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1

Formation of "Chemically Pure" Magnetite from Mg-Fe-Carbonates Implications for the Exclusively Inorganic Origin of Magnetite and Sulfides in Martian Meteorite ALH84001  

NASA Technical Reports Server (NTRS)

Magnetite and sulfides in the black rims of carbonate globules in Martian meteorite ALH84001 have been studied extensively because of the claim by McKay et al. that they are biogenic in origin. However, exclusively inorganic (abiotic) processes are able to account for the occurrence of carbonate-sulfide-magnetite assemblages in the meteorite. We have previously precipitated chemically zoned and sulfide-bearing carbonate globules analogous to those in ALH84001 (at less than or equal to 150 C) from multiple fluxes of variable-composition Ca-Mg-Fe-CO2-S-H2O solutions. Brief heating of precipitated globules to approx. 470 C produced magnetite and pyrrhotite within the globules by thermal decomposition of siderite and pyrite, respectively. We have also shown that morphology of magnetite formed by inorganic thermal decomposition of Fe-rich carbonate is similar to the morphology of so-called biogenic magnetite in the carbonate globules of ALH84001. Magnetite crystals in the rims of carbonate globules in ALH84001 are chemically pure [Note: "Chemically pure" is defined here as magnetite with Mg at levels comparable or lower than Mg detected by [8] in ALH84001 magnetite]. A debate continues on whether or not chemically pure magnetite can form by the thermal decomposition of mixed Mg-Fe-carbonates that have formed under abiotic conditions. Thomas-Keprta et al. argue that it is not possible to form Mg-free magnetite from Mg-Fe-carbonate based on thermodynamic data. We previously suggested that chemically pure magnetite could form by the thermal decomposition of relatively pure siderite in the outer rims of the globules. Mg-Fe-carbonates may also thermally decompose under conditions conducive for formation of chemically pure magnetite. In this paper we show through laboratory experiments that chemically pure magnetite can form by an inorganic process from mixed Mg-Fe-carbonates.

Golden, D. C.; Ming, Douglas W.; Lauer, H. V., Jr.; Morris, R. V.; Trieman, A. H.; McKay, G. A.

2006-01-01

2

Non-chemically Pure Magnetites Produced from Thermal Decomposition of Ankerites  

NASA Astrophysics Data System (ADS)

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

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

2008-12-01

3

Truncated hexa-octahedral magnetite crystals in ALH84001: presumptive biosignatures  

NASA Technical Reports Server (NTRS)

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.

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

4

Truncated hexa-octahedral magnetite crystals in ALH84001: Presumptive biosignatures  

PubMed Central

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

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

5

Process for Making Single-Domain Magnetite Crystals  

NASA Technical Reports Server (NTRS)

A process for making chemically pure, single-domain magnetite crystals substantially free of structural defects has been invented as a byproduct of research into the origin of globules in a meteorite found in Antarctica and believed to have originated on Mars. The globules in the meteorite comprise layers of mixed (Mg, Fe, and Ca) carbonates, magnetite, and iron sulfides. Since the discovery of the meteorite was announced in August 1996, scientists have debated whether the globules are of biological origin or were formed from inorganic materials by processes that could have taken place on Mars. While the research that led to the present invention has not provided a definitive conclusion concerning the origin of the globules, it has shown that globules of a different but related chemically layered structure can be grown from inorganic ingredients in a multistep precipitation process. As described in more detail below, the present invention comprises the multistep precipitation process plus a subsequent heat treatment. The multistep precipitation process was demonstrated in a laboratory experiment on the growth of submicron ankerite crystals, overgrown by submicron siderite and pyrite crystals, overgrown by submicron magnesite crystals, overgrown by submicron siderite and pyrite. In each step, chloride salts of appropriate cations (Ca, Fe, and Mg) were dissolved in deoxygenated, CO2- saturated water. NaHCO3 was added as a pH buffer while CO2 was passed continuously through the solution. A 15-mL aliquot of the resulting solution was transferred into each of several 20 mL, poly(tetrafluoroethylene)-lined hydrothermal pressure vessels. The vessels were closed in a CO2 atmosphere, then transferred into an oven at a temperature of 150 C. After a predetermined time, the hydrothermal vessels were removed from the oven and quenched in a freezer. Supernatant solutions were decanted, and carbonate precipitates were washed free of soluble salts by repeated decantations with deionized water.

Golden, D. C.; Ming, Douglas W.; Morris, Richard V.; Lofgren, Gary E.; McKay, Gordan A.; Schwandt, Craig S.; Lauer, Howard V., Jr.; Socki, Richard A.

2004-01-01

6

Ferromagnetic resonance of intact cells and isolated crystals from cultured and uncultured magnetite-producing magnetotactic bacteria.  

PubMed

Most magnetotactic bacteria (MB) produce stable, single-domain magnetite nanocrystals with species-specific size, shape and chain arrangement. In addition, most crystals are elongated along the [111] direction, which is the easy axis of magnetization in magnetite, chemically pure and structurally perfect. These special characteristics allow magnetite crystal chains from MB to be recognized in environmental samples including old sedimentary rocks. Ferromagnetic resonance (FMR) has been proposed as a powerful and practical tool for screening large numbers of samples possibly containing magnetofossils. Indeed, several studies were recently published on FMR of cultured MB, mainly Magnetospirillum gryphiswaldense. In this work, we examined both uncultured magnetotactic cocci and the cultured MB M. gryphiswaldense using transmission electron microscopy (TEM) and FMR from 10 K to room temperature (RT). The TEM data supported the FMR spectral characteristics of our samples. The FMR spectra of both bacteria showed the intrinsic characteristics of magnetite produced by MB, such as extended absorption at the low field region of the spectra and a Verwey transition around 100 K. As previously observed, the spectra of M. gryphiswaldense isolated crystals were more symmetrical than the spectra obtained from whole cells, reflecting the loss of chain arrangement due to the small size and symmetrical shape of the crystals. However, the FMR spectra of magnetic crystals isolated from magnetotactic cocci were very similar to the FMR spectra of whole cells, because the chain arrangement was maintained due to the large size and prismatic shape of the crystals. Our data support the use of FMR spectra to detect magnetotactic bacteria and magnetofossils in samples of present and past environments. Furthermore, the spectra suggest the use of the temperature transition of spectral peak-to-peak intensity to obtain the Verwey temperature for these systems. PMID:24828297

Abraçado, Leida G; Wajnberg, Eliane; Esquivel, Darci M S; Keim, Carolina N; Silva, Karen T; Moreira, Emílio T S; Lins, Ulysses; Farina, Marcos

2014-06-01

7

Ferromagnetic resonance of intact cells and isolated crystals from cultured and uncultured magnetite-producing magnetotactic bacteria  

NASA Astrophysics Data System (ADS)

Most magnetotactic bacteria (MB) produce stable, single-domain magnetite nanocrystals with species-specific size, shape and chain arrangement. In addition, most crystals are elongated along the [111] direction, which is the easy axis of magnetization in magnetite, chemically pure and structurally perfect. These special characteristics allow magnetite crystal chains from MB to be recognized in environmental samples including old sedimentary rocks. Ferromagnetic resonance (FMR) has been proposed as a powerful and practical tool for screening large numbers of samples possibly containing magnetofossils. Indeed, several studies were recently published on FMR of cultured MB, mainly Magnetospirillum gryphiswaldense. In this work, we examined both uncultured magnetotactic cocci and the cultured MB M. gryphiswaldense using transmission electron microscopy (TEM) and FMR from 10 K to room temperature (RT). The TEM data supported the FMR spectral characteristics of our samples. The FMR spectra of both bacteria showed the intrinsic characteristics of magnetite produced by MB, such as extended absorption at the low field region of the spectra and a Verwey transition around 100 K. As previously observed, the spectra of M. gryphiswaldense isolated crystals were more symmetrical than the spectra obtained from whole cells, reflecting the loss of chain arrangement due to the small size and symmetrical shape of the crystals. However, the FMR spectra of magnetic crystals isolated from magnetotactic cocci were very similar to the FMR spectra of whole cells, because the chain arrangement was maintained due to the large size and prismatic shape of the crystals. Our data support the use of FMR spectra to detect magnetotactic bacteria and magnetofossils in samples of present and past environments. Furthermore, the spectra suggest the use of the temperature transition of spectral peak-to-peak intensity to obtain the Verwey temperature for these systems.

Abraçado, Leida G.; Wajnberg, Eliane; Esquivel, Darci M. S.; Keim, Carolina N.; Silva, Karen T.; Moreira, Emílio T. S.; Lins, Ulysses; Farina, Marcos

2014-06-01

8

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

PubMed

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

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

2011-02-25

9

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

10

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

PubMed

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

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

2015-02-01

11

Dynamic of Iron Accumulation, Crystal Growth and Chain Arrangement During Magnetite Formation in M. gryphiswaldense  

Microsoft Academic Search

Magnetotactic bacteria are microorganisms that have the ability to orient themselves along magnetic fields, and to navigate along the Earth magnetic field. This ability is due to the presence of intracellular magnetic minerals. The crystals can be made of magnetite (Fe3O4) and usually form a chain. This biomineralization involves uptake and accumulation of tremendous amounts of iron when compare to

D. Faivre; B. Matzanke-Markstein; K. Junge; D. Schueler

2005-01-01

12

The differentiation trend of the Skaergaard intrusion and the timing of magnetite crystallization: iron enrichment revisited  

NASA Astrophysics Data System (ADS)

Initial studies of the Skaergaard intrusion [L.R. Wager, J. Petrol. 1 (1960) 364-398] and much of the subsequent work [R.J. Williams, Am. J. Sci. 271 (1971) 132-146; S.A. Morse et al., Am. J. Sci. 280A (1980) 159-170; A.R. McBirney, H.R. Naslund, Contrib. Mineral. Petrol. 104 (1990) 235-247; C. Tegner, Contrib. Mineral. Petrol. 128 (1997) 45-51; A.R. McBirney, Contrib. Mineral. Petrol. 132 (1998) 103-105] concluded that the Skaergaard magma followed an iron-enrichment trend with little or no silica enrichment until the final stages of crystallization. Several recent reports [R.H. Hunter, R.S.J. Sparks, Contrib. Mineral. Petrol. 95 (1987) 451-461; R.H. Hunter, R.S.J. Sparks, Contrib. Mineral. Petrol. 104 (1990) 248-254], however, have suggested that the Skaergaard magma began to follow a silica-enrichment trend in Lower Zone c (LZc) of the Layered Series where magnetite first became an abundant mineral. Magnetite in LZc, however, generally occurs in aggregates of magnetite-ulvöspinel and ilmenite-hematite that have undergone extensive subsolidus reequilibration and exsolution [E.A. Vincent, Neues Jahrb. Mineral. Abh. 94 (1960) 993-1016; E.A. Vincent, Geochim. Cosmochim. Acta 6 (1954) 1-26; A.F. Buddington, D.H. Lindsley, J. Petrol. 5 (1964) 310C357; H.R. Naslund, J. Petrol. 25 (1984) 185-212; A.R. McBirney, J. Petrol. 30 (1989) 363-397; Y.D. Jang, Petrological, Geochemical, and Mineralogical Variations in the Skaergaard Intrusion, East Greenland (Ph.D. Dissertation), State University of New York, Binghamton, NY, 1999, 219 pp.]. As a result, it is not clear if magnetite in these samples was an equilibrium, liquidus mineral fractionated from the main magma reservoir, or if magnetite crystallized as a later, interstitial mineral and did not directly affect the differentiation trend of the main Skaergaard magma. The timing of the initial crystallization of abundant magnetite and ilmenite is a key factor in understanding the trend of Skaergaard differentiation. Because V is a strongly included element in oxides, and is not strongly included in silicate minerals, the V content of an evolving magma is generally controlled by the fractionation of oxide minerals, in particular magnetite. The initial crystallization of magnetite should, therefore, be accompanied by a sudden decrease in the V content of the evolving magma, and in all of the coexisting mafic phases in equilibrium with that magma as well. The V content in Skaergaard pyroxene does not decrease significantly until the upper part of the Middle Zone (MZ), suggesting that the onset of extensive magnetite fractionation is much later than has previously been thought, and that the magnetite in LZc and the lower part of the MZ might not have been a liquidus phase at that level. The observed V trend in Skaergaard pyroxene can be modeled almost perfectly using published partition coefficients for the coexisting minerals in the Skaergaard intrusion, assuming that no magnetite fractionation occurred until the upper part of the MZ. Independently calculated trends for fO 2 in the Skaergaard magma [R.J. Williams, Am. J. Sci. 271 (1971) 132-146; S.A. Morse et al., Am. J. Sci. 280A (1980) 159-170; A.R. McBirney, H.R. Naslund, Contrib. Mineral. Petrol. 104 (1990) 235-247] change in the upper part of the MZ to more reducing conditions. The onset of magnetite fractionation would remove Fe 2O 3 from the magma and could initiate such a change. The timing of magnetite fractionation will have a strong effect on whether magma evolves towards iron enrichment or silica enrichment.

Jang, Yun D.; Naslund, H. R.; McBirney, A. R.

2001-07-01

13

Studies of Inorganic Crystals in Biological Tissue: Magnetite in Human  

E-print Network

bacteria, polyplacophoran mollusks (chitons), salmons, tuna and recently tissues of the human brain bacteria and the chitons. Many studies have described that ferritin were related with cell proliferation crystals are extracted and identified include chitons (Mollucsan class: Polyplacophora) whose teeth consist

14

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

PubMed

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

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

2011-06-15

15

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

NASA Technical Reports Server (NTRS)

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].

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

16

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

PubMed

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

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

2012-08-22

17

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

NASA Astrophysics Data System (ADS)

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.

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

2012-07-01

18

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

ERIC Educational Resources Information Center

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)

Pauling, Linus; Herman, Zelek S.

1985-01-01

19

Sub-Micrometer-Scale Mapping of Magnetite Crystals and Sulfur Globules in Magnetotactic Bacteria Using Confocal Raman Micro-Spectrometry  

PubMed Central

The ferrimagnetic mineral magnetite is biomineralized by magnetotactic microorganisms and a diverse range of animals. Here we demonstrate that confocal Raman microscopy can be used to visualize chains of magnetite crystals in magnetotactic bacteria, even though magnetite is a poor Raman scatterer and in bacteria occurs in typical grain sizes of only 35–120 nm, well below the diffraction-limited optical resolution. When using long integration times together with low laser power (<0.25 mW) to prevent laser induced damage of magnetite, we can identify and map magnetite by its characteristic Raman spectrum (303, 535, 665 ) against a large autofluorescence background in our natural magnetotactic bacteria samples. While greigite (cubic ; Raman lines of 253 and 351 ) is often found in the Deltaproteobacteria class, it is not present in our samples. In intracellular sulfur globules of Candidatus Magnetobacterium bavaricum (Nitrospirae), we identified the sole presence of cyclo-octasulfur (: 151, 219, 467 ), using green (532 nm), red (638 nm) and near-infrared excitation (785 nm). The Raman-spectra of phosphorous-rich intracellular accumulations point to orthophosphate in magnetic vibrios and to polyphosphate in magnetic cocci. Under green excitation, the cell envelopes are dominated by the resonant Raman lines of the heme cofactor of the b or c-type cytochrome, which can be used as a strong marker for label-free live-cell imaging of bacterial cytoplasmic membranes, as well as an indicator for the redox state. PMID:25233081

Eder, Stephan H. K.; Gigler, Alexander M.; Hanzlik, Marianne; Winklhofer, Michael

2014-01-01

20

Structural, optical, mechanical and dielectric studies of pure and doped L-Prolinium Trichloroacetate single crystals  

NASA Astrophysics Data System (ADS)

In the present work, pure and metal substituted L-Prolinium trichloroacetate (LPTCA) single crystals were grown by slow evaporation method. The grown crystals were subjected to single crystal X-ray diffraction (XRD), powder X-ray diffraction, FTIR, UV-Visible-NIR, hardness, photoluminescence and dielectric studies. The dopant concentration in the crystals was measured by inductively coupled plasma (ICP) analysis. Single crystal X-ray diffraction studies of the pure and metal substituted LPTCA revealed that the grown crystals belong to the trigonal system. Ni2+ and Co2+ doping slightly altered the lattice parameters of LPTCA without affecting the basic structure of the crystal. FTIR spectral analysis confirms the presence of various functional groups in the grown crystals. The mechanical behavior of pure and doped crystals was analyzed by Vickers's microhardness test. The optical transmittance, dielectric and photoluminescence properties of the pure and doped crystals were analyzed.

Renuka, N.; Ramesh Babu, R.; Vijayan, N.; Vasanthakumar, Geetha; Krishna, Anuj; Ramamurthi, K.

2015-02-01

21

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

PubMed

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

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

2014-09-01

22

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

NASA Astrophysics Data System (ADS)

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.

Salarian, Samaneh; Dizaji, Hamid Rezagholipour

2014-01-01

23

Growth and characterization of pure and doped bis thiourea zinc acetate: Semiorganic nonlinear optical single crystals  

Microsoft Academic Search

Metal–organic coordination complex single crystals bis thiourea zinc acetate (BTZA) and Cd2+ doped BTZA have been synthesized and grown successfully by slow-cooling technique from their aqueous solutions. Single crystals of pure and Cd2+ doped BTZA with dimensions of 35×4×2mm3 and 10×5×6mm3, respectively were obtained with well defined morphology. The as grown single crystals are characterized by single crystal XRD studies

M. Lydia Caroline; S. Vasudevan

2009-01-01

24

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

NASA Technical Reports Server (NTRS)

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.

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

25

Growth and characterization of pure and glycine doped cadmium thiourea sulphate (GCTS) crystals  

NASA Astrophysics Data System (ADS)

The pure and glycine doped cadmium thiourea sulphate (GCTS) single crystals were grown successfully by slow evaporation method at room temperature. The concentration of dopant in the mother solution was 1 mol%. There is a change in unit cell. The Fourier transform infrared spectroscopy study confirms the incorporation of glycine into CTS crystal. The doped crystals are optically better and more transparent than the pure ones. The dopant increases the hardness value of the material. The grown crystals were also subjected to thermal and NLO studies.

Lawrence, M.; Thomas Joseph Prakash, J.

2012-06-01

26

Growth and characterization of pure and glycine doped cadmium thiourea sulphate (GCTS) crystals.  

PubMed

The pure and glycine doped cadmium thiourea sulphate (GCTS) single crystals were grown successfully by slow evaporation method at room temperature. The concentration of dopant in the mother solution was 1 mol%. There is a change in unit cell. The Fourier transform infrared spectroscopy study confirms the incorporation of glycine into CTS crystal. The doped crystals are optically better and more transparent than the pure ones. The dopant increases the hardness value of the material. The grown crystals were also subjected to thermal and NLO studies. PMID:22349889

Lawrence, M; Thomas Joseph Prakash, J

2012-06-01

27

Optical, thermal and electrical properties of pure and doped bis-thiourea cadmium formate (BTCF) crystal  

NASA Astrophysics Data System (ADS)

A glycine doped bis-thiourea cadmium formate (BTCF) crystal has been grown by a slow solution evaporation technique. The shifts in vibrational frequencies of different functional groups of BTCF were identified by Fourier transform infrared (FT-IR) spectral analysis. UV-visible studies were employed to assess the optical transparency of pure and doped BTCF crystals. The optical band gap of doped BTCF is found to be 5.16 eV. The optical constants, refractive index, reflectance, and optical conductivity have been evaluated, using the transmission data. The dielectric characteristics of pure and doped BTCF were investigated by employing dielectric studies. The decomposition temperature of pure and doped BTCF crystals was determined by using thermogravimetric analysis. The encouraging third-order nonlinear optical properties of pure and doped BTCF crystals were examined by employing the Z-scan technique at 632.8 nm.

Shejwal, N. N.; Anis, Mohd; Hussaini, S. S.; Shirsat, M. D.

2014-12-01

28

INVESTIGATIONS OF PYROELECTRIC PROPERTIES OF PURE AND ALANINE DOPED TGS CRYSTALS  

Microsoft Academic Search

Pyroelectric measurements were performed on pure and on L or D alanine doped TGS. Crystals were grown in paraelectric phase (~52 oC) from solutions by slow evaporation of the solvent. Pyroelectric current was measured by, crossing the Curie point, both on heating and cooling. Spontaneous polarization PS(T) was also recorded using the charge integration method. The pyroelectric current of pure

M. Costache; I. Matei; L. Pintilie; H. V. Alexandru; C. Berbecaru

29

Isolation of isoelectrically pure cholera toxin for crystallization  

SciTech Connect

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

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

1989-01-01

30

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

NASA Technical Reports Server (NTRS)

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.

Turnbull, D.

1979-01-01

31

Photorefractive nonlinearity in pure and doped liquid crystals  

NASA Astrophysics Data System (ADS)

Detailed theoretical analysis and experimental investigation of the photorefractive (PR) effect in liquid crystals (LC) are presented. The photorefractive nonlinearity arises from the formation of spatially modulated space charge field. Two main mechanisms contribute space charge field in liquid crystals. One comes from the formation and the subsequent dissociation of charge transfer complexes between the liquid crystal and the dopant, which produces mobile charge carriers. The generation and redistribution of charge carriers, induced by external dc voltage and inhomogeneous illumination, form the space charge field. Second source comes from the so-called Carr-Helfrich effect, which states that transverse space charge field can be induced by liquid crystal dielectric and conductivity anisotropy under external applied field. Assisted by the space charge field, large optical nonlinearity can be obtained in liquid crystals. Liquid crystal molecular reorientation occurs under the combined action of internal space charge field and external dc field. The subsequent birefringent grating accounts for photorefractive diffraction and beam coupling. Its orientational feature is investigated and evidenced by facts, such as, polarization anisotropy observed in probe diffraction, external threshold behavior, asymmetric two beam coupling, and geometrical dependence of diffraction efficiency. In parallel with the effort to understand basic mechanisms governing photorefractive effect in liquid crystals, we've also attempted to enhance PR performance, mainly by chemical doping. The doping effect, both organic (C60, single walled nanotubes (SWNT)), and inorganic doping (e.g., CdSe nanorodes), is studied. Substantial improvement of photorefractive response can be observed in our doping samples, in terms of larger diffraction efficiency and higher beam coupling gain. Although the underline mechanism is still intricate in molecular level, we believe the enhanced photo-charge generation and transport, and/or the enlarged conductivity anisotropy, may be the possible explanations for the better PR performance in doped LC system. While there is compelling evidence that liquid crystal reorientation under space charge field is responsible for photorefractive grating formation, much less understood, however, are the mechanisms involved in the formation of space charge fields that drive the orientation. The photorefractive effect in undoped LC samples is revisited, with our focus on the study of space charge field origin. Theoretical models were derived to identify the photorefractive threshold voltage. The PR threshold voltage can be substantially lowered with the increase of incident light intensity, which is mainly due to inhomogeneous interface ions distribution induced surface torque. The thickness dependence of threshold voltage lowing effect was also measured, which allows us to estimate the modulation depth of surface charge. Our result shows both bulk and surface optically induced charges and field modulation are responsible for the build up of space charge field. Based on our work, several potential further researches are proposed, which are all related to photorefractive effect, yet fall into three categories. First is to further study doping effect: increase SWNT doping concentration using functionalized nanotubes and try other novel doping materials such as nanometals. Second is to continue the investigation of surface effect in doped LC samples. We anticipate more interesting surface effect exists in doping system. The last one is to study PR effect in new LC composites, such as PSLC (polymer stablilized liquid crystal) and PDLC (polymer dispersed liquid crystal).

Chen, Kan

32

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

PubMed

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

Treiman, Allan H

2003-01-01

33

ACOUSTIC ON-LINE MONITORING OF SOLUTION CRYSTALLIZATION PROCESS IN PURE AND IMPURE MEDIA  

E-print Network

and their kinetic energy are also affected by many other properties such as size, shape, hardness, density preliminary batch solution cooling experiments obtained with the model system Ammonium Oxalate/water (AO morphology was reported [10] . Figure 1. Cooling crystallization of AO in pure water:

Paris-Sud XI, Université de

34

Radiation damage in pure and RE-doped LiBaF{sub 3} crystals  

SciTech Connect

Absorption, emission, excitation and thermoluminescence were investigated for pure, Eu- and Ce-doped LiBaF{sub 3} crystals, both as grown and irradiated. It is shown that the purity of initial crystal is a prerequisite to reduce the afterglow and decrease the radiation damage level. Doping by Ce or Eu ions is a way to vary the spectral and kinetic characteristic. The exciton luminescence and blue afterglow are suppressed in Eu- or Ce-doped crystals. Radiation induced absorption spectrum is complicated and includes more than six overlapped bands. Emission of these color centers appears in the luminescence spectrum.

