Sample records for pure magnetite crystals

  1. Crystal morphology of MV1 magnetite

    Microsoft Academic Search

    SIMON J. CLEMETT; KATHIE L. THOMAS-KEPRTA; JOEL SHIMMIN; MARY MORPHEW; J. RICHARD MCINTOSH; DENNIS A. BAZYLINSKI; JOSEPH L. KIRSCHVINK; SUSAN J. WENTWORTH; DAVID S. MCKAY; HOJATOLLAH VALI; EVERETT K. GIBSON JR.; CHRISTOPHER S. ROMANEK

    2002-01-01

    Intracellular magnetite (Fe 3O4) crystals produced by magnetotactic bacteria strain MV-1 are in the single-domain size range, and are chemically pure. We have previously suggested that they exhibit an unusual crystal habit described as truncated hexa-octahedral. Such a crystal morphology has not been demonstrated for any inorganic population of magnetite, nor would it be expected, given considerations of symmetry and

  2. 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)

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

    2009-03-01

    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.

  3. Non-chemically Pure Magnetites Produced from Thermal Decomposition of Ankerites

    NASA Astrophysics Data System (ADS)

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

    2008-12-01

    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.

  4. Magnetic properties of hydrothermally recrystallized magnetite crystals

    Microsoft Academic Search

    Franz Heider; David J. Dunlop; Naoji Sugiura

    1987-01-01

    The discrepancy between the magnetic hysteresis properties of magnetite crystals that are precipitated from solution and of crushed sifted grains (larger than 300 nm) is not an inherent property of magnetite but is caused by the highly stressed state of crushed material and by adhering finer fragments. The size trends of magnetic properties exhibited by submicron-size precipitated grains continue in

  5. Ferromagnetic Resonance Absorption in Magnetite Single Crystals

    Microsoft Academic Search

    L. R. Bickford

    1950-01-01

    The microwave resonance absorption technique, at both 1.25 and 3.3 cm wave-lengths, was used to study the ferromagnetic crystalline anisotropy characteristics and g-factor of magnetite Fe3O4. The experiments were performed on single crystals, both synthetic and natural, from room temperature to -195°C. Depending upon the temperature, magnetite single crystals were found to have magnetic anisotropy characteristics similar to those of

  6. Hydrothermal synthesis of magnetite crystals: From sheet to pseudo-octahedron

    SciTech Connect

    Hu, Ming; Ji, Rui-Ping [Department of Physics, Center of Functional Nanomaterials and Devices, East China Normal University, Shanghai 200241 (China)] [Department of Physics, Center of Functional Nanomaterials and Devices, East China Normal University, Shanghai 200241 (China); Jiang, Ji-Sen, E-mail: jsjiang@phy.ecnu.edu.cn [Department of Physics, Center of Functional Nanomaterials and Devices, East China Normal University, Shanghai 200241 (China)] [Department of Physics, Center of Functional Nanomaterials and Devices, East China Normal University, Shanghai 200241 (China)

    2010-12-15

    In this paper, we developed a hydrothermal method to fabricate sheet-like and pseudo-octahedral magnetite crystals. X-ray diffraction (XRD) confirmed the products were pure spinel-structured magnetite. Scanning electron microscopy (SEM) was used to investigate the morphology of the obtained crystals. By carefully regulating the initial NaOH concentrations, the morphology of the products could be changed from sheet-like crystals to pseudo-octahedral crystals. Transmission electron microscopy (TEM) analysis indicated the sheet-like crystals were the oriented aggregation of nanoparticles. Pseudo-octahedral magnetite crystals were single crystalline, and were obtained by dissolution-recrystallization of the sheet-like crystals. Vibrating sample magnetometer (VSM)) suggested the magnetic properties of the products were strongly related to the morphology. The coercivity of the sheet-like magnetite crystals was 100 Oe, larger than 30 Oe of the pseudo-octahedral crystals, but the saturation magnetization of the sheet-like magnetite crystals was 40 emu/g, smaller than 85 emu/g of the pseudo-octahedral crystals.

  7. Truncated hexa-octahedral magnetite crystals in ALH84001: presumptive biosignatures.

    PubMed

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

    2001-02-27

    McKay et al. [(1996) Science 273, 924-930] suggested that carbonate globules in the meteorite ALH84001 contained the fossil remains of Martian microbes. We have characterized a subpopulation of magnetite (Fe(3)O(4)) crystals present in abundance within the Fe-rich rims of these carbonate globules. We find these Martian magnetites to be both chemically and physically identical to terrestrial, biogenically precipitated, intracellular magnetites produced by magnetotactic bacteria strain MV-1. Specifically, both magnetite populations are single-domain and chemically pure, and exhibit a unique crystal habit we describe as truncated hexa-octahedral. There are no known reports of inorganic processes to explain the observation of truncated hexa-octahedral magnetites in a terrestrial sample. In bacteria strain MV-1 their presence is therefore likely a product of Natural Selection. Unless there is an unknown and unexplained inorganic process on Mars that is conspicuously absent on the Earth and forms truncated hexa-octahedral magnetites, we suggest that these magnetite crystals in the Martian meteorite ALH84001 were likely produced by a biogenic process. As such, these crystals are interpreted as Martian magnetofossils and constitute evidence of the oldest life yet found. PMID:11226210

  8. Truncated hexa-octahedral magnetite crystals in ALH84001: Presumptive biosignatures

    PubMed Central

    Thomas-Keprta, Kathie L.; Clemett, Simon J.; Bazylinski, Dennis A.; Kirschvink, Joseph L.; McKay, David S.; Wentworth, Susan J.; Vali, Hojatollah; Gibson, Everett K.; McKay, Mary Fae; Romanek, Christopher S.

    2001-01-01

    McKay et al. [(1996) Science 273, 924–930] suggested that carbonate globules in the meteorite ALH84001 contained the fossil remains of Martian microbes. We have characterized a subpopulation of magnetite (Fe3O4) crystals present in abundance within the Fe-rich rims of these carbonate globules. We find these Martian magnetites to be both chemically and physically identical to terrestrial, biogenically precipitated, intracellular magnetites produced by magnetotactic bacteria strain MV-1. Specifically, both magnetite populations are single-domain and chemically pure, and exhibit a unique crystal habit we describe as truncated hexa-octahedral. There are no known reports of inorganic processes to explain the observation of truncated hexa-octahedral magnetites in a terrestrial sample. In bacteria strain MV-1 their presence is therefore likely a product of Natural Selection. Unless there is an unknown and unexplained inorganic process on Mars that is conspicuously absent on the Earth and forms truncated hexa-octahedral magnetites, we suggest that these magnetite crystals in the Martian meteorite ALH84001 were likely produced by a biogenic process. As such, these crystals are interpreted as Martian magnetofossils and constitute evidence of the oldest life yet found. PMID:11226210

  9. Truncated hexa-octahedral magnetite crystals in ALH84001: presumptive biosignatures

    NASA Technical Reports Server (NTRS)

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

    2001-01-01

    McKay et al. [(1996) Science 273, 924-930] suggested that carbonate globules in the meteorite ALH84001 contained the fossil remains of Martian microbes. We have characterized a subpopulation of magnetite (Fe(3)O(4)) crystals present in abundance within the Fe-rich rims of these carbonate globules. We find these Martian magnetites to be both chemically and physically identical to terrestrial, biogenically precipitated, intracellular magnetites produced by magnetotactic bacteria strain MV-1. Specifically, both magnetite populations are single-domain and chemically pure, and exhibit a unique crystal habit we describe as truncated hexa-octahedral. There are no known reports of inorganic processes to explain the observation of truncated hexa-octahedral magnetites in a terrestrial sample. In bacteria strain MV-1 their presence is therefore likely a product of Natural Selection. Unless there is an unknown and unexplained inorganic process on Mars that is conspicuously absent on the Earth and forms truncated hexa-octahedral magnetites, we suggest that these magnetite crystals in the Martian meteorite ALH84001 were likely produced by a biogenic process. As such, these crystals are interpreted as Martian magnetofossils and constitute evidence of the oldest life yet found.

  10. Magnetite Crystal Orientation in Magnetosome Chains

    PubMed Central

    Körnig, André; Winklhofer, Michael; Baumgartner, Jens; Gonzalez, Teresa Perez; Fratzl, Peter; Faivre, Damien

    2014-01-01

    One-dimensional magnetic nanostructures have magnetic properties superior to non-organized materials due to strong uniaxial shape anisotropy. Magnetosome chains in magnetotactic bacteria represent a biological paradigm of such magnet, where magnetite crystals synthesized in organelles called magnetosomes are arranged into linear chains. Two-dimensional synchrotron X-ray diffraction (XRD) is applied to cells of magnetotactic bacteria that are pre-aligned with a magnetic field to determine the crystallographic orientation of magnetosomes relative to the chain axis. The obtained pole figure patterns reveal a [111] fiber texture along the chain direction for magnetospirilla strains MSR-1 and AMB-1, whereas a [100] fiber texture is measured for Desulfovibrio magneticus strain RS-1. The [100] axis appears energetically unfavorable because it represents a magnetic hard axis in magnetite, but can be turned into an effective easy axis by particle elongation along [100] for aspect ratios higher than 1.25, consistent with aspect ratios in RS-1 magnetosomes determined earlier. The pronounced fiber textures can be explained either by a strain-specific biological control on crystal orientation at the chain level or by physical alignment effects due to intra-chain magnetic interactions. In this case, biological control of the axis of elongation would be sufficient to influence the crystallographic texture of the magnetosome chain. PMID:25866495

  11. Single crystal electrical resistivity of magnetite under high pressure

    NASA Astrophysics Data System (ADS)

    Muramatsu, Takaki; Helmuth Berger Collaboration; Lev V Gasparov Collaboration; Viktor V. Struzhkin Collaboration; Russell J. Hemley Collaboration

    2015-03-01

    Magnetite (Fe3O4), the oldest known magnetic mineral has the cubic inversed spinel structure at ambient pressure and temperature. It shows a metal to insulator transition (Verway transition) at about 125 K as temperature decreases at ambient pressure. Under high pressure the Verwey transition is suppressed down to 0 K and above 25 GPa magnetite undergoes a structural transformation to high pressure phase. These behaviors have been intensively examined by various experimental means and computational calculations for decades. However only the limited number of the electrical resistivity measurements on single crystal magnetite under pressure have been performed at the moment. We performed high pressure and low temperature experiments by means of the electrical resistivity on single crystal magnetite to examine Verwey transition under pressure and a structural transformation from cubic spinel phase to high pressure phase. We report the results of the temperature dependence of the electrical resistivity in the pressure range from ambient pressure to more than 50 GPa.

  12. Magnetotransport properties of a percolating network of magnetite crystals embedded in a glass-ceramic matrix

    Microsoft Academic Search

    Paolo Allia; Oana Bretcanu; Enrica Vernè; Federica Celegato; Marco Coisson; Paola Tiberto; Franco Vinai; Federico Spizzo; Melissa Tamisari

    2009-01-01

    Electrical resistance, magnetization, and magnetoresistance have been measured as functions of temperature from 50 to 300 K on three ferromagnetic glass ceramics containing different magnetite crystals by preparing conditions and crystal morphology. Magnetite crystals form a percolating network for electrons with weak links at crystal-crystal contact points. All samples exhibit a broadened Verwey transition, peaked at temperatures lower than measured

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

    NASA Astrophysics Data System (ADS)

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

    1998-01-01

    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.

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

    PubMed

    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

    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

  15. Magnetotransport properties of a percolating network of magnetite crystals embedded in a glass-ceramic matrix

    NASA Astrophysics Data System (ADS)

    Allia, Paolo; Bretcanu, Oana; Vernè, Enrica; Celegato, Federica; Coisson, Marco; Tiberto, Paola; Vinai, Franco; Spizzo, Federico; Tamisari, Melissa

    2009-04-01

    Electrical resistance, magnetization, and magnetoresistance have been measured as functions of temperature from 50 to 300 K on three ferromagnetic glass ceramics containing different magnetite crystals by preparing conditions and crystal morphology. Magnetite crystals form a percolating network for electrons with weak links at crystal-crystal contact points. All samples exhibit a broadened Verwey transition, peaked at temperatures lower than measured in bulk stoichiometric magnetite. The negative magnetoresistance ratio increases in absolute value with sample cooling from RT down to the Verwey temperature and decreases on further cooling. This behavior indicates that electron transfer between magnetite crystals is achieved through spin-dependent and spin-independent channels acting in parallel. Magnetic correlation states for spins at contact points between magnetite crystals are studied by plotting the magnetoresistance as a function of reduced magnetization. The transition from activated hopping to variable range hopping affects the magnetoresistance versus magnetization curves.

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

    PubMed Central

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

    2011-01-01

    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. PMID:21169637

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

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

    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.

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

    NASA Astrophysics Data System (ADS)

    Taylor, G. J.

    2007-10-01

    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!

  19. Pressure effect on magnetic hysteresis parameters of single-domain magnetite contained in natural plagioclase crystal

    NASA Astrophysics Data System (ADS)

    Sato, Masahiko; Yamamoto, Yuhji; Nishioka, Takashi; Kodama, Kazuto; Mochizuki, Nobutatsu; Usui, Yoichi; Tsunakawa, Hideo

    2015-07-01

    This study investigates pressure effects on the magnetic properties of non-interacting single-domain (SD) magnetite. Using a high-pressure cell specially designed for a Magnetic Property Measurement System, magnetic hysteresis measurements were conducted under high pressures of up to 1 GPa on natural plagioclase crystals containing much acicular SD magnetite. Coercivity and saturation magnetization were nearly constant with pressure, while saturation remanent magnetization and coercivity of remanence decreased with pressure at moderate rates of -8 per cent GPa-1 and -18 per cent GPa-1, respectively. These results suggest that temperature effects govern the magnetic behaviour of acicular SD magnetite grains in the middle and lower crusts.

  20. Crystal growth of bullet-shaped magnetite in magnetotactic bacteria of the Nitrospirae phylum.

    PubMed

    Li, Jinhua; Menguy, Nicolas; Gatel, Christophe; Boureau, Victor; Snoeck, Etienne; Patriarche, Gilles; Leroy, Eric; Pan, Yongxin

    2015-02-01

    Magnetotactic bacteria (MTB) are known to produce single-domain magnetite or greigite crystals within intracellular membrane organelles and to navigate along the Earth's magnetic field lines. MTB have been suggested as being one of the most ancient biomineralizing metabolisms on the Earth and they represent a fundamental model of intracellular biomineralization. Moreover, the determination of their specific crystallographic signature (e.g. structure and morphology) is essential for palaeoenvironmental and ancient-life studies. Yet, the mechanisms of MTB biomineralization remain poorly understood, although this process has been extensively studied in several cultured MTB strains in the Proteobacteria phylum. Here, we show a comprehensive transmission electron microscopy (TEM) study of magnetic and structural properties down to atomic scales on bullet-shaped magnetites produced by the uncultured strain MYR-1 belonging to the Nitrospirae phylum, a deeply branching phylogenetic MTB group. We observed a multiple-step crystal growth of MYR-1 magnetite: initial isotropic growth forming cubo-octahedral particles (less than approx. 40 nm), subsequent anisotropic growth and a systematic final elongation along [001] direction. During the crystal growth, one major {111} face is well developed and preserved at the larger basal end of the crystal. The basal {111} face appears to be terminated by a tetrahedral-octahedral-mixed iron surface, suggesting dimensional advantages for binding protein(s), which may template the crystallization of magnetite. This study offers new insights for understanding magnetite biomineralization within the Nitrospirae phylum. PMID:25566884

  1. Co-ordinated functions of Mms proteins define the surface structure of cubo-octahedral magnetite crystals in magnetotactic bacteria.

    PubMed

    Arakaki, Atsushi; Yamagishi, Ayana; Fukuyo, Ayumi; Tanaka, Masayoshi; Matsunaga, Tadashi

    2014-08-01

    Magnetotactic bacteria synthesize magnetosomes comprised of membrane-enveloped single crystalline magnetite (Fe3 O4 ). The size and morphology of the nano-sized magnetite crystals (magnetite crystal morphology remain largely unknown. The group of proteins, called Mms (Mms5, Mms6, Mms7, and Mms13), was previously isolated from the surface of cubo-octahedral magnetite crystals in Magnetospirillum magneticum strain AMB-1. Analysis of an mms6 gene deletion mutant suggested that the Mms6 protein plays a major role in the regulation of magnetite crystal size and morphology. In this study, we constructed various mms gene deletion mutants and characterized the magnetite crystals formed by the mutant strains. Comparative analysis showed that all mms genes were involved in the promotion of crystal growth in different manners. The phenotypic characterization of magnetites also suggested that these proteins are involved in controlling the geometries of the crystal surface structures. Thus, the co-ordinated functions of Mms proteins regulate the morphology of the cubo-octahedral magnetite crystals in magnetotactic bacteria. PMID:24961165

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

    SciTech Connect

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

    2000-01-01

    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.

  3. Hysteresis of Magnetite, Hematite and Pyrrhotite Crystals at High and Low Temperatures

    NASA Astrophysics Data System (ADS)

    Dunlop, D. J.

    2008-12-01

    Alternating gradient force magnetometers and sensitive vibrating-sample magnetometers operating above, at, and below room temperature have enabled rapid reliable measurements of hysteresis and remanence curves. The hysteresis parameters Ms, Mrs, Hc, plus the remanence coercivity Hcr, are routinely determined, at room temperature at least, and reported in the form of a Day plot as an indication of domain state and inferred grain size. Yet our knowledge of the hysteresis and remanence properties of individual crystals or sized crystal aggregates of magnetite, titanomagnetite, hematite, pyrrhotite and other important magnetic minerals has scarcely advanced beyond what was known at the end of the 1980's. Applications have indeed outstripped fundamental studies. This presentation will focus on new hysteresis measurements for well-sized magnetites of a variety of origins; magnetite inclusions in plagioclase, pyroxene, amphiboles and biotite; hematite; and pyrrhotite. Measurements were made at 20oC intervals from 25oC to the Curie point for all magnetites and hematites and at 10oC intervals for pyrrhotite. For one set of sized magnetites (0.6, 3, 6, 9, 14 and 110 micrometers), hysteresis and back-field remanence curves were also measured below room temperature (every 10 K from 10 K to 70 K, every 5 K from 80 K to 140 K, and every 10 K from 150 K to 300 K). These data give a wealth of information about the individual mineral crystals and trends linking crystals of common origin but different sizes. From Ms(T) we obtain precise Curie points and transition temperatures. Mrs(T)/Ms(T) tracks sometimes subtle changes in domain structure with changing temperature. Hc(T) gives an indication of the mechanism(s) of anisotropy, important for understanding TRM acquisition in crystals above single-domain size. Mrs(T) and Hc(T) often show substantial irreversible changes in the first heating- cooling cycle, particularly but not exclusively for synthetic crystals, stabilizing in subsequent cycles. Finally, Mrs(T)/Ms(T) vs. Hcr(T)/Hc(T) data trace curves on a Day plot showing unmistakable differences in domain structure between monoclinic and cubic magnetite, as well as more subtle changes away from the Verwey transition.

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

    Microsoft Academic Search

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

    2011-01-01

    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

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

    Microsoft Academic Search

    Özden Özdemir; David J. Dunlop

    1998-01-01

    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

  6. Size control of in vitro synthesized magnetite crystals by the MamC protein of Magnetococcus marinus strain MC-1.

    PubMed

    Valverde-Tercedor, C; Montalbán-López, M; Perez-Gonzalez, T; Sanchez-Quesada, M S; Prozorov, T; Pineda-Molina, E; Fernandez-Vivas, M A; Rodriguez-Navarro, A B; Trubitsyn, D; Bazylinski, Dennis A; Jimenez-Lopez, C

    2015-06-01

    Magnetotactic bacteria are a diverse group of prokaryotes that share the unique ability of biomineralizing magnetosomes, which are intracellular, membrane-bounded crystals of either magnetite (Fe3O4) or greigite (Fe3S4). Magnetosome biomineralization is mediated by a number of specific proteins, many of which are localized in the magnetosome membrane, and thus is under strict genetic control. Several studies have partially elucidated the effects of a number of these magnetosome-associated proteins in the control of the size of magnetosome magnetite crystals. However, the effect of MamC, one of the most abundant proteins in the magnetosome membrane, remains unclear. In this present study, magnetite nanoparticles were synthesized inorganically in free-drift experiments at 25 °C in the presence of different concentrations of the iron-binding recombinant proteins MamC and MamCnts (MamC without its first transmembrane segment) from the marine, magnetotactic bacterium Magnetococcus marinus strain MC-1 and three commercial proteins [?-lactalbumin (?-Lac), myoglobin (Myo), and lysozyme (Lyz)]. While no effect was observed on the size of magnetite crystals formed in the presence of the commercial proteins, biomimetic synthesis in the presence of MamC and MamCnts at concentrations of 10-60 ?g/mL resulted in the production of larger and more well-developed magnetite crystals (~30-40 nm) compared to those of the control (~20-30 nm; magnetite crystals grown protein-free). Our results demonstrate that MamC plays an important role in the control of the size of magnetite crystals and could be utilized in biomimetic synthesis of magnetite nanocrystals. PMID:25874532

  7. Truncated Hexa-Octahedral Magnetite Crystals in Martian Meteorite ALH84001: Evidence of Biogenic Activity on Early Mars

    NASA Technical Reports Server (NTRS)

    Thomas-Keprta, K.; Clemett, S. J.; Schwartz, C.; McIntosh, J. R.; Bazylinski, D. A.; Kirschvink, J.; McKay, D. S.; Gibson, E. K.; Vali, H.; Romanek, C. S.

    2004-01-01

    The landmark paper by McKay et al. [1] cited four lines of evidence associated with the Martian meteorite ALH84001 to support the hypothesis that life existed on Mars approximately 4 Ga ago. Now, more than five years later, attention has focused on the ALH84001 magnetite grains embedded within carbonate globules in the ALH84001 meteorite. We have suggested that up to approx.25% of the ALH84001 magnetite crystals are products of biological activity [e.g., 2]. The remaining magnetites lack sufficient characteristics to constrain their origin. The papers of Thomas Keprta et al. were criticized arguing that the three dimensional structure of ALH84001 magnetite crystals can only be unambiguously determined using electron tomographic techniques. Clemett et al. [3] confirmed that magnetites produced by magnetotactic bacteria strain MV-I display a truncated hexa-octahedral geometry using electron tomography and validated the use of the multi-tilt classical transmission microscopy technique used by [2]. Recently the geometry of the purported martian biogenic magnetites was shown be identical to that for MV-1 magnetites using electron tomography [6].

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

    PubMed Central

    Friedmann, E. Imre; Wierzchos, Jacek; Ascaso, Carmen; Winklhofer, Michael

    2001-01-01

    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

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

    PubMed

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

    2001-02-27

    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

  10. Pressure-induced crystal structure and spin-state transitions in magnetite (Fe3O4).

    PubMed

    Ju, Sheng; Cai, Tian-Yi; Lu, Hai-Shuang; Gong, Chang-De

    2012-08-22

    High pressure is an important dimension for the emergent phenomena in transition metal oxides, including high-temperature superconductivity, colossal magnetoresistance, and magnetoelectric coupling. In these multiply correlated systems, the interplay between lattice, charge, orbital, and spin is extremely susceptible to external pressure. Magnetite (Fe(3)O(4)) is one of the oldest known magnetic materials and magnetic minerals, yet its high pressure behaviors are still not clear. In particular, the crystal structure of the high-pressure phase has remained contentious. Here, we investigate the pressure-induced phase transitions in Fe(3)O(4) from first-principles density-functional theory. It is revealed that the net magnetic moment, arising from two ferrimagnetically coupled sublattices in Fe(3)O(4), shows an abrupt drop when entering into the high-pressure phase but recovers finite value when the pressure is beyond 65.1 GPa. The origin lies in the redistribution of Fe 3d orbital occupation with the change of crystal field, where successive structural transitions from ambient pressure phase Fd3[combining overline]m to high pressure phase Pbcm (at 29.7 GPa) and further to Bbmm (at 65.1 GPa) are established accurately. These findings not only explain the experimental observations on the structural and magnetic properties of the highly compressed Fe(3)O(4) but also suggest the existence of highly magnetized magnetite in the Earth's lower mantle. PMID:22823905

  11. Variation in trace element content of magnetite crystallized from a fractionating sulfide liquid, Sudbury, Canada: Implications for provenance discrimination

    NASA Astrophysics Data System (ADS)

    Dare, Sarah A. S.; Barnes, Sarah-Jane; Beaudoin, Georges

    2012-07-01

    Laser ablation ICP-MS analysis has been applied to many accessory minerals in order to understand better the process by which the rock formed and for provenance discrimination. We have determined trace element concentrations of Fe-oxides in massive sulfides that form Ni-Cu-PGE deposits at the base of the Sudbury Igneous Complex in Canada. The samples represent the crystallization products of fractionating sulfide liquids and consist of early-forming Fe-rich monosulfide solution (MSS) cumulates and residual Cu-rich intermediate solid solution (ISS). This study shows that Fe-oxide geochemistry is a sensitive petrogenetic indicator for the degree of fractionation of the sulfide liquid and provides an insight into the partitioning of elements between sulfide and Fe-oxide phases. In addition, it is useful in determining the provenance of detrital Fe-oxide. In a sulfide melt, all lithophile elements (Cr, Ti, V, Al, Mn, Sc, Nb, Ga, Ge, Ta, Hf, W and Zr) are compatible into Fe-oxide. The concentrations of these elements are highest in the early-forming Fe-oxide (titanomagnetite) which crystallized with Fe-rich MSS. Upon the continual crystallization of Fe-oxide from the sulfide liquid, the lithophile elements gradually decrease so that late-forming Fe-oxide (magnetite), which crystallized from the residual Cu-rich liquid, is depleted in these elements. This behavior is in contrast with Fe-oxides that crystallized from a fractionating silicate melt, whereby the concentration of incompatible elements, such as Ti, increases rather than decreases. The behavior of the chalcophile elements in magnetite is largely controlled by the crystallization of the sulfide minerals with only Ni, Co, Zn, Mo, Sn and Pb present above detection limit in magnetite. Nickel, Mo and Co are compatible in Fe-rich MSS and thus the co-crystallizing Fe-oxide is depleted in these elements. In contrast, magnetite that crystallized later from the fractionated liquid with Cu-rich ISS is enriched in Ni, Mo and Co because Fe-rich MSS is absent. The concentrations of Sn and Pb, which are incompatible with Fe-rich MSS, are highest in magnetite that formed from the fractionated Cu-rich liquid. At subsolidus temperatures, ilmenite exsolved from titanomagnetite whereas Al-spinel exsolved from the cores of some magnetite, locally redistributing the trace elements. However, during laser ablation ICP-MS analysis of these Fe-oxides both the magnetite and its exsolution products are ablated so that the analysis represents the original magmatic composition of the Fe-oxide that crystallized from the sulfide melt.

  12. Molarity (Aromic Density) of the Elements as Pure Crystals.

    ERIC Educational Resources Information Center

    Pauling, Linus; Herman, Zelek S.

    1985-01-01

    Provides background information for teachers on the atomic density of the elements as pure crystals. Atomic density is defined as the reciprocal of the atomic volume. Includes atomic-density diagrams which were prepared using the atomic-volume values given by Singman, supplemented by additional values for some allotropes. (JN)

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

    NASA Astrophysics Data System (ADS)

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

    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.

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

    NASA Astrophysics Data System (ADS)

    Özdemir, Özden; Dunlop, David J.

    1998-02-01

    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.

  15. Electronic conduction in basalt glass and glass-ceramics - correlation with magnetite crystallization

    Microsoft Academic Search

    J. R. Jurado-Egea; A. E. Owen; A. K. Bandyopadhyay

    1987-01-01

    The d.c. conductivity measurements have been made in a wide range of temperature on a basalt glass heat-treated at different temperatures to form magnetite particles. Small polaron hopping mechanism is operative in the as-annealed glass between Fe2+ and Fe3+ ions in the isolated state. This mechanism is operative in the heat-treated samples between these ions in the magnetite grains. The

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

    NASA Technical Reports Server (NTRS)

    Thomas-Keptra, Katie L.; Clemett, S. J.; Wentworth S. J.; Mckay, D. S.; Gibson, E. K., Jr.

    2010-01-01

    Martian meteorite ALH84001 preserves evidence of interaction with aqueous fluids while on Mars in the form of microscopic carbonate disks believed to have formed approx.3.9 Ga ago at beginning of the Noachian epoch. Intimately associated within and throughout these carbonate disks are nanocrystal magnetites (Fe3O4) with unusual chemical and physical properties, whose ori gins 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. We have sought to resolve between these hypotheses through the detailed characterized of the compositional and structural relationships between the carbonate disks, their associated magnetites and the orthopyroxene matrix in which they are embedded [1]. Comparison of these results with experimental thermal decomposition studies of sideritic carbonates conducted under a range of heating scenarios suggests that the magnetite nanocrystals in the ALH84001 carbonate disks are not the products of thermal decomposition.

  17. Degeneration of biogenic superparamagnetic magnetite.

    PubMed

    Li, Y-L; Pfiffner, S M; Dyar, M D; Vali, H; Konhauser, K; Cole, D R; Rondinone, A J; Phelps, T J

    2009-01-01

    Magnetite crystals precipitated as a consequence of Fe(III) reduction by Shewanella algae BrY after 265 h incubation and 5-year anaerobic storage were investigated with transmission electron microscopy, Mössbauer spectroscopy and X-ray diffraction. The magnetite crystals were typically superparamagnetic with an approximate size of 13 nm. The lattice constants of the 265 h and 5-year crystals are 8.4164A and 8.3774A, respectively. The Mössbauer spectra indicated that the 265 h magnetite had excess Fe(II) in its crystal-chemistry (Fe(3+) (1.990)Fe(2+) (1.015)O(4)) but the 5-year magnetite was Fe(II)-deficient in stoichiometry (Fe(3+) (2.388)Fe(2+) (0.419)O(4)). Such crystal-chemical 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 anaerobic 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. PMID:19200144

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

    E-print Network

    Chen, Ray

    for high-dispersion application in phased array antenna systems based on photonic crystal fiber arraysDesign of a broadband highly dispersive pure silica photonic crystal fiber Harish Subbaraman,1 Tao-concentric-core pure silica photonic crystal fiber is designed with a maximum chromatic dispersion value of about 9500

  19. Origin of magnetite crystals in Martian meteorite ALH84001 carbonate disks

    NASA Astrophysics Data System (ADS)

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

    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.

  20. New insights into the origin of magnetite crystals in ALH84001 carbonate disks

    NASA Technical Reports Server (NTRS)

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

    2009-01-01

    Martian meteorite ALH84001 preserves evidence of interaction with aqueous fluids while on Mars in the form of microscopic carbonate disks which are believed to have precipitated approximately 3.9 Ga ago at beginning of the Noachian epoch. Intimately 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. One group of hypotheses argues that these Fe3O4 are the product of partial thermal decomposition of the host carbonate. Alternatively, the origins of Fe3O4 and carbonate may be unrelated; that is, from the perspective of the carbonate the magnetite is allochthonous. We have sought to resolve between these hypotheses through the detailed characterized of the compositional and structural relationships of the carbonate disks and associated magnetites with the orthopyroxene matrix in which they are embedded. We focus this discussion on the composition of ALH84001 magnetites and then compare these observations with those from experimental thermal decomposition studies of sideritic carbonates under a range of plausible geological heating scenarios.

  1. Origin of Magnetite Crystals in Martian Meteorite ALH84001 Carbonate Disks

    NASA Technical Reports Server (NTRS)

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

    2010-01-01

    Martian meteorite ALH84001 preserves evidence of interaction with aqueous fluids while on Mars in the form of microscopic carbonate disks which are believed to have precipitated approx.3.9 Ga ago at beginning of the Noachian epoch. Intimately 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. One group of hypotheses argues that these Fe3O4 are the product of partial thermal decomposition of the host carbonate. Alternatively, the origins of Fe3O4 and carbonate may be unrelated; that is, from the perspective of the carbonate the magnetite is allochthonous. We have sought to resolve between these hypotheses through the detailed characterized of the compositional and structural relationships of the carbonate disks and associated magnetites with the orthopyroxene matrix in which they are embedded [1]. We focus this discussion on the composition of ALH84001 magnetites and then compare these observations with those from our thermal decomposition studies of sideritic carbonates under a range of plausible geological heating scenarios.

  2. Magnetocrystalline anisotropy of magnetite.

    PubMed

    ?ezní?ek, R; Chlan, V; Št?pánková, H; Novák, P; Maryško, M

    2012-02-01

    The spin reorientation temperature T(SR) of stoichiometric Fe(3)O(4), as well as of magnetite with a small number of vacancies and magnetite containing a low concentration of Ti, Zn, Al and Ga was measured on single-crystal samples using the ac susceptibility. In the same experiment the temperature T(V) of the Verwey transition was also found. The results show that a correlation between T(SR) and T(V) exists. The electronic structure of the compounds studied was determined using the density-functional-based GGA + U method. For stoichiometric magnetite the first and second cubic anisotropy constants were calculated, while for magnetite with defects the distribution of electron density using the 'atoms in molecules' approach was determined. Based on a combination of experimental results with the electronic structure calculations an explanation of the temperature dependence of the magnetocrystalline anisotropy of magnetite is suggested. PMID:22227433

  3. Characterization and phylogenetic identification of a species of spherical multicellular magnetotactic prokaryotes that produces both magnetite and greigite crystals.

    PubMed

    Zhang, Rui; Chen, Yi-Ran; Du, Hai-Jian; Zhang, Wen-Yan; Pan, Hong-Miao; Xiao, Tian; Wu, Long-Fei

    2014-09-01

    Magnetotactic bacteria (MTB) are a group of Gram-negative bacteria synthesizing magnetic crystals that allow them aligning along magnetic field lines. They have diverse morphologies including cocci, rods, vibrio, spirilla, and multicellular magnetotactic prokaryotes (MMPs). MMPs are composed of 10-57 cells with peritrichous flagella on their outer surfaces and swim as an entire unit. Here, we describe a species of spherical MMPs isolated from intertidal sediments of Lake Yuehu (Yellow Sea, China). They were mainly found in the subsurface layer of gray-black sediments. Microscopy revealed that these spherical MMPs were 5.6 ± 0.9 ?m in diameter and composed of approximately 16-32 ovoid cells with a helical arrangement and peritrichous flagellation. High-resolution transmission electron microscopy showed that the MMPs contained both bullet-shaped magnetite and irregular greigite magnetosomes that were arranged in chains or clusters. These MMPs displayed typical escape motility and negative phototaxis. The 16S rRNA genes of micromanipulation-purified spherical MMPs were cloned and sequenced. Phylogenetic analysis revealed that the MMP species was affiliated with Deltaproteobacteria and displayed >2.8% sequence divergence with respect to previously reported MMPs. This is the first phylogenetic identification of a spherical MMP that produces both magnetite and greigite magnetosomes. PMID:25086260

  4. Mechanism for carrier velocity saturation in pure organic crystals V. M. Kenkre

    E-print Network

    Kenkre, V.M.

    of injected charge carriers with increasing electric field has been observed in pure organic crystals of photoinjected charge carriers in pure organic crystals, the analysis having been motivated by observations dt kvk qE, 1 where q is the carrier charge, E is the electric field, vk (1/ )d k /dk is the group

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

    PubMed Central

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

    2013-01-01

    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. PMID:23685871

  6. Unidirectional growth of pure and L-lysine added ADP crystals from aqueous solution

    NASA Astrophysics Data System (ADS)

    Salarian, Samaneh; Dizaji, Hamid Rezagholipour

    2014-01-01

    Pure and L-lysine added ammonium dihydrogen phosphate (ADP) crystals were grown in the <001> direction by Sankaranarayanan-Ramasamy (S-R) method. The grown crystals were characterized by X-Ray diffractometry (XRD), UV-Vis spectroscopy, Fourier Transform Infrared (FT-IR) and Vicker's Microhardness analysis. XRD spectrum of each of the grown crystals proved its crystallinity. The crystals showed good transparency in the entire visible region. FT-IR spectra of the specimens revealed the presence of functional groups in them. The hardness of the pure and L-lysine added ADP crystals were measured and that of the added one was found higher. Meanwhile, it was found that the ADP crystals (pure and L-lysine added) grown by S-R method had higher hardness compared to ADP crystal grown by conventional method.

  7. Morphological Evidence for an Exclusively Inorganic Origin for Magnetite in Martian Meteorite ALH84001

    NASA Technical Reports Server (NTRS)

    Golden, D. C.; Ming, D. W.; Morris, R. V.; Brearley, A. J.; Lauer, H. V., Jr.; Treiman, A.; Zolensky, M. E.; Schwandt, C. S.; Lofgren, G. E.; McKay, G. A.

    2003-01-01

    The origin of magnetite crystals in Martian Meteorite ALH84001 is the focus of a debate about the possibility of past (and present) life on Mars. McKay et al. originally suggested that some of the magnetite crystals associated with carbonate globules in Martian Meteorite ALH84001 are biogenic in ori-gin, because they are single magnetic domain, free of crystalline defects, chemically pure, and coexist with other metastable phases in apparent disequilibrium. Thomas-Keprta et al. reported that a subpopulation of magnetite crystals (approx. 25%) associated with carbonate globules in ALH84001 and magnetite crystals produced by magnetotactic bacterial strain MV-1 have similar morphologies with crystal elongation along the [111] crystallographic axis that they describe as "truncated hexa-octahedral" ([111-THO]) magnetite. Along with several other properties, the [111]-THO morphology has been proposed to constitute a biomarker (i.e., formed only in biogenic processes), so that the presence of [111]-THO magnetite in ALH84001 may be evidence for past life on Mars.

  8. Characterization of pure and urea-doped ?-glycine single crystals grown by solution method

    Microsoft Academic Search

    P. Selvarajan; J. Glorium Arul Raj; S. Perumal

    2009-01-01

    Pure and urea-doped gamma-glycine (?-glycine) single crystals were grown by solution method with slow evaporation technique. When urea was added as dopant, morphological alterations were noticed in ?-glycine crystals. Structural characterization of the grown crystals was carried out by single and powder X-ray diffraction (XRD) methods and it is observed that the samples crystallize in non-centrosymmetric space groups. UV–visible transmittance

  9. Cooling crystallization of aluminum sulfate in pure water

    NASA Astrophysics Data System (ADS)

    Sun, Xiaoxue; Sun, Yuzhu; Yu, Jianguo

    2015-06-01

    This study investigated the cooling crystallization of aluminum sulfate to explore the basic data for the recovery of aluminum resources from coal spoil. First, the metastable zone width (MSZW) of aluminum sulfate was reported. A parallel synthesis platform (CrystalSCAN) was used to determine the solubility from 10 °C to 70 °C, and an automatic lab reactor (LabMax) equipped with focused beam reflectance measurement (FBRM) was adopted to determine the supersolubility. The effects of operating variables on MSZW were experimentally explored. Results show that the MSZW of aluminum sulfate decreases with increasing stirring speed, while it increases with increasing cooling rate. Second, the continuous crystallization kinetics of aluminum sulfate was investigated in a laboratory-scale mixed-suspension mixed-product removal (MSMPR) crystallizer at a steady state. Growth kinetics presented size-dependent growth rate, which was well fitted with the MJ3 model. Both the growth rate (G) and the total nucleation rate (BTOT) were correlated in the power law kinetic expressions with good correlation coefficients. Third, aluminum sulfate products were modified by sodium dodecylbenzenesulfonate (SDBS). Crystals with large sizes and regular hexagonal plate morphologies were obtained. These crystals reveal that SDBS can inhibit crystal nucleation and promote crystal growth.

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

    NASA Astrophysics Data System (ADS)

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

    2012-06-01

    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.

  11. PII S0016-7037(00)00481-6 Elongated prismatic magnetite crystals in ALH84001 carbonate globules

    E-print Network

    examined 206 magnetites recovered from strain MV-1 cells. Natural (Darwinian) selection in terrestrial the physical and chemical properties that optimize their magnetic moment. In this study, we describe six), properties that, collectively, are not observed in any known population of inorganic magnetites

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

    SciTech Connect

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

    2006-05-25

    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.

  13. Crystal nucleation in glass-forming alloy and pure metal melts under containerless and vibrationless conditions

    NASA Technical Reports Server (NTRS)

    Turnbull, D.

    1979-01-01

    Crystal nucleation behavior in metallic alloys known to form glasses in melt quenching was characterized and from this characterization the possibility that massive amounts of certain alloys could be slow cooled to the glass state was assessed. Crystal nucleation behavior of pure liquid metals was examined experimentally, under containerless conditions, and theoretically.

  14. Isolation of isoelectrically pure cholera toxin for crystallization

    SciTech Connect

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

    1989-01-01

    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.

  15. Theory of transport properties of pure, single crystal zinc

    Microsoft Academic Search

    P. G. Tomlinson

    1979-01-01

    Pseudopotential calculations have been performed by Tomlinson and Swihart to obtain phonon frequencies and polarization vectors, the Fermi surface, band velocities, and multi-orthogonalized-plane-wave electron-phonon matrix elements for pure zinc. These results are then used to determine the electrical and thermal resistivities which result from the scattering of electrons by thermal phonons. The same interaction also contributes to the attenuation of

  16. Inorganic Formation of ``Truncated Hexa-Octahedral'' Magnetite: Implications for Inorganic Processes in Martian Meteorite ALH84001

    NASA Astrophysics Data System (ADS)

    Golden, D. C.; Ming, D. W.; Lauer, H. V., Jr.; Schwandt, C. S.; Morris, R. V.; Lofgren, G. E.; McKay, G. A.

    2002-03-01

    We report the first inorganic laboratory synthesis of a unique crystal morphology for magnetite that corresponds to magnetite produced by magnetotactic bacterial strain MV-1 and reported for some magnetite crystals in Martian meteorite ALH84001.

  17. Structure and morphology of magnetite anaerobically-produced by a marine magnetotactic bacterium and a dissimilatory iron-reducing bacterium

    USGS Publications Warehouse

    Sparks, N.H.C.; Mann, S.; Bazylinski, D.A.; Lovley, D.R.; Jannasch, H.W.; Frankel, R.B.

    1990-01-01

    Intracellular crystals of magnetite synthesized by cells of the magnetotactic vibroid organism, MV-1, and extracellular crystals of magnetite produced by the non-magnetotactic dissimilatory iron-reducing bacterium strain GS-15, were examined using high-resolution transmission electron microscopy, electron diffraction and 57Fe Mo??ssbauer spectroscopy. The magnetotactic bacterium contained a single chain of approximately 10 crystals aligned along the long axis of the cell. The crystals were essentially pure stoichiometric magnetite. When viewed along the crystal long axis the particles had a hexagonal cross-section whereas side-on they appeared as rectangules or truncated rectangles of average dimension, 53 ?? 35 nm. These findings are explained in terms of a three-dimensional morphology comprising a hexagonal prism of {110} faces which are capped and truncated by {111} end faces. Electron diffraction and lattice imaging studies indicated that the particles were structurally well-defined single crystals. In contrast, magnetite particles produced by the strain, GS-15 were irregular in shape and had smaller mean dimensions (14 nm). Single crystals were imaged but these were not of high structural perfection. These results highlight the influence of intracellular control on the crystallochemical specificity of bacterial magnetites. The characterization of these crystals is important in aiding the identification of biogenic magnetic materials in paleomagnetism and in studies of sediment magnetization. ?? 1990.

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

    PubMed

    Treiman, Allan H

    2003-01-01

    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

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

    NASA Astrophysics Data System (ADS)

    Treiman, Allan H.

    2003-06-01

    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).

  20. Extracellular synthesis of magnetite and metal-substituted magnetite nanoparticles.

    PubMed

    Roh, Y; Vali, H; Phelps, T J; Moon, J W

    2006-11-01

    We have developed a novel microbial process that exploits the ability of Fe(III)-reducing microorganisms to produce copious amounts of extracellular magentites and metal-substituted magnetite nanoparticles. The Fe(III)-reducing bacteria (Theroanaerobacter ethanolicus and Shewanella sp.) have the ability to reduce Fe(III) and various metals in aqueous media and form various sized magnetite and metal-substituted magnetite nano-crystals. The Fe(III)-reducing bacteria formed metalsubstituted magnetites using iron oxide plus metals (e.g., Co, Cr, Mn, Ni) under conditions of relatively low temperature (<70 degrees C), ambient pressure, and pH values near neutral to slightly basic (pH = 6.5 to 9). Precise biological control over activation and regulation of the biosolid-state processes can produce magnetite particles of well-defined size (typically tens of nanometers) and crystallographic morphology, containing selected dopant metals into the magnetite (Fe(3-y)XyO4) structure (where X = Co, Cr, Mn, Ni). Magnetite yields of up to 20 g/L per day have been observed in 20-L vessels. Water-based ferrofluids were formed with the nanometer sized, magnetite, and metal-substituted biomagnetite particles. PMID:17252802

  1. Optical, dosimetric, and scintillation properties of pure sapphire crystals

    NASA Astrophysics Data System (ADS)

    Futami, Yoshisuke; Yanagida, Takayuki; Fujimoto, Yutaka

    2014-02-01

    Optical, dosimetric, and scintillation properties of undoped sapphire (Al2O3) single crystals fabricated by different methods of the Czochralski (Cz) and the Bridgman were investigated. In X-ray induced radioluminescence spectra, they showed emission peaks at 240 and 300 nm due to exciton and F+ centers, respectively. Scintillation decay times of F+ center was fast around few ns. As a dosimetric property, from 0.01 to 2 Gy X-ray was exposed to them and they exhibited a thermally stimulated luminescence (TSL) with a good linearity. The glow peaks of them were similar, 150, 250, and 325 °C. In TSL, the Bridgeman sample represented only F+-center emission while the Cz sample showed F at 400 nm and F+ at 300 nm centers emission.

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

    NASA Astrophysics Data System (ADS)

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

    2013-04-01

    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.

  3. Trace elements in magnetite as petrogenetic indicators

    NASA Astrophysics Data System (ADS)

    Dare, Sarah A. S.; Barnes, Sarah-Jane; Beaudoin, Georges; Méric, Julien; Boutroy, Emilie; Potvin-Doucet, Christophe

    2014-10-01

    We have characterized the distribution of 25 trace elements in magnetite (Mg, Al, Si, P, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Ga, Ge, Y, Zr, Nb, Mo, Sn, Hf, Ta, W, and Pb), using laser ablation ICP-MS and electron microprobe, from a variety of magmatic and hydrothermal ore-forming environments and compared them with data from the literature. We propose a new multielement diagram, normalized to bulk continental crust, designed to emphasize the partitioning behavior of trace elements between magnetite, the melt/fluid, and co-crystallizing phases. The normalized pattern of magnetite reflects the composition of the melt/fluid, which in both magmatic and hydrothermal systems varies with temperature. Thus, it is possible to distinguish magnetite formed at different degrees of crystal fractionation in both silicate and sulfide melts. The crystallization of ilmenite or sulfide before magnetite is recorded as a marked depletion in Ti or Cu, respectively. The chemical signature of hydrothermal magnetite is distinct being depleted in elements that are relatively immobile during alteration and commonly enriched in elements that are highly incompatible into magnetite (e.g., Si and Ca). Magnetite formed from low-temperature fluids has the lowest overall abundance of trace elements due to their lower solubility. Chemical zonation of magnetite is rare but occurs in some hydrothermal deposits where laser mapping reveals oscillatory zoning, which records the changing conditions and composition of the fluid during magnetite growth. This new way of plotting all 25 trace elements on 1 diagram, normalized to bulk continental crust and elements in order of compatibility into magnetite, provides a tool to help understand the processes that control partitioning of a full suit of trace elements in magnetite and aid discrimination of magnetite formed in different environments. It has applications in both petrogenetic and provenance studies, such as in the exploration of ore deposits and in sedimentology.

  4. Scintillation properties of pure and Ce$^{3+}$-doped SrF$_2$ crystals

    E-print Network

    Shendrik, R; Nepomnyashchikh, A I

    2012-01-01

    In this paper results of scintillation properties measurements of pure and Ce3+-doped strontium fluoride crystals are presented. We measure light output, scintillation decay time profile and temperature stability of light output. X-ray excited luminescence outputs corrected for spectral response of monochromator and photomultiplier for pure SrF2 and SrF2-0.3 mol.% Ce3+ are approximately 95% and 115% of NaI-Tl emission output, respectively. A photopeak with a 10% full width at half maximum is observed at approximately 84% the light output of a NaI-Tl crystal after correction for spectral response of photomultiplier, when sample 10x10 mm of pure SrF2 crystal is excited with 662 KeV photons. Corrected light output of SrF2-0.3 mol.% Ce3+ under 662 KeV photon excitation is found at approximately 64% the light output of the NaI-Tl crystal.

  5. Scintillation properties of pure and Ce$^{3+}$-doped SrF$_2$ crystals

    E-print Network

    R. Shendrik; E. A. Radzhabov; A. I. Nepomnyashchikh

    2012-10-14

    In this paper results of scintillation properties measurements of pure and Ce3+-doped strontium fluoride crystals are presented. We measure light output, scintillation decay time profile and temperature stability of light output. X-ray excited luminescence outputs corrected for spectral response of monochromator and photomultiplier for pure SrF2 and SrF2-0.3 mol.% Ce3+ are approximately 95% and 115% of NaI-Tl emission output, respectively. A photopeak with a 10% full width at half maximum is observed at approximately 84% the light output of a NaI-Tl crystal after correction for spectral response of photomultiplier, when sample 10x10 mm of pure SrF2 crystal is excited with 662 KeV photons. Corrected light output of SrF2-0.3 mol.% Ce3+ under 662 KeV photon excitation is found at approximately 64% the light output of the NaI-Tl crystal.

  6. Magnetism in nanometer-thick magnetite

    NASA Astrophysics Data System (ADS)

    Monti, Matteo; Santos, Benito; Mascaraque, Arantzazu; Rodríguez de La Fuente, Oscar; Niño, Miguel Angel; Mente?, Tevfik Onur; Locatelli, Andrea; McCarty, Kevin F.; Marco, José F.; de La Figuera, Juan

    2012-01-01

    The oldest known magnetic material, magnetite, is of current interest for use in spintronics as a thin film. An open question is how thin can magnetite films be and still retain the robust ferrimagnetism required for many applications. We have grown 1-nm-thick magnetite crystals and characterized them in situ by electron and photoelectron microscopies including selected-area x-ray circular dichroism. Well-defined magnetic patterns are observed in individual nanocrystals up to at least 520 K, establishing the retention of ferrimagnetism in magnetite two unit cells thick.

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

    PubMed

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

    2007-11-01

    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

  8. Radiation effects in pure and doped Al 2O 3 crystals

    NASA Astrophysics Data System (ADS)

    Kristianpoller, N.; Rehavi, A.; Shmilevich, A.; Weiss, D.; Chen, R.

    1998-05-01

    Effects of ?-, X- and UV-radiation on optical properties of nominally pure as well as of variously doped ?-Al 2O 3 crystals were studied. Optical absorption, thermoluminescence (TL) and photoluminescence (PL) were measured. The irradiation with wavelengths below 145 nm had essentially the same effects as X-irradiation, indicating that the same defects were formed in both cases. F and F + emission bands at 410 and 330 nm appeared in the TL and in the PL of all samples. In crystals doped with rare-earth ions the narrow bands, characteristic for these impurities, were dominant. In some of the nominally pure samples also a strong Cr 3+ band appeared at 698 nm. In the C-doped crystals the TL and PL emissions were relatively strong and dominated by the F and F + emission bands. These results support previous suggestions regarding a high anion vacancy concentration in the C-doped crystals. A weak emission band appeared near 500 nm with an excitation maximum near 300 nm and is attributed to interstitial Al i+ ions. Prolonged UV- illumination with F-light caused a notable increase in the PL yield in the C-doped samples. Irradiation into the Al i+ absorption band at 300 nm had a reverse effect and was also efficient for the optical bleaching of the phototransferred TL (PTTL).

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

    NASA Astrophysics Data System (ADS)

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

    2007-06-01

    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.

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

    PubMed

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

    2007-06-01

    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

  11. Statistical Analyses Comparing Prismatic Magnetite Crystals in ALH84001 Carbonate Globules with those from the Terrestrial Magnetotactic Bacteria Strain MV-1

    NASA Technical Reports Server (NTRS)

    Thomas-Keprta, Kathie L.; Clemett, Simon J.; Bazylinski, Dennis A.; Kirschvink, Joseph L.; McKay, David S.; Wentworth, Susan J.; Vali, H.; Gibson, Everett K.

    2000-01-01

    Here we use rigorous mathematical modeling to compare ALH84001 prismatic magnetites with those produced by terrestrial magnetotactic bacteria, MV-1. We find that this subset of the Martian magnetites appears to be statistically indistinguishable from those of MV-1.

  12. Growth and properties of pure and rare earth-doped Ca 3 (BO 3) 2 single crystal

    Microsoft Academic Search

    Xiuai Lu; Zhenyu You; Jianfu Li; Zhaojie Zhu; Guohua Jia; Yan Wang; Baichang Wu; Chaoyang Tu

    2005-01-01

    Large novel birefringent pure and rare earth-doped calcium borate crystals (Ca3(BO3)2) have been grown successfully by Czochralski technique. Thermal expansion coefficients of pure Ca3(BO3)2 have been obtained for the first time. Trivalent rare earth ions (RE3+), such as Dy3+- and Nd3+-doped calcium borate crystal, have been grown for optic application. Absorption and fluorescence spectra as well as fluorescence decay curves

  13. Light response of pure CsI calorimeter crystals painted with wavelength-shifting lacquer

    E-print Network

    Frlez, E; Krause, B; Pocanic, D; Renker, D; Ritt, S; Slocum, P L; Supek, I; Wirtz, H P; Broennimann, Ch.

