties and are promising candidates for hyperthermia treatments.

Iwasaki, Tomohiro; Nakatsuka, Ryo; Murase, Kenya; Takata, Hiroshige; Nakamura, Hideya; Watano, Satoru

2013-01-01

296

Synthesis of pure RDX  

SciTech Connect

For the bioremediation of explosives, there is the need for RDX uncontaminated by HMX. (In the Bachmann process, RDX always has residual HMX.) There are two methods for synthesizing pure RDX: one involving oxidation of R-salt, the other nitration of hexamine. Absence of HMX in the RDX samples was confirmed by NMR and melting points.

Pagoria, P.F.

1994-03-25

297

Synthesis, characterization and applications of magnetite nanoparticles  

Microsoft Academic Search

In the past few years, the synthesis of magnetic nanoparticles has received considerable attention due to their potential use in clinical applications. Since the properties of these nanoparticles depend strongly on their size, shape and crystallinity, there is a need for a general method to produce these particles with a controlled size, shape and crystal type. Of the many magnetic

Vikram Kumar Kanmukhla

2007-01-01

298

Magnetic field induced enhancement in thermal conductivity of magnetite nanofluid  

NASA Astrophysics Data System (ADS)

Magnetite nanofluid is synthesized using continuous chemical process. Powder x-ray diffraction and transmission electron microscopy show single phase spinel structure with size of 9.83 and 9.9 nm, respectively. Thermal conductivity of magnetite nanofluid has been studied as a function of transverse magnetic field and temperature. We found almost 30% enhancements in thermal conductivity for 4.7% volume fraction under transverse magnetic field. This result is explained on the basis of formation of continuous three-dimensional zipperlike structure of magnetic nanoparticles inside magnetic fluid. The temperature dependent thermal conductivity shows no enhancement in the temperature region of 25-65 °C.

Parekh, Kinnari; Lee, Hyo Sook

2010-05-01

299

Heat dissipation mechanism of magnetite nanoparticles in magnetic fluid hyperthermia  

NASA Astrophysics Data System (ADS)

The relative contributions of Néel and Brownian relaxations on magnetic heat dissipation were studied by investigating the physical, magnetic and heating characteristics of magnetite nanoparticle suspensions with average diameters of 12.5 and 15.7 nm. Heating characteristics depended on the dispersion states of particles. The specific absorption rates (SAR) dropped by 27% for the 12.5 nm particles to 16.8×10-9 W g-1 Oe-2 Hz-1 and by 67% for the 15.7 nm particles to 9.69×10-9 W g-1 Oe-2 Hz-1, when the particle rotation was suppressed by dispersing magnetite nanoparticles in hydro-gel.

Suto, Makoto; Hirota, Yasutake; Mamiya, Hiroaki; Fujita, Asaya; Kasuya, Ryo; Tohji, Kazuyuki; Jeyadevan, Balachandran

2009-05-01

300

Magnetite Nanoparticles Stabilized Under Physiological Conditions for Biomedical Application  

Microsoft Academic Search

The biomedical application of water based magnetic fluids (MFs) is of great practical importance.\\u000a Their colloidal stability under physiological conditions (blood pH???7.2–7.4 and\\u000a \\u000a salt concentration ?0.15??M) and more in high magnetic field gradient is crucial. Magnetite\\u000a or maghemite nanoparticles are used in general. In the present work, magnetite nanoparticles were stabilized\\u000a with different compounds (citric acid (CA) and phosphate) and

E. Tombácz; E. Illés; D. Bica; L. Vékás

2008-01-01

301

Spin moment over 10 300 K and delocalization of magnetic electrons above the Verwey transition in magnetite  

NASA Astrophysics Data System (ADS)

In order to probe the magnetic ground state, we have carried out temperature-dependent magnetic Compton scattering experiments on an oriented single crystal of magnetite (Fe3O4), together with the corresponding first-principles band theory computations to gain insight into the measurements. An accurate value of the magnetic moment ?S associated with unpaired spins is obtained directly over the temperature range of 10 300 K. ?S is found to be non-integral and to display an anomalous behavior with the direction of the external magnetic field near the Verwey transition. These results reveal how the magnetic properties enter the Verwey energy scale via spin orbit coupling and the geometrical frustration of the spinel structure, even though the Curie temperature of magnetite is in excess of 800 K. The anisotropy of the magnetic Compton profiles increases through the Verwey temperature Tv and indicates that magnetic electrons in the ground state of magnetite become delocalized on Fe B-sites above Tv.

Li, Yinwan; Montano, P. A.; Barbiellini, B.; Mijnarends, P. E.; Kaprzyk, S.; Bansil, A.

2007-08-01

302

Magnetic fabric development in a highly anisotropic magnetite-bearing ductile shear zone (Seve Nappe Complex, Scandinavian Caledonides)  

NASA Astrophysics Data System (ADS)

Magnetite-bearing mylonitic garnet-micaschists close to the major suture between the Baltica and Iapetus terranes (Seve Nappe Complex, Scandinavian Caledonides) show very high anisotropy of magnetic susceptibility (AMS) with corrected degree of anisotropy ( P') up to 4.8. Three different magnetic fabric types can be distinguished. They correspond to protomylonite (type I, P' < 2), mylonite (type II, 2 < P' < 3), and ultramylonite (type III, P' > 3), respectively. The orientation of the ellipsoid axes from all applied magnetic fabric methods in this study is similar with shallow dips of the metamorphic foliation toward WSW and subhorizontal, mostly NW-SE trending mineral lineation. Differences between subfabrics were minimized under high shear strain as all markers tend to align parallel with the shear plane. The very high anisotropies and mostly oblate ellipsoid shapes of type III correlate with high magnetic susceptibility ( k mean up to 55 × 10-3 SI units) and are related to the concentration of magnetite aggregates with shape-preferred orientation. They show a distinct field dependence of magnetic susceptibility of up to 10% in the k max-direction. We attribute this field dependence to a "memory" of high strains in the domain walls of the crystals acquired during synkinematic magnetite growth during shear zone fabric development at temperatures of 550-570°C.

Kontny, A.; Engelmann, R.; Grimmer, J. C.; Greiling, R. O.; Hirt, A.

2012-04-01

303

Diethylenetriamine Functionalized Silica Coated Magnetite Nanoparticles for Selective Palladium Ion Extraction from Aqueous Solutions  

Microsoft Academic Search

The extraction of Pd(II) over Cu(II) from aqueous solutions by diethylenetriamine functionalized silica particles with superparamagnetic nanosized magnetite core (FeSiDETA) was compared to that of bare magnetite and silica coated magnetite (FeSi). FeSiDETA was found to quantitatively and selectively (at pH <4) extract Pd(II) ions as compared to the magnetite and FeSi with a considerable improvement in material robustness with

Laura L. Vatta; Jurjen Kramer; Klaus R. Koch

2007-01-01

304

Pure nuclear reflexes and combined hyperfine interactions in YIG  

Microsoft Academic Search

Mössbauer spectra of oriented YIG single crystals were taken and the numerical analysis using the transmission integral yielded a consistent set of hyperfine interaction parameters. They are in good agreement with theoretical values obtained by MO-calculations which included clusters up to 62 ions. Finally pure nuclear reflexes are predicted for single crystals and two theoretical spectra are given.

H. Winkler; R. Eisberg; E. Alp; R. Rüffer; E. Gerdau; S. Lauer; A. X. Trautwein; M. Grodzicki; A. Vera

1983-01-01

305

Grain size limits for pseudosingle domain behavior in magnetite: Implications for paleomagnetism  

Microsoft Academic Search

A theoretical model of grain size dependence of domain transitions in magnetite is presented. This domain model is used to predict the grain size range for pseudosingle domain (PSD) behavior in magnetite. For cubic magnetite particles, the single domain (SD) to two-domain (TD) transition occurs at ?800 ± 200 Å, the TD-three-domain transition occurs at ? 1500 Å, and the

BRUCE M. MOSKOWITZ; SUBIR K. BANERJEE

1979-01-01

306

Two types of chemical remanent magnetization during the oxidation of magnetite  

Microsoft Academic Search

The chemical remanent magnetization (CRM), MCRM, resulting from oxidation of equidimensional magnetite to a mixture of 90% hematite and 10% cation-deficient magnetite is jointly controlled by the initial anhysteretic remanent magnetization, (MARM), of the parent magnetite and the field HCRM applied during oxidation. MCRM lies in the plane defined by HCRM and MARM (which were perpendicular in our experiments) in

Franz Heider; David J. Dunlop

1987-01-01

307

Magnetite as a Sintering Aid for Microwave Consolidation of Soda Lime Glass.  

National Technical Information Service (NTIS)

Magnetite, Fe3O4, is a strong absorber of microwave energy, which can be used to enhance heating in microwave transparent or low absorbing matrices. To examine the heat generation of magnetite for ultimate use in materials consolidation, magnetite was dis...

Y. H. Kao J. D. Mackenzie

1992-01-01

308

Ab initio Investigations of Fe2+/Fe3+ Bond Dimerization and Ferroelectricity Induced by Intermediate Site/Bond-Centered Charge Ordering in Magnetite  

NASA Astrophysics Data System (ADS)

Based on ab initio density functional calculations, we have investigated the validity of the recently proposed ``intermediate site/bond-centered charge ordering'' in insulating magnetite, Fe3O4. It is found that, although the Fe\\text{B2+/Fe\\text{B3+ bond dimerization along the monoclinic b direction leads to local electric dipole moments, the latter are arranged in an antiferroelectric fashion in the P2/c and Cc crystal structures. Our results, based on the generalized gradient approximation plus Hubbard U (GGA+U) and Berry phase methods, clearly indicate that for the P2/c crystal structure the Fe\\text{B2+/Fe\\text{B3+ bond dimerization and the local electric dipole moments are suppressed at large U values. This shows that local electric dipole moments in magnetite with the P2/c symmetry are induced by the ``intermediate site/bond-centered charge ordering''.

Fukushima, Tetsuya; Yamauchi, Kunihiko; Picozzi, Silvia

2011-01-01

309

Experimental evidence for non-redox transformations between magnetite and hematite under H-2-rich hydrothermal conditions.  

SciTech Connect

Transformations of magnetite (Fe{sup II}Fe{sub 2}{sup III}O{sub 4}) to hematite (Fe{sub 2}{sup III}O{sub 3}) (and vice versa) have been thought by many scientists and engineers to require molecular O{sub 2} and/or H{sub 2}. Thus, the presence of magnetite and/or hematite in rocks has been linked to a specific oxidation environment. However, the availability of reductants or oxidants in many geologic and industrial environments appears to have been too low to account for the transformations of iron oxides through redox reactions. Here, we report the results of hydrothermal experiments in mildly acidic and H{sub 2}-rich aqueous solutions at 150 C, which demonstrate that transformations of magnetite to hematite, and hematite to magnetite, occur rapidly without involving molecular O{sub 2} or H{sub 2}: Fe{sub 3}O{sub 4}(Mt) + 2H{sub (aq)}{sup +} {leftrightarrow} Fe{sub 2}O{sub 3}(Hm) + Fe{sub (aq)}{sup 2+} + H{sub 2}O. The transformation products are chemically and structurally homogeneous, and typically occur as euhedral single crystals much larger than the precursor minerals. This suggests that, in addition to the expected release of aqueous ferrous species to solution, the transformations involve release of aqueous ferric species from the precursor oxides to the solution, which reprecipitate without being reduced by H{sub 2}. These redox-independent transformations may have been responsible for the formation of some iron oxides in natural systems, such as high-grade hematite ores that developed from Banded Iron Formations (BIFs), hematite-rich deposits formed on Mars, corrosion products in power plants and other industrial systems.

Otake, Tsubasa [Pennsylvania State University; Wesolowski, David J [ORNL; Anovitz, Lawrence {Larry} M [ORNL

2007-05-01

310

Experimental Evidence for Non-Redox Transformation Between Magnetite and Hermatite Under H2-Rich Hydrothermal Conditions  

SciTech Connect

Transformations of magnetite (Fe{sup II}Fe{sub 2}{sup III}O{sub 4}) to hematite (Fe{sub 2}{sup III}O{sub 3}) (and vice versa) have been thought by many scientists and engineers to require molecular O{sub 2} and/or H{sub 2}. Thus, the presence of magnetite and/or hematite in rocks has been linked to a specific oxidation environment. However, the availability of reductants or oxidants in many geologic and industrial environments appears to have been too low to account for the transformations of iron oxides through redox reactions. Here, we report the results of hydrothermal experiments in mildly acidic and H{sub 2}-rich aqueous solutions at 150 C, which demonstrate that transformations of magnetite to hematite, and hematite to magnetite, occur rapidly without involving molecular O{sub 2} or H{sub 2}: Fe{sub 3}O{sub 4}(Mt) + 2H{sub (aq)}{sup +} {leftrightarrow} Fe{sub 2}O{sub 3}(Hm) + Fe{sub (aq)}{sup 2+} + H{sub 2}O The transformation products are chemically and structurally homogeneous, and typically occur as euhedral single crystals much larger than the precursor minerals. This suggests that, in addition to the expected release of aqueous ferrous species to solution, the transformations involve release of aqueous ferric species from the precursor oxides to the solution, which reprecipitate without being reduced by H{sub 2}. These redox-independent transformations may have been responsible for the formation of some iron oxides in natural systems, such as high-grade hematite ores that developed from Banded Iron Formations (BIFs), hematite-rich deposits formed on Mars, corrosion products in power plants and other industrial systems.

Otake, Tsubasa [Pennsylvania State University; Ohmoto, Hiroshi [Pennsylvania State University; Wesolowski, David J [ORNL; Anovitz, Lawrence {Larry} M [ORNL; Allard Jr, Lawrence Frederick [ORNL

2007-01-01

311

Relaxor ferroelectricity and the freezing of short-range polar order in magnetite  

NASA Astrophysics Data System (ADS)

A thorough investigation of single-crystalline magnetite using broadband dielectric spectroscopy and other methods provides evidence for relaxorlike polar order in Fe3O4. We find long-range ferroelectric order to be impeded by the continuous freezing of polar degrees of freedom and the formation of a tunneling-dominated glasslike state at low temperatures. This also explains the lack of clear evidence for a noncentrosymmetric crystal structure below the Verwey transition. Within the framework of recent models assuming an intimate relation of charge and polar order, the charge order, too, can be speculated to be of short-range type only and to be dominated by tunneling at low temperatures.

Schrettle, F.; Krohns, S.; Lunkenheimer, P.; Brabers, V. A. M.; Loidl, A.

2011-05-01

312

Purely Cortical Anaplastic Ependymoma  

PubMed Central

Ependymomas are glial tumors derived from ependymal cells lining the ventricles and the central canal of the spinal cord. It may occur outside the ventricular structures, representing the extraventicular form, or without any relationship of ventricular system, called ectopic ependymona. Less than fifteen cases of ectopic ependymomas were reported and less than five were anaplastic. We report a rare case of pure cortical ectopic anaplastic ependymoma.