Gektin, A.V.; Shiran, N.V.; Voronova, V.V. [Inst. for Single Crystals, Kharkov (Ukraine)

1996-12-31

35

Influence by trajectorial electron transport on anomalous ultrasound attenuation in high pure Gallium single crystal  

E-print Network

The anomalous propagation of longitudinal ultrasound with the frequencies of 70 and 150 MHz in the high pure Gallium single crystal at the weak external magnetic field (the magnetic field H perpendicular to the wave vector k) at the low temperature of 0.4 K was researched experimentally. The delayed ultrasonic signal, comparing to the main ultrasonic signal, is detected. The research on the new magneto-acoustic effects made it possible to find the temperature dependence of the frequency of collisions between the electrons and the thermal phonons in the high pure Gallium single crystal. It is found that the anomalous oscillations of propagation velocity of ultrasonic signal pulses and the signals, propagating by the way of the electron transport in the high pure type I superconductor, can be detected at the directions of the magnetic field H close to the magnetic field H parallel to the wave vector k.

Shepelev, Anatoly G; Filimonov, Genady D

2012-01-01

36

Trace elements in magnetite as petrogenetic indicators  

NASA Astrophysics Data System (ADS)

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.

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

2014-10-01

37

Growth and characterization of pure and doped KHP NLO single crystals  

NASA Astrophysics Data System (ADS)

Single crystals of Potassium Hydrogen Phthalate doped with amino acid L-lysine were grown successfully by slow evaporation method. The concentration of dopant in the mother solution was 0.5 mol%, 1 mol% and 2 mol%. There is a drastic change in the morphology due to variation in doping rates which is also reflected in the X-ray diffraction data. The Fourier Transform infrared spectroscopy study confirms the incorporation of L-lysine into Potassium Hydrogen Phthalate crystal. The thermal study indicates the dissociating nature of the crystal. The nonlinear optical property of the grown crystal has been confirmed by Kurtz-powder second harmonic generation test. The dopant of 0.5 mol% and 1 mol% shows higher second harmonic generation result than pure Potassium Hydrogen Phthalate. Results are discussed.

Thilagavathy, S. R.; Rajesh, P.; Ramasamy, P.; Ambujam, K.

2014-06-01

38

Growth and characterization of pure and doped cadmium thiourea acetate single crystals  

Microsoft Academic Search

Pure and doped (zinc acetate, N-methylurea and glycine) cadmium thiourea acetate single crystals were grown by slow evaporation solution growth method. The UV–visible, high-resolution X-ray diffraction and dielectric studies show the enhancement in the crystalline perfection of the glycine-doped cadmium thiourea acetate. The zinc acetate does not have significant effect on the structural and chemical properties, but has some effect

S. Shahil Kirupavathy; S. Stella Mary; P. Mythili; R. Gopalakrishnan

2008-01-01

39

Magnetism in nanometer-thick magnetite  

NASA Astrophysics Data System (ADS)

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.

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

40

Spectral analysis of TL emission from pure and Eu-doped NaCl crystals  

NASA Astrophysics Data System (ADS)

We have measured emission spectra during thermoluminescence of pure and europium-doped NaCl crystals following irradiation at ambient temperature with X- and -rays. Factors investigated include the effect of pre-irradiation annealing of crystals and the post-irradiation fading of colour centres. Results for other dopants such as chromium, strontium and nickel are considered. Glow curves show some degree of uniformity having common glow peaks for the impurities investigated. A low temperature glow peak near 60 °C emits predominantly high energy photons. A high temperature glow peak near 200 °C shows less consistency, varying both in temperature and in the energy of emitted photons. Samples doped with chromium and nickel impurities inhibit emission at certain wavelengths. Pre-annealing crystals before irradiation produce changes in emission wavelengths.

Davidson, A. T.; Kozakiewicz, A. G.; Derry, T. E.; Comins, J. D.; Suszynska, M.; Valberg, L.; Townsend, P. D.

2005-01-01

41

Evaluation of the Crystal Rotation Behavior at the Fatigue Crack Tip in Pure Titanium Films  

NASA Astrophysics Data System (ADS)

Using a fatigue testing method by which fatigue cracks can be initiated and propagated in a film adhered to cover an elliptical through-hole in a base plate subjected to push-pull cyclic loads, annealed pure titanium films with the thickness of 90µm were fatigued under a constant stress amplitude with a stress ratio of -1. The crystal rotation behavior with the tensile/compressive loading at the fatigue crack tip was evaluated from the crystal orientation measured by EBSD (Electron Back-scatter Diffraction) method. The titanium films under the tensile /compressive stress condition were prepared as follows; the films were adhered to the base plates loaded by a servo hydraulic testing machine, then the base plates were detached from the testing machine. From the crystal rotation behavior at the fatigue crack tip, it was found that the crystal rotation angle was relatively small and the rotation axis tended to different directions between the upper side and lower side of the grain in front of the crack tip. The fatigue crack propagated along the borderline between two regions in the crystal grain where the crystal rotation axes with different directions were obtained before the fatigue crack propagation.

Shimizu, Kenichi; Torii, Tashiyuki; Fujino, Yasuto

42

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)

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.

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

43

Evidence for the role of pure edge dislocations in crystal growth  

NASA Astrophysics Data System (ADS)

X-ray topographic studies have been made of the formation, propagation and character of growth dislocations in the {100} growth sectors of potash alum crystals grown from cut and polished seeds in a kinetic growth cell. Under the conditions of growth used (supersaturation 0.1-6.4%) all dislocations were found to be of pure edge character. As the sectors propagated, the area of the face initially remained constant but then decreased. As the decrease occurred many of the dislocations intersected the growth sector boundaries and became refracted into the adjacent {111} growth sectors. In parallel with the loss of these dislocations from this sector, the growth rate of the facet decreased and became variable. This association is consistent with the contention that the emergent ends of dislocations of pure edge character can act as nucleation centres for crystal growth. Further, more definite proof for such a role was obtained by examining the growth rates of {100} growth sectors containing different numbers of growth edge dislocations, but in the early, constant growth region. The growth rate was found to increase with increasing edge dislocation density. This evidence confirms that edge as well as screw dislocations play a significant role in the crystal growth process.

Sherwood, J. N.; Shripathi, T.

1988-05-01

44

The Lindemann criterion of melting for pure and mixed ionic crystals  

NASA Astrophysics Data System (ADS)

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

Berrebi, David

1991-11-01

45

Growth and characterization of pure and doped cadmium thiourea acetate single crystals  

NASA Astrophysics Data System (ADS)

Pure and doped (zinc acetate, N-methylurea and glycine) cadmium thiourea acetate single crystals were grown by slow evaporation solution growth method. The UV-visible, high-resolution X-ray diffraction and dielectric studies show the enhancement in the crystalline perfection of the glycine-doped cadmium thiourea acetate. The zinc acetate does not have significant effect on the structural and chemical properties, but has some effect on the electrical properties. However, the addition of N-methylurea activates the cadmium thiourea acetate ions, resulting in the decrease of the space charge polarization and increase in intrinsic defects.

Shahil Kirupavathy, S.; Stella Mary, S.; Mythili, P.; Gopalakrishnan, R.

2008-05-01

46

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

NASA Astrophysics Data System (ADS)

Modifications due to swift heavy ion (SHI) beam irradiation on polar surfaces of pure & 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.

Bajpai, P. K.

2009-03-01

47

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

PubMed

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

Prasanyaa, T; Jayaramakrishnan, V; Haris, M

2013-03-01

48

Growth and characterization of pure and potassium chloride-doped Zinc Tris–thiourea Sulphate (ZTS) single crystals  

Microsoft Academic Search

Single crystals of pure and potassium chloride-doped Zinc Tris–thiourea Sulphate (ZTS) were grown from aqueous solution by slow evaporation technique. The grown crystals were subjected to various studies such as XRD, FTIR, atomic absorption, SHG and TGA–DTA studies. The melting point and density of the grown crystals were also measured. The various studies revealed the incorporation of the impurity (potassium

C. Krishnan; P. Selvarajan; T. H. Freeda

2008-01-01

49

Resonance dynamical intermolecular interaction in the crystals of pure and binary mixture n-paraffins  

NASA Astrophysics Data System (ADS)

In the present paper, we report temperature dependent FTIR spectra studies of Davydov splitting value for CH 2 rocking vibrations of pure crystalline n-paraffins C nH 2 n+2 ( n is the number of carbon atoms) and some isomorphically substituted binary mixtures of n-paraffins C 22H 46:C 24H 50. Temperature dependencies of Davydov splitting value have been shown to be characterized by the amount of irregularities (sharp decreasing), which corresponds to the phase transitions into the high-temperature (hexagonal) state for pure n-paraffins or different rotator crystalline states for the mixtures. Statistic and dynamic models have been proposed, which provides an adequate description of the observed effect. In the framework of these models, two different mechanisms are responsible for the temperature behavior of the vibrational mode splitting value. Besides the thermal expansion of crystals at heating, the quenching of vibrational excitons on the orientational defects of different nature takes place, accompanied with the breakage of the crystal lattice translational symmetry. The creation of such defects is resulted from the excitation of librational and rotational molecular degrees of freedom at the crystal polymorphic transitions into different rotary crystalline states. The manifestation of the resonance dynamical intermolecular interaction in the spectra of intramolecular vibrations in these crystals has been theoretically analyzed in terms of stochastic equations, taking into consideration the above mentioned phase transition. We have obtained the explicit expression for the theoretically predicted dependence of Davydov splitting value on temperature. The absorption bands, corresponding to Davydov splitting components, have been shown to approach rapidly each other at the transition to the high-temperature (hexagonal) phase. Computer simulation of such dependence has been performed for some aliphatic compounds. Good agreement between the experimental and computer simulation results has been obtained. The theoretical approach developed in the present paper for the resonance dynamical intermolecular interaction near such transitions from the three-dimensional to one-dimensional phase of crystalline n-paraffins has a general character and can be applied to the description of some specific features observed in the vibrational spectra of rotary crystals.

Puchkovska, G. O.; Danchuk, V. D.; Makarenko, S. P.; Kravchuk, A. P.; Kotelnikova, E. N.; Filatov, S. K.

2004-12-01

50

Growth of InAs/InP core-shell nanowires with various pure crystal structures  

NASA Astrophysics Data System (ADS)

We have studied the epitaxial growth of an InP shell on various pure InAs core nanowire crystal structures by metal-organic vapor phase epitaxy. The InP shell is grown on wurtzite (WZ), zinc-blende (ZB), and {111}- and {110}-type faceted ZB twin-plane superlattice (TSL) structures by tuning the InP shell growth parameters and controlling the shell thickness. The growth results, particularly on the WZ nanowires, show that homogeneous InP shell growth is promoted at relatively high temperatures (˜500?°C), but that the InAs nanowires decompose under the applied conditions. In order to protect the InAs core nanowires from decomposition, a short protective InP segment is first grown axially at lower temperatures (420-460?°C), before commencing the radial growth at a higher temperature. Further studies revealed that the InP radial growth rate is significantly higher on the ZB and TSL nanowires compared to WZ counterparts, and shows a strong anisotropy in polar directions. As a result, thin shells were obtained during low temperature InP growth on ZB structures, while a higher temperature was used to obtain uniform thick shells. In addition, a schematic growth model is suggested to explain the basic processes occurring during the shell growth on the TSL crystal structures.

Gorji Ghalamestani, Sepideh; Heurlin, Magnus; Wernersson, Lars-Erik; Lehmann, Sebastian; Dick, Kimberly A.

2012-07-01

51

Large magnetorefractive effect in magnetite  

Microsoft Academic Search

We carried out a magneto-optical spectroscopic study of magnetite (Fe3O4) thin films and single crystals at optical wavelengths. We observed a relevant quadratic magneto-optic contribution that can be notably larger than first-order linear magneto-optics at some range of wavelengths in the visible region. These unusual quadratic effects are particularly strong at the Verwey temperature (100-120 K) and decay slowly away

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

2010-01-01

52

Magnetite in Chitons  

Microsoft Academic Search

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

Manabu Mizota; Yutaka Maeda

1985-01-01

53

Biogenic Magnetite and EMF Effects  

NASA Astrophysics Data System (ADS)

Magnetite biomineralization is a genetically-controlled biochemical process through which organisms make perfect ferrimagnetic crystals, usually of single magnetic domain size. This process is an ancient one, having evolved about 2 billion years ago in the magnetotactic bacteria, and presumably was incorporated in the genome of higher organisms, including humans. During this time, DNA replication, protein synthesis, and many other biochemical processes have functioned in the presence of strong static fields of up to 400 mT adjacent to these magnetosomes without any obvious deleterious effects. Recent behavioral experiments using short but strong magnetic pulses in honeybees and birds demonstrates that ferromagnetic materials are involved in the sensory transduction of geomagnetic field information to the nervous system, and both behavioral and direct electrophysiological experiments indicate sensitivity thresholds to DC magnetic fields down to a few nT. However, far more biogenic magnetite is present in animal tissues than is needed for magnetoreception, and the biological function of this extra material is unknown. The presence of ferromagnetic materials in biological systems could provide physical transduction mechanisms for ELF magnetic fields, as well for microwave radiation in the .5 to 10 GHz band where magnetite has its peak ferromagnetic resonance. Elucidation of the cellular ultrastructure and biological function(s) of magnetite might help resolve the question of whether anthropogenic EMFs can cause deleterious biological effects. This work has been supported by grants from the NIH and EPRI.

Kirschvink, Joseph L.

1996-03-01

54

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

SciTech Connect

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

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

2008-09-15

55

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

NASA Astrophysics Data System (ADS)

Nominally pure LiF crystals were irradiated with the same dose (0.85 106 R) of gamma rays at ambient and low temperatures (-60 °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 F3+ centers that display a GP at 164 °C. F3(R) centers follow and are responsible for GPs at 193 and 228 °C. A GP at 263 °C is ascribed to F2 centers. Several peaks at temperatures in the range of 280-380 °C are associated with impurity perturbed F centers. A GP at 410 °C is associated with a complex of aggregated F and H centers. These attributions are accomplished by means of TL spectra, optical transmission spectra, and annealing procedures, and are critically discussed. The experimental data confirm the general trend of thermal stability of CCs, which decreases by moving from simple F centers to more complex ones, and the existence of exchange dynamics among CCs.

Baldacchini, G.; Montereali, R. M.; Nichelatti, E.; Kalinov, V. S.; Voitovich, A. P.; Davidson, A. T.; Kozakiewicz, A. G.

2008-09-01

56

Radiation eects in pure and doped Al2O3 crystals N. Kristianpoller *, A. Rehavi, A. Shmilevich, D. Weiss, R. Chen  

E-print Network

Radiation eects in pure and doped Al2O3 crystals N. Kristianpoller *, A. Rehavi, A. Shmilevich, D properties of nominally pure as well as of variously doped a-Al2O3 crystals were studied. Optical absorption.60.Kn; 78.60.Ya; 78.66.Nk Keywords: Radiation defects; Luminescence; Al2O3 1. Introduction The formation

Chen, Reuven

57

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

PubMed Central

Distinct morphological characteristics of magnetite formed intracellularly by magnetic bacteria (magnetosome) are invoked as compelling evidence for biological activity on Earth and possibly on Mars. Crystals of magnetite produced extracellularly by a variety of bacteria including Geobacter metallireducens GS-15, thermophilic bacteria, and psychrotolerant bacteria are, however, traditionally not thought to have nearly as distinct morphologies. The size and shape of extracellular magnetite depend on the culture conditions and type of bacteria. Under typical CO2-rich culture conditions, GS-15 is known to produce superparamagnetic magnetite (crystal diameters of approximately <30 nm). In the current study, we were able to produce a unique form of tabular, single-domain magnetite under nontraditional (low-CO2) culture conditions. This magnetite has a distinct crystal habit and magnetic properties. This magnetite could be used as a biosignature to recognize ancient biological activities in terrestrial and extraterrestrial environments and also may be a major carrier of the magnetization in natural sediments. PMID:15525704

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

2004-01-01

58

Stoichiometric magnetite grown by infrared nanosecond pulsed laser deposition  

NASA Astrophysics Data System (ADS)

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

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

2013-10-01

59

Magnetite thin films  

Microsoft Academic Search

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.

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

1972-01-01

60

Growth and characterization of pure and KCl doped zinc thiourea chloride (ZTC) single crystals.  

PubMed

Potassium Chloride (KCl) as an additive is added into zinc thiourea chloride solution in a small amount (1M%) by the method of slow evaporation solution growth technique at room temperature to get a new crystal. Due to the doping of the impurities on the crystals, remarkable changes in the physical properties were obtained. The grown crystals have been subjected to different instrumentation methods. The incorporation of the amount of potassium and zinc in the crystal lattices has been determined by AAS method. The lattice dimensions have been identified from single crystal X-ray diffraction measurements. The presence of functional group for the grown crystals has been identified by FTIR analysis. The optical, thermal and mechanical behaviors have been assessed by UV-Vis, TG/DTA and Vickers hardness methods respectively. The presence of dislocations of atoms has been identified by etching studies. PMID:23220671

Ruby Nirmala, L; Thomas Joseph Prakash, J

2013-02-01

61

Growth and characterization of pure and KCl doped zinc thiourea chloride (ZTC) single crystals  

NASA Astrophysics Data System (ADS)

Potassium Chloride (KCl) as an additive is added into zinc thiourea chloride solution in a small amount (1 M%) by the method of slow evaporation solution growth technique at room temperature to get a new crystal. Due to the doping of the impurities on the crystals, remarkable changes in the physical properties were obtained. The grown crystals have been subjected to different instrumentation methods. The incorporation of the amount of potassium and zinc in the crystal lattices has been determined by AAS method. The lattice dimensions have been identified from single crystal X-ray diffraction measurements. The presence of functional group for the grown crystals has been identified by FTIR analysis. The optical, thermal and mechanical behaviors have been assessed by UV-Vis, TG/DTA and Vickers hardness methods respectively. The presence of dislocations of atoms has been identified by etching studies.

Ruby Nirmala, L.; Thomas Joseph Prakash, J.

2013-02-01

62

Large magnetorefractive effect in magnetite  

NASA Astrophysics Data System (ADS)

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

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

2010-10-01

63

Structure and superparamagnetic behaviour of magnetite nanoparticles in cellulose beads  

SciTech Connect

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.

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

64

Resistance switching in electrodeposited magnetite superlattices.  

PubMed

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

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

2010-02-01

65

Magnetite-Pentlandite Chondrules in CK Chondrites  

NASA Astrophysics Data System (ADS)

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

Rubin, A. E.

1992-07-01

66

Morphological and growth rate distributions of small self-nucleated paracetamol crystals grown from pure aqueous solutions  

NASA Astrophysics Data System (ADS)

The growth rate dispersion of small paracetamol crystals nucleated and grown from pure solution was measured over the range of supersaturation, 0%< s<20%, in the three different crystallographic directions: [0 0 1], [1 1 0] and [0 1 0]. The results were fitted to three parameter log-normal and gamma distribution functions. The average growth rates obtained from these distributions were used to predict the morphological behaviour of an assembly of small paracetamol crystals as a function of supersaturation. It was shown that a columnar shape (dominant {1 1 0}) was formed in regions of low supersaturation while a plate-like form (dominant {0 0 1}) prevailed at high supersaturations. Using optical microscopy and X-ray topography, the potential causes for both the growth rate distribution and morphological change were investigated.

Finnie, S. D.; Ristic, R. I.; Sherwood, J. N.; Zikic, A. M.

1999-12-01

67

Insight into magnetite's redox catalysis from observing surface morphology during oxidation.  

PubMed

We study how the (100) surface of magnetite undergoes oxidation by monitoring its morphology during exposure to oxygen at ~650 °C. Low-energy electron microscopy reveals that magnetite's surface steps advance continuously. This growth of Fe3O4 crystal occurs by the formation of bulk Fe vacancies. Using Raman spectroscopy, we identify the sinks for these vacancies, inclusions of ?-Fe2O3 (hematite). Since the surface remains magnetite during oxidation, it continues to dissociate oxygen readily. At steady state, over one-quarter of impinging oxygen molecules undergo dissociative adsorption and eventual incorporation into magnetite. From the independence of growth rate on local step density, we deduce that the first step of oxidation, dissociative oxygen adsorption, occurs uniformly over magnetite's terraces, not preferentially at its surface steps. Since we directly observe new magnetite forming when it incorporates oxygen, we suggest that catalytic redox cycles on magnetite involve growing and etching crystal. PMID:23763580

Nie, Shu; Starodub, Elena; Monti, Matteo; Siegel, David A; Vergara, Lucía; El Gabaly, Farid; Bartelt, Norman C; de la Figuera, Juan; McCarty, Kevin F

2013-07-10

68

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

NASA Astrophysics Data System (ADS)

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

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

2008-12-01

69

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

NASA Astrophysics Data System (ADS)

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.

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

2011-06-01

70

Growth, optical, mechanical and dielectric studies on NLO active pure and metal ion doped single crystals of bis-thiourea zinc chloride  

NASA Astrophysics Data System (ADS)

Good quality single crystals of pure and metal ion (Ni 2+) doped bis-thiourea zinc chloride (BTZC) possessing excellent nonlinear optical properties have been grown from aqueous solution by the slow solvent evaporation technique. The lattice parameters of the grown crystals are determined by single crystal X-ray analysis. The well defined sharp peaks in the powder X-ray diffraction pattern reveals the crystalline perfection and the EDAX spectrum confirms the presence of dopant in the lattice of the parent crystal. The DRS UV-visible spectral study reveals improved transparency for the doped crystal, ascertaining the inclusion of metal ion in the lattice. The optical band gap of the pure and doped crystals was calculated to be 4.8 and 5.2 eV respectively from the UV transmission spectrum. The vickers hardness test brings forth higher hardness value for Ni 2+doped BTZC as compared to pure BTZC crystal. The dielectric measurement exhibits very low dielectric constant and dielectric loss at higher frequencies for both the pure and Ni 2+doped BTZC. The existence of second harmonic generation signals in the crystal also has been confirmed by performing the Kurtz powder test.

Parasuraman, K.; Sakthi Murugesan, K.; Uthrakumar, R.; Jerome Das, S.; Milton Boaz, B.

2011-10-01

71

Effect of growth temperature on the structural and transport properties of magnetite thin films prepared by pulse laser deposition on single crystal Si substrate  

Microsoft Academic Search

Magnetite (Fe3O4) thin films are prepared by pulsed laser deposition using an ?-Fe2O3 target on silicon (111) substrate in the substrate temperature range of 350 °C to 550 °C. X-ray diffraction (XRD) measurement shows that the film deposited at 450 °C is a single phase Fe3O4 film oriented along [111] direction. However, the film grown at 350 °C reveals mixed oxide phases (FeO and

Shailja Tiwari; R. J. Choudhary; D. M. Phase

2009-01-01

72

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

PubMed

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

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

2005-07-14

73

Growth, optical, mechanical and dielectric studies on NLO active pure and metal ion doped single crystals of bis-thiourea zinc chloride  

Microsoft Academic Search

Good quality single crystals of pure and metal ion (Ni 2+ ) doped bis-thiourea zinc chloride (BTZC) possessing excellent nonlinear optical properties have been grown from aqueous solution by the slow solvent evaporation technique. The lattice parameters of the grown crystals are determined by single crystal X-ray analysis. The well defined sharp peaks in the powder X-ray diffraction pattern reveals

K. Parasuraman; K. Sakthi Murugesan; R. Uthrakumar; S. Jerome Das; B. Milton Boaz

2011-01-01

74

Growth, optical, mechanical and dielectric studies on NLO active pure and metal ion doped single crystals of bis-thiourea zinc chloride  

Microsoft Academic Search

Good quality single crystals of pure and metal ion (Ni2+) doped bis-thiourea zinc chloride (BTZC) possessing excellent nonlinear optical properties have been grown from aqueous solution by the slow solvent evaporation technique. The lattice parameters of the grown crystals are determined by single crystal X-ray analysis. The well defined sharp peaks in the powder X-ray diffraction pattern reveals the crystalline

K. Parasuraman; K. Sakthi Murugesan; R. Uthrakumar; S. Jerome Das; B. Milton Boaz

2011-01-01

75

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

Microsoft Academic Search

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

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

1960-01-01

76

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)

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.