    2001-01-01

    We have measured scintillation properties of pure CsI crystals used in the shower calorimeter built for a precise determination of the pi+ -> pi0 e+ nu decay rate at the Paul Scherrer Institute (PSI). All 240 individual crystals painted with a special wavelength-shifting solution were examined in a custom-build detection apparatus (RASTA=radioactive source tomography apparatus) that uses a 137Cs radioactive gamma source, cosmic muons and a light emitting diode as complementary probes of the scintillator light response. We have extracted the total light output, axial light collection nonuniformities and timing responses of the individual CsI crystals. These results predict improved performance of the 3 pi sr PIBETA calorimeter due to the painted lateral surfaces of 240 CsI crystals. The wavelength-shifting paint treatment did not affect appreciably the total light output and timing resolution of our crystal sample. The predicted energy resolution for positrons and photons in the energy range of 10-100 MeV was ...

  14. Light response of pure CsI calorimeter crystals painted with wavelength-shifting lacquer

    NASA Astrophysics Data System (ADS)

    Frlež, E.; Brönnimann, Ch.; Krause, B.; Po?ani?, D.; Renker, D.; Ritt, S.; Slocum, P. L.; Supek, I.; Wirtz, H. P.

    2001-03-01

    We have measured scintillation properties of pure CsI crystals used in the shower calorimeter built for a precise determination of the ?+? ?0 e+?e decay rate at the Paul Scherrer Institute (PSI). All 240 individual crystals painted with a special wavelength-shifting solution were examined in a custom-built detection apparatus (RASTA - radioactive source tomography apparatus) that uses a 137Cs radioactive gamma source, cosmic muons and a light-emitting diode as complementary probes of the scintillator light response. We have extracted the total light output, axial light collection nonuniformities and timing responses of the individual CsI crystals. These results predict improved performance of the 3 ? sr PIBETA calorimeter due to the painted lateral surfaces of 240 CsI crystals. The wavelength-shifting paint treatment did not affect appreciably the total light output and timing resolution of our crystal sample. The predicted energy resolution for positrons and photons in the energy range of 10-100 MeV was nevertheless improved due to the more favorable axial light collection probability variation. We have compared simulated calorimeter ADC spectra due to 70 MeV positrons and photons with a Monte Carlo calculation of an ideal detector light response.

  15. Swift Heavy Ion Beam Modified Behaviour of Pure and Doped TGS Crystals

    SciTech Connect

    Bajpai, P. K. [Department of Pure and Applied Physics Guru Ghasidas University, Koni, Bilaspur-495009 India (India)

    2009-03-10

    Modifications due to swift heavy ion (SHI) beam irradiation on polar surfaces of pure and doped tri-glycine sulphate (TGS) crystals are investigated using dielectric, ferroelectric, optical and scanning force microcopy with varying ion beam fluence. The dielectric response becomes diffuse and the loss decreases, the optical band gap gets modified, the surface micro-relief's show pits and protrusions converting into regular hillocks of nano-dimensions. The results are interpreted considering that irradiation takes the crystal to a non-equilibrium state and generates thermal/charge flux leading to thermally generated internal field. The micro-relief is explained as a result of domain orientation; piezoelectric compression and stretching creating inhomogeneous force gradient at domain walls.

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

    NASA Astrophysics Data System (ADS)

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

    2013-03-01

    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.

  17. Panning for Gold and Magnetite

    NSDL National Science Digital Library

    Eleanora Robbins

    In this activity, students can learn to pan for gold and magnetite. They will learn skills such as making observations under field conditions and watching out for poison ivy. They will see the effects of stream flow on sediments and observe sedimentary structures such as stream bars and islands, observe that different sizes of sediment are located in different parts of the stream, distinguish between different sizes of sediment, and recognize that different minerals are different colors. In addition, they can estimate and weigh the content of magnetite and nonmagnetite, observe crystal shapes of some of the mineral grains, and discuss why magnets pick up magnetite but not nonmagnetic grains. Choose desired title from main listing of activities to access individual exercises.

  18. Pure, single crystal Ge nanodots formed using a sandwich structure via pulsed UV excimer laser annealing

    NASA Astrophysics Data System (ADS)

    Liao, Ting-Wei; Chen, Hung-Ming; Shen, Kuan-Yuan; Kuan, Chieh-Hsiung

    2015-04-01

    In this paper, a sandwich structure comprising a SiO2 capping layer, amorphous Germanium (a-Ge) nanodots (NDs), and a pit-patterned Silicon (Si) substrate is developed, which is then annealed by utilizing a pulsed ultraviolet excimer laser in order to fabricate an array of pure, single crystal Ge NDs at room temperature. A wide bandgap SiO2 capping layer is used as a transparent thermally isolated layer to prevent thermal loss and Si–Ge intermixing. The two-dimensional pit-patterned Si substrate is designed to confine the absorbed laser energy, reduce the melting point, and block the surface migration of the Ge. After optimizing the laser radiation parameters such that the laser energy density is 200 mJ cm?2, the laser annealing period is 10 s, and the number of laser shots is 10, pure, single crystal Ge NDs that have both a regular arrangement and a uniform size distribution are obtained in the pits of the Si substrates. The Raman spectrum shows a highly symmetric Ge transversal optical peak with a full width at half maximum of 4.2 cm?1 at 300.7 cm?1, which is close to that of the original Ge wafer. In addition, the high-resolution transmission electron microscopy image for the Ge NDs and the corresponding selected area electron diffraction pattern shows a clear single crystalline structure without any impurities.

  19. Magnetoresistance of magnetite films prepared by reactive evaporation

    Microsoft Academic Search

    Takao Furubayashi

    2003-01-01

    It was attempted to fabricate magnetite films by evaporating metallic iron in an oxygen atmosphere onto substrates at room temperature. From the characterization by x-ray diffraction and Mössbauer spectroscopy, the obtained films were found to consist of alpha-Fe, FeO, and Fe3O4 depending on the oxygen pressure. Pure magnetite was obtained when prepared in 5×10-6 Torr oxygen. The magnetite film exhibited

  20. Growth and properties of pure and rare earth-doped Ca 3 (BO 3) 2 single crystal

    NASA Astrophysics Data System (ADS)

    Lu, Xiuai; You, Zhenyu; Li, Jianfu; Zhu, Zhaojie; Jia, Guohua; Wang, Yan; Wu, Baichang; Tu, Chaoyang

    2005-08-01

    Large novel birefringent pure and rare earth-doped calcium borate crystals (Ca 3(BO 3) 2) have been grown successfully by Czochralski technique. Thermal expansion coefficients of pure Ca 3(BO 3) 2 have been obtained for the first time. Trivalent rare earth ions (RE 3+), such as Dy 3+- and Nd 3+-doped calcium borate crystal, have been grown for optic application. Absorption and fluorescence spectra as well as fluorescence decay curves of Dy 3+-, Nd 3+-doped Ca 3(BO 3) 2 crystals are measured at room temperature. Optical spectra show that there are obvious absorptions at ultraviolet to IR region. The strong emissions in visible and infrared region show that calcium borate is a suitable for rare earth-doped laser crystal.

  1. Magnetite in Chitons

    Microsoft Academic Search

    Manabu Mizota; Yutaka Maeda

    1985-01-01

    Radular teeth of chitons were studied using Mössbauer spectroscopy. Their spectra gave clear evidence of the presence of magnetite and a small amount of paramagnetic substance. These are characteristic features in biogenic magnetite. Measurements on the teeth at different locations along the radular were also performed. The results show that the magnetite in the radular teeth of chitons changes considerably

  2. Structural, spectroscopic, optical, dielectric and mechanical study of pure and l-Proline doped ammonium dihydrogen phosphate single crystals.

    PubMed

    Hasmuddin, Mohd; Singh, Preeti; Shkir, Mohd; Abdullah, M M; Vijayan, N; Bhagavannarayana, G; Wahab, M A

    2014-04-01

    Single crystals of pure and l-Proline (LP) C5H9NO2 doped ammonium dihydrogen phosphate (ADP) (NH4) H2PO4 were grown by slow evaporation solution technique (SEST) at ambient conditions. Powder X-ray diffraction (PXRD) analysis was carried out to confirm the crystal structure and no additional phase was observed due to doping except a systematic variation in peak intensities. FT-Raman analysis also confirms that there is no additional phase formation due to doping. Fourier transform infrared spectral analysis was done to examine the presence of various functional groups in the grown crystals. UV-VIS-NIR spectroscopic analysis was carried out to see the change in optical transparency of pure ADP and crystals due to LP with different doping concentrations. The high-resolution X-ray diffraction (HRXRD) analysis was carried out to examine the crystalline perfection and observed reasonable changes with LP doping. Second harmonic generation (SHG) efficiency measurement was done to examine the enhancement in the nonlinear optical characteristics of the grown crystals. The dielectric behavior of the samples shows that the dielectric constant decreased with increase the value of frequency. The effect of LP dopant on crystal morphology, mechanical properties of ADP has also been presented in this paper. The above studies reveal the effect of incorporation of LP into the lattice of ADP crystals. PMID:24412791

  3. The I-Xe Age of Orgueil Magnetite: New Results

    NASA Technical Reports Server (NTRS)

    Pravdivtseva, O. V.; Hohenberg, C. M.; Meshik, A. P.

    2003-01-01

    I-Xe ages of Murchison and Orgueil magnetites were reported to be the oldest [1] and interpreted as the condensation time of the solar nebula. More recent measurements, conducted on a highly magnetic separate from Orgueil (but not pure magnetite), gave much younger I-Xe ages [2]. We have since performed new studies on two pure separates of Orgueil magnetite, confirming the later closing time of the I-Xe system in this mineral phase. In the previous work of Lewis and Anders [1] special attention was paid to the purity of the analyzed material. It was shown, that the trapped Xe resided mostly in hydrated silicates and the radiogenic 129Xe in magnetite [3]. Therefore, Orgueil was finely ground and stirred with a saturated LiCl solution for 8 days at 60 C to remove the silicate-magnetite intergrowth. Although this procedure yields magnetic fractions that are at least 90% pure [1], it could potentially contaminate the magnetite with iodine and produce noncorrelated 128Xe and spurious I-Xe ages. To avoid this possibility, in our first work with Orgueil we deliberately omitted separation in LiCl solution. Instead, the meteorite was ground into a fine powder and the highly magnetic fraction was separated with a hand magnet and was confirmed to be largely magnetite [2]. The new work, reported here, was done in order to confirm our previous results and investigate the effects of the LiCl treatment on the I-Xe system in magnetite.

  4. Growth, mechanical, thermal and dielectric properties of pure and doped KHP single crystal

    NASA Astrophysics Data System (ADS)

    M, Lakshmipriya.; Babu, D. Rajan; Vizhi, R. Ezhil

    2015-06-01

    L-Arginine doped potassium hydrogen phthalate and L-Histidine doped potassium hydrogen phthalate single crystals were grown by slow evaporation method at room temperature. The grown crystal crystallizes in orthorhombic system which is confirmed by single crystal XRD analysis. The grown crystals are subjected to thermal, mechanical and dielectric analysis.

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

    SciTech Connect

    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

    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.

  6. Growth aspects and characteristic properties of pure and Li-doped L-arginine acetate (LAA) single crystals: A promising nonlinear optical material

    NASA Astrophysics Data System (ADS)

    Natarajan, V.; Arivanandhan, M.; Sankaranarayanan, K.; Ramasamy, P.

    2009-01-01

    Single crystals of pure and lithium (Li)-doped L-arginine acetate (LAA) were grown by the slow evaporation technique. The effect of Li-doping on the growth, structural and optical properties of LAA crystal has been investigated. Powder X-ray diffraction studies confirm the crystal structure of the grown pure and Li-doped LAA single crystals. Various types of functional groups of the grown pure and Li-doped LAA single crystals were identified by the Fourier transform infrared (FTIR) spectroscopic analysis. The presence of Li in the grown crystal was confirmed by atomic absorption spectroscopic analysis. Electrical properties of the Li-doped LAA crystal were analyzed by AC impedance studies. The optical transmission study shows that the Li-doped LAA crystal has good optical transparency in the UV and visible regions.

  7. InxGa1?xAs nanowires with uniform composition, pure wurtzite crystal phase and taper-free morphology

    NASA Astrophysics Data System (ADS)

    Ameruddin, Amira S.; Aruni Fonseka, H.; Caroff, Philippe; Wong-Leung, Jennifer; het Veld, Roy LM Op; Boland, Jessica L.; Johnston, Michael B.; Tan, Hark Hoe; Jagadish, Chennupati

    2015-05-01

    Obtaining compositional homogeneity without compromising morphological or structural quality is one of the biggest challenges in growing ternary alloy compound semiconductor nanowires. Here we report growth of Au-seeded InxGa1?xAs nanowires via metal-organic vapour phase epitaxy with uniform composition, morphology and pure wurtzite (WZ) crystal phase by carefully optimizing growth temperature and V/III ratio. We find that high growth temperatures allow the InxGa1?xAs composition to be more uniform by suppressing the formation of typically observed spontaneous In-rich shells. A low V/III ratio results in the growth of pure WZ phase InxGa1?xAs nanowires with uniform composition and morphology while a high V/III ratio allows pure zinc-blende (ZB) phase to form. Ga incorporation is found to be dependent on the crystal phase favouring higher Ga concentration in ZB phase compared to the WZ phase. Tapering is also found to be more prominent in defective nanowires hence it is critical to maintain the highest crystal structure purity in order to minimize tapering and inhomogeneity. The InP capped pure WZ In0.65Ga0.35As core–shell nanowire heterostructures show 1.54 ?m photoluminescence, close to the technologically important optical fibre telecommunication wavelength, which is promising for application in photodetectors and nanoscale lasers.

  8. Magnetite in carbonaceous chondrites

    NASA Astrophysics Data System (ADS)

    Hua, Xin; Buseck, Peter R.

    1997-03-01

    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.

  9. 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)

    Lohn, B.; El Goresy, A.

    1992-07-01

    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.

  10. Elastic and inelastic diffraction changes upon variation of the relative humidity environment of PurE crystals.

    PubMed

    Oliete, R; Pous, J; Rodríguez-Puente, S; Abad-Zapatero, C; Guasch, A

    2013-02-01

    The different changes observed in the diffraction patterns of three different crystal forms (hexagonal, trigonal and monoclinic) of PurE (EC 4.1.1.21), an enzyme from the purine-biosynthesis pathway of Bacillus anthracis, upon a wide range of changes in the relative humidity environment of the crystals are documented. In addition, the changes in the unit-cell parameters, volume and bulk solvent in the three different crystal forms were systematically followed. In an attempt to explain the elastic (P6(5)22) and inelastic (P3(1)21) changes in the diffraction pattern, refined structures of the three different crystal forms determined at 100 K are presented, with particular emphasis on the tertiary and quaternary structural differences, crystal packing, intermolecular and intramolecular interactions and solvent structure. The refined structures show that the precipitant salts, solvent structure (both ordered and bulk) and conformation of the C-termini all play a role in creating a unique cement at both the intramolecular and intermolecular contacts of the different crystal forms. It is suggested that it is the combination of polyethylene glycol and the structure of the ordered water molecules (first and second layers) as well as the structure of the bulk solvent that are the critical factors in the plasticity of the hexagonal crystal packing as opposed to the inelastic responses of the lower symmetry forms. PMID:23385456

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

    PubMed Central

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

    2004-01-01

    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. PMID:15525704

  12. Magnetite thin films

    Microsoft Academic Search

    J. Feng; C. Bajorek; M.-A. Nicolet

    1972-01-01

    A low temperature process for converting hematite (?-Fe2O3) thin films into magnetite (Fe3O4is described. The films produced are unambiguously identified as magnetite by several complementary methods of analysis. These include ?-backscattering spectrography, X-ray powder diffractometry, and observations of electrical, magnetic, and optical properties.

  13. Stoichiometric magnetite grown by infrared nanosecond pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    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

    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.

  14. Structure and superparamagnetic behaviour of magnetite nanoparticles in cellulose beads

    SciTech Connect

    Correa, Jose R., E-mail: correa@fq.uh.cu [Department of General Chemistry, Faculty of Chemistry, University of Havana, Zapata and G, Havana City 10400 (Cuba); Bordallo, Eduardo [Sugar Cane-Cellulose Research Center, Cuba-9, Quivican (Cuba)] [Sugar Cane-Cellulose Research Center, Cuba-9, Quivican (Cuba); Canetti, Dora [Department of Inorganic Chemistry, Faculty of Chemistry, University of Havana, Zapata and G, Havana City 10400 (Cuba)] [Department of Inorganic Chemistry, Faculty of Chemistry, University of Havana, Zapata and G, Havana City 10400 (Cuba); Leon, Vivian [Sugar Cane-Cellulose Research Center, Cuba-9, Quivican (Cuba)] [Sugar Cane-Cellulose Research Center, Cuba-9, Quivican (Cuba); Otero-Diaz, Luis C. [Department of Inorganic Chemistry-1, Complutense University of Madrid, Madrid 28040 (Spain) [Department of Inorganic Chemistry-1, Complutense University of Madrid, Madrid 28040 (Spain); Electron Microscopy Center, Complutense University of Madrid, Madrid 28040 (Spain); Negro, Carlos [Chemical Engineering Department, Complutense University of Madrid, Madrid 28040 (Spain)] [Chemical Engineering Department, Complutense University of Madrid, Madrid 28040 (Spain); Gomez, Adrian [Electron Microscopy Center, Complutense University of Madrid, Madrid 28040 (Spain)] [Electron Microscopy Center, Complutense University of Madrid, Madrid 28040 (Spain); Saez-Puche, Regino [Department of Inorganic Chemistry-1, Complutense University of Madrid, Madrid 28040 (Spain)] [Department of Inorganic Chemistry-1, Complutense University of Madrid, Madrid 28040 (Spain)

    2010-08-15

    Superparamagnetic magnetite nanoparticles were obtained starting from a mixture of iron(II) and iron(III) solutions in a preset total iron concentration from 0.04 to 0.8 mol l{sup -1} with ammonia at 25 and 70 {sup o}C. The regeneration of cellulose from viscose produces micrometrical spherical cellulose beads in which synthetic magnetite were embedded. The characterization of cellulose-magnetite beads by X-ray diffraction, Scanning and Transmission Electron Microscopy and magnetic measurement is reported. X-ray diffraction patterns indicate that the higher is the total iron concentration and temperature the higher is the crystal size of the magnetite obtained. Transmission Electron Microscopy studies of cellulose-magnetite beads revealed the distribution of magnetite nanoparticles inside pores of hundred nanometers. Magnetite as well as the cellulose-magnetite composites exhibit superparamagnetic characteristics. Field cooling and zero field cooling magnetic susceptibility measurements confirm the superparamagnetic behaviour and the blocking temperature for the magnetite with a mean size of 12.5 nm, which is 200 K.

  15. Resistance switching in electrodeposited magnetite superlattices.

    PubMed

    Switzer, Jay A; Gudavarthy, Rakesh V; Kulp, Elizabeth A; Mu, Guojun; He, Zhen; Wessel, Andrew J

    2010-02-01

    Defect-chemistry magnetite superlattices and compositional superlattices in the magnetite/zinc ferrite system are electrodeposited as epitaxial films onto single-crystal Au(111). The defect-chemistry superlattices have alternating nanolayers with different Fe(III)/Fe(II) ratios, whereas the compositional superlattices have alternating nanolayers with different Zn/Fe ratios. The electrochemical/chemical (EC) nature of the electrodeposition reaction is exploited to deposit the superlattices by pulsing the applied potential during deposition. The defect-chemistry superlattices show low-to-high and high-to-low resistance switching that may be applicable to the fabrication of resistive random access memory (RRAM). PMID:20055488

  16. Nucleation of calcium oxalate crystals on an imprinted polymer surface from pure aqueous solution and urine

    Microsoft Academic Search

    Timothy J. Egan; AllenL Rodgers; Tewolde Siele

    2004-01-01

    Calcium oxalate (CaOx) is the most common component of human kidney stones. Heterogeneous nucleation is regarded as the key mechanism in this process. In this study, we have used an imprinted 6-methacrylamidohexanoic acid\\/divinylbenzene co-polymer as a biomimetic surface to nucleate CaOx crystal formation. The polymer was imprinted with either calcium oxalate monohydrate (COM) or dihydrate (COD) template crystals. These were

  17. Growth conditions, structure and superconductivity of pure and metal-doped FeTe1 - xSex single crystals

    NASA Astrophysics Data System (ADS)

    Gawryluk, D. J.; Fink-Finowicki, J.; Wi?niewski, A.; Pu?niak, R.; Domukhovski, V.; Diduszko, R.; Koz?owski, M.; Berkowski, M.

    2011-06-01

    Superconducting single crystals of pure FeTe1 - xSex and FeTe0.65Se0.35 doped with Co, Ni, Cu, Mn, Zn, Mo, Cd, In, Pb, Hg, V, Ga, Mg, Al, Ti, Cr, Sr or Nd into Fe ion sites have been grown applying Bridgman's method. It has been found that the sharpness of the transition to the superconducting state in FeTe1 - xSex is evidently inversely correlated with the crystallographic quality of the crystals. Among all of the studied dopants only Co, Ni and Cu substitute Fe ions in FeTe0.65Se0.35 crystals. The remaining ions examined do not incorporate into the crystal structure. Nevertheless, they form inclusions together with selenium, tellurium and/or iron, which change the chemical composition of the host matrix and therefore influence the Tc value. The small disorder introduced into the magnetic sublattice, by partial replacement of Fe ions by a slight amount of nonmagnetic ions of Cu (~1.5 at.%) or by magnetic ions of Ni (~2 at.%) and Co (~5 at.%) with spin values different than that of the Fe ion, completely suppresses superconductivity in the FeTe1 - xSex system. This indicates that, even if superconductivity is observed in the system containing magnetic ions, it cannot survive when the disorder in the magnetic ion sublattice is introduced, most likely because of magnetic scattering of Cooper pairs.

  18. Saturation of charge carrier velocity with increasing electric fields: Theoretical investigations for pure organic crystals

    E-print Network

    Kenkre, V.M.

    injected charge carrier velocities to saturate as the applied electric field is increased simply becauseSaturation of charge carrier velocity with increasing electric fields: Theoretical investigations: NEED FOR CLARIFICATION Recent transport experiments on injected charges in ultra- pure organic solids

  19. Magnetite biomineralization in the human brain.

    PubMed Central

    Kirschvink, J L; Kobayashi-Kirschvink, A; Woodford, B J

    1992-01-01

    Although the mineral magnetite (Fe3O4) is precipitated biochemically by bacteria, protists, and a variety of animals, it has not been documented previously in human tissue. Using an ultrasensitive superconducting magnetometer in a clean-lab environment, we have detected the presence of ferromagnetic material in a variety of tissues from the human brain. Magnetic particle extracts from solubilized brain tissues examined with high-resolution transmission electron microscopy, electron diffraction, and elemental analyses identify minerals in the magnetite-maghemite family, with many of the crystal morphologies and structures resembling strongly those precipitated by magnetotactic bacteria and fish. These magnetic and high-resolution transmission electron microscopy measurements imply the presence of a minimum of 5 million single-domain crystals per gram for most tissues in the brain and greater than 100 million crystals per gram for pia and dura. Magnetic property data indicate the crystals are in clumps of between 50 and 100 particles. Biogenic magnetite in the human brain may account for high-field saturation effects observed in the T1 and T2 values of magnetic resonance imaging and, perhaps, for a variety of biological effects of low-frequency magnetic fields. Images PMID:1502184

  20. A comparative study on pure, L-arginine and glycine doped ammonium dihydrogen orthophosphate single crystals grown by slow solvent evaporation and temperature-gradient method

    NASA Astrophysics Data System (ADS)

    Pattanaboonmee, N.; Ramasamy, P.; Yimnirun, R.; Manyum, P.

    2011-01-01

    Single crystals of pure, L-arginine and glycine doped ammonium dihydrogen orthophosphate (ADP) were grown by both the slow solvent evaporation method and the temperature-gradient method of Sankaranarayanan-Ramasamy (SR). The metastable zone width for different saturation temperatures of pure glycine and L-arginine added solutions were carried out. The grown crystals were characterized by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), powder X-ray diffraction (XRD), optical transmission, dielectric constant, dielectric loss, and Vickers microhardness. The DSC and TG curves of the grown crystals indicated that they were stable up to 200 °C. The XRD study confirmed the structure of the grown crystal. The optical transmission analysis revealed that the pure and doped ADP crystals had very high percentage of transmission in the entire visible region. The important optical parameters such as reflectance and extinction coefficients of the grown crystals were calculated. L-arginine and glycine were used as dopants to reduce dielectric constant of ADP. The a.c. resistivity and a.c. conductivity were calculated. Dielectric loss of the doped ADP crystals grown by the SR method is lower than the doped ADP crystals grown by the conventional method. Larger hardness value for the SR method grown crystals confirmed greater crystalline perfection.

  1. Pure and Nd added NBT-BT single crystals - Growth and their characterization

    NASA Astrophysics Data System (ADS)

    Sundari, S. Shanmuga; Baskar, K.; Dhanasekaran, R.

    2014-04-01

    The lead free piezoelectric materials are secured an important place in the field of material science and engineering. In the present work single crystals of sodium bismuth titanate- barium titanate (0.94NBT-0.06BT) and 0.6 wt % of Nd added NBT-BT has been grown by flux method. The addition of 0.6 wt% of Nd shows the inhomogeneity in melt and the crystals collected from the top, middle and bottom portions of the crucible have been characterized for their structural and dielectric properties. The Nd concentration is found to be more in the crystals grown from the bottom portion of crucible and it was confirmed by optical and structural analysis. After the addition of Nd the color of the crystal changes form pale yellow to muddy green. The depolarization temperature (Td) and the temperature where the dielectric constant reaches its maximum (Tm) are increased from 442 K to 475 K and 595 K and 628 K respectively after the addition the of Nd in NBT-BT.

  2. Zeeman Effect of the Purely Cubic Field Fluorescence Line of MgO: Cr3+ Crystals

    Microsoft Academic Search

    S. Sugano; A. L. Schawlow; F. Varsanyi

    1960-01-01

    Both transverse and longitudinal Zeeman effects are studied of the most conspicuous red emission line (14 319 cm-1) of a MgO: Cr3+ single crystal. The Zeeman patterns are examined experimentally, with a magnetic field parallel to the [001], [110] and [111] axes, with linear polarizations parallel and perpendicular to each direction of the magnetic field and with circular polarizations around

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

    Microsoft Academic Search

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

    2000-01-01

    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

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

    Microsoft Academic Search

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

    2000-01-01

    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 (\\/alpha) and optical band gap Eg were deduced. The type of transition was determined and the validity of Urbach's rule was checked. The steepness

  5. Improvement of toughness by stereocomplex crystal formation in optically pure polylactides of high molecular weight.

    PubMed

    López-Rodríguez, N; Martínez de Arenaza, I; Meaurio, E; Sarasua, J R

    2014-09-01

    A solution casting method followed by thermal homogenization was performed for the preparation of 1:1 blends and non-blended films from poly(d-lactide) (PDLA) and poly(l-lactide) (PLLA) of three different molecular weights, and their thermal and mechanical properties were determined via differential scanning calorimetry (DSC) and tensile tests. According to the literature, when Mw is below 1.0×10(5)g/mol only stereocomplex crystallization takes place, and when it is higher, both homocrystallites and stereocomplex crystallites co-exist. In order to promote crystallization as a homocrystal in neat polylactides and to promote the stereoselective crystallization as stereocomplex in the case of non-blended films, and in turn, to achieve different degrees of crystallinity, several thermal treatments of annealing were carried out in this work. Highly stereocomplexed blends were found by the stereospecific thermal treatments. As a consequence, the toughness of 1:1 blends was found significantly enhanced over those of non-blended films, irrespective of molecular weight. For instance, in B2-5050 stereocomplexed blend having poly(l-lactide) and poly(d-lactide) of Mw=1.2×10(5)g/mol, tensile strength increased from 44.0±2.1MPa to 65.1±6.1MPa, and the elongation at break from 10.8±2.5% to 33.1±8.1% with respect to its non-blended poly(l-lactide) counterpart crystallized as homocrystal. This improvement in mechanical properties in stereocomplexed blends is not attributed to the inherent properties of the type of crystal polymorph but to the presence of a higher density of intercrystalline connections through a mobile amorphous phase, i.e. tie chains in the stereocomplexed supramolecular spherulitic entities that provide in the stereocomplexed samples enhanced strength and elongation at break at the same time. PMID:24951928

  6. Scientific, Engineering and Metrological Problems in Producing Pure 28Si and Growing Single Crystals

    NASA Astrophysics Data System (ADS)

    Tarbeyev, Yu V.; Kaliteyevsky, A. K.; Sergeyev, V. I.; Smirnov, R. D.; Godisov, O. N.

    1994-01-01

    The centrifugation method has advantages in producing silicon isotopes. The selection of appropriate working gas, development of gas centrifuges, their arrangement for effective separation of the isotopes and optimization of the production process are considered. The resulting mole fraction of 28Si is better than 0,999 9. The requirements for the production processes in growing single crystals and the related problems are analysed in detail and estimates of the uncertainties associated with the necessary tests are given.

  7. Thermodynamic analysis of pure and impurity doped pentaerythritol tetranitrate crystals grown at room temperature

    Microsoft Academic Search

    R. Pitchimani; W. Zheng; S. L. Simon; A. K. Burnham

    2007-01-01

    Pentaerythritol tetranitrate (PETN) powders are used to initiate other explosives. During long-term storage, changes in powder\\u000a properties can cause changes in the initiation performance. Changes in the morphology and surface area of aging powders are\\u000a observed due to sublimation and growth of PETN crystals through coarsening mechanisms, (e.g. Ostwald ripening, sintering,\\u000a etc.). In order to alleviate the sublimation of PETN

  8. Ultrahigh Efficiency Laser Wavelength Conversion in a Gas-Filled Hollow Core Photonic Crystal Fiber by Pure Stimulated Rotational Raman Scattering in Molecular Hydrogen

    Microsoft Academic Search

    F. Benabid; G. Bouwmans; J. C. Knight; P. St. Russell; F. Couny

    2004-01-01

    We report on the generation of pure rotational stimulated Raman scattering in a hydrogen gas hollow-core photonic crystal fiber. Using the special properties of this low-loss fiber, the normally dominant vibrational stimulated Raman scattering is suppressed, permitting pure conversion to the rotational Stokes frequency in a single-pass configuration pumped by a microchip laser. We report 92% quantum conversion efficiency (40nJ

  9. VUV spectroscopy of pure LiCaAlF 6 crystals

    NASA Astrophysics Data System (ADS)

    Kirm, M.; True, M.; Vielhauer, S.; Zimmerer, G.; Shiran, N. V.; Shpinkov, I.; Spassky, D.; Shimamura, K.; Ichinose, N.

    2005-01-01

    Reflection, excitation and luminescence spectra of as-grown and X-ray irradiated high-purity LiCaAlF 6 crystals were studied in the temperature range of 10-300 K using synchrotron radiation in VUV. The intrinsic luminescence of samples at 10 K consists of a non-elementary broad band with maximum at 4.4 eV under excitation at 11.45 eV. It is ascribed to the radiative decay of self-trapped excitons. The energy gap is estimated to be 12.65 eV in LiCaAlF 6. Under interband excitation a red shift of luminescence was observed. The electron-hole recombination leads to the emission peaking at 3.7 eV. The excitation processes and origin of overlapping emissions of LiCaAlF 6 are discussed.

  10. Magnetite mineral nanoparticles synthesized naturally in an iron ore deposit

    NASA Astrophysics Data System (ADS)

    Rivas-Sanchez, M. L.; Alva-Valdivia, L. M.

    2013-05-01

    We performed a mineralogical characterization and mineral magnetism study of the Peña Colorada iron ore, Mexico. The ore is formed partly by intergranular magnetite intergrowed with berthierine (Fe,Mg,Al)6(Si,Al)4O10(OH)8. The magnetite nanoparticles are forming aggregates of wide grain size spectra, from micro to nanometer scale. The smallest aggregates are formed by magnetite nanoparticles 2 to 30 grain size range, showing unusual physical and chemical behavior. The continuous agglomeration of nanoparticles formed more denser and compact magnetite microparticles. A magnetite concentrate to micrometric scale was reduced and divided into distinct range sizes: 85-56 ?m, 56-30 ?m, 30-22 ?m, 22-15 ?m, 15-10 ?m, 10-7 ?m and 7-1 ?m. Nanometric-scale magnetite 2-30 nm was identified by using high resolution Transmission Electron Microscopy (HRTEM). The magnetite and minerals associated were characterized by X-ray diffraction, transmitted and reflected light polarization, microscope and electron probe X-ray micro-analyzer, differential thermal analysis, gravimetric thermal analysis, and high-resolution transmission electron microscopy. Besides, results of Mössbauer spectroscopy, frequency-dependent magnetic susceptibility, isothermal remanent magnetization and magnetic susceptibility versus temperature were important in the research related to the origin of this deposit. To study magnetite nanoparticles, agglomeration processes and temperature effect implications, we developed an experimental process to re-create the environmental conditions that originated this nanoparticles. These processes start with direct precipitation to synthesize magnetite nanoparticles through a thermal and dehydration treatment of the berthierine base mineral, using diverse temperature ranges, from 360 °C to 750 °C and treatment time of two hours. This process allowed the nucleation and crystalline growth of a high number of magnetite nano-crystals with average size of 2 to 6 nm, homogeneous distribution in the colloidal matrix and a superparamagnetic behavior. Increase temperature provoke new magnetite nano-cores and constant growth of the ones already present. The union to magnetite nanoparticles favored the formation of aggregates nano-micrometric strongly compacted with the acquisition of ferromagnetic behavior. The mineralogical-textural characteristic of magnetite nanoparticles and its magnetic properties were an important guide to explain the environmental conditions for iron deposition, suggesting a marine sedimentary exhalative (SEDEX) origin assisted by bacterial.

  11. Magnetite-Polypyrrole Metacomposites: Dielectric Properties and Magnetoresistance Behavior

    E-print Network

    Guo, John Zhanhu

    : The conductive polypyrrole (PPy) polymer nanocomposites (PNCs) reinforced with different magnetite (Fe3O4 of the as-received Fe3O4 nanoparticles (NPs), pure PPy and Fe3O4/PPy PNCs. The high-resolution transmission. The thermal stability of the Fe3O4/PPy PNCs is assessed by thermogravimetric analysis (TGA). X-ray diffraction

  12. Multiple ordering in magnetite.

    NASA Technical Reports Server (NTRS)

    Cullen, J. R.; Callen, E. R.

    1973-01-01

    Results of a self-consistent band calculation of the ground-state energy and charge orderings based on a tight-binding scheme in magnetite are presented. They show that below a critical (about 2.2) value of the ratio of interatomic Coulomb energy to bandwidth the lowest energy state has no order. Between this critical value and 2.5, the preferred state is multiply ordered.

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

    PubMed Central

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

    2004-01-01

    Bacterial magnetosomes are intracellular compartments that house highly ordered magnetite crystals. By using Magnetospirillum 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 biomineralization proceeds from the same location in each vesicle. The magnetosome-associated protein, MamA, is required for the formation of functional magnetosome vesicles and displays a dynamic subcellular localization throughout the growth cycle of magnetotactic bacteria. Together, these results suggest that the magnetosome precisely coordinates magnetite biomineralization and can serve as a model system for the study of organelle biogenesis in noneukaryotic cells. PMID:15004275

  14. Magnetite Oxidation: A Proposed Mechanism.

    PubMed

    Colombo, U; Gazzarrini, F; Lanzavecchia, G; Sironi, G

    1965-02-26

    All magnetites are oxidized topotactically with formation of solid solution at temperatures below 400 degrees C. The oxidation of hematite-free magnetites proceeds to gammaFe(2)O(3), whereas in the presence of hematite epitaxial growth of alphaFe(2)O(3) takes place, with excess iron ions being returned to the solid solution. A method for synthesizing maghemite from natural magnetites is indicated. PMID:17813310

  15. Dislocation jump distances during creep of pure and doped NaCl single crystals using nuclear magnetic resonance pulse techniques

    NASA Astrophysics Data System (ADS)

    Murty, K. Linga; Kanert, O.

    1990-03-01

    Jump distances of dislocations are determined from the spin-lattice relaxation rates in a rotating frame [1/T1?] using in situ nuclear magnetic resonance pulse techniques during creep of pure and doped NaCl single crystals. Effects of divalent impurity and solid solution are investigated by doping with Ca and LiCl, respectively. Compression creep tests were performed at 10-30 MPa at 473 K. Relaxation rates were evaluated from spin-echo heights following ?/2, locking, and 64° pulse sequence. The amplitude of the spin echo decreased as soon as the load was applied following which it increased until the steady-state creep was reached, at which point a saturation value was observed. Mean jump distance of the mobile dislocations decreased with strain during the transient creep reaching a constant value at the onset and during the secondary creep. While the addition of 0.01 Ca has negligible influence on the jump distance, a solid solution with 0.01 LiCl resulted in about a four-fold increase. The results are compared and correlated with various microstructural parameters.

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

    PubMed

    Barber, David J; Scott, Edward R D

    2002-05-14

    Crystals of magnetite (Fe(3)O(4)) 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 approximately equal to 3 nm) that are preferentially oriented with respect to the carbonate lattice. Larger periclase crystals approximately equal to 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 CO(2). 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. PMID:12011420

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

    PubMed Central

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

    2002-01-01

    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. PMID:12011420

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

    NASA Astrophysics Data System (ADS)

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

    2002-05-01

    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.

  19. Can the presence of structural phosphorus help to discriminate between abiogenic and biogenic magnetites?

    PubMed

    Jurado, María J; Barrón, Vidal; Torrent, José

    2003-11-01

    The influence of phosphate on the competitive formation of magnetite and lepidocrocite and the properties of magnetite prepared from mixtures of Fe(II) and Fe(III) salts were studied. Products were prepared at 90 degrees C and pH 12.5 (series 1), 50 degrees C and pH 7 (series 2) and 20 degrees C and pH 8 (series 3). The P/Fe atomic ratio in the initial solution ranged from 0 to 3% and the pH was kept at the desired value with NaOH or KOH. Air was used as oxidant in series 2 and 3. All products, which were characterized by X-ray diffraction, transmission electron microscopy, chemical analysis and IR spectroscopy, contained a phase intermediate between magnetite and maghemite (referred to as magnetite in this paper). The products of series 1 consisted only of magnetite at all P/Fe ratios, whereas both magnetite and lepidocrocite formed in series 2 and 3 above a certain P/Fe ratio. On increasing the P/Fe ratio in the initial solution, the magnetite crystals became smaller and more oxidized (i.e. closer to maghemite) and the lepidocrocite/magnetite ratio increased. The P associated with magnetite was partly in the form of occluded P, i.e. non-surface-adsorbed phosphate. IR spectra suggested this P to be structural and occurring as low-symmetry PO(4) units. Because abiogenic magnetites produced in various environments incorporate structural P but some well-characterized biogenic magnetites seem to contain no P or be formed in P-poor environments, we hypothesize that natural magnetites containing occluded P are unlikely to be biogenic. However, more studies are needed to discard the presence of P in biogenic magnetites. PMID:12942353

  20. Evidence for exclusively inorganic formation of magnetite in Martian meteorite ALH84001

    NASA Technical Reports Server (NTRS)

    Golden, D. C.; Ming, D. W.; Morris, R. V.; Brearley, A. J.; Lauer, H. V., Jr.; Treiman, A. H.; Zolensky, M. E.; Schwandt, C. S.; Lofgren, G. E.

    2004-01-01

    Magnetite crystals produced by terrestrial magnetotactic bacterium MV-1 are elongated on a [111] crystallographic axis, in a so-called truncated hexa-Octahedral shape. This morphology has been proposed to constitute a biomarker (i.e., formed only in biogenic processes). A subpopulation of magnetite crystals associated with carbonate globules in Martian meteorite ALH84001 is reported to have this morphology, and the observation has been taken as evidence for biological activity on Mars. In this study, we present evidence for the exclusively inorganic origin of [111]-elongated magnetite crystals in ALH84001. We report three-dimensional(3-D) morphologies for approx.1000 magnetite crystals extracted from: (1) thermal decomposition products of Fe-rich carbonate produced by inorganic hydrothermal precipitation in laboratory experiments; (2) carbonate globules in Martian meteoriteeALH84001; and (3) cells of magnetotactic bacterial strain MV-1. The 3-D morphologies were derived by fitting 3-D shape models to two-dimensional bright-field transmission-electron microscope (TEAM) images obtained at a series of viewing angles. The view down the {110} axes closest to the [111] elongation axis of magnetite crystals ([111]x{110) not equal to 0) provides a 2-D projection that uniquely discriminates among the three [111]-elongated magnetite morphologies found in these samples: [111]-elongated truncated hexaoctahedron ([111]-THO), [111]-elongated cubo-octahedron ([111]-ECO), and [111]-elongated simple octahedron ([111]-ESO). All [111] -elongated morphologies are present in the three types of sample, but in different proportions. In the ALH84001 Martian meteorite and in our inorganic laboratory products, the most common [111]-elongated magnetite crystal morphology is [111]-ECO. In contrast, the most common morphology for magnetotactic bacterial strain MV-1 is [111]-THO. These results show that: (1) the morphology of [111]-elongated magnetite crystals associated with the carbonate globules in Martian meteorite ALH84001 is replicated by an inorganic process; and (2) the most common crystal morphology for biogenic (MV-1) magnetite is distinctly different from that in both ALH84001 and our inorganic laboratory products. Therefore, [111]-elongated magnetite crystals in ALH84001 do not constitute, as previously claimed, a robust biosignature and, in fact, an exclusively inorganic origin for the magnetite is fully consistent with our results. Furthermore, the inorganic synthesis method, i.e., the thermal decomposition of hydrothermally precipitated Fe-rich carbonate, is a process analogue for formation of the magnetite on Mars. Namely, precipitation of carbonate globules from carbonate-rich hydrothermal solutions followed at some later time by a thermal pulse, perhaps in association with meteoritic impact or volcanic processes on the Martian surface.

  1. Paleointensity Experiments with pTRM and Tail Checks for Multidomain and PSD Magnetites

    NASA Astrophysics Data System (ADS)

    Dunlop, D. J.; Xu, S.; Zhang, B.; Ozdemir, O.

    2004-05-01

    Simulated Thellier experiments using total TRM as NRM were performed on dark minerals (biotite, amphiboles) from a diabase and on 1, 6, 20 and 135 um fractions of crushed magnetite crystals, all annealed and sealed under vacuum. The 135 um magnetite had strong downward curvature of the Arai plot, as predicted by theory. The 20 um and dark minerals samples, which behaved identically, and the 6 um magnetite had progressively less curvature, and the 1 um magnetite behaved almost ideally. Detailed pTRM checks and pTRM tail checks were performed for the 135 um and dark minerals samples. When the laboratory field H was parallel to the NRM, all pTRM tail checks were zero, as reported by Yu and Dunlop (JGR, Nov. 2003), but when H was perpendicular to NRM, pTRM tails were detected after 3rd heatings in zero field. Undemagnetized pTRM residuals were likely present in both cases, but were hidden when pTRM is parallel to NRM. For the 135 um magnetite, pTRM checks for all temperatures were positive. For the dark minerals, pTRM checks grew larger than the original pTRMs as heating temperatures rose. The most deviant of these was rechecked by giving a new total TRM ("NRM") to the sample and replicating this single pTRM. The second pTRM check was closer to, but still larger than, the original pTRM. Two further experiments were undertaken as closer replications of the complete Thellier experiment. The only differences were that the NRM was pre-treated by either 15 mT AF or LTD. In both experiments, seven new pTRMs closely matched original pTRMs. Neither AF nor LTD made the Thellier results much closer to ideal; the treated NRM and pTRMs still gave convex-down Arai plots with initial slopes of 2-2.5 instead of 1. However, our experiments do verify that these strongly curved Arai plots are reproducible and have a purely physical cause. They do not result from irreversible physiochemical alteration. Conventional pTRM checks depend on magnetic history in multidomain samples and do not always reproduce the original pTRMs. Nevertheless the Arai plots are reproducible if the entire Thellier experiment is repeated ab initio.

  2. Natural Magnetite: an efficient catalyst for the degradation of organic contaminant.

    PubMed

    He, Hongping; Zhong, Yuanhong; Liang, Xiaoliang; Tan, Wei; Zhu, Jianxi; Yan Wang, Christina

    2015-01-01

    Iron (hydr)oxides are ubiquitous earth materials that have high adsorption capacities for toxic elements and degradation ability towards organic contaminants. Many studies have investigated the reactivity of synthetic magnetite, while little is known about natural magnetite. Here, we first report the reactivity of natural magnetites with a variety of elemental impurities for catalyzing the decomposition of H2O2 to produce hydroxyl free radicals ((•)OH) and the consequent degradation of p-nitrophenol (p-NP). We observed that these natural magnetites show higher catalytic performance than that of the synthetic pure magnetite. The catalytic ability of natural magnetite with high phase purity depends on the surface site density while that for the magnetites with exsolutions relies on the mineralogical nature of the exsolved phases. The pleonaste exsolution can promote the generation of (•)OH and the consequent degradation of p-NP; the ilmenite exsolution has little effect on the decomposition of H2O2, but can increase the adsorption of p-NP on magnetite. Our results imply that natural magnetite is an efficient catalyst for the degradation of organic contaminants in nature. PMID:25958854

  3. Magnetoresistance in magnetite: Switching of the magnetic easy axis

    Microsoft Academic Search

    G. Król; W. Tabi?; J. Przewo?nik; T. Ko?odziej; Z. K?kol; A. Koz?owski; Z. Tarnawski

    2009-01-01

    The influence of the external magnetic field B (B?4T) on resistivity in magnetite single crystal was studied at few temperatures both below and above the Verwey transition temperature TV, and in two ?100? type cubic directions. We have succeeded to confirm our predictions that the magnetic axis switching affects electronic transport. It was also found that the transverse resistivity (B?current

  4. Electronic processes in magnetite (or, \\

    Microsoft Academic Search

    Konstantin P Belov

    1993-01-01

    The properties of magnetite in the region of the low-temperature transformation Tt = 100 – 120 K are in many respects still unclear and even enigmatic, in spite of the enormous number of studies that have been undertaken over the years. In this review article a new model for the low-temperature transformation in magnetite is presented, based on an examination

  5. Magnetite morphology and life on Mars

    PubMed Central

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

    2001-01-01

    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. PMID:11717421

  6. Magnetite morphology and life on Mars

    NASA Astrophysics Data System (ADS)

    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

    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.

  7. Iron isotopic fractionation factor between magnetite and hydrous silicic melt

    NASA Astrophysics Data System (ADS)

    Huang, F.; Lundstrom, C. C.

    2006-12-01

    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.

  8. Magnetite biomineralization in termites

    PubMed Central

    Maher, B. A.

    1998-01-01

    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.

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

    PubMed

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

    1998-07-01

    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

  10. Gigantism in unique biogenic magnetite at the Paleocene–Eocene Thermal Maximum

    PubMed Central

    Schumann, Dirk; Raub, Timothy D.; Kopp, Robert E.; Guerquin-Kern, Jean-Luc; Wu, Ting-Di; Rouiller, Isabelle; Smirnov, Aleksey V.; Sears, S. Kelly; Lücken, Uwe; Tikoo, Sonia M.; Hesse, Reinhard; Kirschvink, Joseph L.; Vali, Hojatollah

    2008-01-01

    We report the discovery of exceptionally large biogenic magnetite crystals in clay-rich sediments spanning the Paleocene–Eocene Thermal Maximum (PETM) in a borehole at Ancora, NJ. Aside from previously described abundant bacterial magnetofossils, electron microscopy reveals novel spearhead-like and spindle-like magnetite up to 4 ?m long and hexaoctahedral prisms up to 1.4 ?m long. Similar to magnetite produced by magnetotactic bacteria, these single-crystal particles exhibit chemical composition, lattice perfection, and oxygen isotopes consistent with an aquatic origin. Electron holography indicates single-domain magnetization despite their large crystal size. We suggest 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—drove diversification of magnetite-forming organisms, likely including eukaryotes. PMID:18936486

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

    NASA Astrophysics Data System (ADS)

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

    2013-04-01

    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.

  12. A Comparison between Chemical Synthesis Magnetite Nanoparticles and Biosynthesis Magnetite.

    PubMed

    Kahani, Seyed Abolghasem; Yagini, Zahra

    2014-01-01

    The preparation of Fe3O4 from ferrous salt by air in alkaline aqueous solution at various temperatures was proposed. The synthetic magnetites have different particle size distributions. We studied the properties of the magnetite prepared by chemical methods compared with magnetotactic bacterial nanoparticles. The results show that crystallite size, morphology, and particle size distribution of chemically prepared magnetite at 293?K are similar to biosynthesis of magnetite. The new preparation of Fe3O4 helps to explain the mechanism of formation of magnetosomes in magnetotactic bacteria. The products are characterized by X-ray powder diffraction (XRD), infrared (IR) spectra, vibrating sample magnetometry (VSM), and scanning electron microscopy (SEM). PMID:24982609

  13. Synthesis of stabilized myrrh-capped hydrocolloidal magnetite nanoparticles.

    PubMed

    Atta, Ayman M; Al-Lohedan, Hamad A; Al-Hussain, Sami A

    2014-01-01

    Herein we report a new method for synthesizing stabilized magnetic nanoparticle (MNP) colloids. A new class of monodisperse water-soluble magnetite nano-particles was prepared by a simple and inexpensive co-precipitation method. Iron ions and iodine were prepared by the reaction between ferric chloride and potassium iodide. The ferrous and ferric ions were hydrolyzed at low temperature at pH 9 in the presence of iodine to produce iron oxide nanoparticles. The natural product myrrh gum was used as capping agent to produce highly dispersed coated magnetite nanoparticles. The structure and morphology of the magnetic nanogel was characterized by Fourier transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM), and X-ray diffraction (XRD) was used to examine the crystal structure of the produced magnetite nanoparticles. PMID:25090117

  14. Control of the morphology and size of magnetite particles with peptides mimicking the Mms6 protein from magnetotactic bacteria.

    PubMed

    Arakaki, Atsushi; Masuda, Fukashi; Amemiya, Yosuke; Tanaka, Tsuyoshi; Matsunaga, Tadashi

    2010-03-01

    Mms6 is a dominant protein that tightly associates with the surface of bacterial magnetites in Magnetospirillum magneticum AMB-1. The protein has previously been shown to mediate the formation of uniform magnetite crystals of cubo-octahedral morphology consisting of (1 1 1) and (1 0 0) crystal faces with a narrow size distribution during chemical magnetite synthesis. In order to understand the role of this protein in chemical magnetite synthesis, magnetite formation was investigated using synthetic peptides mimicking the Mms6 protein. Particles that were synthesized in the presence of short peptides harbouring the C-terminal acidic region of Mms6 exhibited a spherical morphology with circularities of 0.70-0.90 similar to those of bacterial magnetites and particles formed in the presence of the Mms6 protein. In contrast, a rectangular morphology with circularities of 0.60-0.85 were obtained when other peptides were used for synthesis. The results indicated that the C-terminal region of the Mms6 protein has significant control over the morphology of magnetite crystals in the chemical synthetic method. This method can, therefore, be useful as an alternative method of controlling the size and morphology of magnetite crystals under ambient conditions. PMID:20006848

  15. Transformation kinetics & magnetism of magnetite nanoparticles

    NASA Astrophysics Data System (ADS)

    Laurenzi, Mark Anthony, III

    This dissertation presents the results of a study of the nucleation and growth kinetics and magnetic properties of iron-oxide based nanoparticles that are formed by crystallization of a Na-Ca borate amorphous precursor. In addition to the interesting phase transformation kinetics and concentration dependent growth phenomena observed in this system, it also provides an opportunity to study finite-size effects on the magnetic properties of single domain particles. The crystallization of iron oxide nanoparticles and the phase identity (magnetite or maghemite) upon heat treatment was investigated over a range of time, temperature, and redox conditions. X-ray diffraction (XRD), transmission electron microscopy (TEM) and electron diffraction (ED) were used to structurally characterize the resulting nanoparticles. Magnetite formation was favored under more reducing conditions whereas maghemite was formed under more oxidizing conditions. Under all conditions investigated, the particle size fell in the narrow range of about 2.5 to 4.5 nm and showed no evidence of further growth with time. This is believed to result from the increased viscosity in the iron-depleted diffusion field surrounding each particle. The magnetic properties were characterized using a superconducting quantum interference device (SQUID) and Mossbauer spectrometer (MS). Magnetization measurements were made from room temperature down to ˜10 K under field-cooled (FC) and zero-field-cooled (ZFC) conditions. The average blocking temperature obtained from these measurements is generally consistent with the measured particle size for reasonable values of the anisotropy constant. Unlike maghemite, bulk magnetite exhibits a metal-insulator transition, first reported by Verwey in 1939. The effect was attributed by Verwey and others to a charge-ordering transition. However, very recent data suggest that the Verwey transition is instead associated with a structural transition from inverse to normal spinel. In the present work, the magnetization data for samples produced under more reducing conditions show clear evidence of a Verwey transition in 4--4.5 nm magnetite nanoparticles. However, the transition is found to be shifted from the bulk value of ˜120 K to 85--95 K, which is attributed to finite-size effects.