Romero, Flavio Ramalho; Zanini, Marco Antonio; Ducati, Luis Gustavo; Vital, Roberto Bezerra; de Lima Neto, Newton Moreira; Gabarra, Roberto Colichio

2012-01-01

313

Glucose oxidase–magnetite nanoparticle bioconjugate for glucose sensing  

Microsoft Academic Search

Immobilization of bioactive molecules on the surface of magnetic nanoparticles is of great interest, because the magnetic properties of these bioconjugates promise to greatly improve the delivery and recovery of biomolecules in biomedical applications. Here we present the preparation and functionalization of magnetite (Fe 3O 4) nanoparticles 20 nm in diameter and the successful covalent conjugation of the enzyme glucose oxidase

Liane M. Rossi; Ashley D. Quach; Zeev Rosenzweig

2004-01-01

314

Superparamagnetic and Single-Domain Threshold Sizes in Magnetite  

Microsoft Academic Search

Particle size distributions have been obtained by grain counts on electron micrographs of four samples containing submicroscopic equant magnetite particles. Blocking temperature data indicate thermally unstable (superparamagnetic, SPM) magnetic behavior in one sample whose grains range from 100 to 650 A in size. The SPM is confirmed by a large increase of saturation remshence when the hysteresis of the sample

D. J. Dunlop

1973-01-01

315

Physical limits of hyperthermia using magnetite fine particles  

Microsoft Academic Search

Structural and magnetic properties of fine particles of magnetite are investigated with respect to the application for hyperthermia. Magnetic hysteresis losses are measured in dependence on the field amplitude for selected commercial powders and are discussed in terms of grain size and structure of the particles. For ferromagnetic powders as well as for ferrofluids, results of heating experiments within organic

Rudolf Hergt; Wilfried Andra; Carl G. d'Ambly; Ingrid Hilger; Werner A. Kaiser; Uwe Richter; Hans-Georg Schmidt

1998-01-01

316

Interacting Single-Domain Properties of Magnetite Intergrowths  

Microsoft Academic Search

experimentally under nondemagnetizing conditions is found to be 0.51. The reduction is shown to be entirely explicable in terms of localized array demagnetizing fields arising from surface poles. A similar effect is seen in magnetite\\/ulvospinei intergrowths. Qualitative evidence that this reduction proceeds mainly by rotation of the spontaneous magnetization from easy axes is seen in a measured anisotropy of low

P. M. Davis; M. E. Evans

1976-01-01

317

Synthesis of magnetite nanoparticles by high energy ball milling  

NASA Astrophysics Data System (ADS)

We report on the preparation of magnetite nanoparticles, with size ranging from 12 nm to 20 nm, by high energy ball milling. The synthesis is made using stoichiometric amounts of distilled water and metallic iron powder. The milled powder samples were analyzed by Mossbauer spectroscopy (MS), X-ray diffraction (XRD) and vibrating sample magnetometry (VSM). Our results indicate that the milling time is a key parameter of the synthesis. By increasing the milling time one achieves high purity magnetite samples. Also, the particle size decreases with the milling time. The sample milled during 10 h contained a fraction of 56 nm metallic Fe particles and 20 nm magnetite particles. By increasing the milling time to 96 h we have obtained a sample that is mainly composed of 12 nm magnetite particles. MS performed at room temperature showed a spectrum consisting of two sextets with hyperfine parameters related to iron ions occupying octahedral (A) and tetrahedral (B) sites. We have used a self-consistent method to investigate the impact of the dipolar interaction to drive the system to a magnetically blocked regime.

de Carvalho, J. F.; de Medeiros, S. N.; Morales, M. A.; Dantas, A. L.; Carriço, A. S.

2013-06-01

318

Optimization of magnetite carrier precipitation process for transuranic waste reduction  

SciTech Connect

Transuranic (TRU) waste that is being generated at Argonne National Laboratory has a TRU activity ranging from 10{sup 2} to 10{sup 7} nCi/g with a wide variety of chemical compositions. Currently, the waste is stored in highly acidic solutions that must be neutralized for intermediate storage. A magnetite carrier precipitation process has been adapted to concentrate TRU isotopes in a noncorrosive solid phase. In this paper, the authors report the results of a series of laboratory tests done to optimize the process. The parameters they optimized included (1) magnetite concentration used to precipitate the TRUs from solution, (2) formation of magnetite (in situ or ex situ), (3) processing pH, and (4) temperature and mixing time of the carrier precipitation. They also studied the effects of anions, cations, and complexing agents in the waste solutions on the carrier precipitation and the effect of magnetite solids loading on the filtration equipment. An overview is given of the planned full-scale process, which will be operated in a glovebox.

Slater, S.A.; Chamberlain, D.B.; Aase, S.A.; Babcock, B.D.; Conner, C.; Sedlet, J.; Vandegrift, G.F. [Argonne National Lab., IL (United States). Chemical Technology Div.

1995-12-31

319

Electrosorption and reduction of pertechnetate by anodically polarized magnetite  

Microsoft Academic Search

The radionuclide technetium is a common surface and groundwater contaminant at many nuclear fuels processing facilities. This research investigated a new method for removing pertechnetate from contaminated waters based on the low aqueous solubility of reduced technetium species. The removal method involved electrostatic adsorption of pertechnetate at an anodically polarized magnetite electrode, followed by reduction of the adsorbed Tc(VII). This

James Farrell; William D. Bostick; Robert J. Jarabek; Joseph N. Fiedor

1999-01-01

320

One-step wet chemistry for preparation of magnetite nanorods  

Microsoft Academic Search

A magnetite with high aspect ratio has been synthesized by a wet chemical process. A surfactant, polyethylene glycol, was used as the template, and a ferrous ammonia sulphate was used as iron source. In the one-step synthesis, a suitable ratio between the rates of deposition and oxidation of ferrous ions was achieved by adjusting the diffusion of ammonia and resulted

Shuyi Chen; Jian Feng; Xuefeng Guo; Jianming Hong; Weiping Ding

2005-01-01

321

SEPARATION OF TECHNETIUM FROM AQUEOUS SOLUTIONS BY COPRECIPITATION WITH MAGNETITE  

DOEpatents

A method of separating technetium in the 4+ oxidation state from an aqueous basic solution containing products of uranium fission is described. The method consists of contacting the solution with finely divided magnetite and recovering a technetium-bearing precipitate. (AEC)

Rimshaw, S.J.

1961-10-24

322

Avian magnetite-based magnetoreception: a physiologist's perspective  

PubMed Central

It is now well established that animals use the Earth's magnetic field to perform long-distance migration and other navigational tasks. However, the transduction mechanisms that allow the conversion of magnetic field variations into an electric signal by specialized sensory cells remain largely unknown. Among the species that have been shown to sense Earth-strength magnetic fields, birds have been a model of choice since behavioural tests show that their direction-finding abilities are strongly influenced by magnetic fields. Magnetite, a ferromagnetic mineral, has been found in a wide range of organisms, from bacteria to vertebrates. In birds, both superparamagnetic (SPM) and single-domain magnetite have been found to be associated with the trigeminal nerve. Electrophysiological recordings from cells in the trigeminal ganglion have shown an increase in action potential firing in response to magnetic field changes. More recently, histological evidence has demonstrated the presence of SPM magnetite in the subcutis of the pigeon's upper beak. The aims of the present review are to review the evidence for a magnetite-based mechanism in birds and to introduce physiological concepts in order to refine the proposed models.

Cadiou, Herve; McNaughton, Peter A.

2010-01-01

323

Identification and significance of magnetite in human tissues.  

PubMed

Magnetite or iron oxide has been identified in humans as well as certain animals and bacteria. With the current popularity of magnetic resonance imaging, the presence of these ferromagnetic particles in the tissues may impose biological significance. So far, identification of magnetite in tissue has been mainly based on magnetometry. Hence, a simple technique for direct identification of the magnetic particles in tissues is described. Lung tissues with abundant iron material and particles were digested in 1N sodium hydroxide solution. After rinsing, the sediments were suspended in 95% alcohol and placed on a glass slide located on a strong magnet. The iron-containing particles from the digestion procedure were aligned in a parallel manner along the north-south poles of the magnet and were confirmed to be magnetite by x-ray diffraction. No such effect was observed with hemosiderin-containing granules from the control liver tissues. The results of this experiment show that the "biological magnetite" is distinctly different from hemosiderin and has characteristic properties when subjected to a magnetic field. PMID:3755025

Moatamed, F; Johnson, F B

1986-07-01

324

In situ synthesis of magnetite nanoparticles in carrageenan gels.  

PubMed

Magnetite nanoparticles have been successfully synthesized in the presence of carrageenan polysaccharides using an in situ coprecipitation method. Iron coordination to the sulfate groups of the polysaccharide was confirmed by FTIR. The polysaccharide type (kappa, iota, or lambda) and concentration have been varied and their effects on particle morphology and chemical stability of the resultant nanocomposite investigated. The presence of carrageenan induces the formation of smaller particles, compared to those formed in the absence of polymer, and their average size depends on the nature and concentration of the polysaccharide used. The chemical stability of magnetite nanoparticles toward oxidation was also seen to depend on biopolymer type with magnetite formed in iota-carrageenan showing the highest chemical stability. A general tendency toward lower stability is observed as the polysaccharide concentration is increased. It is suggested that magnetite chemical stability in the carrageenan composites is determined by a fine balance between particle size and gel strength, the latter determining oxygen diffusion rates through the medium. PMID:17625907

Daniel-da-Silva, Ana L; Trindade, T; Goodfellow, Brian J; Costa, Benilde F O; Correia, Rui N; Gil, Ana M

2007-07-11

325

Carbide-magnetite assemblages in type-3 ordinary chondrites  

NASA Astrophysics Data System (ADS)

Abundant carbide-magnetite assemblages occur in matrix, chondrules, and chondrule rims in several H3, L3, and LL3 chondrites. Carbides, cohenite ((Fe,Ni)3C), and haxonite ((Fe,Ni)23C6) show compositional variations between different meteorites and appreciable ranges within meteorites. Carbides in H chondrites have lower Co contents (0 0.6 wt%) than those in L and LL chondrites (0.3 1.2 wt%). Metal associated with carbides and magnetite consists of high-Ni (50 70 wt%) taenite and, in L and LL chondrites, Co-rich (up to 35 wt%) kamacite; minor element contents of troilite and magnetite are very low. Textural observations indicate that carbide-magnetite assemblages formed by replacement of metal-sulfide nodules. The high Co contents of residual kamacite in association with carbides indicates that Co is not incorporated into carbides (i.e., Fe/Co is much higher in the carbides than in kamacite). Because Ni in carbides and magnetite is low, the Ni contents of residual taenite tend to be high. Ni-rich sulfides were found only in LL3 chondrites, possibly indicating their more extensive oxidation and/or aqueous alteration. We suggest that carbide-magnetite assemblages in type-3 ordinary chondrites formed as the result of hydrothermal alteration of metallic Fe in metal-troilite nodules by a COH-bearing fluid on their parent bodies. This alteration resulted in carbidization of FeNi metal, probably by CO gas (e.g., 15 Fe(s) + 4 CO(g) = Fe3C(s) + Fe3O4(s) or 3 Fe(s) + 2 CO(g) = Fe3C(s) + CO2(g)), and oxidation, probably by H2O gas (e.g., 3Fe(s) + 4H2O(g) = Fe3O4(S) + 4H2(g)). The COH-bearing fluids, which were possibly released during metamorphism and transported through zones of high permeability, may have been derived from ices, adsorbed gases, or hydrated minerals. The CO may be the result of the reaction of carbon compounds (e.g., hydrocarbons) with water vapor or magnetite.

Krot, Alexander N.; Zolensky, Michael E.; Wasson, John T.; Scott, Edward R. D.; Keil, Klaus; Ohsumi, Kazumasa

1997-01-01

326

Arsenic removal from aqueous solutions by mixed magnetite–maghemite nanoparticles  

Microsoft Academic Search

In this study, magnetite–maghemite nanoparticles were used to treat arsenic-contaminated water. X-ray photoelectron spectroscopy\\u000a (XPS) studies showed the presence of arsenic on the surface of magnetite–maghemite nanoparticles. Theoretical multiplet analysis\\u000a of the magnetite–maghemite mixture (Fe3O4-?Fe2O3) reported 30.8% of maghemite and 69.2% of magnetite. The results show that redox reaction occurred on magnetite–maghemite\\u000a mixture surface when arsenic was introduced. The study

Saidur Rahman Chowdhury; Ernest K. Yanful; Allen R. Pratt

327

Cytochrome cd1 nitrite reductase NirS is involved in anaerobic magnetite biomineralization in Magnetospirillum gryphiswaldense and requires NirN for proper d1 heme assembly.  

PubMed

The alphaproteobacterium Magnetospirillum gryphiswaldense synthesizes magnetosomes, which are membrane-enveloped crystals of magnetite. Here we show that nitrite reduction is involved in redox control during anaerobic biomineralization of the mixed-valence iron oxide magnetite. The cytochrome cd1-type nitrite reductase NirS shares conspicuous sequence similarity with NirN, which is also encoded within a larger nir cluster. Deletion of any one of these two nir genes resulted in impaired growth and smaller, fewer, and aberrantly shaped magnetite crystals during nitrate reduction. However, whereas nitrite reduction was completely abolished in the ?nirS mutant, attenuated but significant nitrite reduction occurred in the ?nirN mutant, indicating that only NirS is a nitrite reductase in M. gryphiswaldense. However, the ?nirN mutant produced a different form of periplasmic d(1) heme that was not noncovalently bound to NirS, indicating that NirN is required for full reductase activity by maintaining a proper form of d1 heme for holo-cytochrome cd(1) assembly. In conclusion, we assign for the first time a physiological function to NirN and demonstrate that effective nitrite reduction is required for biomineralization of wild-type crystals, probably by contributing to oxidation of ferrous iron under oxygen-limited conditions. PMID:23893106

Li, Yingjie; Bali, Shilpa; Borg, Sarah; Katzmann, Emanuel; Ferguson, Stuart J; Schüler, Dirk

2013-07-26

328

Intensified magneto-resistance by rapid thermal annealing in magnetite (Fe3O4) thin film on SiO2 glass substrate  

NASA Astrophysics Data System (ADS)

We have observed large magneto-resistance (MR) intensified by rapid thermal annealing (RTA) in magnetite (Fe3O4) thin film (MTF) on SiO2 glass (a-SiO2) substrate. The MTF was produced by the RF magnetron sputtering method by using a magnetite target. The electrical resistivity (ER) of as-grown MTF (AG-MTF) showed the Mott's variable range hopping behavior, which implies that the AG-MTF is amorphous-like. Although the magneto-resistance (MR) ratio of bulk single crystal is very small except around the Verwey transition temperature (VTT), that of the AG-MTF showed moderately large below room temperature. Due to RTA of the AG-MTF by use of an IR image furnace, the MR ratio of MTFs was intensified, and especially by the annealing around the Curie temperature (585°C) of magnetite. Furthermore the ER of the rapid thermally annealed MTF (RTA-MTF) showed a slight kink at around the VTT, which indicates that the crystallinity of the RTA-MTF is higher than that of the AG-MTF The MTF produced by the RF magnetron sputtering method are composed of magnetite fine particles (MFPs). We consider that the directions of magnetic moments of MFPs in the MTF were spatially randomized by the RTA and the strong spin scattering of itinerant electrons transferring between adjacent MFPs caused the intensification of the MR ratio.

Kobori, H.; Morii, K.; Yamasaki, A.; Sugimura, A.; Taniguchi, T.; Horie, T.; Naitoh, Y.; Shimizu, T.

2012-12-01

329

FeII induced mineralogical transformations of ferric oxyhydroxides into magnetite of variable stoichiometry and morphology  

NASA Astrophysics Data System (ADS)

The Mössbauer spectroscopy was used to monitor the mineralogical transformations of ferrihydrite (F), lepidocrocite (L) and goethite (G) into magnetite as a function of aging time. Ferric oxyhydroxides were reacted with soluble FeII and OH- in stoichiometric amounts to form magnetite at an initial pH of ˜9.7. Observed transformation extent into magnetite followed the order: F>L>G with almost 30% of untransformed G after 1 month. The departure from stoichiometry, ?, of magnetite (Fe3-?O4) generated from F (?˜0.04) and L (?˜0.05) was relatively low as compared to that in magnetite from G (?˜0.08). The analysis by transmission electron microscopy and BET revealed that generated magnetite was also different in terms of morphology, particle size and surface area depending on the nature of initial ferric oxyhydroxide. This method of preparation is a possible way to form nano-sized magnetite.