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

2011-01-01

77

About the nature of phase transition in pure n-paraffin crystals  

NASA Astrophysics Data System (ADS)

It is known that in long-chain aliphatic crystals a first order phase transition from three-dimensional translationally symmetric phase to one-dimensional translationally symmetric (hexagonal) one may occur in the temperature range below the melting point. During this transition, the molecules might be involved in torsion rotations around their long axes. It is clear that any distortions in periodic location of the atoms in the plane perpendicular to the long axis of the molecules must result in some peculiarities in the intermolecular interactions. In particular, one could expect changes in resonance dynamic intermolecular interaction (Davydov splitting of vibrational excitons) in orientationally disordered phase. Theoretical analysis of manifestation of resonance dynamical intermolecular interaction in the spectra of intramolecular vibrations in these crystals has been carried out in terms of stochastic equations with taking into consideration the above mentioned phase transition. We obtained the explicit expression for theoretical dependence of Davydov splitting value on temperature. We showed that at the transition to the high-temperature (hexagonal) phase, the absorption bands, which correspond to Davydov splitting components rapidly approach each other. This spectral effect is connected to the damping of vibrational excitons at their interaction with orientational defects in the crystal lattice. Such defects arise due to the thermal activation of molecular torsional-rotation degrees of freedom during the crystal transition to one-dimensional phase. Computer simulation of such dependence has been performed for some aliphatic compounds. Good agreement between the experimental and computer simulation results has been obtained. Theoretical approach developed in the present paper for resonance dynamical intermolecular interaction near the transition from three-dimensional to one-dimensional phase of crystalline n-paraffins is of general nature and may be applied to the description of some specific features observed in the vibrational spectra of rotary crystals.

Puchkovska, G. O.; Danchuk, V. D.; Kravchuk, A. P.; Kukielski, Jan I.

2004-10-01

78

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

NASA Technical Reports Server (NTRS)

The undercooling behavior of large spheroids of Pd40Ni40P40 was investigated. By surface etching, supporting the specimens on a fused silica substrate, and successive heating and cooling, crystallization can be eliminated, presumable due to the removal of surface heterogeneities. By this method samples up to 3.2g with a 0.53 mm minor diameter, were made entirely glassy, except for some superficial crystals comprising less than 0.5% of the volume. These experiments show that a cooling rate of approximately 1 K/sec is adequate to avoid copious homogeneous nucleation in the alloy, and that by eliminating or reducing the effectiveness of heterogeneous nucleation sites, it is possible to form bulk samples of this metallic glass with virtually unlimited dimensions.

Spaepen, F.; Turnbull, D.

1982-01-01

79

Magnetite biomineralization in the human brain.  

PubMed Central

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

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

1992-01-01

80

ac electrical transport properties of magnetite (abstract)  

Microsoft Academic Search

Electrical transport properties of synthetic magnetite (Fe3(1??)O4) single crystals of controlled stoichiometry have been characterized by ac impedance measurements between 5 Hz and 10 MHz, as a function of temperature (77 K

R. J. Rasmussen; J. M. Honig

1988-01-01

81

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

NASA Astrophysics Data System (ADS)

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

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

2013-11-01

82

Synthesis, magnetic and ethanol gas sensing properties of semiconducting magnetite nanoparticles  

NASA Astrophysics Data System (ADS)

The superparamagnetic magnetite (Fe3O4) nanoparticles with an average size of 7 nm were synthesized using a rapid and facile microwave hydrothermal technique. The structure of the magnetite nanoparticles was characterized by X-ray diffraction (X-ray), field effect scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDS), and transmission electron microscopy (TEM). The prepared Fe3O4 was shown to have a cubic phase of pure magnetite. Magnetization hysteresis loop shows that the synthesized magnetite exhibits no hysteretic features with a superparamagnetic behavior. The ethanol gas sensing properties of the synthesized magnetite were investigated, and it was found that the responsibility time is less than 10 s with good reproducibility for ethanol sensor. Accordingly, it is evaluated that the magnetite nanoparticles can be effectively used as a solid state ethanol sensor in industrial commercial product applications.

Al-Ghamdi, Ahmed A.; Al-Hazmi, Faten; Al-Tuwirqi, R. M.; Alnowaiser, F.; Al-Hartomy, Omar A.; El-Tantawy, Farid; Yakuphanoglu, F.

2013-05-01

83

Nanophase Magnetite and Pyrrhotite in ALH84001 Martian Meteorite: Evidence for an Abiotic Origin  

NASA Technical Reports Server (NTRS)

The nanophase magnetite crystals in the black rims of pancake-shaped carbonate globules of the Martian meteorite ALH84001 have been studied extensively because of the claim by McKay et al.that they are biogenic in origin. A subpopulation of these magnetite crystals are reported to conform to a unique elongated shape called "truncated hexa-octahedral" or "THO" by Thomas-Keprta et al. They claim these THO magnetite crystals can only be produced by living bacteria thus forming a biomarker in the meteorite. In contrast, thermal decomposition of Fe-rich carbonate has been suggested as an alternate hypothesis for the elongated magnetite formation in ALH84001 carbonates. The experimental and observational evidence for the inorganic formation of nanophase magnetite and pyrrhotite in ALH84001 by decomposition of Fe-rich carbonate in the presence of pyrite are provided.

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

2006-01-01

84

Magnetite: What it reveals about the origin of the banded iron formations. [Abstract only  

NASA Technical Reports Server (NTRS)

Magnetite, Fe3O4 is produced abiotically and biotically. Abiotically, magnetite is a late magmatic mineral and forms as a consequence of the cooling of iron rich magma. Biotically, magnetite is produced by several organisms, including magnetotactic bacteria. Hematite, Fe2O3, is also produced abiotically and biotically. Abiotically, hematite rarely occurs as a primary mineral in igneous rocks, but is common as an alteration product, fumarole deposit, and in some metamorphosed Fe-rich rocks. Biotically, hematite is produced by several types of microorganisms. Biologically-produced magnetite and hematite are formed under the control of the host organism, and consequently, have characteristics not found in abiotically produced magnetite and hematite crystals. To determine if the magnetite and hematite in the Banded Iron Formation was biologically or abiotically produced, the characteristics of biologically-produced magnetite and hematite (concentrated from Aquaspirillum magnetotacticum) and abiotically-produced magnetite and hematite obtained from Wards Scientific Supply Company, were compared with characteristics of magnetite and hematite concentrated from the Gunflint Banded Iron Formation (Ontario, Canada) using thermal and crystallographic analytical techniques. Whole rock analysis of the Gunflint Banded Iron Formation by x-ray diffraction (XRD) and differential thermal analysis (DTA) revealed the presence of quartz, hematite, siderite and dolomite as the major minerals, and magnetite, greenalite, pyrite, pyrrhotite and apatite as the minor minerals. Analysis of a crude magnetic fraction of the Gunflint showed the minerals quartz, hematite, siderite, dolomite, and magnetite. Analysis of the crude magnetic fraction from Aquaspirillum magnetotacticum revealed organic compounds plus hematite and magnetite. The mineral identification and particle size distribution data obtained from the DTA along with XRD data indicate that the magnetite and hematite from the Gunflint BIF share some similarities with biologically formed magnetite and hematite.

Schwartz, D. E.; Mancinelli, R. L.; White, M. R.

1994-01-01

85

Effect of cation trapping on thermal stability of magnetite nanoparticles.  

PubMed

We investigate the effect of sodium trapping on thermal stability of magnetite (Fe3O4) nanoparticles. The pure magnetite nanoparticles incubated in sodium hydroxide solutions and subsequently washed with water to remove the excess sodium. The amount of sodium in magnetite is measured using atomic absorption spectroscopy. The size distribution obtained from Small angle X-ray scattering measurements show that particles are fairly monodisperse. The FTIR spectra of nanoparticles show transmission bands at 441 and 611 cm(-1) are due to the symmetric stretching vibrations (v) of Fe-O in octahedral and tetrahedral sites respectively. With 500 ppm of sodium ions (Na+) in magnetite, the cubic ferrite structure of maghemite (gamma-Fe2O3) to hexagonal hematite (alpha-Fe2O3) phase transition is enhanced by -150 degrees C in air. The Rietveld analysis of sodium doped magnetite nanoparticles show that above 99% of metastable gamma-Fe2O3 is converted to a thermodynamically stable alpha-Fe2O3 after air annealing at 700 degrees C. A decrease in enthalpy observed in doped magnetite unambiguously confirms that the activation energy for maghemite to hematite transition is increased due to the presence of trapped sodium ions. These results suggest that the trapped cations in ferrite nanoparticles can stabilize them by increasing the activation energy. PMID:24738360

Pati, S S; Philip, John

2014-06-01

86

Multiple ordering in magnetite.  

NASA Technical Reports Server (NTRS)

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.

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

1973-01-01

87

Exsolution of Iron-Titanium Oxides in Magnetite in Miller Range (MIL) 03346 Nakhlite: Evidence for Post Crystallization Reduction in the Nakhlite Cumulate Pile  

NASA Technical Reports Server (NTRS)

MIL 03346 is one of the most mesostasis-rich nakhlites [1] and thought to have equilibrated at oxygen fugacities near the fayalite-magnetite-quartz oxygen (FMQ) buffer ([2,3]). Studies of FeTi oxides in nakhlites have led to additional constraints on their equilibration temperatures and fO2s [4,5,6,7]. Comparison of these results to fO2s calculated for shergottites indicates that nakhlites are among the most oxidized samples from the martian meteorite suite [2]. The mesostasis of MIL 03346 contains skeletal titanomagnetite. Several scientists noticed several years ago (e.g. [8]) that this titanomagnetite contains very fine oxidation-driven exsolution lamellae (Figure 1). However, the lamellae are so small that they cannot be characterized by electron microprobe analysis (EMPA). Here we select several areas for focused ion beam (FIB) extraction, prepare transmission electron microscopy (TEM) foils, and identify and analyze the lamellae using TEM at the Johnson Space Center (JSC). The resulting analyses are combined with previous work on nakhlites to interpret the thermal and oxidation history of this meteorite group.

Righter, Kevin; Keller, L. P.; Rahman, Z.; Christoffersen, R.

2012-01-01

88

Experimental low-grade alteration of biogenic magnetite indicates microbial involvement in generation of banded iron formations  

NASA Astrophysics Data System (ADS)

During the deposition of banded iron formation (BIF), the downward flux of ferric oxyhydroxides and phytoplankton biomass should have facilitated Fe(III) reduction during burial, with the end product being ferrous iron-containing minerals including magnetite. Although earlier studies have attempted to quantify the significance of this pathway based on models of the ancient Fe cycle, the only direct evidences of a biological role in magnetite formation in BIF are their iron isotope compositions and unique crystallography which are reminiscent of biologically-generated magnetite. However, the biogenesis hypothesis lacks an explanation as to why modern biogenic magnetite crystals are generally a few hundred nm or smaller in size, yet the magnetite crystals in BIF are mostly tens of micrometers or larger in size. In this study, we demonstrate that biogenic magnetite crystals can grow in size upon reaction between oxyhydroxide and microbial biomass after compression and heating to 1 kbar and 150 °C, respectively. The magnetite crystals previously produced by Thermoanaerobacter spp. TOR39 reach sizes in excess of 700 nm after the P-T experiments, while new magnetite grains >400 nm formed from the superparamagnetic magnetite-dominated end product of Shewanella sp. culture. This study indicates that the large magnetite crystals observed in BIF can be derived through a three-stage sequence, beginning with dissimilatory iron reduction of an initial ferric iron-rich sediment coupled to the oxidation of dead phytoplankton biomass, followed by magnetite crystal aging, and ultimately pressure-temperature induced abiotic alteration of the biogenic magnetite during metamorphism.

Li, Yi-Liang; Konhauser, Kurt O.; Kappler, Andreas; Hao, Xi-Luo

2013-01-01

89

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

NASA Astrophysics Data System (ADS)

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

Moon, Ji-Won; Yeary, Lucas W.; Rondinone, Adam J.; Rawn, Claudia J.; Kirkham, Melanie J.; Roh, Yul; Love, Lonnie J.; Phelps, Tommy J.

2007-06-01

90

Electrically driven phase transition in magnetite nanostructures.  

PubMed

Magnetite (Fe3O4), an archetypal transition-metal oxide, has been used for thousands of years, from lodestones in primitive compasses to a candidate material for magnetoelectronic devices. In 1939, Verwey found that bulk magnetite undergoes a transition at TV approximately 120 K from a high-temperature 'bad metal' conducting phase to a low-temperature insulating phase. He suggested that high-temperature conduction is through the fluctuating and correlated valences of the octahedral iron atoms, and that the transition is the onset of charge ordering on cooling. The Verwey transition mechanism and the question of charge ordering remain highly controversial. Here, we show that magnetite nanocrystals and single-crystal thin films exhibit an electrically driven phase transition below the Verwey temperature. The signature of this transition is the onset of sharp conductance switching in high electric fields, hysteretic in voltage. We demonstrate that this transition is not due to local heating, but instead is due to the breakdown of the correlated insulating state when driven out of equilibrium by electrical bias. We anticipate that further studies of this newly observed transition and its low-temperature conducting phase will shed light on how charge ordering and vibrational degrees of freedom determine the ground state of this important compound. PMID:18084295

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

2008-02-01

91

Electrically driven phase transition in magnetite nanostructures  

NASA Astrophysics Data System (ADS)

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

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

2008-02-01

92

Fluid-induced martitization of magnetite in BIFs from the Dharwar Craton, India.  

NASA Astrophysics Data System (ADS)

Banded iron formations (BIFs) represent the largest iron deposits on Earth, which mainly formed in the Late Archean and Early Proterozoic. The complex geological history of BIFs makes it difficult to reconstruct the primary mineralogy and thus the initial depositional environment. Magnetite and hematite are the most important iron oxide minerals in BIFs. Magnetite (FeOFe2O3) comprising of both ferrous and ferric iron, easily undergoes transformation at low temperature. Hematite (?-Fe2O3) is often a result of the pseudomorphic replacement of magnetite, in the processus called martitisation. Despite the process of martitization having been widely studied, in both synthetic and natural magnetites, the mechanics of the transformation are poorly understood. What is generally agreed is that the transformation from magnetite to hematite occurs via a maghemite (g-Fe2O3) intermediate. The 2.9 Ga BIF from the Western Dharwar Craton, Southern India (a 500 m thick Archean BIF), is characterized by millimetric to centrimetric alternating white quartz and grey Fe-oxide bands. The Fe-oxide bands consist of martite crystals (~20µm) which represent the hematitisation of euhedral magnetite. The hematite crystals are in part euhedral, cubic shaped pointing to the replacement of magnetite. The crystals show a trellis pattern. Magnetite patches occur within the hematite. Raman spectroscopy, X-Ray diffraction, Curie balance and magnetic hysteresis analyses and FIB-TEM investigation indicate the presence of maghemite, and the presence of subhedral magnetite and interstitial hematite crystal. The latter are characterized by dislocation with fluid inclusions and high porosity zones. The magnetite grains contain lamellae and the interfaces between magnetite-maghemite and hematite are curved suggesting grain boundary migrations with the growth of hematite at the expense of magnetite and maghemite. It is thus suggested that martite result from low-T exsolutions along cleavage resulting in the formation of maghemite at the interface between magnetite and hematite with the migration of excess Fe3+ through the magnetite crystal lattice to the surface. Martitization is thus due to hydrothermal events associated with grain boundary migration during dynamic recrystallization.

Wagner, Christiane; Orberger, Beate; Tudryn, Alina; Wirth, Richard; Morgan, Rachael

2013-04-01

93

Crystal structure of raw pure Mysore silk fibre based on (Ala-Gly)2-Ser-Gly peptide sequence using Linked-Atom-Least-Squares method.  

PubMed

We have carried out crystal structure analysis of raw pure Mysore silk fibers belonging to Bombyx mori on the basis of model parameters of Marsh et al using Linked-Atom-Least-Squares technique. The intensity of all the reflections were computed employing CCP13 software. We observe that the molecular modification is essentially same as b-pleated structure with antipolar-antiparallel arrangements formed by hydrogen bonds. The essential differences observed in the structure are highlighted and discussed. PMID:15933415

Sangappa, Emptyyn Y; Mahesh, S S; Somashekar, R

2005-03-01

94

Magnetite morphology and life on Mars  

PubMed Central

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

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

95

Magnetite biomineralization in termites  

PubMed Central

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

Maher, B. A.

1998-01-01

96

Structural, optical, spectral and thermal studies of nonlinear optical pure and deuterated l-alanine single crystals  

Microsoft Academic Search

l-Alanine single crystals have been grown from H2O and D2O by slow evaporation and temperature lowering methods. The grown crystals were characterized by powder X-ray diffraction analysis and the vibrational frequencies of various functional groups in the crystals have been derived from FTIR spectrum. Optical transparency of the grown crystals was investigated by UV–vis–NIR spectrum. Differential scanning calorimetry (DSC) was

K. Suriya Kumar; Thenneti Raghavalu; V. Mathivanan; M. Kovendhan; B. Sivakumar; G. Ramesh Kumar; S. Gokul Raj; R. Mohan

2008-01-01

97

A Comparison between Chemical Synthesis Magnetite Nanoparticles and Biosynthesis Magnetite  

PubMed Central

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

Kahani, Seyed Abolghasem; Yagini, Zahra

2014-01-01

98

Hydrothermal Preparation of Apatite Composite with Magnetite or Anatase  

SciTech Connect

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

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

2006-05-15

99

Correlation between magnetic spin structure and the three-dimensional geometry in chemically synthesized nanoscale magnetite rings  

E-print Network

synthesized nanoscale magnetite rings M. Eltschka,1,a M. Kläui,1,b U. Rüdiger,1 T. Kasama,2 L. Cervera% spin polarization at the Fermi level. An example is magnetite Fe3O4 , which has been extensively The magnetic properties of thin films of vari- ous thicknesses and bulk single crystal Fe3O4 have been in

Dunin-Borkowski, Rafal E.

100

Incorporation and retention of 99-Tc(IV) in magnetite under high pH conditions.  

PubMed

Technetium incorporation into magnetite and its behavior during subsequent oxidation has been investigated at high pH to determine the technetium retention mechanism(s) on formation and oxidative perturbation of magnetite in systems relevant to radioactive waste disposal. Ferrihydrite was exposed to Tc(VII)(aq) containing cement leachates (pH 10.5-13.1), and crystallization of magnetite was induced via addition of Fe(II)aq. A combination of X-ray diffraction (XRD), chemical extraction, and X-ray absorption spectroscopy (XAS) techniques provided direct evidence that Tc(VII) was reduced and incorporated into the magnetite structure. Subsequent air oxidation of the magnetite particles for up to 152 days resulted in only limited remobilization of the incorporated Tc(IV). Analysis of both X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) data indicated that the Tc(IV) was predominantly incorporated into the magnetite octahedral site in all systems studied. On reoxidation in air, the incorporated Tc(IV) was recalcitrant to oxidative dissolution with less than 40% remobilization to solution despite significant oxidation of the magnetite to maghemite/goethite: All solid associated Tc remained as Tc(IV). The results of this study provide the first direct evidence for significant Tc(IV) incorporation into the magnetite structure and confirm that magnetite incorporated Tc(IV) is recalcitrant to oxidative dissolution. Immobilization of Tc(VII) by reduction and incorporation into magnetite at high pH and with significant stability upon reoxidation has clear and important implications for limiting technetium migration under conditions where magnetite is formed including in geological disposal of radioactive wastes. PMID:25236360

Marshall, Timothy A; Morris, Katherine; Law, Gareth T W; Mosselmans, J Frederick W; Bots, Pieter; Parry, Stephen A; Shaw, Samuel

2014-10-21

101

Reflectance anisotropy spectroscopy of magnetite (110) surfaces  

NASA Astrophysics Data System (ADS)

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.

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

102

Thickness dependence of the resistivity tensor in epitaxial magnetite thin films  

NASA Astrophysics Data System (ADS)

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

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

2013-07-01

103

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

SciTech Connect

Iron oxide films were deposited onto Si substrates using ion-beam-assisted deposition. The films were ~300 nm thick polycrystalline magnetite with an average crystallite size of ~6 nm. Additionally, 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. However, Raman spectroscopy and x-ray diffraction both indicate that the films are single-phase magnetite. Since no direct evidence of a second phase could be found, exchange bias likely arises due to defects at grain boundaries, possibly amorphous, creating frustrated spins. Since these samples have such small grains, a large fraction of the material consists of grain boundaries, where spins are highly disordered and reverse independently with external field. The high energy deposition process results in an oxygen-rich, argon-containing magnetite film with low temperature exchange bias due to defects at the high concentration of grain boundaries.

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

2014-11-03

104

Raman study of the Verwey transition in magnetite thin films  

NASA Astrophysics Data System (ADS)

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.

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

2013-10-01

105

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

106

Biophysics of Magnetic Orientation: Radical Pairs, Biogenic Magnetite, or both?  

NASA Astrophysics Data System (ADS)

Two major biophysical mechanisms for magnetoreception in terrestrial animals, one based on biogenic magnetite and another on radical-pair biochemical reactions, have been the subject of experiment and debate for the past 30 years. The magnetite hypothesis has stood the test of time: biogenic magnetite is synthesized biochemically in Bacteria, Protists, and numerous Animal phyla, as well as in some plants. Chains of single-domain crystals have been detected by clean-lab based SQUID magnetometry in animal tissues in all major phyla, followed by high-resolution TEM in selected model organisms, as well as by electrophysiological studies demonstrating the role of the ophthalmic branch of the trigeminal nerve in the magnetoreceptive process. Pulse-remagnetization - configured to uniquely flip the polarity of single-domain ferromagnets - has dramatic effects on the behavior of many birds, honeybees, mole rats, turtles, and bats, to cite a growing list. Magnetite-containing cells in the vicinity of these neurons in fish are now the subject of intense study by our consortium. The existence of a specialized class of magnetite-containing magnetoreceptor cells in animal tissues is no longer controversial. In contrast, less success has been achieved in gaining experimental support across a range of taxa for the radical-pair hypothesis. Although this mechanism was proposed to explain an early observation that birds would not respond to complete inversion of the magnetic vector, many organisms (even some birds) do indeed respond to the field polarity. We also note that few, if any, of these critical experiments have been done using fully double-blind methods. This is joint work with: M. M. Walker (University of Auckland, New Zealand) and M. Winklhofer (LMU Munich, Germany).

Kirschvink, Joe

2011-03-01

107

Coherent optical phonons in pure and Pr3+ doped YAG crystal studied by Optical Kerr Effect spectroscopy: Temperature and concentration dependence  

NASA Astrophysics Data System (ADS)

Herewith we present the results of the investigation of coherent phonons in pure and Pr3+ doped YAG crystals, by means of the femtosecond Optical Kerr Effect spectroscopy. In the experiment we have followed the dynamics of the Raman-active phonon modes at different temperatures in range between 263 K and 373 K and for different dopant concentrations. We found that the temperature dependence of phonon frequencies and lifetimes is linear, which is characteristic for 3-phonon relaxation process. We have used our fit results to calculate the widths of homogeneously broadened Raman lines and to find the anharmonic coupling constants. The observed dependence of phonon frequency and lifetime on dopant concentration is interpreted in terms of small, dopant induced alterations in the crystal structure, where the most influenced modes involve motion of the substituted ion. High precision of the OKE experiment is of great value, as such changes are small and thus hard to measure, when only low doping is possible, which is the case for Pr:YAG.

Polok, K.; Ratajska-Gadomska, B.; Konarska, J.; Gadomski, W.