  16. EFFECTS OF FEATHER CRYSTALS IN THE MACROSTRUCTURE ON EARING BEHAVIOR AND ELOXAL STRUCTURE OF SHEETS OF PURE ALUMINUM

    Microsoft Academic Search

    Zieger

    1961-01-01

    The as-cast structure of d.c.-cast aluminum ingots sometimes shows ; feather-like crystals. The influence of this type of crystals on the earing ; behavior and on the surface markings after anodizing was investigated on Al 99.5-; sheets of 2 mm thickness. Feather-like crystals gave rise to more irregular and ; higher earings in all cases. Hot and afterwards cold rolled

  17. Possible Eukaryotic Magnetite in the Paleocene-Eocene Boundary Clay, Ancora, New Jersey

    NASA Astrophysics Data System (ADS)

    Schumann, D.; Raub, T. D.; Kopp, R. E.; Tikoo, S. M.; Sears, S. K.; Leucken, U.; Rouiller, I.; Smirnov, A. V.; Kirschvink, J. L.; Vali, H.

    2007-12-01

    We report the discovery of new forms of magnetic particles in the Paleocene-Eocene (P-E) boundary clay from the borehole at Ancora, New Jersey (Ocean Drilling Program Leg 174AX). The P-E boundary clay shows anomalous magnetic properties suggesting enrichment in single-domain (SD) magnetite. Transmission electron microscopy of the magnetic separates shows that the majority of the SD particles are magnetofossils of known crystal shape and size [1]. There are, however, larger magnetite particles having unusual morphology, including: (1) elongated prismatic magnetite of 100 nm width and up to 1 micron length, (2) leaflike magnetite particles up to 2 microns in length, and (3) elongated, conelike particles with an aspect ratio of 4:1. Lattice-fringe images and X-ray microanalysis of these particles show single-crystal structure and stochiometric magnetite composition, similar to magnetite crystals produced by magnetotactic bacteria. Although the dimensions of some of the type 2 and type 3 particles are outside that expected for single-domain behaviour as typically calculated for parallelepipeds and ellipsoids [2], electron holographic analysis reveals a SD signature. It is likely that these magnetic particles are of biogenic origin, as we were unable to find significant amounts of obviously detrital magnetite in the sediments. As these unusual magnetic particles are confined to the narrow P-E boundary layer, environmental changes along the eastern Atlantic margin of North America during the Paleocene-Eocene Thermal Maximum (PETM) may have led to enhanced growth, and perhaps diversification, of magnetite-forming microorganisms. The dimensions of the observed magnetite particles, however, exceed the size of prokaryotes; if they were, indeed, biogenic, they were likely formed by an unknown eukaryotic organism. References: [1] R. E. Kopp et al., 2007. Paleoceanography (in press). [2] R. E. Kopp and J. L. Kirschvink, 2007. Earth Science Reviews. doi:10.1016/j.earscirev.2007.08.001.

  18. Ultrahigh efficiency laser wavelength conversion in a gas-filled hollow core photonic crystal fiber by pure stimulated rotational Raman scattering in molecular hydrogen.

    PubMed

    Benabid, F; Bouwmans, G; Knight, J C; Russell, P St J; Couny, F

    2004-09-17

    We report on the generation of pure rotational stimulated Raman scattering in a hydrogen gas hollow-core photonic crystal fiber. Using the special properties of this low-loss fiber, the normally dominant vibrational stimulated Raman scattering is suppressed, permitting pure conversion to the rotational Stokes frequency in a single-pass configuration pumped by a microchip laser. We report 92% quantum conversion efficiency (40 nJ pulses in 2.9 m fiber) and threshold energies (3 nJ in 35 m) more than 1 x 10(6) times lower than previously reported. The control of the output spectral components by varying only the pump polarization is also shown. The results point to a new generation of highly engineerable and compact laser sources. PMID:15447265

  19. Magnetoresistance of magnetite

    Microsoft Academic Search

    J. M. D. Coey; A. E. Berkowitz; Ll. Balcells; F. F. Putris; F. T. Parker

    1998-01-01

    The magnetoresistance behavior of Fe3O4 in polycrystalline thin film, powder compact, and single-crystal form are compared. Negative magnetoresistance with peaks at the coercive field, observed in thin films and powder compacts but not in the single crystal, is due to field-induced alignment of the magnetization of contiguous grains. The effect is associated with intergranular transport of spin-polarized electrons.

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

    NASA Astrophysics Data System (ADS)

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

    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.

  1. Reflectance anisotropy spectroscopy of magnetite (110) surfaces

    NASA Astrophysics Data System (ADS)

    Fleischer, K.; Verre, R.; Mauit, O.; Sofin, R. G. S.; Farrell, L.; Byrne, C.; Smith, C. M.; McGilp, J. F.; Shvets, I. V.

    2014-05-01

    Reflectance anisotropy spectroscopy (RAS) has been used to measure the optical anisotropies of bulk and thin-film Fe3O4(110) surfaces. The spectra indicate that small shifts in energy of the optical transitions, associated with anisotropic strain or electric field gradients caused by the (110) surface termination or a native oxide layer, are responsible for the strong signal observed. The RAS response was then measured as a function of temperature. A distinct change in the RAS line-shape amplitude was observed in the spectral range from 0.8 to 1.6 eV for temperatures below the Verwey transition of the crystal. Finally, thin-film magnetite was grown by molecular beam epitaxy on MgO(110) substrates. Changes in the RAS spectra were found for different film thickness, suggesting that RAS can be used to monitor the growth of magnetite (110) films in situ. The thickness dependence of the RAS is discussed in terms of various models for the origin of the RAS signal.

  2. Thickness dependence of the resistivity tensor in epitaxial magnetite thin films

    NASA Astrophysics Data System (ADS)

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

    2013-07-01

    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.

  3. Site-specific magnetization reversal studies of magnetite

    SciTech Connect

    Cady, A.; Haskel, D.; Lang, J. C.; Islam, Z.; Srajer, G. [Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439 (United States); Ankudinov, A. [Department of Physics, University of Washington, Seattle, Washington 98195 (United States); Subias, G.; Garcia, J. [Instituto de Ciencia de Materiales de Aragon, CSIC-Universidad de Zaragoza, Pza. San Francisco s/n 50009 Zaragoza (Spain)

    2006-04-01

    The mechanism of magnetization reversal in magnetite (Fe{sub 3}O{sub 4}) single crystals was studied using site-specific magnetic sensitive diffraction anomalous near-edge structure. By exploiting the angular dependence of the cross section, we are able to show that the mechanism of reversal involves a mixture of coherent rotation and domain formation. The results reveal additional details to that provided by XMCD measurements, which average over nonequivalent sites.

  4. Magnetics and magnetoresistance in epitaxial magnetite heterostructures

    Microsoft Academic Search

    R. V. Chopdekar; G. Hu; A. C. Ford; Y. Suzuki

    2004-01-01

    We have synthesized and characterized epitaxial magnetite (Fe3O4) heterostructures that have been grown by pulsed laser deposition. Trilayers of magnetite, separated by a paramagnetic insulating\\u000a CoCr2O4 layer, exhibit two distinct coercive fields corresponding to the two magnetite layers. However, detailed magnetic measurements\\u000a indicate that the two magnetite layers are exchange coupled across CoCr2O4 layers as thick as 10 nm. Current-voltage

  5. Electron transport in magnetite nanoparticles

    NASA Astrophysics Data System (ADS)

    Lee, Sungbae; Mayo, John T.; Colvin, Vikki L.; Natelson, Douglas

    2007-03-01

    Magnetite (Fe3O4) is an example of a strongly correlated, mixed valence oxide. Electron transport through small numbers of monodisperse magnetite nanocrystals (20nm in diameter) is measured on nanometer-scale three-terminal devices where nanoparticles are decorated on lithographically defined platinum electrodes. The abrupt development of discontinuities on IV curves around 120K and below strongly suggests the particles are going through the Verwey transition. Initial measurements of the full range of IV characteristics and magnetoresistive behaviors of these devices are presented.

  6. Enhanced magnetoresistance in nanocrystalline magnetite

    Microsoft Academic Search

    M. Venkatesan; S. Nawka; S. C. Pillai; J. M. D. Coey

    2003-01-01

    The magnetic and magnetotransport properties of nanoparticulate magnetite with different grain sizes are investigated using x-ray diffraction, microscopy, magnetometry, and magnetoresistance measurements. The magnetization varies significantly with grain size and is sensitive to preparation conditions. The reduction in saturation magnetization in coprecipitated particles is probably due to the surface spin disorder. Magnetoresistance of pressed powder compacts is significantly enhanced in

  7. Raman study of the Verwey transition in magnetite thin films

    NASA Astrophysics Data System (ADS)

    Baghaie Yazdi, M.; Choi, K.-Y.; Wulferding, D.; Lemmens, P.; Alff, L.

    2013-10-01

    We have grown epitaxial thin films of magnetite on MgO and Al2O3 substrates with sharp and distinct signatures of the Verwey transition in resistivity and magnetization. We have used Raman scattering to separate the footprint of purely structural changes from the effect of additional charge and orbital order. Raman modes related to the structural phase transition occur first at temperatures above the Verwey transition temperature. In contrast, newly emerging modes indicating additional charge and orbital order appear at the Verwey transition. These results suggest that the completion of the structural phase transition in magnetite is a necessary precursor triggering a transition into a complex charge and orbitally ordered state.

  8. Comparison between the crystallization processes by laser and furnace annealing of pure and doped aSi:H

    Microsoft Academic Search

    R. Beserman; Yu. L Khait; A Chack; R Weil; W Beyer

    2002-01-01

    A comparison between the annealing processes is made for undoped hydrogenated amorphous Si (a-Si:H), boron and phosphorus doped amorphous silicon. It is found that in all cases the crystallization onset in the furnace always occurs at higher temperature than for the laser-annealed material. The free-carrier phonon interaction shows up in furnace-annealed doped a-Si but is not seen in laser-annealed doped

  9. Formation of Magnetite Nanoparticles at Low Temperature: From Superparamagnetic to Stable Single Domain Particles

    PubMed Central

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

    2013-01-01

    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

  10. Compositional optimization of magnetite thin films prepared by rf sputtering from a composite target of wüstite and Ge

    Microsoft Academic Search

    Seishi Abe; Shintaro Nakamura; Shigehiro Ohnuma

    2011-01-01

    This study investigated the compositional optimization of magnetite (Fe3O4) thin films containing a small amount of Ge to enhance magnetization. No substrate bias was applied during deposition. In a pure Ar atmosphere, the film structure changed from the phase mixture of magnetite and wüstite (Fe1?xO) to the weak appearance of wüstite with increasing Ge content. The antiferromagnetic wüstite thus obtained

  11. Dissolution and reduction of magnetite by bacteria

    NASA Technical Reports Server (NTRS)

    Kostka, J. E.; Nealson, K. H.

    1995-01-01

    Magnetite (Fe3O4) is an iron oxide of mixed oxidation state [Fe(II), Fe(III)] that contributes largely to geomagnetism and plays a significant role in diagenesis in marine and freshwater sediments. Magnetic data are the primary evidence for ocean floor spreading and accurate interpretation of the sedimentary magnetic record depends on an understanding of the conditions under which magnetite is stable. Though chemical reduction of magnetite by dissolved sulfide is well known, biological reduction has not been considered likely based upon thermodynamic considerations. This study shows that marine and freshwater strains of the bacterium Shewanella putrefaciens are capable of the rapid dissolution and reduction of magnetite, converting millimolar amounts to soluble Fe(II)in a few days at room temperature. Conditions under which magnetite reduction is optimal (pH 5-6, 22-37 degrees C) are consistent with an enzymatic process and not with simple chemical reduction. Magnetite reduction requires viable cells and cell contact, and it appears to be coupled to electron transport and growth. In a minimal medium with formate or lactate as the electron donor, more than 10 times the amount of magnetite was reduced over no carbon controls. These data suggest that magnetite reduction is coupled to carbon metabolism in S. putrefaciens. Bacterial reduction rates of magnetite are of the same order of magnitude as those estimated for reduction by sulfide. If such remobilization of magnetite occurs in nature, it could have a major impact on sediment magnetism and diagenesis.

  12. Thermoremanent Magnetization in Submicroscopic Magnetite

    Microsoft Academic Search

    D. J. Dunlop

    1973-01-01

    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,

  13. Magnetotransport of magnetite nanoparticle arrays

    Microsoft Academic Search

    Hao Zeng; C. T. Black; R. L. Sandstrom; P. M. Rice; C. B. Murray; Shouheng Sun

    2006-01-01

    We combine a material self-assembly with conventional lithographic processes in order to fabricate magnetoelectronic devices composed of ordered three-dimensional arrays of magnetite (Fe3O4) nanoparticles. The device magnetoresistance reaches 35% at 60 K, corresponding to an electron spin polarization of 73%. Magnetoresistance of 12% remains at room temperature. Magnetoresistance decreases with both increasing temperature and bias voltage, however, the magnetoresistance of

  14. Extrinsic magnetoresistance in magnetite nanoparticles

    Microsoft Academic Search

    Kai Liu; L. Zhao; P. Klavins; Frank E. Osterloh; H. Hiramatsu

    2003-01-01

    Magnetite (Fe3O4) nanoparticles, 8 to 9 nm in size, have been synthesized using an aqueous precipitation technique. X-ray diffraction and chemical titration confirm a single cubic spinel phase with expected stoichiometry. Superparamagnetic behavior has been observed in pressed pellets of the nanoparticles above 200 K. Spin-dependent tunneling through adjacent particles has led to a negative magnetoresistance, -8.6% at 200 K

  15. Thermal treatment of magnetite nanoparticles

    PubMed Central

    Wykowska, Urszula; Satula, Dariusz; Nordblad, Per

    2015-01-01

    Summary This paper presents the results of a thermal treatment process for magnetite nanoparticles in the temperature range of 50–500 °C. The tested magnetite nanoparticles were synthesized using three different methods that resulted in nanoparticles with different surface characteristics and crystallinity, which in turn, was reflected in their thermal durability. The particles were obtained by coprecipitation from Fe chlorides and decomposition of an Fe(acac)3 complex with and without a core–shell structure. Three types of ferrite nanoparticles were produced and their thermal stability properties were compared. In this study, two sets of unmodified magnetite nanoparticles were used where crystallinity was as determinant of the series. For the third type of particles, a Ag shell was added. By comparing the coated and uncoated particles, the influence of the metallic layer on the thermal stability of the nanoparticles was tested. Before and after heat treatment, the nanoparticles were examined using transmission electron microscopy, IR spectroscopy, differential scanning calorimetry, X-ray diffraction and Mössbauer spectroscopy. Based on the obtained results, it was observed that the fabrication methods determine, to some extent, the sensitivity of the nanoparticles to external factors. PMID:26199842

  16. Hydrogen-bond-dynamics-based switching of conductivity and magnetism: a phase transition caused by deuterium and electron transfer in a hydrogen-bonded purely organic conductor crystal.

    PubMed

    Ueda, Akira; Yamada, Shota; Isono, Takayuki; Kamo, Hiromichi; Nakao, Akiko; Kumai, Reiji; Nakao, Hironori; Murakami, Youichi; Yamamoto, Kaoru; Nishio, Yutaka; Mori, Hatsumi

    2014-08-27

    A hydrogen bond (H-bond) is one of the most fundamental and important noncovalent interactions in chemistry, biology, physics, and all other molecular sciences. Especially, the dynamics of a proton or a hydrogen atom in the H-bond has attracted increasing attention, because it plays a crucial role in (bio)chemical reactions and some physical properties, such as dielectricity and proton conductivity. Here we report unprecedented H-bond-dynamics-based switching of electrical conductivity and magnetism in a H-bonded purely organic conductor crystal, ?-D3(Cat-EDT-TTF)2 (abbreviated as ?-D). This novel crystal ?-D, a deuterated analogue of ?-H3(Cat-EDT-TTF)2 (abbreviated as ?-H), is composed only of a H-bonded molecular unit, in which two crystallographically equivalent catechol-fused ethylenedithiotetrathiafulvalene (Cat-EDT-TTF) skeletons with a +0.5 charge are linked by a symmetric anionic [O···D···O](-1)-type strong H-bond. Although the deuterated and parent hydrogen systems, ?-D and ?-H, are isostructural paramagnetic semiconductors with a dimer-Mott-type electronic structure at room temperature (space group: C2/c), only ?-D undergoes a phase transition at 185 K, to change to a nonmagnetic insulator with a charge-ordered electronic structure (space group: P1). The X-ray crystal structure analysis demonstrates that this dramatic switching of the electronic structure and physical properties originates from deuterium transfer or displacement within the H-bond accompanied by electron transfer between the Cat-EDT-TTF ?-systems, proving that the H-bonded deuterium dynamics and the conducting TTF ?-electron are cooperatively coupled. Furthermore, the reason why this unique phase transition occurs only in ?-D is qualitatively discussed in terms of the H/D isotope effect on the H-bond geometry and potential energy curve. PMID:25127315

  17. Magnetite in the radular teeth of chitons

    Microsoft Academic Search

    Manabu Mizota; Yutaka Maeda

    1986-01-01

    To understand the process by which living organisms synthesize magnetite, we measured the Mössbauer spectra on the teeth at\\u000a different maturation stages along the radula of chitons. Our results show that magnetite is progressively mineralized from\\u000a hydrous ferric oxide precursor in the early stage of maturation. As the denticles become fully mineralized, a part of magnetite\\u000a is oxidized to maghemite

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

    PubMed

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

    2013-01-01

    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

  19. Understanding the biological stabilization of ferrihydrite and its transformation to magnetite

    NASA Astrophysics Data System (ADS)

    Gordon, Lyle; Joester, Derk

    2013-03-01

    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.

  20. ?Magnetotransport of magnetite nanoparticle arrays

    NASA Astrophysics Data System (ADS)

    Zeng, Hao; Black, C. T.; Sandstrom, R. L.; Rice, P. M.; Murray, C. B.; Sun, Shouheng

    2006-01-01

    We combine a material self-assembly with conventional lithographic processes in order to fabricate magnetoelectronic devices composed of ordered three-dimensional arrays of magnetite (Fe3O4) nanoparticles. The device magnetoresistance reaches 35% at 60 K, corresponding to an electron spin polarization of 73%. Magnetoresistance of 12% remains at room temperature. Magnetoresistance decreases with both increasing temperature and bias voltage, however, the magnetoresistance of nanoparticle-based structures is only weakly dependent on the voltage—a favorable attribute for application to electronics.

  1. Magnetite (Fe3O4) Core-Shell Nanowires: Synthesis and

    E-print Network

    Zhou, Chongwu

    Magnetite (Fe3O4) Core-Shell Nanowires: Synthesis and Magnetoresistance Daihua Zhang,,§ Zuqin Liu, 2004; Revised Manuscript Received October 1, 2004 ABSTRACT High quality MgO/Fe3O4 core-shell nanowires have been successfully synthesized by depositing an epitaxial shell of Fe3O4 onto single crystal Mg

  2. The role of grain boundaries in determining the transport properties of magnetite

    E-print Network

    Montfrooij, Wouter

    -effect measurements on single-crystal magnetite Fe3O4 close to the Verwey transition TV=123.8 K. We show on 9 November 2004; published online 28 April 2005 We present magnetoresistance and Hall, magnetoresistance RM, magnetization M, Hall-effect RH, and ac susceptibility on synthetic, high-purity single

  3. Ultrafine-grained magnetite in deep-sea sediments: Possible bacterial magnetofossils

    E-print Network

    Kirschvink, Joseph L.

    -562, September 1984 sea sediments. Extant bacteria have been found living in both marine and freshwater559 Ultrafine-grained magnetite in deep-sea sediments: Possible bacterial magnetofossils Joseph L crystals to be separated from a variety of deep-sea sediments. Morphologic characterization

  4. Magnetotransport in exchange-coupled magnetite junctions

    Microsoft Academic Search

    Rajesh V. Chopdekar; Guohan Hu; Alexandra C. Ford; Yuri Suzuki

    2004-01-01

    Epitaxial magnetic junctions of theoretically half-metallic electrode material magnetite were fabricated with a cobalt chromite paramagnetic insulating tunnel barrier. This spinel structure barrier was chosen to be isostructural to the magnetite electrodes. Highly crystalline trilayers with low surface roughness were grown. Strong exchange coupling between the electrodes is observed across the barrier. Magnetoresistance measurements are reminiscent of a single ferromagnetic

  5. Step-edge magnetoresistance of magnetite films

    Microsoft Academic Search

    M. Ziese; R. Hohne; K. Zimmer; P. Esquinazi

    2002-01-01

    The magnetoresistance induced by step edges in magnetite films was investigated. The films were fabricated on MgAl2O4 substrates patterned by ion-beam etching prior to film deposition. If the crystallographic quality of the magnetite film is good enough, a clear magnetoresistance anisotropy is observed with respect to the relative direction of current and step edge.

  6. Metal-doped magnetite thin films.

    PubMed

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

    2012-06-01

    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

  7. Three-Dimensional Morphological Analysis of ALH84001 Magnetite Using Electron Tomography

    NASA Technical Reports Server (NTRS)

    Thomas-Keprta, Kathie L.; Clemett, Simon J.; Shimmin, Joel; Morphew, Mary; McIntosh, J. Richard; Bazylinski, Dennis A.; Kirschvink, Joseph L.; Wentworth, Susan J.; McKay, David S.; Vali, Hojatollah

    2003-01-01

    We report here the crystal morphologies of MV-1 and ALH84001 magnetites as calculated by back-projection using electron tomography. In the present study, we used a 300 keV TEM with a field emission gun (Tecnai F-30 from FEI Inc.), equipped with a 2048 x 2048 pixel CCD camera from Gatan Inc. to image magnetite crystals over tilt ranges of approx. +/- 72 deg in 2 deg tilt intervals. The images were aligned for back-projection, either manually, or through the use of fiducial 5 nm Au spheres affixed to the specimen prior to microscopy. Three-dimensional (3-D) reconstructions were computed using weighted back-projection of the tilted views. The tomograms were viewed and analyzed as a series of slices 1.0 nm thick, taken parallel to the specimen-supporting grid, using the IMOD software package. The shape of each magnetite crystal was determined by defining the external contour of a given magnetite in each slice and assembling a stack of these contours in 3-D. To aid in visualization, the stacked contour array was reduced to an optimal mesh by Delaunay triangulation. The surface normal to each of the triangles in the mesh was calculated and the triangle faces colored according to the orientation of that surface normal relative to the principal crystallographic axis of magnetite. Green surfaces correspond to {111} orientations, blue surfaces to {100} orientations, and red surfaces to {110} orientations. Triangles whose surface normal did not correspond to one of the principal axes were colored gray. Within the experimental and numerical uncertainties of the deconvolution, the tomographic reconstruction of both MV-1 and ALH84001 magnetites are equivalent and correspond to a truncated hexa-octahedral morphology.

  8. The role of grain boundaries in determining the transport properties of magnetite

    NASA Astrophysics Data System (ADS)

    Mertens, D. C.; Montfrooij, W.; McQueeney, R. J.; Yethiraj, M.; Honig, J. M.

    2005-05-01

    We present magnetoresistance and Hall-effect measurements on single-crystal magnetite (Fe3O4) close to the Verwey transition TV=123.8K. We show that the formation of grain boundaries accompanying the reduction in crystal symmetry plays a significant role in the electron-scattering mechanism, and that grain boundaries can account for the apparent change in sign of the charge carriers below TV.

  9. Fabrication of a Spin-Polarized Electron Source with a Single Magnetite Whisker

    NASA Astrophysics Data System (ADS)

    Okada, Morihiro; Nagai, Shigekazu; Neo, Youichiro; Hata, Koichi; Mimura, Hidenori

    2009-06-01

    <110>-oriented single crystal magnetite whiskers 30 to 200 nm in diameter were synthesized on a stainless steel plate by means of the combustion flame thermal oxidation process. Microscopic analyses have revealed that the whiskers have some defects such as stacking faults and dislocations and also that manganese is the dominant impurity. A spin-polarized electron source with a single magnetite whisker was fabricated by using a micro-sampling instrument in a focused ion beam (FIB) system. The spin polarization of this sample was measured by using a Mott electron polarimeter and was found to be 15% at room temperature.

  10. Magnetite and magnetite/silver core/shell nanoparticles with diluted magnet-like behavior

    SciTech Connect

    Garza-Navarro, Marco [Facultad de Ingenieria Mecanica y Electrica, Universidad Autonoma de Nuevo Leon, Av. Universidad s/n, Cd. Universitaria, San Nicolas de los Garza, Nuevo Leon 66450 (Mexico); Torres-Castro, Alejandro, E-mail: alejandro.torrescs@uanl.edu.m [Facultad de Ingenieria Mecanica y Electrica, Universidad Autonoma de Nuevo Leon, Av. Universidad s/n, Cd. Universitaria, San Nicolas de los Garza, Nuevo Leon 66450 (Mexico); Centro de Innovacion, Investigacion y Desarrollo en Ingenieria y Tecnologia, Universidad Autonoma de Nuevo Leon, Apodaca, Nuevo Leon 66600 (Mexico); Gonzalez, Virgilio; Ortiz, Ubaldo [Facultad de Ingenieria Mecanica y Electrica, Universidad Autonoma de Nuevo Leon, Av. Universidad s/n, Cd. Universitaria, San Nicolas de los Garza, Nuevo Leon 66450 (Mexico); Centro de Innovacion, Investigacion y Desarrollo en Ingenieria y Tecnologia, Universidad Autonoma de Nuevo Leon, Apodaca, Nuevo Leon 66600 (Mexico); De la Rosa, Elder [Centro de Investigaciones en Optica, A.P. 1-948, Leon Gto. 37160 (Mexico)

    2010-01-15

    In the present work is reported the use of the biopolymer chitosan as template for the preparation of magnetite and magnetite/silver core/shell nanoparticles systems, following a two step procedure of magnetite nanoparticles in situ precipitation and subsequent silver ions reduction. The crystalline and morphological characteristics of both magnetite and magnetite/silver core/shell nanoparticles systems were analyzed by high resolution transmission electron microscopy (HRTEM) and nanobeam diffraction patterns (NBD). The results of these studies corroborate the core/shell morphology and the crystalline structure of the magnetite core and the silver shell. Moreover, magnetization temperature dependent, M(T), measurements show an unusual diluted magnetic behavior attributed to the dilution of the magnetic ordering in the magnetite and magnetite/silver core/shell nanoparticles systems. - Graphical abstract: Biopolymer chitosan was used as stabilization media to synthesize both magnetite and magnetite/silver core/shell nanoparticles. Results of HRTEM and NBD patterns confirm core/shell morphology of the obtained nanoparticles. It was found that the composites show diluted magnet-like behavior.

  11. Crystals

    NSDL National Science Digital Library

    Lawrence Hall of Science

    2009-01-01

    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.

  12. Extraterrestrial magnetite studied by Mössbauer spectroscopy

    NASA Astrophysics Data System (ADS)

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

    1989-06-01

    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.

  13. Is magnetite a universal memory molecule?

    PubMed

    Størmer, Fredrik C

    2014-11-01

    Human stem cells possess memory, and consequently all living human cells must have a memory system. How memory is stored in cells and organisms is an open question. Magnetite is perhaps the best candidate to be a universal memory molecule. Magnetite may give us a clue, because it is the Earth's most distributed and important magnetic material. It is found in living organisms with no known functions except for involvement in navigation in some organisms. In humans magnetite is found in the brain, heart, liver and spleen. Humans suffer from memory dysfunctions in many cases when iron is out of balance. Anomalous concentrations of magnetite is known to be associated with a neurodegenerative disorder like Alzheimer's disease. Due to the rapid speed and accuracy of our brain, memory and its functions must be governed by quantum mechanics. PMID:25236401

  14. Simultaneously Discrete Biomineralization of Magnetite and Tellurium Nanocrystals in Magnetotactic Bacteria?

    PubMed Central

    Tanaka, Masayoshi; Arakaki, Atsushi; Staniland, Sarah S.; Matsunaga, Tadashi

    2010-01-01

    Magnetotactic bacteria synthesize intracellular magnetosomes comprising membrane-enveloped magnetite crystals within the cell which can be manipulated by a magnetic field. Here, we report the first example of tellurium uptake and crystallization within a magnetotactic bacterial strain, Magnetospirillum magneticum AMB-1. These bacteria independently crystallize tellurium and magnetite within the cell. This is also highly significant as tellurite (TeO32?), an oxyanion of tellurium, is harmful to both prokaryotes and eukaryotes. Additionally, due to its increasing use in high-technology products, tellurium is very precious and commercially desirable. The use of microorganisms to recover such molecules from polluted water has been considered as a promising bioremediation technique. However, cell recovery is a bottleneck in the development of this approach. Recently, using the magnetic property of magnetotactic bacteria and a cell surface modification technology, the magnetic recovery of Cd2+ adsorbed onto the cell surface was reported. Crystallization within the cell enables approximately 70 times more bioaccumulation of the pollutant per cell than cell surface adsorption, while utilizing successful recovery with a magnetic field. This fascinating dual crystallization of magnetite and tellurium by magnetotactic bacteria presents an ideal system for both bioremediation and magnetic recovery of tellurite. PMID:20581185

  15. Spin-filter effect in magnetite nanowire.

    PubMed

    Liao, Zhi-Min; Li, Ya-Dong; Xu, Jun; Zhang, Jing-Min; Xia, Ke; Yu, Da-Peng

    2006-06-01

    Spin-dependent electron transport in individual magnetite (Fe3O4) nanowires contacted with normal metallic electrodes was investigated. Such a configured device demonstrated a spin-filter effect, that is, only the minority spin carriers can transport through the magnetite nanowire due to its negative spin polarization. An anomalous positive magnetoresistance approximately 7.5% is observed at room temperature. Moreover, the magnetoresistance can be controlled via bias voltage. PMID:16771558

  16. Magnetite nanoparticles for nonradionuclide brachytherapy1

    PubMed Central

    Safronov, Victor; Sozontov, Evgeny; Polikarpov, Mikhail

    2015-01-01

    Magnetite nanoparticles possess several properties that can make them useful for targeted delivery of radiation to tumors for the purpose of brachytherapy. Such particles are biodegradable and magnetic and can emit secondary radiation when irradiated by an external source. In this work, the dose distribution around a magnetite particle of 10?nm diameter being irradiated by monochromatic X-rays with energies in the range 4–60 keV is calculated. PMID:26089761

  17. Magnetoelectric properties of magnetite thin films

    Microsoft Academic Search

    J S-Y Feng; R D Pashley; M-A Nicolet

    1975-01-01

    Resistivity, DC Hall effect and transverse magnetoresistance measurements were made on polycrystalline thin films of magnetite (Fe3O4) from 104K to room temperature. The Verwey transition is observed at TV=123K, about 4K higher than reported for bulk magnetite. The ordinary and extraordinary Hall coefficients are negative over the entire temperature range, consistent with negatively charged carriers. The extraordinary Hall coefficient exhibits

  18. Thermal Analysis of Acicular Shaped Magnetite

    NASA Technical Reports Server (NTRS)

    Lauer, H. V., Jr.; Ming, D. W.; Golden, D. C.

    2003-01-01

    We are in the process of developing a database on the thermal properties of well-characterized Martian analog materials in support of future Mars surface missions. The database contains the thermal behaviors of these analog materials under reduced and Earth ambient pressures. Magnetite in planetary materials has received considerable attention in recent years since the identification of fine grain single-domain magnetite in Martian meteorite ALH84001 and their possible link to past life on Mars (i.e., possible biominerals of magnetotactic bacteria). Because of its possible importance to Mars science, we report here the thermal properties of magnetite particles with acicular morphology, i.e., needle-shaped magnetite. Acicular shaped magnetite can be commercially produced from goethite (FeOOH) as the starting material via a H2 reduction process. However, instead of using this process or procedure, we report here on the thermal characterization of acicular magnetite formed under reducing conditions from well-characterized needle-shaped goethite at low temperature in controlled CO-CO2 1-bar atmosphere gas mixing furnaces.

  19. Geochemistry of magnetite from Proterozoic Fe-Cu deposits in the Kangdian metallogenic province, SW China

    NASA Astrophysics Data System (ADS)

    Chen, Wei Terry; Zhou, Mei-Fu; Gao, Jian-Feng; Hu, Ruizhong

    2015-01-01

    Fe-Cu deposits in the Kangdian Fe-Cu metallogenic province, SW China, are hosted in Paleoproterozoic meta-volcanic-sedimentary sequences and are spatially associated with coeval mafic intrusions. Several well-known examples are the giant Lala, Dahongshan, and Yinachang deposits. They have a common paragenetic sequence of an early Fe-oxide stage associated with sodic alteration and a late Cu-sulfide stage associated with potassic-carbonate alteration. Magnetite dominates the Fe-oxide stage of these deposits but is also present in the Cu-sulfide stage of the Lala deposit. This study uses trace element compositions of magnetite to examine the nature and origin of the ore-forming fluids. The magnetite has variable concentrations of Ti, Al, Mg, Mn, Si, V, Cr, Ca, Co, Ni, Sc, Zn, Cu, Mo, Sn, and Ga, which are thought to have been controlled mainly by fluid compositions and/or intensive parameters (e.g., temperature and oxygen fugacity (fO2)). Fluid-rock interaction and coprecipitating mineral phases appear to be less important in controlling the magnetite compositions. Magnetite grains in the Fe-oxide stage of the Lala and Dahongshan deposits have comparable trace element compositions and were likely precipitated from chemically similar fluids. High Ni contents of magnetite in both deposits, coupled with previous isotopic data and the fact that the two deposits are spatially associated with coeval mafic intrusions, strongly suggest that the ore-forming fluids were genetically related to the mafic magmas that formed the intrusions. Magnetite grains in the Fe-oxide stage of the Yinachang deposit have much lower V and Ni but higher Sn and Mo contents than those of the Lala and Dahongshan deposits and are thus thought to have precipitated from more oxidized and Mo-Sn-rich fluids that may have evolved from relatively felsic magmas. Magnetite grains from the Cu-sulfide and Fe-oxide stages of the Lala deposit are broadly similar in composition, but those in the Cu-sulfide stage have slightly higher Cu, Zn, and Mn and are thought to have crystallized from relatively low-temperature and Cu-Zn-Mn-rich fluids evolved from the fluids of the early Fe-oxide stage. Our results show that magnetite from the Fe-Cu deposits in the Kangdian Province, banded iron formation, Fe skarn deposits, diabase-hosted hydrothermal Fe deposits, and magmatic deposits has significantly different compositions. We propose that covariations of Co-Ni, Zn-Sn, and Co/Ni-Mn can be used to effectively discriminate different deposit types.

  20. The chemistry of hydrothermal magnetite: a review

    USGS Publications Warehouse

    Nadoll, Patrick; Angerer, Thomas; Mauk, Jeffrey L.; French, David; Walshe, John

    2014-01-01

    Magnetite (Fe3O4) is a well-recognized petrogenetic indicator and is a common accessory mineral in many ore deposits and their host rocks. Recent years have seen an increased interest in the use of hydrothermal magnetite for provenance studies and as a pathfinder for mineral exploration. A number of studies have investigated how specific formation conditions are reflected in the composition of the respective magnetite. Two fundamental questions underlie these efforts — (i) How can the composition of igneous and, more importantly, hydrothermal magnetite be used to discriminate mineralized areas from barren host rocks, and (ii) how can this assist exploration geologists to target ore deposits at greater and greater distances from the main mineralization? Similar to igneous magnetite, the most important factors that govern compositional variations in hydrothermal magnetite are (A) temperature, (B) fluid composition — element availability, (C) oxygen and sulfur fugacity, (D) silicate and sulfide activity, (E) host rock buffering, (F) re-equilibration processes, and (G) intrinsic crystallographic controls such as ionic radius and charge balance. We discuss how specific formation conditions are reflected in the composition of magnetite and review studies that investigate the chemistry of hydrothermal and igneous magnetite from various mineral deposits and their host rocks. Furthermore, we discuss the redox-related alteration of magnetite (martitization and mushketovitization) and mineral inclusions in magnetite and their effect on chemical analyses. Our database includes published and previously unpublished magnetite minor and trace element data for magnetite from (1) banded iron formations (BIF) and related high-grade iron ore deposits in Western Australia, India, and Brazil, (2) Ag–Pb–Zn veins of the Coeur d'Alene district, United States, (3) porphyry Cu–(Au)–(Mo) deposits and associated (4) calcic and magnesian skarn deposits in the southwestern United States and Indonesia, and (5) plutonic igneous rocks from the Henderson Climax-type Mo deposit, United States, and the un-mineralized Inner Zone Batholith granodiorite, Japan. These five settings represent a diverse suite of geological settings and cover a wide range of formation conditions. The main discriminator elements for magnetite are Mg, Al, Ti, V, Cr, Mn, Co, Ni, Zn, and Ga. These elements are commonly present at detectable levels (10 to > 1000 ppm) and display systematic variations. We propose a combination of Ni/(Cr + Mn) vs. Ti + V, Al + Mn vs. Ti + V, Ti/V and Sn/Ga discriminant plots and upper threshold concentrations to discriminate hydrothermal from igneous magnetite and to fingerprint different hydrothermal ore deposits. The overall trends in upper threshold values for the different settings can be summarized as follows: (I) BIF (hydrothermal) — low Al, Ti, V, Cr, Mn, Co, Ni, Zn, Ga and Sn; (II) Ag–Pb–Zn veins (hydrothermal) — high Mn and low Ga and Sn; (III) Mg-skarn (hydrothermal) — high Mg and Mn and low Al, Ti, Cr, Co, Ni and Ga; (IV) skarn (hydrothermal) — high Mg, Al, Cr, Mn, Co, Ni and Zn and low Sn; (V) porphyry (hydrothermal) — high Ti and V and low Sn; (VI) porphyry (igneous) — high Ti, V and Cr and low Mg; and (VII) Climax-Mo (igneous) — high Al, Ga and Sn and low Mg and Cr.

  1. Pond sediment magnetite grains show a distinctive microbial community.

    PubMed

    Song, H-K; Sonkaria, S; Khare, V; Dong, K; Lee, H-T; Ahn, S-H; Kim, H-K; Kang, H-J; Lee, S-H; Jung, S P; Adams, J M

    2015-07-01

    Formation of magnetite in anaerobic sediments is thought to be enhanced by the activities of iron-reducing bacteria. Geobacter has been implicated as playing a major role, as in culture its cells are often associated with extracellular magnetite grains. We studied the bacterial community associated with magnetite grains in sediment of a freshwater pond in South Korea. Magnetite was isolated from the sediment using a magnet. The magnetite-depleted fraction of sediment was also taken for comparison. DNA was extracted from each set of samples, followed by PCR for 16S bacterial ribosomal RNA (rRNA) gene and HiSeq sequencing. The bacterial communities of the magnetite-enriched and magnetite-depleted fractions were significantly different. The enrichment of three abundant operational taxonomic units (OTUs) suggests that they may either be dependent upon the magnetite grain environment or may be playing a role in magnetite formation. The most abundant OTU in magnetite-enriched fractions was Geobacter, bolstering the case that this genus is important in magnetite formation in natural systems. Other major OTUs strongly associated with the magnetite-enriched fraction, rather than the magnetite-depleted fraction, include a Sulfuricella and a novel member of the Betaproteobacteria. The existence of distinct bacterial communities associated with particular mineral grain types may also be an example of niche separation and coexistence in sediments and soils, which cannot usually be detected due to difficulties in separating and concentrating minerals. PMID:25592636

  2. Magnetite: a search for the half-metallic state.

    PubMed

    Fonin, M; Dedkov, Yu S; Pentcheva, R; Rüdiger, U; Güntherodt, G

    2007-08-01

    We present a detailed study of the spin-dependent electronic structure of thin epitaxial magnetite films of different crystallographic orientations. Using spin- and angle-resolved photoelectron spectroscopy at room temperature, we determine for epitaxial Fe(3)O(4)(111) films a maximum spin polarization value of -(80 ± 5)% near E(F). The spin-resolved photoelectron spectra for binding energies between 1.5 eV and E(F) show good agreement with the spin-split band structure from density functional theory (DFT) calculations which predict an overall energy gap in the spin-up electron bands in high symmetry directions, thus providing evidence for the half-metallic ferromagnetic state of Fe(3)O(4) in the [111] direction. In the case of the Fe(3)O(4)(100) surface, both the spin-resolved photoelectron spectroscopy experiments and the DFT density of states give evidence for a half-metal to metal transition: the measured spin polarization of about -(55 ± 10)% at E(F) and the theoretical value of -40% are significantly lower than the -100% predicted by local spin density approximation (LSDA) calculations for the bulk magnetite crystal as well as the -(80 ± 5)% obtained for the Fe(3)O(4)(111) films. The experimental findings were corroborated by DFT calculations as due to a surface reconstruction leading to the electronic states in the majority-spin band gap and thus to the reduced spin polarization. PMID:21694117

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

    Microsoft Academic Search

    Thapanapong Theppaleak; Gamolwan Tumcharern; Uthai Wichai; Metha Rutnakornpituk

    2009-01-01

    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

  4. Effect of hydrostatic pressure on magnetostriction and magnetocrystalline anisotropy of magnetite

    Microsoft Academic Search

    Takesi Nagata; Hazimu Kinoshita

    1967-01-01

    The saturation magnetostriction coefficients, lambda100 and lambda111, and the magnetocrystalline anisotropy constants, K1 and K2, of single crystals of magnetite are measured under the effect of hydrostatic pressure P of 0-2 kbar in range at the room temperature. Both | lambda100 | and lambda111 increase with increasing hydrostatic pressure with rate of about 15%\\/kbar, whereas both | K1 | and

  5. Transport and magnetic properties of epitaxial and polycrystalline magnetite thin films

    Microsoft Academic Search

    X. W. Li; A. Gupta; Gang Xiao; G. Q. Gong

    1998-01-01

    The transport and magnetic properties of magnetite (Fe3O4) thin films grown epitaxially on single crystal MgO(100) and SrTiO3(100) substrates, and with multiple grain orientations on polycrystalline SrTiO3 substrates, have been investigated. The films are grown using pulsed laser deposition and their epitaxial quality determined using ion channeling measurements. Transport and magnetic studies of Fe3O4 films as a function of thickness

  6. Field-dependent anisotropic magnetoresistance and planar Hall effect in epitaxial magnetite thin films

    Microsoft Academic Search

    N. Naftalis; A. Kaplan; M. Schultz; C. A. F. Vaz; J. A. Moyer; C. H. Ahn; L. Klein

    2011-01-01

    A systematic study of the temperature and magnetic field dependence of the longitudinal and transverse resistivities of epitaxial thin films of magnetite (Fe3O4) is reported. The anisotropic magnetoresistance (AMR) and the planar Hall effect are sensitive to the in-plane orientation of current and magnetization with respect to crystal axes in a way consistent with the cubic symmetry of the system.

  7. Magnetotransport anisotropy effects in epitaxial magnetite (Fe3O4) thin films

    Microsoft Academic Search

    S. B. Ogale; K. Ghosh; R. P. Sharma; R. L. Greene; R. Ramesh; T. Venkatesan

    1998-01-01

    Epitaxial films of magnetite (Fe3O4) have been grown on SrTiO3 (100) and sapphire (alpha-Al2O3, 0001) substrates by pulsed laser deposition, and they exhibit crystal orientations of [100] and [111], respectively. Films of both orientations show a clear Verwey transition near 120 K. The temperature dependence of magnetoresistance of the films is examined at fields up to 8.5 T applied parallel

  8. Uniaxial Strain Effect on TV and Electrical Resistivity in Magnetite (Fe3O4)

    NASA Astrophysics Data System (ADS)

    Nagasawa, Yasuo; Hara, Ryohei; Seino, Toshiaki; Kosaka, Masashi; Môri, Nobuo; Todo, Sakae; Uwatoko, Yoshiya

    2006-09-01

    Magnetization and electrical resistivity studies are reported for a single crystal of magnetite under uniaxial strain applied along the [110] and [100] directions. The metal-insulator transition temperature, TV, shifted to higher temperatures with increasing uniaxial compression which is opposite to the result obtained under hydrostatic pressure. Furthermore, the electrical resistivity was found to increase at temperatures below TV, and to decrease at temperatures above TV, with increasing uniaxial compression. Differences between the present results and those under hydrostatic pressure are discussed.

  9. Rock magnetism linked to human brain magnetite

    NASA Astrophysics Data System (ADS)

    Kirschvink, Joseph L.

    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.

  10. Magnetoresistance of magnetite point contacts and nanoconstrictions

    Microsoft Academic Search

    O. Ce´spedes; E. Clifford; J. M. D. Coey

    2005-01-01

    Point contacts of magnetite exhibit large, reversible increases of conductance by a factor of up to 5 in the presence of a small magnetic field (<10 mT), provided the conductance is less than the quantum of conductance G0(12 900 ?)?1. Smaller effects are found in (La0.7Sr0.3)MnO3 and Co2Cr0.6Fe0.4Al. Comparable effects observed in magnetite nanoconstrictions milled using a focused-ion beam in

  11. Magnetoresistance of magnetite point contacts and nanoconstrictions

    Microsoft Academic Search

    O. Céspedes; E. Clifford; J. M. D. Coey

    2005-01-01

    Point contacts of magnetite exhibit large, reversible increases of conductance by a factor of up to 5 in the presence of a small magnetic field (<10 mT), provided the conductance is less than the quantum of conductance G0 (12 900 Omega)-1. Smaller effects are found in (La0.7Sr0.3)MnO3 and Co2Cr0.6Fe0.4Al. Comparable effects observed in magnetite nanoconstrictions milled using a focused-ion beam

  12. Immobilization of peroxidase onto magnetite modified polyaniline.

    PubMed

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

    2012-01-01

    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

  13. Structural transformation in magnetite below the Verwey transition

    NASA Astrophysics Data System (ADS)

    Blasco, Javier; García, Joaquín; Subías, Gloria

    2011-03-01

    The magnetite structure was studied with synchrotron x-ray powder diffraction above and below the Verwey transition. A symmetry-mode analysis was performed to obtain the atomic displacements from the amplitudes of condensing modes. The main contributing modes that drive the structural phase transition at the Verwey temperature correspond to the irreducible representations ?5, X1, X4, W1, and W2. The W modes, neglected so far, must be taken into account so a reliable description of the low-temperature crystal structure can be obtained. This is refined in the nonpolar space group C2/c with ten nonequivalent octahedral irons. The condensation of the mentioned modes leads to a wide distribution of local environments around the octahedral iron atoms, whose valences range between 2.53 and 2.84. This finding rules out any bimodal charge disproportionation of the octahedral iron atoms, i.e., an Fe2+-like/Fe3+-like ordering.

  14. Magnetite Thin Films Containing a Small Amount of Ge

    NASA Astrophysics Data System (ADS)

    Abe, Seishi; Ohnuma, Shigehiro

    2008-11-01

    This paper investigates the crystal structure and magnetization of iron oxide thin film by rf sputtering with a composite target of Ge chips set on an Fe3O4 compound target. No substrate bias was applied and no oxygen was added to argon during deposition. Ge concentration in the films ranged from 0 to 14 at % with the use of different Ge chips. The X-ray diffraction result revealed that as-deposited films were structurally changed with respect to Ge concentration, and a magnetite film was successfully obtained at 5 at %Ge and room temperature, exhibiting ferrimagnetic behavior with magnetization of 3.5 kG at 8×105 Am-1 (10 kOe).

  15. Synthetic clay-magnetite aggregates designed for controlled deposition experiments

    E-print Network

    Dunin-Borkowski, Rafal E.

    Synthetic clay-magnetite aggregates designed for controlled deposition experiments Feinberg, J M of synthetic clay-magnetite aggregates whose physical attributes can be tailored for controlled depositional orientation or oriented aggregation. Grain size distributions of magnetite in three different clay

  16. Quantification of Biogenic Magnetite by Synchrotron X-ray Microscopy During the PETM

    NASA Astrophysics Data System (ADS)

    Wang, H.; Wang, J.; Kent, D. V.; Chen-Wiegart, Y. C. K.

    2014-12-01

    Exceptionally large biogenic magnetite crystals, including spearhead-like and spindle-like ones up to 4 microns, have been reported in clay-rich sediments recording the ~56 Ma Paleocene-Eocene thermal maximum (PETM) and carbon isotope excursion (CIE) in a borehole at Ancora, NJ and along with magnetotactic bacteria (MTB) chains, were suggested [Schumann et al. 2008 PNAS; Kopp et al. 2009 Paleoceanography] to account for the distinctive single domain (SD) rock magnetic properties of these sediments [Lanci et al. 2002 JGR]. However, because uncalibrated magnetic extraction techniques were used to provide material for TEM imaging of the biogenic magnetite, it is difficult to quantitatively analyze their concentration in the bulk clay. In this study, we use a synchrotron transmission X-ray microscope to image bulk CIE clay. We first take mosaic images of sub-millimeter-sized bulk clay samples, in which we can identify many of the various types of giant biogenic magnetite crystals, as well as several other types of iron minerals, such as pyrite framboids, siderite, and detrital magnetite. However, limited by the instrument resolution (~50 nm), we are not able to identify MTB chains let alone isolated magnetic nanoparticles that may be abundant the clay. To quantitatively estimate the concentration of the giant biogenic magnetite, we re-deposited the bulk clay sample in an alcohol solution on a silicon nitride membrane for 2D X-ray scans. After scanning a total area of 0.55 mm2 with average clay thickness of 4 ?m, we identified ~40 spearheads, ~5 spindles and a few elongated rods and estimated their total magnetization as SD particles to be less than about 10% of the mass normalized clay for the scanned area. This result suggests that the giant biogenic magnetite is not a major source of the SD signal for the clay and is in good agreement with rock magnetic analyses using high-resolution first-order reversal curves and thermal fluctuation tomography on bulk CIE clay showing that most of the magnetite occurs as isolated, near-equant SD particles [Wang et al. 2013 PNAS]. This would also exclude a significant contribution from MTB chains and points to a non-biogenic origin, such as a comet impact plume condensate, for the magnetic nanoparticles [Kent et al. 2003 EPSL] in the very rapidly deposited CIE clays [Wright & Schaller 2014 PNAS].

  17. Origin of magnetite in oxidized CV chondrites: in situ measurement of oxygen isotope compositions of Allende magnetite and olivine

    Microsoft Academic Search

    Byeon-Gak Choi; Kevin D. McKeegan; Laurie A. Leshin; John T. Wasson

    1997-01-01

    Magnetite in the oxidized CV chondrite Allende mainly occurs as spherical nodules in porphyritic-olivine (PO) chondrules, where it is associated with Ni-rich metal and\\/or sulfides. To help constrain the origin of the magnetite, we measured oxygen isotopic compositions of magnetite and coexisting olivine grains in PO chondrules of Allende by an in situ ion microprobe technique. Five magnetite nodules form

  18. Ferromagnetic resonance and low-temperature magnetic tests for biogenic magnetite

    NASA Astrophysics Data System (ADS)

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

    2004-07-01

    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.

  19. Energy transfer in pure and Ce-doped LiCaAlF 6 and LiSrAlF 6 crystals

    NASA Astrophysics Data System (ADS)

    Shiran, N.; Gektin, A.; Neicheva, S.; Weber, M.; Derenzo, S.; Kirm, M.; True, M.; Shpinkov, I.; Spassky, D.; Shimamura, K.; Ichinose, N.

    2005-01-01

    Intrinsic ultra-fast scintillations at pulsed X-ray excitation were found in LiCaAlF 6 and LiSrAlF 6. Radiative recombination features of Ce-doped crystals are explained by differences of lattice properties, defect structure and Ce 3+ ion environment in these crystals. The role of exciton formation, electron and hole traps, and energy transfer to the activator centers are discussed.

  20. Influence of magnetite stoichiometry on U(VI) reduction.

    PubMed

    Latta, Drew E; Gorski, Christopher A; Boyanov, Maxim I; O'Loughlin, Edward J; Kemner, Kenneth M; Scherer, Michelle M

    2012-01-17

    Hexavalent uranium (U(VI)) can be reduced enzymatically by various microbes and abiotically by Fe(2+)-bearing minerals, including magnetite, of interest because of its formation from Fe(3+) (oxy)hydroxides via dissimilatory iron reduction. Magnetite is also a corrosion product of iron metal in suboxic and anoxic conditions and is likely to form during corrosion of steel waste containers holding uranium-containing spent nuclear fuel. Previous work indicated discrepancies in the extent of U(VI) reduction by magnetite. Here, we demonstrate that the stoichiometry (the bulk Fe(2+)/Fe(3+) ratio, x) of magnetite can, in part, explain the observed discrepancies. In our studies, magnetite stoichiometry significantly influenced the extent of U(VI) reduction by magnetite. Stoichiometric and partially oxidized magnetites with x ? 0.38 reduced U(VI) to U(IV) in UO(2) (uraninite) nanoparticles, whereas with more oxidized magnetites (x < 0.38) and maghemite (x = 0), sorbed U(VI) was the dominant phase observed. Furthermore, as with our chemically synthesized magnetites (x ? 0.38), nanoparticulate UO(2) was formed from reduction of U(VI) in a heat-killed suspension of biogenic magnetite (x = 0.43). X-ray absorption and Mössbauer spectroscopy results indicate that reduction of U(VI) to U(IV) is coupled to oxidation of Fe(2+) in magnetite. The addition of aqueous Fe(2+) to suspensions of oxidized magnetite resulted in reduction of U(VI) to UO(2), consistent with our previous finding that Fe(2+) taken up from solution increased the magnetite stoichiometry. Our results suggest that magnetite stoichiometry and the ability of aqueous Fe(2+) to recharge magnetite are important factors in reduction of U(VI) in the subsurface. PMID:22148359

  1. The contribution of vanadium and titanium on improving methylene blue decolorization through heterogeneous UV-Fenton reaction catalyzed by their co-doped magnetite.