Usman, M.; Abdelmoula, M.; Hanna, K.; Grégoire, B.; Faure, P.; Ruby, C.

2012-10-01

330

Pressure effect on the low-temperature remanences of multidomain magnetite: Change in the Verwey transition temperature  

NASA Astrophysics Data System (ADS)

The Verwey transition of magnetite is the basic issues for the rock magnetism, since main magnetic mineral of terrestrial rocks is magnetite and its associates. One of the most important issues concerning the Verwey transition is the change in transition temperature (Tv) due to pressure, which is thought to improve our understanding of its electric and magnetic nature in relation to the phase diagram. Recently, the opposite pressure effects of the transition temperature were reported applying the different experimental method. Measuring the electrical resistivity of single crystalline samples, Môri et al. [2002] reported that Tv becomes lower with increasing pressure by 9 GPa. In contrast, Pasternak et al. [2003] reported from Mössbauer experiment that transition temperature becomes higher with increasing pressure by 30 GPa. Thus the change in transition temperature with pressure has been controversial, and nature of the Verwey transition is still unclear. The magnetic property measurements using low temperature cycle are a powerful tool for identifying the state of magnetic minerals. Carporzen and Gilder [2010] conducted the thermal demagnetization experiment of low-temperature remanences of magnetite, and observed an increase in Tv with increasing pretreated pressure. From this result, they suggested that the Verwey transition of magnetite have the potential of a geobarometer. Modern techniques of high-pressure experiments enable us to measure sample magnetizations under pressure [Gilder et al., 2002; Kodama and Nishioka, 2005; Sadykov et al., 2008]. In the present study, systematic experiments of low-temperature remanences have been conducted for powder samples of stoichiometric magnetite under pressure up to 0.7 GPa using the high-pressure cell specially designed for MPMS, which was made of CuBe and ZrO2 [Kodama and Nishioka, 2005]. Natural magnetite of large single crystals were crushed by hand and sieved in an ultrasonic bath to be ~50 ?m in size. For relaxation of internal stress, powder samples were annealed in vacuum at 700 C with carbon buffer for several hours. The magnetite powders were dispersed in the glass wool and it was then placed in a Teflon capsule, which was filled by a pressure transmitting fluid. The high-pressure cell was connected with the end of the sample rod of MPMS and measured in a regular manner. We precisely measured thermal demagnetization curves of low-temperature isothermal remanent magnetization imparted at 20 K after cooling in zero-field and remanence acquired by cooling in 2.5 T DC field. The magnetite samples showed decrease in Tv under high-pressure, although decompressed samples exhibited the increase in Tv. Negative Clapeyron slope of the transition boundary is calculated to be -2.5 K/GPa to -4.0 K/GPa, supporting the results obtained by recent electrical resistivity measurement [Môri et al., 2002] and magnetic susceptibility measurement [Wieche? et al., 2005]. Decompressed samples also showed similar results obtained by thermal demagnetization experiment of low-temperature remanences [Carporzen and Gilder, 2010].

Sato, M.; Yamamoto, Y.; Nishioka, T.; Kodama, K.; Mochizuki, N.; Tsunakawa, H.

2011-12-01

331

Magnetite-based Magnetoreception in Animals: 25+ Years of Theory & Experimentation  

NASA Astrophysics Data System (ADS)

Living organisms ranging from bacteria through higher vertebrates rely on orientation, navigation, and homing to survive. Any sensory cue that enhances these behaviors will be subject to intense natural selection over geological time. Reproducible behavioral responses to earth-strength magnetic fields(1) have been documented in Bacteria, Protoctists, and in nearly every major group of animals, and are possibly also present in the Archaea. Several groups of animals, including birds and cetaceans, respond behaviorally to magnetic anomalies below 100 nT in magnitude, implying that their magnetoreception ability approaches the thermal noise limit. This approach to thermal noise is commonly observed in other sensory systems, including hearing, olfaction, and electroreception. The hypothesis of magnetite-based magnetoreception(2) is the only theory proposed so far that is capable of explaining all of the magnetic behavioral data. Tiny crystals of single-domain magnetite (or in some bacteria, greigite) rotate the cells of microorganisms passively like a simple compass needle. The initial detection of biogenic magnetite with rock magnetic techniques in birds and bees over 25 years ago has led progressively to the identification of a group of specialized cells in fish and birds which contain organized magnetite-containing structures. In these animals (and presumably all vertebrates) magnetic signals are transmitted to the brain via the ophthalmic branch of the trigeminal nerve(3, 4). Experiments with pulse-remagnetization, like those that convert North-seeking bacteria into South-seekers, have dramatic effects on animal behavior, confirming the role of magnetite in the sensory system. This is therefore a general mechanism for a highly sensitive magnetic sense, the origin of which probably dates to the ancestral metazoan, and perhaps earlier. The largest debate presently occurring in the field concerns the interpretation of magnetic compass responses that vary with intensity and color of light. Some biologists interpret the tendency of birds and amphibians to orient randomly under red lights, but not under shorter wavelengths, as evidence for the existence of a separate compass receptor involving light. However, even some magnetotactic bacteria change their behavior in red light,(5) and all such effects reported to date in animals can be explained simply as a visual influence on an animal's choice of behavior. Although the light-dependent mechanism might be physically plausible for a compass (but not for a high-resolution magnetic), natural selection cannot develop it without a separation from the visual system (exaptation), for which there is no evidence. 1. R. Wiltschko, W. Wiltschko, Magnetic orientation in animals, Zoophysiology (Springer, Berlin, 1995), pp. 297. 2. J. L. Kirschvink, Ph.D. Thesis, Princeton University (1979). 3. J. L. Kirschvink, M. M. Walker, C. Deibel, Current Opinion in Neurobiology 11, 462 (2001). 4. M. M. Walker, T. E. Dennis, J. L. Kirschvink, Current Opinion in Neurobiology 12, 735 (Dec, 2002). 5. R. B. Frankel, D. A. Bazylinski, M. S. Johnson, B. L. Taylor, Biophysical Journal 73, 994 (1997).

Kirschvink, J. L.; Walker, M. M.

2005-12-01

332

Identification of simultaneous U(VI) sorption complexes and U(IV) nanoprecipitates on the magnetite (111) surface.  

PubMed

Sequestration of uranium (U) by magnetite is a potentially important sink for U in natural and contaminated environments. However, molecular-scale controls that favor U(VI) uptake including both adsorption of U(VI) and reduction to U(IV) by magnetite remain poorly understood, in particular, the role of U(VI)-CO(3)-Ca complexes in inhibiting U(VI) reduction. To investigate U uptake pathways on magnetite as a function of U(VI) aqueous speciation, we performed batch sorption experiments on (111) surfaces of natural single crystals under a range of solution conditions (pH 5 and 10; 0.1 mM U(VI); 1 mM NaNO(3); and with or without 0.5 mM CO(3) and 0.1 mM Ca) and characterized surface-associated U using grazing incidence extended X-ray absorption fine structure spectroscopy (GI-EXAFS), grazing incidence X-ray diffraction (GI-XRD), and scanning electron microscopy (SEM). In the absence of both carbonate ([CO(3)](T), denoted here as CO(3)) and calcium (Ca), or in the presence of CO(3) only, coexisting adsorption of U(VI) surface species and reduction to U(IV) occurs at both pH 5 and 10. In the presence of both Ca and CO(3), only U(VI) adsorption (VI) occurs. When U reduction occurs, nanoparticulate UO(2) forms only within and adjacent to surface microtopographic features such as crystal boundaries and cracks. This result suggests that U reduction is limited to defect-rich surface regions. Further, at both pH 5 and 10 in the presence of both CO(3) and Ca, U(VI)-CO(3)-Ca ternary surface species develop and U reduction is inhibited. These findings extend the range of conditions under which U(VI)-CO(3)-Ca complexes inhibit U reduction. PMID:22364181

Singer, David M; Chatman, Shawn M; Ilton, Eugene S; Rosso, Kevin M; Banfield, Jillian F; Waychunas, Glenn A

2012-03-14

333

Haemorrhagic pure motor stroke.  

PubMed

To describe the clinical characteristics of haemorrhagic pure motor stroke (PMS). Twelve patients with haemorrhagic PMS were identified. Haemorrhagic PMS accounted for 3.2% of all cases of pure motor hemiparesis (n = 380) and 3.3% of intracerebral haemorrhage (n = 364) entered in the database. When compared with PMS of ischaemic origin, patients with haemorrhagic PMS were more likely to be younger (62.2 vs. 75.2 years, P = 0.003) and to have headache (33% vs. 6.3%, P =0.007) and thalamus involvement (25% vs. 2.4%, P = 0.005). Limb weakness (100% vs. 74.1%; P = 0.03), involvement of the internal capsule (50% vs. 17.3%, P = 0.012) and symptom free at discharge (25% vs. 3.7%, P = 0.012) were significantly more frequent in patients with haemorrhagic PMS than in the remaining cases of haemorrhagic stroke, whereas nausea and vomiting (0% vs. 25.9%, P = 0.03), altered consciousness (0% vs. 42.9%, P = 0.001), sensory symptoms (8.3% vs. 46.9%, P =0.007) and ventricular haemorrhage (0% vs. 26.1%, P = 0.028) were significantly less frequent. Haemorrhagic PMS is a very infrequent stroke subtype. Headache at stroke onset may be useful sign for distinguishing haemorrhagic PMS from other causes of lacunar stroke. There are important differences between haemorrhagic PMS and the remaining intracerebral haemorrhages. PMID:17250733

Arboix, A; García-Eroles, L; Massons, J; Oliveres, M; Balcells, M

2007-02-01

334

The cation diffusion facilitator proteins MamB and MamM of Magnetospirillum gryphiswaldense have distinct and complex functions, and are involved in magnetite biomineralization and magnetosome membrane assembly.  

PubMed

Magnetotactic bacteria form chains of intracellular membrane-enclosed, nanometre-sized magnetite crystals for navigation along the earth's magnetic field. The assembly of these prokaryotic organelles requires several specific polypeptides. Among the most abundant proteins associated with the magnetosome membrane of Magnetospirillum gryphiswaldense are MamB and MamM, which were implicated in magnetosomal iron transport because of their similarity to the cation diffusion facilitator family. Here we demonstrate that MamB and MamM are multifunctional proteins involved in several steps of magnetosome formation. Whereas both proteins were essential for magnetite biomineralization, only deletion of mamB resulted in loss of magnetosome membrane vesicles. MamB stability depended on the presence of MamM by formation of a heterodimer complex. In addition, MamB was found to interact with several other proteins including the PDZ1 domain of MamE. Whereas any genetic modification of MamB resulted in loss of function, site-specific mutagenesis within MamM lead to increased formation of polycrystalline magnetite particles. A single amino acid substitution within MamM resulted in crystals consisting of haematite, which coexisted with magnetite crystals. Together our data indicate that MamM and MamB have complex functions, and are involved in the control of different key steps of magnetosome formation, which are linked by their direct interaction. PMID:22007638

Uebe, René; Junge, Katja; Henn, Verena; Poxleitner, Gabriele; Katzmann, Emanuel; Plitzko, Jürgen M; Zarivach, Raz; Kasama, Takeshi; Wanner, Gerhard; Pósfai, Mihály; Böttger, Lars; Matzanke, Berthold; Schüler, Dirk

2011-10-18

335

Pure delta-oriented programming  

Microsoft Academic Search

Delta-oriented programming (DOP) is a modular approach for implementing software product lines. Delta modules generalize feature modules by allowing removal of functionality. However, DOP requires to select one particular product as core product from which all products are generated. In this paper, we propose pure delta-oriented programming (Pure DOP) that is a conceptual simplification of traditional DOP. In Pure DOP,

Ina Schaefer; Ferruccio Damiani

2010-01-01

336

Pure parsimony xor haplotyping.  

PubMed

The haplotype resolution from xor-genotype data has been recently formulated as a new model for genetic studies. The xor-genotype data is a cheaply obtainable type of data distinguishing heterozygous from homozygous sites without identifying the homozygous alleles. In this paper, we propose a formulation based on a well-known model used in haplotype inference: pure parsimony. We exhibit exact solutions of the problem by providing polynomial time algorithms for some restricted cases and a fixed-parameter algorithm for the general case. These results are based on some interesting combinatorial properties of a graph representation of the solutions. Furthermore, we show that the problem has a polynomial time k-approximation, where k is the maximum number of xor-genotypes containing a given single nucleotide polymorphisms (SNP). Finally, we propose a heuristic and produce an experimental analysis showing that it scales to real-world large instances taken from the HapMap project. PMID:20498511

Bonizzoni, Paola; Della Vedova, Gianluca; Dondi, Riccardo; Pirola, Yuri; Rizzi, Romeo

337

Preparation of magnetite aqueous dispersion for magnetic fluid hyperthermia  

NASA Astrophysics Data System (ADS)

An aqueous magnetic suspension was prepared by dispersing amphiphilic co-polymer-coated monodispersed magnetite nanoparticles synthesized through thermal decomposition of iron acetylacetonate (Fe(acac)3) in a mixture of oleic acid and oleylamine. The average diameter of narrow-size-distributed magnetite nanoparticles varied between 5 and 12 nm depending on the experimental parameters such as reaction temperature, metal salt concentration and oleic acid/oleylamine ratio. Though the as-synthesized particles were coated with oleate and were dispersible in organic solvent, their surfaces were modified using amphiphilic co-polymers composed of poly(maleic anhydride-alt-1-octadecene) and polyethylene glycol-methyl ether and made dispersible in water. Infrared spectra of the sample indicated the existence of -COOH groups on the surface for further conjugation with biomolecules for targeted cancer therapy.

Kikuchi, Teppei; Kasuya, Ryo; Endo, Shota; Nakamura, Akira; Takai, Toshiyuki; Metzler-Nolte, Nils; Tohji, Kazuyuki; Balachandran, Jeyadevan

2011-05-01

338

Investigation of heteroepitaxial growth of magnetite thin films.  

SciTech Connect

Epitaxial magnetite (Fe{sub 3}O{sub 4}) thin films were deposited by molecular beam epitaxy using molecular oxygen as the oxidant. Films deposited on (001) SrTiO{sub 3}, (001) MgO, and (001) BaTiO{sub 3} surfaces are epitaxial with the film (001) parallel to the substrate (001) and the film <100> parallel to the substrate <100>. X-ray magnetic circular dichroism was used to determine the relative Fe{sup 2+}/Fe{sup 3+} stoichiometry of the magnetite films, which was nearly independent of oxygen partial pressure over the range studied. All films show no in-plane magnetic anisotropy. Coercive fields ranged from 0.019 to 0.039 T and depended on film roughness.

Sterbinsky, G. E.; Cheng, J.; Chiu, P. T.; Wessels, B. W.; Keavney, D. J.; X-Ray Science Division; Northwestern Univ.

2007-07-01

339

Skeletal muscle tissue engineering using functional magnetite nanoparticles  

Microsoft Academic Search

Skeletal muscular tissues were constructed using magnetic force-based tissue engineering (Mag-TE) techniques. Mouse myoblast C2C12 cells labeled with magnetite cationic liposomes (MCLs) were seeded into a well of 24-well ultra-low cell attachment culture plates. When a magnet was positioned underneath the well, cells accumulated evenly onto the culture surface and formed a multilayered cell sheet. Furthermore, because an angiogenic potential

Akira Ito; Hirokazu Akiyama; Yasunori Yamamoto; Yoshinori Kawabe; Masamichi Kamihira

2009-01-01

340

A molecular dynamics investigation of surface reconstruction on magnetite (001)  

Microsoft Academic Search

Molecular dynamics calculations using analytical potential functions with polarizable oxygen ions have been used to identify a novel mode of reconstruction on the half-occupied tetrahedral layer termination of the magnetite (Fe3O4) (001) surface. In the proposed reconstruction, the twofold coordinated iron ion in the top monolayer rotates downward to occupy a vacant half-octahedral site in the plane of the second-layer

J. R. Rustad; E. Wasserman; A. R. Felmy

1999-01-01

341

SIZE-OPTIMIZED MAGNETITE NANOPARTICLES FOR MAGNETIC PARTICLE IMAGING  

SciTech Connect

We present experimental results to demonstrate that there is an optimum size for magnetite nanoparticles that are used to generate MPI signal, where the signal is detected as the third harmonic of nanoparticle magnetization, M, for any driving field frequency, ?. Our experimental results, for an arbitrarily chosen ? = 250 kHz, agree with predictions for a nanoparticle magnetization model based on the Langevin theory of superparamagnetism.