2014-10-01

108

A facile approach to enhance the high temperature stability of magnetite nanoparticles with improved magnetic property  

NASA Astrophysics Data System (ADS)

We study the effect of Zn2+ doping on crystal structure, magnetic properties, blocking and Curie temperatures, and the high temperature phase stability of magnetite nanoparticles under air and vacuum annealing. The Zn2+ doped nanoparticles (ZnxFe3-xO4 with x = 0, 0.2, 0.4, and 0.6) are prepared by simple co-precipitation technique and are characterized by high temperature X-ray powder diffraction (HTXRD), vibrating sample magnetometer, small angle X-ray scattering, thermogravimetry, differential scanning calorimetry (DSC), and transmission electron microscopy. Our HTXRD studies show that the decomposition temperature of pure magnetite (Fe3O4) in vacuum is increased by 300 °C (from 700 to 1000 °C), with 0.2 fraction of Zn2+ doping. The DSC studies under air environment also show that the ?-Fe2O3 to ?-Fe2O3 phase transition temperature increases with the zinc fraction. The increase in transition temperature is attributed to the increase in the activation energy of the maghemite to hematite phase transition after the replacement of Fe3+ with larger diameter Zn2+ in the A site. Interestingly, the saturation magnetization increases from 61 to 69 emu/g upon 0.2 fraction of Zn2+, which augments the utility of the doped compound for practical applications. While the Curie temperature is found to increase with doping concentration, the blocking temperature shows an opposite trend. The blocking temperature values were found to be 262, 196, 144, and 153 K for 0, 0.2, 0.4, and 0.6 fraction of zinc, respectively. The reduction in TB is attributed to weak dipole-dipole interactions and local exchange coupling between nanoparticles. All the Zn2+ doped samples show superparamagnetic nature. These findings are extremely useful in producing superparamagnetic nanoparticles with enhanced magnetic properties for high temperature applications.

Pati, S. S.; Philip, John

2013-01-01

109

Dissolution and reduction of magnetite by bacteria  

NASA Technical Reports Server (NTRS)

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.

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

1995-01-01

110

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

PubMed Central

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

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

2013-01-01

111

Thermoremanent Magnetization in Submicroscopic Magnetite  

Microsoft Academic Search

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

D. J. Dunlop

1973-01-01

112

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

NASA Astrophysics Data System (ADS)

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.

Garza-Navarro, Marco; Torres-Castro, Alejandro; González, Virgilio; Ortiz, Ubaldo; De la Rosa, Elder

2010-01-01

113

Deposition of anatase titania onto carbon encapsulated magnetite nanoparticles  

NASA Astrophysics Data System (ADS)

A novel magnetically separable photocatalyst (titania-coated carbon encapsulated magnetite: TCCEF) was prepared. The prepared composite photocatalyst was characterized with an x-ray diffractometer (XRD), a transmission electron microscope (TEM), a Fourier transform infrared spectrometer (FT-IR) and a vibrating sample magnetometer (VSM). The photocatalytic activity of the samples was determined by degrading model contaminated water, a phenol aqueous solution. The results were compared with single-phase titania (pure titania and Degussa P25) and Fe3O4/TiO2, and enhanced photocatalytic activity was obtained. It is suggested that the enhanced photocatalytic activity is ascribed to two major factors. First, the encapsulation of magnetite into the carbon layer may inhibit the direct electrical contact of titania and magnetite, hence preventing the photodissolution of the iron oxide phase. Second, the enhanced hydroxyl groups on TCCEF may inhibit the recombination of electron-hole pairs. On the other hand, the magnetic photocatalyst can be easily recovered from a slurry with the application of an external magnetic field.

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

2008-10-01

114

Magnetite in the radular teeth of chitons  

Microsoft Academic Search

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

Manabu Mizota; Yutaka Maeda

1986-01-01

115

From iron(III) precursor to magnetite and vice versa  

SciTech Connect

The syntheses of nanosize magnetite particles by wet-chemical oxidation of Fe{sup 2+} have been extensively investigated. In the present investigation the nanosize magnetite particles were synthesised without using the Fe(II) precursor. This was achieved by {gamma}-irradiation of water-in-oil microemulsion containing only the Fe(III) precursor. The corresponding phase transformations were monitored. Microemulsions (pH {approx} 12.5) were {gamma}-irradiated at a relatively high dose rate of {approx}22 kGy/h. Upon 1 h of {gamma}-irradiation the XRD pattern of the precipitate showed goethite and unidentified low-intensity peaks. Upon 6 h of {gamma}-irradiation, reductive conditions were achieved and substoichiometric magnetite ({approx}Fe{sub 2.71}O{sub 4}) particles with insignificant amount of goethite particles found in the precipitate. Hydrated electrons (e{sub aq}{sup -}), organic radicals and hydrogen gas as radiolytic products were responsible for the reductive dissolution of iron oxide in the microemulsion and the reduction Fe{sup 3+} {yields} Fe{sup 2+}. Upon 18 h of {gamma}-irradiation the precipitate exhibited dual behaviour, it was a more oxidised product than the precipitate obtained after 6 h of {gamma}-irradiation, but it contained magnetite particles in a more reduced form ({approx}Fe{sub 2.93}O{sub 4}). It was presumed that the reduction and oxidation processes existed as concurrent competitive processes in the microemulsion. After 18 h of {gamma}-irradiation the pH of the medium shifted from the alkaline to the acidic range. The high dose rate of {approx}22 kGy/h was directly responsible for this shift to the acidic range. At a slightly acidic pH a further reduction of Fe{sup 3+} {yields} Fe{sup 2+} resulted in the formation of more stoichiometric magnetite particles, whereas the oxidation conditions in the acidic medium permitted the oxidation Fe{sup 2+} {yields} Fe{sup 3+}. The Fe{sup 3+} was much less soluble in the acidic medium and it hydrolysed and recrystallised as goethite. The {gamma}-irradiation of the microemulsion for 25 h at a lower dose rate of 16 kGy/h produced pure substoichiometric nanosize magnetite particles of about 25 nm in size and with the stoichiometry of Fe{sub 2.83}O{sub 4}.

Gotic, M., E-mail: gotic@irb.hr [Division of Materials Chemistry, Ruder Boskovic Institute, P.O. Box 180, HR-10002 Zagreb (Croatia); Jurkin, T.; Music, S. [Division of Materials Chemistry, Ruder Boskovic Institute, P.O. Box 180, HR-10002 Zagreb (Croatia)

2009-10-15

116

College of Engineering Electromagnetically Enhanced Hydrocyclone for Magnetite Separation during  

E-print Network

PENNSTATE College of Engineering Electromagnetically Enhanced Hydrocyclone for Magnetite Separation, but pose a safety risk due to the constant magnetic field. The Spring 2011 team des electromagnetic Electromagnetically Enhanced Hydrocyclone for Magnetite Separation during Coal Beneficiation Magnetite is used

Demirel, Melik C.

117

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

PubMed

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

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

2013-01-01

118

Understanding the biological stabilization of ferrihydrite and its transformation to magnetite  

NASA Astrophysics Data System (ADS)

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

Gordon, Lyle; Joester, Derk

2013-03-01

119

[Adsorption of methylene blue onto vanadium-doped magnetite].  

PubMed

A series of vanadium-doped magnetite (Fe3-x VxO4, x < 0.4) synthesized by an oxidation-precipitation method, were characterized using chemical analysis, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), as well as thermogravimetric and differential scanning calorimetry (TG-DSC) analyses. The obtained results show that the synthetic Fe3-x VxO4 has spinel structure while vanadium mostly replaces Fe3+ in the octahedral sites. The synthetic Fe3-x VxO4 is magnetic material, with crystal size ranging from 28 to 35 nm. The substitution of vanadium in the magnetite structure increases the amount of surface hydroxyls. The experimental adsorption results indicate that, in neutral pH condition, the maximum adsorption capacities of Fe3-x VxO4 increase obviously with the increase of vanadium concentration in magnetite while the adsorption isotherm complies well with the Langmuir model. The adsorption of methylene blue (MB) on Fe3-x VxO4 can get equilibrium in the first 25 min, supporting a pseudo-second order equation. Moreover, the rise of the solution pH value results in an increase of the adsorption capability of MB on Fe3-x VxO4. PMID:20698274

Zhong, Yuan-Hong; Liang, Xiao-Liang; Zhu, Jian-Xi; He, Hong-Ping; Yuan, Peng

2010-06-01

120

Metal-doped magnetite thin films.  

PubMed

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

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

2012-06-01

121

Pure Paracetamol for direct compression Part II. Study of the physicochemical and mechanical properties of sintered-like crystals of Paracetamol  

Microsoft Academic Search

Part I described the production of sintered-like Paracetamol crystals. In this second part, the physicochemical and technological behaviour of these crystals is investigated. The wettability and dissolution properties are then studied. The crystals exhibit a polyhedric habit which induces good flow properties. The porous crystal structure, resulting from the arrangement of the microcrystallites inside the crystalline particle, greatly improves compression

J.-M. Fachaux; A.-M. Guyot-Hermann; J.-C. Guyot; P. Conflant; M. Drache; S. Veesler; R. Boistelle

1995-01-01

122

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

SciTech Connect

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.

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

123

Crystals  

NSDL National Science Digital Library

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

Science, Lawrence H.

2009-01-01

124

Formation of single domain magnetite by green rust oxidation promoted by microbial anaerobic nitrate-dependent iron oxidation  

NASA Astrophysics Data System (ADS)

Biomineralization of magnetite is a central geomicrobiological process that might have played a primordial role over Earth’s history, possibly leaving traces of life in the geological record or controlling trace metal(loid)s and organic pollutants mobility in modern environments. Magnetite biomineralization has been attributed to two main microbial pathways to date (namely magnetotactic bacteria and dissimilatory iron-reducing bacteria). Here, we uncover a new route of magnetite biomineralization involving the anaerobic nitrate-reducing iron(II) oxidizing bacterium Acidovorax sp. strain BoFeN1. Using transmission electron microscopy, scanning transmission X-ray microscopy, transmission Mössbauer spectroscopy and rock magnetic analyses, this strain is shown to promote the transformation of hydroxychloride green rust in equilibrium with dissolved Fe(II) to (1) periplasmic lepidocrocite (?-FeOOH) and (2) extracellular magnetite, thus leading to strong redox heterogeneities at the nanometer scale. On the one hand, lepidocrocite was associated with protein moieties and exhibited an anisotropic texture, with the elongated axis parallel to the cell wall. On the other hand, magnetite crystals exhibited grain sizes and magnetic properties consistent with stable single domain particles. By comparison, abiotic controls led to a very slow (4 months vs. 2 days in BoFeN1 cultures) and incomplete oxidation of hydroxychloride green rust towards magnetite. As this abiotic magnetite exhibited the same size and magnetic properties (stable single domain particles) as magnetite produced in BoFeN1 cultures, only the co-occurrence of textured Fe(III)-oxides and magnetite, associated with the persistence of organic carbon molecules, might constitute valuable biosignatures to be looked for in the geological record. Our results furthermore contribute to a more complex picture of Fe redox cycling in the environment, providing an additional process of Fe(II)-bearing phase biomineralization that is not specific of Fe bio-reduction, but can also result from Fe bio-oxidation.

Miot, Jennyfer; Li, Jinhua; Benzerara, Karim; Sougrati, Moulay Tahar; Ona-Nguema, Georges; Bernard, Sylvain; Jumas, Jean-Claude; Guyot, François

2014-08-01

125

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

NASA Astrophysics Data System (ADS)

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

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

2005-03-01

126

Nano-magnetic probing on magnetite (110)  

Microsoft Academic Search

In this study, magnetite Fe3O4(110) thin films were grown epitaxially on MgO substrates. Scanning tunneling microscopy (STM) was used to observe surface structure after annealing the films in UHV at 1000 K. The conductivity character of the films was analyzed by means of scanning tunneling spectroscopy (STS). Nanometer scale magnetism of magnetite film was also observed from the STS data.

G. A. Maris; L. C. Jdira; J. G. H. Hermsen; S. Murphy; I. Shvets; S. Speller

2006-01-01

127

Electrically driven phase transition in magnetite nanostructures  

Microsoft Academic Search

Magnetite (Fe3O4), an archetypal transition-metal oxide, has been used for thousands of years, from lodestones in primitive compasses to a candidate material for magnetoelectronic devices. In 1939, Verwey found that bulk magnetite undergoes a transition at TV~120K from a high-temperature `bad metal' conducting phase to a low-temperature insulating phase. He suggested that high-temperature conduction is through the fluctuating and correlated

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

2008-01-01

128

Thermal Analysis of Acicular Shaped Magnetite  

NASA Technical Reports Server (NTRS)

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.

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

2003-01-01

129

Synthesis, characterization and applications of magnetite nanoparticles  

NASA Astrophysics Data System (ADS)

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

Kanmukhla, Vikram Kumar

130

Magnetite: a search for the half-metallic state.  

PubMed

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

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

2007-08-01

131

Investigation of magnetite thin films produced by pulsed laser deposition  

NASA Astrophysics Data System (ADS)

Thin films of magnetite (Fe 3O 4) with thicknesses in the range 10-1000 nm have been produced by the XeCl excimer laser ( ? = 308 nm) ablation of both Fe 3O 4 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 been shown to produce a smaller concentration of boulders than the ablation of bulk magnetite. It is believed that this is mainly due to the difference in primary ablation mechanisms between the two target materials. The use of single-crystal, lattice-matching substrates was found to be necessary at lower fluences (1-3 J cm -2) for the ablation of metallic Fe, whereas polycrystalline, non-lattice-matching substrates were adequate for deposition with moderate laser fluences (5-6 J cm -2). Film quality has been assessed by a range of techniques including XRD, SEM, AFM/MFM and CEMS. Using CEMS it has been established that the films produced from a metallic target contained a significant amount of metallic Fe, together with secondary oxide phases. The influence of film thickness on the Verwey transition has been investigated via electrical conductivity and SQUID magnetometry. It is found that there is a systematic reduction of Verwey temperature with decreasing film thickness; this is attributed to the effect of strain.

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

1997-02-01

132

Electrically-driven phase transition in magnetite nanostructures  

NASA Astrophysics Data System (ADS)

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

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

2008-03-01

133

Testing the apatite-magnetite geochronometer: U-Pb and 40Ar/ 39Ar geochronology of plutonic rocks, massive magnetite-apatite tabular bodies, and IOCG mineralization in Northern Chile  

NASA Astrophysics Data System (ADS)

Detailed zircon and apatite U-Pb dating and 40Ar/ 39Ar dating of actinolite have been carried out on the Carmen-Sierra Aspera Kiruna type magnetite-apatite and iron oxide Cu-Au (IOCG) district in the Coastal Cordillera of northern Chile (˜26°S). They define a precise succession of magmatic and hydrothermal events associated with early Cretaceous Andean magmatism. Apatite and magnetite from a magnetite-apatite tabular body with intergrowth texture in the Carmen deposit yield a total Pb-U isochron age of 131.0 ± 1.0 Ma. This result is the first direct dating of magnetite-apatite mineralization in an early Andean deposit, and the age coincides with zircon ages of a quartz diorite stock that partially hosts mineralization (130.6 ± 0.3 Ma). Magnetite from the studied tabular body contains only small amounts of radiogenic Pb and serves to constrain the initial common Pb isotopic composition. The high degree of correlation suggests that both minerals closed for Pb diffusion at essentially the same time and at a relatively high temperature (close to that of zircon), making the apatite-magnetite pair a reliable geochronometer for igneous or hydrothermal crystallization. Zircon from the Sierra Aspera composite pluton yields ages between 131.3 ± 0.3 Ma and 127.4 ± 0.1 Ma, clearly resolving the timing of intrusion of discrete intrusive phases. Actinolite 40Ar/ 39Ar ages partially overlap the ages of plutonic phases of the Sierra Aspera pluton, but are younger than the magnetite-apatite tabular body. The initial Pb isotopic composition of the melts and/or fluids from which the magnetite-apatite tabular bodies crystallized is very similar to the primitive Pb isotopic composition of granitic magmas associated with early Cretaceous plutons measured in K-feldspar. The Pb isotopic correspondence, combined with the temporal and spatial association between magnetite-apatite mineralization and the dioritic-quartz dioritic magmatism, strongly suggests a genetic relationship between early Cretaceous continental arc magmatism, massive magnetite-apatite deposits, and IOCG mineralization.

Gelcich, Sergio; Davis, Donald W.; Spooner, Edward T. C.

2005-07-01

134

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

NASA Astrophysics Data System (ADS)

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

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

135

Oxidation of pyrite in coal to magnetite  

USGS Publications Warehouse

When bituminous coal is heated in an inert atmosphere (He) containing small amounts of oxygen at 393-455 ??C, pyrite (FeS2) in coal is partially converted to magnetite (Fe304). The maximum amount of Fe304 formed during the time of heating corresponds to 5-20% of the total pyrite present, depending on the coal sample. The magnetite forms as an outer crust on the pyrite grains. The fact that the magnetic properties of the pyrite grains are substantially increased by the magnetite crust suggests that pyrite can be separated from coal by use of a low magnetic field. In a laboratory test, 75% removal is obtained by means of a 500 Oe magnet on three samples, and 60% on a fourth sample. ?? 1984.

Thorpe, A.N.; Senftle, F.E.; Alexander, C.C.; Dulong, F.T.

1984-01-01

136

Thermal analysis of two types of dextran-coated magnetite  

Microsoft Academic Search

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

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

2010-01-01

137

Thermal, dielectric studies on pure and amino acid ( L-glutamic acid, L-histidine, L-valine) doped KDP single crystals  

NASA Astrophysics Data System (ADS)

Amino acids ( L-glutamic acid, L-histidine, L-valine) doped potassium dihydrogen phospate crystals are grown by solution growth technique. Slow cooling as well as slow evaporation methods were employed to grow these crystals. The concentration of dopants in the mother solution was varied from 0.1 mol% to 10 mol%. The solubility data for all dopants concentration were determined. There is variation in pH value and hence, there is habit modification of the grown crystals were characterized with UV-VIS, FT-IR studies, SHG trace elements and dielectric studies reveal slight distortion of lattice parameter for the heavily doped KDP crystals. UV-Visible spectra confirm the improvement in the transparency of these crystals on doping metal ions. FT-IR spectra reveal strong absorption band between 1400 and 1600 cm -1 for metal ion doped crystals. TGA-DTA studies reveal good thermal stability. The dopants increase the hardness value of the material and it also depends on the concentration of the dopants. Amino acids doping improved the NLO properties. The detailed results on the spectral parameters, habit modifications and constant values will be presented.

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

2008-05-01

138

Remanent and induced magnetic anomalies over a layered intrusion: Effects from crystal fractionation and magma recharge  

NASA Astrophysics Data System (ADS)

The Bjerkreim-Sokndal (BKS) norite - quartz mangerite layered intrusion is part of the early Neoproterozoic Rogaland Anorthosite Province intruded into the Fennoscandian shield in south Norway at ~ 930 Ma. The BKS is exposed over an area of 230 km 2 with a thickness of ~ 7000 m and is of economic interest for ilmenite, magnetite and apatite deposits. From the point of view of magnetic minerals, in the course of fractional crystallization and magma evolution, the ilmenite becomes less Fe 3+-rich reflected by a change from ilmenite with hematite exsolution to nearly pure ilmenite. Magnetite starts to crystallize relatively late in the intrusive history, but its crystallization is interrupted by influxes of more primitive magma. The variations in aeromagnetic and ground-magnetic anomalies measured over the BKS can be explained in terms of the measured magnetic properties of NRM, susceptibility, and hysteresis presented here, and in terms of mineralogy. Early layers in the intrusion contain hemo-ilmenite. As the magma evolved and magnetite started to crystallize, this caused a distinct change over the layering from remanence-controlled negative anomalies to induced positive anomalies. When new, more primitive magma was injected into the system, hemo-ilmenite returned as the major oxide and the resulting magnetic anomalies are again negative. The most dramatic change in the magnetic signature is in the upper part of the intrusion in MCU IVe, where magnetite became a well established cumulate phase as indicated by susceptibility, but its induced magnetization is overcome by large NRMs associated either with hemo-ilmenite, or with hemo-ilmenite and magnetite exsolved from pyroxenes. The average natural remanent magnetizations change from ~ 3 A/m in MCU IVd, to 15 A/m in MCU IVe, and back to 2 A/m in the overlying MCU IVf, producing a strong negative remanent anomaly that has been followed along strike for at least 20 km by ground-magnetic measurements. The highly varied magnetic properties of this intrusion, caused by varied magmatic crystallization of combinations of opaque minerals, illustrate some of the possibilities to be considered in evaluating crustal magnetic anomalies.

McEnroe, Suzanne A.; Brown, Laurie L.; Robinson, Peter

2009-12-01

139

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

NASA Astrophysics Data System (ADS)

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

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

2012-06-01

140

Immobilization of peroxidase onto magnetite modified polyaniline.  

PubMed

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

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

2012-01-01

141

Magnetoresistance of magnetite point contacts and nanoconstrictions  

Microsoft Academic Search

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

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

2005-01-01

142

Magnetoresistance of magnetite point contacts and nanoconstrictions  

Microsoft Academic Search

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

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

2005-01-01

143

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

Microsoft Academic Search

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.

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

2011-01-01

144

Magnetotransport anisotropy effects in epitaxial magnetite (Fe3O4) thin films  

Microsoft Academic Search

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

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

1998-01-01

145

Transport and magnetic properties of epitaxial and polycrystalline magnetite thin films  

Microsoft Academic Search

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

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

1998-01-01

146

Biogenic Magnetite Formation through Anaerobic Biooxidation of Fe(II)  

PubMed Central

The presence of isotopically light carbonates in association with fine-grained magnetite is considered to be primarily due to the reduction of Fe(III) by Fe(III)-reducing bacteria in the environment. Here, we report on magnetite formation by biooxidation of Fe(II) coupled to denitrification. This metabolism offers an alternative environmental source of biogenic magnetite. PMID:11375205

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

2001-01-01

147

Magnetite Biomineralization: Fifty years of progress, from beach-combing to the SQUID microscope  

NASA Astrophysics Data System (ADS)

Magnetite biomineralization was first discovered 50 years ago as a hardening agent in the teeth of the Polyplacophoran molluscs (chitons) by the late Prof. Heinz A. Lowenstam of Caltech, when he noticed unusual erosional effects produced by their grazing in the intertidal zones of Palau (Lowenstam, 1962). Since then, biogenic magnetite has been detected in a broad range of organisms, including magnetotactic bacteria, protists, insects, fish, amphibians, reptiles, birds, and mammals including humans. In many species, the role of ferromagnetic material as a neurophysiological transducer is demonstrated clearly through the effects of pulse-remagnetization on behavior. A brief (1 uS), properly configured magnetic discharge from a rectified LC circuit, tailored to exceed the coercivity of the magnetite, will often abolish a magnetic behavioral response, or in some cases make the organism go the wrong way. This is a unique ferromagnetic effect. The genes controlling magnetite biomineralization are well characterized in several species of bacteria, and the ability of some of these bacterial genes to initiate magnetite precipitation in mammalian cell lines argues for a common descent, probably via a magnetotactic mitochondrial ancestor. Previous studies in fish reported the presence of single-domain magnetite crystals in cells near projections of the trigeminal nerve, co-located in the olfactory epithelium. Although the cells are rare, the recent development of a spinning magnetic field technique allows easy identification and isolation of these cells for individual study (Eder et al., 2012). The cells are surprisingly magnetic, with moments hundreds of times larger than typical magnetotactic bacteria. Subsequent efforts to identify the anatomical seat of magnetoreceptors have focused on the same locations in new organisms, excluding other areas. Using SQUID moment magnetometry and SQUID scanning microscopy, we report here the unexpected presence of biogenic magnetite in the lateral line region of the zebrafish, Danio rerio. We suspect that the magnetic field receptor cells of the trigeminal system in animals may be co-located within a variety of other sensory tissues (olfaction, lateral line, vision, hearing, taste, etc.) as a means of spatially dispersing cells with large magnetic moments to prevent magnetostatic interactions between them. References: Eder et al., Magnetic characterization of isolated candidate vertebrate magnetoreceptor cells. Proc. Natl. Acad. Sci. USA 2012; 109:12022-12027. Lowenstam, H.A., 1962. Magnetite in denticle capping in recent chitons (Polyplacophora). Bulletin of the Geological Society of America 73, 435-438.