    PubMed

    Liang, Xiaoliang; Zhong, Yuanhong; Zhu, Sanyuan; Ma, Lingya; Yuan, Peng; Zhu, Jianxi; He, Hongping; Jiang, Zheng

    2012-01-15

    This study investigated the methylene blue (MB) decolorization through heterogeneous UV-Fenton reaction catalyzed by V-Ti co-doped magnetites, with emphasis on comparing the contribution of V and Ti cations on improving the adsorption and catalytic activity of magnetite. In the well crystallized spinel structure, both Ti(4+) and V(3+) occupied the octahedral sites. Ti(4+) showed a more obvious effect on increasing specific surface area and superficial hydroxyl amount than V(3+) did, resulting in a significant improvement of the adsorption ability of magnetite to MB. The UV introduction greatly accelerated MB degradation. And magnetite with more Ti and less V displayed better catalytic activity in MB degradation through heterogeneous UV-Fenton reaction. The transformation of degradation products and individual contribution from vanadium and titanium on improving adsorption and catalytic activity of magnetite were also investigated. These new insights are of high importance for well understanding the interface interaction between contaminants and metal doped magnetites, and the environmental application of natural and synthetic magnetites. PMID:22119302

  2. Magnetic properties of dispersed magnetite powders

    Microsoft Academic Search

    L. G. Parry

    1965-01-01

    Measurements have been made of coercive force, susceptibility, isothermal remanence, thermoremanence and thermal and alternating field demagnetization of annealed magnetite powders in nine size ranges from 1·5 ? to 120 ?. The samples were dispersed in plaster to occupy a few per cent by volume of the specimens and thus to simulate the magnetic properties of rocks. The results are

  3. Rock magnetism linked to human brain magnetite

    Microsoft Academic Search

    Joseph L. Kirschvink

    1994-01-01

    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

  4. Magnetite nanoparticles with no surface spin canting

    Microsoft Academic Search

    A. G. Roca; D. Niznansky; J. Poltierova-Vejpravova; B. Bittova; M. A. González-Fernández; C. J. Serna; M. P. Morales

    2009-01-01

    Surface spin canting has been studied for high quality magnetite nanoparticles in terms of size and shape uniformity. Particles were prepared by thermal decomposition of organic precursors in organic media and in the presence of oleic acid. Results are compared to spin canting effect for magnetic iron oxide nanoparticles of similar size prepared by coprecipitation and subsequently coated with silica.

  5. Magnetic properties of biosynthesized magnetite nanoparticles

    Microsoft Academic Search

    Lucas W. Yeary; Ji-Won Moon; L. J. Love; J. R. Thompson; C. J. Rawn; T. J. Phelps

    2005-01-01

    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

  6. Polyaniline Stabilized Magnetite Nanoparticle Reinforced Epoxy Nanocomposites

    E-print Network

    Guo, John Zhanhu

    from the comprehensive analysis based on the TGA, DSC, and FTIR in this work. KEYWORDS: epoxy resinPolyaniline Stabilized Magnetite Nanoparticle Reinforced Epoxy Nanocomposites Hongbo Gu,, Sruthi,|| Suying Wei,*,§ and Zhanhu Guo*, Integrated Composites Lab (ICL), Dan F. Smith Department of Chemical

  7. Adsorption of arsenic using high surface area magnetites.

    PubMed

    Ohe, Kaoru; Oshima, Tatsuya; Baba, Yoshinari

    2010-08-01

    Magnetites (MEBWx) were prepared by precipitation in 1-butanol/water mixtures of various mole ratios of 1-butanol to water. It was found that the magnetites prepared in the mixture with high mole ratio of 1-butanol to water have high specific surface area. The adsorption isotherms of As(III) and As(V) with the magnetites at 303 K fitted the Langmuir model well. The adsorption capacities of the magnetite prepared in the mixtures were higher than those of the magnetite prepared without 1-butanol. Their adsorption capacities increased with increasing specific surface area. PMID:20379842

  8. Exchange bias in polycrystalline magnetite films made by ion-beam assisted deposition

    NASA Astrophysics Data System (ADS)

    Kaur, Maninder; Jiang, Weilin; Qiang, You; Burks, Edward C.; Liu, Kai; Namavar, Fereydoon; McCloy, John S.

    2014-11-01

    Iron oxide films were produced using ion-beam-assisted deposition, and Raman spectroscopy and x-ray diffraction indicate single-phase magnetite. However, incorporation of significant fractions of argon in the films from ion bombardment is evident from chemical analysis, and Fe/O ratios are lower than expected from pure magnetite, suggesting greater than normal disorder. Low temperature magnetometry and first-order reversal curve measurements show strong exchange bias, which likely arises from defects at grain boundaries, possibly amorphous, creating frustrated spins. Since these samples contain grains ˜6 nm, a large fraction of the material consists of grain boundaries, where spins are highly disordered and reverse independently with external field.

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

    PubMed Central

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

    2011-01-01

    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. PMID:21414040

  10. Structural purity of magnetite nanoparticles in magnetotactic bacteria

    PubMed Central

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

    2011-01-01

    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

  11. Magnetic anisotropy and magnetite textures from experimental shear deformation

    NASA Astrophysics Data System (ADS)

    Till, Jessica; Moskowitz, Bruce

    2015-04-01

    Magnetite is a common accessory mineral in crustal rocks and exerts a dominant influence on the magnetic anisotropy of rocks when present. Therefore the deformation behavior of magnetite strongly determines how magnetic fabric develops with increasing strain in a deforming rock. Here we show results from experimental deformation of magnetite-silicate aggregates in high-temperature transpressional shear experiments (1000-1200°C) under moderate shear stresses (10-130 MPa) using a gas-medium deformation apparatus. Anisotropy of magnetic susceptibility, shape preferred orientation (SPO) of magnetite, and electron backscatter diffraction (EBSD) were each used to characterize the magnetite deformation fabrics and intragrain microstructures. Magnetic anisotropy and SPO each increase strongly with increasing strain, which ranged between 100-300%. An interesting feature of the deformation fabrics is that both magnetite SPO and magnetic fabric intensity are stronger at higher temperatures, indicating that strain partitioning between magnetite and the plagioclase matrix decreases at higher temperatures. Although flow laws for magnetite predict it to be weaker than dry plagioclase at the experimental conditions, the temperature-dependence of the fabric strength indicates that magnetite is more viscous than the "wet" plagioclase used in the experiments. In contrast to the magnetic and shape fabrics, crystallographic preferred orientation (CPO) of magnetite is very weak in all deformed samples. In EBSD orientation mapping of individual particles, incipient subgrain boundary formation is evident in magnetite grains, indicating that dislocation creep processes were active in magnetite despite the lack of a well-developed CPO. The weak magnetite CPOs are primarily attributed to multiple slip systems acting in parallel. These findings support the observations of previous studies that crystallographic textures in cubic minerals such as magnetite may be inherently weak or slow to develop and that CPO alone is not always a reliable indicator of deformation mechanisms.

  12. Hexagonal Platelet-like Magnetite as a Biosignature of Thermophilic Iron-Reducing Bacteria and Its Applications to the Exploration of the Modern Deep, Hot Biosphere and the Emergence of Iron-Reducing Bacteria in Early Precambrian Oceans

    PubMed Central

    2012-01-01

    Abstract Dissimilatory iron-reducing bacteria are able to enzymatically reduce ferric iron and couple to the oxidation of organic carbon. This mechanism induces the mineralization of fine magnetite crystals characterized by a wide distribution in size and irregular morphologies that are indistinguishable from authigenic magnetite. Thermoanaerobacter are thermophilic iron-reducing bacteria that predominantly inhabit terrestrial hot springs or deep crusts and have the capacity to transform amorphous ferric iron into magnetite with a size up to 120?nm. In this study, I first characterize the formation of hexagonal platelet-like magnetite of a few hundred nanometers in cultures of Thermoanaerobacter spp. strain TOR39. Biogenic magnetite with such large crystal sizes and unique morphology has never been observed in abiotic or biotic processes and thus can be considered as a potential biosignature for thermophilic iron-reducing bacteria. The unique crystallographic features and strong ferrimagnetic properties of these crystals allow easy and rapid screening for the previous presence of iron-reducing bacteria in deep terrestrial crustal samples that are unsuitable for biological detection methods and, also, the search for biogenic magnetite in banded iron formations that deposited only in the first 2 billion years of Earth with evidence of life. Key Words: Biosignatures—Magnetite—Iron-reducing bacteria—Deep subsurface biosphere—Banded iron formation. Astrobiology 12, 1100–1108. PMID:23145573

  13. Origin of carbonate-magnetite-sulfide assemblages in Martian meteorite ALH84001.

    PubMed

    Scott, E R

    1999-02-25

    A review of the mineralogical, isotopic, and chemical properties of the carbonates and associated submicrometer iron oxides and sulfides in Martian meteorite ALH84001 provides minimal evidence for microbial activity. Some magnetites resemble those formed by magnetotactic microorganisms but cubic crystals <50 nm in size and elongated grains <25 nm long are too small to be single-domain magnets and are probably abiogenic. Magnetites with shapes that are clearly unique to magnetotactic bacteria appear to be absent in ALH84001. Magnetosomes have not been reported in plutonic rocks and are unlikely to have been transported in fluids through fractures and uniformly deposited where abiogenic magnetite was forming epitaxially on carbonate. Submicrometer sulfides and magnetites probably formed during shock heating. Carbonates have correlated variations in Ca, Mg, and 18O/16O, magnetite-rich rims, and they appear to be embedded in pyroxene and plagiociase glass. Carbonates with these features have not been identified in carbonaceous chondrites and terrestrial rocks, suggesting that the ALH84001 carbonates have a unique origin. Carbonates and hydrated minerals in ALH84001, like secondary phases in other Martian meteorites, have O and H isotopic ratios favoring formation from fluids that exchanged with the Martian atmosphere. I propose that carbonates originally formed in ALH84001 from aqueous fluids and were subsequently shock heated and vaporized. The original carbonates were probably dolomite-magnesite-siderite assemblages that formed in pores at interstitial sites with minor sulfate, chloride, and phyllosilicates. These phases, like many other volatile-rich phases in Martian meteorites, may have formed as evaporate deposits from intermittent floods. PMID:11542931

  14. The oxidation state and microstructural environment of transition metals (V, Co, and Ni) in magnetite: an XAFS study

    NASA Astrophysics Data System (ADS)

    Liang, Xiaoliang; He, Zisen; Tan, Wei; Liu, Peng; Zhu, Jianxi; Zhang, Jing; He, Hongping

    2015-05-01

    Transition metal-substituted magnetite minerals have attracted increasing attention for their wide application in industry and environmental protection. In this study, the valence and atomic environment of some substituting metals in magnetites (Fe3- x M x O4, M = V, Co, and Ni) were investigated using X-ray absorption fine structure spectroscopy. The results deduced from X-ray absorption near-edge structure spectroscopy indicated that the valences of V, Co, and Ni in Fe3- x M x O4 were +3, +2, and +2, respectively. The valences did not change as the substitution extent increased. Extended X-ray absorption fine structure spectroscopy suggested that the substituting cations occupied octahedral sites in the magnetite structure. The M-O and M-M/Fe distances were consistent with the Feoct-O and Feoct-Fe distances, respectively, in the magnetite (Fe3O4) structure. The occupancy of the substituting cations was assessed by crystal-field theory. We also considered the relationship between the chemical environment of substituting cations and their effects on the physicochemical properties of magnetite, including thermal stability, surface properties, and catalytic reactivity.

  15. Field-dependent anisotropic magnetoresistance and planar Hall effect in epitaxial magnetite thin films

    NASA Astrophysics Data System (ADS)

    Naftalis, N.; Kaplan, A.; Schultz, M.; Vaz, C. A. F.; Moyer, J. A.; Ahn, C. H.; Klein, L.

    2011-09-01

    A systematic study of the temperature and magnetic field dependence of the longitudinal and transverse resistivities of epitaxial thin films of magnetite (Fe3O4) is reported. The anisotropic magnetoresistance (AMR) and the planar Hall effect are sensitive to the in-plane orientation of current and magnetization with respect to crystal axes in a way consistent with the cubic symmetry of the system. We also show that the AMR exhibits a sign reversal as a function of temperature, and that it shows significant field dependence without saturation up to 9 T. Our results provide a unified description of the anisotropic magnetoresistance effects in epitaxial magnetite films and illustrate the need for a full determination of the resistivity tensor in crystalline systems.

  16. Pressure-induced magnetoresistivity reversal in magnetite

    NASA Astrophysics Data System (ADS)

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

    2011-11-01

    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.

  17. Magnetoresistance of magnetite point contacts and nanoconstrictions

    NASA Astrophysics Data System (ADS)

    Céspedes, O.; Clifford, E.; Coey, J. M. D.

    2005-03-01

    Point contacts of magnetite exhibit large, reversible increases of conductance by a factor of up to 5 in the presence of a small magnetic field (<10mT), provided the conductance is less than the quantum of conductance G0 (12900?)-1. Smaller effects are found in (La0.7Sr0.3)MnO3 and Co2Cr0.6Fe0.4Al. Comparable effects observed in magnetite nanoconstrictions milled using a focused-ion beam in thin films deposited on oxide substrates are only reversible on a time scale of hours. High-resistance nanogaps show evidence of field emission beyond a voltage threshold, which is itself field dependent. The results are discussed in terms of spin-polarized transport, magnetostriction, magnetic dipole strain, and Fowler-Nordheim tunneling.

  18. Hybrid DFT calculation of Fe57 NMR resonances and orbital order in magnetite

    NASA Astrophysics Data System (ADS)

    Patterson, C. H.

    2014-08-01

    The crystal structure and charge and orbital order of magnetite below the Verwey temperature are calculated using a first-principles hybrid density functional theory (DFT) method. The initial atomic positions in the crystal-structure calculation are those recently refined from x-ray diffraction data for the Cc space-group unit cell [Senn, Wright, and Attfield, Nature (London) 481, 173 (2012), 10.1038/nature10704]. Fermi contact and magnetic dipolar contributions to hyperfine fields at Fe57 nuclei obtained from hybrid DFT calculations are used to obtain NMR resonance frequencies for magnetite for a range of external magnetic field directions in a relatively weak field. NMR frequencies from hybrid density functional theory calculations are compared to NMR data [M. Mizoguchi, J. Phys. Soc. Jpn. 70, 2333 (2001), 10.1143/JPSJ.70.2333] for a range of applied magnetic field directions. NMR resonance frequencies of B-site Fe ions show large relative variations with applied field direction owing to anisotropic hyperfine fields from charge and orbital ordered Fe 3d minority-spin electrons at those sites. Good agreement between computed and measured NMR resonance frequencies confirms the pattern of charge and orbital order obtained from calculations. The charge and orbital order of magne-tite in its low-temperature phase obtained from hybrid DFT calculations is analyzed in terms of one-electron bonds between Fe ions. The Verwey transition in magnetite therefore resembles Mott-Peierls transitions in vanadium oxides which undergo symmetry-breaking transitions owing to electron-pair bond formation.

  19. Magnetocrystalline Anisotropy of Magnetite at Low Temperature

    Microsoft Academic Search

    Wilfred Palmer

    1963-01-01

    The magnetocrystalline anisotropy of magnetite has been measured by the torque method between 4.2 and 110°K. The anisotropy energy of the orthorhombic phase which exists below 114.5°K is represented by the formula Ea=Kaalphaa2+Kbalphab2+Kaaalphaa4+Kabalphaa2alphab2+Kbbalphab4, where alphaa and alphab are the direction cosines of the magnetization with respect to the hard and intermediate axes, respectively. The five anisotropy coefficients were determined from

  20. Step edge magnetoresistance of magnetite films

    Microsoft Academic Search

    M. Ziese; R. Hohne; K. Zimmer; P. Esquinazi

    2002-01-01

    Summary form only given. The phenomenon of grain-boundary magnetoresistance in half-metallic oxides has attracted an intense research activity in recent years. The Curie temperature of ferromagnetic oxides, however, is too low in order to realize magnetoresistive devices operating at room temperature. There is only one notable exception: the half-metallic ferrimagnet magnetite (Fe3O4) with a Curie temperature of 858 K. It

  1. Self-assembly of liquid crystal block copolymer PEG-b-smectic polymer in pure state and in dilute aqueous solution

    E-print Network

    B. Xu; R. Pinol; M. Nono-Djamen; S. Pensec; P. Keller; P. -A. Albouy; D. Levy; M. -H. Li

    2009-09-03

    A series of amphiphilic LC block copolymers, in which the hydrophobic block is a smectic polymer poly(4-methoxyphenyl 4-(6-acryloyloxy-hexyloxy)-benzoate) (PA6ester1) and the hydrophilic block is polyethyleneglycol (PEG), were synthesized and characterized. The self-assembly of one of them in both the pure state and the dilute aqueous solution was investigated in detail. Nano-structures in the pure state were studied by SAXS and WAXS on samples aligned by a magnetic field. A hexagonal cylindrical micro-segregation phase was observed with a lattice distance of 11.2 nm. The PEG blocks are in the cylinder, while the smectic polymer blocks form a matrix with layer spacing 2.4 nm and layer normal parallel to the long axis of the cylinders. Faceted unilamellar polymer vesicles, polymersomes, were formed in water, as revealed by cryo-TEM. In the lyotropic bilayer membrane of these polymersomes, the thermotropic smectic order in the hydrophobic block is clearly visible with layer normal parallel to the membrane surface.

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

    NASA Astrophysics Data System (ADS)

    Marquez-Linares, F.; Uwakweh, O. N. C.; Lopez, N.; Chavez, E.; Polanco, R.; Morant, C.; Sanz, J. M.; Elizalde, E.; Neira, C.; Nieto, S.; Roque-Malherbe, R.

    2011-03-01

    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 Mössbauer 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.

  3. Mechanical spectroscopy of magnetite filled polyurethane shape memory polymers

    Microsoft Academic Search

    Muhammad Yasar Razzaq; Mathias Anhalt; Lars Frormann; Bernd Weidenfeller

    2007-01-01

    Magnetite-polyurethane (PU) shape memory polymer (SMP) composites containing 10–40vol.% magnetite have been prepared and their mechanical properties in a temperature range from 255K to 355K at vibrating frequencies of 0.1Hz, 1.0Hz and 10Hz were investigated. The damping peak at glass transition around 318K is decreased by the addition of magnetite while it becomes simultaneously broader. Also activation energies for the

  4. Facile method to synthesize oleic acid-capped magnetite nanoparticles

    Microsoft Academic Search

    Chun Yu Wang; Jian Ming Hong; Gong Chen; Yu Zhang; Ning Gu

    2010-01-01

    We described a simple one-step process for the synthesis of oleic acid-capped magnetite nanoparticles using the dimethyl sulfoxide (DMSO) to oxidize the precursor Fe2+ at 140°C. By adjusting the alkalinity of the reaction system, magnetite nanoparticles with two sizes of 4 and 7nm could be easily achieved. And the magnetite nanoparticles coated by oleate were well-monodispersed in organic solvent.

  5. Electrodeposition of copper–magnetite magnetic composite films

    Microsoft Academic Search

    A. Roldan; E. Gómez; S. Pané; E. Vallés

    2007-01-01

    Electrodeposition was demonstrated to be useful for the preparation of copper–magnetite magnetic composites. An acidic bath\\u000a was tested for the incorporation of nanometric magnetite (Fe3O4) particles into an electrodeposited copper matrix. Cationic surfactant (dodecyltrimethylammonium chloride—DTAC) was used\\u000a to keep particles suspended in the electrolyte as well as to assist magnetite incorporation. The influence of several parameters\\u000a (bath temperature, deposition technique,

  6. The study on magnetite particles coated with bilayer surfactants

    NASA Astrophysics Data System (ADS)

    Wang, Xuman; Zhang, Caining; Wang, Xiaoliang; Gu, Hongchen

    2007-07-01

    Magnetite particles were prepared by co-precipitation, then sodium oleic (SO) and sodium dodecyl benzene sulfonate (SDBS) were applied as inner and outer surfactants, respectively. IR and TG were used to study the surface adsorption of SO and SDBS on magnetite particles. The experimental results demonstrated that SO molecules were linked to the magnetite particles through chemical bond and SDBS coated on the surface of magnetite particles covered with SO by means of Van der Waals attraction. Furthermore, based on the adsorption isotherms of surfactants on the magnetite particles and the dependence of Zeta potential of particles on the surfactants concentrations, the adsorption mechanisms of these two surfactants on the magnetite particles were studied. The isotherm adsorption model for SO on magnetite particles showed excellent correlation to Langmuir type and the adsorption equation was ?=0.162c1+0.303c (25 °C), while that for SDBS on magnetite particles coated with SO showed excellent consistence with Freundlich type and the adsorption equation was ? = 0.32 c0.475 (25 °C). In addition, the results demonstrated that both SO and SDBS formed monolayer adsorption on the surface of magnetite particles.

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

    SciTech Connect

    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

    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.

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

    SciTech Connect

    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

    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.

  9. Genes Necessary for Bacterial Magnetite Biomineralization Identified by Transposon Mutagenesis

    NASA Astrophysics Data System (ADS)

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

    2004-12-01

    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).

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

    Microsoft Academic Search

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

    2008-01-01

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2008-04-01

    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.

  12. Magnetite as Possible Template for the Synthesis of Chiral Organics in Carbonaceous Chondrites

    NASA Technical Reports Server (NTRS)

    Chan, Q. H. S.; Zolensky, M. E.

    2014-01-01

    The main goal of the Japanese Aerospace Ex-ploration Agency (JAXA) Hayabusa-2 mission is to visit and return to Earth samples of a C-type asteroid (162173) 1999 JU3 in order to understand the origin and nature of organic materials in the Solar System. Life on Earth shows preference towards the set of organics with particular spatial arrangements, this 'selectivity' is a crucial criterion for life. With only rare exceptions, life 'determines' to use the left- (L-) form over the right- (D-) form of amino acids, resulting in a L-enantiomeric excess (ee). Recent studies have shown that L-ee is found within the alpha-methyl amino acids in meteorites [1, 2], which are amino acids with rare terrestrial occurrence, and thus point towards a plausible abiotic origin for ee. One of the proposed origins of chiral asymmetry of amino acids in meteorites is their formation with the presence of asymmetric catalysts [3]. The catalytic mineral grains acted as a surface at which nebular gases (CO, H2 and NH3) were allowed to condense and react through Fisher Tropsch type (FTT) syntheses to form the organics observed in meteorites [4]. Magnetite is shown to be an effective catalyst of the synthesis of amino acids that are commonly found in meteorites [5]. It has also taken the form as spiral magnetites (a.k.a. 'plaquettes'), which were found in various carbonaceous chondrites (CCs), including C2s Tagish Lake and Esseibi, CI Orgueil, and CR chondrites [e.g., 6, 7, 8]. In addition, L-ee for amino acids are common in the aqueously altered CCs, as opposed to the unaltered CCs [1]. It seems possible that the synthesis of amino acids with chiral preferences is correlated to the alteration process experienced by the asteroid parent body, and related to the configuration of spiral magnetite catalysts. Since C-type asteroids are considered to be enriched in organic matter, and the spectral data of 1999 JU3 indicates a certain de-gree of aqueous alteration [9], the Hayabusa-2 mission serves as a perfect chance to attest this argument. In order to understand the distribution of spiral magnetites among different meteorite classes, as well as to investigate their spiral configurations and correlation to molecular asymmetry, we observed polished thin sections of CCs using scanning electron microscope (SEM) imaging. Individual magnetite grains were picked, embedded in epoxy, thin-sectioned using an ultra-microtome, and studied with electron backscatter diffraction (EBSD) in order to reconstruct the crystal orientation along the stack of magnetite disks.

  13. Fe atom exchange between aqueous Fe2+ and magnetite.

    PubMed

    Gorski, Christopher A; Handler, Robert M; Beard, Brian L; Pasakarnis, Timothy; Johnson, Clark M; Scherer, Michelle M

    2012-11-20

    The reaction between magnetite and aqueous Fe(2+) has been extensively studied due to its role in contaminant reduction, trace-metal sequestration, and microbial respiration. Previous work has demonstrated that the reaction of Fe(2+) with magnetite (Fe(3)O(4)) results in the structural incorporation of Fe(2+) and an increase in the bulk Fe(2+) content of magnetite. It is unclear, however, whether significant Fe atom exchange occurs between magnetite and aqueous Fe(2+), as has been observed for other Fe oxides. Here, we measured the extent of Fe atom exchange between aqueous Fe(2+) and magnetite by reacting isotopically "normal" magnetite with (57)Fe-enriched aqueous Fe(2+). The extent of Fe atom exchange between magnetite and aqueous Fe(2+) was significant (54-71%), and went well beyond the amount of Fe atoms found at the near surface. Mössbauer spectroscopy of magnetite reacted with (56)Fe(2+) indicate that no preferential exchange of octahedral or tetrahedral sites occurred. Exchange experiments conducted with Co-ferrite (Co(2+)Fe(2)(3+)O(4)) showed little impact of Co substitution on the rate or extent of atom exchange. Bulk electron conduction, as previously invoked to explain Fe atom exchange in goethite, is a possible mechanism, but if it is occurring, conduction does not appear to be the rate-limiting step. The lack of significant impact of Co substitution on the kinetics of Fe atom exchange, and the relatively high diffusion coefficients reported for magnetite suggest that for magnetite, unlike goethite, Fe atom diffusion is a plausible mechanism to explain the rapid rates of Fe atom exchange in magnetite. PMID:22577839

  14. Hexagonal platelet-like magnetite as a biosignature of thermophilic iron-reducing bacteria and its applications to the exploration of the modern deep, hot biosphere and the emergence of iron-reducing bacteria in early precambrian oceans.

    PubMed

    Li, Yi-Liang

    2012-12-01

    Dissimilatory iron-reducing bacteria are able to enzymatically reduce ferric iron and couple to the oxidation of organic carbon. This mechanism induces the mineralization of fine magnetite crystals characterized by a wide distribution in size and irregular morphologies that are indistinguishable from authigenic magnetite. Thermoanaerobacter are thermophilic iron-reducing bacteria that predominantly inhabit terrestrial hot springs or deep crusts and have the capacity to transform amorphous ferric iron into magnetite with a size up to 120?nm. In this study, I first characterize the formation of hexagonal platelet-like magnetite of a few hundred nanometers in cultures of Thermoanaerobacter spp. strain TOR39. Biogenic magnetite with such large crystal sizes and unique morphology has never been observed in abiotic or biotic processes and thus can be considered as a potential biosignature for thermophilic iron-reducing bacteria. The unique crystallographic features and strong ferrimagnetic properties of these crystals allow easy and rapid screening for the previous presence of iron-reducing bacteria in deep terrestrial crustal samples that are unsuitable for biological detection methods and, also, the search for biogenic magnetite in banded iron formations that deposited only in the first 2 billion years of Earth with evidence of life. PMID:23145573

  15. crystals

    NASA Astrophysics Data System (ADS)

    Badalyan, A.; Hovsepyan, R.; Mantashyan, P.; Mekhitaryan, V.; Drampyan, R.

    2014-07-01

    A novel combined interferometric-mask method for the formation of micro- and nanometric scale three-dimensional (3D) rotational symmetry quasi-crystalline refractive lattice structures in photorefractive materials is demonstrated experimentally. The method is based on micrometric scale spatial modulation of the light by amplitude mask in the radial directions and along the azimuthal angle and the use of counter-propagating beam geometry building up Gaussian standing wave, which defines the light modulation in the axial direction with half-wavelength periodicity. 3D intensity pattern can be represented as numerous mask-generated 2D quasi-periodic structures located in each anti-node of the standing wave. The formed 3D intensity distributions of the optical beams can be imparted into the photorefractive medium thus creating the micro- and sub-micrometric scale 3D refractive index volume lattices. The used optical scheme allows also the formation of 2D lattices by removing the back-reflecting mirror. 2D and 3D refractive lattices were recorded with the use of 532 nm laser beam and rotational symmetry mask in doped lithium niobate crystals and were tested by the probe beam far-field diffraction pattern imaging and direct observation by phase microscope. The formed rotational symmetry 3D refractive structures have the periods of 20-60 ?m in the radial directions, 60 ?m along the azimuthal angle and half-wavelength 266 nm in the axial direction.

  16. Magnetic process for removing heavy metals from water employing magnetites

    DOEpatents

    Prenger, F. Coyne; Hill, Dallas D.

    2006-12-26

    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 majority of, the heavy metal in the water is bound to the magnetite. Once this occurs the magnetite and absorbed metal is removed from the water by application of a magnetic field. In most applications the process is achieved by flowing the water through a solid magnetized matrix, such as steel wool, such that the magnetite magnetically binds to the solid matrix. The magnetized matrix preferably has remnant magnetism, but may also be subject to an externally applied magnetic field. Once the magnetite and associated heavy metal is bound to the matrix, it can be removed and disposed of, such as by reverse water or air and water flow through the matrix. The magnetite may be formed in-situ by the addition of the necessary quantities of Fe(II) and Fe(III) ions, or pre-formed magnetite may be added, or a combination of seed and in-situ formation may be used. The invention also relates to an apparatus for performing the removal of heavy metals from water using the process outlined above.

  17. Magnetic process for removing heavy metals from water employing magnetites

    DOEpatents

    Prenger, F. Coyne; Hill, Dallas D.; Padilla, Dennis D.; Wingo, Robert M.; Worl, Laura A.; Johnson, Michael D.

    2003-07-22

    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 majority of, the heavy metal in the water is bound to the magnetite. Once this occurs the magnetite and absorbed metal is removed from the water by application of a magnetic field. In most applications the process is achieved by flowing the water through a solid magnetized matrix, such as steel wool, such that the magnetite magnetically binds to the solid matrix. The magnetized matrix preferably has remnant magnetism, but may also be subject to an externally applied magnetic field. Once the magnetite and associated heavy metal is bound to the matrix, it can be removed and disposed of, such as by reverse water or air and water flow through the matrix. The magnetite may be formed in-situ by the addition of the necessary quantities of Fe(II) and Fe(III) ions, or pre-formed magnetite may be added, or a combination of seed and in-situ formation may be used. The invention also relates to an apparatus for performing the removal of heavy metals from water using the process outlined above.

  18. THE MAGNETOCRYSTALLINE ANISOTROPY OF GALLIUM AND ALUMINIUM SUBSTITUTED MAGNETITE

    E-print Network

    Paris-Sud XI, Université de

    409 THE MAGNETOCRYSTALLINE ANISOTROPY OF GALLIUM AND ALUMINIUM SUBSTITUTED MAGNETITE By R. F of the magnetocrystalline anisotropy in magnetite (Fe3O4) as this shows a rather anomalous variation with temperature constante d'anisotropie K1 ont été mesurées de 120 °K à 400 °K par la méthode de torsion, pour sept cristaux

  19. Magnetite morphology and life on Mars Peter R. Buseck*

    E-print Network

    Dunin-Borkowski, Rafal E.

    Magnetite morphology and life on Mars Peter R. Buseck* , Rafal E. Dunin-Borkowski , Bertrand (received for review July 25, 2001) Nanocrystals of magnetite (Fe3O4) in a meteorite from Mars pro- vide is inadequate to support the inference of former life on Mars. The startling report by McKay et al. (1

  20. A comparison of ARM and TRM in magnetite

    Microsoft Academic Search

    Shaul Levi; Ronald T. Merrill

    1976-01-01

    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

  1. Vibrational Spectroscopic Characterization of Hematite, Maghemite, and Magnetite Thin

    E-print Network

    Vibrational Spectroscopic Characterization of Hematite, Maghemite, and Magnetite Thin Films University, 100 West 18th Avenue, Columbus, Ohio 43210 ABSTRACT Thin films of three iron oxide polymorphs, hematite, maghemite, and magnetite, were produced on KBr substrates using a conventional electron beam

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

    NASA Astrophysics Data System (ADS)

    Vodyanitskii, Yu. N.

    2013-03-01

    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.

  3. No evidence for intracellular magnetite in putative vertebrate magnetoreceptors identified by magnetic screening

    PubMed Central

    Edelman, Nathaniel B.; Fritz, Tanja; Nimpf, Simon; Pichler, Paul; Lauwers, Mattias; Hickman, Robert W.; Papadaki-Anastasopoulou, Artemis; Ushakova, Lyubov; Heuser, Thomas; Resch, Guenter P.; Saunders, Martin; Shaw, Jeremy A.; Keays, David A.

    2015-01-01

    The cellular basis of the magnetic sense remains an unsolved scientific mystery. One theory that aims to explain how animals detect the magnetic field is the magnetite hypothesis. It argues that intracellular crystals of the iron oxide magnetite (Fe3O4) are coupled to mechanosensitive channels that elicit neuronal activity in specialized sensory cells. Attempts to find these primary sensors have largely relied on the Prussian Blue stain that labels cells rich in ferric iron. This method has proved problematic as it has led investigators to conflate iron-rich macrophages with magnetoreceptors. An alternative approach developed by Eder et al. [Eder SH, et al. (2012) Proc Natl Acad Sci USA 109(30):12022–12027] is to identify candidate magnetoreceptive cells based on their magnetic moment. Here, we explore the utility of this method by undertaking a screen for magnetic cells in the pigeon. We report the identification of a small number of cells (1 in 476,000) with large magnetic moments (8–106 fAm2) from various tissues. The development of single-cell correlative light and electron microscopy (CLEM) coupled with electron energy loss spectroscopy (EELS) and energy-filtered transmission electron microscopy (EFTEM) permitted subcellular analysis of magnetic cells. This revealed the presence of extracellular structures composed of iron, titanium, and chromium accounting for the magnetic properties of these cells. Application of single-cell CLEM to magnetic cells from the trout failed to identify any intracellular structures consistent with biogenically derived magnetite. Our work illustrates the need for new methods to test the magnetite hypothesis of magnetosensation. PMID:25535350

  4. Magnetoresistance extremum at the first-order Verwey transition in magnetite (Fe3O4)

    Microsoft Academic Search

    V. V. Gridin; G. R. Hearne; J. M. Honig

    1996-01-01

    A large negative magnetoresistance (MR) sharply peaked at the first-order Verwey transition temperature TV=119.79+\\/-0.02 K has been measured in a synthetic single crystal of magnetite Fe3(1-delta)O4, delta=0.0006. At H=7.7 T the MR extremum exhibited a peak value of -17% and a full width at half maximum of 0.53+\\/-0.08 K. At the lower and higher ends of the measurement interval 114-126

  5. NMR of 57Fe, 69Ga and 71Ga in Ga substituted magnetite

    NASA Astrophysics Data System (ADS)

    Kohout, J.; Gamaliy, E.; Št?pánková, H.; Englich, J.; Procházka, V.; Chlan, V.; Brabers, V. A. M.

    2005-04-01

    We report the NMR spectra of gallium substituted magnetite measured at temperatures 4.2, 77 and 273 K. A single crystal of Fe 3-xGa xO 4, x=0.05 has been prepared by a floating zone technique. The Ga-lines found in the NMR spectrum above Verwey temperature T˜117 K indicate a preferency of Ga substitution into the tetrahedral A-sites. The well-resolved structure of Ga-lines has been identified and assigned to both Ga isotopes below TV. A weak quadrupolar interaction contributes only to the line broadening.

  6. Low-temperature magnetic properties of siderite and magnetite in marine sediments

    NASA Astrophysics Data System (ADS)

    Housen, B. A.; Banerjee, S. K.; Moskowitz, B. M.

    Low temperature magnetic techniques provide useful tools to detect the presence of magnetite and pyrrhotite in sediments through identification of their low temperature transitions, to determine the amount of ultrafine-grained (superparamagnetic) material in sediments, and can potentially detect the presence of certain types of magnetotactic bacteria. Application of these types of experiments to nannofossil chalks from beneath the Barbados accretionary prism led to some unusual results, which are attributed to the presence of siderite. Thermal demagnetization of low-temperature remanence after cooling in zero field and in a 2.5 T field both displayed large remanence losses from 20 K to 40 K. Below 40 K, the magnetization of the chalks was much higher in the field-cooled experiments than in the zero-field-cooled experiments. Low temperature hysteresis experiments, made after cooling in a 2.5 T field, displayed offsets in magnetization parallel to the direction of the initial applied field, when measured below 40 K. The offset loops can be due to either an exchange anisotropy between siderite and magnetite phases in the sediments, a defect moment in the siderites, or a canted moment in the siderites. Apparent similarity between the low-temperature thermal demagnetization results from these siderite-bearing sediments, pure siderite, and pure rhodochrosite samples and the well-known 34 K transition in pyrrhotite should lead to caution in identification of pyrrhotite in marine sediments based on low-temperature remanence studies alone.

  7. Pyroelectric detection of spontaneous polarization in magnetite thin films

    NASA Astrophysics Data System (ADS)

    Takahashi, R.; Misumi, H.; Lippmaa, M.

    2012-10-01

    We have investigated the spontaneous polarization in Fe3O4 thin films by using dynamic and static pyroelectric measurements. The magnetic and dielectric behavior of Fe3O4 thin films grown on Nb:SrTiO3(001) substrates was consistent with bulk crystals. The well-known metal-insulator (Verwey) transition was observed at 120 K. The appearance of a pyroelectric response in the Fe3O4 thin films just below the Verwey temperature shows that spontaneous polarization appeared in Fe3O4 at the charge-ordering transition temperature. The polar state characteristics are consistent with bond- and site-centered charge ordering of Fe2+ and Fe3+ ions sharing the octahedral B sites. The pyroelectric response in Fe3O4 thin films was dependent on the dielectric constant. Quasistatic pyroelectric measurement of Pd/Fe3O4/Nb:SrTiO3 junctions showed that magnetite has a very large pyroelectric coefficient of 735 nC cm-2 K-1 at 60 K.

  8. Electronic phase transitions in ultrathin magnetite films.

    PubMed

    Bernal-Villamil, I; Gallego, S

    2015-07-29

    Magnetite (Fe3O4) shows singular electronic and magnetic properties, resulting from complex electron-electron and electron-phonon interactions that involve the interplay of charge, orbital and spin degrees of freedom. The Verwey transition is a manifestation of these interactions, with a puzzling connection between the low temperature charge ordered state and the dynamic charge fluctuations still present above the transition temperature. Here we explore how these rich physical phenomena are affected by thin film geometries, particularly focusing on the ultimate size limit defined by thicknesses below the minimum bulk unit cell. On one hand, we address the influence of extended defects, such as surfaces or antiphase domains, on the novel features exhibited by thin films. On the other, we try to isolate the effect of the reduced thickness on the electronic and magnetic properties. We will show that a distinct phase diagram and novel charge distributions emerge under reduced dimensions, while holding the local high magnetic moments. Altogether, thin film geometries offer unique possibilities to understand the complex interplay of short- and long-range orders in the Verwey transition. Furthermore, they arise as interesting candidates for the exploitation of the rich physics of magnetite in devices that demand nanoscale geometries, additionally offering novel functionalities based on their distinct properties with respect to the bulk form. PMID:26153727

  9. Did the massive magnetite "lava flows" of El Laco (Chile) form by magmatic or hydrothermal processes? New constraints from magnetite composition by LA-ICP-MS

    NASA Astrophysics Data System (ADS)

    Dare, Sarah A. S.; Barnes, Sarah-Jane; Beaudoin, Georges

    2015-06-01

    The El Laco magnetite deposits consist of more than 98 % magnetite but show field textures remarkably similar to mafic lava flows. Therefore, it has long been suggested that they represent a rare example of an effusive Fe oxide liquid. Field and petrographic evidence, however, suggest that the magnetite deposits represent replacement of andesite flows and that the textures are pseudomorphs. We determined the trace element content of magnetite by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) from various settings at El Laco and compared them with magnetite from both igneous and hydrothermal environments. This new technique allows us to place constraints on the conditions under which magnetite in these supposed magnetite "lava flows" formed. The trace element content of magnetite from the massive magnetite samples is different to any known magmatic magnetite, including primary magnetite phenocrysts from the unaltered andesite host rocks at El Laco. Instead, the El Laco magnetite is most similar in composition to hydrothermal magnetite from high-temperature environments (>500 °C), such as iron oxide-copper-gold (IOCG) and porphyry-Cu deposits. The magnetite trace elements from massive magnetite are characterised by (1) depletion in elements considered relatively immobile in hydrothermal fluids (e.g. Ti, Al, Cr, Zr, Hf and Sc); (2) enrichment in elements that are highly incompatible with magmatic magnetite (rare earth elements (REE), Si, Ca, Na and P) and normally present in very low abundance in magmatic magnetite; (3) high Ni/Cr ratios which are typical of magnetite from hydrothermal environments; and (4) oscillatory zoning of Si, Ca, Mg, REE and most high field strength elements, and zoning truncations indicating dissolution, similar to that formed in hydrothermal Fe skarn deposits. In addition, secondary magnetite in altered, brecciated host rock, forming disseminations and veins, has the same composition as magnetite from the massive lenses. Euhedral magnetite lining both open-spaced veins in the brecciated host rock and along the walls of large, hollow chimneys in the massive magnetite lenses also displays oscillatory zoning and most likely formed by fluctuating composition and/or physio-chemical conditions of the fluid. Thus, the chemical fingerprint of magnetite from the supposed El Laco magnetite lava flows supports the hydrothermal model of metasomatic replacement of andesite lava flows, by dissolution and precipitation of magnetite from high-temperature fluids, rather than a magmatic origin from an effusive Fe oxide liquid.

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

    PubMed

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

    2012-06-01

    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

  11. Field-induced decoupling of NiO-magnetite multilayers

    SciTech Connect

    Erwin, R.W.; Borchers, J.A. [National Inst. of Standards and Technology, Gaithersburg, MD (United States). Reactor Radiation Div.; Berry, S.D.; Lind, D.M.; Lochner, E.; Shaw, K.A. [Florida State Univ., Tallahassee, FL (United States). Dept. of Physics

    1995-12-31

    NiO-magnetite multilayers exhibit long range antiferromagnetic order with the magnetite ferrimagnetic correlations confined to a single layer due to stacking faults of the spinel structure at the interfaces. A systematic study of the field-dependence of the interlayer coupling in a series of NiO-magnetite multilayers has been made using neutron diffraction. Both NiO and magnetite single thin films were included in the measurements for comparison. In the magnetite film, intensity changes with magnetic field are consistent with domain reorientation of the net ferrimagnetic moments, while in the NiO film there are essentially no intensity changes. There is no significant field dependence of the magnetic correlation lengths in either film. For multilayers where the ratio of NiO to magnetite layer thickness is far from unity, the field dependence approximates that of the bulk films. However, for a Fe{sub 3}O{sub 4} (68{angstrom}){vert_bar}NiO (34{angstrom}) multilayer the NiO antiferromagnetic intensity decreases with increasing field, and there is a broadening of the NiO peak on the order of 30%. Concomitantly, the magnetite spins rotate collinear with the field, as expected, due to the net 4.2 {micro}{sub B} moment per unit-cell. The NiO moments appear to rotate into domains where the direction of propagation of the ferromagnetic sheets is closer to the field direction.

  12. Controlled cobalt doping in biogenic magnetite nanoparticles.

    PubMed

    Byrne, J M; Coker, V S; Moise, S; Wincott, P L; Vaughan, D J; Tuna, F; Arenholz, E; van der Laan, G; Pattrick, R A D; Lloyd, J R; Telling, N D

    2013-06-01

    Cobalt-doped magnetite (CoxFe3 -xO4) nanoparticles have been produced through the microbial reduction of cobalt-iron oxyhydroxide by the bacterium Geobacter sulfurreducens. The materials produced, as measured by superconducting quantum interference device magnetometry, X-ray magnetic circular dichroism, Mössbauer spectroscopy, etc., show dramatic increases in coercivity with increasing cobalt content without a major decrease in overall saturation magnetization. Structural and magnetization analyses reveal a reduction in particle size to less than 4 nm at the highest Co content, combined with an increase in the effective anisotropy of the magnetic nanoparticles. The potential use of these biogenic nanoparticles in aqueous suspensions for magnetic hyperthermia applications is demonstrated. Further analysis of the distribution of cations within the ferrite spinel indicates that the cobalt is predominantly incorporated in octahedral coordination, achieved by the substitution of Fe(2+) site with Co(2+), with up to 17 per cent Co substituted into tetrahedral sites. PMID:23594814

  13. Controlled cobalt doping in biogenic magnetite nanoparticles

    PubMed Central

    Byrne, J. M.; Coker, V. S.; Moise, S.; Wincott, P. L.; Vaughan, D. J.; Tuna, F.; Arenholz, E.; van der Laan, G.; Pattrick, R. A. D.; Lloyd, J. R.; Telling, N. D.

    2013-01-01

    Cobalt-doped magnetite (CoxFe3 ?xO4) nanoparticles have been produced through the microbial reduction of cobalt–iron oxyhydroxide by the bacterium Geobacter sulfurreducens. The materials produced, as measured by superconducting quantum interference device magnetometry, X-ray magnetic circular dichroism, Mössbauer spectroscopy, etc., show dramatic increases in coercivity with increasing cobalt content without a major decrease in overall saturation magnetization. Structural and magnetization analyses reveal a reduction in particle size to less than 4 nm at the highest Co content, combined with an increase in the effective anisotropy of the magnetic nanoparticles. The potential use of these biogenic nanoparticles in aqueous suspensions for magnetic hyperthermia applications is demonstrated. Further analysis of the distribution of cations within the ferrite spinel indicates that the cobalt is predominantly incorporated in octahedral coordination, achieved by the substitution of Fe2+ site with Co2+, with up to 17 per cent Co substituted into tetrahedral sites. PMID:23594814

  14. Charge Transport in Magnetite Nanoparticle Arrays

    NASA Astrophysics Data System (ADS)

    Jang, Seongjin; Zeng, Hao

    2007-03-01

    Charge transport properties of magnetite (Fe3O4) nanoparticle arrays were studied as a function of annealing conditions. These arrays were prepared by self-assembling chemically synthesized nanoparticles with micro-gaps between lateral electrodes. Annealing removed surfactant molecules and varied the interparticle spacing systematically. Arrays annealed under 200 ^oC are insulating. Arrays annealed between 200 ^oC to 500 ^oC show thermally assisted tunneling behavior, with the tunneling barrier decreasing with increasing annealing temperatures. Above 500 ^oC, a transition from tunneling to hopping mechanism is observed. Magnetoresistance decreases with increasing annealing temperature. For the hopping samples, Verway transition is observed from both the resistivity and magnetoresistance measurements. Work supported by NSF DMR 0547036

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

    PubMed Central

    Li, Yingjie; Katzmann, Emanuel; Borg, Sarah

    2012-01-01

    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

  16. Magnetic Properties of Bio-Synthesized Magnetite Nanoparticles

    SciTech Connect

    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

    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.

  17. Magnetite Plaquettes Provide an Extraterrestrial Source of Asymmetric Components

    NASA Technical Reports Server (NTRS)

    Chan, Q. H. S.; Zolensky, M. E.; Martinez, J. E.

    2015-01-01

    Molecular selectivity is a crucial criterion for life. A possible abiotic mechanism that can produce chiral asymmetry in meteoritic amino acids is their formation with the presence of asymmetric catalysts. Magnetite (Fe3O4), a common mineral in some carbonaceous chondrites (CCs), has been shown to be an effective catalyst for the formation of amino acids that are commonly found in these meteorites. Magnetite sometimes takes the form of plaquettes that consist of barrel-shaped stacks of magnetite disks that resemble a spiral. However, a widely accepted description of the internal morphology of this particular magnetite form is still lacking, which is necessary in order to confirm or disprove the spiral configuration.

  18. Effect of La{sub 2}O{sub 3}, CoO, Cr{sub 2}O{sub 3} and MoO{sub 3} nucleating agents on crystallization behavior and magnetic properties of ferromagnetic glass-ceramic in the system Fe{sub 2}O{sub 3}{center_dot}CaO{center_dot}ZnO{center_dot}SiO{sub 2}

    SciTech Connect

    Abdel-Hameed, Salwa A.M., E-mail: Salwa_NRC@hotmail.com [Glass Research Department, National Research Center, Dokki, Cairo (Egypt); Elwan, Rawhia L. [Glass Research Department, National Research Center, Dokki, Cairo (Egypt)] [Glass Research Department, National Research Center, Dokki, Cairo (Egypt)

    2012-05-15

    Highlights: Black-Right-Pointing-Pointer Crystallization of magnetic glass ceramic with different nucleating agents. Black-Right-Pointing-Pointer The effect of La{sub 2}O{sub 3}, CoO, Cr{sub 2}O{sub 3} and MoO{sub 3} as nucleating agents was studied. Black-Right-Pointing-Pointer XRD for as prepared samples revealed crystallization of pure magnetite. Black-Right-Pointing-Pointer Heat treatment revealed minor calcium silicate, hematite and cristobalite. Black-Right-Pointing-Pointer TEM revealed crystallization of crystallite size in the range 50-100 nm. -- Abstract: Preparation and characterization of ferromagnetic glass ceramic in the system Fe{sub 2}O{sub 3}{center_dot}CaO{center_dot}ZnO{center_dot}SiO{sub 2} with different nucleating agents was studied. The effect of La{sub 2}O{sub 3}, CoO, Cr{sub 2}O{sub 3} and MoO{sub 3} as nucleating agents was investigated. Differential thermal analysis; X-ray diffraction and transmission electron microscope were used to investigate thermal behavior, sequence of crystallization and microstructure of the samples. XRD analysis for as prepared samples revealed the crystallization of single magnetite phase. Heat treatment at 900 Degree-Sign C/2 h revealed the appearance of minor amounts of calcium silicate, hematite and cristobalite beside magnetite. TEM revealed crystallization of crystallite size in the range 50-100 nm. Lattice parameters, cell volume and crystallite size were stimulated from XRD data. Magnetic properties of quenched samples were measured under 20 kG.

  19. Microfabrication and characterization of magnetite-based magnetic tunnel junctions

    NASA Astrophysics Data System (ADS)

    Park, Chando

    Magnetic tunnel junctions (MTJs) consisting of two magnetic layers separated by a thin insulating barrier have emerged as the major candidate for magnetic based information storage systems because of their relatively high tunneling magnetoresistance (MR). The magnitude of the MR is determined by the spin polarization of the magnetic layers. One of the most promising materials for MTJs is magnetite (Fe3O4), which has 100% spin polarization. In theory, the MR of Fe3O4-based MTJ should be large and inverse. However, to date most experimental results have shown a small, positive MR, especially when using an aluminum oxide barrier (AlOx). However, the origin of the sign and low magnitude of the MR for these tunnel junctions remains unclear. In this thesis, single phase Fe3O4 films and Fe 3O4-based MTJs (junction size: 2 x 2mum 2 ˜ 18 x 12mum) were fabricated with standard photolithography and characterized in terms of electrical, magnetic and microstructual properties. A reactive sputtering can produce high quality Fe3O4 films having smooth surface, which is confirmed by transmission electron microscopy (TEM), vibrating sample magnetometer (VSM) and atomic force microscope (AFM). When a reactive sputtered Fe3O4 film was used as a top or bottom electrode for MTJs, the phase at the interface was not single phase Fe3O4. This is because the interface reaction, which can be written as: Fe3O4 + Al => Fe + AlOx (amorphous) , occurs. This causes the junctions to have poor transport. By using in situ oxidation of a thin Fe layer, it was possible to achieve a pure polycrystalline Fe3O4 interface with the AlOx barrier, resulting in an inverse MR. The results showed that the phases and quality of the interface adjacent to the AlOx barrier determine the sign and magnitude of the MR. To obtain inverse and large MR for an MTJ, pure and defect free Fe3O4 should exist at the interface adjacent to the AlOx barrier.

  20. Extrinsic magnetoresistance in magnetite nanoparticles L. Zhao, and P. Klavins

    E-print Network

    Osterloh, Frank

    Magnetite (Fe3O4) nanoparticles, 8 to 9 nm in size, have been synthesized using an aqueous precipitation, such as CrO2 and Fe3O4 .1­3 The size of the pow- ders studied has ranged from a few hundred nanometers and MR in 8 to 9 nm magnetite (Fe3O4) nanoparticle pellets. We have observed a spin-dependent tunneling

  1. Synthesis of magnetite nanoparticles in the presence of aminoacids

    Microsoft Academic Search

    Gabriela Marinescu; Luminita Patron; Daniela C. Culita; Cristian Neagoe; Costinel I. Lepadatu; Ioan Balint; Lotfi Bessais; Corneliu Bazil Cizmas

    2006-01-01

    A new synthesis route to prepare magnetite nanoparticles in only one step is described. The precipitation of magnetite is\\u000a performed in the presence of aminoacid solution. The experimental protocol is original and the nanomagnetites are characterized\\u000a by XRD, FTIR, TEM and SQUID magnetometry. A theoretical study of the consistent experimental results was performed using QSPR\\u000a (Quantitative Structure Property Relationsheep). According

  2. Electrophoretic mobility of magnetite particles in high temperature water

    SciTech Connect

    Vidojkovic, Sonja [Pennsylvania State University; Rodriguez-Santiago, V [Oak Ridge National Laboratory (ORNL); Fedkin, Mark V. [Pennsylvania State University; Wesolowski, David J [ORNL; Lvov, Serguei N. [Pennsylvania State University

    2011-01-01

    Magnetite(Fe3O4) isoneofthemostcommonoxidesformingdepositsandparticulatephasesin industrialhightemperaturewatercircuits.Itscolloidalcharacteristicsplayaprincipalroleinthe mechanismofdepositformationandcanbeusedascontrollingfactorstopreventorminimizedeposit formationanddamageofindustrialpipelinesduetounder-depositcorrosion.Inthisstudy,ahigh temperatureparticleelectrophoresistechniquewasemployedtomeasurethezetapotentialatthe magnetite/waterinterface the parameterthatcontrolscolloidalstabilityofparticles,theiraggrega- tion, anddeposition.Themeasurementsweremadeattemperaturesupto200 1C overawiderangeofpH. The isoelectricpointsofmagnetite,atwhichthedepositionofparticlesisincreased,weredeterminedatpH 6.35, 6.00,5.25,and5.05fortemperatures25,100,150,and200 1C, respectively.Theobserved temperaturedependenceofzetapotentialandtheisoelectricpHpointofmagnetitecanhelptoexplain the extentofinteractionsbetweenthecolloidalparticlesandthesteelwallsurfacesunderhydro- thermalconditions,andindicatemethodsforcontrollingandmitigatingoxidedepositioninhigh temperaturewatercycles.