Ferguson, R. Matthew; Khandhar, Amit P.; Minard, Kevin R.; Krishnan, Kannan M.

2010-06-01

342

A kinematic model of TRM acquisition in multidomain magnetite  

Microsoft Academic Search

Samples containing 10-15 mum, 30-40 mum and 100-150 mum magnetite grains have been used in a series of experiments to study the behaviour of pTRM. pTRMs were induced by cooling each sample through a range of temperature intervals in a field of 0.84 mT, and a vibrating sample magnetometer was used to obtain a continuous record of the change in

E. McClelland; N. Sugiura

1987-01-01

343

Microaerobic conditions are required for magnetite formation within aquaspirillum magnetotacticum  

Microsoft Academic Search

The amount of magnetite (Fe3O4) within magnetosomes of the microaerophilic bacterium Aquaspirillum magnetotacticum varies with oxygen and nitrogen supply. The development of optical methods for directly measuring cell magnetism in culture samples has enabled us to quantitate bacterial Fe3O4 yields. We measured final cell yields, average cell magnetic moments, and magnetosome yields of growing cells. Cultures were grown with NO3?,

R. P. Blakemore; K. A. Short; D. A. Bazylinski; C. Rosenblatt; R. B. Frankel

1985-01-01

344

Magnetite from magnetotactic bacteria: Size distributions and twinning  

Microsoft Academic Search

We studied intracellular magnetite particles produced by several morphological types of magnetotactic bacteria including the spirillar (helical) freshwater species, Magnetospirillum magnetotacticum,and four incompletely characterized marine strains: MV-1, a curved rod- shaped bacterium; MC-1 and MC-2, two coccoid (spherical) microorganisms; and MV-4, a spirillum. Particle morphologies, size distributions, and structural features were examined using conventional and high-resolution transmission electron microscopy. The

BERTRAND DEVOUARD; MIHALY POSFAI; XIN HUA; DENNIS A. BAZYLINSKI; RICHARD B. FRANKEL; PETER R. BUSECK

1998-01-01

345

Immobilization of lipase on hydrophobic nano-sized magnetite particles  

Microsoft Academic Search

As a tool for the stable enzyme reuse, enzyme immobilization has been studied for several decades. Surface-modified nano-sized magnetite (S-NSM) particles have been suggested as a support for the immobilization of enzyme in this study. Based on the finding that a lipase is strongly adsorbed onto a hydrophobic surface, NSM particles (8–12nm) were made hydrophobic by binding of sodium dodecyl

Dong-Geun Lee; Kanagasabai M. Ponvel; Mir Kim; Sangpill Hwang; Ik-Sung Ahn; Chang-Ha Lee

2009-01-01

346

Synthesis of Monodispersed Magnetite Particles From Different Organometallic Precursors  

Microsoft Academic Search

Magnetite (Fe3O4) nanoparticles with very narrow particle size distribution can be obtained by decomposition of an organometallic compound in the presence of oleic acid. It has been shown that the carboxylic acid catalyzes the reaction leading to decreased decomposition temperatures and, consequently, as the surfactant concentration increases, smaller particles are formed. Precursors such as Fe(CO)5, iron acetylacetonate, and iron-oleate complexes,

A. G. Roca; M. P. Morales; C. J. Serna

2006-01-01

347

Properties of magnetite nanoparticles synthesized through a novel chemical route  

Microsoft Academic Search

We have developed a simple precipitation route to synthesize magnetite\\u000a(Fe3O4) nano-particles with controlled size without any requirement of\\u000acalcination step at high temperatures. The study of these nano-particles\\u000aindicates an enhancement in saturation magnetization with reduction in size\\u000adown to ~10 nm beyond which the magnetization reduces. The latter is attributed\\u000ato surface effects becoming predominant as surface to

Deepa Thapa; V. R. Palkar; M. B. Kurup; S. K. Malik

2004-01-01

348

Cooling behaviour of partial thermoremanences induced in multidomain magnetite  

NASA Astrophysics Data System (ADS)

The cooling behaviour of partial thermoremanences (pTRMs) below the acquisition temperature ( T2) is reported for the first time for well defined, sized, synthetic multidomain magnetite samples produced by hydrothermal recrystallisation. The pTRM cooling behaviour of low-stress magnetite samples is similar but not identical to that reported for higher stress crushed magnetite samples, that is, it displays a decrease in pTRM on cooling below T2, indicating domain re-organisation. This agrees with recent kinetic theories and domain observations, but strongly disagrees with the classical hysteretic models based on Néel's ideas which assume that the remanence increases with the increase in spontaneous magnetisation. It is demonstrated that the rate of decrease in remanence on cooling is not a viscous effect, and the rate of decrease increases with inducing field dependency. pTRM acquired from the Curie temperature Tc (pTRM TcT2) is found to be more stable to cooling than pTRM acquired from a temperature T1 which is less than Tc (pTRM T1T2). It is suggested that for low-stress samples, pTRM acquired at high temperatures has a wider range of metastable stable states available than pTRM acquired at lower temperatures. The results support the theories that domain wall nucleation is relatively easy during cooling. Differences between the cooling behaviour of the low-stress samples and those previously published for crushed magnetite samples can be attributed to differences in the dislocation densities and the available metastable domain states.

Muxworthy, Adrian R.

2000-12-01

349

Mechanisms of ciprofloxacin removal by nano-sized magnetite.  

PubMed

An understanding of the interaction mechanisms of antibiotics with environmentally relevant sorbents is important to determine the environmental fate of antibiotics and to develop wastewater treatment strategies. Magnetite (Fe(3)O(4)(s)) is ubiquitous in the environment and occurs as a secondary corrosion product of iron nanoparticles that are commonly used as a remediation material. In this study, we aimed to assess the sorption mechanisms of ciprofloxacin (CIP), an important class of fluoroquinolone antibiotics, with magnetite nanoparticles using a combination of wet chemical and in situ ATR-FTIR spectroscopic measurements. Ciprofloxacin sorption was characterized as a function of pH (3.4-8.0), CIP concentration (1-500 ?M), ionic strength (0.5, 0.1, and 0.01 M NaCl), and competing anion such as phosphate (0.1mM) to cover a broad range of environmentally relevant geochemical conditions. Results indicated a bell-shaped sorption envelop where sorption of CIP on nano-Fe(3)O(4)(s) increased from 45% to 80% at pH 3.44-5.97; beyond that sorption gradually decreased to a value of 25% at pH 8.39. Phosphate had negligible effect on CIP sorption. In situ ATR-FTIR results indicated inner-sphere coordination of CIP at the magnetite surface mediated by carboxylic acid groups. Results suggest that nano-Fe(3)O(4)(s) has the potential to remove CIP from wastewater effectively. PMID:23313895

Rakshit, Sudipta; Sarkar, Dibyendu; Elzinga, Evert J; Punamiya, Pravin; Datta, Rupali

2012-12-26

350

Magnetite-Alginate-AOT nanoparticles based drug delivery platform  

NASA Astrophysics Data System (ADS)

Iron oxide having the magnetite structure is a widely used biomaterial, having applications ranging from cell separation and drug delivery to hyperthermia. In order to increase the efficacy of drug treatments, magnetite nanoparticles can be incorporated into a composite system with a surfactant-polymer nanoparticle, which can act as a platform for sustained and enhanced cellular delivery of water-soluble molecules. Here we report a composite formulation based on magnetite and Alginate-aerosol OT (AOT) nanoparticles formulated using an emulsion-cross-linking process loaded with Rhodamine 6G [1]. We prepared two set of nanoparticles by using Ca^2+ or Fe^2+ to cross-link the alginate polymer. Additionally, we added ˜8 nm diameter Fe3O4 magnetic nanoparticles prepared by a soft chemical method to these alginate-AOT nanoparticles. The resulting composites were superparamagnetic at room temperature, with a saturation magnetization of approximately 0.006 emu/g of solution. We will present detailed studies on the structural and magnetic properties of these samples. We will also discuss HPLC measurements on Rhodamine uploading in these composites. [1] M.D.Chavanpatil, Pharmaceutical Research, vol.24, (2007) 803.

Regmi, R.; Sudakar, C.; Dixit, A.; Naik, R.; Lawes, G.; Toti, U.; Panyam, J.; Vaishnava, P. P.

2008-03-01

351

Biogenic Magnetite in Humans and New Magnetic Resonance Hazard Questions  

NASA Astrophysics Data System (ADS)

The widespread use of magnetic resonance (MR) techniques in clinical practice, and recent discovery of biogenic ferrimagnetic substances in human tissue, open new questions regarding health hazards and MR. Current studies are restricted just to the induction of Faraday currents and consequent thermal effects, or ‘inoffensive’ interaction with static magnetic field. We outlined that magnetic energies associated with interaction of ferrimagnetic particles and MR magnetic fields can be dangerous for sensitive tissues like the human brain is. To simulate the interaction mechanism we use our. ‘Cube’ model approach, which allows more realistic calculation of the particle's magnetic moments. Biogenic magnetite nanoparticles face during MR examination three principal fields: (i) main B0 field, (ii) gradient field, and (iii) B1 field. Interaction energy of biogenic magnetite nanoparticle with static magnetic field B0 exceeds the covalent bond energy 5 times for particles from 4 nm up to 150 nm. Translation energy in gradient field exceeds biochemical bond energy for particles bigger than 50 nm. Biochemical bond disruption and particle release to the tissue environment, in the presence of all MR fields, are the most critical points of this interaction. And together with relaxation processes after application of RF pulses, they make biogenic magnetite nanoparticles a potential MR health hazard issue.

Strbak, O.; Kopcansky, P.; Frollo, I.

2011-01-01

352

Contamination of New Jersey beach sand with magnetite spherules from industrial air pollution  

Microsoft Academic Search

Spherical particles composed of magnetite, typically 120 [mu]m to 2,450 [mu]m in diameter, are accumulating in the beach sands of New Jersey. Most magnetite spherule surfaces are highly polished but some are corroded or abraded. Their interiors are typically vesicular. Magnetite spherules from 213 New Jersey beach sand samples collected during May 1991 are chemically and morphologically the same as

W. T. Hassinan; J. H. Puffer

1992-01-01

353

A comparison of magnetite particles produced anaerobically by magnetotactic and dissimilatory iron-reducing bacteria  

Microsoft Academic Search

The authors compare the magnetic properties of fine-grained magnetite produced by two newly isolated anaerobic bacteria, a magnetotactic bacterium (MV-1) and a dissimilatory iron-reducing bacterium (GS-15). Although room-temperature magnetic properties are generally different between the two microorganisms, MV-1 and GS-15 magnetites can be most easily distinguished by the temperature variation of saturation remanence obtained at liquid helium temperatures. Magnetite produced

Bruce M. Moskowitz; Richard B. Frankel; Dennis A. Bazylinski; Holger W. Jannasch; Derek R. Lovley

1989-01-01

354

Preparation and characterization of (3-aminopropyl)triethoxysilane-coated magnetite nanoparticles  

Microsoft Academic Search

Magnetite nanoparticles coated with (3-aminopropyl)triethoxysilane, NH2(CH2)3Si(OC2H5)3, were prepared by silanization reaction and characterized by X-ray diffractometry, transmission electron microscopy, atomic force microscopy, Fourier transform infrared spectroscopy and magnetization measurements. Both uncoated and organosilane-coated magnetite exhibited superparamagnetic behavior and strong magnetization at room temperature. Basic groups anchored on the external surface of the coated magnetite were observed. The superparamagnetic particles of

M Yamaura; R. L Camilo; L. C Sampaio; M. A Macêdo; M Nakamura; H. E Toma

2004-01-01

355

Vanadium bearing titaniferous magnetite ore bodies of Ganjang, Karbi-Anglong District, Northeastern India  

Microsoft Academic Search

A new occurrence of (syenite-hosted) Vanadium bearing titaniferous magnetite ore body has been reported from Ganjang (26°09?35?\\u000a N: 93°20? E), Karbi-Anglong, Northeastern India. The magnetite ore bodies have lumpy and sporadic occurrences within the host\\u000a syenite pluton intrusive into gneissic country rocks. Ore microscopic studies reveal that magnetite is often associated with\\u000a haematite and ilmenite depicting different textural patterns. Critical

Abhishek Saha; Sohini Ganguly; Jyotisankar Ray; Avik Dhang

2010-01-01

356

Synthesis of magnetite octahedrons from iron powders through a mild hydrothermal method  

SciTech Connect

Magnetite (Fe{sub 3}O{sub 4}) octahedral particles were fabricated from iron powders through a simple one-step alkali-assisted hydrothermal process. The crystallinity, morphology, and structural features of the as-prepared magnetite particles were investigated using powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). The values of saturation magnetization (M {sub s}) and coercivity (H) of the magnetite octahedrons characterized on a vibrating sample magnetometer (VSM) are 89.81 emu/g and 70.6 Oe, respectively. The concentration of NaOH and the reaction temperature played a key role in the formation of the magnetite octahedrons.

Mao Baodong [Institute of Polyoxometalate Chemistry, Department of Chemistry, Northeast Normal University, Changchun, Jilin 130024 (China); Kang Zhenhui [Institute of Polyoxometalate Chemistry, Department of Chemistry, Northeast Normal University, Changchun, Jilin 130024 (China); Wang Enbo [Institute of Polyoxometalate Chemistry, Department of Chemistry, Northeast Normal University, Changchun, Jilin 130024 (China)]. E-mail: wangenbo@public.cc.jl.cn; Lian Suoyuan [Institute of Polyoxometalate Chemistry, Department of Chemistry, Northeast Normal University, Changchun, Jilin 130024 (China); Gao Lei [Institute of Polyoxometalate Chemistry, Department of Chemistry, Northeast Normal University, Changchun, Jilin 130024 (China); Tian Chungui [Institute of Polyoxometalate Chemistry, Department of Chemistry, Northeast Normal University, Changchun, Jilin 130024 (China); Wang Chunlei [Institute of Polyoxometalate Chemistry, Department of Chemistry, Northeast Normal University, Changchun, Jilin 130024 (China)

2006-12-14

357

Synthesis of chiral hybrid nanotubes of magnetite nanoparticles and conducting polymers  

NASA Astrophysics Data System (ADS)

New chiral magnetite nanoparticles with a polymerizable group produced polymer composite films on an electrode surface and the hybrid nanotubes of magnetite nanoparticles and polythiophene from their template-based electropolymerization.New chiral magnetite nanoparticles with a polymerizable group produced polymer composite films on an electrode surface and the hybrid nanotubes of magnetite nanoparticles and polythiophene from their template-based electropolymerization. Electronic supplementary information (ESI) available: Synthesis of a chiral stabilizer 1 and the spectral data. See DOI: 10.1039/c1nr11312g

Mitsumori, Masashi; Nakahodo, Tsukasa; Fujihara, Hisashi

2011-12-01

358

The Effect Of Temperature On Magnetic Behavior Of Magnetite Nanoparticles And Its Nanocomposites  

NASA Astrophysics Data System (ADS)

The magnetic properties of magnetite nanoparticles and magnetite-thermoplastic natural rubber (TPNR) nanocomposites was prepared by melt-blending method has been studied using vibrating sample magnetometer (VSM). The saturation magnetization (MS), remanence (MR), squareness (MR/MS), coercivity (HC) and exchange-bias field (Heb) for magnetite nanoparticles and its nanocomposites increased with decreasing temperature from 298 to 93 K. The increment of magnetization might be due to the decrease in thermal energy while the enhancement of coercivity and exchange-bias field is attributed to the exchange interaction at the interface between the ferrimagnetic (Fe3O4) and spin-glass-like surface layer on the nanocrystalline magnetite.