Kirschvink, J. L.; Dixson, A. D.; Raub, T.

2012-12-01

148

Biomimetic Magnetite Formation: From Biocombinatorial Approaches to Mineralization Effects  

PubMed Central

Biological materials typically display complex morphologies and hierarchical architectures, properties that are hardly matched by synthetic materials. Understanding the biological control of mineral properties will enable the development of new synthetic approaches toward biomimetic functional materials. Here, we combine biocombinatorial approaches with a proteome homology search and in vitro mineralization assays to assess the role of biological determinants in biomimetic magnetite mineralization. Our results suggest that the identified proteins and biomimetic polypeptides influence nucleation in vitro. Even though the in vivo role cannot be directly determined from our experiments, we can rationalize the following design principles: proteins, larger complexes, or membrane components that promote nucleation in vivo are likely to expose positively charged residues to a negatively charged crystal surface. In turn, components with acidic (negatively charged) functionality are nucleation inhibitors, which stabilize an amorphous structure through the coordination of iron. PMID:24499323

2014-01-01

149

Title: Biogenic Magnetite Prevails in Oxic Pelagic Red Clay Core in the South Pacific Gyre  

NASA Astrophysics Data System (ADS)

Magnetotactic bacteria have been observed in wide variety of environments, including soils, freshwater lakes, and marine sediments, since Blakemore (1975) first described in 1975. Magnetotactic bacteria, which most commonly live within the oxic-anoxic transition zone (OATZ) of aquatic environments, produce intracellular crystals of magnetic minerals, specifically magnetite or greigite. It is considered that the magnetite/greigite crystals facilitate the bacteria's search for optimal conditions within the sharp chemical gradients of the OATZ. Petermann and Bleil (1993) reported living magnetotactic bacteria in pelagic and hemipelagic sediments near OATZ in the eastern South Atlantic at water depths to about 3,000 m, but they couldn't find actively swimming magnetotactic bacteria in sediments of deeper water depths. The South Pacific Gyre (SPG) is far from continents and the lowest productivity region on Earth. IODP site U1365 (water depth ~5,700 m) cored pelagic red clay of 75.5 m thick above ~100 Ma basement (except for the chart layer from ~42 to 63.5 m) in the western edge of the SPG. The core mainly consists of iron rich clay. The color is dark reddish and/or dark brown throughout the core. We conducted a paleomagnetic and environmental rock magnetic study of the pelagic clay core. The magnetostratigraphy revealed the top 5 m sediments cover the last 5 My, and sedimentation rate decreases downward from 1.7 to 0.6 m/m.y. Geochemical measurements of pore water indicate that dissolved oxygen was present throughout the core (>50 ?M). Thus oxygen penetrates through the entire sediment column to the sediment/basalt interface, and there is no OATZ. Magnetic mineral assemblage of this core is dominated by biogenic magnetite despite no OATZ. First-order reversal curve (FORC) diagrams of all specimens have a narrow central ridge along the Hc axis with very small vertical spread. This indicates very weak magnetostatic interaction (Roberts et al., 2000), and is the characteristic of biogenic magnetite (Egli et al., 2010; Roberts et al., 2011). Presence of biogenic magnetite was confirmed by TEM observation. Occurrence of biogenic magnetite was reported also in pelagic red clay of the North Pacific with TEM observations (Yamazaki and Ioka, 1997), and these samples also display the characteristic FORC diagrams. These observations suggest that biogenic magnetites commonly occur in oxic pelagic red clay without OATZ.

Shimono, T.; Yamazaki, T.

2012-12-01

150

Ferromagnetic resonance and low-temperature magnetic tests for biogenic magnetite  

NASA Astrophysics Data System (ADS)

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

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

2004-07-01

151

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

NASA Astrophysics Data System (ADS)

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

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

2010-09-01

152

Preparation of magnetite dextran microspheres by ultrasonication  

NASA Astrophysics Data System (ADS)

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

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

2005-05-01

153

Structural purity of magnetite nanoparticles in magnetotactic bacteria  

PubMed Central

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

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

2011-01-01

154

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

NASA Astrophysics Data System (ADS)

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

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

2009-04-01

155

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

E-print Network

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.

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

2009-09-03

156

Remanent and Induced Magnetic Anomalies over the Bjerkreim-Sokndal Layered Intrusion: Effects from Crystal Fractionation and Magma Recharge  

NASA Astrophysics Data System (ADS)

The Bjerkreim-Sokndal (BKS) norite-quartz mangerite layered intrusion is part of the early Neoproterozoic Rogaland Anorthosite Province intruded into the Fennoscandian shield in south Norway at ~930 Ma. The BKS is exposed over an area of 230 km2 with a thickness of ~7000m and is of economic interest for hemo-ilmenite, magnetite and apatite deposits. From the point of view of magnetic minerals, in the course of fractional crystallization and magma evolution, the ilmenite becomes less Fe3+-rich reflected by a change from ilmenite with hematite exsolution to nearly pure ilmenite. Magnetite starts to crystallize relatively late in the intrusive history, but its crystallization is interrupted by influxes of more primitive magma containing hemo-ilmenite. The variations in aeromagnetic and ground-magnetic anomalies measured over the BKS can be explained in terms of the magnetic properties of NRM, susceptibility, and hysteresis. Magnetic properties are correlated with the oxide mineralogy and mineral chemistry. Early layers in the intrusion contain hemo-ilmenite. As the magma evolved and magnetite started to crystallize, this caused a distinct change over the layering from remanence-controlled negative anomalies to induced positive anomalies. When new, more primitive magma was injected into the system, hemo-ilmenite returned as the major oxide and the resulting magnetic anomalies are again negative. The most dramatic change in the magnetic signature is in the upper part of the intrusion in MCU IVe, where magnetite became a well established cumulate phase as indicated by susceptibility, but its induced magnetization is overcome by large NRM's associated either with hemo-ilmenite or with hemo-ilmenite and magnetite exsolved from pyroxenes. The average natural remanent magnetizations change from ~3 A/m in MCU IVd, to 15 A/m in MCU IVe, and back to 2 A/m in the overlying MCU IVf, producing a strong negative remanent anomaly that has been followed along strike for at least 20 km by ground-magnetic measurements. The highly varied magnetic properties of this intrusion, caused by varied magmatic crystallization of combinations of oxide minerals illustrate some of the possibilities to be considered in evaluating crustal magnetic anomalies.

McEnroe, S. A.; Brown, L. L.; Robinson, P.

2013-12-01

157

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

NASA Astrophysics Data System (ADS)

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.

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

2014-12-01

158

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

NASA Astrophysics Data System (ADS)

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.

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

2011-09-01

159

Experimental Shock Decomposition of Siderite to Magnetite  

NASA Technical Reports Server (NTRS)

The debate about fossil life on Mars includes the origin of magnetites of specific sizes and habits in the siderite-rich portions of the carbonate spheres in ALH 84001 [1,2]. Specifically [2] were able to demonstrate that inorganic synthesis of these compositionally zoned spheres from aqueous solutions of variable ion-concentrations is possible. They further demonstrated the formation of magnetite from siderite upon heating at 550 C under a Mars-like CO2-rich atmosphere according to 3FeCO3 = Fe3O4 + 2CO2 + CO [3] and they postulated that the carbonates in ALH 84001 were heated to these temperatures by some shock event. The average shock pressure for ALH 84001, substantially based on the refractive index of diaplectic feldspar glasses [3,4,5] is some 35-40 GPa and associated temperatures are some 300-400 C [4]. However, some of the feldspar is melted [5], requiring local deviations from this average as high as 45-50 GPa. Indeed, [5] observes the carbonates in ALH 84001 to be melted locally, requiring pressures in excess of 60 GPa and temperatures > 600 C. Combining these shock studies with the above inorganic synthesis of zoned carbonates it seems possible to produce the ALH 84001 magnetites by the shock-induced decomposition of siderite.

Bell, M. S.; Golden, D. C.; Zolensky, M. E.

2005-01-01

160

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

NASA Astrophysics Data System (ADS)

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.

Patterson, C. H.

2014-08-01

161

crystals  

NASA Astrophysics Data System (ADS)

We present the crystal growth, optical spectroscopy, and room temperature continuous-wave (CW) laser operation of monoclinic Ho:KLu(WO4)2 crystals. Macro defect-free crystals of several dopant concentrations were grown by top-seeded solution growth slow-cooling method. The evolution of unit cell parameters with holmium doping level and temperature was studied using X-ray powder diffraction. The spectroscopic properties were characterized in terms of room- and low-temperature optical absorption and photoluminescence. From low-temperature optical absorption measurements, the energy of the Stark levels was determined. Calculation of the emission and gain cross sections is presented. CW laser action was realized for 3 and 5 at. % Ho-doped KLu(WO4)2 by in-band pumping using a Tm:KLu(WO4)2 pump laser. A maximum output power of 507 mW with a slope efficiency of ~38 % with respect to the incident power was achieved at 2,080 nm with the Ho:KLu(WO4)2 laser.

Jambunathan, V.; Mateos, X.; Pujol, M. C.; Carvajal, J. J.; Zaldo, C.; Griebner, U.; Petrov, V.; Aguiló, M.; Díaz, F.

2014-08-01

162

Mechanical spectroscopy of magnetite filled polyurethane shape memory polymers  

Microsoft Academic Search

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

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

2007-01-01

163

Structure and superparamagnetic behaviour of magnetite nanoparticles in cellulose beads  

Microsoft Academic Search

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 0.8moll?1 with ammonia at 25 and 70°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

José R. Correa; Eduardo Bordallo; Dora Canetti; Vivian León; Luis C. Otero-Díaz; Carlos Negro; Adrián Gómez; Regino Sáez-Puche

2010-01-01

164

Electrodeposition of copper–magnetite magnetic composite films  

Microsoft Academic Search

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,

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

2007-01-01

165

Silicon dioxide nanoporous structure with liquid crystal for optical sensors  

NASA Astrophysics Data System (ADS)

It has been studied the spectral characteristics of the porous silicon dioxide and cholesteric liquid crystal. It has been shown that doping of the EE1 cholesteric liquid crystal with Fe3O4 magnetite nanoparticles doesn't shift significantly the position of the transmittance minimum of the material. It has been found that the deformation of chiral pitch of cholesteric liquid crystal with magnetite is observed in case of doping of porous nanocomposite host with following shifting of minimum of transmittance into short wavelength direction. It has been shown that influence of carbon monoxide on optical characteristics of the cholesteric liquid crystal with magnetite can be explained by the interaction of CARBON MONOXIDE molecules with magnetite nanodopants.

Sushynskyi, Orest; Vistak, Maria; Gotra, Zenon; Fechan, Andriy; Mikityuk, Zinoviy

2013-05-01

166

Magnetite-bubble aggregates at mixing interfaces in andesite magma bodies  

E-print Network

. In the andesite there is no spatial association between bubbles and magnetite and the magnetite content of the andesite is small. We suggest a mechanism for enclave formation whereby in vapour-saturated magma, bubbles nucleate on magnetite. Upon intrusion...

Edmonds, M.; Brett, A.; Herd, R. A.; Humphreys, M. C. S.; Woods, A.

2014-08-14

167

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

SciTech Connect

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

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

2009-01-12

168

Electron thermalization and trapping rates in pure and doped alkali and alkaline-earth iodide crystals studied by picosecond optical absorption  

NASA Astrophysics Data System (ADS)

Although light continues to be emitted from insulating crystals used as scintillators over a period of nanoseconds to microseconds after stopping of an energetic particle, much of what determines the nonlinearity of response goes on in the first picoseconds. On this time scale, free carriers and excitons are at high density near the track core and thus are subject to nonlinear quenching. The hot (free) electrons eventually cool to low enough energy that trapping on holes, dopants, or defects can commence. In the track environment, spatial distributions of trapped carriers determined on the picosecond time scale can influence the proportionality between light yield and the initial particle energy throughout the whole light pulse. Picosecond spectroscopy of optical absorption induced by a short pulse of above-gap excitation provides a useful window on what occurs during the crucial early evolution of excited populations. The laser excitation can be tuned to excite carriers that are initially very hot (˜3 eV) relative to the band edges, or that are almost thermalized (˜0.1 eV excess energy) at the outset. Undoped and doped samples of NaI:Tl(0%, 0.1%), CsI:Tl(0%, 0.01%, 0.04%, 0.3%), and SrI2:Eu(0%, 0.2%, 0.5%, 3%) are studied in this work.

Ucer, K. B.; Bizarri, G.; Burger, A.; Gektin, A.; Trefilova, L.; Williams, R. T.

2014-04-01

169

Fe atom exchange between aqueous Fe2+ and magnetite.  

PubMed

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

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

2012-11-20

170

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

Microsoft Academic Search

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

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

2008-01-01

171

http://www.jstor.org Magnetite Biomineralization in Termites  

E-print Network

http://www.jstor.org Magnetite Biomineralization in Termites Author(s): Barbara A. Maher Source@jstor.org. #12;7 kvaZ cWe Magnetite biomineralizationin termites Barbara A. Maher Schoolof EnvironmentalSciences,Universityof East Anglia, NorwichNR4 77, UK Experimental evidence exists for magnetoreception in termites, a major

172

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

NASA Astrophysics Data System (ADS)

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

Vodyanitskii, Yu. N.

2013-03-01

173

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

174

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

PubMed Central

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

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

175

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

PubMed

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 fAm(2)) 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

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

176

Coating agents affected toward magnetite nanoparticles properties  

NASA Astrophysics Data System (ADS)

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

Petcharoen, Karat; Sirivat, Anuvat

2012-02-01

177

Pyroelectric detection of spontaneous polarization in magnetite thin films  

NASA Astrophysics Data System (ADS)

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.

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

2012-10-01

178

Copper partitioning in a melt vapor brine magnetite pyrrhotite assemblage  

NASA Astrophysics Data System (ADS)

The effect of sulfur on the partitioning of Cu in a melt-vapor-brine ± magnetite ± pyrrhotite assemblage has been quantified at 800 °C, 140 MPa, f = nickel-nickel oxide (NNO), logf=-3.0 (i.e., on the magnetite-pyrrhotite curve at NNO), logfS=-1.3 and logf=-1. All experiments were vapor + brine saturated. Vapor and brine fluid inclusions were trapped in silicate glass and self-healed quartz fractures. Vapor and brine are dominated by NaCl, KCl and HCl in the S-free runs and NaCl, KCl and FeCl 2 in S-bearing runs. Pyrrhotite served as the source of sulfur in S-bearing experiments. The composition of fluid inclusions, glass and crystals were quantified by laser-ablation inductively coupled plasma mass spectrometry. Major element, chlorine and sulfur concentrations in glass were quantified by using electron probe microanalysis. Calculated Nernst-type partition coefficients (±2 ?) for Cu between melt-vapor, melt-brine and vapor-brine are DCuv/m=63±31, DCub/m=240±80, and DCuv/b=0.27±0.10, respectively, in the S-free system. The partition coefficients (±2 ?) for Cu between melt-vapor, melt-brine and vapor-brine are DCuv/m=316±22, DCub/m=443±68, and DCuv/b=0.69±0.16, respectively, in the S-bearing system. Apparent equilibrium constants (±1 ?) describing Cu and Na exchange between vapor and melt and brine and melt were also calculated. The values of KCu,Nav/m are 34 ± 21 and 128 ± 29 in the S-free and S-bearing runs, respectively. The values of KCu,Nab/m are 33 ± 22 and60 ± 5 in the S-free and S-bearing runs, respectively. The data presented here indicate that the presence of sulfur increases the mass transfer of Cu into vapor from silicate melt. Further, the nearly threefold increase in DCuv/b suggests that Cu may be transported as both a chloride and sulfide complex in magmatic vapor, in agreement with hypotheses based on data from natural systems. Most significantly, the data demonstrate that the presence of sulfur enhances the partitioning of Cu from melt into magmatic volatile phases.

Simon, Adam C.; Pettke, Thomas; Candela, Philip A.; Piccoli, Philip M.; Heinrich, Christoph A.

2006-11-01

179

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

PubMed

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

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

2012-06-01

180

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

SciTech Connect

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

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

2009-06-12

181

Bats use magnetite to detect the earth's magnetic field.  

PubMed

While the role of magnetic cues for compass orientation has been confirmed in numerous animals, the mechanism of detection is still debated. Two hypotheses have been proposed, one based on a light dependent mechanism, apparently used by birds and another based on a "compass organelle" containing the iron oxide particles magnetite (Fe(3)O(4)). Bats have recently been shown to use magnetic cues for compass orientation but the method by which they detect the Earth's magnetic field remains unknown. Here we use the classic "Kalmijn-Blakemore" pulse re-magnetization experiment, whereby the polarity of cellular magnetite is reversed. The results demonstrate that the big brown bat Eptesicus fuscus uses single domain magnetite to detect the Earths magnetic field and the response indicates a polarity based receptor. Polarity detection is a prerequisite for the use of magnetite as a compass and suggests that big brown bats use magnetite to detect the magnetic field as a compass. Our results indicate the possibility that sensory cells in bats contain freely rotating magnetite particles, which appears not to be the case in birds. It is crucial that the ultrastructure of the magnetite containing magnetoreceptors is described for our understanding of magnetoreception in animals. PMID:18301753

Holland, Richard A; Kirschvink, Joseph L; Doak, Thomas G; Wikelski, Martin

2008-01-01

182

Field-induced decoupling of NiO-magnetite multilayers  

SciTech Connect

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.

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

183

Controlled cobalt doping in biogenic magnetite nanoparticles.  

PubMed

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

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

184

Controlled cobalt doping in biogenic magnetite nanoparticles  

PubMed Central

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

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

185

In vitro study of magnetite-amyloid ? complex formation.  

PubMed

Biogenic magnetite (Fe(3)O(4)) has been identified in human brain tissue. However, abnormal concentration of magnetite nanoparticles in the brain has been observed in different neurodegenerative pathologies. In the case of Alzheimer's disease (AD), these magnetic nanoparticles have been identified attached to the characteristic brain plaques, which are mainly formed by fibrils of amyloid ? peptide (A?). However, few clues about the formation of the magnetite-A? complex have been reported. We have investigated the interaction between these important players in AD with superconducting quantum interference, scanning electron microscope, surface plasmon resonance, and magnetic force microscopy. The results support the notion that the magnetite-A? complex is created before the synthesis of the magnetic nanoparticles, bringing a highly stable interaction of this couple. . PMID:22115601

Mir, Mònica; Tahirbegi, Islam Bogachan; Valle-Delgado, Juan José; Fernàndez-Busquets, Xavier; Samitier, Josep

2012-08-01

186

Pure and gravitational radiation  

E-print Network

The well-known treatment of asymptotically flat vacuum fields is adapted to pure radiation fields. In this approach we find a natural normalization of the radiation null vector. The energy balance at null infinity shows that the mass loss results from a linear superposition of the pure and the gravitational radiation parts. By transformation to Bondi-Sachs coordinates the Kinnersley photon rocket is found to be the only axisymmetric Robinson-Trautman pure radiation solution without gravitational radiation.

U. von der Goenna; D. Kramer

1997-11-03

187

Microfabrication and characterization of magnetite-based magnetic tunnel junctions  

NASA Astrophysics Data System (ADS)

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.

Park, Chando

188

Electrophoretic mobility of magnetite particles in high temperature water  

SciTech Connect

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.

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

189

Study of pulsed laser deposited magnetite thin film  

Microsoft Academic Search

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

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

2007-01-01

190

Uniaxial anisotropy in magnetite thin film—Magnetization studies  

Microsoft Academic Search

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

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

2006-01-01

191

Parametric investigation for direct chemical vapour deposition of magnetite films  

Microsoft Academic Search

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

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

192

Deposition of magnetite films by reactive sputtering of iron  

Microsoft Academic Search

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

J. Heller

1976-01-01

193

Investigation of Electrically Driven Phase Transition in Magnetite Thin Films  

Microsoft Academic Search

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

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

2009-01-01

194

In Situ Mineralization of Magnetite Nanoparticles in Chitosan Hydrogel  

NASA Astrophysics Data System (ADS)

Based on chelation effect between iron ions and amino groups of chitosan, in situ mineralization of magnetite nanoparticles in chitosan hydrogel under ambient conditions was proposed. The chelation effect between iron ions and amino groups in CS-Fe complex, which led to that chitosan hydrogel exerted a crucial control on the magnetite mineralization, was proved by X-ray photoelectron spectrum. The composition, morphology and size of the mineralized magnetite nanoparticles were characterized by X-ray diffraction, Raman spectroscopy, transmission electron microscopy and thermal gravity. The mineralized nanoparticles were nonstoichiometric magnetite with a unit formula of Fe2.85O4 and coated by a thin layer of chitosan. The mineralized magnetite nanoparticles with mean diameter of 13 nm dispersed in chitosan hydrogel uniformly. Magnetization measurement indicated that superparamagnetism behavior was exhibited. These magnetite nanoparticles mineralized in chitosan hydrogel have potential applications in the field of biotechnology. Moreover, this method can also be used to synthesize other kinds of inorganic nanoparticles, such as ZnO, Fe2O3 and hydroxyapatite.

Wang, Yongliang; Li, Baoqiang; Zhou, Yu; Jia, Dechang

2009-09-01

195

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

PubMed

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

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

2011-04-20

196

Production Rate of Cosmogenic 10Be in Magnetite  

NASA Astrophysics Data System (ADS)

Cosmogenic 10Be is widely used for determining exposure ages, soil production rates, and catchment-wide erosion rates. To date, measurements have been almost exclusively in the mineral quartz (SiO2), which is resistant to weathering and easily cleaned of meteoric 10Be contamination. However, this limits the method to quartz-bearing rocks and requires specialized laboratories due to the need for large quantities of hydrofluoric acid (HF). Here, we present initial results for 10Be production in the mineral magnetite (Fe3O4). Magnetite offers several advantages over quartz; it is (1) present in mafic rocks, (2) easily collected in the field, (3) quickly and easily separated in the lab, and (4) digested without HF. In addition, 10Be can be measured in both detrital quartz and magnetite from the same catchment to yield information about the intensity of chemical weathering (Rogers et al., this conference). The 10Be production rate in magnetite relative to quartz was determined for a granitic boulder from Mt. Evans, Colorado, USA. The boulder was crushed and homogenized to facilitate production rate comparisons among various minerals. We separated magnetite using a combination of hand magnets, froth flotation, and a variety of selective chemical dissolutions in dithionite-citrate-bicarbonate solution, 5% nitric acid (HNO3) and 1% HF/HNO3. Six aliquots of magnetite were analyzed for 10Be and compared to quartz. Three aliquots that were not exposed to 1% HF/HNO3 were contaminated with meteoric 10Be, probably associated with residual mica. Three aliquots that were exposed to 1% HF/HNO3 treatments agreed to within 2% measurement uncertainty. Our preliminary results indicate that the relative production rate by mass of 10Be in magnetite and quartz is 0.462 × 0.012. Our results are similar to theoretically predicted values. Recently updated excitation functions for neutron and proton spallation reactions allow us to partition 10Be production in quartz and magnetite among silicon, oxygen, and iron. While most of the production in both magnetite and quartz is from spallation of oxygen, our experimental results indicate that approximately (13 × 3)% of 10Be in the Mt. Evans quartz sample is produced from silicon.

Granger, D. E.; Rogers, H. E.; Riebe, C. S.; Lifton, N. A.

2013-12-01

197

Use of magnetite as anode for electrolysis of water  

NASA Astrophysics Data System (ADS)

We have studied the oxidation of magnetite to Fe2O3 in an electrolytic cell in which the anode is magnetite and the cathode is platinum. We report cyclic voltammagram data consistent with the hypothesis that magnetite, without oxygen gas production but with hydrogen gas production at the cathode, is occurring. The reaction occurs at a potential at the anode of about 0.3 V vs SCE in 1 M NaOH electrolyte, consistent with colloid experiments which also estimated the equilibrium potential of the hypothesized reaction. Electrode characterization results using BET, XEDS, and macroscopic volume and mass measurements are reported, as well as the measurements of the amount of hydrogen gas generated per unit current. The quantity of gas generated is also consistent with our hypothesis concerning the electrode chemistry. Some samples exhibit evidence of two oxidation reactions occurring at the anode and a possible interpretation of these is also discussed. These results suggest the use of magnetite as an anode in a cell electrolysing water to produce hydrogen gas and Fe2O3. In such an electrolyser, the electrical energy cost of producing hydrogen gas could be significantly lower than the cost in a standard electrolyser. The measured steady state currents, equivalent to about 400 mA/g of magnetite, are too low to make a practical electrolyser. We briefly discuss several ways in which the currents might be increased to the levels required.