  3. Magnetooptical Response of Gold-Magnetite Nanocomposite Films

    Microsoft Academic Search

    Fred E. Moolekamp III; Kevin L. Stokes

    2009-01-01

    We present experimental evidence of an enhanced magnetooptical response in chemically synthesized noble metal-magnetic oxide nanocomposites. Colloidal gold and magnetite (Fe3O4) nanoparticles were chemically linked using a bifunctional organic ligand creating clusters of the two nanoparticle components. The linked gold-magnetite clusters were blended with a transparent polymer and cast as films. Three samples were produced with a different ratios of

  4. Parametric investigation for direct chemical vapour deposition of magnetite films

    Microsoft Academic Search

    Sandip Dhara; B. R. Awasthy; A. C. Rastogi; B. K. Das; N. V. Gelfond; N. E. Fedotova; A. F. Bykov; I. K. Igumenov

    1994-01-01

    A direct growth of magnetite (Fe3O4) phase has been obtained by a low-pressure chemical vapour deposition (LPCVD) technique using metal-organic ferric dipivaloylmethanate (Fe(DPM)3) as precursor. On oxidation these films are converted to gamma-Fe2O3 phase which give superior magnetic coercivity values. Crystallographic structures are determined by small-angle XRD analysis. As deposited magnetite and oxidized gamma-Fe2O3 films are reported with coercivity values

  5. Study of pulsed laser deposited magnetite thin film

    Microsoft Academic Search

    Murtaza Bohra; N. Venkataramani; Shiva Prasad; N. Kumar; D. S. Misra; S. C. Sahoo; R. Krishnan

    2007-01-01

    Magnetite thin film with a predominant (110) texture has been deposited by pulsed laser ablation of ?-Fe2O3 target onto fused quartz substrate. Spontaneous magnetization of 5400G and room temperature electrical resistivity of 4.2×10?3?cm were measured for an annealed magnetite thin film. Zero-field-cooled magnetization data clearly show the Verwey transition near 120K through an abrupt change, and is consistent with the

  6. Uniaxial anisotropy in magnetite thin film—Magnetization studies

    Microsoft Academic Search

    A. Wiechec; J. Korecki; B. Handke; Z. Kakol; D. Owoc; D. A. Antolak; A. Kozlowski

    2006-01-01

    Magnetization and electrical resistivity measurements have been performed on a stoichiometric single crystalline magnetite Fe3O4 thin film (thickness of ca. 500nm) MBE deposited on MgO (100) substrate. The aim of these studies was to check the influence of preparation method and sample form (bulk vs. thin film) on magnetic anisotropy properties in magnetite. The film magnetization along ?001? versus applied

  7. Deposition of magnetite films by reactive sputtering of iron

    Microsoft Academic Search

    J. Heller

    1976-01-01

    Iron is sputtered reactively in an argon-oxygen glow discharge to form deposits of magnetite. Cycling the oxygen partial pressure between a low and a high value during sputtering causes deposition of alternating layers of Fe-metal and Fe2O3-oxide. Depending on the cycle length, a layered structure results or homogeneous films form. For all films pronounced magnetite peaks were found by X-ray

  8. Investigation of Electrically Driven Phase Transition in Magnetite Thin Films

    Microsoft Academic Search

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

    2009-01-01

    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

  9. High-field cantilever magnetometry as a tool for the determination of the magnetocrystalline anisotropy of single crystals

    E-print Network

    Utrecht, Universiteit

    : Magnetocrystalline anisotropy constants; Cantilever magnetometer; Magnetite; Rock magnetism 1. Introduction MagnetiteHigh-field cantilever magnetometry as a tool for the determination of the magnetocrystalline anisotropy of single crystals Fátima Martín-Hernández a,, Iris M. Bominaar-Silkens b,1 , Mark J. Dekkers a,2

  10. EPR evidence for maghemitization of magnetite in a tropical soil

    NASA Astrophysics Data System (ADS)

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

    2007-06-01

    Electron paramagnetic spectroscopy (EPR) was used in combination with standard rock magnetic 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 dominant magnetic remanence carriers in the soil. A minor Ti content in the magnetite was found by energy dispersive X-ray analysis. In order to get insight into the weathering status of the magnetite, different chemical treatments, including oxalate and citrate-bicarbonate-dithionite (CBD) extraction, were applied to the soil samples. The hysteretic properties exhibited no significant differences between the untreated and the CBD or oxalate treated samples. By contrast, the comparison of the EPR spectra revealed a significant broadening of the linewidth (?B) and a shift of the g-values (geff) to lower fields after the CBD treatment. Furthermore, the spectral parameters geff and ?B exhibited an angular dependence. At low temperature, the CBD treated samples showed a jump in ?B between 120 and 100 K, the temperature range characteristic for the Verwey transition in magnetite. The changes in the spectral properties after the CBD treatment, which dissolves ferric oxides, were attributed to the removal of maghemite formed by the oxidation of magnetite, that is, during the maghemitization of the magnetite grains.

  11. Magnetic and transport properties of magnetite thin films

    NASA Astrophysics Data System (ADS)

    Zhang, Guomin; Fan, Chongfei; Pan, Liqing; Wang, Fengping; Wu, Ping; Qiu, Hong; Gu, Yousong; Zhang, Yue

    2005-05-01

    Magnetite (Fe 3O 4) films were prepared by DC reactive magnetron sputtering at various oxygen partial pressures with the ratio ? of oxygen to argon changing from 0.50:50 to 0.70:50 at room temperature, and then the Fe 3O 4 films were annealed at 480 °C for 80 min. The properties of the films were studied by X-ray diffraction, scanning electron microscopy, magnetic hysteresis loops, magnetoresistance (MR), etc. The results showed when ? increased, resistivity of magnetite films were increased exponentially, and only these magnetite films of ?>0.60:50 showed MR effects. After annealing, the resistivity decreased about one order; and all magnetite films showed MR effects. The Verwey transition of the magnetite films was confirmed by MR- T curves. XRD and SEM showed that the films were composed of Fe 3O 4 nanoparticles with highly preferential orientation and the best conditions for high-quality magnetite films were ?=0.65:50 and 0.675:50. The magnetic transport properties of the films infer that strong coupling between Fe 3O 4 nanoparticles originated from RKKY exchange interaction and dipolar interaction, this made the films differ from metallic granular ones and higher-order terms of (M/M s) 2, such as (M/M s) 4 and (M/M s) 6, should be added to the fitting functions of the MR-(M/M s) curves.

  12. Influence of different magnetites on properties of magnetic Pseudomonas aeruginosa immobilizates used for biosurfactant production.

    PubMed

    Heyd, M; Weigold, P; Franzreb, M; Berensmeier, S

    2009-01-01

    During the last decades, whole-cell immobilization has been used successfully in many bioprocesses. In particular, it is aimed at implementing continuous production processes, reaching higher production rates, and reusing the biocatalyst. In some cases, effective retention of immobilizates in the bioprocess is not feasible by membranes or sieves due to pore plugging or undesired losses of immobilizates. In the present publication, it is reported about the investigation of magnetic immobilizates of Pseudomonas aeruginosa for application in continuous biosurfactant production of rhamnolipids by foam fractionation and retention of entrained immobilizates by high-gradient magnetic separation from foam. Different materials and methods were tested with respect to important parameters, such as stability, diffusion properties or magnetic separation. Good magnetic separation of immobilizates was achieved at 5% (w/w) magnetite loading. Best results in terms of homogeneous embedding, good diffusion properties, and stability enhancement vis-à-vis pure alginate beads was achieved with alginate beads with embedded Bayoxide magnetite or MagPrep silica particles. Although polyurethane immobilizates showed higher stabilities compared with alginate beads, rhamnolipid diffusion in immobilizates was superior in magnetic alginate beads. Regarding bead production, smaller immobilizates were achieved with suspension polymerization compared to droplet extrusion by the JetCutting technology. In total, magnetic immobilizates are a promising tool for an easier handling of biocatalysts in a continuous biological production process, but they have to be adapted to the current production task. PMID:19691121

  13. Synthesis and characterization of magnetite/silver/antibiotic nanocomposites for targeted antimicrobial therapy.

    PubMed

    Ivashchenko, Olena; Lewandowski, Miko?aj; Pepli?ska, Barbara; Jarek, Marcin; Nowaczyk, Grzegorz; Wiesner, Maciej; Za??ski, Karol; Babutina, Tetyana; Warowicka, Alicja; Jurga, Stefan

    2015-10-01

    The article is devoted to preparation and characterization of magnetite/silver/antibiotic nanocomposites for targeted antimicrobial therapy. Magnetite nanopowder was produced by thermochemical technique; silver was deposited on the magnetite nanoparticles in the form of silver clusters. Magnetite/silver nanocomposite was investigated by XRD, SEM, TEM, AFM, XPS, EDX techniques. Adsorptivity of magnetite/silver nanocomposite towards seven antibiotics from five different groups was investigated. It was shown that rifampicin, doxycycline, ceftriaxone, cefotaxime and doxycycline may be attached by physical adsorption to magnetite/silver nanocomposite. Electrostatic surfaces of antibiotics were modeled and possible mechanism of antibiotic attachment is considered in this article. Raman spectra of magnetite, magnetite/silver and magnetite/silver/antibiotic were collected. It was found that it is difficult to detect the bands related to antibiotics in the magnetite/silver/antibiotic nanocomposite spectra due to their overlap by the broad carbon bands of magnetite nanopowder. Magnetic measurements revealed that magnetic saturation of the magnetite/silver/antibiotic nanocomposites decreased on 6-19 % in comparison with initial magnetite nanopowder. Pilot study of antimicrobial properties of the magnetite/silver/antibiotic nanocomposites were performed towards Bacillus pumilus. PMID:26117765

  14. Structure of the magnetite-oleic acid-decalin magnetic fluid from small-angle neutron scattering data

    NASA Astrophysics Data System (ADS)

    Nagornyi, A. V.; Petrenko, V. I.; Bulavin, L. A.; Avdeev, M. V.; Almásy, L.; Rosta, L.; Aksenov, V. L.

    2014-01-01

    Structural parameters of the magnetite-oleic acid-decalin magnetic fluid at various excesses of oleic acid (up to 25 vol %) have been determined using small-angle neutron scattering. Based on the comparison of the behavior of oleic acid in the magnetic fluid and in the pure solvent (decalin), it has been concluded that the interaction between the molecules of free (unadsorbed) surfactant changes in the presence of magnetic nanoparticles. However, the system remains stable and does not form aggregates of magnetic particles or free oleic acid. These results are compared with the previously presented data for similar benzene-based magnetic fluids.

  15. Origins of Magnetite Nanocrystals in Martian Meteorite ALH84001

    NASA Technical Reports Server (NTRS)

    Thomas-Keprta, Kathie L.; Clemett, Simon J.; Mckay, David S.; Gibson, Everett K.; Wentworth, Susan J.

    2009-01-01

    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 (Fe3O4) 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 mag- netite 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 characterized of the compo- sitional 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 car- bonate 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.

  16. Magnetite colloidal nanocrystals: a facile pathway to prepare mesoporous hematite thin films for photoelectrochemical water splitting.

    PubMed

    Gonçalves, Ricardo H; Lima, Bruno H R; Leite, Edson R

    2011-04-20

    In this study, we demonstrate an alternative and promising way to produce hematite photoanodes with high performance and without the addition of doping or catalytic coating. In this approach, we processed hematite thin films using a colloidal dispersion of magnetite nanocrystals as the precursor. The photoelectrochemical characterization shows that the colloidal approach used to process an undoped hematite photoanode produced a high-performance electrode for water photooxidation with an onset potential as low as 0.8 V(RHE). This value is comparable to the best results reported in the literature for a hematite photoanode modified with catalytic materials. We demonstrate that pure hematite thin films reach 1.1 mA·cm(-2) at 1.23 V(RHE) with back-side illumination. PMID:21443221

  17. Experimental studies of magnetite formation in the solar nebula

    NASA Astrophysics Data System (ADS)

    Hong, Y.; Fegley, B., Jr.

    1998-09-01

    Oxidation of Fe metal and Gibeon meteorite metal to magnetite via the net reaction 3 Fe (metal) + 4 H2O (gas) = Fe3O4 (magnetite) + 4 H2 (gas) was experimentally studied at ambient atmospheric pressure at 91-442oC in H2 and H2-He gas mixtures with H2/H2O molar ratios of ~4-41. The magnetite produced was identified by X-ray diffraction. Electron microprobe analyses showed 3.3 wt% NiO and 0.24 wt% CoO (presumably as NiFe2O4 and CoFe2O4) in magnetite formed from Gibeon metal. The NiO and CoO concentrations are higher than expected from equilibrium between metal and oxide under the experimental conditions. Elevated NiO contents in magnetite were also observed by metallurgists during initial stages of oxidation of Fe-Ni alloys. The rate constants for magnetite formation were calculated from the weight gain data using a constant surface area model and the Jander, Ginstling-Brounshtein, and Valensi-Carter models for powder reactions. Magnetite formation followed parabolic (i.e., diffusion controlled) kinetics. The rate constants and apparent activation energies for Fe metal and Gibeon metal are: cm2 hour-1 Eact = 92=B15(2s) kJ mol-1 cm2 hour-1 Eact = 95=B112(2s) kJ mol-1 These rate constants are significantly smaller than the parabolic rate constants for FeS growth on Fe metal in H2S-H2 gas mixtures containing 1000 or 10,000 ppmv H2S (Lauretta et al. 1996a). The experimental data for Fe and Gibeon metal are used to model the reaction time of Fe alloy grains in the solar nebula as a function of grain size and temperature. The reaction times for 0.1-1 micron radius metal grains are generally within estimated lifetimes of the solar nebula (0.1-10 million years). However, the calculated reaction times are probably lower limits and further study of magnetite formation at larger H2/H2O ratios, at lower temperatures and pressures, and as a function of metal alloy composition is needed for further modeling of nebular magnetite formation.

  18. Structural changes in the 6CHBT liquid crystal doped with spherical, rodlike, and chainlike magnetic particles.

    PubMed

    Kopcanský, Peter; Tomasovicová, Natália; Koneracká, Martina; Závisová, Vlasta; Timko, Milan; Dzarová, Anezka; Sprincová, Adriana; Eber, Nándor; Fodor-Csorba, Katalin; Tóth-Katona, Tibor; Vajda, Aniko; Jadzyn, Jan

    2008-07-01

    In this work the 4-(trans- 4'-n -hexylcyclohexyl)-isothiocyanatobenzene (6CHBT) liquid crystal was doped with differently shaped magnetite nanoparticles. The structural changes were observed by capacitance measurements and showed significant influence of the shape and size of the magnetic particles on the magnetic Fréedericksz transition. For the volume concentration phi= 2 x 10(-4) of the magnetic particles, the critical magnetic field was established for the pure liquid crystal, and for liquid crystals doped with spherical, chainlike, and rodlike magnetic particles. The influence of the magnetic field depends on the type of anchoring, which is characterized by the density of anchoring energy and by the initial orientation between the liquid crystal molecules and the magnetic moment of the magnetic particles. The experimental results indicated soft anchoring in the case of spherical magnetic particles and rigid anchoring in the case of rodlike and chainlike magnetic particles, with parallel initial orientation between the magnetic moments of the magnetic particles and director. PMID:18763968

  19. Abnormal Elastic and Vibrational Behaviors of Magnetite at High Pressures

    PubMed Central

    Lin, Jung-Fu; Wu, Junjie; Zhu, Jie; Mao, Zhu; Said, Ayman H.; Leu, Bogdan M.; Cheng, Jinguang; Uwatoko, Yoshiya; Jin, Changqing; Zhou, Jianshi

    2014-01-01

    Magnetite exhibits unique electronic, magnetic, and structural properties in extreme conditions that are of great research interest. Previous studies have suggested a number of transitional models, although the nature of magnetite at high pressure remains elusive. We have studied a highly stoichiometric magnetite using inelastic X-ray scattering, X-ray diffraction and emission, and Raman spectroscopies in diamond anvil cells up to ~20?GPa, while complementary electrical conductivity measurements were conducted in a cubic anvil cell up to 8.5?GPa. We have observed an elastic softening in the diagonal elastic constants (C11 and C44) and a hardening in the off-diagonal constant (C12) at ~8?GPa where significant elastic anisotropies in longitudinal and transverse acoustic waves occur, especially along the [110] direction. An additional vibrational Raman band between the A1g and T2g modes was also detected at the transition pressure. These abnormal elastic and vibrational behaviors of magnetite are attributed to the occurrence of the octahedrally-coordinated Fe2+-Fe3+-Fe2+ ions charge-ordering along the [110] direction in the inverse spinel structure. We propose a new phase diagram of magnetite in which the temperature for the metal-insulator and distorted structural transitions decreases with increasing pressure while the charge-ordering transition occurs at ~8?GPa and room temperature. PMID:25186916

  20. Magnetic Separations with Magnetite: Theory, Operation, and Limitations

    SciTech Connect

    G. B. Cotten

    2000-08-01

    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.

  1. Functionalization of Magnetite Nanoparticles as Oil Spill Collector

    PubMed Central

    Atta, Ayman M.; Al-Lohedan, Hamad A.; Al-Hussain, Sami A.

    2015-01-01

    In the present study, a new magnetic powder based on magnetite can be used as a petroleum crude oil collector. Amidoximes based on rosin as a natural product can be prepared from a reaction between hydroxylamine and rosin/acrylonitrile adducts. The produced rosin amidoximes were used as capping agents for magnetite nanoparticles to prepare hydrophobic coated magnetic powders. A new class of monodisperse hydrophobic magnetite nanoparticles was prepared by a simple and inexpensive co-precipitation method. Iron ions and iodine were prepared by the reaction between ferric chloride and potassium iodide. The structure and morphology of magnetite capped with rosin amidoxime were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), transmission electron microscopy (TEM), zeta potential, thermogravimetric analysis (TGA) and dynamic light scattering (DLS). The magnetic properties were determined from vibrating sample magnetometer (VSM) analyses. These prepared magnetite nanoparticles were tested as bioactive nanosystems and their antimicrobial effects were investigated. The prepared nanomaterials were examined as a crude oil collector using magnetic fields. The results show promising data for the separation of the petroleum crude oil from aqueous solution in environmental pollution cleanup. PMID:25822876

  2. Fabrication of chitosan-magnetite nanocomposite strip for chromium removal

    NASA Astrophysics Data System (ADS)

    Sureshkumar, Vaishnavi; Kiruba Daniel, S. C. G.; Ruckmani, K.; Sivakumar, M.

    2015-03-01

    Environmental pollution caused by heavy metals is a serious threat. In the present work, removal of chromium was carried out using chitosan-magnetite nanocomposite strip. Magnetite nanoparticles (Fe3O4) were synthesized using chemical co-precipitation method at 80 °C. The nanoparticles were characterized using UV-visible spectroscopy, fourier transform infrared spectroscopy, X-ray diffraction spectrometer, atomic force microscope, dynamic light scattering and vibrating sample magnetometer, which confirm the size, shape, crystalline nature and magnetic behaviour of nanoparticles. Atomic force microscope revealed that the particle size was 15-30 nm and spherical in shape. The magnetite nanoparticles were mixed with chitosan solution to form hybrid nanocomposite. Chitosan strip was casted with and without nanoparticle. The affinity of hybrid nanocomposite for chromium was studied using K2Cr2O7 (potassium dichromate) solution as the heavy metal solution containing Cr(VI) ions. Adsorption tests were carried out using chitosan strip and hybrid nanocomposite strip at different time intervals. Amount of chromium adsorbed by chitosan strip and chitosan-magnetite nanocomposite strip from aqueous solution was evaluated using UV-visible spectroscopy. The results confirm that the heavy metal removal efficiency of chitosan-magnetite nanocomposite strip is 92.33 %, which is higher when compared to chitosan strip, which is 29.39 %.

  3. Biogeochemical Conditions Favoring Magnetite Formation during Anaerobic Iron Reduction

    PubMed Central

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

    1987-01-01

    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). PMID:16347480

  4. Equilibrium high-temperature Fe isotope fractionation between fayalite and magnetite: An experimental calibration

    E-print Network

    Manning, Craig

    Equilibrium high-temperature Fe isotope fractionation between fayalite and magnetite 2008 Abstract The iron isotopic fractionation factor between magnetite and fayalite was measured equilibrium fractionation between two minerals directly. The experimentally-determined temperature

  5. Synthesis of chiral hybrid nanotubes of magnetite nanoparticles and conducting polymers.

    PubMed

    Mitsumori, Masashi; Nakahodo, Tsukasa; Fujihara, Hisashi

    2012-01-01

    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. PMID:22038075

  6. The microstructure and characteristics of magnetite thin films prepared by ultrasound-enhanced ferrite plating

    Microsoft Academic Search

    Chun-Young Oh; Jae-Hee Oh; Tae-Kyung Ko

    2002-01-01

    Summary form only given. In this study, magnetite (Fe3O4) thin films were prepared by ultrasound-enhanced ferrite plating. The effects of ferrite plating condition on the microstructure and magnetic properties of magnetite thin films were investigated.

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

    PubMed Central

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

    2013-01-01

    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

  8. Investigation of Electrically Driven Phase Transition in Magnetite Thin Films

    NASA Astrophysics Data System (ADS)

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

    2009-03-01

    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.

  9. Drastic Magnetoresistance Enhancement on Spin-Dependent-Transport and Appearance of Spin-Glass-Like Behavior for Magnetite Nanoparticle Sinter Calcined at Low Temperature

    Microsoft Academic Search

    H. Kobori; K. Ohnishi; A. Sugimura; T. Taniguchi

    2007-01-01

    We have studied the spin-dependent-transport and magnetization for magnetite nanoparticle sinter (MNPS) calcined at low temperature. As compared with a bulk crystal, the drastic enhancement of negative differential magnetoresistance has been obtained for the MNPS. Below the Verwey transition temperature, we have observed the difference of magnetization between zero-field-cooling and field-cooling. This phenomenon indicates that localized spins in amorphous-like grain-boundary

  10. Drastic Magnetoresistance Enhancement on Spin-Dependent-Transport and Appearance of Spin-Glass-Like Behavior for Magnetite Nanoparticle Sinter Calcined at Low Temperature

    NASA Astrophysics Data System (ADS)

    Kobori, H.; Ohnishi, K.; Sugimura, A.; Taniguchi, T.

    2007-04-01

    We have studied the spin-dependent-transport and magnetization for magnetite nanoparticle sinter (MNPS) calcined at low temperature. As compared with a bulk crystal, the drastic enhancement of negative differential magnetoresistance has been obtained for the MNPS. Below the Verwey transition temperature, we have observed the difference of magnetization between zero-field-cooling and field-cooling. This phenomenon indicates that localized spins in amorphous-like grain-boundary region in the MNPS are spin-glass-like.

  11. Relationship between altered pyroxene diorite and the magnetite mineralization in the Chilean Iron Belt, with emphasis on the El Algarrobo iron deposits (Atacama region, Chile)

    Microsoft Academic Search

    J.-J. Ménard

    1995-01-01

    North of El Algarrobo (one of the four main deposits of the Chilean Iron Belt), the iron-mineralization (magnetite-etrmolite\\/actinolite-apatite) is related to clinoand orthopyroxene diorite intrusions which have crystallized at shallow depth (4km) under increasing oxygen fugacities. The supercritical fluid phase exsolved during cooling after the consolidation of the plutons (800–900°C), results in a H+, Cl- and sodic enrichment, and in

  12. Structure, Charge Distribution, and Electron Hopping Dynamics in Magnetite (Fe3O4) (100) Surfaces from First Principles

    SciTech Connect

    Skomurski, Frances N.; Kerisit, Sebastien N.; Rosso, Kevin M.

    2010-08-01

    For the purpose of improving fundamental understanding of the redox reactivity of magnetite, quantum mechanical calculations were applied to predict Fe2+ availability and electron hopping rates at magnetite (100) surfaces, with and without the presence of adsorbed water. Using a low free energy surface reconstruction (½ Fetet layer relaxed into the Feoct (100) plane), the relaxed outermost layer of both the hydrated and vacuum-terminated surfaces were found to be predominantly enriched in Fe2+ within the octahedral sublattice, irrespective of the presence of adsorbed water. At room temperature, mobile electrons move through the octahedral sublattice by Fe2+-Fe3+ valence interchange small polaron hopping, calculated at 1010-1012 hops/second for bulk and bulk-like (i.e. near-surface) environments. This process is envisioned to control sustainable overall rates of interfacial redox reactions. These rates decrease by up to three orders of magnitude (109 hops/second) at the (100) surface, and no significant difference is observed for vacuum-terminated versus hydrated cases. Slower hopping rates at the surface appear to arise primarily from larger reorganization energies associated with octahedral Fe2+-Fe3+ valence interchange in relaxed surface configurations, and secondarily on local charge distribution patterns surrounding Fe2+-Fe3+ valence interchange pairs. These results suggest that, with respect to the possibility that the rate and extent of surface redox reactions depend on Fe2+ availability and its replenishment rate, bulk electron hopping mobility is an upper-limit for magnetite and slower surface rates may need to be considered as potentially rate-limiting. They also suggest hopping mobilities in magnetite nanoparticles may be slower than for bulk single crystals, towards time-scales amenable to Fe2+-Fe3+ site discrimination by conventional spectroscopic probes.

  13. Microscale oxygen isotopic exchange and magnetite formation in the Ningqiang anomalous carbonaceous chondrite

    Microsoft Academic Search

    Byeon-Gak Choi; John T. Wasson

    2003-01-01

    We report in situ measurements of O-isotopic compositions of magnetite, olivine and pyroxene in chondrules of the Ningqiang anomalous carbonaceous chondrite. The petrographic setting of Ningqiang magnetite is similar to those in oxidized-CV chondrites such as Allende, where magnetite is found together with Ni-rich metal and sulfide in opaque assemblages in chondrules. Both magnetite and silicate oxygen data fall close

  14. Nanoparticulate magnetite thin films as electrode materials for the fabrication of electrochemical capacitors

    Microsoft Academic Search

    Suh Cem Pang; Wai Hwa Khoh; Suk Fun Chin

    2010-01-01

    Magnetite nanoparticles in stable colloidal suspension were prepared by the co-precipitation method. Nanoparticulate magnetite\\u000a thin films on supporting stainless steel plates were prepared by drop-coating followed by heat treatment under controlled\\u000a conditions. The effects of calcination temperature and atmosphere on the microstructure and electrochemical properties of\\u000a nanoparticulate magnetite thin films were investigated. Nanoparticulate magnetite thin films prepared under optimized conditions

  15. Surface modification of superparamagnetic magnetite nanoparticles and their intracellular uptake

    Microsoft Academic Search

    Y Zhang; Nathan Kohler; Miqin Zhang

    2002-01-01

    Superparamagnetic magnetite nanoparticles were surface-modified with\\u000a poly (ethylene glycol) (PEG) and folic acid, respectively, to improve\\u000a their intracellular uptake and ability to tat-get specific cells. PEG\\u000a and folic acid were successfully immobilized on the surfaces of\\u000a magnetite nanoparticles and characterized using fourier transform\\u000a infrared spectra. The nanoparticle internalization into mouse macrophage\\u000a (RAW 264.7) and human breast cancer (BT20) cells was

  16. In Situ Measurement of Oxygen Isotope Compositions of Magnetite in the Allende CV3 Chondrite

    Microsoft Academic Search

    B.-G. Choi; C. D. Coath; L. Leshin; J. Wang; K. D. McKeegan; J. T. Wasson

    1995-01-01

    Magnetite is relatively abundant in the oxidized CV chondrites. This study was undertaken to examine possible origins in nebular or in parent-body processes. Magnetite in Allende has several distinct characteristics compared to that of the other CV chondrites. Unlike Mokoia and Vigarano, magnetite in Allende is almost exclusively found in chondrules, where it typically forms spherical nodules often associated with

  17. Dissolution behaviour of magnetite film formed over carbon steel in dilute organic acid media

    Microsoft Academic Search

    A. A. M. Prince; S. Velmurugan; S. V. Narasimhan; C. Ramesh; N. Murugesan; P. S. Raghavan; R. Gopalan

    2001-01-01

    Magnetite is the major corrosion product formed over the carbon steel in the primary heat transport system of the pressurized heavy water reactor (PHWR). This magnetite usually accumulates radioactivity during reactor operation. The dissolution of the host magnetite is achieved by chemical formulations in order to get rid of the radioactivity trapped in the oxide; the underlying base metal also

  18. Magnetite composition in Ni-Cu-PGE deposits worldwide: application to mineral exploration

    E-print Network

    Magnetite composition in Ni-Cu-PGE deposits worldwide: application to mineral exploration Emilie October 2013 Accepted 13 May 2014 Available online 21 May 2014 Keywords: Magnetite Ni Cu Sulfides Mineral in the exploration of ore deposits. Magnetite is a common accessory mineral in magmatic Ni­Cu­Platinum-Group Element

  19. Cytochrome cd1 Nitrite Reductase NirS Is Involved in Anaerobic Magnetite Biomineralization in Magnetospirillum gryphiswaldense and Requires NirN for Proper d1 Heme Assembly

    PubMed Central

    Li, Yingjie; Bali, Shilpa; Borg, Sarah; Katzmann, Emanuel

    2013-01-01

    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 d1 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 cd1 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

  20. Low-temperature oxidation of magnetite - a humidity sensitive process?

    NASA Astrophysics Data System (ADS)

    Appel, Erwin; Fang, Xiaomin; Herb, Christian; Hu, Shouyun

    2015-04-01

    Extensive multi-parameter palaeoclimate records were obtained from two long-term lacustrine archives at the Tibetan Plateau: the Qaidam basin (2.69-0.08 Ma) and Heqing basin (0.90-0.03 Ma). At present the region of the Qaidam site has an arid climate (<100 mm mean annual precipitation) while the Heqing site is located in the sub-tropical region with monsoonal rainfall. Magnetic properties play a prominent role for palaeoclimate interpretation in both records. Several parameters show a 100 kyr eccentricity cyclicity; in the Qaidam record also the Mid-Pleistocene Transition is seen. Both magnetic records are controlled by different absolute and relative contributions of magnetite and its altered (maghemitized) phases as well as hematite. Weathering conditions likely cause a systematic variation of magnetic mineralogy due to low-temperature oxidation (LTO). Maghemitization is well recognized as an alteration process in submarine basalts but about its relevance for climate-induced weathering in continental environments little is known. Various factors i.e., humidity, temperature, seasonality, duration of specific weathering conditions, and bacterial activity could be responsible for maghemitization (LTO) and transformation to hematite (or goethite) when a critical degree of LTO is reached. These factors may lead to a complex interplay, but one has to note that water acts as an electrolyte for Fe(II) to Fe(III) oxidation at the crystal surface and due to maghemitization-induced lattice shrinking a larger internal particle surface area becomes exposed to oxidation. We suggest that humidity is the most crucial driver for the two studied archives - for the following reasons: (1) The overall parameter variations and catchment conditions are well in agreement with an LTO scenario. (2) In the Qaidam record we observe a direct relationship of a humidity sensitive pollen Ratio with magnetic susceptibility (reflecting the degree of alteration by LTO). (3) In the Heqing record carbonate erosion that reflects higher precipitation matches with stronger maghemitization. In the arid Qaidam region we interpret the humidity variation by regional water recycling related to glacial-interglacial periods. In the sub-tropical Heqing region humidity fluctuations may be caused by a changing relative influence of the Indian summer monsoon.

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

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

    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.

  2. Purely radiative perfect fluids

    E-print Network

    B. Bastiaensen; H. R. Karimian; N. Van den Bergh; L. Wylleman

    2007-05-08

    We study `purely radiative' (div E = div H = 0) and geodesic perfect fluids with non-constant pressure and show that the Bianchi class A perfect fluids can be uniquely characterized --modulo the class of purely electric and (pseudo-)spherically symmetric universes-- as those models for which the magnetic and electric part of the Weyl tensor and the shear are simultaneously diagonalizable. For the case of constant pressure the same conclusion holds provided one also assumes that the fluid is irrotational.

  3. 7 CFR 917.8 - Pure grower or pure producer.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ...Vegetables, Nuts), DEPARTMENT OF AGRICULTURE FRESH PEARS AND PEACHES GROWN IN CALIFORNIA Order Regulating Handling Definitions § 917.8 Pure grower or pure producer. (a) For peaches, pure grower means any grower: (1) Who...

  4. 7 CFR 917.8 - Pure grower or pure producer.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ...Agreements and Orders; Fruits, Vegetables, Nuts), DEPARTMENT OF AGRICULTURE FRESH PEARS AND PEACHES GROWN IN CALIFORNIA Order Regulating Handling Definitions § 917.8 Pure grower or pure producer. (a) For peaches, pure...

  5. Magnetoresistive polyaniline-magnetite nanocomposites with negative dielectrical properties

    E-print Network

    Guo, John Zhanhu

    s t r a c t Magnetic polyaniline (PANI) polymer nanocomposites (PNCs) reinforced with magnetite (Fe3O4 polymerization (SIP) method. The chemical structures of the PANI/Fe3O4 PNCs are characterized by Fourier transform infrared (FT-IR) spectroscopy. The thermal stability of the PANI/Fe3O4 PNCs is performed

  6. Benefaction studies on the Hasan Celebi magnetite deposit, Turkey

    USGS Publications Warehouse

    Pressler, Jean W.; Akar, Ali

    1972-01-01

    Bench-scale and semicontinuous tests were performed on surface, trench, and diamond drill core samples from the Hasan Celebi low-grade magnetite deposit to determine the optimum benefication procedures utilizing wet magnetic separation techniques. Composite core samples typically contain about 27 percent recoverable magnetite and require crushing and grinding through 1 mm in size to insure satisfactory separation of the gangue from the magnetite. Regrinding and cleaning the magnetite concentrate to 80 percent minus 150-mesh is necessary to obtain an optimum of 66 percent iron. Semicontinuous pilot-plant testing with the wet magnetic drum using the recycled middling technique indicates that as much as 83 percent of the acid-soluble iron can be recovered into a concentrate containing 66 percent iron, with minimum deleterious elements. This represents 27 weight percent of the original ore. Further tests will continue when the Maden Tetkik ve Arama Enstitusu (MTA) receives 24 tons of bulk sample from an exploratory drift and cross-cut now being driven through a section of the major reserve area.

  7. Magnetic Core-Shell Morphology of Structurally Uniform Magnetite Nanoparticles

    Microsoft Academic Search

    Kathryn Krycka

    2011-01-01

    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

  8. Avian magnetite-based magnetoreception: a physiologist's perspective

    PubMed Central

    Cadiou, Hervé; McNaughton, Peter A.

    2010-01-01

    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. PMID:20106875

  9. Anti-phase domains and magnetism in epitaxial magnetite layers

    Microsoft Academic Search

    T. Hibma; F. C. Voogt; L. Niesen; P. A. A. van der Heijden; W. J. M. de Jonge; J. J. T. M. Donkers; P. J. van der Zaag

    1999-01-01

    Recent studies show that the magnetic properties of epitaxial thin films of magnetite (Fe3O4) deviate strongly from bulk behavior: it is difficult to saturate thin films, ultrathin films may become super paramagnetic, their saturation magnetization drops to zero, and the local magnetic moments are oriented out of plane in zero field. The possible relationship between this anomalous behavior and the

  10. Microfabrication and characterization of magnetite-based magnetic tunnel junctions

    Microsoft Academic Search

    Chando Park

    2004-01-01

    Magnetic tunnel junctions (MTJs) consisting of two magnetic layers separated by a thin insulating barrier have emerged as the major candidate for magnetic based information storage systems because of their relatively high tunneling magnetoresistance (MR). The magnitude of the MR is determined by the spin polarization of the magnetic layers. One of the most promising materials for MTJs is magnetite

  11. Magnetic and magnetotransport properties of magnetite films with step edges

    NASA Astrophysics Data System (ADS)

    Ziese, M.; Höhne, R.; Semmelhack, H. C.; Han, K. H.; Esquinazi, P.; Zimmer, K.

    2004-08-01

    The magnetoresistance of step edges in magnetite films was systematically studied. An enhancement of the magnetoresistance by the introduction of step edges was observed, especially in the high-field regime. This was modelled by spin-disorder scattering. The analysis revealed magnetic cluster formation at the step edges.

  12. Magnetic and magnetotransport properties of magnetite films with step edges

    Microsoft Academic Search

    M. Ziese; R. Höhne; H. C Semmelhack; K. H Han; P. Esquinazi; K. Zimmer

    2004-01-01

    The magnetoresistance of step edges in magnetite films was systematically studied. An enhancement of the magnetoresistance by the introduction of step edges was observed, especially in the high-field regime. This was modelled by spin-disorder scattering. The analysis revealed magnetic cluster formation at the step edges.

  13. Magnetite and Carbonate Textures in ALH84001: Experimental Insights

    NASA Technical Reports Server (NTRS)

    Koziol, Andrea M.

    2001-01-01

    Synthetic siderite and synthetic siderite-magnesite carbonates were equilibrated with hematite, magnetite, and CO2 at elevated pressure and temperature. Comparisons are made to textures seen in the carbonate globules in ALH84001. Additional information is contained in the original extended abstract.

  14. Carbide-magnetite assemblages in type-3 ordinary chondrites

    NASA Astrophysics Data System (ADS)

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

    1997-01-01

    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) 23C 6) 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 C sbnd O sbnd H-bearing fluid on their parent bodies. This alteration resulted in carbidization of Fe sbnd Ni metal, probably by CO gas (e.g., 15 Fe(s) + 4 CO(g) = Fe 3C(s) + Fe3O4(s) or 3 Fe(s) + 2 CO(g) = Fe 3C(s) + CO 2(g)), and oxidation, probably by H 2O gas (e.g., 3Fe(s) + 4H 2O(g) = Fe 3O 4(S) + 4H 2(g)). The C sbnd O sbnd H-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.

  15. Pure aluminum process solution for advanced LCDs

    NASA Astrophysics Data System (ADS)

    Pethe, Rajiv G.; Bedekar, Milind; Demaray, Richard E.; Deshpandey, Chandra V.; Shao, Henry

    1997-04-01

    Large size high-resolution liquid crystal displays put severe restriction on metal selection for gate lines where very low resistivity is required. Pure aluminum (Al) could be used of hillocking issues could be resolved. In this paper we demonstrated an Al deposition process on glass substrates with ultra low hillock density after photoresist and dielectric processing. Effects of process parameters such as substrate temperature, substrate roughness, base pressure and underlayer thickness on morphology and texture of aluminum are discussed.

  16. Magnetite Formation from Thermal Decomposition of Siderite: Implications for Inorganic Magnetite Formation in Martian Meteorite ALH84001

    NASA Technical Reports Server (NTRS)

    Morris, RIchard V.

    2002-01-01

    A biogenic mechanism for formation of a subpopulation magnetite in Martian meteorite ALH84001 has been suggested [McKay et al., 1996; Thomas-Keprta, et al., 2000]. We are developing experimental evidence for an alternating working hypothesis, that the subpopulation was produced inorganically by the thermal decomposition of siderite [Golden et al., 2000].

  17. Geochemistry of magnetite from porphyry Cu and skarn deposits in the southwestern United States

    NASA Astrophysics Data System (ADS)

    Nadoll, Patrick; Mauk, Jeffrey L.; Leveille, Richard A.; Koenig, Alan E.

    2015-04-01

    A combination of petrographic observations, laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), and statistical data exploration was used in this study to determine compositional variations in hydrothermal and igneous magnetite from five porphyry Cu-Mo and skarn deposits in the southwestern United States, and igneous magnetite from the unmineralized, granodioritic Inner Zone Batholith, Japan. The most important overall discriminators for the minor and trace element chemistry of magnetite from the investigated porphyry and skarn deposits are Mg, Al, Ti, V, Mn, Co, Zn, and Ga—of these the elements with the highest variance for (I) igneous magnetite are Mg, Al, Ti, V, Mn, Zn, for (II) hydrothermal porphyry magnetite are Mg, Ti, V, Mn, Co, Zn, and for (III) hydrothermal skarn magnetite are Mg, Ti, Mn, Zn, and Ga. Nickel could only be detected at levels above the limit of reporting (LOR) in two igneous magnetites. Equally, Cr could only be detected in one igneous occurrence. Copper, As, Mo, Ag, Au, and Pb have been reported in magnetite by other authors but could not be detected at levels greater than their respective LORs in our samples. Comparison with the chemical signature of igneous magnetite from the barren Inner Zone Batholith, Japan, suggests that V, Mn, Co, and Ga concentrations are relatively depleted in magnetite from the porphyry and skarn deposits. Higher formation conditions in combination with distinct differences between melt and hydrothermal fluid compositions are reflected in Al, Ti, V, and Ga concentrations that are, on average, higher in igneous magnetite than in hydrothermal magnetite (including porphyry and skarn magnetite). Low Ti and V concentrations in combination with high Mn concentrations are characteristic features of magnetite from skarn deposits. High Mg concentrations (<1,000 ppm) are characteristic for magnetite from magnesian skarn and likely reflect extensive fluid/rock interaction. In porphyry deposits, hydrothermal magnetite from different vein types can be distinguished by varying Ti, V, Mn, and Zn contents. Titanium and V concentrations are highly variable among hydrothermal and igneous magnetites, but Ti concentrations above 3,560 ppm could only be detected in igneous magnetite, and V concentrations are on average lower in hydrothermal magnetite. The highest Ti concentrations are present in igneous magnetite from gabbro and monzonite. The lowest Ti concentrations were recorded in igneous magnetite from granodiorite and granodiorite breccia and largely overlap with Ti concentrations found in hydrothermal porphyry magnetite. Magnesium and Mn concentrations vary between magnetite from different skarn deposits but are generally greater than in hydrothermal magnetite from the porphyry deposits. High Mg, and low Ti and V concentrations characterize hydrothermal magnetite from magnesian skarn deposits and follow a trend that indicates that magnetite from skarn (calcic and magnesian) commonly has low Ti and V concentrations.

  18. Geochemistry of magnetite from porphyry Cu and skarn deposits in the southwestern United States

    USGS Publications Warehouse

    Nadoll, Patrick; Mauk, Jeffrey L.; LeVeille, Richard A.; Koenig, Alan E.

    2015-01-01

    A combination of petrographic observations, laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), and statistical data exploration was used in this study to determine compositional variations in hydrothermal and igneous magnetite from five porphyry Cu–Mo and skarn deposits in the southwestern United States, and igneous magnetite from the unmineralized, granodioritic Inner Zone Batholith, Japan. The most important overall discriminators for the minor and trace element chemistry of magnetite from the investigated porphyry and skarn deposits are Mg, Al, Ti, V, Mn, Co, Zn, and Ga—of these the elements with the highest variance for (I) igneous magnetite are Mg, Al, Ti, V, Mn, Zn, for (II) hydrothermal porphyry magnetite are Mg, Ti, V, Mn, Co, Zn, and for (III) hydrothermal skarn magnetite are Mg, Ti, Mn, Zn, and Ga. Nickel could only be detected at levels above the limit of reporting (LOR) in two igneous magnetites. Equally, Cr could only be detected in one igneous occurrence. Copper, As, Mo, Ag, Au, and Pb have been reported in magnetite by other authors but could not be detected at levels greater than their respective LORs in our samples. Comparison with the chemical signature of igneous magnetite from the barren Inner Zone Batholith, Japan, suggests that V, Mn, Co, and Ga concentrations are relatively depleted in magnetite from the porphyry and skarn deposits. Higher formation conditions in combination with distinct differences between melt and hydrothermal fluid compositions are reflected in Al, Ti, V, and Ga concentrations that are, on average, higher in igneous magnetite than in hydrothermal magnetite (including porphyry and skarn magnetite). Low Ti and V concentrations in combination with high Mn concentrations are characteristic features of magnetite from skarn deposits. High Mg concentrations (<1,000 ppm) are characteristic for magnetite from magnesian skarn and likely reflect extensive fluid/rock interaction. In porphyry deposits, hydrothermal magnetite from different vein types can be distinguished by varying Ti, V, Mn, and Zn contents. Titanium and V concentrations are highly variable among hydrothermal and igneous magnetites, but Ti concentrations above 3,560 ppm could only be detected in igneous magnetite, and V concentrations are on average lower in hydrothermal magnetite. The highest Ti concentrations are present in igneous magnetite from gabbro and monzonite. The lowest Ti concentrations were recorded in igneous magnetite from granodiorite and granodiorite breccia and largely overlap with Ti concentrations found in hydrothermal porphyry magnetite. Magnesium and Mn concentrations vary between magnetite from different skarn deposits but are generally greater than in hydrothermal magnetite from the porphyry deposits. High Mg, and low Ti and V concentrations characterize hydrothermal magnetite from magnesian skarn deposits and follow a trend that indicates that magnetite from skarn (calcic and magnesian) commonly has low Ti and V concentrations.

  19. Synthesis of pure RDX

    SciTech Connect

    Pagoria, P.F.

    1994-03-25

    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.

  20. X-ray diffraction study on size effects in epitaxial magnetite thin films on MgO(0?0?1)

    NASA Astrophysics Data System (ADS)

    Bertram, F.; Deiter, C.; Hoefert, O.; Schemme, T.; Timmer, F.; Suendorf, M.; Zimmermann, B.; Wollschläger, J.

    2012-10-01

    Epitaxial ultrathin iron oxide films of different thicknesses were grown by reactive molecular beam epitaxy in 10-6 mbar oxygen atmosphere on MgO(0?0?1) single crystal substrates at room temperature. Afterwards, the films were studied by x-ray diffraction, x-ray reflectivity and x-ray photoelectron spectroscopy to provide information regarding film structure as well as chemical composition of the films. Except for a very thin interface layer of subnanometre thickness, the iron oxide films have magnetite stoichiometry and structure and Mg does not diffuse from the substrate into the iron oxide film. The interface layer has a wuestite structure as determined by kinematic diffraction analysis. The magnetite films exhibit very homogeneous thickness while the vertical lattice constant decreases gradually towards its bulk value.

  1. Synthesis and characterization of silica-coated nanoparticles of magnetite

    NASA Astrophysics Data System (ADS)

    Ferreira, R. V.; Pereira, I. L. S.; Cavalcante, L. C. D.; Gamarra, L. F.; Carneiro, S. M.; Amaro, E.; Fabris, J. D.; Domingues, R. Z.; Andrade, A. L.

    2010-01-01

    Magnetic nanoparticles coated with silica have been subjected of extensive, and, in many aspects, also intensive investigations because of their potential application in different technological fields, particularly in biomedicine. This work was conceived and is being carried out in two main parts: (1) synthesis of the ferrimagnetic nanoparticles, specifically magnetite, and (2) coating these particles with tetraethyl orthosilicate (TEOS). The nanosized magnetite sample was prepared by the reduction-precipitation and the nanomagnetite particles were coated by the sol-gel method, based on the hydrolysis of tetraethyl orthosilicate (TEOS). The so obtained materials were characterized with powder X-ray diffraction (XRD), FTIR spectroscopy, saturation magnetization measurements, and 57Fe Mössbauer spectroscopy at room temperature.

  2. Investigation of heteroepitaxial growth of magnetite thin films.

    SciTech Connect

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

    2007-07-01

    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.

  3. Early Gaseous Oxygen Enrichment to Enhance Magnetite Pellet Oxidation

    NASA Astrophysics Data System (ADS)

    Tang, Ming; Cho, Hyeon Jeong; Pistorius, Petrus Christiaan

    2014-08-01

    It is suggested that oxygen enrichment in the gas atmosphere, during continuous heating of magnetite pellets, can cause pellets to be oxidized throughout their volumes, eliminating unoxidized cores. The peculiarities of the oxidation kinetics of magnetite concentrate imply that such oxygen enrichment might be particularly effective at lower temperatures. This suggestion was tested by developing and testing a mixed-control model for pellet oxidation (to allow the sizes of unreacted cores to be predicted), and by experimentally testing the effects of oxygen enrichment at relatively low temperatures ("early oxygen enrichment"). The results confirmed that the extents (depth) of oxidation and pellet strength were both improved significantly by applying oxygen enrichment up to 873 K (600 °C), as part of a heating cycle up to 1073 K (800 °C).

  4. Supercritical fluid synthesis of magnetic hexagonal nanoplatelets of magnetite.

    PubMed

    Li, Zhonglai; Godsell, Jeffrey F; O'Byrne, Justin P; Petkov, Nikolay; Morris, Michael A; Roy, Saibal; Holmes, Justin D

    2010-09-15

    A supercritical fluid technique was used to prepare hexagonal nanoplatelets of magnetite. Ferrocene was used as the Fe source, and sc-CO(2) acted as both a solvent and oxygen source in the process. Powder X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, and magnetic measurements were used to characterize the products. It was found that the morphology and structure of the product strongly depended on the reaction conditions. PMID:20718484

  5. Direct deposition of magnetite thin films on organic semiconductors

    Microsoft Academic Search

    Emilia Arisi; Ilaria Bergenti; Massimiliano Cavallini; Alberto Riminucci; Giampiero Ruani; Valentin Dediu; Massimo Ghidini; Chiara Pernechele; Massimo Solzi

    2008-01-01

    Technological procedures able to produce high quality electrodes from magnetic oxides in vertical organic-inorganic hybrid devices is a challenging task in the field of organic spintronics. Thin films of magnetite (Fe3O4) have been successfully grown directly on top of organic semiconductor layers, tris(8-hydroxyquinoline)aluminium(III) (Alq3), by pulsed-electron ablation technique. The films show ferromagnetic behavior and good structural quality, properties detected by

  6. Magnetoresistance enhancement in epitaxial magnetite films grown on vicinal substrates

    Microsoft Academic Search

    S. K. Arora; R. G. S. Sofin; I. V. Shvets

    2005-01-01

    The magnetoresistance (MR) behavior of epitaxial magnetite Fe3O4 grown on low-vicinal (small miscut) and high-vicinal (large miscut) MgO substrates is compared. Magnetization measurements on Fe3O4 films on high-vicinal substrates showed reduced magnetic moment as compared with the films grown on low-vicinal MgO, which correlates well with the expected reduction in magnetic moment due to step edge induced additional antiphase boundaries

  7. Carbonyl groups anchoring for the water dispersibility of magnetite nanoparticles

    Microsoft Academic Search

    Ke Tao; Sheng Song; Jing Ding; Hongjing Dou; Kang Sun

    2011-01-01

    Magnetite nanoparticles, which were synthesized by using diethylene glycol (DEG) as both solvent and reductant, displayed\\u000a excellent hydrophilicity and water dispersibility. The influences of the amount of carboxymethyl-dextran sodium salt and NaOH\\u000a on nanoparticles dispersibility were evaluated in terms of zeta potentials, concentration variation under centrifugal field,\\u000a Fourier transform infrared, and X-ray photoelectron spectra, respectively. The results showed that the

  8. Skeletal muscle tissue engineering using functional magnetite nanoparticles

    Microsoft Academic Search

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

    2009-01-01

    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

  9. Hematite Versus Magnetite as the Signature for Planetary Magnetic Anomalies?

    NASA Technical Reports Server (NTRS)

    Kletetshka, Gunther; Taylor, Patrick T.; Wasilewski, Peter J.

    1999-01-01

    Crustal magnetic anomalies are the result of adjacent geologic units having contrasting magnetization. This magnetization arises from induction and/or remanence. In a planetary context we now know that Mars has significant crustal magnetic anomalies due to remanent magnetization, while the Earth has some anomalies where remanence can be shown to be important. This picture, however, is less clear because of the nature and the magnitude of the geomagnetic field which is responsible for superimposed induced magnetization. Induced magnetization assumes a magnetite source, because of its much greater magnetic susceptibility when compared with other magnetic minerals. We investigated the TRM (thermoremanent magnetization) acquisition of hematite, in weak magnetic fields up to 1 mT, to determine if the remanent and induced magnetization of hematite could compete with magnetite. TRM acquisition curves of magnetite and hematite show that multi-domain hematite reaches TRM saturation (0.3 - 0.4 A sq m/kg) in fields as low as 100 microT. However, multi-domain magnetite reaches only a few percent of its TRM saturation in a field of 100 microT (0.02 - 0.06 A sq m/kg). These results suggest that a mineral such as hematite and, perhaps, other minerals with significant remanence and minor induced magnetization may play an important role in providing requisite magnetization contrast. Perhaps, and especially for the Mars case, we should reevaluate where hematite and other minerals, with efficient remanence acquisition, exist in significant concentration, allowing a more comprehensive explanation of Martian anomalies and better insight into the role of remanent magnetization in terrestrial crustal magnetic anomalies.

  10. Adsorption of naphthenic acid on magnetite at different temperatures

    NASA Astrophysics Data System (ADS)

    Balmasova, O. V.; Ramazanova, A. G.; Korolev, V. V.

    2015-03-01

    Isotherms of naphthenic acid adsorption from heptane solutions on highly dispersed magnetite are studied using the adsorption equilibrium approach. The isosteric heats of naphthenic acid adsorption from heptane solutions are calculated over a temperature range of 293-308 K. The adsorption isotherms can be approximated using the equation for a straight line. Experimental adsorption isotherms are shown to be linear in the coordinates of the equation for the theory of volume filling of micropores (TVFM).