Kong, I.; Ahmad, S. H.; Abdullah, M. H.; Yusoff, A. N.

2009-06-01

359

Soft X-ray Spectroscopy Study of the Electronic Structure of Oxidized and Partially Oxidized Magnetite Nanoparticles  

SciTech Connect

The crystal structure of magnetite nanoparticles may be transformed to maghemite by complete oxidation, but under many relevant conditions the oxidation is partial, creating a mixed-valence material with structural and electronic properties that are poorly characterized. We used X-ray diffraction, Fe K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy, and soft X-ray absorption and emission spectroscopy to characterize the products of oxidizing uncoated and oleic acid-coated magnetite nanoparticles in air. The oxidization of uncoated magnetite nanoparticles creates a material that is structurally and electronically indistinguishable from maghemite. By contrast, while oxidized oleic acid-coated nanoparticles are also structurally indistinguishable from maghemite, Fe L-edge spectroscopy revealed the presence of interior reduced iron sites even after a 2-year period. We used X-ray emission spectroscopy at the O K-edge to study the valence bands (VB) of the iron oxide nanoparticles, using resonant excitation to remove the contributions from oxygen atoms in the ligands and from low-energy excitations that obscured the VB edge. The bonding in all nanoparticles was typical of maghemite, with no detectable VB states introduced by the long-lived, reduced-iron sites in the oleic acid-coated sample. However, O K-edge absorption spectroscopy observed a 0.2 eV shift in the position of the lowest unoccupied states in the coated sample, indicating an increase in the semiconductor band gap relative to bulk stoichiometric maghemite that was also observed by optical absorption spectroscopy. The results show that the ferrous iron sites within ferric iron oxide nanoparticles coated by an organic ligand can persist under ambient conditions with no evidence of a distinct interior phase and can exert an effect on the global electronic and optical properties of the material. This phenomenon resembles the band gap enlargement caused by electron accumulation in the conduction band of TiO2.

Gilbert, Benjamin; Katz, Jordan E.; Denlinger, Jonathan D.; Yin, Yadong; Falcone, Roger; Waychunas, Glenn A.

2010-10-24

360

A mixture of ferritin and magnetite nanoparticles mimics the magnetic properties of human brain tissue  

NASA Astrophysics Data System (ADS)

Magnetic properties of a two-component system, consisting of horse spleen ferritin (HoSF) which contains a 5-8nm sized antiferromagnetic ferrihydrite (5Fe2O3•9H2O) core and ferrimagnetic magnetite (Fe3O4) nanoparticles (MNP) with an average size of 10-20nm , have been investigated by using four different methods: induced magnetization versus (1) temperature and (2) field; (3) AC susceptibility; and (4) first-order reversal curves (FORC). All measurements were done on a mixed system of HoSF and MNP, as well as separately on the individual components. The average blocking temperature (TB) of the mixed system at 50mT is 15.6K , which is a shift towards higher temperatures compared to pure HoSF (TB=12K) . The contribution of the MNP component to magnetic ordering is evident only as a separation of the zero-field-cooled and field-cooled measurement curves. ac susceptibility is dominated by the ferrimagnetic MNP and shows strong frequency dependence. The peak ac susceptibilities can be described by the Vogel-Fulcher law, indicating the influence of interactions within the system. Hysteresis measurements at 5K show a wasp-waisted shape due to the mixture of a high coercivity phase (HoSF) with a low coercivity phase (MNP). Initial magnetization curves above TB can be fitted by a sum of Langevin functions, showing superparamagnetic behavior of both components. FORC diagrams are effective in illustrating the change from that of blocked MNP particles together with the superparamagnetic HoSF at 20K to purely superparamagnetic behavior in both components above 50K . We conclude that the mixed nanoparticle system is a good model for complex natural samples, such as human brain tissue.

Brem, Franziska; Tiefenauer, Louis; Fink, Alke; Dobson, Jon; Hirt, Ann M.

2006-06-01

361

Synthesis of monodispersed magnetite nanoparticles from iron pivalate clusters.  

PubMed

The iron pivalate clusters [Fe(3)O(O(2)C(t)Bu)(6)(H(2)O)(3)](O(2)C(t)Bu)·HO(2)C(t)Bu (1), [Fe(8)(OH)(4)(O(2)C(t)Bu)(12)(OC(6)H(4)C(6)H(5))(8)] (2) and [Fe(3)O(O(2)C(t)Bu)(6)(C(5)H(5)N)(3)] (3) have been used as single source precursors to synthesise iron oxide nanoparticles by a hot injection thermal decomposition method in oleylamine, hexadecanol, oleic acid, oleylamine/oleic acid with dodecanol or octyl ether as solvent. The effect of the different reaction parameters such as temperature, reaction time and capping agents on the phase and morphology were studied. The reaction time was studied for (1) by thermolysis in a mixture of oleylamine, oleic acid, hexadecanol and dodecanol (solvent) at 260 °C. The results obtained showed that a mixture of maghemite-C (Fe(2)O(3)) and magnetite (Fe(3)O(4)) were obtained for aliquots withdrawn for reaction times of less than 30 minutes whilst only magnetite was obtained after one hour. The nanoparticles were characterised by p-XRD, TEM and magnetic measurements. TEM showed that monodispersed magnetite particles were obtained when the precursor was injected at the boiling point of the solvent. The diameter of the monodispersed nanoparticles obtained by the thermolysis of [Fe(3)O(O(2)C(t)Bu)(6)(H(2)O)(3)](O(2)C(t)Bu)·HO(2)C(t)Bu (1) in oleylamine, hexadecanol, oleic acid with dodecanol or octyl ether as solvent were 4.3 ± 0.4 and 4.9 ± 0.5 nm respectively. Magnetic measurements revealed that all the particles are superparamagnetic. PMID:23132230

Abdulwahab, Khadijat; Malik, Mohammad A; O'Brien, Paul; Govender, Kuveshni; Muryn, Christopher A; Timco, Grigore A; Tuna, Floriana; Winpenny, Richard E P

2013-01-01

362

Preparation of size-controlled nanoparticles of magnetite  

NASA Astrophysics Data System (ADS)

Samples of ferrofluids containing chemically stabilized nanoparticles of magnetite (Fe3O4) with tetramethylammonium hydroxide (TMAOH) were prepared by a direct reduction-precipitation method. The influences of aging time and temperature on the size and monodispersion characteristics of the produced nanoparticles were investigated. Transmission electron microscopy, powder X-ray diffraction, Fourier-transform infrared, and magnetization measurements with applied magnetic field up to 2 T were used to characterize the synthesized iron oxides. Raising the temperature of the synthesized material in autoclave affects positively the monodispersion of the nanoparticles, but it was not found to significantly influence the size itself of individual particles.

Andrade, Ângela L.; Valente, Manuel A.; Ferreira, José M. F.; Fabris, José D.

2012-05-01

363

Structural characterization of temperature- and pressure-induced inverse{r_reversible}normal spinel transformation in magnetite  

SciTech Connect

High-precision powder x-ray diffraction and {sup 57}Fe Moessbauer studies up to 20 GPa show that magnetite (Fe{sub 3}O{sub 4}) undergoes a reversible normal{r_reversible}inverse transition with increasing pressure or decreasing temperature. There is no resolvable change in the spinel-type crystal structure or unit-cell volume at the phase transition. However, the volume of the tetrahedral (A) site increases (17%) and that of the octahedral (B) site decreases ({approx}7%) as electron charge density is transferred from the B to the A site. The corresponding valence changes cause the inverse {yields} normal transition with increasing pressure: Fe{sub A}{sup 3+}{yields}Fe{sub A}{sup 2+} and Fe{sub B}{sup 2.5+}{yields}Fe{sub B}{sup 3+}. There is an intermediate mixed configuration region at pressure-temperature (P-T) conditions lying between those at which magnetite is normal, TT{sub inv}(P)

Rozenberg, G. Kh.; Amiel, Y.; Xu, W. M.; Pasternak, M. P. [School of Physics and Astronomy, Tel Aviv University, 69978 Tel Aviv (Israel); Jeanloz, R. [Department of Earth and Planetary Science, University of California, Berkeley, California 94720 (United States); Hanfland, M. [European Synchrotron Research Facility, Boite Postale 220, 38043 Grenoble (France); Taylor, R. D. [MPA-10, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)

2007-01-01

364

A Magnetite-Dolomite-rich Clast in Orgueil: Differentiation on the CI Parent Body  

Microsoft Academic Search

In a thin section of CI Orgueil a 4x5 mm clast was found with an unusual composition. It consists mainly of magnetite (63 wt%) and dolomite (12 wt%) in the usual fine matrix. The magnetite occurs in rounded grains of 5 to 20 micron, occasionally also as framboidal spherules composed of many tiny grains. The dolomite grains have about the

F. Wlotzka; R. Thacker; K. Fredriksson

1995-01-01

365

Transformation Products of Submicron-Sized Aluminum-Substituted Magnetite: Color and Reductant Solubility (Abstract Only).  

National Technical Information Service (NTIS)

Magnetite, when present as fine particles, is soluble in acid ammonium oxalate (pH equals 3). However, the commonly used extractant for free iron oxides (i.e., citrate dithionite-bicarbonate (CDB) is not very effective in dissolving magnetite in soils and...

D. C. Golden D. W. Ming H. V. Lauer

1991-01-01

366

Diagenetic magnetite carries ancient yet secondary remanence in some Paleozoic sedimentary carbonates  

Microsoft Academic Search

Many sedimentary carbonate rocks carry stable magnetizations that can be shown to reside in magnetite. When such magnetizations are observed, it is often argued or demonstrated that the magnetite was incorporated into the sediment during deposition. However, paleomagnetic and rock magnetic studies in conjunction with analyses of magnetic extracts from the Helderberg and Bonneterre carbonates (United States) indicate that the

Chad McCabe; Rob van der Voo; Donald R. Peacor; Christopher R. Scotese; Roy Freeman

1983-01-01

367

Mechanisms in oxidation and sintering of magnetite iron ore green pellets  

Microsoft Academic Search

Thermal volume changes and oxidation mechanisms in magnetite iron ore green pellets balled with 0.5% bentonite binder, as a function of raw material fineness and pellet porosity, are shown. When a pellet starts to oxidize, a shell of hematite is formed around the pellet while the core still is magnetite. Dilatation curves were measured under non-oxidizing and oxidizing atmospheres to

S. P. E. Forsmo; P.-O. Samskog; B. M. T. Björkman

2008-01-01

368

Replacement of pyrite framboids by magnetite in limestone and implications for palaeomagnetism  

Microsoft Academic Search

LIMESTONES are an important source of palaeomagnetic data, with magnetite the dominant carrier of the magnetization. Because the magnetite is present in low concentrations, however, it has been directly observed only rarely and in trace amounts in acid-treated separates. Such residues are composed primarily of spheres, the ultimate origin of which has been enigmatic7. Yet interpretation of the palaeomagnetic data

D. Suk; D. R. Peacor; R. Van der Voo

1990-01-01

369

Determination of the capture radii of magnetite bearing hydroxide flocs in magnetic filtration  

Microsoft Academic Search

Magnetic filtration may be applied in water technology for the separation of flocs which are formed in a flocculation tank together with magnetite as an additive. The capture radius is an important mathematical quantity to calculate the performance of such filters in advance. Thus, the capture radii of magnetite bearing copper hydroxide flocs were measured with a direct visual evaluation

Markus Franz; Matthias Franzreb

1998-01-01

370

The late diagenetic conversion of pyrite to magnetite by organically complexed ferric iron  

Microsoft Academic Search

The geochemistry of late stage diagenetic replacement of pyrite by magnetite was investigated by laboratory experiments of pyrite dissolution and magnetite precipitation involving organically complexed ferric iron. The design of the experiments is based on the hypothesized geochemical conditions for in situ diagenesis in the Pennsylvanian age Belden Formation, an organic-rich carbonate in northwestern Colorado with pyrite grains rimmed with

L. A. Brothers; M. H. Engel; R. D. Elmore

1996-01-01

371

Effects of magnetic fields on the transformation of rust (hematite) to magnetite  

Microsoft Academic Search

The effects of magnetic fields on the transformation of rust (hematite) to magnetite (passivity state) were investigated under a fluid flow condition. The composition variation of rust was analyzed every 15 days by X-ray diffraction analysis to investigate the transformation mechanism. Samples used were rusted iron plates and fine powders of hematite and magnetite, which are chemical reagents. The magnetic

Masao Kuroda; Zhang Xin; Riichi Yamagami

2008-01-01

372

Biomimetic Control of Magnetite Shape and Morphology using Polyaminoacids  

NASA Astrophysics Data System (ADS)

Inspired by nature, this work explores the use of randomly sequenced poly(aminoacids)s to control the size, morphology and magnetic properties of magnetite via synthetic methods in a controlled manner as in the case of magnetotactic bacteria. Aqueous partial oxidation and chemical precipitation methods are employed for the synthesis of 7 - 50 nm iron oxide nanoparticles at room temperature. X -- ray diffraction (XRD) and Transmission Electron Microscopy (TEM) revealed formation of iron oxide nanoparticles both in the presence and absence of poly(amino acids). In the presence of random poly(amino acid)s with different compositions consisting of E, K and A amino acids the mean particle size for the chemical precipitation method is decreased regardless of amino acid composition. For partial oxidation method, mean particle size is also decreased and nanoparticle strings are observed while synthesized in the presence of poly(aspartic acid). Magnetic properties of particles obtained via different routes are also investigated. This provides a bio-inspired route for control over size, morphology and magnetic properties of magnetite nanoparticles.

Altan, Cem Levent; Bucak, Seyda; Sommerdijk, Nico

2012-02-01

373

Monodisperse magnetite nanofluids: Synthesis, aggregation, and thermal conductivity  

NASA Astrophysics Data System (ADS)

Magnetic nanofluids possess some unique properties that can significantly affect their thermal conductivity. We synthesize monodispersed magnetite (Fe3O4) nanofluids in toluene with the particle size from 4 to 12 nm and obtain aqueous nanofluids by a simple ``one-step'' phase transfer. Even without the effect of external field, the magnetic-interaction-induced self-assembled aggregation can still be significant in magnetite nanofluids. Investigation of the microstructures of self-assembled aggregation is carried out by the dynamic light scattering, which unveils the variation of aggregated configurations with particle concentration and time. Based on the calculation from the existing models, the aggregates decrease the thermal conductivity of both themselves and the entire system, mainly due to the less solid contents and weaker mobility compared with the single particles as well as the increase in interfacial thermal resistance. As the manifestation of the aggregation-structure variation, the measured thermal conductivity is of a wavelike shape as a function of particle concentration. The particle coating layers are also of importance in cluster formation so that nanofluid thermal conductivity can be manipulated for some nanofluids by changing the stabilizer used and thus controlling the particle aggregated structures. Due to the effects of temperature, viscosity and coating layers, the thermal conductivity for aqueous system varies in a different way as that for the toluene system.