Halley, J. W.; Schofield, A.; Berntson, B.

2012-06-01

198

Abnormal elastic and vibrational behaviors of magnetite at high pressures.  

PubMed

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 Fe(2+)-Fe(3+)-Fe(2+) 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

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

199

Abnormal Elastic and Vibrational Behaviors of Magnetite at High Pressures  

PubMed Central

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

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

200

Magnetic Separations with Magnetite: Theory, Operation, and Limitations  

SciTech Connect

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

G. B. Cotten

2000-08-01

201

The Verwey transition in nanostructured magnetite produced by a combination of chimie douce and spark plasma sintering  

NASA Astrophysics Data System (ADS)

Magnetite nanoparticles about 10 nm sized were synthesized by the polyol method. Zero-field-cooled (ZFC)-FC measurements showed a blocking temperature ˜170 K and the absence of the Verwey transition. They were subsequently consolidated by spark plasma sintering at 750 °C for 15 min, leading to a high density (92% of the theoretical density), solid body, with grains in the 150 nm range. X-ray diffraction patterns exhibited a spinel single phase with cell parameters corresponding to the magnetite structure. Magnetic measurements showed a decrease of coercivity from 685 Oe (54.5 kA/m) at 118 K to 90 Oe (7.2 kA/m) at 139 K. ZFC measurements at 25 Oe presented a three-fold magnetization increase as temperature increased; a small transition between 116 and 117.5 K, followed by a larger one from 117.6 to 124 K. The first transition can be associated with a complex crystallographic transition and delocalization of Fe2+-Fe3+, while the second one can be attributed to spin reorientation due to the magnetocrystalline anisotropy constant (K1) change of sign as previously observed only in magnetite single crystals.

Gaudisson, T.; Vázquez-Victorio, G.; Bañobre-López, M.; Nowak, S.; Rivas, J.; Ammar, S.; Mazaleyrat, F.; Valenzuela, R.

2014-05-01

202

The Verwey transition in nanostructured magnetite produced by a combination of chimie douce and spark plasma sintering  

SciTech Connect

Magnetite nanoparticles about 10?nm sized were synthesized by the polyol method. Zero-field-cooled (ZFC)-FC measurements showed a blocking temperature ?170?K and the absence of the Verwey transition. They were subsequently consolidated by spark plasma sintering at 750?°C for 15?min, leading to a high density (92% of the theoretical density), solid body, with grains in the 150?nm range. X-ray diffraction patterns exhibited a spinel single phase with cell parameters corresponding to the magnetite structure. Magnetic measurements showed a decrease of coercivity from 685?Oe (54.5?kA/m) at 118?K to 90?Oe (7.2?kA/m) at 139?K. ZFC measurements at 25?Oe presented a three-fold magnetization increase as temperature increased; a small transition between 116 and 117.5?K, followed by a larger one from 117.6 to 124?K. The first transition can be associated with a complex crystallographic transition and delocalization of Fe{sup 2+}-Fe{sup 3+}, while the second one can be attributed to spin reorientation due to the magnetocrystalline anisotropy constant (K{sub 1}) change of sign as previously observed only in magnetite single crystals.

Gaudisson, T.; Nowak, S.; Ammar, S. [ITODYS, Université Paris Diderot, PRES Sorbonne Paris Cité, CNRS-UMR 7086, 75205 Paris Cedex (France); Vázquez-Victorio, G.; Valenzuela, R., E-mail: raulvale@yahoo.com [Depto Materiales Metálicos y Cerámicos, Instituto de Investigaciones en Materiales, Universidad Nacional Autónoma de México, Mexico 04510 (Mexico); Bañobre-López, M.; Rivas, J. [International Iberian Nanotechnology Laboratory, 4715-310 Braga (Portugal); Mazaleyrat, F. [SATIE, ENS Cachan, CNRS, UniverSud, F-94230 Cachan (France)

2014-05-07

203

In situ hybridization to chitosan/magnetite nanocomposite induced by the magnetic field  

NASA Astrophysics Data System (ADS)

Chitosan/magnetite nanocomposite was synthesized induced by magnetic field via in situ hybridization in ambient condition. Results of XRD patterns and TEM micrographs indicated that magnetite particles with 10-20 nm were dispersed in chitosan homogeneously. An interesting result is that magnetite nanoparticles were assembled to form chain-like structures under the influence of the external magnetic field, which mimics the magnetite chains inside of magnetotatic bacteria. The saturated magnetization (Ms) of nano-magnetite in chitosan was 50.54 emu/g, which is as high as 54% of bulk magnetite. The remanence (Mr) and coercivity (Hc) were 4 emu/g and14.8 Oe, respectively, which indicated that magnetite nanoparticles were superparamagnetic. The key of route is that a pre-precipitated chitosan hydrogel membrane, used as chemical reactor, which controlled the precipitation of chitosan precipitation and in situ transformation of magnetite from the precursor simultaneously in the magnetic field environment.

Li, Baoqiang; Jia, Dechang; Zhou, Yu; Hu, Qiaoling; Cai, Wei

2006-11-01

204

Department of Earth and Mineral Engineering Spring 2011 Electromagnetically Enhanced Hydrocyclone for Magnetite Separation  

E-print Network

PENNSTATE Department of Earth and Mineral Engineering Spring 2011 Electromagnetically Enhanced Hydrocyclone for Magnetite Separation during Coal Beneficiation Overview Consol Energy uses magnetite to design a lab-scale electromagnetically enhanced hydrocyclone and test the separation efficiency

Demirel, Melik C.

205

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

PubMed Central

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

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

2013-01-01

206

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

Microsoft Academic Search

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.

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

2002-01-01

207

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

PubMed

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

Mitsumori, Masashi; Nakahodo, Tsukasa; Fujihara, Hisashi

2012-01-01

208

Size selected synthesis of magnetite nanoparticles in chitosan matrix  

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

209

Investigation of Electrically Driven Phase Transition in Magnetite Thin Films  

NASA Astrophysics Data System (ADS)

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

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

2009-03-01

210

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

Microsoft Academic Search

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

Suh Cem Pang; Wai Hwa Khoh; Suk Fun Chin

2010-01-01

211

Study of magnetite nanoparticle suspensions by photometry and NMR relaxometry  

NASA Astrophysics Data System (ADS)

A method has been described for preparation of suspensions of magnetite nanoparticles stabilized by porous silicon dioxide. The process of sedimentation of nanoparticles in suspensions of different compositions and concentrations has been analyzed by transmission coefficient measurements. Spectra of the transmission coefficient have been obtained for suspensions containing composite nanoparticles, the initial silicon dioxide, and macroscopic magnetite particles. The average effective radius of nanoparticles has been calculated from the time dependences of the transmission coefficient. It has been demonstrated that the synthesized nanoparticles possess magnetic-resonance contrast properties.

Bogachev, Yu. V.; Gareev, K. G.; Matyushkin, L. B.; Moshnikov, V. A.; Naumova, A. N.

2013-12-01

212

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

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

J.-J. Ménard

1995-01-01

213

Sorption of nalidixic acid onto micrometric and nanometric magnetites: experimental study and modeling  

E-print Network

affected by the particle size of tested magnetites. Ionic strength effect was less significant suggesting was identified as the main constituent of iron corrosion scale in drinking water distribution systems [8]. Top layers of corrosion scale were dominated by magnetite [8, 9]. Magnetite can also be formed in laboratory

Boyer, Edmond

214

Ab initio study of the half-metal to metal transition in strained magnetite  

E-print Network

does not lead to a metallic state for magnetite films grown on (111)-oriented substrates. 3 PresentAb initio study of the half-metal to metal transition in strained magnetite Martin Friák1 of magnetite under different strain conditions. The effects of volume relaxation and internal degrees

215

The relationship between magnetic microstructure and anti-phase domain size in epitaxial magnetite thin films  

E-print Network

-axis electron holography Thin films of magnetite (Fe3O4) that have been grown epitaxially on MgO exhibit unusual suggested that 50-nm-thick magnetite films contain distinct magnetic regions that are 2-4 times the anti induction and the positions of the APBs, we have examined a 25-nm-thick magnetite film using off

Dunin-Borkowski, Rafal E.

216

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

Microsoft Academic Search

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

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

2001-01-01

217

Bats Use Magnetite to Detect the Earth's Magnetic Field Richard A. Holland1,2  

E-print Network

Bats Use Magnetite to Detect the Earth's Magnetic Field Richard A. Holland1,2 *, Joseph L magnetite (Fe3O4). Bats have recently been shown to use magnetic cues for compass orientation but the method demonstrate that the big brown bat Eptesicus fuscus uses single domain magnetite to detect the Earths magnetic

218

Spin and orbital magnetic moment of reconstructed ?{2 }×?{2 }R 45? magnetite(001)  

NASA Astrophysics Data System (ADS)

The surface of a magnetite single crystal with (001) orientation has been prepared by sputtering/annealing cycles providing the ?{2 }×?{2 }R 45? reconstruction. The distribution of magnetic domains on the surface has been imaged by x-ray magnetic dichroism in a photoemission microscope. The easy axes are along the surface in-plane <110 > directions. The near-surface magnetic moment was determined by applying the sum rules to XMCD spectra obtained with different kinetic energies of the secondary electrons. A reduced total moment of 3.3 ?B and a ratio of about 0.10 between orbital and spin moment was found, which we attribute to the surface reconstruction.

Martín-García, Laura; Gargallo-Caballero, Raquel; Monti, Matteo; Foerster, Michael; Marco, José F.; Aballe, Lucía; de la Figuera, Juan

2015-01-01

219

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

PubMed

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

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

2013-09-01

220

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

221

Synthesis of pure RDX  

SciTech Connect

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

Pagoria, P.F.

1994-03-25

222

Physical limits of hyperthermia using magnetite fine particles  

Microsoft Academic Search

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

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

1998-01-01

223

Cell-specific cytotoxicity of dextran-stabilized magnetite nanoparticles  

Microsoft Academic Search

Cytotoxicity of dextran-hybridized magnetite nanoparticles which were prepared by a novel polyol method was evaluated by incubation with four different kinds of cells, including rat liver cells BRL 3A, renal cells NRK, astrocyte and periphery blood mononuclear cells (PBMC). The study was designed not only to evaluate their cytotoxicity but also to reflect the interaction between nanoparticles and related cells

Jing Ding; Ke Tao; Jiyu Li; Sheng Song; Kang Sun

2010-01-01

224

Magnetite or Hematite? The Iron-Oxides Returned by Stardust  

NASA Astrophysics Data System (ADS)

Two Stardust samples were examined; a section of C2044,0,41 and C2005,2,121,2,0 have both shown strong Raman signals of hematite. However, the origin of this hematite is unclear and we show it may be due to heating of magnetite.

Foster, N. J.; Burchell, M. J.; Creighton, J. A.; Cole, M. J.

2008-03-01

225

Raman spectroscopy investigation of magnetite nanoparticles in ferrofluids  

NASA Astrophysics Data System (ADS)

Raman spectroscopy is used to investigate magnetite nanoparticles dispersed in two types of ?-cyclodextrin suspensions. An approach is presented for characterization of the magnetic core in liquid surrounding at room temperature and atmospheric pressure. The effect of elevating laser power on the structural stability and chemical composition of magnetite in the ferrofluids is discussed. The data are compared with data from dry by-products from the fluids. Powder samples undergo total phase transition from magnetite to hematite at laser power of 1.95 mW. The same nanoparticles in the fluid undergo transformation at 9 mW, but no hematite positions appear throughout that investigation. The Raman spectra revealed that the main phase of the magnetic core in the fluids is magnetite. That is indicated by a strong and non-diminishing in intensity peak at 670 cm -1. A second phase is present at the nanoparticle's surface with Raman spectroscopy unveiling maghemite-like and small fractions of goethite-like structures. The Fourier transform infrared spectroscopy investigations confirm deviations in the surface structure and also point to the fact that the oxidation process starts at an early stage after formation of the nanoparticles. The analyses of the infrared data also show that ?-cyclodextrin molecules retain their cyclic character and the coating does not affect the oxidation process once the particles are evicted from the fluids. A Mössbauer spectroscopy measurement on a ferrofluidic sample is also presented.

Slavov, L.; Abrashev, M. V.; Merodiiska, T.; Gelev, Ch.; Vandenberghe, R. E.; Markova-Deneva, I.; Nedkov, I.

2010-07-01

226

Effect of Dispersant on Preparation of Colloidal Magnetite Nanocrystals  

Microsoft Academic Search

Nanometer scale magnetite particles were prepared in a very low concentration dispersing system with a dispersant. The average size of the particles prepared under optimum conditions was determined by transmission electron microscopy to be approximately 1.8 nm. The magnetic properties were investigated using a superconducting quantum interference device (SQUID) magnetometer. The dried samples exhibited approximately superparamagnetic behavior. Rhelogical property measurement

Chang-Neng Shauo; Chuen-Guang Chao

2006-01-01

227

Benefaction studies on the Hasan Celebi magnetite deposit, Turkey  

USGS Publications Warehouse

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.

Pressler, Jean W.; Akar, Ali

1972-01-01

228

Bats Use Magnetite to Detect the Earth's Magnetic Field  

Microsoft Academic Search

While the role of magnetic cues for compass orientation has been confirmed in numerous animals, the mechanism of detection is still debated. Two hypotheses have been proposed, one based on a light dependent mechanism, apparently used by birds and another based on a ''compass organelle'' containing the iron oxide particles magnetite (Fe3O4). Bats have recently been shown to use magnetic

Richard A. Holland; Joseph L. Kirschvink; Thomas G. Doak; Martin Wikelski

2008-01-01

229

Bats Use Magnetite to Detect the Earth's Magnetic Field  

Microsoft Academic Search

While the role of magnetic cues for compass orientation has been confirmed in numerous animals, the mechanism of detection is still debated. Two hypotheses have been proposed, one based on a light dependent mechanism, apparently used by birds and another based on a “compass organelle” containing the iron oxide particles magnetite (Fe3O4). Bats have recently been shown to use magnetic

Richard A. Holland; Joseph L. Kirschvink; Thomas G. Doak; Martin Wikelski; Sarah Frances Brosnan

2008-01-01

230

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

E-print Network

Extrinsic magnetoresistance in magnetite nanoparticles Kai Liu,a) L. Zhao, and P. Klavins. Spin-dependent tunneling through adjacent particles has led to a negative magnetoresistance, 8 magnetoresistance MR effects have been reported in compact powder pellets of high spin-polarization materials

Osterloh, Frank

231

Magnetic and magnetotransport properties of magnetite films with step edges  

Microsoft Academic Search

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.

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

2004-01-01

232

Avian magnetite-based magnetoreception: a physiologist's perspective  

PubMed Central

It is now well established that animals use the Earth's magnetic field to perform long-distance migration and other navigational tasks. However, the transduction mechanisms that allow the conversion of magnetic field variations into an electric signal by specialized sensory cells remain largely unknown. Among the species that have been shown to sense Earth-strength magnetic fields, birds have been a model of choice since behavioural tests show that their direction-finding abilities are strongly influenced by magnetic fields. Magnetite, a ferromagnetic mineral, has been found in a wide range of organisms, from bacteria to vertebrates. In birds, both superparamagnetic (SPM) and single-domain magnetite have been found to be associated with the trigeminal nerve. Electrophysiological recordings from cells in the trigeminal ganglion have shown an increase in action potential firing in response to magnetic field changes. More recently, histological evidence has demonstrated the presence of SPM magnetite in the subcutis of the pigeon's upper beak. The aims of the present review are to review the evidence for a magnetite-based mechanism in birds and to introduce physiological concepts in order to refine the proposed models. PMID:20106875

Cadiou, Hervé; McNaughton, Peter A.

2010-01-01

233

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

234

Magnetism of pure iron jarosites  

NASA Astrophysics Data System (ADS)

Stoichiometrically pure jarosites of the formula AFe3(OH)6(SO4)2 with A=Na+, K+, Rb+, and NH+4 have been afforded by a newly developed redox-based, hydrothermal method. The jarosites exhibit an intralayer antiferromagnetic exchange interaction (-829 Kcrystal analyses of the pure Fe3+ jarosite compounds reveal that the kagomé layers are structurally invariant with those of their Cr3+ and V3+ relatives. This structural homology allows the sign and magnitude of exchange coupling within kagomé layers to be correlated to the different orbital parentages engendered by the M3+ d-electron count. Infrared studies show the presence of H2O within the kagomé layers of alkali metal and hydronium ion Fe3+ jarosites prepared by conventional precipitation methods; conversely, H2O is absent within the kagomé layers of jarosites prepared by the new redox-based hydrothermal methods. These results suggest that the absence of LRO in (H3O)Fe3(OH)6(SO4)2 is due to structural and magnetic disorder arising from proton transfer from the interlayer hydronium ion to the bridging hydroxide ions of the kagomé layers.

Grohol, Daniel; Nocera, Daniel G.; Papoutsakis, Dimitris

2003-02-01

235

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.

236

Optical studies of anthracene single crystals  

Microsoft Academic Search

Recently the polyacene crystals such as pentacene, tetracene and anthracene have attracted great interest both in research and applications. These ultra-pure molecular crystals are very promising materials for FETs, organic photovoltaic diodes, LEDs and lasing. High purity anthracene crystal have been grown by physical vapor transport. High photo luminecense (PL) quantum efficiency(over 20%) was observed in these pure anthracene single

Yuhong Jiang; Matthew Delong; Z. Valy Vardeny

2001-01-01

237

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

NASA Astrophysics Data System (ADS)

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.

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

2014-08-01

238

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

NASA Astrophysics Data System (ADS)

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.

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

2012-10-01

239

Direct deposition of magnetite thin films on organic semiconductors  

NASA Astrophysics Data System (ADS)

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 magneto-optical Kerr effect, superconductor quantum interference device, micro-Raman spectroscopy, and Atomic Force Microscopy. The ferromagnetic behavior persists even for 10nm thick films. Charge injection at magnetite-organic interface has been finally demonstrated by detecting electroluminescence from Alq3.

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

2008-09-01

240

Investigation of heteroepitaxial growth of magnetite thin films.  

SciTech Connect

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

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

2007-07-01

241

SIZE-OPTIMIZED MAGNETITE NANOPARTICLES FOR MAGNETIC PARTICLE IMAGING  

SciTech Connect

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

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

2010-06-01

242

Investigation of magnetite thin films produced by pulsed laser deposition  

Microsoft Academic Search

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

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

1997-01-01

243

Magnetoresistance at grain boundaries artificially introduced into magnetite films  

Microsoft Academic Search

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

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

2002-01-01

244

Investigation of magnetite thin films produced by pulsed laser deposition  

Microsoft Academic Search

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

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

1997-01-01

245

Patterned magnetite films prepared via soft lithography and thermal decomposition  

Microsoft Academic Search

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

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

2006-01-01

246

Photoemission electronic states of epitaxially grown magnetite films  

Microsoft Academic Search

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

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

2007-01-01

247

Magnetic and transport properties of magnetite thin films  

Microsoft Academic Search

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),

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

2005-01-01

248

UV pulsed laser deposition of magnetite thin films  

Microsoft Academic Search

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

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

2005-01-01

249

Investigation of heteroepitaxial growth of magnetite thin films  

Microsoft Academic Search

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

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

2007-01-01

250

Magnetite films grown directly on organic semiconductor layers  

Microsoft Academic Search

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)

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

2006-01-01

251

Magnetization and susceptibility of ion-irradiated granular magnetite films  

Microsoft Academic Search

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

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

2011-01-01

252

Electrically-driven phase transition in magnetite nanostructures  

Microsoft Academic Search

In 1939 Verwey found that bulk magnetite undergoes a first-order transition at TV 120 K from a high temperature conducting phase to a low-temperature insulating phase. High-T conduction occurs via the fluctuating valences of the octahedral iron atoms, and the transition comes from the interplay of charge ordering and structural distortion upon cooling. The Verwey transition mechanism and charge ordering

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

2008-01-01

253

Synthesis and characterization of polypyrrole–magnetite–vitamin B12 hybrid composite electrodes  

Microsoft Academic Search

In this study vitamin B12 covered magnetite nanoparticles have been incorporated into a conducting polypyrrole. This polymer\\u000a was electrochemically synthesized in the presence of the B12-coated magnetite. The adsorption of B12 was demonstrated by the\\u000a decrease in absorbance of the vitamin in the supernatant liquid after B12 has been in contact with magnetite sol overnight.\\u000a The composition of the layers

Csaba Janaky; Balazs Endrodi; Angela Hajdu; Csaba Visy

2010-01-01

254

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

SciTech Connect

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.

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

2013-07-01

255

Magnetic Microstructure of Closely-Spaced Ferrimagnetic Crystals in Magnetotactic Bacteria  

E-print Network

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

Dunin-Borkowski, Rafal E.

256

Soft X-ray Spectroscopy Study of the Electronic Structure of Oxidized and Partially Oxidized Magnetite Nanoparticles  

SciTech Connect

The crystal structure of magnetite nanoparticles may be transformed to maghemite by complete oxidation, but under many relevant conditions the oxidation is partial, creating a mixed-valence material with structural and electronic properties that are poorly characterized. We used X-ray diffraction, Fe K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy, and soft X-ray absorption and emission spectroscopy to characterize the products of oxidizing uncoated and oleic acid-coated magnetite nanoparticles in air. The oxidization of uncoated magnetite nanoparticles creates a material that is structurally and electronically indistinguishable from maghemite. By contrast, while oxidized oleic acid-coated nanoparticles are also structurally indistinguishable from maghemite, Fe L-edge spectroscopy revealed the presence of interior reduced iron sites even after a 2-year period. We used X-ray emission spectroscopy at the O K-edge to study the valence bands (VB) of the iron oxide nanoparticles, using resonant excitation to remove the contributions from oxygen atoms in the ligands and from low-energy excitations that obscured the VB edge. The bonding in all nanoparticles was typical of maghemite, with no detectable VB states introduced by the long-lived, reduced-iron sites in the oleic acid-coated sample. However, O K-edge absorption spectroscopy observed a 0.2 eV shift in the position of the lowest unoccupied states in the coated sample, indicating an increase in the semiconductor band gap relative to bulk stoichiometric maghemite that was also observed by optical absorption spectroscopy. The results show that the ferrous iron sites within ferric iron oxide nanoparticles coated by an organic ligand can persist under ambient conditions with no evidence of a distinct interior phase and can exert an effect on the global electronic and optical properties of the material. This phenomenon resembles the band gap enlargement caused by electron accumulation in the conduction band of TiO2.

Gilbert, Benjamin; Katz, Jordan E.; Denlinger, Jonathan D.; Yin, Yadong; Falcone, Roger; Waychunas, Glenn A.

2010-10-24

257

Synthesis of chiral hybrid nanotubes of magnetite nanoparticles and conducting polymers  

NASA Astrophysics Data System (ADS)

New chiral magnetite nanoparticles with a polymerizable group produced polymer composite films on an electrode surface and the hybrid nanotubes of magnetite nanoparticles and polythiophene from their template-based electropolymerization.New chiral magnetite nanoparticles with a polymerizable group produced polymer composite films on an electrode surface and the hybrid nanotubes of magnetite nanoparticles and polythiophene from their template-based electropolymerization. Electronic supplementary information (ESI) available: Synthesis of a chiral stabilizer 1 and the spectral data. See DOI: 10.1039/c1nr11312g

Mitsumori, Masashi; Nakahodo, Tsukasa; Fujihara, Hisashi

2011-12-01

258

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

Microsoft Academic Search

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

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

259

Typical Pure Nonequilibrium Steady States  

E-print Network

We show that typicality holds for a class of nonequilibrium systems, i.e., nonequilibrium steady states (NESSs): almost all the pure states properly sampled from a certain Hilbert space well represent a NESS and characterize its intrinsic thermal nature. We clarify the relevant Hilbert space from which the pure states are to be sampled, and construct practically all the typical pure NESSs. The scattering approach leads us to the natural extension of the typicality for equilibrium systems. Each pure NESS correctly yields the expectation values of observables given by the standard ensemble approach. It means that we can calculate the expectation values in a NESS with only a single pure NESS. We provide an explicit construction of the typical pure NESS for a model with two reservoirs, and see that it correctly reproduces the Landauer-type formula for the current flowing steadily between the reservoirs.