  11. Magnetocrystalline Anisotropy of Low Temperature Phase of Magnetite

    Microsoft Academic Search

    Koki Abe; Yoshiko Miyamoto; Soshin Chikazumi

    1976-01-01

    The magnetocrystalline anisotropy of low temperature phase of magnetite (Fe3O4) was measured for a monoclinic single phase specimen by using computerized fully-automatic torque magnetometer. The anisotropy is expressed by Ea{=}Kaalphaa2+Kbalphab2+Kaaalphaa4+Kbbalphab4+Kabalphaa2alphab2-Kualpha1112, where alphaa, alphab and alpha111 are direction cosines of the magnetization with respect to the monoclinic a-, b- and cubic [111] axes, respectively, the last of which coincides with the

  12. Influence of titanium doping on the magnetocrystalline anisotropy of magnetite

    Microsoft Academic Search

    Z. Kakol; J. Sabol; J. Stickler; A. Kozlowski; J. M. Honig

    1994-01-01

    Magnetization measurements, reported for Fe3-xTixO4 in the compositional range 0<=x<0.04, were used to determine magnetocrystalline anisotropy constants as a function of x and temperature. Magnetic measurements were performed along the principal crystallographic directions on single-crystalline specimens that had been annealed so as to preserve ideal oxygen stoichiometry. In contrast with the differences in the anisotropy of magnetite with Ti substitution,

  13. Synthesis of Monodispersed Magnetite Particles From Different Organometallic Precursors

    Microsoft Academic Search

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

    2006-01-01

    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,

  14. A kinematic model of TRM acquisition in multidomain magnetite

    Microsoft Academic Search

    E. McClelland; N. Sugiura

    1987-01-01

    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

  15. Magnetic and transport properties of magnetite thin films

    Microsoft Academic Search

    Guomin Zhang; Chongfei Fan; Liqing Pan; Fengping Wang; Ping Wu; Hong Qiu; Yousong Gu; Yue Zhang

    2005-01-01

    Magnetite (Fe3O4) films were prepared by DC reactive magnetron sputtering at various oxygen partial pressures with the ratio ? of oxygen to argon changing from 0.50:50 to 0.70:50 at room temperature, and then the Fe3O4 films were annealed at 480°C for 80min. The properties of the films were studied by X-ray diffraction, scanning electron microscopy, magnetic hysteresis loops, magnetoresistance (MR),

  16. Patterned magnetite films prepared via soft lithography and thermal decomposition

    Microsoft Academic Search

    Lijuan An; Zhaoqiang Li; Wei Li; Yaru Nie; Zhimin Chen; Yanping Wang; Bai Yang

    2006-01-01

    A method for the fabrication of patterned magnetite (Fe3O4) films is presented. We first prepared an ordered 2D array of Fe(acac)3 through a selective deposition technique on patterned self-assembled monolayers. Using thermal decomposition at elevated temperature (300°C), we transformed the patterned Fe(acac)3 into patterned Fe3O4 films in a short reaction time. These patterned films have been confirmed by using optical

  17. Investigation of magnetite thin films produced by pulsed laser deposition

    Microsoft Academic Search

    S. P. Sena; R. A. Lindley; H. J. Blythe; Ch. Sauer; M. Al-Kafarji; G. A. Gehring

    1997-01-01

    Thin films of magnetite (Fe3O4) with thicknesses in the range 10–1000 nm have been produced by the XeCl excimer laser (? = 308 nm) ablation of both Fe3O4 and metallic 57Fe targets. Deposition conditions have been investigated in an attempt to fabricate films reproducibly at low laser fluences so as to minimize ablation bouldering. The ablation of metallic Fe has

  18. UV pulsed laser deposition of magnetite thin films

    Microsoft Academic Search

    M. L. Paramês; J. Mariano; M. S. Rogalski; N. Popovici; O. Conde

    2005-01-01

    Magnetite thin films were grown by pulsed laser deposition in O2 reactive atmosphere from Fe3O4 targets. The ablated material was deposited onto Si(100) substrates at various temperatures up to 623K. The temperature dependence of structure and stoichiometry was investigated by X-ray diffraction (XRD) and conversion electron Mössbauer spectroscopy (CEMS). The XRD results show that films grown between 483 and 623K

  19. Magnetite films grown directly on organic semiconductor layers

    Microsoft Academic Search

    V. Dediu; E. Arisi; I. Bergenti; A. Riminucci; M. Murgia; G. Ruani

    2006-01-01

    Magnetite (Fe3O4) films were grown directly on thin layers of two organic semiconductors (p-conjugated oligomers), 8-hydroxyquinoline aluminium (Alq3) and sexitiophene (T6) by pulsed electron beam deposition, also called channel spark ablation (CSA), for which spin injection effects have been demonstrated at low and room temperatures. The room temperature ferromagnetism for both kind of films found by magneto-optical Kerr rotation (MOKE)

  20. Photoemission electronic states of epitaxially grown magnetite films

    Microsoft Academic Search

    R. Zalecki; A. Ko?odziejczyk; J. Korecki; N. Spiridis; M. Zaj?c; A. Koz?owski; Z. K?kol; D. Antolak

    2007-01-01

    The valence band photoemission spectra of epitaxially grown 300? single crystalline magnetite films were measured by the angle-resolved ultraviolet photoemission spectroscopy (ARUPS) at 300K. The samples were grown either on MgO(001) (B termination) or on (001) Fe (iron-rich A termination), thus intentionally presenting different surface stoichiometry, i.e. also different surface electronic states. Four main features of the electron photoemission at

  1. Magnetization and susceptibility of ion-irradiated granular magnetite films

    Microsoft Academic Search

    Weilin Jiang; John S. McCloy; Alan S. Lea; J. A. Sundararajan; Qi Yao; Y. Qiang

    2011-01-01

    Porous granular films of magnetite (Fe3O4) with grains of ˜3 nm in size were prepared using a state-of-the-art nanocluster deposition system. The films are initially superparamagnetic but become magnetized following Si2+ ion irradiation. A significant increase in the grain size and a dramatic change in the microstructure are observed. There are dipolar interactions between the nanoparticles in both the unirradiated

  2. Investigation of heteroepitaxial growth of magnetite thin films

    Microsoft Academic Search

    G. E. Sterbinsky; J. Cheng; P. T. Chiu; B. W. Wessels; D. J. Keavney

    2007-01-01

    Epitaxial magnetite (FeO) thin films were deposited by molecular beam epitaxy using molecular oxygen as the oxidant. Films deposited on (001) SrTiO, (001) MgO, and (001) BaTiO 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. Investigation of magnetite thin films produced by pulsed laser deposition

    Microsoft Academic Search

    H. J. Blythe; S. P. Sena; R. A. Lindley; G. A. Gehring; Ch. Sauer; M. Al-Kafarji

    1997-01-01

    Thin films of magnetite (Fe3O4) with thicknesses in the range 10-1000 nm have been produced by the XeCl excimer laser (lambda = 308 nm) ablation of both Fe3O4 and metallic e57Fe targets. Deposition conditions have been investigated in an attempt to fabricate films reproducibly at low laser fluences so as to minimize ablation bouldering. The ablation of metallic Fe has

  4. Interparticle spin-polarized tunneling in arrays of magnetite nanocrystals

    Microsoft Academic Search

    Nurit Taub; Alexander Tsukernik; Gil Markovich

    2009-01-01

    Inter-particle spin-polarized tunneling was measured in an organically capped magnetite nanocrystal (NC) array deposited between 30nm spaced gold electrodes. Magnetoresistance (MR) measurements performed around the blocking temperature (Tb) of the magnetic moments of the particles in the array, which was relatively high (220K), yielded negative MR values of the order of 10–25% under moderate magnetic fields of several kOe. The

  5. Magnetic and Spin-Transport Properties of Magnetite Nanoparticles

    Microsoft Academic Search

    Kai Liu; L. Zhao; P. Klavins; Frank E. Osterloh; H. Hiramatsu; S. B. Ritchey; C. S. Fadley

    2003-01-01

    Nanoparticles of magnetite (Fe_3O_4) have been synthesized using an aqueous precipitation technique. The particles are spherical in shape, with an average size of 8-9 nm and a small size distribution, revealed by transmission electron microscopy and atomic force microscopy. Structural and chemical characterizations have been carried out by x-ray diffraction, x-ray photoelectron spectroscopy, and chemical titration. Dispersed nanoparticles displays superparamagnetic

  6. Effect of grain boundaries on the magnetoresistance of magnetite

    Microsoft Academic Search

    S. I. Rybchenko; Y. Fujishiro; H. Takagi; M. Awano

    2005-01-01

    The effects of grain boundary morphology and stoichiometry had been systematically examined to clarify the role of natural grain boundaries in magnetoresistance of magnetite Fe3(1-delta)O4 . We found that the excess resistance, caused by presence of the grain boundaries, is negligibly low in stoichiometric polycrystals. Accordingly, there was no grain boundary magnetoresistance detected in dense polycrystals. Moreover, the incorporation of

  7. Magnetoresistance at grain boundaries artificially introduced into magnetite films

    Microsoft Academic Search

    M. Ziese; R. Höhne; N. H Hong; J. Dienelt; K. Zimmer; P. Esquinazi

    2002-01-01

    Magnetotransport data of step-edge junctions fabricated in magnetite (Fe3O4) films are presented. An enhancement of the low field magnetoresistance of these step-edge junctions as evidenced by measurements with the electrical current along and across the step edges was observed. This is especially pronounced in a film on patterned MgAl2O4 which additionally shows a significant geometrically induced resistivity anisotropy. The enhanced

  8. Polypyrrole coated magnetite nanoparticles from water based nanofluids

    NASA Astrophysics Data System (ADS)

    Turcu, R.; Pana, O.; Nan, A.; Craciunescu, I.; Chauvet, O.; Payen, C.

    2008-12-01

    The synthesis and characterization of hybrid structures obtained by coating Fe3O4 magnetic nanoparticles from water based nanofluid with a polypyrrole (PPy) layer are reported. The thin amorphous layer of polypyrrole surrounding the crystalline magnetic core was observed by HRTEM. The FTIR spectra of the nanocomposites show that the absorption bands characteristic for pyrrole ring vibrations significantly shifted to lower frequencies in the nanocomposite spectra, which indicates a higher degree of oxidation of the PPy shell covering the magnetite as compared with conventional PPy. The existence of superparamagnetism in the investigated nanocomposites is evidenced by the missing hysterezis loop in the magnetization versus applied magnetic field dependences. The comparison between the physical size of nanoparticles determined from TEM analysis and the magnetic size deduced from magnetization measurements is discussed. The surface modification of magnetite by polypyrrole coating results in an increase in the saturation magnetization and of the apparent magnetic diameter of the nanoparticles. This novel effect is attributed to a charge transfer process from the conducting polymer to the surface iron ions of magnetite, producing an increase in the surface contribution to the overall magnetic moment of the nanoparticles.

  9. Structural and magnetic properties of sonoelectrocrystallized magnetite nanoparticles

    NASA Astrophysics Data System (ADS)

    Mosivand, S.; Monzon, L. M. A.; Ackland, K.; Kazeminezhad, I.; Coey, J. M. D.

    2014-02-01

    The effect of ultrasound power on the morphology, structure and magnetic properties of magnetite nanoparticles synthesized from iron electrodes by the electro-oxidation method was investigated. Samples made in aqueous solution in the absence or presence of an organic stabilizer (thiourea, tetramethylammonium chloride, sodium butanoate or ?-cyclodextrine) were characterized by x-ray diffraction, transmission and scanning electron microscopy, magnetometry and Mössbauer spectrometry. The iron is almost all in the form of 20-85 nm particles of slightly nonstoichiometric Fe3-?O4, with ? ? 0.10. Formation of a paramagnetic secondary phase in the presence of sodium butanoate or ?-cyclodextrine is supressed by ultrasound. Specific magnetization of the magnetite nanoparticles ranges from 19 to 90 A m2 kg-1 at room temperature, and it increases with particle size in each series. The particles show no sign of superparamagnetism, and the anhysteretic and practically temperature-independent magnetization curves are associated with a stable magnetic vortex state throughout the size range. The spin structure of the particles and the use of magnetization measurements to detect magnetite in unknown mixtures are discussed.

  10. Lanthanide sorbent based on magnetite nanoparticles functionalized with organophosphorus extractants

    NASA Astrophysics Data System (ADS)

    Basualto, Carlos; Gaete, José; Molina, Lorena; Valenzuela, Fernando; Yañez, Claudia; Marco, Jose F.

    2015-06-01

    In this work, an adsorbent was prepared based on the attachment of organophosphorus acid extractants, namely, D2EHPA, CYANEX 272, and CYANEX 301, to the surface of superparamagnetic magnetite (Fe3O4) nanoparticles. The synthesized nanoparticles were coated with oleic acid, first by a chemisorption mechanism and later by the respective extractant via physical adsorption. The obtained core–shell functionalized magnetite nanoparticle composites were characterized by dynamic light scattering, scanning electron microscopy, transmission electron microscopy, thermogravimetry, infrared absorption and vibrating sample magnetometry. All the prepared nanoparticles exhibited a high saturation magnetization capacity that varied between 72 and 46 emu g?1 and decreased as the magnetite nanoparticle was coated with oleic acid and functionalized. The scope of this study also included adsorption tests for lanthanum, cerium, praseodymium, and neodymium and the corresponding analysis of their results. Sorption tests indicated that the functionalized nanoparticles were able to extract the four studied lanthanide metal ions, although the best extraction performance was observed when the sorbent was functionalized with CYANEX 272, which resulted in a loading capacity of approximately 12–14 mgLa/gMNP. The magnetization of the synthesized nanoparticles was verified during the separation of the lanthanide-loaded sorbent from the raffinate by using a conventional magnet.

  11. Stable ferrofluids of magnetite nanoparticles in hydrophobic ionic liquids

    NASA Astrophysics Data System (ADS)

    Mestrom, Luuk; Lenders, Jos J. M.; de Groot, Rick; Hooghoudt, Tonnis; Sommerdijk, Nico A. J. M.; Vilaplana Artigas, Marcel

    2015-07-01

    Ferrofluids (FFs) of metal oxide nanoparticles in ionic liquids (ILs) are a potentially useful class of magnetic materials for many applications because of their properties related to temperature/pressure stability, hydrophobicity, viscosity and recyclability. In this work, the screening of several designer surfactants for their stabilizing capabilities has resulted in the synthesis of stable FFs of superparamagnetic 7 ± 2 nm magnetite (Fe3O4) nanoparticles in the hydrophobic IL 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([CRMIM][NTf2]). The designed and synthesized 1-butyl-3-(10-carboxydecyl)-1H-imidazol-3-ium bromide (ILC10-COOH) surfactant that combines the same imidazole moiety as the IL with a long alkyl chain ensured compatibility with the IL and increased the steric repulsion between the magnetite nanoparticles sufficiently such that stable dispersions of up to 50 wt% magnetite were obtained according to stability tests in the presence of a magnetic field (0.5–1 Tesla). Cryo-transmission electron microscopy (cryo-TEM) of the IL-based FFs allowed direct visualization of the surfactant-stabilized nanoparticles in the ILs and the native, hardly aggregated state of their dispersion.

  12. Stable ferrofluids of magnetite nanoparticles in hydrophobic ionic liquids.

    PubMed

    Mestrom, Luuk; Lenders, Jos J M; de Groot, Rick; Hooghoudt, Tonnis; Sommerdijk, Nico A J M; Artigas, Marcel Vilaplana

    2015-07-17

    Ferrofluids (FFs) of metal oxide nanoparticles in ionic liquids (ILs) are a potentially useful class of magnetic materials for many applications because of their properties related to temperature/pressure stability, hydrophobicity, viscosity and recyclability. In this work, the screening of several designer surfactants for their stabilizing capabilities has resulted in the synthesis of stable FFs of superparamagnetic 7 ± 2 nm magnetite (Fe3O4) nanoparticles in the hydrophobic IL 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([CRMIM][NTf2]). The designed and synthesized 1-butyl-3-(10-carboxydecyl)-1H-imidazol-3-ium bromide (ILC10-COOH) surfactant that combines the same imidazole moiety as the IL with a long alkyl chain ensured compatibility with the IL and increased the steric repulsion between the magnetite nanoparticles sufficiently such that stable dispersions of up to 50 wt% magnetite were obtained according to stability tests in the presence of a magnetic field (0.5-1 Tesla). Cryo-transmission electron microscopy (cryo-TEM) of the IL-based FFs allowed direct visualization of the surfactant-stabilized nanoparticles in the ILs and the native, hardly aggregated state of their dispersion. PMID:26118409

  13. Magnetic Microstructure of Closely-Spaced Ferrimagnetic Crystals in Magnetotactic Bacteria

    E-print Network

    Dunin-Borkowski, Rafal E.

    Magnetic Microstructure of Closely-Spaced Ferrimagnetic Crystals in Magnetotactic Bacteria R. E of Cambridge, Pembroke Street, Cambridge CB2 3QZ, United Kingdom Magnetotactic bacteria migrate along of magnetite and greigite crystals in air-dried cells of magnetotactic bacteria, with sub-10-nm spatial

  14. Pure and Applied Chemistry

    NSDL National Science Digital Library

    Established in 1960, the journal Pure and Applied Chemistry is committed to publishing notable research papers arising from various international scientific events and projects that are sponsored by the International Union of Pure and Applied Chemistry (IUPAC). First-time visitors can view the "News" area to learn about the most recent work published in the journal, and then they may wish to move on to the embedded search engine displayed prominently on the homepage. Other sections on the site include "Editorial Board", "Notes For Authors", and "Publication Policy". Visitors with a deep and abiding interest in the journal may also wish to consult their RSS feeds, which include those related to the publication of new articles and reports from the IUPAC. Finally, the site also contains a drop down menu titled "PAC Archives" where visitors can browse the contents of each volume.

  15. Production of nano zinc, zinc sulphide and nanocomplex of magnetite zinc oxide by Brevundimonas diminuta and Pseudomonas stutzeri.

    PubMed

    Mirhendi, Mansoureh; Emtiazi, Giti; Roghanian, Rasoul

    2013-12-01

    ZnO (Zincite) nanoparticle has many industrial applications and is mostly produced by chemical reactions, usually prepared by decomposition of zinc acetate or hot-injection and heating-up method. Synthesis of semi-conductor nanoparticles such as ZnS (Sphalerite) by ultrasonic was previously reported. In this work, high-zinc tolerant bacteria were isolated and used for nano zinc production. Among all isolated microorganisms, a gram negative bacterium which was identified as Brevundimonas diminuta could construct nano magnetite zinc oxide on bacterial surface with 22 nm in size and nano zinc with 48.29 nm in size. A piece of zinc metal was immersed in medium containing of pure culture of B. diminuta. Subsequently, a yellow-white biofilm was formed which was collected from the surface of zinc. It was dried at room temperature. The isolated biofilm was analysed by X-ray diffractometer. Interestingly, the yield of these particles was higher in the light, with pH 7 at 23°C. To the best of the authors knowledge, this is the first report about the production of nano zinc metal and nano zinc oxide that are stable and have anti-bacterial activities with magnetite property. Also ZnS (sized 12 nm) produced by Pseudomonas stutzeri, was studied by photoluminescence and fluorescent microscope. PMID:24206770

  16. Purely electromagnetic spacetimes

    SciTech Connect

    Ivanov, B. V. [Institute for Nuclear Research and Nuclear Energy, Bulgarian Academy of Sciences Tzarigradsko Shausse 72, Sofia 1784 (Bulgaria)

    2008-02-15

    The Rainich's program of describing metrics induced by pure electromagnetic fields is implemented in a simpler way by using the Ernst formalism and increasing the symmetry of spacetime. Stationary metrics possessing one, two or three Killing vectors are studied and classified. Three branches of solutions exist. Electromagnetically induced mass terms appear in two of them, including a class of solutions in harmonic functions. The static subcase is discussed too. Relations to other well-known electrovacuum metrics are elucidated.

  17. Pure Lovelock Kasner metrics

    E-print Network

    Camanho, Xián O; Molina, Alfred

    2015-01-01

    We study pure Lovelock vacuum and perfect fluid equations for Kasner-type metrics. These equations correspond to a single $N$th order Lovelock term in the action in $d=2N+1,\\,2N+2$ dimensions, and they capture the relevant gravitational dynamics when aproaching the big-bang singularity within the Lovelock family of theories. Pure Lovelock gravity also bears out the general feature that vacuum in the critical odd dimension, $d=2N+1$, is kinematic; i.e. we may define an analogue Lovelock-Riemann tensor that vanishes in vacuum for $d=2N+1$, yet the Riemann curvature is non-zero. We completely classify isotropic and vacuum Kasner metrics for this class of theories in several isotropy types. The different families can be characterized by means of certain higher order 4th rank tensors. We also analyze in detail the space of vacuum solutions for five and six dimensional pure Gauss-Bonnet theory. It possesses an interesting and illuminating geometric structure and symmetries that carry over to the general case. We al...

  18. Pure Lovelock Kasner metrics

    E-print Network

    Xián O. Camanho; Naresh Dadhich; Alfred Molina

    2015-05-25

    We study pure Lovelock vacuum and perfect fluid equations for Kasner-type metrics. These equations correspond to a single $N$th order Lovelock term in the action in $d=2N+1,\\,2N+2$ dimensions, and they capture the relevant gravitational dynamics when aproaching the big-bang singularity within the Lovelock family of theories. Pure Lovelock gravity also bears out the general feature that vacuum in the critical odd dimension, $d=2N+1$, is kinematic; i.e. we may define an analogue Lovelock-Riemann tensor that vanishes in vacuum for $d=2N+1$, yet the Riemann curvature is non-zero. We completely classify isotropic and vacuum Kasner metrics for this class of theories in several isotropy types. The different families can be characterized by means of certain higher order 4th rank tensors. We also analyze in detail the space of vacuum solutions for five and six dimensional pure Gauss-Bonnet theory. It possesses an interesting and illuminating geometric structure and symmetries that carry over to the general case. We also comment on a closely related family of exponential solutions and on the possibility of solutions with complex Kasner exponents. We show that the latter imply the existence of closed timelike curves in the geometry.

  19. Application of magnetite hexacyanoferrate composites in magnetically assisted chemical separation of cesium

    Microsoft Academic Search

    R. D. Ambashta; D. S. Deshingkar; P. K. Wattal; D. Bahadur

    2006-01-01

    Summary  Potassium nickel hexacyanoferrate composite with magnetite finds application in the recovery of cesium from low-level liquid\\u000a waste using magnetic assistance. The apparent sorption capability of hexacyanoferrate-magnetite composite and potassium nickel(II)\\u000a hexacyanoferrate(II) matched indicating no loss in sorption capability as a consequence of coating to nanoscale magnetite\\u000a substrate. Selectivity for cesium in a broad pH range, selectivity in the presence of

  20. Selective Product of Magnetite through Addition of Small Amount of Metal Element

    Microsoft Academic Search

    Seishi Abe; De Hai Ping; Masato Ohnuma; Shigehiro Ohnuma

    2011-01-01

    In this study, we investigate the transformation mechanism from a phase mixture of magnetite (Fe3O4) and hematite (alpha-Fe2O3) to a single-phase magnetite through the addition of a specific metal element. The thin films were prepared by rf sputtering with a composite target of metal chips set on a ceramic magnetite (or hematite) target in Ar atmosphere. It is revealed that

  1. Bias and temperature dependence on junction magnetoresistance in manganite\\/magnetite based magnetic tunnel junctions

    Microsoft Academic Search

    Rajesh Chopdekar; Guohan Hu; Yuri Suzuki

    2005-01-01

    Studies of the bias and temperature dependence of junction magnetoresistance (JMR) in manganite\\/magnetite trilayer junctions have revealed non-monotonic dependence on both quantities. Such junctions were constructed to probe the spin-polarization of magnetite using the well-established majority spin-polarized oxide (La,Sr)MnO3 as a counter-electrode. We have found that using an isostructural oxide cobalt chromite tunnel barrier reduces disorder at the chromite-magnetite interface

  2. Searching for a magnetic proximity effect in magnetite–carbon structures

    Microsoft Academic Search

    R. Höhne; M. Ziese; P. Esquinazi

    2004-01-01

    In order to study a possible magnetic proximity effect in magnetite–carbon structures, we have performed magnetization measurements of graphite–magnetite composites with different mass ratios as well as the measurement of the magnetoresistance of one of them and of the magnetization of a magnetite–carbon bilayer. The overall results do not indicate the induction of bulk ferromagnetism in graphite and disordered carbon

  3. Experimental Shock Decomposition of Siderite and the Origin of Magnetite in Martian Meteorite ALH84001

    NASA Technical Reports Server (NTRS)

    Bell, Mary Sue

    2007-01-01

    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), Mossbauer spectroscopy, and magnetic susceptibility measurements to be sure that the starting material did not contain detectable magnetite. Samples were shocked in tungsten-alloy holders (W=90%, Ni=6%, Cu=4%) to further insure that any iron phases in the shock products were contributed by the siderite rather than the sample holder. Each sample was shocked to a specific pressure between 30 to 49 GPa. Previously reported results of TEM analyses on 49 GPa experiments indicated the presence of nano-phase spinel-structured iron oxide. Transformation of siderite to magnetite as characterized by TEM was found in the 49 GPa shock experiment. Compositions of most magnetites are greater than 50% Fe sup(+2) in the octahedral site of the inverse spinel structure. Magnetites produced in shock experiments display the same range of single-domain, superparamagnetic sizes (approx. 50 100 nm), compositions (100% magnetite to 80% magnetite-20% magnesioferrite), and morphologies (equant, elongated, euhedral to subhedral) as magnetites synthesized by Golden et al. (2001) or magnetites grown naturally by MV1 magnetotactic bacteria, and as the magnetites in Martian meteorite ALH84001. Fritz et al. (2005) previously concluded that ALH84001 experienced approx. 32 GPa pressure and a resultant thermal pulse of approx. 100 - 110 C. However, ALH84001 contains evidence of local temperature excursions high enough to 1 melt feldspar, pyroxene, and a silica-rich phase. This 49 GPa experiment demonstrates that magnetite can be produced by the shock decomposition of siderite as a result of local heating to greater than 470 C. Therefore, magnetite in the rims of carbonates in Martian meteorite ALH84001 could be a product of shock devolatilization of siderite as well.

  4. Reaction of U-VI with titanium-substituted magnetite: Influence of Ti on U-IV speciation

    SciTech Connect

    Latta, Drew; Pearce, Carolyn I.; Rosso, Kevin M.; Kemner, Kenneth M.; Boyanov, Maxim I.

    2013-07-01

    Reduction of hexavalent uranium (UVI) to less soluble tetravalent uranium (UIV) through enzymatic or abiotic redox reactions has the potential to alter U mobility in subsurface environments. As a ubiquitous natural mineral, magnetite (Fe3O4) is of interest because of its ability to act as a rechargeable reductant for UVI. Natural magnetites are often impure with titanium, and structural Fe3+ replacement by TiIV yields a proportional increase in the relative Fe2+ content in the metal sublattice to maintain bulk charge neutrality. In the absence of oxidation, the Ti content sets the initial bulk Fe2+/Fe3+ ratio (R). Here, we demonstrate that Ti-doped magnetites (Fe3 xTixO4) reduce UVI to UIV. The UVI-Fe2+ redox reactivity was found to be controlled directly by R, but was otherwise independent of Ti content (xTi). However, in contrast to previous studies with pure magnetite where UVI was reduced to nanocrystalline uraninite (UO2), the presence of structural Ti (xTi = 0.25 0.53) results in the formation of UIV species that lack the bidentate U-O2-U bridges of uraninite. Extended x-ray absorption fine structure spectroscopic analysis indicated that the titanomagnetite-bound UIV phase has a novel UIV-Ti binding geometry, different from the coordination of UIV in the mineral brannerite (UIVTi2O6). The observed UIV-Ti coordination at a distance of 3.43 Å suggests a binuclear corner-sharing adsorption/incorporation UIV complex with the solid phase. Furthermore, we explored the effect of oxidation (decreasing R) and solids-to-solution ratio on the reduced UIV phase. The formation of the non-uraninite UIV-Ti phase appears to be controlled by availability of surface Ti sites, rather than R. Our work highlights a previously unrecognized role of Ti in the environmental chemistry of UIV and suggests that further work to characterize the long-term stability of UIV phases formed in the presence of Ti is warranted.

  5. Reaction of U(VI) with titanium-substituted magnetite: influence of Ti on U(IV) speciation.

    PubMed

    Latta, Drew E; Pearce, Carolyn I; Rosso, Kevin M; Kemner, Kenneth M; Boyanov, Maxim I

    2013-05-01

    Reduction of hexavalent uranium (U(VI)) to less soluble tetravalent uranium (U(IV)) through enzymatic or abiotic redox reactions has the potential to alter U mobility in subsurface environments. As a ubiquitous natural mineral, magnetite (Fe3O4) is of interest because of its ability to act as a rechargeable reductant for U(VI). Natural magnetites are often impure with titanium, and structural Fe(3+) replacement by Ti(IV) yields a proportional increase in the relative Fe(2+) content in the metal sublattice to maintain bulk charge neutrality. In the absence of oxidation, the Ti content sets the initial bulk Fe(2+)/Fe(3+) ratio (R). Here, we demonstrate that Ti-doped magnetites (Fe3 - xTixO4) reduce U(VI) to U(IV). The U(VI)-Fe(2+) redox reactivity was found to be controlled directly by R but was otherwise independent of Ti content (xTi). However, in contrast to previous studies with pure magnetite where U(VI) was reduced to nanocrystalline uraninite (UO2), the presence of structural Ti (xTi = 0.25-0.53) results in the formation of U(IV) species that lack the bidentate U-O2-U bridges of uraninite. Extended X-ray absorption fine structure spectroscopic analysis indicated that the titanomagnetite-bound U(IV) phase has a novel U(IV)-Ti binding geometry different from the coordination of U(IV) in the mineral brannerite (U(IV)Ti2O6). The observed U(IV)-Ti coordination at a distance of 3.43 Å suggests a binuclear corner-sharing adsorption/incorporation U(IV) complex with the solid phase. Furthermore, we explored the effect of oxidation (decreasing R) and solids-to-solution ratio on the reduced U(IV) phase. The formation of the non-uraninite U(IV)-Ti phase appears to be controlled by availability of surface Ti sites rather than R. Our work highlights a previously unrecognized role of Ti in the environmental chemistry of U(IV) and suggests that further work to characterize the long-term stability of U(IV) phases formed in the presence of Ti is warranted. PMID:23597442

  6. Tuning of multiferroic orders correlated to oxygen stoichiometry in magnetite films

    NASA Astrophysics Data System (ADS)

    Dey, K.; Ghosh, A.; Modak, P.; Indra, A.; Majumdar, S.; Giri, S.

    2014-10-01

    Magnetite films are grown on Si(100) substrate using pulsed laser deposition technique. The deposition is performed at three fixed oxygen pressures of 0.4 × 10-6, 4.0 × 10-6, and 10 × 10-6 Torr keeping other conditions fixed. Raman and x-ray photoemission spectroscopies confirm formation of single magnetite phase for the first two pressures and a mixed phase composed of magnetite and hematite for the highest pressure. A trivial change in oxygen stoichiometry of magnetite is found crucial for the multiferroic orders at room temperature and below the charge ordering temperature. Possible mechanisms of multiferroic orders driven by change in oxygen stoichiometry are discussed.

  7. Synthesis of chiral hybrid nanotubes of magnetite nanoparticles and conducting polymers

    NASA Astrophysics Data System (ADS)

    Mitsumori, Masashi; Nakahodo, Tsukasa; Fujihara, Hisashi

    2011-12-01

    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

  8. Synthesis, characterization and magnetoresistance properties study of magnetite thin films by electroless plating in aqueous solution

    Microsoft Academic Search

    Jianrong Sun; Zhiguang Wang; Yuyu Wang; Yabin Zhu; Kongfang Wei; Tielong Shen; Fashen Li

    Polycrystalline half-metallic Fe3O4 films with 1 ?m in thickness were synthesized on glass substrates directly by electroless plating in aqueous solution at 90 °C without heat treatment. The films have single pure spinal phase structure and the well-crystallized columnar grains grow perpendicularly to the substrates, as revealed by XRD, XPS and SEM. At room temperature, the films exhibit negative magnetoresistance (MR) ratio

  9. Experimental shock decomposition of siderite and the origin of magnetite in Martian meteorite ALH 84001

    NASA Astrophysics Data System (ADS)

    Bell, M. S.

    2007-06-01

    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 a variety of techniques to be sure that the starting material did not contain detectable magnetite. Samples were shocked in tungsten-alloy holders (W = 90%, Ni = 6%, Cu = 4%) to further ensure that any iron phases in the shock products were contributed by the siderite rather than the sample holder. Each sample was shocked to a specific pressure between 30 to 49 GPa. Transformation of siderite to magnetite as characterized by TEM was found in the 49 GPa shock experiment. Compositions of most magnetites are >50% Fe+2 in the octahedral site of the inverse spinel structure. Magnetites produced in shock experiments display the same range of sizes (˜50-100 nm), compositions (100% magnetite to 80% magnetite-20% magnesioferrite), and morphologies (equant, elongated, euhedral to subhedral) as magnetites synthesized by Golden et al. (2001) and as the magnetites in Martian meteorite Allan Hills (ALH) 84001. Fritz et al. (2005) previously concluded that ALH 84001 experienced ˜32 GPa pressure and a resultant thermal pulse of ˜100-110 °C. However, ALH 84001 contains evidence of local temperature excursions high enough to melt feldspar, pyroxene, and a silica-rich phase. This 49 GPa experiment demonstrates that magnetite can be produced by the shock decomposition of siderite as a result of local heating to > 470 °C. Therefore, magnetite in the rims of carbonates in Martian meteorite ALH 84001 could be a product of shock devolatilization of siderite as well.

  10. Crystal structures of carbonates up to Mbar pressures determined by single crystal synchrotron radiation diffraction

    NASA Astrophysics Data System (ADS)

    Merlini, M.

    2013-12-01

    The recent improvements at synchrotron beamlines, currently allow single crystal diffraction experiments at extreme pressures and temperatures [1,2] on very small single crystal domains. We successfully applied such technique to determine the crystal structure adopted by carbonates at mantle pressures. The knowledge of carbon-bearing phases is in fact fundamental for any quantitative modelling of global carbon cycle. The major technical difficulty arises after first order transitions or decomposition reactions, since original crystal (apx. 10x10x5 ?m3) is transformed in much smaller crystalline domains often with random orientation. The use of 3D reciprocal space visualization software and the improved resolution of new generation flat panel detectors, however, allow both identification and integration of each single crystal domain, with suitable accuracy for ab-initio structure solution, performed with direct and charge-flipping methods and successive structure refinements. The results obtained on carbonates, indicate two major crystal-chemistry trends established at high pressures. The CO32- units, planar and parallel in ambient pressure calcite and dolomite structures, becomes non parallel in calcite- and dolomite-II and III phases, allowing more flexibility in the structures with possibility to accommodate strain arising from different cation sizes (Ca and Mg in particular). Dolomite-III is therefore also observed to be thermodynamically stable at lower mantle pressures and temperatures, differently from dolomite, which undergoes decomposition into pure end-members in upper mantle. At higher pressure, towards Mbar (lowermost mantle and D'' region) in agreement with theoretical calculations [3,4] and other experimental results [5], carbon coordination transform into 4-fold CO4 units, with different polymerisation in the structure depending on carbonate composition. The second important crystal chemistry feature detected is related to Fe2+ in Fe-bearing magnesite, which spontaneously oxidises at HP/HT, forming Fe3+ carbonates, Fe3+ oxides and reduced carbon (diamonds). Single crystal diffraction approach allowed full structure determination of these phases, yielding to the discovery of few unpredicted structures, such as Mg2Fe2C4O13 and Fe13O19, which can be well reproduced in different experiments. Mg2Fe2C4O13 carbonate present truncated chain C4O13 groups, and Fe13O19 oxide, whose stoichiometry is intermediate between magnetite and hematite, is a one-layer structure, with features encountered in superconducting materials. The results fully support the ideas of unexpected complexities in the mineralogy of the lowermost mantle, and single crystal technique, once properly optimized in ad-hoc synchrotron beamlines, is fundamental for extracting accurate structural information, otherwise rarely accessible with other experimental techniques. References: [1] Merlini M., Hanfland M. (2013). Single crystal diffraction at Mbar conditions by synchrotron radiation. High Pressure Research, in press. [2] Dubrovinsky et al., (2010). High Pressure Research, 30, 620-633. [3] Arapan et al. (1997). Phys. Rev. Lett., 98, 268501. [4] Oganov et al. (2008) EPSL, 273, 38-47. [5] Boulard et al. (2011) PNAS, 108, 5184-5187.

  11. Electrical impedance spectroscopy investigation of surfactant-magnetite-polypyrrole particles.

    PubMed

    de Oliveira, H P; Andrade, C A S; de Melo, C P

    2008-03-15

    We report an electrical impedance spectroscopy (EIS) characterization of composite systems formed by emulsion polymerization of polypyrrole (PPY) in concentrated aqueous solutions of sodium dodecyl sulfate (SDS) containing dispersed magnetite particles. SDS-(Fe3O4)-(conducting polymer) microaggregates with different iron contents were prepared by varying in a reciprocal manner the relative amounts of the metal oxide and PPY. We have measured the zeta-potential and the average size of the corresponding dispersed particles and examined their relative composition through energy dispersive X-ray (EDX) microanalysis and Fourier transform infrared (FTIR) spectroscopy. Important aspects of the charge transport in these composite particles can be identified by mapping the real and imaginary parts of their complex impedance as a function of the frequency of the applied external electric field. For instance, for binary composites SDS-(Fe3O4) polarization effects are dominant at the low-frequency regime, with a well-defined dielectric relaxation easily identifiable. On the other hand, when the relative amount of PPY is progressively increased in the ternary SDS-(Fe3O4)-PPY composites, a transition between different charge transport mechanisms is observed at higher frequencies. The EIS results suggest that in these ternary aggregates the PPY chains envelop the metal oxide clusters and effectively shield them from the external field, and that only in binary samples that do not contain PPY is that the surfactant molecules can directly enclose the magnetite particles. These results are consistent with the fact that the average size of the aggregates in the ternary composites is in general larger than those of either SDS-PPY or SDS-magnetite binary particles. PMID:18155017

  12. Mechanism of fast growth of magnetite on carbon steel

    SciTech Connect

    Macdonald, D.D.

    1985-07-01

    The corrosion of and the growth of magnetite on carbon steel in chloride-containing aqueous solutions at temperatures from 200 to 270/sup 0/C and for times up to 400 hours have been studied using ac impedance and scanning electron microscopy techniques. Thick and porous magnetite films form in solutions which are acidic because of the presence of HCL or by hydrolysis of cupric, ferric, nickelous and ferrous chlorides. The reciprocal of the polarization resistance, which is proportional to the corrosion rate, increases with time (i.e., autocatalysis), but eventually tends to a constant value (i.e., a linear rate law). Autocatalytic corrosion is attributed to the gradual development of a highly aggressive solution within the porous film due to the hydrolysis of ferrous ions dissolved from the base metal and the transport of chloride ions from the bulk solution into the pores. However, the reciprocal decreases with time (i.e., self-passivation) when thin and compact magnetite films form in neutral or slightly acidic chloride solutions. The frequency dispersion of the impedance of the growing film has been successfully accounted for by a finite electrical transmission line model. Numerical analysis has shown that the total impedance is a sensitive function of the film geometry and of the inter-facial impedances along the pore wall and at the base of the pore. These analyses have demonstrated that the ac impedance technique is well suited for studying the corrosion of metals and the growth of corrosion product films in aqueous systems. 39 refs., 25 figs., 1 tab.

  13. Preparation of size-controlled nanoparticles of magnetite

    NASA Astrophysics Data System (ADS)

    Andrade, Ângela L.; Valente, Manuel A.; Ferreira, José M. F.; Fabris, José D.

    2012-05-01

    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.

  14. Rheological Study of Dextran-Modified Magnetite Nanoparticle Water Suspension

    NASA Astrophysics Data System (ADS)

    Józefczak, A.; Hornowski, T.; Rozynek, Z.; Skumiel, A.; Fossum, J. O.

    2013-04-01

    The aim of this work is to investigate the effect of surface modification of superparamagnetic magnetite nanoparticles (sterically stabilized by sodium oleate) by the dextran biocompatible layer on the rheological behavior of water-based magnetic fluids. The flow curves were measured as a function of the magnetic field strength by means of rheometry. The measured viscosity is generally dependent on both the particle concentration and the geometrical factors such as the particle shape and thickness of the adsorbed layers. The rheological properties of the magnetic fluids studied show the effect of the magnetic field strength and the presence of the surfactant second layer (dextran) on their viscosity.

  15. Sticking polydisperse hydrophobic magnetite nanoparticles to lipid membranes.

    PubMed

    Paulus, Michael; Degen, Patrick; Brenner, Thorsten; Tiemeyer, Sebastian; Struth, Bernd; Tolan, Metin; Rehage, Heinz

    2010-10-19

    The formation of a layer of hydrophobic magnetite (Fe(3)O(4)) nanoparticles stabilized by lauric acid is analyzed by in situ X-ray reflectivity measurements. The data analysis shows that the nanoparticles partially disperse their hydrophobic coating. Consequently, a Langmuir layer was formed by lauric acid molecules that can be compressed into an untilted condensed phase. A majority of the nanoparticles are attached to the Langmuir film integrating lauric acid residue on their surface into the Langmuir film. Hence, the particles at the liquid-gas interface can be identified as so-called Janus beads, which are amphiphilic solids having two sides with different functionality. PMID:20873726

  16. Observation of inverse magnetoresistance in epitaxial magnetite\\/manganite junctions

    Microsoft Academic Search

    Guohan Hu; Rajesh Chopdekar; Y. Suzuki

    2003-01-01

    We have fabricated and characterized epitaxial Fe3O4\\/CoCr2O4\\/La0.7Sr0.3MnO3 magnetic trilayer junctions (MTJs) grown on (110) and (100) SrTiO3 substrates. Large inverse junction magnetoresistance (JMR) as high as -25% has been observed at a field of 4 kOe in (110) oriented MTJs. The improvement of the JMR over that observed in previous epitaxial magnetite junctions is attributed to the choice of the

  17. Grain size dependence of low-temperature remanent magnetization in natural and synthetic magnetite: Experimental study

    Microsoft Academic Search

    A. V. Smirnov

    2009-01-01

    Magnetic measurements at cryogenic temperatures (<300 K) proved to be useful in paleomagnetic and rock magnetic research, stimulating continuous interest to low-temperature properties of magnetite and other magnetic minerals. Here I report new experimental results on a grain size dependence of the ratio (RLT) between a low-temperature (20 K) saturation isothermal remanent magnetization (SIRM) imparted in magnetite after cooling in

  18. Diagenetic magnetite carries ancient yet secondary remanence in some Paleozoic sedimentary carbonates

    Microsoft Academic Search

    Chad McCabe; Rob van der Voo; Donald R. Peacor; Christopher R. Scotese; Roy Freeman

    1983-01-01

    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

  19. Hydrothermal synthesis of magnetite nanoparticles via sequential formation of iron hydroxide precipitates

    Microsoft Academic Search

    Tomohiro Iwasaki; Naoya Mizutani; Satoru Watano; Takeshi Yanagida; Tomoji Kawai

    2012-01-01

    A novel method for preparing fine magnetite nanoparticles without using any additives and organic solvents has been developed. In this method, a sequential precipitates formation method, ferrous and ferric hydroxides are not coprecipitated but sequentially formed in an alkaline solution, and then the resulting suspension is subjected to a hydrothermal treatment. The obtained magnetite nanoparticles were characterised through scanning electron

  20. Accessible and green manufacturing of magnetite (ferrous ferric oxide) nanocrystals and their use in magnetic separations

    NASA Astrophysics Data System (ADS)

    Yavuz, Cafer Tayyar

    This work describes the first size dependent magnetic separation in nanoscale. Magnetite (Fe3O4) nanocrystals of high quality and uniform size were synthesized with monodispersity below 10%. Magnetite nanocrystals of 4 nm to 33 nm (average diameter) were produced. Batch synthesis was shown to go up to 20 grams which is more than 10 times of a standard nanocrystal synthesis, without loosing the quality and monodispersity. Reactor design for mass (1 gram per hour) production of magnetite nanocrystals is reported for the first time. The cost of a kg of lab purity magnetite nanocrystals was shown to be 2600. A green synthesis that utilizes rust and edible oils was developed. The cost of a kg was brought down to 22. Size dependency of magnetism was shown in nanoscale for the first time. Reversible aggregation theory was developed to explain the low field magnetic separation and solution behavior of magnetite nanocrystals. Arsenic was removed from drinking water with magnetite nanocrystals 200 times better than commercial adsorbents. Silica coating was successfully applied to enable the known silica related biotechnologies. Magnetite-silica nanoshells were functionalized with amino groups. For the first time, silver was coated on the magnetite-silica nanoshells to produce triple multishells. Anti-microbial activity of multishells is anticipated.

  1. Physical and chemical properties of nanoscale magnetite-based solvent extractant

    Microsoft Academic Search

    Ritu D. Ambashta; Seikh Mohammad Yusuf; Mayuresh D. Mukadam; Sher Singh; Piaray Kishan Wattal; Dhirendra Bahadur

    2005-01-01

    Nanoscale magnetite bearing magnetic carrier with an adsorbed layer of dibenzo-18-crown-6 was evaluated for removing radionuclides from nuclear waste solutions using magnetically assisted separation method. TEM results indicate that the average size of the base magnetite particles is ?19 nm. The results of Mössbauer spectroscopy and field cooled (FC) and zero field cooled (ZFC) magnetization confirm the superparamagnetic behaviour of

  2. Physical and chemical properties of nanoscale magnetite-based solvent extractant

    Microsoft Academic Search

    Ritu D. Ambashta; Seikh Mohammad Yusuf; Mayuresh D. Mukadam; Sher Singh; Piaray Kishan Wattal; Dhirendra Bahadur

    2005-01-01

    Nanoscale magnetite bearing magnetic carrier with an adsorbed layer of dibenzo-18-crown-6 was evaluated for removing radionuclides from nuclear waste solutions using magnetically assisted separation method. TEM results indicate that the average size of the base magnetite particles is ˜19 nm. The results of Mössbauer spectroscopy and field cooled (FC) and zero field cooled (ZFC) magnetization confirm the superparamagnetic behaviour of

  3. Internal magnetic field effects on the photochemistry of a xanthone derivate covalently anchored to magnetite nanoparticles

    NASA Astrophysics Data System (ADS)

    Alvaro, Mercedes; Cabeza, Jose F.; Carbonell, Esther; Garcia, Hermenegildo

    2005-07-01

    Irradiation of azaxanthone in the presence of colloidal magnetite nanoparticles gives rise to the generation of the corresponding azaxanthone triplet, whose lifetime is influenced by internal magnetic field effects. In contrast, covalent tethering between magnetite and azaxanthone promotes photoinduced electron transfer leading to the observation of azaxanthone radical anion.

  4. Synthesis of magnetite nanoparticles with ferric iron recovered from acid mine drainage: Implications for environmental engineering

    Microsoft Academic Search

    Xinchao Wei; Roger C. Viadero Jr.

    2007-01-01

    The synthesis of magnetite nanoparticles has been the focus of numerous recent research efforts, with emerging focus on environmental applications. In previous research, reagent-grade chemicals have been used as the iron source in magnetite nanoparticle synthesis, which presents an economic challenge to the application of this technology in areas such as water and wastewater treatment. It is known that acid

  5. Morphology of thin nanocomposite films of asymmetric diblock copolymer and magnetite nanoparticles

    E-print Network

    Morphology of thin nanocomposite films of asymmetric diblock copolymer and magnetite nanoparticles nanocomposite films of asymmetric diblock copolymer and magnetite nanoparticles Valeria Lauter1,3 , Peter M films of an asymmetric diblock copolymer and nanoparticles are fabricated. The morphologies of the films

  6. Magnesium outdiffusion through magnetite films grown on magnesium oxide (001) (abstract)

    E-print Network

    Diebold, Ulrike

    Magnesium outdiffusion through magnetite films grown on magnesium oxide (001) (abstract) K. A. Shaw the cubic constant of magnetite, Fe3O4, 8.396 Å , which is already strained in thin-film growth Scanning tunneling microscopy STM studies of 1 m thick films of single crystalline Fe3O4 grown on MgO 001

  7. 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)

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

    2009-02-01

    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.

  8. Structure-Disorder induced MagnetoResistance intensification on spin-dependent-conduction in magnetite (Fe3O4) thin film produced by RF magnetron sputtering method

    Microsoft Academic Search

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

    2009-01-01

    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

  9. Preparing a magnetically responsive single-wall carbon nanohorn colloid by anchoring magnetite nanoparticles.

    PubMed

    Utsumi, Shigenori; Urita, Koki; Kanoh, Hirofumi; Yudasaka, Masako; Suenaga, Kazutomo; Iijima, Sumio; Kaneko, Katsumi

    2006-04-13

    A single-wall carbon nanohorn (SWNH) colloid was made to be magnetically responsive by anchoring magnetite nanoparticles prepared by the homogeneous mixing of FeCl(2)-FeCl(3) and NaOH solutions. Transmission electron microscopy observation showed the high dispersion of magnetite particles of 2-9 nm on the surface of the SWNH colloid, coinciding with the broad X-ray diffraction peaks of the magnetites. The magnetization measurements showed that the magnetite nanoparticles-anchored SWNH (mag-SWNH) colloid has the hybrid property of ferrimagnetism and superparamagnetism. It was demonstrated that mag-SWNH colloid dispersed in water by sonication responded to an external magnetic field, gathering toward a magnet. N(2) adsorption experiments showed the high nanoporosity of mag-SWNHs and that magnetite nanoparticles were preferably anchored at "nanowindow" sites and the entrance sites of interstitial pores. This magnetically responsive SWNH colloid should contribute to the field of drug delivery. PMID:16599481

  10. Simple and facile approach to synthesize magnetite nanoparticles and assessment of their effects on blood cells

    NASA Astrophysics Data System (ADS)

    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

    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.

  11. IR spectroscopic investigation of adsorption of oleic and stearic acids on a magnetite surface from CCI4 solutions

    Microsoft Academic Search

    V. V. Korolev; L. N. Savina

    1994-01-01

    Adsorption of oleic and stearic acids on a magnetite surface from CCl4 solutions is investigated by the methods of internal reflection spectroscopy and classical transmission spectroscopy. Highly dispersed magnetite with a particle size from 2 to 20 nm was obtained by the method of chemical condensation. It was found from the IR spectra that after the synthesis, the magnetite surface

  12. Off-axis electron holography observation of magnetic microstructure in a magnetite (001) thin film containing antiphase domains

    E-print Network

    Dunin-Borkowski, Rafal E.

    Off-axis electron holography observation of magnetic microstructure in a magnetite (001) thin film; published 21 March 2006 Magnetic remanent states in a self-supporting 25-nm-thick magnetite 001 film for use in spin valve devices, attempts to integrate magnetite films into multilayer structures using Mg

  13. Investigation of the Presence of Charge Order in Magnetite by Measurement of the Sprin Wave Spectrum

    SciTech Connect

    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

    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.

  14. Cell-surface interactions involving immobilized magnetite nanoparticles on flat magnetic substrates.

    PubMed

    Loichen, Juliane; Hartmann, Uwe

    2009-09-01

    A new method to affect cells by cell-surface interaction is introduced. Biocompatible magnetic nanobeads are deposited onto a biocompatible magnetic thin layer. The particles are composed of small magnetite crystals embedded in a matrix which can be functionalized by different molecules, proteins or growth factors. The magnetic interaction between surface and beads prevents endocytosis if the setup is utilized for cell culturing. The force acting between particles and magnetic layer is calculated by a magnetostatic approach. Biocompatibility is ensured by using garnet layers which turned out to be nontoxic and stable under culturing conditions. The garnet thin films exhibit spatially and temporally variable magnetic domain configurations in changing external magnetic fields and depending on their thermal pretreatment. Several patterns and bead deposition methods as well as the cell-surface interactions were analyzed. In some cases the cells show directed growth. Theoretical considerations explaining particular cell behavior on this magnetic material involve calculations of cell growth on elastic substrates and bending of cell membranes. PMID:19488746

  15. Magnetite deposits near Klukwan and Haines, southeastern Alaska

    USGS Publications Warehouse

    Robertson, Eugene C.

    1956-01-01

    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.

  16. PEG conjugated citrate-capped magnetite nanoparticles for biomedical applications

    NASA Astrophysics Data System (ADS)

    Cheraghipour, Elham; Tamaddon, A. M.; Javadpour, S.; Bruce, I. J.

    2013-02-01

    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.

  17. Speed limit of the insulator-metal transition in magnetite

    NASA Astrophysics Data System (ADS)

    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

    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.

  18. Magnetic Core-Shell Morphology of Structurally Uniform Magnetite Nanoparticles

    NASA Astrophysics Data System (ADS)

    Krycka, Kathryn

    2011-03-01

    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. 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.

  19. Low temperature oxidation mechanisms of nanocrystalline magnetite thin film

    NASA Astrophysics Data System (ADS)

    Bourgeois, F.; Gergaud, P.; Renevier, H.; Leclere, C.; Feuillet, G.