Jiang, Wei; Wang, Liqiu

2010-12-01

374

PEG conjugated citrate-capped magnetite nanoparticles for biomedical applications  

NASA Astrophysics Data System (ADS)

We aim to develop polyethylene glycol decorated, citric acid capped magnetite nanoparticles (MNPs) with proper physicochemical characteristics including particle size distribution, morphology, magnetic property and stability in a biologic medium. MNP of about 10 nm were synthesized by a biocompatible chemical co-precipitation of Fe2+ and Fe3+ in an ammonia solution. A synthetic methodology has been developed to get a well dispersed and homogeneous aqueous suspension of MNPs. The naked MNPs are often insufficient for their stability, hydrophilicity and further functionalization. In order to overcome these limitations, citric acid was used to stabilize the magnetite particle suspension, which was anchored on the surface of freshly prepared MNPs by a direct addition method. Polyethylene glycol was covalently attached to the carboxylic moieties of citric acid anchored MNPs by carbodiimide chemistry. The microstructure and morphology of the nanoparticles were characterized by X-ray diffraction and transmission electron microscopy, and Fourier transform infrared spectroscopy. Also, the magnetic properties were investigated by vibrating sample magnetometry. It was found that the nanoparticles demonstrated superparamagnetic behavior.

Cheraghipour, Elham; Tamaddon, A. M.; Javadpour, S.; Bruce, I. J.

2013-02-01

375

Magnetite deposits near Klukwan and Haines, southeastern Alaska  

USGS Publications Warehouse

Low-grade iron ore is found in magnetite-bearing pyroxenite bodies near Klukwan and Haines in Southeastern Alaska. An alluvial fan at Haines also contains magnetite-bearing rock of possible economic significance. The Haines-Klukwan area is underlain by rocks of Mesozoic Including epidote diorite, quartz diorite, and alaskite of the Coast Range batholith, metabasalt (recrystallized lava flows and pyroclastic rocks), and, in the southern part, interbedded slate and limestone. Layering and foliation, where perceptible, generally strike northwest and dip steeply northeast. The iron deposits are found at or near the contact between the metabasalt and epidote diorite; they appear to represent highly-altered lava flows that were metamorphosed during the emplacement of the batholith. Several billion tens of rock containing about 13 percent magnetic iron are included in the pyroxenite body at Klukwan. Sampling and dip-needle data suggest the presence there of two or three tabular aches in which the rock has an average magnetic iron content of 20 percent or more. Pyroxenite bodies outcropping in three areas near Haines apparently are lower in grade than the Klukwan deposit; lack of exposures prevented thorough sampling but reconnaissance traverses with a dip needle failed to reveal important zones of high-grade iron ore. An alluvial fan adjoining the pyroxenite body at Klukwan contains several hundred million tons of broken rock having a magneticiron content of about 10 percent.

Robertson, Eugene C.

1956-01-01

376

Mössbauer Characterization of Magnetite/Polyaniline Magnetic Nanocomposite  

NASA Astrophysics Data System (ADS)

Aniline surface coated Fe3O4 nanoparticles have been successfully synthesized by UV irradiation varying the time and the acid media (HCl, HNO3, or H2SO4). The synthesized material represents a promising platform for application in nerve regeneration. XRD patterns are consistent with the crystalline structure of magnetite. Nevertheless, for UV irradiation times longer than 2 h, extra XRD lines reveal the presence of goethite. The mean crystallite size of uncoated particles is estimated to be 25.4 nm, meanwhile that size is reduced to 19.9 nm for the UV irradiated sample in HCl medium for 4 h. Mössbauer spectra of uncoated nanoparticles reveal the occurrence of thermal relaxation at room temperature, while the 77 K-Mössbauer spectrum suggests the occurrence of electron localization effects similar to that expected in bulk magnetite. The Mossbauer spectra of UV irradiated sample in HCl medium during 4 h, confirms the presence of the goethite phase. For this sample, the thermal relaxation is more evident, since the room temperature spectrum shows larger spectral area for the nonmagnetic component due to the smaller crystallite size. Meanwhile, the 77 K-Mössbauer spectrum suggests the absence of the electron localization effect above 77 K.

Rodriguez, Anselmo F. R.; Faria, Fernando S. E. D. V.; Lopez, Jorge L.; Mesquita, Antonio G. G.; Coaquira, José A. H.; Oliveira, Aderbal C.; Azevedo, Ricardo B.; de Araújo, Ana C. V.; Alves, Severino; de Azevedo, Walter M.; Morais, Paulo C.

2010-12-01

377

Magnetic Core-Shell Morphology of Structurally Uniform Magnetite Nanoparticles  

NASA Astrophysics Data System (ADS)

Magnetic nanoscale structures are intriguing, in part, because of the exotic properties that emerge compared with bulk. The reduction of magnetic moment per atom in magnetite with decreasing nanoparticle size, for example, has been hypothesized to originate from surface disordering to anisotropy-induced radial canting, which are difficult to distinguish using conventional magnetometry. Small-angle neutron scattering (SANS) is ideal for probing structure, both chemical and magnetic, from nm to microns across an ensemble of particles. Adding polarization analysis (PASANS) of the neutron spin orientation before and after interaction with the scattering particles allows the magnetic structure to be separated into its vector components. Application of this novel technique to 9 nm magnetite nanoparticles closed-packed into face-centered crystallites with order of a micron revealed that at nominal saturation the missing magnetic moments unexpectedly interacted to form well-ordered shells 1.0 to 1.5 nm thick canted perpendicular to their ferrimagnetic cores between 160 to 320 K [1]. These shells additionally displayed intra-particle "cross-talk", selecting a common orientation over clusters of tens of nanoparticles. However, the shells disappeared when the external field was removed and interparticle magnetic interactions were negligible (300 K), confirming their magnetic origin. This work has been carried out in collaboration with Ryan Booth, Julie Borchers, Wangchun Chen, Liv Dedon, Thomas Gentile, Charles Hogg, Yumi Ijiri, Mark Laver, Sara Majetich, James Rhyne, and Shannon Watson.[4pt] [1] K.L. Krycka et al., Phys. Rev. Lett. 104, 207203 (2010)

Krycka, Kathryn

2011-03-01

378

Moessbauer Characterization of Magnetite/Polyaniline Magnetic Nanocomposite  

SciTech Connect

Aniline surface coated Fe{sub 3}O{sub 4} nanoparticles have been successfully synthesized by UV irradiation varying the time and the acid media (HCl, HNO{sub 3}, or H{sub 2}SO{sub 4}). The synthesized material represents a promising platform for application in nerve regeneration. XRD patterns are consistent with the crystalline structure of magnetite. Nevertheless, for UV irradiation times longer than 2 h, extra XRD lines reveal the presence of goethite. The mean crystallite size of uncoated particles is estimated to be 25.4 nm, meanwhile that size is reduced to 19.9 nm for the UV irradiated sample in HCl medium for 4 h. Moessbauer spectra of uncoated nanoparticles reveal the occurrence of thermal relaxation at room temperature, while the 77 K-Moessbauer spectrum suggests the occurrence of electron localization effects similar to that expected in bulk magnetite. The Mossbauer spectra of UV irradiated sample in HCl medium during 4 h, confirms the presence of the goethite phase. For this sample, the thermal relaxation is more evident, since the room temperature spectrum shows larger spectral area for the nonmagnetic component due to the smaller crystallite size. Meanwhile, the 77 K-Moessbauer spectrum suggests the absence of the electron localization effect above 77 K.

Rodriguez, Anselmo F. R.; Faria, Fernando S. E. D. V.; Lopez, Jorge L.; Mesquita, Antonio G. G. [Universidade Federal do Acre, Centro de Ciencias Biologicas e da Natureza, Rio Branco AC 69915-900 (Brazil); Coaquira, Jose A. H.; Oliveira, Aderbal C.; Morais, Paulo C. [Universidade de Brasilia, Instituto de Fisica, Brasilia DF 70910-900 (Brazil); Azevedo, Ricardo B. [Universidade de Brasilia, Instituto de Ciencias Biologicas, Brasilia DF 70910-900 (Brazil); Araujo, Ana C. V. de; Alves, Severino Jr.; Azevedo, Walter M. de [Universidade Federal de Pernambuco, Laboratorio de Quimica do Estado Solido, Departamento de Quimica Fundamental, Recife PE 50970-901 (Brazil)

2010-12-02

379

Speed limit of the insulator-metal transition in magnetite  

NASA Astrophysics Data System (ADS)

As the oldest known magnetic material, magnetite (Fe3O4) has fascinated mankind for millennia. As the first oxide in which a relationship between electrical conductivity and fluctuating/localized electronic order was shown, magnetite represents a model system for understanding correlated oxides in general. Nevertheless, the exact mechanism of the insulator-metal, or Verwey, transition has long remained inaccessible. Recently, three-Fe-site lattice distortions called trimerons were identified as the characteristic building blocks of the low-temperature insulating electronically ordered phase. Here we investigate the Verwey transition with pump-probe X-ray diffraction and optical reflectivity techniques, and show how trimerons become mobile across the insulator-metal transition. We find this to be a two-step process. After an initial 300?fs destruction of individual trimerons, phase separation occurs on a 1.5±0.2?ps timescale to yield residual insulating and metallic regions. This work establishes the speed limit for switching in future oxide electronics.

de Jong, S.; Kukreja, R.; Trabant, C.; Pontius, N.; Chang, C. F.; Kachel, T.; Beye, M.; Sorgenfrei, F.; Back, C. H.; Bräuer, B.; Schlotter, W. F.; Turner, J. J.; Krupin, O.; Doehler, M.; Zhu, D.; Hossain, M. A.; Scherz, A. O.; Fausti, D.; Novelli, F.; Esposito, M.; Lee, W. S.; Chuang, Y. D.; Lu, D. H.; Moore, R. G.; Yi, M.; Trigo, M.; Kirchmann, P.; Pathey, L.; Golden, M. S.; Buchholz, M.; Metcalf, P.; Parmigiani, F.; Wurth, W.; Föhlisch, A.; Schüßler-Langeheine, C.; Dürr, H. A.

2013-10-01

380

Simple and facile approach to synthesize magnetite nanoparticles and assessment of their effects on blood cells  

NASA Astrophysics Data System (ADS)

In this paper, a very simple and facile approach for the large scale synthesis of uniform and size-controllable single-domain magnetite nanoparticles is reported. These magnetite nanoparticles were synthesized via thermal decomposition of a ferric nitrate/ethylene glycol solution. The structural and morphological properties of the synthesized nanoparticles were carefully studied. Nearly spherical nanoparticles with inverted spinel structure and average particle and crystallite sizes smaller than 20 nm were obtained. The magnetic measurements revealed that magnetite nanoparticles have a magnetic saturation value near that of the bulk magnetite. The erythrocyte cytotoxicity assays showed no hemolytic potential of the samples containing magnetite nanoparticles, indicating no cytotoxic activity on human erythrocytes, which makes these interesting for biotechnological applications.

Cótica, Luiz F.; Freitas, Valdirlei F.; Dias, Gustavo S.; Santos, Ivair A.; Vendrame, Sheila C.; Khalil, Najeh M.; Mainardes, Rubiana M.; Staruch, Margo; Jain, Menka

2012-02-01

381

Operators on Pure Spinor Spaces  

SciTech Connect

Pure spinors are relevant to the formulation of supersymmetric theories, and provide the only known way to maintain manifest maximal supersymmetry. The (non-linear) pure spinor constraint makes it nontrivial to find well defined operators on pure spinor wave functions. We discuss how such operators are defined. One application concerns covariant gauge fixing in maximally supersymmetric Yang-Mills (and string theory). Another issue is the construction of a manifestly supersymmetric action for 11-dimensional supergravity in terms of a scalar superfield. We describe some work in progress.

Cederwall, Martin [Fundamental Physics, Chalmers University of Technology, SE 412 96 Goteborg (Sweden)

2010-06-17

382

Magnetic and Physical Characteristics of Magnetite Associated with Deformation and Exsolution  

NASA Astrophysics Data System (ADS)

This thesis contains a collection of laboratory-based studies designed to characterize the magnetic properties and physical aspects of magnetite that result from deformation or high temperature growth. In Chapter 2, a detailed rock magnetic characterization of rocks containing nanoscale magnetite exsolved from volcanic glass identifies the location of domain-state thresholds through distinct transitions in remanence and susceptibility properties. This unique material is an excellent candidate for standard material to be used in studies of magnetite granulometry. In Chapter 3, theoretical timescales for the growth of sub-microscopic magnetite needles during exsolution from plagioclase are calculated using results of diffusion experiments. Measured diffusivities are modeled to calculate the amount of diffusion-limited growth possible under different conditions of nucleation temperature and cooling rate. In Chapters 4 and 5, the development and evolution of magnetic fabrics are investigated through deformation experiments on synthetic rock-analogues at high temperatures and ductile conditions. Stress-induced changes in rock magnetic properties after deformation are significant. Examination of deformation-induced remagnetization demonstrates that a primary remanence can survive conditions equivalent to moderate metamorphism in certain cases and that petrofabric can play an important role in determining the remanence stability. High-temperature deformation experiments result in a pattern of anisotropy development that indicates plastic deformation of magnetic grains, which is distinct from anisotropy development resulting from different magnetite strain responses. Experimental data are combined with theoretical magnetic anisotropy models and used to estimate effective magnetite strains and strain partitioning from magnetic fabric data in deformed samples. Finally, observations of strong shape-preferred orientation and deformation-induced microstructures in magnetite grains from high-temperature shear experiments indicate plastic deformation of magnetite. Microstructural observations place constraints on the rheological behavior of magnetite and the conditions in which dislocation creep is dominant. These observations prompt a re-examination of the previously established magnetite flow laws which are modified and used to construct new deformation mechanism maps.

Till, Jessica Lynn

383

Simulation of ferromagnetic resonance spectra of linear chains of magnetite nanocrystals  

NASA Astrophysics Data System (ADS)

Ensembles of linear chains of stable single domain magnetite crystals, as found in magnetotactic bacteria, exhibit a distinctly asymmetric ferromagnetic resonance (FMR) signal, with a pronounced high-field minimum and two or three low-field maxima in the derivative spectrum. To identify the microscopic origin of these traits, we have simulated FMR spectra of dilute suspensions of linear chains oriented randomly in space by modeling the chain as a Stoner-Wohlfarth-type rotation ellipsoid whose long axis coincides with an easy [111] axis of the cubic magnetocrystalline anisotropy system. The validity of the model is examined by comparing the results with explicit calculations of the interactions among the particles in the chain. The single ellipsoid model reproduces the experimentally observed FMR traits and can be related to the explicit chain model by adjusting the contribution to the uniaxial anisotropy along the chain axis to account for the magnetostatic interactions. Finally, we provide a practical approximation for simulating and fitting the FMR spectra of one-dimensional assemblies.

Charilaou, Michalis; Winklhofer, Michael; Gehring, Andreas U.

2011-05-01

384

Investigation of the Presence of Charge Order in Magnetite by Measurement of the Sprin Wave Spectrum  

SciTech Connect

Inelastic neutron scattering results on magnetite (Fe{sub 3}O{sub 4}) show a large splitting in the acoustic spin wave branch, producing a 7 meV gap midway to the Brillouin zone boundary at q = (0,0,1/2) and {h_bar}{omega} = 43 meV. The splitting occurs below the Verwey transition temperature, where a metal-insulator transition occurs simultaneously with a structural transformation, supposedly caused by the charge ordering on the iron sublattice. The wavevector (0,0,1/2) corresponds to the superlattice peak in the low symmetry structure. The dependence of the magnetic superexchange on changes in the crystal structure and ionic configurations that occur below the Verwey transition affect the spin wave dispersion. To better understand the origin of the observed splitting, several Heisenberg models intended to reproduce the pair-wise variation of the magnetic superexchange arising from both small crystalline distortions and charge ordering were studied. None of the models studied predicts the observed splitting, whose origin may arise from charge-density wave formation or magnetoelastic coupling.