Takaaki Monnai; Kazuya Yuasa

2014-04-13

260

Magnetorheological behavior of magnetite covered clay particles in aqueous suspensions  

NASA Astrophysics Data System (ADS)

Montmorillonite clay particles coated with magnetite nanoparticles suspended in aqueous media behave as magnetorheological fluids with enhanced stability as compared to conventional ones. In this work, the study of the magnetorheological behavior of these suspensions of magnetite-clay composite particles has been carried out. For this purpose, both steady and dynamic rheological measurements were carried out in the absence and in the presence of external magnetic fields. In the first kind of experiments, the rheograms of the suspensions (shear stress versus shear rate plot) are analyzed as a function of the strength of the magnetic field applied. In the second one, oscillatory stresses are applied to the system, and the storage modulus is studied as a function of the external magnetic field. In the absence of magnetic field, the suspensions develop a weak yield stress due to the aggregation of the magnetite covered clay particles. In the presence of magnetic field, the yield stress is strongly dependent on the magnetic field strength inside the samples, demonstrating that the suspensions experience a magnetorheological effect, moderate when the magnetic field strength is weak and stronger for values of magnetic field higher than 150-200 kA/m. Actually, the most intriguing result is the change of the trend in the dependence of the yield stress with the field. This dependence is approximately linear with the field for strength values smaller than 150-200 kA/m. On the other hand, for higher values, the yield stress increases with magnetic field following a power law with exponent 4.5.The results are interpreted by means of a model that relates the structure of the particles in the suspensions to the magnetic field applied and using the interaction energy between particles calculated by the extended DLVO theory to include magnetic interaction.

Galindo-Gonzalez, C.; Lopez-Lopez, M. T.; Duran, J. D. G.

2012-08-01

261

Mechanism of fast growth of magnetite on carbon steel  

SciTech Connect

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.

Macdonald, D.D.

1985-07-01

262

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

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...

Mouneyrac, David; Floch, Jean-Michel Le; Tobar, Michael E; Cros, Dominique; Krupka, Jerzy

2010-01-01

263

Enhanced oxygen transfer rate and bioprocess yield by using magnetite nanoparticles in fermentation media of erythromycin.  

PubMed

BackgroundMagnetite nanoparticles have widespread biomedical applications. In the aerobic bioprocesses, oxygen is a limiting factor for the microbial metabolic rate; hence a high availability of oxygen in the medium is crucial for high fermentation productivity. This study aimed to examine the effect of using magnetite nanoparticles on oxygen transfer rate in erythromycin fermentation culture.MethodsMagnetite nanoparticles were synthetized through co-precipitation method. After observing the enhanced oxygen transfer rate in deionized water enriched with magnetite nanoparticles, these nanoparticles were used in the media of by Saccharopolyspora erythraea growth to explore their impact on erythromycin fermentation titer. Treatments comprised different concentrations of magnetite nanoparticles, (0, 0.005, 0.02 v/v).ResultsIn the medium containing 0.02 v/v magnetite nanoparticles, KLa was determined to be 1.89 time higher than that in magnetite nanoparticle-free broth. An improved 2.25 time higher erythromycin titer was obtained in presence of 0.02 v/v nanoparticles.ConclusionsOur results, demonstrate the potential of magnetite nanoparticles for enhancing the productivity of aerobic pharmaceutical bioprocesses. PMID:25223458

Labbeiki, Ghazal; Attar, Hossein; Heydarinasab, Amir; Sorkhabadi, Sayed; Rashidi, Alimorad

2014-09-16

264

Monodispersed magnetite nanoparticles optimized for magnetic fluid hyperthermia: Implications in biological systems  

E-print Network

Monodispersed magnetite nanoparticles optimized for magnetic fluid hyperthermia: Implications 2011) Magnetite (Fe3O4) nanoparticles (MNPs) are suitable materials for Magnetic Fluid Hyperthermia of Physics. [doi:10.1063/1.3556948] I. INTRODUCTION Magnetic fluid hyperthermia (MFH) is a promising approach

Krishnan, Kannan M.

265

Fe-Ni Metal and Magnetite Nano-Particles in ``Brown'' Color Olivines from Martian Meteorites  

NASA Astrophysics Data System (ADS)

Our TEM study revealed that brown olivines in Dhofar 019, LAR 06319 and NWA 1950 contained magnetite nano-particles instead of Fe-Ni metal nano-particles. These results indicate that magnetite nano-particles are widely present in martian meteorites.

Kurihara, T.; Mikouchi, T.; Saruwatari, K.; Kameda, J.; Miyamoto, M.

2009-03-01

266

Influence of the olivine additive fineness on the oxidation of magnetite pellets  

Microsoft Academic Search

Olivine is used as an additive in Luossavaara–Kiirunavaara AB (LKAB) blast furnace pellets. The LKAB iron ore is magnetite which oxidizes to hematite during the sintering process. Olivine retards the oxidation of magnetite pellets if the threshold temperature of magnesioferrite formation is exceeded.In this study, we have developed a thermogravimetric measuring method to study the relationship between the olivine reactivity

S. P. E. Forsmo; A. Hägglund

2003-01-01

267

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

Microsoft Academic Search

In a thin section of CI Orgueil a 4x5 mm clast was found with an unusual composition. It consists mainly of magnetite (63 wt%) and dolomite (12 wt%) in the usual fine matrix. The magnetite occurs in rounded grains of 5 to 20 micron, occasionally also as framboidal spherules composed of many tiny grains. The dolomite grains have about the

F. Wlotzka; R. Thacker; K. Fredriksson

1995-01-01

268

Magnetite (Fe3O4) Core-Shell Nanowires: Synthesis and  

E-print Network

Magnetite (Fe3O4) Core-Shell Nanowires: Synthesis and Magnetoresistance Daihua Zhang,,§ Zuqin Liu. As has been theoretically predicted on the basis of electron band structure calculations, magnetite (Fe3O films,13-17 nanocluster assemblies,18-21 and compacted powders,14 where the MR was ascribed

Zhou, Chongwu

269

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

270

Characterization of interfacial reactions in magnetite tunnel junctions with transmission electron microscopy  

E-print Network

Characterization of interfacial reactions in magnetite tunnel junctions with transmission electron of Physics. DOI: 10.1063/1.1688535 I. INTRODUCTION Half metallic magnetite (Fe3O4) has been thought to be one is also discussed. II. EXPERIMENT Thin films were deposited onto Si or oxidized Si wafers by either rf

Laughlin, David E.

271

Magnetic field dependence of the nonequilibrium metal-insulator transition in magnetite nanostructures  

Microsoft Academic Search

At low temperatures magnetite undergoes a Verwey transition from a comparatively conducting state to a strongly correlated, ordered, more insulating state, the detailed nature of which remains under active debate. Recent experiments using nanostructures based on epitaxial magnetite films have shown that an applied dc electric field can lead to a nonequilibrium transition out of the insulating state. The kinetics

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

2011-01-01

272

Ab initio study of the half-metal to metal transition in strained magnetite  

Microsoft Academic Search

Using density-functional theory, we investigate the stability of the half-metallic ground state of magnetite under different strain conditions. The effects of volume relaxation and internal degrees of freedom are fully taken into account. For hydrostatic compression, planar strain in the (001) plane and uniaxial strain along the [001] direction, we derive quantitative limits beyond which magnetite becomes metallic. As a

Martin Friák; Arno Schindlmayr; Matthias Scheffler

2007-01-01

273

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

NASA Astrophysics Data System (ADS)

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.

Merlini, M.

2013-12-01

274

Avian orientation: the pulse effect is mediated by the magnetite receptors in the upper beak  

PubMed Central

Migratory silvereyes treated with a strong magnetic pulse shift their headings by approximately 90°, indicating an involvement of magnetite-based receptors in the orientation process. Structures containing superparamagnetic magnetite have been described in the inner skin at the edges of the upper beak of birds, while single-domain magnetite particles are indicated in the nasal cavity. To test which of these structures mediate the pulse effect, we subjected migratory silvereyes, Zosterops l. lateralis, to a strong pulse, and then tested their orientation, while the skin of their upper beak was anaesthetized with a local anaesthetic to temporarily deactivate the magnetite-containing structures there. After the pulse, birds without anaesthesia showed the typical shift, whereas when their beak was anaesthetized, they maintained their original headings. This indicates that the superparamagnetic magnetite-containing structures in the skin of the upper beak are most likely the magnetoreceptors that cause the change in headings observed after pulse treatment. PMID:19324756

Wiltschko, Wolfgang; Munro, Ursula; Ford, Hugh; Wiltschko, Roswitha

2009-01-01

275

Off-axis electron holography observation of magnetic microstructure in a magnetite (001) thin film containing antiphase domains  

E-print Network

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

Dunin-Borkowski, Rafal E.

276

Synthesizing cysteine-coated magnetite nanoparticles as MRI contrast agent: Effect of pH and cysteine addition on particles size distribution  

NASA Astrophysics Data System (ADS)

Cysteine capped magnetite nanoparticles (10 to 20 nm) were synthesized via coprecipitation method under ultrasonic irradiation. The influence of pH value of the solution and cysteine addition on the size distribution and hydrodynamic size of nanoparticles were studied via TEM and PCS methods, respectively. The crystal structure and magnetic properties of the nanoparticles were characterized by XRD and VSM techniques, respectively. Coating density was calculated using TGA and TEM results. Cytotoxicity assessment performed by incubation of L929 cells, confirmed that ferrofluids are biocompatible. MRI studies conducted on rats demonstrated suitability of synthesized nanoparticles as contrast agents, especially for imaging of the lymph nodes.

Ahmadi, R.; Ranjbarnodeh, E.; Gu, N.

2012-12-01

277

Structure-Disorder induced MagnetoResistance intensification on spin-dependent-conduction in magnetite (Fe3O4) thin film produced by RF magnetron sputtering method  

Microsoft Academic Search

The intensification of magneto-resistance (MR) caused by structure-disorder has been observed in magnetite (Fe3O4) thin film (MTF) produced by the rf magnetron sputtering method. The MTFs with the thickness of 20nm, 50nm and 100nm were deposited on the substrates of SiO2-glass, MgAl2O4 (100) and MgO (100) single crystals. We have observed that the MR of the MTF on SiO2-glass substrate

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

2009-01-01

278

HOW APPLIED MATHEMATICS BECAME PURE  

Microsoft Academic Search

This paper traces the evolution of thinking on how mathematics relates to the world— from the ancients, through the beginnings of mathematized science in Galileo and Newton, to the rise of pure mathematics in the nineteenth century. The goal is to better understand the role of mathematics in contemporary science. My goal here is to explore the relationship between pure

PENELOPE MADDY

2008-01-01

279

Synthesis and characterization of magnetite nanoparticles coated with lauric acid  

SciTech Connect

Understanding the process of synthesis of magnetic nanoparticles is important for its implementation in in vitro and in vivo studies. In this work we report the synthesis of magnetic nanoparticles made from ferrous oxide through coprecipitation chemical process. The nanostructured material was coated with lauric acid and dispersed in aqueous medium containing surfactant that yielded a stable colloidal suspension. The characterization of magnetic nanoparticles with distinct physico-chemical configurations is fundamental for biomedical applications. Therefore magnetic nanoparticles were characterized in terms of their morphology by means of TEM and DLS, which showed a polydispersed set of spherical nanoparticles (average diameter of ca. 9 nm) as a result of the protocol. The structural properties were characterized by using X-ray diffraction (XRD). XRD pattern showed the presence of peaks corresponding to the spinel phase of magnetite (Fe{sub 3}O{sub 4}). The relaxivities r{sub 2} and r{sub 2}* values were determined from the transverse relaxation times T{sub 2} and T{sub 2}* at 3 T. Magnetic characterization was performed using SQUID and FMR, which evidenced the superparamagnetic properties of the nanoparticles. Thermal characterization using DSC showed exothermic events associated with the oxidation of magnetite to maghemite. - Highlights: • Synthesis of magnetic nanoparticles coated with lauric acid • Characterization of magnetic nanoparticles • Morphological, structural, magnetic, calorimetric and relaxometric characterization.

Mamani, J.B., E-mail: javierbm@einstein.br [Instituto do Cérebro-InCe, Hospital Israelita Albert Einstein-HIAE, 05651-901 São Paulo (Brazil); Costa-Filho, A.J. [Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Universidade de São Paulo, Ribeirão Preto (Brazil); Cornejo, D.R. [Instituto de Física Universidade de São Paulo, USP, São Paulo (Brazil); Vieira, E.D. [Instituto de Física, Universidade Federal de Goiás, Goiânia (Brazil); Gamarra, L.F. [Instituto do Cérebro-InCe, Hospital Israelita Albert Einstein-HIAE, 05651-901 São Paulo (Brazil)

2013-07-15

280

Characterization of Modified Magnetite Nanoparticles for Albumin Immobilization  

PubMed Central

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

Bordbar, A. K.; Rastegari, A. A.; Amiri, R.; Ranjbakhsh, E.; Abbasi, M.; Khosropour, A. R.

2014-01-01

281

PEG conjugated citrate-capped magnetite nanoparticles for biomedical applications  

NASA Astrophysics Data System (ADS)

We aim to develop polyethylene glycol decorated, citric acid capped magnetite nanoparticles (MNPs) with proper physicochemical characteristics including particle size distribution, morphology, magnetic property and stability in a biologic medium. MNP of about 10 nm were synthesized by a biocompatible chemical co-precipitation of Fe2+ and Fe3+ in an ammonia solution. A synthetic methodology has been developed to get a well dispersed and homogeneous aqueous suspension of MNPs. The naked MNPs are often insufficient for their stability, hydrophilicity and further functionalization. In order to overcome these limitations, citric acid was used to stabilize the magnetite particle suspension, which was anchored on the surface of freshly prepared MNPs by a direct addition method. Polyethylene glycol was covalently attached to the carboxylic moieties of citric acid anchored MNPs by carbodiimide chemistry. The microstructure and morphology of the nanoparticles were characterized by X-ray diffraction and transmission electron microscopy, and Fourier transform infrared spectroscopy. Also, the magnetic properties were investigated by vibrating sample magnetometry. It was found that the nanoparticles demonstrated superparamagnetic behavior.

Cheraghipour, Elham; Tamaddon, A. M.; Javadpour, S.; Bruce, I. J.

2013-02-01

282

Low temperature oxidation mechanisms of nanocrystalline magnetite thin film  

NASA Astrophysics Data System (ADS)

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.

Bourgeois, F.; Gergaud, P.; Renevier, H.; Leclere, C.; Feuillet, G.

2013-01-01

283

Low temperature oxidation mechanisms of nanocrystalline magnetite thin film  

SciTech Connect

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.

Bourgeois, F.; Gergaud, P.; Feuillet, G. [CEA, LETI, MINATEC Campus, 17 rue des Martyrs, 38054 GRENOBLE, Cedex 9 (France); Renevier, H.; Leclere, C. [Grenoble INP Minatec, LMGP, 3 parvis Louis Neel, 38016 Grenoble (France)

2013-01-07

284

Electric conductivity of doped triglycine sulphate crystals  

NASA Astrophysics Data System (ADS)

Attention is given to the conductivity values of both pure and doped triglycine sulfate (TGS) crystals at room and transition temperatures. TGS doped with such organic and inorganic dopants as nitroanilines, serine, and leucine, exhibit an increase in DC conductivity, while those doped with L-alanine show a decrease in conductivity by comparison with a pure TGS crystal.

Batra, A. K.; Mathur, S. C.

1985-06-01

285

Cell-surface interactions involving immobilized magnetite nanoparticles on flat magnetic substrates.  

PubMed

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

Loichen, Juliane; Hartmann, Uwe

2009-09-01

286

Micromagnetics and magnetomineralogy of ultrafine magnetite inclusions in the Modipe Gabbro  

NASA Astrophysics Data System (ADS)

Iron oxide inclusions in pyroxene crystals from the Modipe Gabbro, Botswana, have been studied to determine their recording fidelity. Hysteresis parameters, first-order reversal curves, isothermal remanent magnetization acquisition curves, and thermomagnetic data all indicate that the iron oxide occurs as stoichiometric magnetite in the form of single-domain and/or small pseudo single-domain particles. Using distributions for the grain shape and nearest-neighbor spacings determined from optical micrographs as input, a first-order reversal curve (FORC) diagram was simulated using a numerical micromagnetic model. The simulated FORC diagram was found to closely match the measured FORC distributions. Analysis of the interaction fields in the model found that the standard deviation of the interaction field distribution was 2.7 mT compared to a bulk coercivity of ~20 mT, suggesting that the majority of particles are unlikely to be affected by magnetostatic interactions. Thellier analysis of the samples induced with an initial laboratory thermoremanence yielded near-perfect behavior. It is suggested that the Modipe Gabbro dated at 2784.0 ± 1.5 (2?) Ma is potentially an ideal recorder of the geomagnetic field.

Muxworthy, A. R.; Evans, M. E.

2013-04-01

287

Carbon nanotubes/magnetite hybrids prepared by a facile synthesis process and their magnetic properties  

NASA Astrophysics Data System (ADS)

In this paper, a facile synthesis process is proposed to prepare multiwalled carbon nanotubes/magnetite (MWCNTs/Fe 3O 4) hybrids. The process involves two steps: (1) water-soluble CNTs are synthesized by one-pot modification using potassium persulfate (KPS) as oxidant. (2) Fe 3O 4 is assembled along the treated CNTs by employing a facile hydrothermal process with the presence of hydrazine hydrate as the mineralizer. The treated CNTs can be easily dispersed in aqueous solvent. Moreover, X-ray photoelectron spectroscopy (XPS) analysis reveals that several functional groups such as potassium carboxylate (-COOK), carbonyl (-C dbnd O) and hydroxyl (-C-OH) groups are formed on the nanotube surfaces. The MWCNTs/Fe 3O 4 hybrids are characterized with respect to crystal structure, morphology, element composition and magnetic property by X-ray diffraction (XRD), transmission electron microscopy (TEM), XPS and superconducting quantum interference device (SQUID) magnetometer. XRD and TEM results show that the Fe 3O 4 nanoparticles with diameter in the range of 20-60 nm were firmly assembled on the nanotube surface. The magnetic property investigation indicated that the CNTs/Fe 3O 4 hybrids exhibit a ferromagnetic behavior and possess a saturation magnetization of 32.2 emu/g. Further investigation indicates that the size of assembled Fe 3O 4 nanoparticles can be turned by varying experiment factors. Moreover, a probable growth mechanism for the preparation of CNTs/Fe 3O 4 hybrids was discussed.

Zhang, Li; Ni, Qing-Qing; Natsuki, Toshiaki; Fu, Yaqin

2009-07-01

288

Magnetotransport anisotropy effects in epitaxial magnetite (Fe3O4) thin films  

NASA Astrophysics Data System (ADS)

Epitaxial films of magnetite (Fe3O4) have been grown on SrTiO3 (100) and sapphire (?-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 to the film plane. The [100] oriented films show a pronounced extremum in magnetoresistance (MR) at the Verwey transition temperature (Tv), while no such feature is observed in the case of the [111] oriented films. However, the [111] oriented films exhibit a sudden change in the MR dependence on T at Tv and films of both orientations show a rapid increase of MR as the temperature is decreased below about 110 K. An attempt is made to analyze these data in terms of the known anisotropy in magnetostriction and optical magnon-phonon dispersions, and the small polaron band and hopping conductivity mechanisms.

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

1998-04-01

289

Lysozyme crystallization by vapor diffusion: characterization and modeling in the absence and presence of exogenous minerals  

NASA Astrophysics Data System (ADS)

A model accounting for water evaporation and crystal growth was synthesized to simulate protein concentration profiles in the crystallization wells of a vapor-diffusion apparatus. The model calculations were compared with experimental results obtained with chicken egg white lysozyme crystallized in the absence and presence of exogenous mineral particles. The model predicted the increase in protein concentration during water evaporation and the decrease during crystal growth. The effects of magnetite, galena and chalcopyrite on the time profile of dissolved lysozyme concentration appeared minimal, except for the occurrence of earlier nucleation in the presence of magnetite. Few of the lysozyme crystals formed were physically associated with these minerals. More protein crystals were associated with topaz, lepidolite and apophyllite, which exhibit a close match of their crystalline lattice to that of lysozyme.

Kimble, W. L.; Rousseau, R. W.; Sambanis, A.

1995-01-01

290

Impact of high energy ball milling on the nanostructure of magnetite–graphite and magnetite–graphite–molybdenum disulphide blends  

SciTech Connect

Different, partly complementary and partly redundant characterization methods were applied to study the transition of magnetite, graphite and MoS{sub 2} powders to mechanically alloyed nanostructures. The applied methods were: Transmission electron microscopy (TEM), Mössbauer spectroscopy (MS), Raman spectroscopy (RS), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The main objective was to prepare a model material providing the essential features of a typical tribofilm forming during automotive braking, and to assess the impact of different constituents on sliding behaviour and friction level. Irrespective of the initial grain size, the raw materials were transferred to a nanocrystalline structure and mixed on a nanoscopic scale during high energy ball milling. Whereas magnetite remained almost unchanged, graphite and molybdenum disulphide were transformed to a nanocrystalline and highly disordered structure. The observed increase of the coefficient of friction was attributed to a loss of lubricity of the latter ingredient due to this transformation and subsequent oxidation. - Highlights: • Characterization of microstructural changes induced by high energy ball milling • Assessment of the potential of different characterization methods • Impact of mechanical alloying on tribological performance revealed by tests • Preparation of an artificial third body resembling the one formed during braking.

Österle, W., E-mail: Werner.oesterle@bam.de [BAM Federal Institute for Materials Research and Testing, 12200 Berlin (Germany); Orts-Gil, G.; Gross, T.; Deutsch, C. [BAM Federal Institute for Materials Research and Testing, 12200 Berlin (Germany); Hinrichs, R. [Instituto de Geociências, UFRGS, P.O. Box 15001, 91501-970 Porto Alegre (Brazil); Vasconcellos, M.A.Z. [Instituto de Física, UFRGS, P.O. Box 15051, 91501-970 Porto Alegre (Brazil); Zoz, H.; Yigit, D.; Sun, X. [Zoz Group, 57482 Wenden (Germany)

2013-12-15

291

Pure lead is pure gold for electric vehicles  

Microsoft Academic Search

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.

Kana

1995-01-01

292

Operators on Pure Spinor Spaces  

SciTech Connect

Pure spinors are relevant to the formulation of supersymmetric theories, and provide the only known way to maintain manifest maximal supersymmetry. The (non-linear) pure spinor constraint makes it nontrivial to find well defined operators on pure spinor wave functions. We discuss how such operators are defined. One application concerns covariant gauge fixing in maximally supersymmetric Yang-Mills (and string theory). Another issue is the construction of a manifestly supersymmetric action for 11-dimensional supergravity in terms of a scalar superfield. We describe some work in progress.

Cederwall, Martin [Fundamental Physics, Chalmers University of Technology, SE 412 96 Goteborg (Sweden)

2010-06-17

293

Transformation products of submicron-sized aluminum-substituted magnetite: Color and reductant solubility  

NASA Technical Reports Server (NTRS)

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.

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

1991-01-01

294

Arsenic sorption by nanocrystalline magnetite: an example of environmentally promising interface with geosphere.  