    2013-01-01

    A detailed investigation of the mechanisms related to the low temperature oxidation of nanocrystalline magnetite thin films into maghemite is presented. Despite strong differences in the functional properties of these two phases, structural similarities make it difficult to distinguish between them, and to quantify the oxidation process, particularly in the case of nanostructured polycrystalline layers. Contrary to the case of bulk materials or monocrystalline films and particles, the oxidation processes in nanocrystalline thin film have only scarcely been studied. In this work, structural and optical techniques, including X-ray diffraction (XRD), EXAFS/X-ray absorption near edge structure, FTIR, and Raman scattering, have been used to estimate the oxidation rate of magnetite. The overall oxidation reaction rates are discussed in the framework of two limiting cases corresponding to intra grain diffusion and to grain boundary diffusion. SIMS profiling and electrical measurements were also carried out to better assess the oxidation quantification in order to conclude on the predominant oxidation mechanisms in this heterogeneous material. We propose a qualitative model for the structure, in terms of insulating zone distribution, for partially oxidized films.

  20. Characterization of Modified Magnetite Nanoparticles for Albumin Immobilization

    PubMed Central

    Bordbar, A. K.; Rastegari, A. A.; Amiri, R.; Ranjbakhsh, E.; Abbasi, M.; Khosropour, A. R.

    2014-01-01

    Magnetite Fe3O4 nanoparticles (NPs) were prepared by chemical coprecipitation method. Silica-coated magnetite NPs were prepared by sol-gel reaction, subsequently coated with 3-aminopropyltriethoxysilane (APTES) via silanization reaction, and then were activated with 2,4,6-trichloro-1,3,5-triazine (TCT) and covalently immobilized with bovine serum albumin (BSA). The size and structure of the particles were characterized by transmission electron microscopy (TEM), X-ray powder diffraction (XRD), and dynamic light scattering (DLS) techniques. The immobilization was confirmed by Fourier transform infrared spectroscopy (FT-IR). XRD analysis showed that the binding process has not done any phase change to Fe3O4. The immobilization time for this process was 4?h and the amount of immobilized BSA for the initial value of 1.05?mg BSA was about 120?mg/gr nanoparticles. Also, the influences of three different buffer solutions and ionic strength on covalent immobilization were evaluated. PMID:24963410

  1. Magnetic and Physical Characteristics of Magnetite Associated with Deformation and Exsolution

    NASA Astrophysics Data System (ADS)

    Till, Jessica Lynn

    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.

  2. Detrapping and retrapping of free carriers in nominally pure single crystal GaP, GaAs and 4H-SiC semiconductors under light illumination at cryogenic temperatures

    E-print Network

    Mouneyrac, David; Floch, Jean-Michel Le; Tobar, Michael E; Cros, Dominique; Krupka, Jerzy

    2010-01-01

    We report on extremely sensitive measurements of changes in the microwave properties of high purity non-intentionally-doped single-crystal semiconductor samples of gallium phosphide, gallium arsenide and 4H-silicon carbide when illuminated with light of different wavelengths at cryogenic temperatures. Whispering gallery modes were excited in the semiconductors whilst they were cooled on the coldfinger of a single-stage cryocooler and their frequencies and Q-factors measured under light and dark conditions. With these materials, the whispering gallery mode technique is able to resolve changes of a few parts per million in the permittivity and the microwave losses as compared with those measured in darkness. A phenomenological model is proposed to explain the observed changes, which result not from direct valence to conduction band transitions but from detrapping and retrapping of carriers from impurity/defect sites with ionization energies that lay in the semiconductor band gap. Detrapping and retrapping relax...

  3. Pure optical photoacoustic microscopy

    PubMed Central

    Xie, Zhixing; Chen, Sung-Liang; Ling, Tao; Guo, L. Jay; Carson, Paul L.; Wang, Xueding

    2011-01-01

    The concept of pure optical photoacoustic microscopy(POPAM) was proposed based on optical rastering of a focused excitation beam and optically sensing the photoacoustic signal using a microring resonator fabricated by a nanoimprinting technique. After the refinements of the microring’s working wavelength and in the resonator structure and mold fabrication, an ultrahigh Q factor of 3.0×105 was achieved which provided high sensitivity with a noise equivalent detectable pressure(NEDP) value of 29Pa. This NEDP is much lower than the hundreds of Pascals achieved with existing optical resonant structures such as etalons, fiber gratings and dielectric multilayer interference filters available for acoustic measurement. The featured high sensitivity allowed the microring resonator to detect the weak photoacoustic signals from micro- or submicroscale objects. The inherent superbroad bandwidth of the optical microring resonator combined with an optically focused scanning beam provided POPAM with high resolution in the axial as well as both lateral directions while the axial resolution of conventional photoacoustic microscopy (PAM) suffers from the limited bandwidth of PZT detectors. Furthermore, the broadband microring resonator showed similar sensitivity to that of our most sensitive PZT detector. The current POPAM system provides a lateral resolution of 5 ?m and an axial resolution of 8 ?m, comparable to that achieved by optical microscopy while presenting the unique contrast of optical absorption and functional information complementing other optical modalities. The 3D structure of microvasculature, including capillary networks, and even individual red blood cells have been discerned successfully in the proof-of-concept experiments on mouse bladders ex vivo and mouse ears in vivo. The potential of approximately GHz bandwidth of the microring resonator also might allow much higher resolution than shown here in microscopy of optical absorption and acoustic propagation properties at depths in unfrozen tissue specimens or thicker tissue sections, which is not now imageable with current optical or acoustic microscopes of comparable resolution. PMID:21643156

  4. Characterization and cytotoxicity studies on liposome-hydrophobic magnetite hybrid colloids.

    PubMed

    Floris, Alice; Sinico, Chiara; Fadda, Anna Maria; Lai, Francesco; Marongiu, Francesca; Scano, Alessandra; Pilloni, Martina; Angius, Fabrizio; Vázquez-Vázquez, Carlos; Ennas, Guido

    2014-07-01

    The aim of this study was to highlight the main features of magnetoliposomes prepared by TLE, using hydrophobic magnetite, and stabilized with oleic acid, instead of using the usual hydrophilic magnetite surrounded by sodium citrate. These biocompatible magnetoliposomes (MLs) were prepared with the purpose of producing a magnetic carrier capable of loading either hydrophilic or lipophilic drugs. The effect of different liposome/magnetite weight ratios on the stability of magnetoliposomes was evaluated by monitoring the mean diameter of the particles, their polydispersity index, and zeta potential over time. The prepared magnetoliposomes showed a high liposome-magnetite association, with magnetoliposomes containing PEG (polyethylene glycol) showing the best magnetite loading values. To verify the position of magnetite nanoparticles in the vesicular structures, the morphological characteristics of the structures were studied using transmission electron microscopy (TEM). TEM studies showed a strong affinity between hydrophobic magnetite nanoparticles, the surrounding oleic acid molecules, and phospholipids. Furthermore, the concentration above which one would expect to find a cytotoxic effect on cells as well as morphological cell-nanoparticle interactions was studied in situ by using the trypan blue dye exclusion assay, and the Prussian Blue modified staining method. PMID:24776672

  5. Transformation products of submicron-sized aluminum-substituted magnetite: Color and reductant solubility

    NASA Astrophysics Data System (ADS)

    Golden, D. C.; Ming, D. W.; Lauer, H. V., Jr.

    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 geologic materials. Upon oxidation, magnetite transforms to maghemite; at elevated temperatures, maghemite inverts to hematite. This transformation causes a change in color from black to red and may affect the reductant solubility as well. The objectives here were to examine the color and reflectance spectral characteristics of products during the transformation of magnetite to maghemite to hematite and to study the effect of Al-substitution in magnetite on the above process. Reductant solubility of Al-substituted magnetite, maghemite, and hematite was also studied. In summary, the transformation of magnetite to maghemite was accompanied by a change in color from black to red because of the oxidation of Fe2(+) to Fe3(+). The phase change maghemite to hematite had a relatively minor effect on the color and the reflectance spectra.

  6. Transformation products of submicron-sized aluminum-substituted magnetite: Color and reductant solubility

    NASA Technical Reports Server (NTRS)

    Golden, D. C.; Ming, D. W.; Lauer, H. V., Jr.

    1991-01-01

    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 geologic materials. Upon oxidation, magnetite transforms to maghemite; at elevated temperatures, maghemite inverts to hematite. This transformation causes a change in color from black to red and may affect the reductant solubility as well. The objectives here were to examine the color and reflectance spectral characteristics of products during the transformation of magnetite to maghemite to hematite and to study the effect of Al-substitution in magnetite on the above process. Reductant solubility of Al-substituted magnetite, maghemite, and hematite was also studied. In summary, the transformation of magnetite to maghemite was accompanied by a change in color from black to red because of the oxidation of Fe2(+) to Fe3(+). The phase change maghemite to hematite had a relatively minor effect on the color and the reflectance spectra.

  7. High-temperature magnetic fabric development from plastically deformed magnetite in experimental shear zones

    NASA Astrophysics Data System (ADS)

    Till, J. L.; Moskowitz, B. M.; Jackson, M. J.

    2012-04-01

    Magnetic fabric development has been studied in synthetic magnetite-silicate aggregates in a series of high-temperature simple shear deformation experiments. Samples composed of magnetite grains with a nominal size of 20-40 ?m dispersed at 3 wt % in a matrix of plagioclase were deformed between 1000 and 1200 °C with a confining pressure of 300 MPa, shear stresses in the range 10-130 MPa, and shear strains up to ?= 3. We determined that both magnetite and plagioclase were deformed plastically at these conditions. An oblate magnetic fabric ellipsoid develops subparallel to the shear plane and the degree of AMS rapidly increases with strain up to a value of 2.5. Theoretical strain response models of magnetic fabric development were applied to the data to obtain estimated magnetite strains. The shape-preferred orientation of magnetite grains after deformation, determined from reflected light image analysis, was used to calculate independent magnetite strain estimates. These results were then compared with strains estimated from theoretical magnetic anisotropy development. Both strain estimation methods indicate strain partitioning between magnetite and the plagioclase matrix and the results are used to determine approximate viscosity ratios between the two phases at the experimental conditions.

  8. Anaerobic production of magnetite by a dissimilatory iron-reducing microorganism

    USGS Publications Warehouse

    Lovley, D.R.; Stolz, J.F.; Nord, G.L., Jr.; Phillips, E.J.P.

    1987-01-01

    The potential contribution of microbial metabolism to the magnetization of sediments has only recently been recognized. In the presence of oxygen, magnetotactic bacteria can form intracellular chains of magnetite while using oxygen or nitrate as the terminal electron acceptor for metabolism1. The production of ultrafine-grained magnetite by magnetotactic bacteria in surficial aerobic sediments may contribute significantly to the natural remanent magnetism of sediments2-4. However, recent studies on iron reduction in anaerobic sediments suggested that bacteria can also generate magnetite in the absence of oxygen5. We report here on a sediment organism, designated GS-15, which produces copious quantities of ultrafine-grained magnetite under anaerobic conditions. GS-15 is not magnetotactic, but reduces amorphic ferric oxide to extracellular magnetite during the reduction of ferric iron as the terminal electron acceptor for organic matter oxidation. This novel metabolism may be the mechanism for the formation of ultrafine-grained magnetite in anaerobic sediments, and couldaccount for the accumulation of magnetite in ancient iron formations and hydrocarbon deposits. ?? 1987 Nature Publishing Group.

  9. Anti-phase domains and magnetism in epitaxial magnetite layers

    NASA Astrophysics Data System (ADS)

    Hibma, T.; Voogt, F. C.; Niesen, L.; van der Heijden, P. A. A.; de Jonge, W. J. M.; Donkers, J. J. T. M.; van der Zaag, P. J.

    1999-04-01

    Recent studies show that the magnetic properties of epitaxial thin films of magnetite (Fe3O4) deviate strongly from bulk behavior: it is difficult to saturate thin films, ultrathin films may become super paramagnetic, their saturation magnetization drops to zero, and the local magnetic moments are oriented out of plane in zero field. The possible relationship between this anomalous behavior and the occurrence of anti-phase boundaries (APBs) is discussed. Transmission electron microscopy images confirm that APBs are present in our Fe3O4 films grown by molecular beam epitaxy on MgO(100). Only APBs with out-of-plane shift vectors are visible. The much higher APB density found in sputtered films suggests that preparation conditions are important. To explain the deviating saturation and the superparamagnetic behavior of thin Fe3O4 films at the same time, the magnetic coupling over the APB must be dramatically reduced due to spin disorder along the boundaries.

  10. Influence of Magnetite Nanoparticles on Human Leukocyte Activity

    NASA Astrophysics Data System (ADS)

    Džarová, Anežka; Dubni?ková, Martina; Závišová, Vlasta; Koneracká, Martina; Kop?anský, Peter; Gojzewski, Hubert; Timko, Milan

    2010-12-01

    Chemically synthesized magnetite particles coated by sodium oleate and PEG (MNP), and magnetosomes (MS) influence the process of phagocytosis and the metabolic activity (lysozyme and peroxidase activity) in leukocytes. Lysozyme activity is oxygen-independent liquidation mechanisms of engulfed microorganism, peroxidase activity is an oxygen-dependent mechanism. Both tested types of nanoparticles lysed leukocyte cells during incubation. MNP at concentrations of 10 and 20 ?g/mL lysed almost all leukocytes and their cell viability was in the 14±0.05% range. On the other hand MS begin to influence leukocytes activity at the concentration of 1 ?g/ml and this influence grows with increasing concentration up to 20 ?g/ml. MS are more suitable for biological applications than MNP which are more aggressive material than MS. MS should not be used above 10 ?g/mL.

  11. Hydrocolloid-stabilized magnetite for efficient removal of radioactive phosphates.

    PubMed

    Vellora Thekkae Padil, Vinod; Rouha, Michael; Cerník, Miroslav

    2014-01-01

    Liquid radioactive waste is a common by-product when using radioactive isotopes in research and medicine. Efficient remediation of such liquid waste is crucial for increasing safety during the necessary storage of the material. Herein, we present a novel Gum Karaya stabilized magnetite for the efficient removal of radioactive phosphorus (32)P from liquid radioactive waste. This environmentally friendly material is well suited to be used as a nanohydrogel for the removal of liquid waste, which can then be stored in a smaller space and without the risk of the spills inherent to the initial liquid material. The maximum adsorption capacity of the GK/M in this study was found to be 15.68 GBq/g. We present a thorough morphological characterization of the synthesised GK/M, as well as a discussion of the possible phosphorus adsorption mechanisms. PMID:24696854

  12. Preparation of pure stearic acid

    Microsoft Academic Search

    J. M. Philipson; M. J. Heldman; L. L. Lyon; R. D. Vold

    1944-01-01

    N order to interpret data on commercial soaps it is frequently necessary to investigate the behavior of systems of single pure soaps. For significant results, this often necessitates the preparation of purer fatty acids than any which can be purchased. Although there are numerous (1, 2) descriptions in the literature of methods for the preparation of pure stearic acid these

  13. Selective separation of fluorescent-magnetic nanoparticles with different magnetite-doping levels.

    PubMed

    Park, Sang-Eun; Park, Sang-Joon; Lee, Sang-Wha; Lee, Joong-Kee

    2011-05-01

    Fluorescent-labeled magnetic nanoparticles were explored as a biomedical agent for selective magnetic separation. By adjusting the loading volume of citrate-stabilized magnetites during a sol-gel reaction with silicon alkoxide, magnetites were simultaneously embedded into both the surface and inside the silica matrix, consequently leading to magnetic nanoparticles with different doping levels of magnetites. For endowing them with multifunctional tools in biomedical fields, magnetic nanoparticles were further encapsulated with silica thin layer labeled with fluorescent organic dyes (such as Alexa Fluor 488 and 594). Fluorescent-magnetic nanoparticles with different magnetism successfully displayed the differential separation of fluorescence spectra under an external magnetic field. PMID:21780495

  14. Efficacy of lytic peptide-bound magnetite nanoparticles in destroying breast cancer cells.

    PubMed

    Kumar, Challa S; Leuschner, Carola; Doomes, E E; Henry, Larry; Juban, Martha; Hormes, Josef

    2004-03-01

    A 23-amino-acid synthetic lytic peptide (Hecate) was covalently linked to magnetite nanoparticles and the lytic peptide-bound nanoparticles were characterized by X-ray absorption near-edge structure spectroscopy, transmission electron microscopy, and electron diffraction. Investigation of magnetic properties with a superconducting quantum interference device (SQUID) magnetometer has shown a reduction in the saturation magnetization (Ms) of magnetite nanoparticles after binding with lytic peptide. An in vitro cell culture assay with breast cancer cell lines MDA-MB-435S revealed that the lytic peptide-bound magnetite nanoparticles were therapeutically active. PMID:15233083

  15. Paleomagnetism of a new magnetite-rich carbonaceous chondrite

    NASA Astrophysics Data System (ADS)

    Gattacceca, J.; Rochette, P.; Gounelle, M.; Bonal, L.; Weiss, B. P.; Sonzogni, C.

    2012-12-01

    Recent studies of CV carbonaceous chondrites have led to the conclusion that their parent body was partially differentiated and possessed a convecting core [1]. This possibility has been validated by modeling of asteroid accretion [2]. Were partially differentiated chondritic asteroid the rule or the exception? We will present petrographic and paleomagnetic data obtained on an unusual carbonaceous chondrite that we discovered in 2011 in the Atacama desert. This meteorite is a fully crusted stone with a total weight of 2.4 g. Although classification is still ongoing, its petrography, and oxygen isotopes (d18O=-1.74‰, d17O=-5.15‰, D17O=-4.25‰) point to a C2 ungrouped chondrite. Preliminary Raman spectroscopy data confirm that it has not suffered thermal metamorphism. Magnetic properties show that the meteorite contains ~13 wt.% of pseudo-single domain magnetite, making it a rock with remarkable paleomagnetic recorder. Indeed, this is the most magnetic magnetite-bearing chondrite ever described. Paleomagnetic measurements show that the meteorite possesses a uniform and unidirectional stable component of magnetization unblocked up to 120 mT during alternating field demagnetization. Paleointensity is estimated to a few ?T using normalization techniques [3]. The nature of the magnetizaiton, and the origin of the magnetizing field will be discussed. [1] Carporzen et al., 2011. Proc. National Acad. Sci., 108, 6386-6389. [2] Elkins-Tanton et al., 2011. Earth Planet . Sci. Lett., 305, 1-10. [3] Gattacceca and Rochette P. 2004 Earth Planet . Sci. Lett., 227, 377-393.

  16. Synthesis of carbon-iron(II) oxide layer on the surface of magnetite and its reactivity with H2O for hydrogen generation

    Microsoft Academic Search

    Y. Tamaura; K. Akanuma; N. Hasegawa; M. Tsuji

    1994-01-01

    Synthesis of a carbon-iron(II) oxide layer on the surface of magnetite and its reactivity with H2O for hydrogen generation reaction have been studied. X-ray diffractometry and chemical analysis showed that the carbon-bearing magnetite synthesized by the carbon-deposition reaction from CO2 gas with the hydrogen-reduced magnetite, was magnetite with a carbon-iron(II) oxide layer (CIO layer-M; M is stoichiometric magnetite) represented by

  17. Pure lead is pure gold for electric vehicles

    Microsoft Academic Search

    Kana

    1995-01-01

    Many electric-powered vehicle designers have found that, when applied properly, pure lead-tin batteries (sealed-lead with tin additive) are an ideal choice when considering power requirements. Desired performance requirements are discussed.

  18. Morphological features of elongated-anisotropic magnetosome crystals in magnetotactic bacteria of the Nitrospirae phylum and the Deltaproteobacteria class

    NASA Astrophysics Data System (ADS)

    Lefèvre, Christopher T.; Pósfai, Mihály; Abreu, Fernanda; Lins, Ulysses; Frankel, Richard B.; Bazylinski, Dennis A.

    2011-12-01

    High resolution transmission electron microscopy was used to study the crystallographic habits of the elongated magnetite crystals, variously described as bullet-, tooth- or arrowhead-shaped, in two recently described, uncultured, magnetotactic bacteria belonging to the Nitrospirae phylum designated Candidatus Magnetoovum mohavensis strain LO-1, and Candidatus Thermomagnetovibrio paiutensis strain HSMV-1; and a cultured sulfate-reducing magnetotactic bacterium of the Deltaproteobacteria class of the Proteobacteria phylum designated strain AV-1. The elongation axes of the magnetosomes do not coincide with the easy magnetization axis (which is [111]) but they are parallel to [100] in LO-1 and AV-1 and parallel to [110] in HSMV-1. In all three strains, magnetosome magnetite crystals appear to elongate at constant width, resulting in asymmetric shapes. Idealized crystal morphologies are proposed. Neither the control mechanism over crystal growth, nor the adaptiveness, if any, of such unusual crystal habits are known at the moment. Since similar elongated and asymmetric morphologies are unknown in inorganically-formed magnetite crystals, these forms of magnetosome magnetite appear to be excellent biomarkers.

  19. Controllable in situ synthesis of magnetite coated silica-core water-dispersible hybrid nanomaterials.

    PubMed

    Qu, Haiou; Tong, Sheng; Song, Kejing; Ma, Hui; Bao, Gang; Pincus, Seth; Zhou, Weilie; O'Connor, Charles

    2013-08-20

    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

  20. Truncated Hexa-Octahedral Magnetites: Biosignatures in Terrestrial Samples and Martian Meteorite ALH84001

    NASA Technical Reports Server (NTRS)

    Thomas-Keprta, Kathie L.; Clemett, Simon J.; Bazylinski, Dennis A.; Kirschvink, Joseph L.; McKay, David S.; Wentworth, Susan J.; Vali, H.; Gibson, Everett K.

    2001-01-01

    We suggest that the observation of truncated hexa-octahedral magnetites in ALH84001 are both consistent with, and in the absence of terrestrial inorganic analogs, likely formed by biogenic processes. Additional information is contained in the original extended abstract.

  1. Magnetic and Structural Properties of Magnetite in Radular Teeth of Chiton Acanthochiton Rubrolinestus

    NASA Astrophysics Data System (ADS)

    Han, Y. N.; Liu, C. L.; Yao, L. D.; Wang, Y.; Han, X. F.

    2008-03-01

    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.

  2. Controllable In-Situ Synthesis of Magnetite Coated Silica-Core Water-Dispersible Hybrid Nanomaterials

    PubMed Central

    Qu, Haiou; Tong, Sheng; Song, Kejing; Ma, Hui; Bao, Gang; Pincus, Seth; Zhou, Weilie; O'Connor, Charles

    2013-01-01

    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 nanotube 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

  3. In Situ Measurement of Oxygen Isotope Compositions of Magnetite in the Allende CV3 Chondrite

    NASA Astrophysics Data System (ADS)

    Choi, B.-G.; Coath, C. D.; Leshin, L.; Wang, J.; McKeegan, K. D.; Wasson, J. T.

    1995-09-01

    Magnetite is relatively abundant in the oxidized CV chondrites. This study was undertaken to examine possible origins in nebular or in parent-body processes. Magnetite in Allende has several distinct characteristics compared to that of the other CV chondrites. Unlike Mokoia and Vigarano, magnetite in Allende is almost exclusively found in chondrules, where it typically forms spherical nodules often associated with metal and/or sulfides. In addition, the Ni contents of metal in most CV chondrites seldom exceed 50 wt%, while in Allende nearly all of metal grains are Ni rich (64-71 wt% Ni [e.g., 1]), which we designate awaruite even though the Ni range is below that of awaruite. Rare kamacite grains are present in chondrules [2]. A few rare Allende nodules have euhedral to subhedral awaruite grains [e.g., 3]. Nodules of magnetite + sulfides, magnetite + metal, and metal + sulfide exhibit different textures implying that magnetite grains are not simply pseudomorphs of preexisting metal grains. Tiny magnetite grains (< 1 micrometer) are found in Ni-rich metal ; in turn, the host metal is surrounded by magnetite. The textural evidence is not sufficient to distinguish between a high temperature and a low temperature origin for the magnetite. Six magnetite nodules, which had relatively clean areas of ~ 25 micrometers diameter, from 4 Allende PO chondrules were selected for in situ oxygen isotope study using the UCLA Cameca ims 1270, a high resolution - high sensitivity ion microprobe. A ~0.3 nA primary Cs+ beam was defocused to a 20-25 micrometers spot and a field aperture inserted into the secondary ion beam to restrict the analyzed area to the central 10-12 micrometers of each nodule. Negative ions were collected at a mass resolving power of ~6500, sufficient to eliminate hydride interferences. A normal incidence electron gun was employed to compensate possible sample charging. To monitor the instrumental mass fractionation (-11.2+/-0.5 per mil/amu) analyses of terrestrial magnetite LP204a [4] were made interspersed amongst the chondrule analyses. Chondrule data corrected for mass fractionation and normalized to the SMOW scale are shown in Figure 1. Oxygen isotope ratios from inclusion and crack free regions in four magnetite nodules are tightly clustered below the terrestrial mass fractionation (TF) line and are distinct from oxygen isotope fields observed in magnetite from CI and Essebi chondrites [5] and from isolated grains in CI meteorites [6]. The data plot near the ^(16)O mixing line of refractory minerals in Allende (CCAM), but the spread in the ratios is too low relative to the precision of the measurements to define any linear trend for these samples. In 2 chondrules, magnetite nodules with cracks or Ni-Fe metal have very different oxygen compositions; they plot near the TF line at low delta^(18)O (-10 per mil). At this time, it is not clear if this difference could be due to a sputtering artifact, or if it reflects alteration or inclusion of another phase in these "magnetite" nodules. The question of the origin of CV magnetite has not yet been resolved. Data on additional samples including other CV chondrites will help clarify this point. References: [1] McSween H. Y. Jr. (1977) GCA, 41, 1777-1790. [2] Fuchs L. H. and Olsen E. (1973) EPSL, 18, 379-384. [3] Rubin A. E. (1991) Am. Mineral., 76, 1356-1362. [4] Valley J. W. and Graham G. M. (1991) Contrib. Mineral. Petrol., 109, 38-52. [5] Rowe M. W. et al. (1994) GCA, 58, 5341-5347. [6] Hyman M. et al. (1991) Meteoritics, 26, 350.

  4. Wind Mediated Oxidation of Magnetite: A Putative Mechanism for Hematite Production on Mars

    NASA Astrophysics Data System (ADS)

    Merrison, J. P.; Gunnlaugsson, H. P.; Nørnberg, P.; Knak Jensen, S.

    2011-03-01

    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.

  5. Bias and temperature dependence on junction magnetoresistance in manganite/magnetite based magnetic tunnel junctions

    NASA Astrophysics Data System (ADS)

    Chopdekar, Rajesh; Hu, Guohan; Suzuki, Yuri

    2005-03-01

    Studies of the bias and temperature dependence of junction magnetoresistance (JMR) in manganite/magnetite trilayer junctions have revealed non-monotonic dependence on both quantities. Such junctions were constructed to probe the spin-polarization of magnetite using the well-established majority spin-polarized oxide (La,Sr)MnO3 as a counter-electrode. We have found that using an isostructural oxide cobalt chromite tunnel barrier reduces disorder at the chromite-magnetite interface as compared to junctions with a rocksalt structure MgO barrier. An order of magnitude increase in JMR for these junctions is strongly peaked as a function of bias magnitude and sign, but has weak temperature dependence. The Verwey transition in magnetite, the paramagnetic-ferrimagnetic transition in cobalt chromite, and the interface roughness in the junctions all play a role in determining the temperature and bias dependence of the measured magnetoresistance.

  6. Operators on Pure Spinor Spaces

    SciTech Connect

    Cederwall, Martin [Fundamental Physics, Chalmers University of Technology, SE 412 96 Goteborg (Sweden)

    2010-06-17

    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.

  7. Fabrication of magnetite-hydrogel nanocomposites with clustered magnetite cores and poly(N-isopropylacrylamide-co-acrylic acid) shells for drug delivery application.

    PubMed

    Lim, Sera; Yang, Daniel; Lee, Sang-Wha

    2010-11-01

    Magnetite-hydrogel nanocomposites were fabricated through the combination of sol-gel process and radical polymerization. The incorporation of magnetite clusters into silica matrix was facilely conducted by the sol-gel reaction of APTMS-complexed CMNPs (citrate-stabilized magnetites) and tetraethoxysilane (TEOS) in ethanol solution. The core-shell magnetic nanoparticles were further encapsulated with poly(N-isopropylacrylamide-co-acrylic acid) hydrogeals via a free radical polymerization. The magnetic nanoparticles exhibited superparamagnetic characteristics with negligible remanence and coercivity. Hydrogel-encapsulated magnetic nanoparticles showed systematic changes of particle size corresponding to the alteration of pH and temperature. The resulting nanocomposites can be a smart drug delivery agent with magnetic and stimuli (pH, temperature)-sensitive properties. PMID:21137918

  8. Spectral and other physicochemical properties of submicron powders of hematite (alpha-Fe2O3), maghemite (gamma-Fe2O3), magnetite (Fe3O4), goethite (alpha-FeOOH), and lepidocrocite (gamma-FeOOH).

    PubMed

    Morris, R V; Lauer, H V; Lawson, C A; Gibson, E K; Nace, G A; Stewart, C

    1985-03-10

    Spectral and other physicochemical properties were determined for a suite of submicron powders of hematite (alpha-Fe2O3), maghemite (gamma-Fe2O3), magnetite (Fe3O4), goethite (alpha-FeOOH), and lepidocrocite (gamma-FeOOH). The spectral reflectivity measurements were made between 0.35 and 2.20 micrograms over the temperature interval between about -110 degrees and 20 degrees C. Other physicochemical properties determined were mean particle diameter, particle shape, chemical composition, crystallographic phase, magnetic properties, and Mossbauer properties. Only the magnetite powders have significant departures from the stoichiometric phase; they are actually cation-deficient magnetites having down to about 18.0 wt % FeO as compared with 31.0 wt % FeO for stoichiometric magnetite. A structured absorption edge due to crystal field transitions and extending from weak absorption in the near-IR to intense absorption in the near-UV is characteristic of the ferric oxides and oxyhydroxides and is responsible for their intense color. Particularly for hematite, the number and position of the spectral features are consistent with significant splitting of the degenerate cubic levels by noncubic components of the crystal field. The position of the crystal-field band at lowest energy, assigned to the envelope of the components of the split cubic 4T1 level, is near 0.86, 0.91, 0.92, and 0.98 microgram at room temperature for hematite, goethite, maghemite, and lepidocrocite, respectively. Comparison with Mossbauer data suggests covalent character increases sequentially through the aforementioned series. The positions of the spectra features are relatively independent of temperature down to about -110 degrees C. The maximum shifts observed were on the order of about 0.02 microgram shortward for the ferric oxyhydroxides. Variations in the magnitude of the reflectivity of the hematite powders as a function of mean particle diameter are consistent with scattering theory. The absorption strength of the crystal-field bands increases with increasing mean particle diameter over the range 0.1-0.8 micrometer; visually this corresponds to a change in color from orange to deep purple. The position of the split cubic 4T1 band shifts longward by about 0.02 micrometer with decreasing mean particle diameter over the same range; this trend is consistent with wavelength-dependent scattering. The cation-deficient magnetite powders are very strong absorbers throughout the near-UV, visible and near-IR; their spectral properties are independent of temperature between about -110 and 20 degrees C. PMID:11542003

  9. Non-stoichiometric magnetite and maghemite in the mature teeth of the chiton Acanthopleura hirtosa

    NASA Astrophysics Data System (ADS)

    St. Pierre, T. G.; Evans, L. A.; Webb, J.

    1992-04-01

    Mature radula pieces from the chiton Acanthopleura hirtosa were studied using Mössbauer spectroscopy. The magnetite present in the radulae was found to have a distribution of Verwey transition temperatures in the range 85-100K. It was deduced that the magnetite was non-stoichiometric with an average formula Fe2.98O3. About 10% of the Fe in the radulae was in the form of maghemite and about 19% was in the form of paramagnetic or superparamagnetic phases.

  10. Study of magnetite film formation at metal-scale interface during cooling of steel products

    Microsoft Academic Search

    J. Baud; A. Ferrier; J. Manenct

    1978-01-01

    A thin layer of magnetite is sometimes observed in the scales of hot-rolled sheets and wire rod at the scale-metal interface. The results of this study show that this layer of magnetite is produced, during the cooling of the products, by the wustite decomposition. The time\\/temperature field in which it appears has been defined. This inner layer is composed of

  11. Thermal, electrical and magnetic studies of magnetite filled polyurethane shape memory polymers

    Microsoft Academic Search

    Muhammad Yasar Razzaq; Mathias Anhalt; Lars Frormann; Bernd Weidenfeller

    2007-01-01

    Thermal, electrical and magnetic properties of polyurethane shape memory polymer (SMP) samples filled with 0–40vol% magnetite particles prepared by mixing and injection molding were investigated. Shape recovery in the shape memory polymer was initiated by a magnetizing field of H=4.4kA\\/m at a frequency f=50Hz. Electric resistivity was decreased by magnetite particles from ?el?1010?m to ?el?106?m. The percolation threshold is achieved

  12. Theoretical Single-Domain Grain Size Range in Magnetite and Titanomagnetite

    Microsoft Academic Search

    Robert F. Butler; Subir K. Banerjee

    1975-01-01

    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

  13. Trace elements in disseminated sulfides, magnetite, and massive sulfides, West Shasta district, California.

    USGS Publications Warehouse

    Botinelly, T.; Siems, D.F.; Sanzolone, R.F.

    1985-01-01

    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.

  14. Introduction of biotin or folic acid into polypyrrole magnetite core-shell nanoparticles

    SciTech Connect

    Nan, Alexandrina; Turcu, Rodica [National Institute of Research and Development for Isotopic and Molecular Technologies, Donath 65-103, Cluj-Napoca (Romania)] [National Institute of Research and Development for Isotopic and Molecular Technologies, Donath 65-103, Cluj-Napoca (Romania); Liebscher, Jürgen [National Institute of Research and Development for Isotopic and Molecular Technologies, Donath 65-103, Cluj-Napoca, Romania and Institute of Chemistry, Humboldt-University Berlin, Brook-Taylor 2, D-12489 Berlin (Germany)] [National Institute of Research and Development for Isotopic and Molecular Technologies, Donath 65-103, Cluj-Napoca, Romania and Institute of Chemistry, Humboldt-University Berlin, Brook-Taylor 2, D-12489 Berlin (Germany)

    2013-11-13

    In order to contribute to the trend in contemporary research to develop magnetic core shell nanoparticles with better properties (reduced toxicity, high colloidal and chemical stability, wide scope of application) in straightforward and reproducible methods new core shell magnetic nanoparticles were developed based on polypyrrole shells functionalized with biotin and folic acid. Magnetite nanoparticles stabilized by sebacic acid were used as magnetic cores. The morphology of magnetite was determined by transmission electron microscopy TEM, while the chemical structure investigated by FT-IR.

  15. Diagenetic Dissolution of Biogenic Magnetite in Surface Sediments of the Benguela Upwelling System

    Microsoft Academic Search

    K. Hilgenfeldt

    2000-01-01

    Intense primary biologic productivity in the surface waters of the Benguela upwelling system provides a high supply of organic\\u000a matter to the sea floor at the continental slope off Namibia and sustains extreme concentrations of magnetite producing bacteria\\u000a in the top sediment layers. Biogenic magnetite is thus by far the dominant carrier of the magnetic signal in these deposits\\u000a also

  16. A new approach to modification of polyelectrolyte capsule shells by magnetite nanoparticles

    NASA Astrophysics Data System (ADS)

    Bukreeva, T. V.; Orlova, O. A.; Sulyanov, S. N.; Grigoriev, Yu. V.; Dorovatovskiy, P. V.

    2011-09-01

    A new method for modifying polyelectrolyte capsule shells by magnetic nanoparticles is proposed: the in situ synthesis of magnetite by chemical condensation. The capsule cores were spherical calcium carbonate microparticles, while polymer shells were prepared using the layer-by-layer electrostatic adsorption of polyallylamine and polystyrene sulfonate. After in situ synthesis, nanoparticles of different shapes are formed on the capsule shell; the main crystalline phase of nanoparticles is magnetite. The thus obtained nanocomposite capsules are highly sensitive to external magnetic fields.

  17. Nano-aggregates of hexacyanoferrate (II)-loaded magnetite for removal of cesium from radioactive wastes

    Microsoft Academic Search

    R. D. a Ambashta; P. K. a Wattal; S. b Singh; D. c Bahadur

    2003-01-01

    Nano-sized magnetic sorbents can be promising candidate materials for treatment of low-level effluents resulting in effective decontamination and very high volume reduction of radioactive wastes. Preparation of magnetite-hexacyanoferrate composite was based upon wet-dispersion and in situ precipitation for synthesizing coatings on magnetite. Superior magnetic properties were rendered to potassium nickel (II) hexacyanoferrate (II), a sorbent with high specificity for cesium

  18. Mössbauer hyperfine parameters of iron species in the course of Geobacter -mediated magnetite mineralization

    Microsoft Academic Search

    Yi-Liang LiSan-Yuan; San-Yuan Zhu; Kun Deng

    2011-01-01

    Amorphous ferric iron species (ferrihydrite or akaganeite of <5 nm in size) is the only known solid ferric iron oxide that\\u000a can be reductively transformed by dissimilatory iron-reducing bacteria to magnetite completely. The lepidocrocite crystallite\\u000a can be transformed into magnetite in the presence of abiotic Fe(II) at elevated pH or biogenic Fe(II) with particular growth\\u000a conditions. The reduction of lepidocrocite by

  19. Cathodic Fenton degradation of 4,6-dinitro-o-cresol with nano-magnetite

    Microsoft Academic Search

    Xia Zeng; Khalil Hanna; Ann T. Lemley

    2011-01-01

    The successful removal of 4,6-dinitro-o-cresol (DNOC) is reported using nano-magnetite (Fe3O4) as the iron source and cathodic Fenton generation of hydrogen peroxide. Operating conditions were optimized by varying the electrolyte concentration, electric current, and O2 flow. The effects of different DNOC initial concentrations, pH values and nano-magnetite quantities on the degradation rate of DNOC were also examined. The results showed

  20. Study of the electronic paraprocess and antiphase boundaries as sources of the demagnetisation phenomenon in magnetite

    Microsoft Academic Search

    F. Delille; B. Dieny; J.-B. Moussy; M.-J. Guittet; S. Gota; M. Gautier-Soyer; C. Marin

    2005-01-01

    In this paper, a detailed study of the magnetic behaviour particularly at the Verwey transition is presented for some stoichiometric magnetite samples, as a function of their shape (film\\/bulk) and crystalline structure (single\\/polycrystal). Travelling solvent floating zone technique was first used to obtain crystalline bulk magnetite samples (110) oriented, while molecular beam epitaxy allowed us to grow a 68nm Fe3O4

  1. Size control of nanocrystalline magnetite thin films containing a small amount of Ge

    Microsoft Academic Search

    Seishi Abe; De Hai Ping; Hiroyuki Usui; Masato Ohnuma; Shigehiro Ohnuma

    2010-01-01

    This study investigated the preparation and particle size control of nanocrystalline magnetite (Fe3O4) containing a small amount of Ge. Thin films were prepared by radio-frequency sputtering with a composite target of Ge chips set on a Fe3O4 compound target in a mixed atmosphere of Ar and O2. X-ray diffraction revealed that the diffraction peak of magnetite gradually broadened as the

  2. Microstructure and magnetic properties of magnetite thin films prepared by reactive sputtering

    Microsoft Academic Search

    Hongmei Qiu; Liqing Pan; Liwei Li; Hao Zhu; Xuedan Zhao; Mei Xu; Liangqiang Qin; John Q. Xiao

    2007-01-01

    Highly oriented magnetite (Fe3O4) thin films have been produced by reactive sputtering in a mixture of hydrogen and argon. While different phases can be achieved by varying the ratio between hydrogen and argon, single phase magnetite films can be achieved with hydrogen concentration gamma=0.75%-1%. For the sample grown at gamma=1.0%, a Verwey transition at about 111 K can be seen

  3. The microstructure and characteristics of magnetite thin films prepared by ultrasound-enhanced ferrite plating

    Microsoft Academic Search

    Chun-Young Oh; Jae-Hee Oh; Taegyung Ko

    2002-01-01

    Magnetite thin films were produced using the ultrasound-enhanced ferrite plating method. The effect of ferrite plating conditions on the microstructure and magnetic properties was investigated. The saturation magnetization (Ms) and the coercive force (Hc) of the magnetic thin films were 465-475 emu\\/cm3 and 60-65 Oe, respectively. Then, the applicability of the magnetite thin films as a CO gas sensor was

  4. Squid measurement of the Verwey transition on epitaxial (1 0 0) magnetite thin films

    Microsoft Academic Search

    V. Dediu; E. Arisi; I. Bergenti; A. Riminucci; M. Solzi; C. Pernechele; M. Natali

    2007-01-01

    We report results on epitaxial magnetite (Fe3O4) thin films grown by electron beam ablation on (100) MgAl2O4 substrates. At 120K magnetite undergoes a structural and electronic transition, the so-called Verwey transition, at which magnetic and conducting properties of the material change. We observed the Verwey transition on epitaxial films with a thickness of 50nm by comparing zero-field cooling (ZFC) and

  5. Characterization of nanostructured magnetite thin films produced by sol–gel processing

    Microsoft Academic Search

    Ali Erdem Eken; Macit Ozenbas

    2009-01-01

    Nanocrystalline films of magnetite have been prepared by a novel sol–gel route in which, a solution of iron (III) nitrate\\u000a dissolved in ethylene glycol was applied on glass substrates by spin coating. Coating solution showed Newtonian behaviour\\u000a and viscosity was found as 0.0215 Pa.s. Annealing temperature was selected between 291 and 350 °C by DTA analysis in order\\u000a to obtain magnetite films.

  6. Optical magnetic circular dichroism in threshold photoemission from a magnetite thin film

    Microsoft Academic Search

    K. Hild; J. Maul; T. Meng; M. Kallmayer; G. Schönhense; H. J. Elmers; R. Ramos; S. K. Arora; I. V. Shvets

    2008-01-01

    Threshold photoemission excited by polarization-modulated ultraviolet femtosecond laser light is exploited for phase-sensitive detection of magnetic circular dichroism (MCD) for a magnetite thin film. Magnetite (Fe3O4) shows a magnetic circular dichroism of ~(4.5 ± 0.3) × 10-3 for perpendicularly incident circularly polarized light and a magnetization vector switched parallel and antiparallel to the helicity vector by an external magnetic field.

  7. Magnetic and magneto-optical properties of heteroepitaxial magnetite thin films

    Microsoft Academic Search

    J. Cheng; G. E. Sterbinsky; B. W. Wessels

    2008-01-01

    The magnetic and magneto-optical properties of heteroepitaxial magnetite (Fe3O4) thin films were investigated. Of interest was the role of misfit strain on determining its magnetic properties. Epitaxial magnetite thin films were deposited by molecular beam epitaxy using molecular oxygen on (100) oriented SrTiO3, BaTiO3 and MgO. Polar spectroscopic magneto-optic Kerr effect (MOKE) measurements on the thin films over near infrared

  8. Enhancement of the magnetization saturation in magnetite (100) epitaxial films by thermo-chemical treatment

    Microsoft Academic Search

    Y. Zhou; Xuesong Jin; I. V. Shvets

    2004-01-01

    The effect of thermo-chemical treatment on the ease of saturation in a magnetic field of epitaxial magnetite (100) thin films grown on MgO (100) substrates was investigated. It was found that the films maintained a fully strained state with the MgO substrate during the treatment in air. No other iron oxide phase apart from the magnetite was observed in the

  9. Magnetite polymer nanospheres loaded by Indomethacin for anti-inflammatory therapy

    NASA Astrophysics Data System (ADS)

    Timko, Milan; Koneracká, Martina; Tomas?ovi?ová, Natália; Kop?anský, Peter; Závis?ová, Vlasta

    2006-05-01

    This contribution is devoted to preparation and characterization of magnetite nanoparticles loaded by Indomethacin (IND) as anti-inflammatory drug suitable for magnetic drug targeting. The poorly water-soluble drug IND was successfully encapsulated in polylactic acid (PLA) magnetic nanospheres (NPs) by nanoprecipitation method. The evidence of successful entrapment of IND was confirmed by FTIR and spectrophotometric measurements. The prepared magnetite-PLA-IND NPs shown the response on external magnetic field and so availability for magnetic drug targeting.

  10. CVD synthesis of polycrystalline magnetite thin films: structural, magnetic and magnetotransport properties

    Microsoft Academic Search

    R. Mantovan; A. Lamperti; M. Georgieva; G. Tallarida; M. Fanciulli

    2010-01-01

    Magnetite (Fe3O4) is predicted to be half metallic at room temperature (RT) and it shows the highest Curie temperature among oxides. The use of Fe3O4 thin films is therefore promising for spintronic devices such as magnetic tunnel junctions (MTJs) and magnetoresistive sensors. The structural, magnetic and magnetotransport properties of magnetite are reported to be strongly dependent on the growth conditions.

  11. Introduction of biotin or folic acid into polypyrrole magnetite core-shell nanoparticles

    NASA Astrophysics Data System (ADS)

    Nan, Alexandrina; Turcu, Rodica; Liebscher, Jürgen

    2013-11-01

    In order to contribute to the trend in contemporary research to develop magnetic core shell nanoparticles with better properties (reduced toxicity, high colloidal and chemical stability, wide scope of application) in straightforward and reproducible methods new core shell magnetic nanoparticles were developed based on polypyrrole shells functionalized with biotin and folic acid. Magnetite nanoparticles stabilized by sebacic acid were used as magnetic cores. The morphology of magnetite was determined by transmission electron microscopy TEM, while the chemical structure investigated by FT-IR.

  12. Sulfur isotopic composition of the magnetite-series and ilmenite-series granitoids in Japan

    Microsoft Academic Search

    Akira Sasaki; Shunso Ishihara

    1979-01-01

    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

  13. Magnetic and structural properties of magnetite in radular teeth of chiton Acanthochiton rubrolinestus.

    PubMed

    Han, Yunan; Liu, Chuanlin; Zhou, Dong; Li, Fashen; Wang, Yong; Han, Xiufeng

    2011-04-01

    The teeth of the Polyplacophora Chiton Acanthochiton Rubrolinestus contain biomineralized magnetite crystallites whose biological functions in relation to structure and magnetic properties are not well understood. Here, using superconducting quantum interference device (SQUID) magnetometry, we find that the saturation magnetization (?(s)) and the Verwey transition temperature (T(v)) of tooth particles are 78.4 emu/g and 105 K, respectively. These values are below those of the stoichiometric magnetite. An in situ examination of the structure of the magnetite-bearing region within an individual tooth using high-resolution transmission electron microscopy indicates magnetite microcrystals form electron dense polycrystalline sheets with typical lengths of about 800 nm and widths of about 150 nm. These polycrystalline sheets are arranged regularly along the longitudinal direction of the tooth cutting surface. In addition, the crystallites in polycrystalline sheets take on generally good crystallinity. The magnetic microstructures of in situ magnetic force microscopy demonstrate that the [111] easy direction of magnetite microcrystals are aligned along the length of the tooth, whereas the [111] direction is parallel to the thickness of the tooth. Both Mössbauer spectra and magnetization versus temperature measurements under field cooled and zero-field cooled conditions do not detect superparamagnetic magnetite crystallites in the mature major lateral tooth particles of this chiton. PMID:21365666

  14. Selective Product of Magnetite through Addition of Small Amount of Metal Element

    NASA Astrophysics Data System (ADS)

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

    2011-06-01

    In this study, we investigate the transformation mechanism from a phase mixture of magnetite (Fe3O4) and hematite (?-Fe2O3) to a single-phase magnetite through the addition of a specific metal element. The thin films were prepared by rf sputtering with a composite target of metal chips set on a ceramic magnetite (or hematite) target in Ar atmosphere. It is revealed that the addition of Ge to the polycrystalline hematite film obviously produces single-phase magnetite, indicating that the hematite is fully transformed to magnetite through an addition of Ge. Such transformation is also seen with slight additions of Mo, W, Cr, and Mg, whereas the addition of Sn does not affect the phase mixture of magnetite and hematite. According to the free energy of the reaction, elements of Ge, Mo, W, Cr, and Mg are capable of reducing hematite, whereas hematite remains unreactive with addition of Sn. This is in good agreement with the experiment results. This unique technique additionally provides the maximum magnetization of 3.9 kG at 8 ×105 A·m-1(10 kOe) at a Mo concentration of 1.3 at. %.

  15. Research of the acoustic influence on residual magnetization of rocks containing magnetite from the various geological structures of the Kola Peninsula

    NASA Astrophysics Data System (ADS)

    Zhirova, Anzhela

    2015-04-01

    The aim of the study is influence of acoustic waves on the magnetization of rocks of Kola Peninsula under different experimental parameters. The results and further research in this field are of interest in the development of problems of nonlinear geophysics, as well as address some issues in materials science. To study the acoustic influence on the residual magnetization of rocks we used the samples of magnetite-calcite rocks with a high content of magnetite from the Kovdor massif, and weakly magnetic rocks: (a) ultramafic rock of the Kola composite terrane; (b) gabbro-norite from layered intrusions of Pana; c) metagabbro-norite of the Belomorsky mobile belt. The samples previously demagnetized by the time-variable magnetic field, subjected to three cycles of ultrasonic influence with increasing time of influence and further measurement of the residual magnetization. The dependence of the residual magnetization of the magnetite-calcite rock from the time of testing is determined. As a result of multiple influences on the samples of gabbro-norit, ultramafic rock and metagabbro-norit was obtained a weak change of the vector of the residual magnetization. Thus the study of the residual magnetization of the samples with different content of ferromagnetic mineral found a significant difference in the nature of the magnetic response of rocks. So the high magnetic magnetite-calcite rock from the Kovdor massif detects a significant increase of the magnetization from the first seconds of the ultrasound influence. The magnetic response of other rocks to external influence is weaker. The dependence of the residual magnetization of these rocks from the time of influence either not observed or observed on the last cycle of the experiment in terms of a significant increase of time of the acoustic influence. Magnetic properties of rocks associated with the ferromagnetic minerals. These minerals are usually dispersed in the form of small grains in total dia - and paramagnetic mass, which is the main volume of the rocks. The number of the dispersed (accessory) minerals determines the magnetic susceptibility and residual magnetization of rocks. Magnetite-calcite rock from Kovdor massif, for which the dependence of the magnetic state from the time of acoustic influence was determined, contains a significant amount of the ferromagnetic mineral. While in the others of the samples the content of the ferromagnetic does not exceed 1 - 2 %. As a result of three cycles of the experiment it is found that the magnetite-calcite rocks with the large crystals of magnetite and the complex domain structure reveals significant changes of the vector of the residual magnetization and its dependence on time of the influence of the elastic oscillations. While the magnetic properties of the samples with insignificant inclusions of the ferromagnetic minerals are more stable. This study was supported by the Russian Science Fund (project nos. 14-17-00751).

  16. Magnetite Nucleation in Mantle Xenoliths During Quasi-Adiabatic Ascent

    NASA Astrophysics Data System (ADS)

    Walsh, K. B., Jr.; Filiberto, J.; Friedman, S. A.; Knafelc, J.; Conder, J. A.; Ferre, E. C.; Khakhalova, E.; Feinberg, J. M.; Neal, C. R.; Ionov, D. A.; Hernandez, F. M.

    2014-12-01

    Can magnetite be a stable phase in the lithospheric mantle? Equilibrium-based thermodynamic calculations and petrologic models predict that it should not be stable. Studies of mantle xenoliths during the 1980s concluded that even though there were rare exceptions, mantle rocks do not host sufficient concentrations of ferromagnetic minerals and are too hot to allow any magnetic remanence. Thus, conventional wisdom dictates that the Moho constitutes a fundamental magnetic boundary. Yet, growing evidence from a more complete global mantle xenolith survey indicates the presence of ferromagnetic minerals in mantle materials. Examination of mantle xenoliths devoid of serpentinization and meteoric alteration show the presence of ferromagnetic minerals within primary silicate mineral phases, including olivine, pyroxene, and spinel. Nucleation of these magnetic minerals could occur at three different stages: in-situ in the mantle, upon ascent, and at the surface. This study reports the results of laboratory-based quasi-adiabatic decompression experiments that aim to simulate the ascent of mantle xenoliths through the lithosphere and test if magnetite growth is promoted during the process. The starting material for these experiments is San Carlos olivine, which holds a magnetic remanence of less than ~10-10 A/m2-1kg2 (the detection limit of the vibrating sample magnetometer). This low starting remanence will allow us to identify whether new magnetic minerals are formed during the decompression experiments using either vibrating sample magnetometry or SQUID-based rock magnetometers. All olivine grains in these experiments were hand-picked under a light microscope in an effort to avoid the inclusion of grains with spurious magnetic minerals. Olivine powders from these carefully selected grains will be used to represent average mantle olivine compositions (Fo90-Fo92). Experiments will start at 1 GPa and be decompressed to 0.3 GPa over 60 hrs at constant temperature (1200° C). These experiments will provide an assessment of the stability of magnetic mineral assemblages within the mantle, unfettered by the effects of serpentinization and surficial oxidation, which in turn will better inform our understanding of long wavelength magnetic anomalies in the Earth.

  17. The synthesis and characterization of poly(?-glutamic acid)-coated magnetite nanoparticles and their effects on antibacterial activity and cytotoxicity

    NASA Astrophysics Data System (ADS)

    Inbaraj, B. Stephen; Kao, T. H.; Tsai, T. Y.; Chiu, C. P.; Kumar, R.; Chen, B. H.