McQueeny, R. J. [Ames Laboratory; Yethiraj, Mohana [ORNL; Montfrooij, W. [University of Missouri, Columbia; Garner, J. S. [Brookhaven National Laboratory (BNL); Metcalf, P. [Purdue University; Honig, J. M. [University of Purdue

2006-01-01

385

Carbon nanotubes/magnetite hybrids prepared by a facile synthesis process and their magnetic properties  

NASA Astrophysics Data System (ADS)

In this paper, a facile synthesis process is proposed to prepare multiwalled carbon nanotubes/magnetite (MWCNTs/Fe 3O 4) hybrids. The process involves two steps: (1) water-soluble CNTs are synthesized by one-pot modification using potassium persulfate (KPS) as oxidant. (2) Fe 3O 4 is assembled along the treated CNTs by employing a facile hydrothermal process with the presence of hydrazine hydrate as the mineralizer. The treated CNTs can be easily dispersed in aqueous solvent. Moreover, X-ray photoelectron spectroscopy (XPS) analysis reveals that several functional groups such as potassium carboxylate (-COOK), carbonyl (-C dbnd O) and hydroxyl (-C-OH) groups are formed on the nanotube surfaces. The MWCNTs/Fe 3O 4 hybrids are characterized with respect to crystal structure, morphology, element composition and magnetic property by X-ray diffraction (XRD), transmission electron microscopy (TEM), XPS and superconducting quantum interference device (SQUID) magnetometer. XRD and TEM results show that the Fe 3O 4 nanoparticles with diameter in the range of 20-60 nm were firmly assembled on the nanotube surface. The magnetic property investigation indicated that the CNTs/Fe 3O 4 hybrids exhibit a ferromagnetic behavior and possess a saturation magnetization of 32.2 emu/g. Further investigation indicates that the size of assembled Fe 3O 4 nanoparticles can be turned by varying experiment factors. Moreover, a probable growth mechanism for the preparation of CNTs/Fe 3O 4 hybrids was discussed.

Zhang, Li; Ni, Qing-Qing; Natsuki, Toshiaki; Fu, Yaqin

2009-07-01

386

Structure-Disorder induced MagnetoResistance intensification on spin-dependent-conduction in magnetite (Fe3O4) thin film produced by RF magnetron sputtering method  

Microsoft Academic Search

The intensification of magneto-resistance (MR) caused by structure-disorder has been observed in magnetite (Fe3O4) thin film (MTF) produced by the rf magnetron sputtering method. The MTFs with the thickness of 20nm, 50nm and 100nm were deposited on the substrates of SiO2-glass, MgAl2O4 (100) and MgO (100) single crystals. We have observed that the MR of the MTF on SiO2-glass substrate

H. Kobori; D. Shimizu; A. Sugimura; T. Taniguchi; A. Ando; H. Kawanaka; Y. Naitoh; T. Shimizu

2009-01-01

387

Structure-Disorder induced Magneto-Resistance intensification on spin-dependent-conduction in magnetite (Fe3O4) thin film produced by RF magnetron sputtering method  

NASA Astrophysics Data System (ADS)

The intensification of magneto-resistance (MR) caused by structure-disorder has been observed in magnetite (Fe3O4) thin film (MTF) produced by the rf magnetron sputtering method. The MTFs with the thickness of 20nm, 50nm and 100nm were deposited on the substrates of SiO2-glass, MgAl2O4 (100) and MgO (100) single crystals. We have observed that the MR of the MTF on SiO2-glass substrate changes 3-5 times larger than that of the MTFs on MgAl2O4 and MgO substrates. From the AFM, SEM and XRD measurements, we have found that the MTFs are composed of magnetite nano-particles (MNPs) and the crystal-axis directions of the MNPs in the MTF on SiO2-glass are mutually random and those of the MTFs on MgAl2O4 and MgO are almost aligned along (100) direction. In addition, from the electrical and magnetization measurements, we have found that the MNPs in the MTF on SiO2-glass show the amorphous-like behavior and those of the MTFs on MgAl2O4 and MgO indicate the crystal-like behavior.

Kobori, H.; Shimizu, D.; Sugimura, A.; Taniguchi, T.; Ando, A.; Kawanaka, H.; Naitoh, Y.; Shimizu, T.

2009-02-01

388

Quartz crystal microbalance biosensor study of endothelial cells and their extracellular matrix following cell removal: Evidence for transient cellular stress and viscoelastic changes during detachment and the elastic behavior of the pure matrix.  

PubMed

A quartz crystal microbalance (QCM) cell biosensor utilizing living endothelial cells (ECs) or human breast cancer cells (MCF-7) adhering to the gold QCM surface was used to study the relative contributions of the cells and their underlying extracellular matrix (ECM) to the measured QCM Deltaf and DeltaR shifts. The ECM represents a natural biomaterial that is synthesized by the cells to enable their attachment to surfaces. We followed the detachment of the ECs or MCF-7 cells from their ECM using a nonproteolytic method and were able to apportion the total frequency, Deltaf, decrease of the biosensor into contributions from cell attachment and from the intact underlying ECM. We also demonstrated that the Deltaf shift remaining after EC removal corresponds to ECM as determined by light microscopic visualization of the stained protein. During the process of cell detachment, we observed a novel transient increase in viscoelastic behavior expressed as a transient increase in the motional resistance, DeltaR, parameter. Then we showed via a simulation experiment using ECs stained with fluorescent rhodamine-labeled phalloidin, an actin stain, that the transient viscoelastic increase correlated with cellular stress exhibited by the cells during removal with ethylene glycol bis(2-aminoethyl ether)-N,N,N',N'- tetraacetic acid. Prior to cells lifting from their ECM, the attached ECs rearrange their actin microfilaments first into peripheral stress fibers and second into internal aggregates, to maintain cell-cell connectivity, retain their spread morphology, and attempt to adhere more tightly to their underlying ECM. The decrease in DeltaR following its transient rise corresponds to cells finally losing their attachment focal points and lifting from the ECM. We also characterized the normalized f shifts, -Delta(Deltaf)(ECM)/attached cell and -Delta(Deltaf)(cells)/attached cell, as a function of varying the number of adherent cells. Finally, we demonstrate that the underlying native ECM biomaterial, from which all cells have been removed, does not exhibit any significant level of energy dissipation, in contrast to the cells when they are attached to the ECM. PMID:15979557

Marx, Kenneth A; Zhou, Tiean; Montrone, Anne; McIntosh, Donna; Braunhut, Susan J

2005-08-01

389

Magnetite (Fe3O4) microcapsules prepared using a glass membrane and solvent removal.  

PubMed

Fine magnetite powders dispersed in polymer solution were encapsulated from an oil-in-water emulsion prepared by an emulsification process employing a porous glass membrane and subsequent evaporation of the solvent. Styrene-based copolymers were dissolved in a magnetic fluid, and then continuously pushed through the pores of glass membrane into the aqueous phase, which had dissolved polyvinyl alcohol (PVA) and sodium dodecyl sulphate (SDS) as a mixed stabilizer. P(styrene-co-acrylic acid) (PS-AA), P(stryrene-co-butyl acrylate) (PS-BA) and styrene-butadiene rubber (SBR) were dissolved in the specially ordered magnetite fluid (25 wt% magnetite dispersed in toluene) separately or as a mixture, and uniform droplets suspending the magnetic particles were obtained. After the evaporation of toluene, PS-AA capsules retained a spherical shape and uniformity, whereas PS-AA/PS-BA capsules revealed a creased surface and broader size distribution. The microcapsules entrapped 30-40 wt% of magnetite, and the encapsulation yield of magnetite was 20-40%. Glass membranes with 9.5, 5.25 and 1.42 microm pore size were employed and 5-40 microm microcapsules were obtained depending on the pore size. When magnetite suspended in chloroform was used, magnetite capsules with broader size distributions were obtained because of the sticking of the droplets to the membrane wall. The advantage of the membrane emulsification which provides uniform sized droplets was lost. PMID:11695639

Omi, S; Kanetaka, A; Shimamori, Y; Supsakulchai, A; Nagai, M; Ma, G H

390

Zener Double Exchange from Local Valence Fluctuations in Magnetite  

SciTech Connect

Magnetite (Fe3O4) is a mixed valent system where electronic conductivity occurs on the B site (octahedral) iron sublattice of the spinel structure. Below Tv = 123 K, a metal-insulator transition occurs which is argued to arise from the charge ordering of 2+ and 3+ iron valences on the B sites (Verwey transition). Inelastic neutron scattering measurements show that optical spin waves propagating on the B site sublattice (~80 meV) are shifted upwards in energy above TV due to the occurrence of B-B ferromagnetic double exchange in the mixed valent phase. The double exchange interaction affects only spin waves of 5 symmetry, not all modes, indicating that valence fluctuations are slow and the double exchange is constrained by short-range electron correlations above Tv.

McQueeney, Robert John [Iowa State University; Yethiraj, M. [Bragg Institute, ANSTO; Chang, S. [National Institute of Standards and Technology (NIST); Montfrooij, W. [University of Missouri, Columbia; Perring, T. G. [ISIS Facility, Rutherford Appleton Laboratory; Honig, J. M. [University of Purdue; Metcalf, P. [Purdue University

2007-01-01

391

Electromagnetic nanocomposite of bacterial cellulose using magnetite nanoclusters and polyaniline.  

PubMed

Magnetic BC was biosynthesized by culturing Gluconacetobacter xylinus in a medium containing magnetite nanoparticle (MNP) clusters. The stable dispersion of MNP clusters in an aqueous solution was achieved using amphiphilic comb-like polymer (CLP) stabilizers to disperse the MNPs. Subsequently, a conducting polymer was synthesized on the magnetic BC fibers by the chemical oxidative polymerization of aniline. The BC fiber was fully coated with polyaniline, forming hydrogen bonds. The colloidal stability of the CLP-modified MNPs was characterized by optical imaging and UV-visible spectroscopy. The chemical structure and morphology of the hybrid BC layers were observed using Fourier transform infrared spectroscopy and scanning electron microscopy. Magnetic and conductive properties were measured to confirm the immobilization of MNPs and polyaniline. PMID:23000681

Park, Minsung; Cheng, Jie; Choi, Jaeyoo; Kim, Jaehwan; Hyun, Jinho

2012-08-19

392

The effect of low-temperature oxidation on large multi-domain magnetite  

NASA Astrophysics Data System (ADS)

Natural samples of oxidized and unoxidized magnetite have been used to study the effect of low-temperature oxidation on magnetic domain state. All of the magnetites studied were large multi-domain (MD) grains, ranging in size from 53 micrometers to at least 250 micrometers. Hysteresis data typical of MD grains are obtained from unoxidized magnetite samples while data from partially oxidized samples are characteristic of pseudo-single domain (PSD) grains. Our results demonstrate that low-temperature oxidation can seriously affect the magnetic properties of magnetite by significantly increasing the PSD-MD threshold size. The presence of a suppressed Verwey transition at 118 K in the oxidized samples indicates that the oxidation may only be surficial and that there may exist a core of magnetite under the maghemitized surface shell. We suggest three possible mechanisms for the observed PSD-like behavior. First, the magnetite core could be reduced sufficiently in volume to make it a PSD grain, independent of the surficial maghemite. Second, internal stress in the composite grain due to lattice mismatches between the magnetite core and maghemite rim will increase the domain wall energy and make it more difficult to add walls for a given grain size. Coupled with a reduced volume of the magnetite core, this could give rise to PSD-like behavior. Third, the composite grain could be a mixture of SD maghemite and MD magnetite which gives rise to bulk PSD-like properties. Our results have potentially important implications for paleomagnetic records because they provide a mechanism whereby a stable chemical remanent magnetization can be acquired by MD grains in sediments and igneous rocks.

Cui, Yulong; Verosub, Kenneth L.; Roberts, Andrew P.

1994-05-01

393

Evaluation of in vitro mutagenicity and genotoxicity of magnetite nanoparticles.  

PubMed

For successful application of nanomaterials in bioscience, it is essential to understand the biological fate and potential toxicity of nanoparticles. The aim of this study is to evaluate the genetic safety of magnetite nanoparticles (MNPs) (Fe(3)O(4)) in order to provide their diverse applications in life sciences, such as drug development, protein detection, and gene delivery. Concentrations of 10 ppm, 30 ppm, and 70 ppm (10-70 ?g/mL) of the MNPs of 8.0 ± 2.0 nm were used. Characterization of MNPs was done with transmission electron microscopy (TEM), X-Ray Diffractometry (XRD) and a vibrating sample magnetometer (VSM). The MNPs mutagenic potential was evaluated using the Salmonella Ames test with Salmonella strains TA100, TA2638, TA102, and TA98 in the presence and the absence of metabolic activation with S9-liver extract. Genetic mutations at the chromosomal level and extent of DNA damage using the alkaline Comet assay were applied to peripheral blood lymphocytes and HEK-293 cell lines respectively. There were significant changes in the results of the Salmonella mutagenicity test at the 70 ppm concentration of MNPs which might reflect their mutagenic activity at higher concentrations. Cytogenetic evaluation revealed the absence of genetic mutations at the chromosomal level. The extent of DNA damage quantified by Comet assay and the mutagenicity study using Ames test were significantly correlated for the MNPs. Our results indicated that magnetite nanoparticles with the defined physicochemical properties caused apparent toxicity at higher concentrations of 30 ppm and 70 ppm without chromosomal abnormalities under the experimental conditions of this study. PMID:23917860

Gomaa, I O; Kader, M Ha; Salah, T A; Heikal, O A

2013-06-01

394

Negativity of random pure states  

SciTech Connect

This paper deals with the entanglement, as quantified by the negativity, of pure quantum states chosen at random from the invariant Haar measure. We show that it is a constant (0.72037) multiple of the maximum possible entanglement. In line with the results based on the concentration of measure, we find evidence that the convergence to the final value is exponentially fast. We compare the analytically calculated mean and standard deviation with those calculated numerically for pure states generated via pseudorandom unitary matrices proposed by Emerson et al. [Science 302, 2098 (2003)]. Finally, we draw some conclusions about the geometry of quantum states based on our result.

Datta, Animesh [Institute for Mathematical Sciences, 53 Prince's Gate, Imperial College, London, SW7 2PG (United Kingdom); QOLS, Blackett Laboratory, Imperial College London, Prince Consort Road, SW7 2BW (United Kingdom)

2010-05-15

395

Spontaneous Symmetry-Breaking Vortex Lattice Transitions in Pure Niobium  

SciTech Connect

We report an extensive investigation of magnetic vortex lattice (VL) structures in single crystals of pure niobium with the magnetic field applied parallel to a fourfold symmetry axis, so as to induce frustration between the cubic crystal symmetry and hexagonal VL coordination expected in an isotropic situation. We observe new VL structures and phase transitions; all the VL phases observed (including those with an exactly square unit cell) spontaneously break some crystal symmetry. One phase even has the lowest possible symmetry of a two-dimensional Bravais lattice. This is quite unlike the situation in high-T{sub c} or borocarbide superconductors, where VL structures orient along particular directions of high crystal symmetry. The causes of this behavior are discussed.