    2011-02-01

    Magnetite nanoparticles (MNPs) modified with sodium and calcium salts of poly(?-glutamic acid) (NaPGA and CaPGA) were synthesized by the coprecipitation method, followed by characterization and evaluation of their antibacterial and cytotoxic effects. Superparamagnetic MNPs are particularly attractive for magnetic driving as well as bacterial biofilm and cell targeting in in vivo applications. Characterization of synthesized MNPs by the Fourier transform infrared spectra and magnetization curves confirmed the PGA coating on MNPs. The mean diameter of NaPGA- and CaPGA-coated MNPs as determined by transmission electron microscopy was 11.8 and 14 nm, respectively, while the x-ray diffraction pattern revealed the as-synthesized MNPs to be pure magnetite. Based on agar dilution assay, both NaPGA- and CaPGA-coated MNPs showed a lower minimum inhibitory concentration in Salmonella enteritidis SE 01 than the commercial antibiotics linezolid and cefaclor, but the former was effective against Escherichia coli ATCC 8739 and Staphylococcus aureus ATCC 10832, whereas the latter was effective against Escherichia coli O157:H7 TWC 01. An in vitro cytotoxicity study in human skin fibroblast cells as measured by MTT assay implied the as-synthesized MNPs to be nontoxic. This outcome demonstrated that both ?-PGA-modified MNPs are cytocompatible and possess antibacterial activity in vitro, and thereby should be useful in in vivo studies for biomedical applications.

  18. IR spectroscopic investigation of adsorption of oleic and stearic acids on a magnetite surface from CCI4 solutions

    NASA Astrophysics Data System (ADS)

    Korolev, V. V.; Savina, L. N.

    1994-04-01

    Adsorption of oleic and stearic acids on a magnetite surface from CCl4 solutions is investigated by the methods of internal reflection spectroscopy and classical transmission spectroscopy. Highly dispersed magnetite with a particle size from 2 to 20 nm was obtained by the method of chemical condensation. It was found from the IR spectra that after the synthesis, the magnetite surface is covered with adsorbed water molecules hindering the process of acid adsorption. The adsorbed water was removed by washing magnetite suspension in ethyl alcohol. It was discovered that following adsorption, molecules of oleic and stearic acids are in a chemosorbed state. Using polarized radiation in the investigation of the magnetite surface, it was found that adsorbed acid molecules are randomly oriented with respect to the magnetite surface.

  19. Magnetite-sulfide chondrules and nodules in CK carbonaceous chondrites - Implications for the timing of CK oxidation

    NASA Technical Reports Server (NTRS)

    Rubin, Alan E.

    1993-01-01

    CK carbonaceous chondrites contain rare (about 0.1 vol pct) magnetite-sulfide chondrules that range from about 240 to 500 microns in apparent diameter and have ellipsoidal to spheroidal morphologies, granular textures, and concentric layering. They resemble the magnetite-sulfide nodules occurring inside mafic silicate chondrules in CK chondrites. It seems likely that the magnetite-sulfide chondrules constitute the subset of magnetite-sulfide nodules that escaped as immiscible droplets from their molten silicate chondrule hosts during chondrule formation. The intactness of the magnetite-sulfide chondrules and nodules implies that oxidation of CK metal occurred before agglomeration. Hence, the pervasive silicate darkening of CK chondrites was caused by the shock mobilization of magnetite and sulfide, not metallic Fe-Ni and sulfide as in shock-darkened ordinary chondrites.

  20. Redox equilibria of iron oxides in aqueous-based magnetite dispersions: effect of pH and redox potential.

    PubMed

    Pang, Suh Cem; Chin, Suk Fun; Anderson, Marc A

    2007-07-01

    The effect of pH and redox potential on the redox equilibria of iron oxides in aqueous-based magnetite dispersions was investigated. The ionic activities of each dissolved iron species in equilibrium with magnetite nanoparticles were determined and contoured within the Eh-pH framework of a composite stability diagram. Both standard redox potentials and equilibrium constants for all major iron oxide redox equilibria in magnetite dispersions were found to differ from values reported for noncolloidal systems. The "triple point" position of redox equilibrium among Fe(II) ions, magnetite, and hematite shifted to a higher standard redox potential and an equilibrium constant which was several orders of magnitude higher. The predominant area of magnetite stability was enlarged to cover a wider range of both pH and redox potentials as compared to that of a noncolloidal magnetite system. PMID:17395194

  1. The growth and dissolution of ammonium perchlorate crystals in a fluidized bed crystallizer

    Microsoft Academic Search

    S. Ü. Tanrikulu; I. Ero?lu; A. N. Bulutcu; S. Özkar

    1998-01-01

    The growth and the dissolution of ammonium perchlorate crystals were studied in pure and in sodium chloride containing aqueous solutions, in a fluidized bed crystallizer. The presence of sodium chloride in the solution reduced the growth and the dissolution rates of ammonium perchlorate crystals. The growth rates were interpreted in terms of supersaturation levels. The orders and rate constants were

  2. Bi-functional gold-coated magnetite composites with improved biocompatibility.

    PubMed

    Arsianti, Maria; Lim, May; Lou, Shi Nee; Goon, Ian Y; Marquis, Christopher P; Amal, Rose

    2011-02-15

    The effect of gold attachment on the physical characteristics, cellular uptake, gene expression efficiency, and biocompatibility of magnetic iron oxide (MNP) vector was investigated in vitro in BHK21 cells. The surface modification of magnetite with gold was shown to alter the morphology and surface charge of the vector. Nonetheless, despite the differences in the surface charge with and without gold attachment, the surface charge of all vectors were positive when conjugated with PEI/DNA complex, and switched from positive to negative when suspended in cell media containing serum, indicating the adsorption of serum components onto the composite. The cellular uptake of all MNP vectors under the influence of a magnetic field increased when the composite loadings increased, and was higher for the MNP vector that was modified with gold. Both bare magnetite and gold-coated magnetite vectors gave similar optimal gene expression efficiency, however, the gold-coated magnetite vector required a 25-fold higher overall loading to achieve a comparable efficiency as the attachment of gold increased the particle size, thus reducing the surface area for PEI/DNA complex conjugation. The MNP vector without gold showed optimal gene expression efficiency at a specific magnetite loading, however further increases beyond the optimum loading decreased the efficiency of gene expression. The drop in efficiency at high magnetite loadings was attributed to the significant reduction in cellular viability, indicating the bare magnetite became toxic at high intracellular levels. The gene expression efficiency of the gold-modified vector, on the other hand, did not diminish with increasing magnetite loadings. Intracellular examination of both bare magnetite and gold-coated magnetite vectors at 48h post-magnetofection using transmission electron microscopy provided evidence of the localization of both vectors in the cell nucleus for gene expression and elucidated the nuclear uptake mechanism of both vectors. The results of this work demonstrate the efficacy of gold-modified vectors to be used in cellular therapy research that can function both as a magnetically-driven gene delivery vehicle and an intracellular imaging agent with negligible impact on cell viability. PMID:21131002

  3. Formation of magnetite by bacteria and its application.

    PubMed

    Arakaki, Atsushi; Nakazawa, Hidekazu; Nemoto, Michiko; Mori, Tetsushi; Matsunaga, Tadashi

    2008-09-01

    Magnetic particles offer high technological potential since they can be conveniently collected with an external magnetic field. Magnetotactic bacteria synthesize bacterial magnetic particles (BacMPs) with well-controlled size and morphology. BacMPs are individually covered with thin organic membrane, which confers high and even dispersion in aqueous solutions compared with artificial magnetites, making them ideal biotechnological materials. Recent molecular studies including genome sequence, mutagenesis, gene expression and proteome analyses indicated a number of genes and proteins which play important roles for BacMP biomineralization. Some of the genes and proteins identified from these studies have allowed us to express functional proteins efficiently onto BacMPs, through genetic engineering, permitting the preservation of the protein activity, leading to a simple preparation of functional protein-magnetic particle complexes. They were applicable to high-sensitivity immunoassay, drug screening and cell separation. Furthermore, fully automated single nucleotide polymorphism discrimination and DNA recovery systems have been developed to use these functionalized BacMPs. The nano-sized fine magnetic particles offer vast potential in new nano-techniques. PMID:18559314

  4. Optimizing Magnetite Nanoparticles for Mass Sensitivity in Magnetic Particle Imaging

    SciTech Connect

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

    2011-03-01

    Purpose: Magnetic particle imaging (MPI), using magnetite nanoparticles (MNPs) as tracer material, shows great promise as a platform for fast tomographic imaging. To date, the magnetic properties of MNPs used in imaging have not been optimized. As nanoparticle magnetism shows strong size dependence, we explore how varying MNP size impacts imaging performance in order to determine optimal MNP characteristics for MPI at any driving field frequency, ?. Methods: Monodisperse MNPs of varying size were synthesized and their magnetic properties characterized. Their MPI response was measured experimentally, at an arbitrarily chosen ? = 250 kHz, using a custom-built MPI transceiver designed to detect the third harmonic of MNP magnetization. Results were interpreted using a model of dynamic MNP magnetization that is based on the Langevin theory of superparamagnetism and accounts for sample size distribution, and size-dependent magnetic relaxation. Results: Our experimental results show clear variation in the MPI signal intensity as a function of MNP size that is in good agreement with modeled results. A maxima in the plot of MPI signal vs. MNP size indicates there is a particular size that is optimal for the chosen frequency of 250 kHz. Conclusions: For MPI at any chosen frequency, there will exist a characteristic particle size that generates maximum signal amplitude. We illustrate this at 250 kHz with particles of 15 nm core diameter.

  5. Water treatment using activated carbon supporting silver and magnetite.

    PubMed

    Valušová, Eva; Vandžurová, Anna; Pristaš, Peter; Antalík, Marián; Javorský, Peter

    2012-01-01

    Recent efforts in water purification have led to the development of novel materials whose unique properties can offer effective biocidal capabilities with greater ease of use and at lower cost. In this study, we introduce a novel procedure for the preparation of activated carbon (charcoal) composite in which magnetite and silver are incorporated (MCAG); we also describe the use of this material for the disinfection of surface water. The formation process of magnetic MCAG composite was studied using ultraviolet-visible spectroscopy. The results demonstrated the high sorption efficiency of AgNO? to magnetic activated carbon. The antimicrobial capabilities of the prepared MCAG were examined and the results clearly demonstrate their inhibitory effect on total river water bacteria and on Pseudomonas koreensis and Bacillus mycoides cultures isolated from river water. The bacterial counts in river water samples were reduced by five orders of magnitude following 30 min of treatment using 1 g l?¹ of MCAG at room temperature. The removal of all bacteria from the surface water samples implies that the MCAG material would be a suitable disinfectant for such waters. In combination with its magnetic character, MCAG would be an excellent candidate for the simple ambulatory disinfection of surface water. PMID:23109597

  6. Domain states in fine particle magnetite and titanomagnetite

    NASA Astrophysics Data System (ADS)

    Moon, T. S.

    1991-06-01

    The domain state (single domain versus multidomain) of fine magnetic particles has long been associated with their remanent and hysteresis properties. Both domain observations and micromagnetic theory indicate that a large number of local energy minimum (LEM) domain states are available to single domain and multidomain particles. Theoretical calculations based on a simple model of domain structure are made to determine the particle size, mineralogical, stress and temperature dependence of the LEM domain states available to fine particles of magnetite and titanomagnetite (TM56). The global (or absolute) energy minimum (AEM) domain state depends primarily on the balance between magnetostatic and exchange energies and shows only a weak temperature dependence. The range of local energy minima (LEM) domain states depends primarily on the anisotropy energies (magnetocrystalline and magnetoelastic) and is strongly temperature dependent. From the evolution of domain structure as a function of temperature and grain size implied from the domain state calculations, the relative stabilities of Thermoremanent Magnetization (TRM), grain growth Chemical Remanent Magnetization (CRM) and trans-domain Viscous Remanent Magnetization (VRM) are discussed. The magnetic behavior of an ensemble of fine particles will depend on the LEM states initially occupied by the particles.

  7. Observing thermomagnetic stability of nonideal magnetite particles: Good paleomagnetic recorders?

    NASA Astrophysics Data System (ADS)

    Almeida, Trevor P.; Kasama, Takeshi; Muxworthy, Adrian R.; Williams, Wyn; Nagy, Lesleis; Dunin-Borkowski, Rafal E.

    2014-10-01

    The thermomagnetic behavior of remanence-induced magnetite (Fe3O4) particles in the pseudo-single-domain (PSD) size range (~0.1-10 µm), which dominate the magnetic signature of many rock lithologies, is investigated using off-axis electron holography. Construction of magnetic induction maps allowed for the visualization of the vortex domain state in an individual Fe3O4 grain (~200 nm in diameter) as a function of temperature. Acquisition of a series of electron holograms at 100°C intervals during in situ heating up to 700°C demonstrates the vortex state of the Fe3O4 grain, in this instance, remains thermally stable close to its unblocking temperature and exhibits a similar in-plane remanent state upon cooling; i.e., the particle is effectively behaving like a uniaxial single-domain particle to temperatures near TC. Such particles are thought to be robust magnetic recorders. It is suggested that evidence for PSD behavior should therefore not preclude paleomagnetic investigation.

  8. Identification of Magnetite in B-type Asteroids

    NASA Astrophysics Data System (ADS)

    Yang, Bin; Jewitt, David

    2010-09-01

    Spectrally blue (B-type) asteroids are rare, with the second discovered asteroid, Pallas, being the largest and most famous example. We conducted a focused, infrared spectroscopic survey of B-type asteroids to search for water-related features in these objects. Our results show that the negative optical spectral slope of some B-type asteroids is due to the presence of a broad absorption band centered near 1.0 ?m. The 1 ?m band can be matched in position and shape using magnetite (Fe3O4), which is an important indicator of past aqueous alteration in the parent body. Furthermore, our observations of B-type asteroid (335) Roberta in the 3 ?m region reveal an absorption feature centered at 2.9 ?m, which is consistent with the absorption due to phyllosilicates (another hydration product) observed in CI chondrites. The new observations suggest that at least some B-type asteroids are likely to have incorporated significant amounts of water ice and to have experienced intensive aqueous alteration.

  9. Enhanced thermal stability of phosphate capped magnetite nanoparticles

    SciTech Connect

    Muthukumaran, T.; Philip, John, E-mail: philip@igcar.gov.in [SMARTS, Metallurgy and Materials Group, Indira Gandhi Centre for Atomic Research, Kalpakkam, Tamil Nadu-603 102 (India)

    2014-06-14

    We have studied the effect of phosphate capping on the high temperature thermal stability and magnetic properties of magnetite (Fe{sub 3}O{sub 4}) nanoparticles synthesized through a single-step co-precipitation method. The prepared magnetic nanoparticles are characterized using various techniques. When annealed in air, the phosphate capped nanoparticle undergoes a magnetic to non-magnetic phase transition at a temperature of 689?°C as compared to 580?°C in the uncoated nanoparticle of similar size. The observed high temperature phase stability of phosphate capped nanoparticle is attributed to the formation of a phosphocarbonaceous shell over the nanoparticles, which acts as a covalently attached protective layer and improves the thermal stability of the core material by increasing the activation energy. The phosphocarbonaceous shell prevents the intrusion of heat, oxygen, volatiles, and mass into the magnetic core. At higher temperatures, the coalescence of nanoparticles occurs along with the restructuring of the phosphocarbonaceous shell into a vitreous semisolid layer on the nanoparticles, which is confirmed from the small angle X-ray scattering, Fourier transform infra red spectroscopy, and transmission electron microscopy measurements. The probable mechanism for the enhancement of thermal stability of phosphocarbonaceous capped nanoparticles is discussed.

  10. IDENTIFICATION OF MAGNETITE IN B-TYPE ASTEROIDS

    SciTech Connect

    Yang Bin [Institute for Astronomy, University of Hawaii, Honolulu, HI 96822 (United States); Jewitt, David, E-mail: yangbin@ifa.hawaii.ed, E-mail: jewitt@ucla.ed [Department of Earth and Space Sciences, Institute for Geophysics and Planetary Physics and Department of Physics and Astronomy, UCLA, Los Angeles, CA 90095 (United States)

    2010-09-15

    Spectrally blue (B-type) asteroids are rare, with the second discovered asteroid, Pallas, being the largest and most famous example. We conducted a focused, infrared spectroscopic survey of B-type asteroids to search for water-related features in these objects. Our results show that the negative optical spectral slope of some B-type asteroids is due to the presence of a broad absorption band centered near 1.0 {mu}m. The 1 {mu}m band can be matched in position and shape using magnetite (Fe{sub 3}O{sub 4}), which is an important indicator of past aqueous alteration in the parent body. Furthermore, our observations of B-type asteroid (335) Roberta in the 3 {mu}m region reveal an absorption feature centered at 2.9 {mu}m, which is consistent with the absorption due to phyllosilicates (another hydration product) observed in CI chondrites. The new observations suggest that at least some B-type asteroids are likely to have incorporated significant amounts of water ice and to have experienced intensive aqueous alteration.

  11. Magnetization and susceptibility of ion irradiated granular magnetite films

    SciTech Connect

    Jiang, Weilin; McCloy, John S.; Lea, Alan S.; Sundararajan, J. A.; Yao, Qi; Qiang, Y.

    2011-04-26

    Superparamagnetic granular magnetite (Fe3O4) films with an average grain size of 3 nm have been found to be magnetized following 5.5 MeV Si2+ ion irradiation to a fluence of 1.0E16 ions/cm2 near room temperature. The film underwent a phase transition to ferromagnetism after the irradiation. X-ray diffraction study shows that the average grain size increased to 23 nm. There is a dramatic change in the microstructure, featuring particle aggregation and material condensation. Magnetic domains in the irradiated film are observed in the size range of tens to several hundreds of nanometers. The change in the magnetic properties is attributed to irradiation induced grain growth and structural modifications that lead to occurrence of magnetic anisotropy. There are dipolar interactions between the nanoparticles in both the unirradiated and irradiated films. Data fits for the in-phase alternating current magnetic susceptibility of the unirradiated film indicate that the blocking temperature is ~150 K, depending on frequency. A gradual Verwey transition for the irradiated film occurs at ~75 K, above which the susceptibility exhibits unusual behavior: a linear decrease with decreasing temperature. There are irreversible processes of magnetic domains during cooling and warming up between 10 and 300 K.

  12. Magnetization and susceptibility of ion-irradiated granular magnetite films

    SciTech Connect

    Jiang, W.; McCloy, J. S.; Lea, A. S.; Sundararajan, J. A.; Yao, Q.; Qiang, Y. [Pacific Northwest National Laboratory, Richland, Washington 99352 (United States); Physics Department, University of Idaho, Moscow, Idaho 83844 (United States)

    2011-04-01

    Porous granular films of magnetite (Fe{sub 3}O{sub 4}) with grains of {approx}3 nm in size were prepared using a state-of-the-art nanocluster deposition system. The films are initially superparamagnetic but become magnetized following Si{sup 2+} ion irradiation. A significant increase in the grain size and a dramatic change in the microstructure are observed. There are dipolar interactions between the nanoparticles in both the unirradiated and irradiated films. The in-phase alternating current magnetic susceptibility of the unirradiated film shows a blocking temperature of {approx}150 K, depending on frequency. A broadened Verwey transition for the irradiated film occurs at {approx}75 K, above which the susceptibility exhibits unusual behavior: a nearly linear decrease with decreasing temperature. There are irreversible domain rotations in the irradiated film during zero-field cooling and warming cycles between 10 and 300 K. The observed behavior of the irradiated granular films is quite distinct from that of metallic nanostructures after irradiation, and is due to the dramatic change in microstructures.

  13. Lipolytic biocatalyst based on recyclable magnetite-polysiloxane nanoparticles

    NASA Astrophysics Data System (ADS)

    Durdureanu-Angheluta, Anamaria; Ignat, Maurusa-Elena; Maier, Stelian Sergiu; Pricop, Lucia; Coroaba, Adina; Fifere, Adrian; Pinteala, Mariana; Chiriac, Anca

    2014-02-01

    This work presents a novel hydrophobic magnetizable nanosupport able to load and valorize the lipase derived from Candida cylindracea (CCL). Nude magnetite nanoparticles (MP) were coated by covalent binding with an ester-polysiloxane (PS). The chemical composition, dimensions, morphology and magnetic properties of the resulted core-shell nanoparticles (MP-PS-CCL) are analyzed. The amount of immobilized lipase increase when loaded from aqueous solutions of up to 12.8 mg/mL CCL, when a lipolytic activity of 74.76 U/g is achieved. For higher concentrations of the loading solution, the activity of immobilized lipase decreases, probably due to the enzyme steric hindrance. MP-PS-CCL exhibits a good lipolytic activity against 4-nitrophenyl laurate (4-NPL), which allows the kinetic study of lipolysis reaction by measuring the amount of released 4-nitrophenol (4-NP), when working at room temperature, in TRIS buffer (pH 8.2). Even after three months of storage, the product is able to sustain up to 4 reusing cycles.

  14. Magnetoresistance enhancement in epitaxial magnetite films grown on vicinal substrates

    NASA Astrophysics Data System (ADS)

    Arora, S. K.; Sofin, R. G. S.; Shvets, I. V.

    2005-10-01

    The magnetoresistance (MR) behavior of epitaxial magnetite Fe3O4 grown on low-vicinal (small miscut) and high-vicinal (large miscut) MgO substrates is compared. Magnetization measurements on Fe3O4 films on high-vicinal substrates showed reduced magnetic moment as compared with the films grown on low-vicinal MgO, which correlates well with the expected reduction in magnetic moment due to step edge induced additional antiphase boundaries (APBs) with out-of-plane shift vectors. The MR is significantly higher (12.3% at 2T ) for a 45nm Fe3O4 film on high-vicinal substrate than that observed (7.2% at 2T ) for a film on low-vicinal substrate. A strong anisotropy in the MR is observed in correlation with the direction of atomic step edges. In addition to the increase in MR, the field dependency of the MR is also modified. The observed modification in the magnetotransport behavior of epitaxial Fe3O4 films is attributed to an enhanced spin scattering arising due to the presence of atomic height steps that lead to the formation of a greater density of antiferromagnetically coupled APBs.

  15. Removal of hexavalent chromium [Cr(VI)] from aqueous solutions by the diatomite-supported\\/unsupported magnetite nanoparticles

    Microsoft Academic Search

    Peng Yuan; Dong Liu; Mingde Fan; Dan Yang; Runliang Zhu; Fei Ge; JianXi Zhu; Hongping He

    2010-01-01

    Diatomite-supported\\/unsupported magnetite nanoparticles were prepared by co-precipitation and hydrosol methods, and characterized by X-ray diffraction, nitrogen adsorption, elemental analysis, differential scanning calorimetry, transmission electron microscopy and X-ray photoelectron spectroscopy. The average sizes of the unsupported and supported magnetite nanoparticles are around 25 and 15nm, respectively. The supported magnetite nanoparticles exist on the surface or inside the pores of diatom shells,

  16. 76 FR 69284 - Pure Magnesium From China

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-11-08

    ...731-TA-696 (Third Review)] Pure Magnesium From China Determination On the basis...of the antidumping duty order on pure magnesium from China would be likely to lead to...4274 (October 2011), entitled Pure Magnesium from China: Investigation No....

  17. Pure iron and other magnetic minerals in meteorites

    NASA Astrophysics Data System (ADS)

    Pechersky, D. M.; Markov, G. P.; Tsel'movich, V. A.

    2015-01-01

    The results of thermomagnetic and microprobe analyses of 37 samples from 25 different types of meteorite are analyzed with the focus on the presence of pure (nickel-free) iron in them. It is established that the metallic particles in the studied meteorites cluster in three isolated groups: (1) pure iron, (2) kamacite with mode 3-6% Ni, and (3) taenite with mode ˜50% Ni. The hiatuses in the Fe-Ni alloy compositions between these groups of magnetic grains contradict the Fe-Ni phase diagram, which predicts a continuous series of solid solutions in this system. This isolated distribution of the compositions of the metallic particles in the meteorites is reasonably accounted for by the specific properties of the melt (melts) and the processes of their crystallization and decomposition in space. It is suggested that pure iron in the meteorites could have been formed by either of two scenarios. According to the "primary," pure iron crystallizes from the melt, and according to the "secondary" scenario, it is produced by the decomposition of the solid solution.

  18. Negativity of random pure states

    SciTech Connect

    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

    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.

  19. Magnetite magnetosome and fragmental chain formation of Magnetospirillum magneticum AMB-1: transmission electron microscopy and magnetic observations

    NASA Astrophysics Data System (ADS)

    Li, Jinhua; Pan, Yongxin; Chen, Guanjun; Liu, Qingsong; Tian, Lanxiang; Lin, Wei

    2009-04-01

    Stable single-domain (SD) magnetite formed intracellularly by magnetotactic bacteria is of fundamental interest in sedimentary and environmental magnetism. In this study, we studied the time course of magnetosome growth and magnetosome chain formation (0-96 hr) in Magnetospirillum magneticum AMB-1 by transmission electron microscopy (TEM) observation and rock magnetism. The initial non-magnetic cells were microaerobically batch cultured at 26 °C in a modified magnetic spirillum growth medium. TEM observations indicated that between 20 and 24 hr magnetosome crystals began to mineralize simultaneously at multiple sites within the cell body, followed by a phase of rapid growth lasting up to 48 hr cultivation. The synthesized magnetosomes were found to be assembled into 3-5 subchains, which were linearly aligned along the long axis of the cell, supporting the idea that magnetosome vesicles were linearly anchored to the inner membrane of cell. By 96 hr cultivation, 14 cubo-octahedral magnetosome crystals in average with a mean grain size of ~44.5 nm were formed in a cell. Low-temperature (10-300 K) thermal demagnetization, room-temperature hysteresis loops and first-order reversal curves (FORCs) were conducted on whole cell samples. Both coercivity (4.7-18.1 mT) and Verwey transition temperature (100-106 K) increase with increasing cultivation time length, which can be explained by increasing grain size and decreasing non-stoichiometry of magnetite, respectively. Shapes of hysteresis loops and FORCs indicated each subchain behaving as an `ideal' uniaxial SD particle and extremely weak magnetostatic interaction fields between subchains. Low-temperature thermal demagnetization of remanence demonstrated that the Moskowitz test is valid for such linear subchain configurations (e.g. ?FC/?ZFC > 2.0), implying that the test is applicable to ancient sediments where magnetosome chains might have been broken up into short chains due to disintegration of the organic scaffold structures after cell death. These findings provide new insights into magnetosome biomineralization of magnetotactic bacteria and contribute to better understanding the magnetism of magnetofossils in natural environments.

  20. Magneto-transport study of magnetite (Fe3O4) nanoparticles between Au nanogap electrodes on surface-oxidized Si substrate

    NASA Astrophysics Data System (ADS)

    Kobori, H.; Takata, N.; Fukutome, N.; Yamasaki, A.; Sugimura, A.; Taniguchi, T.; Horie, T.; Naitoh, Y.; Shimizu, T.

    2013-04-01

    We have studied the magneto-transport of magnetite (Fe3O4) nanoparticles (MNPs) between Au nanogap electrodes (ANGEs) on surface-oxidized Si substrate. The MNP sizes are approximately 40 nm and the 100 nm thick magnetite thin film (which is formed of the MNP aggregation) was prepared between and around the ANGEs by use of the RF reactive magnetron sputtering method. The distance between the ANGEs and the bridge width of the ANGEs are approximately 50 nm and 1.5 ?m, respectively. The ANGEs were produced by the tilted-angle-deposition method. The optical microscope, scanning electron microscope and atomic force microscope were used to observe the sample surface structure and morphology. To investigate the crystal structure and crystallinity of the MNPs, the X-ray diffraction measurement was performed. The electrical resistance and magneto-resistance ratio of the MNPs between the ANGEs were measured as a function of temperature. The magneto-transport mechanism is discussed on the basis of the spin dependent transport.

  1. Impedimetric sensor for toxigenic Penicillium sclerotigenum detection in yam based on magnetite-poly(allylamine hydrochloride) composite.

    PubMed

    Silva, Gilcelia J L; Andrade, Cesar A S; Oliveira, Idjane S; de Melo, Celso P; Oliveira, Maria D L

    2013-04-15

    We describe a new DNA biosensor for the detection of toxigenic Penicillium sclerotigenum in pure culture or infected yams. The P. sclerotigenum detection takes place on a self-assembled monolayer of a (magnetite)/(poly(allylamine hydrochloride)) (Fe3O4-PAH) composite that serves as an anchoring layer for the DNA hybridization interaction. Electrical impedance spectroscopy (EIS) was used to evaluate and quantify the hybridization degree. The Fe3O4-PAH composite is a good platform for the immobilization of biomolecules, due to the presence of many possible binding sites for nucleotides and to its large surface-to-volume ratio and good biocompatibility. The biosensor was capable of not only qualitatively detecting the presence of the fungus genome at low concentrations, but also shown a good quantitative impedimetric response its electrical resistance was monitored along the time of exposure. A Fe3O4-PAH-probe biosensor would require only small volumes and low concentrations of the analyte when used, for instance, in detecting P. sclerotigenum contamination of food, besides presenting many comparative advantages, such as selectivity, specificity and reproducibility, relative to alternative techniques. PMID:23465186

  2. Microwave resonant and zero-field absorption study of doped magnetite prepared by a co-precipitation method.

    PubMed

    Aphesteguy, Juan Carlos; Jacobo, Silvia E; Lezama, Luis; Kurlyandskaya, Galina V; Schegoleva, Nina N

    2014-01-01

    Fe3O4 and ZnxFe3-xO4 pure and doped magnetite magnetic nanoparticles (NPs) were prepared in aqueous solution (Series A) or in a water-ethyl alcohol mixture (Series B) by the co-precipitation method. Only one ferromagnetic resonance line was observed in all cases under consideration indicating that the materials are magnetically uniform. The shortfall in the resonance fields from 3.27 kOe (for the frequency of 9.5 GHz) expected for spheres can be understood taking into account the dipolar forces, magnetoelasticity, or magnetocrystalline anisotropy. All samples show non-zero low field absorption. For Series A samples the grain size decreases with an increase of the Zn content. In this case zero field absorption does not correlate with the changes of the grain size. For Series B samples the grain size and zero field absorption behavior correlate with each other. The highest zero-field absorption corresponded to 0.2 zinc concentration in both A and B series. High zero-field absorption of Fe3O4 ferrite magnetic NPs can be interesting for biomedical applications. PMID:24950442

  3. Epitaxial Fe3-xTixO4 films from magnetite to ulvöspinel by pulsed laser deposition

    SciTech Connect

    Droubay, Timothy C.; Pearce, Carolyn I.; Ilton, Eugene S.; Engelhard, Mark H.; Jiang, Weilin; Heald, Steve M.; Arenholz, Elke; Shutthanandan, V.; Rosso, Kevin M.

    2011-10-13

    Epitaxial films along the Fe3-xTixO4 (titanomagnetite) compositional series from pure end-members magnetite (Fe3O4) to ulvöspinel (Fe2TiO4) were successfully grown by pulsed laser deposition on MgO(100) substrates. Spectroscopic characterization including high resolution x-ray diffraction, x-ray photoelectron spectroscopy, and synchrotron-based x-ray absorption and magnetic circular dichroism consistently shows that Ti(IV) substitutes for Fe(III) in the inverse spinel lattice with a proportional increase in lattice Fe(II) concentration. No evidence of Ti interstitials, spinodal decomposition, or secondary phases was found in the bulk of the grown films. At the uppermost few nanometers of the Ti-bearing film surfaces, evidence suggests that Fe(II) is susceptible to facile oxidation, and that an associated lower Fe/Ti ratio in this region is consistent with surface compositional incompleteness or alteration to a titanomaghemite-like composition and structure. The surface of these films nonetheless appear to remain highly ordered and commensurate with the underlying structure despite facile oxidation, a surface condition that is found to be reversible to some extent by heating in low oxygen environments.

  4. Crystallization of hollow mesoporous silica nanoparticles.

    PubMed

    Drisko, Glenna L; Carretero-Genevrier, Adrian; Perrot, Alexandre; Gich, Martí; Gàzquez, Jaume; Rodriguez-Carvajal, Juan; Favre, Luc; Grosso, David; Boissière, Cédric; Sanchez, Clément

    2015-03-11

    Complex 3D macrostructured nanoparticles are transformed from amorphous silica into pure polycrystalline ?-quartz using catalytic quantities of alkaline earth metals as devitrifying agent. Walls as thin as 10 nm could be crystallized without losing the architecture of the particles. The roles of cation size and the mol% of the incorporated devitrifying agent in crystallization behavior are studied, with Mg(2+), Ca(2+), Sr(2+) and Ba(2+) all producing pure ?-quartz under certain conditions. PMID:25503642

  5. Small magnetite antiretroviral therapeutic nanoparticle probes for MRI of drug biodistribution

    PubMed Central

    Guo, Dongwei; Li, Tianyuzi; McMillan, JoEllyn; Sajja, Balasrinivasa R; Puligujja, Pavan; Boska, Michael D; Gendelman, Howard E; Liu, Xin-Ming

    2013-01-01

    Aim Drug toxicities, compliance and penetrance into viral reservoirs have diminished the efficacy of long-term antiretroviral therapy (ART) for treatment of HIV infection. Cell-targeted nanoformulated ART was developed to improve disease outcomes. However, rapid noninvasive determination of drug biodistribution is unrealized. To this end, small magnetite ART (SMART) nanoparticles can provide assessments of ART biodistribution by MRI. Materials & methods Poly(lactic-co-glycolic acid), 1,2-distearoyl-sn-glycero-3-phosphocholine- and 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-(methoxy-PEG 2000)-encased particles were synthesized with atazanavir (ATV) and magnetite. Uptake and retention of ATV and magnetite administered at 3:1 ratios (weight/weight) were determined in human monocyte-derived macrophages and mice. Results SMART particles were taken up and retained in macrophages. In mice, following parenteral SMART injection, magnetite and drug biodistribution paralleled one another with MRI signal intensity greatest in the liver and spleen at 24 h. Significantly, ATV and magnetite levels correlated. Conclusion SMART can permit rapid assessment of drug tissue concentrations in viral reservoirs. PMID:23905578

  6. Control of nanoparticle size, reactivity and magnetic properties during the bioproduction of magnetite by Geobacter sulfurreducens.

    PubMed

    Byrne, J M; Telling, N D; Coker, V S; Pattrick, R A D; van der Laan, G; Arenholz, E; Tuna, F; Lloyd, J R

    2011-11-11

    The bioproduction of nanoscale magnetite by Fe(III)-reducing bacteria offers a potentially tunable, environmentally benign route to magnetic nanoparticle synthesis. Here, we demonstrate that it is possible to control the size of magnetite nanoparticles produced by Geobacter sulfurreducens by adjusting the total biomass introduced at the start of the process. The particles have a narrow size distribution and can be controlled within the range of 10-50 nm. X-ray diffraction analysis indicates that controlled production of a number of different biominerals is possible via this method including goethite, magnetite and siderite, but their formation is strongly dependent upon the rate of Fe(III) reduction and total concentration and rate of Fe(II) produced by the bacteria during the reduction process. Relative cation distributions within the structure of the nanoparticles have been investigated by x-ray magnetic circular dichroism and indicate the presence of a highly reduced surface layer which is not observed when magnetite is produced through abiotic methods. The enhanced Fe(II)-rich surface, combined with small particle size, has important environmental applications such as in the reductive bioremediation of organics, radionuclides and metals. In the case of Cr(VI), as a model high-valence toxic metal, optimized biogenic magnetite is able to reduce and sequester the toxic hexavalent chromium very efficiently to the less harmful trivalent form. PMID:22020365

  7. Effect of grain boundaries on the magnetoresistance of magnetite

    NASA Astrophysics Data System (ADS)

    Rybchenko, S. I.; Fujishiro, Y.; Takagi, H.; Awano, M.

    2005-08-01

    The effects of grain boundary morphology and stoichiometry had been systematically examined to clarify the role of natural grain boundaries in magnetoresistance of magnetite Fe3(1-?)O4 . We found that the excess resistance, caused by presence of the grain boundaries, is negligibly low in stoichiometric polycrystals. Accordingly, there was no grain boundary magnetoresistance detected in dense polycrystals. Moreover, the incorporation of grain boundaries was found to decrease the resistance of polycrystalline samples below the Verwey transition temperature. That was connected to the enhanced conductivity of grain boundaries appearing due to the local suppression of charge ordering. On the other hand, the essential negative magnetoresistance was detected in granular samples, exploring the point contact geometry for intergrain contacts. That magnetoresistance is characterized by large high-field component and appearance over a wide range of oxidation. It has been explained within the model of magnetically inhomogeneous grain boundary with the characteristic magnetic thickness of the order of exchange length. The magnetoresistance effect was connected to the spin-dependent scattering at the transition layers of magnetization formed around hard magnetic defects. The contraction of these transition layers by external magnetic field is supposed to provide the origin of the observed magnetoresistance. The analysis of appropriate microscopic scattering mechanisms reveals the important role of point defects in the spin-dependent scattering. The second magnetoresistance component was separated at highly oxidized grain boundaries and associated with tunneling transport across the isolating grain boundaries. Although the oxidation was shown to improve the isolating properties of natural grain boundaries, the performance of oxidized grain boundary as a tunneling barrier is still poor.

  8. Synthesis of magnetite-porphyrin nanocomposite and its application as a novel magnetic adsorbent for removing heavy cations

    SciTech Connect

    Bakhshayesh, Sara, E-mail: s_bakhshayesh@yahoo.com; Dehghani, Hossein, E-mail: dehghani@kashanu.ac.ir

    2013-07-15

    Graphical abstract: Magnetite-porphyrin nanocomposite (MPNC) as a novel magnetic adsorbent for removing heavy cations was synthesized. - Highlights: • Nanosized Fe{sub 3}O{sub 4} was prepared by hydrothermal reaction of iron salt in alkaline media. • The synthesized magnetite and nanocomposite had soft ferromagnetic property. • Magnetic nanocomposite as a novel magnetic adsorbent for heavy cations was prepared. • Satisfactory separation from solutions in the order of Pb{sup 2+} > Cd{sup 2+} > Hg{sup 2+} was obtained. - Abstract: Magnetite-porphyrin nanocomposite (MPNC) was synthesized as a novel magnetic adsorbent for removing heavy cations. Firstly, we prepared nano-sized magnetite using a simple hydrothermal route. The synthesis of nanoscaled magnetite was carried out through reaction between iron source and various amines. In this paper, we studied effective parameters in controlling shape and size of nanoscaled magnetite. These parameters were presence of alkaline, reaction time, kind of amine and iron salt. Morphology, particle size and magnetic properties of the nanoscaled magnetite were obtained by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), Fourier transform infrared (FT-IR), diffuse reflectance spectra (DRS) and vibrating sample magnetometer (VSM). Our study showed that the synthesized magnetite from reaction between FeSO{sub 4} and hydrazinum hydrate has spherical shape. The synthesized magnetite was a nanosized compound and used for preparation of magnetite-porphyrin nanocomposite. The synthesized magnetite-porphyrin hybrid material had magnetic property and was used as magnetic adsorbent for removing heavy cations of water. Satisfactory separation from solutions in the order of Pb{sup 2+} > Cd{sup 2+} > Hg{sup 2+} was obtained.

  9. Fe{sup II} induced mineralogical transformations of ferric oxyhydroxides into magnetite of variable stoichiometry and morphology

    SciTech Connect

    Usman, M. [Universite de Lorraine, Laboratoire de Chimie Physique et Microbiologie pour l'Environnement, LCPME, UMR 7564, Institut Jean Barriol, CNRS-, 405 rue de Vandoeuvre, 54600 Villers-les-Nancy (France) [Universite de Lorraine, Laboratoire de Chimie Physique et Microbiologie pour l'Environnement, LCPME, UMR 7564, Institut Jean Barriol, CNRS-, 405 rue de Vandoeuvre, 54600 Villers-les-Nancy (France); CNRS, Laboratoire de Chimie Physique et Microbiologie pour l'Environnement, LCPME, UMR 7564, Institut Jean Barriol, CNRS-, 405 rue de Vandoeuvre, 54600 Villers-les-Nancy (France); Institute of Soil and Environmental Sciences, University of Agriculture, Faisalabad 38040 (Pakistan); Abdelmoula, M. [Universite de Lorraine, Laboratoire de Chimie Physique et Microbiologie pour l'Environnement, LCPME, UMR 7564, Institut Jean Barriol, CNRS-, 405 rue de Vandoeuvre, 54600 Villers-les-Nancy (France) [Universite de Lorraine, Laboratoire de Chimie Physique et Microbiologie pour l'Environnement, LCPME, UMR 7564, Institut Jean Barriol, CNRS-, 405 rue de Vandoeuvre, 54600 Villers-les-Nancy (France); CNRS, Laboratoire de Chimie Physique et Microbiologie pour l'Environnement, LCPME, UMR 7564, Institut Jean Barriol, CNRS-, 405 rue de Vandoeuvre, 54600 Villers-les-Nancy (France); Hanna, K. [Universite de Lorraine, Laboratoire de Chimie Physique et Microbiologie pour l'Environnement, LCPME, UMR 7564, Institut Jean Barriol, CNRS-, 405 rue de Vandoeuvre, 54600 Villers-les-Nancy (France) [Universite de Lorraine, Laboratoire de Chimie Physique et Microbiologie pour l'Environnement, LCPME, UMR 7564, Institut Jean Barriol, CNRS-, 405 rue de Vandoeuvre, 54600 Villers-les-Nancy (France); CNRS, Laboratoire de Chimie Physique et Microbiologie pour l'Environnement, LCPME, UMR 7564, Institut Jean Barriol, CNRS-, 405 rue de Vandoeuvre, 54600 Villers-les-Nancy (France); Ecole Nationale Superieure de Chimie de Rennes, UMR CNRS 6226 'Sciences Chimiques de Rennes', Avenue du General Leclerc, 35708 Rennes Cedex 7 (France); and others

    2012-10-15

    The Moessbauer 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 Fe{sup II} and OH{sup -} in stoichiometric amounts to form magnetite at an initial pH of {approx}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, {delta}, of magnetite (Fe{sub 3-{delta}}O{sub 4}) generated from F ({delta}{approx}0.04) and L ({delta}{approx}0.05) was relatively low as compared to that in magnetite from G ({delta}{approx}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. - Graphical abstract: Moessbauer spectrum of the early stage of magnetite formation formed from the interaction of adsorbed Fe{sup II} species with goethite. Highlights: Black-Right-Pointing-Pointer Ferric oxides were reacted with hydroxylated Fe{sup II} to form magnetite. Black-Right-Pointing-Pointer Magnetite formation was quantified as a function of aging time. Black-Right-Pointing-Pointer Complete transformation of ferrihydrite and lepidocrocite was achieved. Black-Right-Pointing-Pointer Almost 70% of initial goethite was transformed. Black-Right-Pointing-Pointer Resulting magnetites have differences in stoichiometry and morphological properties.

  10. Production of substantially pure fructose

    DOEpatents

    Hatcher, Herbert J. (Idaho Falls, ID); Gallian, John J. (Twin Falls, ID); Leeper, Stephen A. (Idaho Falls, ID)

    1990-01-01

    A process is disclosed for the production of substantially pure fructose from sucrose-containing substrates. The process comprises converting the sucrose to levan and glucose, purifying the levan by membrane technology, hydrolyzing the levan to form fructose monomers, and recovering the fructose.

  11. Pure pseudoboehmite from sodium aluminate

    Microsoft Academic Search

    B. Ozimek; J. Grzechowiak; B. Radomyski

    1980-01-01

    The influence of the Na2O\\/Al2O3 mole ratio in sodium aluminate, the pH and the temperature of precipitation upon physicochemical properties of pseudoboehmite obtained from sodium aluminate has been studied. A mole ratio of 1?1 and low pH are favorable for the preparation of pure alumina.

  12. Optical properties of pure water

    Microsoft Academic Search

    Hendrik Buiteveld; J. H. Hakvoort; M. Donze

    1994-01-01

    The optical properties of pure water are basic input data for many geophysical investigations such as remote sensing of surface water and underwater radiative transfer calculations. Knowledge of the spectral properties of components in surface water is required for accurate interpretation of measured reflection and attenuation spectra in terms of their concentrations. Also the sources and sizes of errors in

  13. Crystallization Stages of the Bishop Tuff Magma Body Recorded in Crystal Textures in Pumice Clasts

    SciTech Connect

    Pamukcu, Ayla; Gualda, Guilherme A.R.; Anderson, Jr. , Alfred T. (Vanderbilt); (UC)

    2012-07-25

    The Bishop Tuff is a giant silicic ignimbrite erupted at 0.76 Ma in eastern California, USA. Five pumice clasts from the late-erupted Bishop Tuff (Aeolian Buttes) were studied in an effort to better understand the pre- and syn-eruptive history of the Bishop magma body and place constraints on the timescales of its existence. This study complements and expands on a previous study that focused on early-erupted Bishop Tuff pumice clasts. Bulk densities of pumice clasts were measured using an immersion method, and phenocryst crystal contents were determined using a sieving and winnowing procedure. X-ray tomography was used to obtain qualitative and quantitative textural information, particularly crystal size distributions (CSDs). We have determined CSDs for crystals ranging in size from {approx}10 to {approx}1000 {micro}m for three groups of mineral phases: magnetite ({+-}ilmenite), pyroxene + biotite, quartz + feldspar. Similar to early-erupted pumice, late-erupted pumice bulk density and crystal contents are positively correlated, and comparison of crystal fraction vs size trends suggests that the proportion of large crystals is the primary control on crystallinity. Porosity is negatively correlated with crystal content, which is difficult to reconcile with closed-system crystallization. Magnetite and pyroxene + biotite size distributions are fractal in nature, often attributed to fragmentation; however, crystals are mostly whole and euhedral, such that an alternative mechanism is necessary to explain these distributions. Quartz + feldspar size distributions are kinked, with a shallow-sloped log-linear section describing large crystals (> 140 {micro}m) and a steep-sloped log-linear section describing small crystals (< 140 {micro}m). We interpret these two crystal populations as resulting from a shift in crystallization regime. We suggest that the shallow-sloped section describes a pre-eruptive quartz + feldspar growth-dominated regime, whereas the steep-sloped section represents a population that grew during a nucleation-dominated regime that began as a result of decompression at the onset of eruption. Timescales of quartz growth calculated from the slopes of these two segments of the size distributions indicate that the pre-eruptive crystal population grew on timescales on the order of millennia and may describe the timescale of crystallization of the Bishop magma body. The syn-eruptive population gives timescales of < 1-2 years (but possibly much less) and probably marks the onset of eruptive decompression.

  14. Infrared photonic crystal fiber

    Microsoft Academic Search

    E. Rave; K. Roodenko; A. Katzir

    2003-01-01

    An infrared photonic crystal fiber has been made by multiple extrusions of silver halide (AgClxBr1-x) crystalline materials. The core of the fiber consisted of pure AgBr, and the cladding area included fiberoptic elements made of AgCl (with lower refractive index). Fibers of outer diameter 1 mm and length of the order of 1 m were flexible and transparent in the

  15. Large-scale exploratory tests of sodium/magnetite-concrete interactions. [LMFBR

    SciTech Connect

    Randich, E.; Acton, R.U.

    1983-04-01

    Two large-scale tests examining the interaction between molten sodium at 825 K and magnetite concrete were performed. In the first test, bare magnetite concrete was exposed to the sodium and in the second test the concrete was partially protected by a flawed steel liner and a layer of dense silica firebrick. The results demonstrated that energetic chemical reactions can occur between sodium and magnetite concrete. In the first test, reaction zone temperatures exceeded 1150 K and the maximum heat generation rate was approx. 1.3 x 10/sup 5/ J/m/sup 2/-s. The maximum observed penetration rate was 2.5 mm/min. In the second test, the silica firebrick provided little protection for the underlying concrete. The reaction debris that formed between the steel liner and the concrete caused gross deformation of the liner as well as extensive cracking of the reinforced concrete.

  16. Reordering between tetrahedral and octahedral sites in ultrathin magnetite films grown on MgO(001)

    SciTech Connect

    Bertram, F.; Deiter, C. [Hamburger Synchrotronstrahlungslabor am Deutschen Elektronen-Synchrotron, Notkestr. 85, 22607 Hamburg (Germany)] [Hamburger Synchrotronstrahlungslabor am Deutschen Elektronen-Synchrotron, Notkestr. 85, 22607 Hamburg (Germany); Schemme, T.; Jentsch, S.; Wollschlaeger, J. [Fachbereich Physik, Universitaet Osnabrueck, Barbarastr. 7, 49069 Osnabrueck (Germany)] [Fachbereich Physik, Universitaet Osnabrueck, Barbarastr. 7, 49069 Osnabrueck (Germany)

    2013-05-14

    Magnetite ultrathin films were grown using different deposition rates and substrate temperatures. The structure of these films was studied using (grazing incidence) x-ray diffraction, while their surface structure was characterized by low energy electron diffraction. In addition to that, we performed x-ray photoelectron spectroscopy and magneto optic Kerr effect measurements to probe the stoichiometry of the films as well as their magnetic properties. The diffraction peaks of the inverse spinel structure, which originate exclusively from Fe ions on tetrahedral sites are strongly affected by the preparation conditions, while the octahedral sites remain almost unchanged. With both decreasing deposition rate as well as decreasing substrate temperature, the integrated intensity of the diffraction peaks originating exclusively from Fe on tetrahedral sites is decreasing. We propose that the ions usually occupying tetrahedral sites in magnetite are relocated to octahedral vacancies. Ferrimagnetic behaviour is only observed for well ordered magnetite films.

  17. Reflective and magnetic properties of photonic polymer composite materials based on porous silicon and magnetite nanoparticles.

    PubMed

    Kim, Jihoon; Koh, Youngdae; Jang, Seunghyun; Jung, Kyoungsun; Woo, Hee-Gweon; Kim, Sungsoo; Sohn, Honglae

    2010-05-01

    Photonic polymer composite materials exhibiting both reflective and magnetic properties were prepared by the replication of rugate porous silicon (PS) using polystyrene and magnetite nanoparticle (Fe3O4). Rugate PS prepared by applying a computer-generated pseudo-sinusoidal current waveform resulted in a mirror with high reflectivity in a specific narrow spectral region and served as a template for replicating its nanostructure with polystyrene containing the magnetic nanoparticles of magnetite. The composite films replicated a sharp photonic resonance with full-width at half maximum (FWHM) of 20 nm from rugate PS in the reflectivity spectrum as well as displayed a magnetic property of magnetite nanoparticles in SQUID magnetometry. Optical characteristics of composite films indicated that the surface of polymer film had a negative structure of rugate PS. The composite films were stable in aqueous solutions for several days without any degradation. PMID:20358975

  18. Reordering between tetrahedral and octahedral sites in ultrathin magnetite films grown on MgO(001)

    NASA Astrophysics Data System (ADS)

    Bertram, F.; Deiter, C.; Schemme, T.; Jentsch, S.; Wollschläger, J.

    2013-05-01

    Magnetite ultrathin films were grown using different deposition rates and substrate temperatures. The structure of these films was studied using (grazing incidence) x-ray diffraction, while their surface structure was characterized by low energy electron diffraction. In addition to that, we performed x-ray photoelectron spectroscopy and magneto optic Kerr effect measurements to probe the stoichiometry of the films as well as their magnetic properties. The diffraction peaks of the inverse spinel structure, which originate exclusively from Fe ions on tetrahedral sites are strongly affected by the preparation conditions, while the octahedral sites remain almost unchanged. With both decreasing deposition rate as well as decreasing substrate temperature, the integrated intensity of the diffraction peaks originating exclusively from Fe on tetrahedral sites is decreasing. We propose that the ions usually occupying tetrahedral sites in magnetite are relocated to octahedral vacancies. Ferrimagnetic behaviour is only observed for well ordered magnetite films.

  19. Acoustically Bound Microfluidic Bubble Crystals

    NASA Astrophysics Data System (ADS)

    Rabaud, David; Thibault, Pierre; Mathieu, Mylène; Marmottant, Philippe

    2011-04-01

    Bubbles confined in microchannels self-organize without directly contacting one another when excited by an external acoustic field. The bubbles tend to form periodic “crystal”-like lattices with a finite interbubble distance. This equilibrium distance can be adjusted by simply tuning the acoustic frequency. This new type of crystal is purely mediated by acoustic surface waves emitted by the pulsating bubbles. Because these waves are reflected at the channel boundaries, the bubbles interact with their own images across the boundary.

  20. The distinct effects of Mn substitution on the reactivity of magnetite in heterogeneous Fenton reaction and Pb(II) adsorption.

    PubMed

    Liang, Xiaoliang; He, Zisen; Wei, Gaoling; Liu, Peng; Zhong, Yuanhong; Tan, Wei; Du, Peixin; Zhu, Jianxi; He, Hongping; Zhang, Jing

    2014-07-15

    In this study, a series of Mn substituted magnetites were synthesized and used in catalyzing the heterogeneous Fenton degradation of acid orange II and Pb(II) adsorption, in order to investigate the effect of Mn substitution on the reactivity of magnetite. The valence and local environment of both Fe and Mn in the spinel structure of magnetite were investigated by X-ray absorption fine structure (XAFS) spectroscopy. The incorporation of Mn did not change the valence and local structure of Fe in the synthetic magnetite, while Mn was in the valences of +2 and +3. The Mn distribution on the octahedral sites of magnetite surface increased with the increase in Mn content. The Mn introduction led to an improvement of catalytic activity of magnetite. The sample with the minimum Mn content displayed the best efficiency in OH production and the degradation of acid orange II, while the other substituted samples did not show obvious difference in their catalytic performance. The adsorption capacity of magnetite samples toward Pb(II) gradually increased with the increase in Mn content. The above influences of Mn substitution on the reactivity of magnetite were discussed in views of the variations in microstructural environment and physicochemical properties. PMID:24863781