Laver, M. [Institut Laue-Langevin, BP 156, F-38042 Grenoble (France); School of Physics and Astronomy, University of Birmingham, Birmingham B15 2TT (United Kingdom); Forgan, E.M.; Brown, S.P.; Bowell, C.; Ramos, S.; Lycett, R.J. [School of Physics and Astronomy, University of Birmingham, Birmingham B15 2TT (United Kingdom); Charalambous, D. [School of Physics and Astronomy, University of Birmingham, Birmingham B15 2TT (United Kingdom); Meteorological Service, Ministry of Agriculture, 28 Nikis Avenue, 1086 Lefkosia (Cyprus); Fort, D. [Metallurgy and Materials Science, University of Birmingham, Birmingham B15 2TT (United Kingdom); Christen, D.K. [Solid State Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6393 (United States); Kohlbrecher, J. [Paul Scherrer Institut, Villigen PSI, CH 5232 (Switzerland); Dewhurst, C.D.; Cubitt, R. [Institut Laue-Langevin, BP 156, F-38042 Grenoble (France)

2006-04-28

396

Rapid growth of KDP crystal with new additive  

Microsoft Academic Search

A chelating reagent sulfosalicylic acid (SSA) as a new additive was added into the KDP solutions in a small amount (1wt%) and metastable zone widths were measured for different saturation temperatures when compared to the pure system. Potassium dihydrogen orthophosphate crystals were rapidly grown from both pure and SSA-added solutions by adopting the same crystal growth procedure. The crystal grown

Guohui Li; Genbo Su; Xinxin Zhuang; Zhengdong Li; Youping He

2004-01-01

397

Surface Tension of Pure Metals.  

National Technical Information Service (NTIS)

A literature survey of the experimentally determined values for the surface tension (gamma) of molten pure metals has been carried out in order to provide an assessed data-base for use with a mathematical model currently being developed to predict the sur...

B. J. Keene

1991-01-01

398

Turbulence in Pure Superfluid Flow  

NASA Astrophysics Data System (ADS)

A series of experiments is described which provides an unambiguous description of the steady-state properties of turbulence in pure superfluid flow. The turbulence is qualitatively different from that observed in counterflow but comparable to the homogeneous turbulence described by theory.

Ashton, R. A.; Opatowsky, L. B.; Tough, J. T.

1981-03-01

399

Turbulence in pure superfluid flow  

SciTech Connect

A series of experiments is described which provide an unambiguous description of the steady-state properties of turbulence in pure superfluid flow. The turbulence is qualitatively different from that observed in counterflow but comparable to the homogeneous turbulence described by theory.

Ashton, R.A.; Opatowsky, L.B.; Tough, J.T.

1981-03-09

400

Chemical Characterization of Apricot Puree  

Microsoft Academic Search

The chemical compositions of apricot purees made from 11 varieties of apricots from Italy were determined. The analyses included ash, total solids, soluble solids, organic acids (citric, malic, D-isocitric, succinic, and ascorbic), sugars (glucose, fructose, sucrose, sorbitol, and raffinose), minerals (Na, K, Ca, Mg, and P), amino acids, and total protein. Liquid chromatography was used for the separation, identification, and

A. Lo Voi; M. Impembo; G. Fasanaro; D. Castaldo

1995-01-01

401

Experimental Shock Decomposition of Siderite and the Origin of Magnetite in Martian Meteorite ALH84001.  

National Technical Information Service (NTIS)

Shock recovery experiments to determine whether magnetite could be produced by the decomposition of iron-carbonate were initiated. Naturally occurring siderite was first characterized by electron microprobe (EMP), transmission electron microscopy (TEM), M...

M. S. Bell

2007-01-01

402

Wind Mediated Oxidation of Magnetite: A Putative Mechanism for Hematite Production on Mars  

NASA Astrophysics Data System (ADS)

Experiments on magnetite (Fe3O4) to produce hematite (Fe2O3) under martian conditions are reported. Water and atmospheric oxygen are not involved in oxidation. The findings represent a putative mechanism for the reddish color of Mars.

Merrison, J. P.; Gunnlaugsson, H. P.; Nørnberg, P.; Knak Jensen, S.

2011-03-01

403

Metallization of magnetite (Fe{sub 3}O{sub 4}) under high pressure  

SciTech Connect

Electrical resistivity measurements have been made on a good qualified single crystalline magnetite (Fe{sub 3}O{sub 4}) at temperatures from 300 down to 3.0 K under pressure up to 10 GPa. A steep change in resistivity at the Verwey transition temperature has been observed at pressure below 6.5 GPa, which shows a quite distinct result reported in prior work. Moreover, the Verwey transition temperature has been found to decrease nonlinearly with increasing pressure and it disappears at around 8 GPa. Above 8 GPa magnetite exhibits metallic behavior. The residual-resistivity ratio of the metallic state is observed to be more than 350. This finding of a metallic ground state in magnetite provides insight into the understanding of the Verwey transition in magnetite. {copyright} 2001 American Institute of Physics.

Todo, S.; Takeshita, N.; Kanehara, T.; Mori, T.; Mori, N.

2001-06-01

404

Replacement of pyrite framboids by magnetite in limestone and implications for palaeomagnetism  

NASA Astrophysics Data System (ADS)

LIMESTONES are an important source of palaeomagnetic data, with magnetite the dominant carrier of the magnetization. Because the magnetite is present in low concentrations, however, it has been directly observed only rarely and in trace amounts in acid-treated separates. Such residues are composed primarily of spheres, the ultimate origin of which has been enigmatic7. Yet interpretation of the palaeomagnetic data depends on a knowledge of the origin of the magnetite, which has been inferred to carry either a chemical or a viscous remanent magnetization. Here we present electron microscope data obtained from a sequence of samples of Onondaga Limestone from an east-west traverse across northern New York, which unambiguously show that magnetite spheres are derived by alteration and replacement of framboidal pyrite. Remagnetization is thus caused by chemical, rather than viscous, processes. This chemical remanent magnetization is compatible with a fluid-mediated event occurring on a regional scale, induced by tectonic stress of Alleghenian (late Palaeozoic) age.

Suk, D.; Peacor, D. R.; der Voo, R. Van

1990-06-01

405

Magnetic and Structural Properties of Magnetite in Radular Teeth of Chiton Acanthochiton Rubrolinestus  

NASA Astrophysics Data System (ADS)

The major radular lateral teeth of Polyplacophora Chiton comprise a magnetite biomineral cap.We have investigated the structure and magnetic properties of the biomineralized magnetite crystallites in mature teeth of Chiton Acanthochiton Rubrolinestus. From the measurement of magnetic properties of tooth particles using SQUID magnetometry we find that the saturation magnetization and the Verwey transition temperature (Tv) are 78.4 emu/g and 105 K, respectively. An in situ examination of the structure of magnetite-bearing region within individual tooth using the high resolution TEM, together with electron diffraction (ED) pattern and energy-dispersive X-ray (EDX) analyses indicates magnetite microcrystal form electron-dense polycrystalline sheets with typical length 800 nm and width 150 nm or so. These polycrystalline sheets are arranged regularly along the longitude direction of the tooth cutting surface. Furthermore, the microcrystallites in polycrystalline sheet take on the generally good crystallinity.

Han, Y. N.; Liu, C. L.; Yao, L. D.; Wang, Y.; Han, X. F.

2008-03-01

406

Controllable in situ synthesis of magnetite coated silica-core water-dispersible hybrid nanomaterials.  

PubMed

Magnetite nanoparticle coated silica (Fe3O4@SiO2) hybrid nanomaterials hold an important position in the fields of cell imaging and drug delivery. Here we report a large scale synthetic procedure that allows attachment of magnetite nanoparticles onto a silica surface in situ. Many different silica nanomaterials such as Stöber silica nanospheres, mesoporous silica nanoparticles, and hollow silica nanotubes have been coated with a high density layer of water-dispersible magnetite nanoparticles. The size and attachment efficiency of the magnetite nanoparticle can be well tuned by adjusting the precursor concentration and reflux time. The functionalization of Fe3O4@SiO2 nanoparticles with dye molecules and biocompatible polymers impart optical imaging modality and good colloidal stability in either buffer solution or serum. The functionalized materials also exhibited strong potential as negative contrast agents in T2 weighted magnetic resonance imaging. PMID:23889037

Qu, Haiou; Tong, Sheng; Song, Kejing; Ma, Hui; Bao, Gang; Pincus, Seth; Zhou, Weilie; O'Connor, Charles

2013-08-12

407

[High-temperature microbial sulfate reduction can be accompanied by magnetite formation].  

PubMed

The hyperthermophilic sulfate-reducing archaeon Archaeoglobus fulgidus was found to be capable of lithoautotrophic growth on medium containing molecular hydrogen, sulfate, and amorphous Fe(III) oxide. During the growth of this microorganism, amorphous Fe(III) oxide was transformed into black strongly magnetic sediment rich in magnetite, as shown by Mossbauer studies. Experiments involving inhibition of microbial sulfate reduction and abiotic controls revealed that magnetite production resulted from chemical reactions proceeding at elevated temperatures (83 degrees C) between molecular hydrogen, amorphous Fe(III) oxide, and sulfide formed enzymatically in the course of dissimilatory sulfate reduction. It follows that magnetite production in this system can be characterized as biologically mediated mineralization. This is the first report of magnetite formation as a result of activity of sulfate-reducing microorganisms. PMID:15521182

Slobodkin, A I; Chistiakova, N I; Rusakov, V S

408

The enhanced coercivity for the magnetite/silica nanocomposite at room temperature  

SciTech Connect

Magnetite/silica nanocomposite was synthesized by a facile solvothermal processing at 150 deg. C for about 10 h. X-ray diffraction (XRD) analysis revealed the effect of annealing on the crystallinity of silica. Transmission electron microscopy (TEM) images showed the good dispersion of magnetite in the silica matrix. Magnetic properties of the nanocomposite were characterized by vibration sample magnetometer (VSM), and the enhanced coercivity was explained by the intrinsic anisotropy of the particles enhanced by the interparticle dipolar fields.

Wu Mingzai [Structure Research Laboratory, Department of Materials Science and Engineering, University of Science and Technology of China, Hefei 230026 (China); Xiong Ying [Structure Research Laboratory, Department of Materials Science and Engineering, University of Science and Technology of China, Hefei 230026 (China); Peng Zhenmeng [Structure Research Laboratory, Department of Materials Science and Engineering, University of Science and Technology of China, Hefei 230026 (China); Jiang Nan [Structure Research Laboratory, Department of Materials Science and Engineering, University of Science and Technology of China, Hefei 230026 (China); Qi Haiping [Structure Research Laboratory, Department of Materials Science and Engineering, University of Science and Technology of China, Hefei 230026 (China); Chen Qianwang [Structure Research Laboratory, Department of Materials Science and Engineering, University of Science and Technology of China, Hefei 230026 (China)]. E-mail: cqw@ust.edu.cn

2004-10-04

409

Natural magnetite nanoparticles from an iron-ore deposit: size dependence on magnetic properties  

NASA Astrophysics Data System (ADS)

We report on the discovery of magnetite nanoparticles ranging in size from 2 to 14 nm in the mineralized zones of the Peña Colorada iron-ore deposit, southern Mexico. Micrometric scale magnetite was magnetically reduced and divided into distinct size ranges: 85-56 ?m, 56-30 ?m, 30-22 ?m, 22-15 ?m, 15-10 ?m, 10-7 ?m and 7-2 ?m. Nanometric-scale magnetite in the size range 2-14 nm was identified. The magnetite was characterized by X-ray diffraction, transmitted and reflected light microscope, high-resolution transmission electron microscopy (TEM), high angle annular dark field, Mössbauer spectroscopy and its magnetic properties. Crystallographic identification of nanostructures was performed using high-resolution TEM. Characteristic changes were observed when the particles make the size transition from micro- to nanometric sizes, as follows: (1) frequency-dependent magnetic susceptibility percentage (?FD%) measurements show high values (13%) for the 2-14 nm fractions attributed to dominant fractions of superparamagnetic particles; (2) variations of ?FD% < 4.5% in fractions of 56-0.2 ?m occur in association with the presence of microparticles formed by magnetite aggregates of nanoparticles (<15 nm) embedded in berthierine; (3) Mössbauer spectroscopy results identified a superparamagnetic fraction; (4) nanometric and 0.2-7 ?m grain size magnetite particles require a magnetic field up to 152 mT to reach saturation during the isothermal remanent magnetization experiment; (5) coercivity and remanent magnetization of the magnetite increase when the particle size decreases, probably due to parallel coupling effects; (6) two-magnetic susceptibility versus temperature experiments of the same 2-14 nm sample show that the reversibility during the second heating is due to the formation of new magnetite nanoparticles and growth of those already present during the first heating process.

Rivas-Sánchez, M. L.; Alva-Valdivia, L. M.; Arenas-Alatorre, J.; Urrutia-Fucugauchi, J.; Perrin, M.; Goguitchaichvili, A.; Ruiz-Sandoval, M.; Ramos Molina, M. A.

2009-01-01

410

Adsorption of polymer coated magnetite composite particles onto carbon nanotubes and their magnetorheology  

Microsoft Academic Search

Polymer coated nano-sized magnetite (Fe3O4) particles with multiwalled carbon nanotube (MWNT) nanohybrid were prepared by four step procedures in this study. Initially, magnetic particles were synthesized by a co-precipitation method with ammonium hydroxide and oleic acid, and then the produced particles were coated with polyacrylamide (PAAm). Finally PAAm coated magnetite particles (Mag-PAAm) were physically adsorbed onto multiwalled carbon nanotubes (MWNT)

S. W. Ko; M. S. Yang; H. J. Choi

2009-01-01

411

The effect of magnetite particle size on paleointensity determinations of the geomagnetic field  

Microsoft Academic Search

The Thellier method for paleointensity determinations has been applied to prepared samples containing magnetites whose mean particle sizes range from single domain, SD, to multidomain, MD. Linear (ideal) PNRM-PTRM curves are obtained for samples containing SD and submicron magnetite particles. However, for MD particles non-linear (concave-up) PNRM-PTRM curves are observed such that a linear approximation to the lower blocking-temperature data

Shaul Levi

1977-01-01

412

Sulfur isotopic composition of the magnetite-series and ilmenite-series granitoids in Japan  

Microsoft Academic Search

Sulfur isotopic composition has been measured on 30 granitoids and 11 gabbroids from the Cretaceous and Tertiary granitic terranes of Japan. The two series of granitoids, the magnetite-series and ilmenite-series, defined by Ishihara (1977), show two specific isotope trends. The magnetite-series granioids all have positive d (su34)S (CDT) values from +1 to +9‰, while the ilmenite-series rocks are dominated by

Akira Sasaki; Shunso Ishihara

1979-01-01

413

Simulation of magnetic hysteresis in pseudo-single-domain grains of magnetite  

Microsoft Academic Search

Magnetic hysteresis has been simulated in grains of magnetite for the size range 0.1-0.7 microns. This was achieved using an unconstrained three-dimensional micromagnetic model of single grains of magnetite with cubic magnetocrystalline anisotropy. Hysteresis loops were obtained for fields applied along both the easy and hard magnetocrystalline axes. Both discrete (Barkhausen) jumps and gradual changes in the magnetic structure are

W. Williams; David J. Dunlop

1995-01-01

414

Theoretical Single-Domain Grain Size Range in Magnetite and Titanomagnetite  

Microsoft Academic Search

A theoretical model of single-domain (SD) grain sizes is applied to magnetite and titanomagnetite. In this model, transition to a two-domain configuration takes place at the SD threshold do. This two-domain configuration is shown to be more applicable to fine-grained magnetites in igneous rocks than previous models involving transition to a circular spin configuration at do. Calculations of the stable

Robert F. Butler; Subir K. Banerjee

1975-01-01

415

Trace elements in disseminated sulfides, magnetite, and massive sulfides, West Shasta district, California.  

USGS Publications Warehouse

Samples of pyrite separates from massive sulphide layers vary stratigraphically in trace-element content, and show an enrichment of many of the elements in the centre of the layers. Trace-element contents of pyrite of massive sulphide deposits, of magnetite from a magnetite deposit, and of disseminated sulphides differ, presumably reflecting different origins. Trace-element contents of pyrite separates also differ among the sampled massive sulphide deposits. -G.J.N.

Botinelly, T.; Siems, D. F.; Sanzolone, R. F.

1985-01-01