PubMed

In this paper, the sorption of arsenic onto nanocrystalline magnetite mineral Fe3O4 was studied in a model system. Nanocrystalline magnetite was produced by mechanical activation in a planetary ball mill from natural microcrystalline magnetite. As a consequence of milling, the specific surface area increased from 0.1m(2)/g to 11.9 m(2)/g and the surface site concentration enhanced from 2.2 sites/nm(2) to 8.4 sites/nm(2). These changes in surface properties of magnetite lead to the enhancement of arsenic removal from model system. The best sorption ability was achieved with magnetite sample activated for 90 min. In this case the sample was able to absorb around 4 mg/g. The structural changes of magnetite were also observed and the new hematite phase was detected after 120 min of milling. A good correlation between the decreasing particle size, increasing specific surface area and reduction of saturation magnetization was found. In desorption study, KOH and NaOH were found as the best eluents where more than 70% of arsenic was released back into the solution. The principal novelty of the paper is that mineral magnetite, truly one nature's gift can be used after "smart" milling (mechanical activation) as an effective arsenic sorbent. PMID:23531452

Buj?áková, Z; Baláž, P; Zorkovská, A; Sayagués, M J; Ková?, J; Timko, M

2013-11-15

295

Microreactor and electron spectroscopy studies of Fischer-Tropsch synthesis on magnetite  

SciTech Connect

The Fischer-Tropsch synthesis from CO and H/sub 2/ (1:3 mixture) at 1 bar total pressure and 570 K has been studied in a differential microreactor system on reduced and unreduced Fe/sub 3/O/sub 4/ (magnetite). The catalytic reactivity data were complemented by surface analytical measurements using Auger electron and x-ray photoelectron spectroscopy (XPS, ESCA). XPS measurements showed evidence of carbon deposition, mostly in the form of graphite on all samples. The rate of methanation on reduced magnetite was characterized by a maximum and subsequent decrease. Both features were dependent on the reduction history of the sample. All samples gave rise to the production of higher-molecular-weight species. The selectivity of reduced magnetite tended towards the formation of saturated hydrocarbons while that of the unreduced magnetite favoured the formation of alkenes. It was concluded that the reduction of magnetite led to a considerable increase in surface area and porosity and that secondary reactions of the alkenes caused the primary product spectrum to shift from alkenes to alkanes. Accordingly the polymerisation probability increased from 0.3 for unreduced magnetite (also for clean foil) to greater than or equal to 0.42 for reduced magnetite.

Krebs, H.J. (Kernforschungsanlage Juelich GmbH, Germany); Bonzel, H.P.; Schwarting, W.; Gafner, G.

1981-12-01

296

Arsenic(III) and Arsenic(V) Speciation during Transformation of Lepidocrocite to Magnetite.  

PubMed

Bioreduction of As(V) and As-bearing iron oxides is considered to be one of the key processes leading to arsenic pollution in groundwaters in South and Southeast Asia. Recent laboratory studies with simple aqueous media showed that secondary Fe(II)-bearing phases (e.g., magnetite and green rust), which commonly precipitate during bioreduction of iron oxides, captured arsenic species. The aim of the present study was to follow arsenic speciation during the abiotic Fe(II)-induced transformation of As(III)- and As(V)-doped lepidocrocite to magnetite, and to evaluate the influence of arsenic on the transformation kinetics and pathway. We found green rust formation is an intermediate phase in the transformation. Both As(III) and As(V) slowed the transformation, with the effect being greater for As(III) than for As(V). Prior to the formation of magnetite, As(III) adsorbed on both lepidocrocite and green rust, whereas As(V) associated exclusively with green rust, When magnetite precipitated, As(III) formed surface complexes on magnetite nanoparticles and As(V) is thought to have been incorporated into the magnetite structure. These processes dramatically lowered the availability of As in the anoxic systems studied. These results provide insights into the behavior of arsenic during magnetite precipitation in reducing environments. We also found that As(V) removal from solution was higher than As(III) removal following magnetite formation, which suggests that conversion of As(III) to As(V) is preferred when using As-magnetite precipitation to treat As-contaminated groundwaters. PMID:25425339

Wang, Yuheng; Morin, Guillaume; Ona-Nguema, Georges; Brown, Gordon E

2014-12-16

297

Brownian rotational relaxation and power absorption in magnetite nanoparticles  

NASA Astrophysics Data System (ADS)

We present a study of the power absorption efficiency in several magnetite-based colloids, to asses their potential as magnetic inductive hyperthermia (MIH) agents. Relaxation times ? were measured through the imaginary susceptibility component ??(T), and analyzed within Debye's theory of dipolar fluid. The results indicated Brownian rotational relaxation and allowed to calculate the hydrodynamic radius close to the values obtained from photon correlation. The study of the colloid performances as power absorbers showed no detectable increase of temperature for dextran-coated Fe 3O 4 nanoparticles, whereas a second Fe 3O 4-based dispersion of similar concentration could be heated up to 12 K after 30 min under similar experimental conditions. The different power absorption efficiencies are discussed in terms of the magnetic structure of the nanoparticles.

Goya, G. F.; Fernandez-Pacheco, R.; Arruebo, M.; Cassinelli, N.; Ibarra, M. R.

2007-09-01

298

Sorption of actinides on magnetite and goethite under reducing conditions  

NASA Astrophysics Data System (ADS)

The present study investigated the sorption of 237Np, 239Pu and 241Am onto magnetite and goethite as a typical iron corrosion product under reducing conditions as a function of solution pH, both in the presence and absence of CO2 at 25°C. The sorption experiments were carried out for each actinide independently and for the simultaneous presence of the three actinides. Alpha-spectrometry of the liquid phase was performed to determine the equilibrium concentrations of the actinides after the sorption period. The sorption was strongly pH dependent. The sorption of 237Np onto iron minerals was enhanced by the presence of CO2 to some extent. In other cases, the presence of CO2 did not affect or prevented the actinides from sorption. There seems to be no simple tendency in the observed data under the conditions examined, probably due to the effects of aqueous and surface complexation reactions with carbonate ions.

Tsukamoto, M.; Fujita, T.; Christensen, H.

2006-01-01

299

Observation of inverse magnetoresistance in epitaxial magnetite/manganite junctions  

NASA Astrophysics Data System (ADS)

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 spinel structure CoCr2O4 barrier, which minimizes structural disorder at the barrier/Fe3O4 interface. As a comparison, studies on (100) MTJs elucidate the effect of the magnetic domain state of the ferromagnetic electrodes on the JMR.

Hu, Guohan; Chopdekar, Rajesh; Suzuki, Y.

2003-05-01

300

Iron metabolism after application of modified magnetite nanoparticles in rats.  

PubMed

The influence of modified nanosized magnetite (NSM) particles (magnetic microspheres coated with chitosan and magnetoliposomes) after a single intravenous infusion of their suspensions on iron metabolism in rats has been studied. Modern physical and chemical methods (X-ray fluorescence, dynamic light scattering, transmission electron microscopy) were used for standardization of the modified NSM particles (their size, structure, ?-potential, and concentration were determined). Atomic emission spectroscopy was used to reveal the dynamics of iron content in rat liver, spleen, lungs, and kidneys during 120 days. Colorimetric and immunoturbidimetric methods were used to determine the concentrations of plasma iron and the proteins involved in its metabolism - ceruloplasmin, transferrin, and ferritin. Their dynamics throughout the experiments were studied. PMID:25540010

Milto, I V; Grishanova, A Yu; Klimenteva, T K; Suhodolo, I V; Vasukov, G Yu; Ivanova, V V

2014-11-01

301

Highly sensitive magnetite nano clusters for MR cell imaging  

PubMed Central

High sensitivity and suitable sizes are essential for magnetic iron oxide contrast agents for cell imaging. In this study, we have fabricated highly MR sensitive magnetite nanoclusters (MNCs) with tunable sizes. These clusters demonstrate high MR sensitivity. Especially, water suspensions of the MNCs with average size of 63 nm have transverse relaxivity as high as 630 s-1mM-1, which is among the most sensitive iron oxide contrast agents ever reported. Importantly, such MNCs have no adverse effects on cells (RAW 264.7). When used for cell imaging, they demonstrate much higher efficiency and sensitivity than those of SHU555A (Resovist), a commercially available contrast agent, both in vitro and in vivo, with detection limits of 3,000 and 10,000 labeled cells, respectively. The studied MNCs are sensitive for cell imaging and promising for MR cell tracking in clinics. PMID:22462693

2012-01-01

302

Paleomagnetism of a new magnetite-rich carbonaceous chondrite  

NASA Astrophysics Data System (ADS)

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.

Gattacceca, J.; Rochette, P.; Gounelle, M.; Bonal, L.; Weiss, B. P.; Sonzogni, C.

2012-12-01

303

Synthesis of magnetite/amphiphilic polymer composite nanoparticles as potential theragnostic agents.  

PubMed

This study describes the synthesis of magnetite/amphiphilic polymer composite nanoparticles that can be potentially used simultaneously for cancer diagnosis and therapy. The synthesis method was a one-shot process wherein magnetite nanoparticles were mixed with core-crosslinked amphiphilic polymer (CCAP) nanoparticles, prepared using a copolymer of a urethane acrylate nonionomer (UAN) and a urethane acrylate anionomer (UAA). The CCAP nanoparticles had a hydrophobic core and a hydrophilic exterior with both PEG segments and carboxylic acid groups, wherein the magnetite nanoparticles were coordinated and stabilized. According to DLS data, the ratio of UAN to UAA and the ratio of magnetite to polymer are keys to controlling the size and thus, the stability of the composite nanoparticles. The magnetic measurement indicated that the composite nanoparticles had superparamagnetic properties and high saturation magnetization. The preliminary magnetic resonance imaging showed that the particles produced an enhanced image even when their concentration was as low as 80 microg/ml. PMID:22966681

Wainaina, James; Kim, Na Hae; Kim, Juyoung; Jin, Moonsoo; Park, Soo Haeng

2012-07-01

304

Magnetic and Structural Properties of Magnetite in Radular Teeth of Chiton Acanthochiton Rubrolinestus  

NASA Astrophysics Data System (ADS)

The major radular lateral teeth of Polyplacophora Chiton comprise a magnetite biomineral cap.We have investigated the structure and magnetic properties of the biomineralized magnetite crystallites in mature teeth of Chiton Acanthochiton Rubrolinestus. From the measurement of magnetic properties of tooth particles using SQUID magnetometry we find that the saturation magnetization and the Verwey transition temperature (Tv) are 78.4 emu/g and 105 K, respectively. An in situ examination of the structure of magnetite-bearing region within individual tooth using the high resolution TEM, together with electron diffraction (ED) pattern and energy-dispersive X-ray (EDX) analyses indicates magnetite microcrystal form electron-dense polycrystalline sheets with typical length 800 nm and width 150 nm or so. These polycrystalline sheets are arranged regularly along the longitude direction of the tooth cutting surface. Furthermore, the microcrystallites in polycrystalline sheet take on the generally good crystallinity.

Han, Y. N.; Liu, C. L.; Yao, L. D.; Wang, Y.; Han, X. F.

2008-03-01

305

Water-dispersible magnetite-reduced graphene oxide composites for arsenic removal.  

PubMed

Magnetite-graphene hybrids have been synthesized via a chemical reaction with a magnetite particle size of approximately 10 nm. The composites are superparamagnetic at room temperature and can be separated by an external magnetic field. As compared to bare magnetite particles, the hybrids show a high binding capacity for As(III) and As(V), whose presence in the drinking water in wide areas of South Asia has been a huge problem. Their high binding capacity is due to the increased adsorption sites in the M-RGO composite which occurs by reducing the aggregation of bare magnetite. Since the composites show near complete (over 99.9%) arsenic removal within 1 ppb, they are practically usable for arsenic separation from water. PMID:20552997

Chandra, Vimlesh; Park, Jaesung; Chun, Young; Lee, Jung Woo; Hwang, In-Chul; Kim, Kwang S

2010-07-27

306

Truncated Hexa-Octahedral Magnetites: Biosignatures in Terrestrial Samples and Martian Meteorite ALH84001  

NASA Technical Reports Server (NTRS)

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.

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

307

Magnetite Content and Carbonate Mineralogy as Constraints for Parent Body Hydrothermal Alteration  

NASA Astrophysics Data System (ADS)

We present a mineralogical study of magnetite and carbonates from various C1s and C2s in order to improve our understanding of the relationships between these two minerals and between these meteorite groups.

Petitat, M.; Gounelle, M.

2010-03-01

308

Dependence of microbial magnetite formation on humic substance and ferrihydrite concentrations  

NASA Astrophysics Data System (ADS)

Iron mineral (trans)formation during microbial Fe(III) reduction is of environmental relevance as it can influence the fate of pollutants such as toxic metal ions or hydrocarbons. Magnetite is an important biomineralization product of microbial iron reduction and influences soil magnetic properties that are used for paleoclimate reconstruction and were suggested to assist in the localization of organic and inorganic pollutants. However, it is not well understood how different concentrations of Fe(III) minerals and humic substances (HS) affect magnetite formation during microbial Fe(III) reduction. We therefore used wet-chemical extractions, magnetic susceptibility measurements and X-ray diffraction analyses to determine systematically how (i) different initial ferrihydrite (FH) concentrations and (ii) different concentrations of HS (i.e. the presence of either only adsorbed HS or adsorbed and dissolved HS) affect magnetite formation during FH reduction by Shewanella oneidensis MR-1. In our experiments magnetite formation did not occur at FH concentrations lower than 5 mM, even though rapid iron reduction took place. At higher FH concentrations a minimum fraction of Fe(II) of 25-30% of the total iron present was necessary to initiate magnetite formation. The Fe(II) fraction at which magnetite formation started decreased with increasing FH concentration, which might be due to aggregation of the FH particles reducing the FH surface area at higher FH concentrations. HS concentrations of 215-393 mg HS/g FH slowed down (at partial FH surface coverage with sorbed HS) or even completely inhibited (at complete FH surface coverage with sorbed HS) magnetite formation due to blocking of surface sites by adsorbed HS. These results indicate the requirement of Fe(II) adsorption to, and subsequent interaction with, the FH surface for the transformation of FH into magnetite. Additionally, we found that the microbially formed magnetite was further reduced by strain MR-1 leading to the formation of either dissolved Fe(II), i.e. Fe 2+, in HEPES buffered medium or Fe(II) carbonate (siderite) in bicarbonate buffered medium. Besides the different identity of the Fe(II) compound formed at the end of Fe(III) reduction, there was no difference in the maximum rate and extent of microbial iron reduction and magnetite formation during FH reduction in the two buffer systems used. Our findings indicate that microbial magnetite formation during iron reduction depends on the geochemical conditions and can be of minor importance at low FH concentrations or be inhibited by adsorption of HS to the FH surface. Such scenarios could occur in soils with low iron mineral or high organic matter content.

Piepenbrock, Annette; Dippon, Urs; Porsch, Katharina; Appel, Erwin; Kappler, Andreas

2011-11-01

309

Signaling and Game Theory Pure Common Interest  

E-print Network

Signaling and Game Theory Pure Common Interest Partial Common Interest Game Theory.S. Zollman Signaling #12;Signaling and Game Theory Pure Common Interest Partial Common Interest Introduction Pure Common Interest Partial Common Interest Introduction Methodologies in game theory Signaling

Zollman, Kevin

310

76 FR 69284 - Pure Magnesium From China  

Federal Register 2010, 2011, 2012, 2013

...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....

2011-11-08

311

Influence of metal dopants (Cu and Mg) on the thermal, mechanical and optical properties of l-alanine acetate single crystals  

Microsoft Academic Search

Single crystals of pure, Cu2+and Mg2+ doped L-alanine acetate (LAlA) were grown successfully by slow evaporation technique. In the present study, to improve the device characteristics of LAlA crystals, metal dopants of Cu2+ and Mg2+ were incorporated into the pure crystals. The grown pure and doped LAlA crystals were confirmed by X-ray powder diffraction studies. The pure and doped crystals

D. Sankar; P. Praveen Kumar; J. Madhavan

2010-01-01

312

Non-stoichiometric magnetite and maghemite in the mature teeth of the chiton Acanthopleura hirtosa  

NASA Astrophysics Data System (ADS)

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.

St. Pierre, T. G.; Evans, L. A.; Webb, J.

1992-04-01

313

Thermal, electrical and magnetic studies of magnetite filled polyurethane shape memory polymers  

Microsoft Academic Search

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

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

2007-01-01

314

Introduction of biotin or folic acid into polypyrrole magnetite core-shell nanoparticles  

SciTech Connect

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.

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

315

Using Magnetites to Remediate Heavy Metal Wastewaters from Acid-Mine Drainage  

Microsoft Academic Search

\\u000a The remediation of heavy metal wastewaters using magnetites, also known as ferrites, has been an area of investigation for\\u000a many years. Early investigators used a synthetic procedure for the production of magnetites at 70 °C. Although quite effective,\\u000a as demonstrated by remediation of small waste streams from universities in Japan, this method is too energy intensive for\\u000a application to large

M. D. Johnson; R. Wingo; M. Valdez

316

Investigation on the effects of milling atmosphere on synthesis of barium ferrite\\/magnetite nanocomposite  

Microsoft Academic Search

In this research, barium ferrite \\/magnetite nanocomposites synthesized via a mechano-chemical route.\\u000aGraphite was used in order to reduce hematite content of barium ferrite to magnetite to produce a magnetic nanocomposite. The effects of processing conditions on the powder characteristics were investigated by XRD, VSM, and HRTEM techniques. XRD results revealed that milling under air and argon atmospheres resulted in

M. J. Molaei; A. Ataie; S. Raygan; n S. J. Picken

2011-01-01

317

Reduction of haematite to magnetite under controlled hydrothermal conditions with hydrogen gas  

Microsoft Academic Search

Haematite (a-Fe2O3) was reduced to magnetite (Fe3O4) under hydrothermal conditions, by the use of an autoclave into which hydrogen gas was able to be admitted. The stable reduced conditions for magnetite precipitation were produced even at 100 °C. In acid and neutral mineralizers, the rate of haematite reduction was small below 300 °C and increased with an increase in reaction

Kazumichi Yanagisawa; Nakamichi Yamasaki

1991-01-01

318

Theoretical Single-Domain Grain Size Range in Magnetite and Titanomagnetite  

Microsoft Academic Search

A theoretical model of single-domain (SD) grain sizes is applied to magnetite and titanomagnetite. In this model, transition to a two-domain configuration takes place at the SD threshold do. This two-domain configuration is shown to be more applicable to fine-grained magnetites in igneous rocks than previous models involving transition to a circular spin configuration at do. Calculations of the stable

Robert F. Butler; Subir K. Banerjee

1975-01-01

319

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

Microsoft Academic Search

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

Chun-Young Oh; Jae-Hee Oh; Taegyung Ko

2002-01-01

320

Characterization of nanostructured magnetite thin films produced by sol–gel processing  

Microsoft Academic Search

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.

Ali Erdem Eken; Macit Ozenbas

2009-01-01

321

Size control of nanocrystalline magnetite thin films containing a small amount of Ge  

Microsoft Academic Search

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

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

2010-01-01

322

Microstructure and magnetic properties of magnetite thin films prepared by reactive sputtering  

Microsoft Academic Search

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

Hongmei Qiu; Liqing Pan; Liwei Li; Hao Zhu; Xuedan Zhao; Mei Xu; Liangqiang Qin; John Q. Xiao

2007-01-01

323

Squid measurement of the Verwey transition on epitaxial (1 0 0) magnetite thin films  

Microsoft Academic Search

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

V. Dediu; E. Arisi; I. Bergenti; A. Riminucci; M. Solzi; C. Pernechele; M. Natali

2007-01-01

324

Study of magnetite film formation at metal-scale interface during cooling of steel products  

Microsoft Academic Search

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

J. Baud; A. Ferrier; J. Manenct

1978-01-01

325

Magnetic and magneto-optical properties of heteroepitaxial magnetite thin films  

Microsoft Academic Search

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

J. Cheng; G. E. Sterbinsky; B. W. Wessels

2008-01-01

326

Enhancement of the magnetization saturation in magnetite (100) epitaxial films by thermo-chemical treatment  

Microsoft Academic Search

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

Y. Zhou; Xuesong Jin; I. V. Shvets

2004-01-01

327

CVD synthesis of polycrystalline magnetite thin films: structural, magnetic and magnetotransport properties  

Microsoft Academic Search

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.

R. Mantovan; A. Lamperti; M. Georgieva; G. Tallarida; M. Fanciulli

2010-01-01

328

Optical magnetic circular dichroism in threshold photoemission from a magnetite thin film  

Microsoft Academic Search

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.

K. Hild; J. Maul; T. Meng; M. Kallmayer; G. Schönhense; H. J. Elmers; R. Ramos; S. K. Arora; I. V. Shvets

2008-01-01

329

Evidence for magnetic interactions among magnetite nanoparticles dispersed in photoreticulated PEGDA-600 matrix  

Microsoft Academic Search

Magnetite nanoparticles having mean diameter of about 8 nm have been prepared by a thermo-chemical route. Different amounts\\u000a (5 and 10% wt) of a stable dispersion of magnetite nanoparticles in n-hexane were added to polyethylene glycol diacrylate (PEGDA-600) oligomer containing 2% wt of radicalic photoinitiator. The\\u000a homogenized mixture was poured on a silica glass substrate and the resulting film was photoreticulated in N2

P. Allia; P. Tiberto; M. Coisson; A. Chiolerio; F. Celegato; F. Vinai; M. Sangermano; L. Suber; G. Marchegiani

330

Origin of hysteresis in resistive switching in magnetite is Joule heating  

Microsoft Academic Search

In many transition-metal oxides the electrical resistance is observed to undergo dramatic changes induced by large biases. In magnetite, Fe3O4 , below the Verwey temperature, an electric-field-driven transition to a state of lower resistance was recently found, with hysteretic current-voltage response. We report the results of pulsed electrical conduction measurements in epitaxial magnetite thin films. We show that while the

A. A. Fursina; R. G. S. Sofin; I. V. Shvets; D. Natelson

2009-01-01

331

Magnetic hybrid modified electrodes, based on magnetite nanoparticle containing polyaniline and poly(3,4-ethylenedioxythiophene)  

Microsoft Academic Search

In this paper, we report on the direct electrodeposition of magnetic hybrids based on magnetite nanoparticle containing poly(3,4-ethylenedioxythiophene)\\u000a (PEDOT) and polyaniline (PANI) in the presence of magnetite and the special conducting electrolyte, potassium tetraoxalate.\\u000a The optimal electropolymerization processes (monitored by scanning electron microscopy) were performed potentiostatically,\\u000a and the incorporation of the iron oxide into the polymeric film was demonstrated by

Csaba Janáky; Attila Kormányos; Csaba Visy

332

Sorption of nalidixic acid onto micrometric and nanometric magnetites: Experimental study and modeling  

NASA Astrophysics Data System (ADS)

The sorption of nalidixic acid (NA) was studied onto three kinds of magnetite characterized by different particle sizes (from micrometric to nanometric) and surface properties. Experiments were performed under static batch and dynamic flow conditions. Obtained results indicate that kinetics and extent of sorption was strongly affected by the particle size of tested magnetites. Ionic strength effect was less significant suggesting that aggregation state of the magnetite particles did not affect the sorption. During kinetic sorption experiments, apparent rate constant normalized to solid mass was faster for nanosized magnetite while an opposite trend was observed for the surface area-normalized rate constants. Infrared data suggested the possibility of similar surface interactions on both microsized and nanosized magnetites. Transport of NA in magnetite-packed column was found associated to the instantaneous sorption without any significant effect of kinetic limitation. Breakthrough curves (BC) and sorption extent in columns were calculated by using Thomas, Yan and Yoon-Nelson models. Sorption capacities predicted by Thomas or Yan model were in good agreement with that determined by integrating total area above BC. However, Thomas model failed particularly to predict an accurate concentration at lower and higher time points of the BC. These findings have strong implications in relation to the transport and removal of environmental pollutants in natural and engineered systems.

Usman, M.; Martin, S.; Cimetière, N.; Giraudet, S.; Chatain, V.; Hanna, K.

2014-04-01

333

Magnetic and structural properties of magnetite in radular teeth of chiton Acanthochiton rubrolinestus.  

PubMed

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

Han, Yunan; Liu, Chuanlin; Zhou, Dong; Li, Fashen; Wang, Yong; Han, Xiufeng

2011-04-01

334

Estimation of Sintering Kinetics of Oxidized Magnetite Pellet Using Optical Dilatometer  

NASA Astrophysics Data System (ADS)

The quality of magnetite pellet is primarily determined by the physico-chemical changes the pellet undergoes as it makes excursion through the gaseous and thermal environment in the induration furnace. Among these physico-chemical processes, the oxidation of magnetite phase and the sintering of oxidized magnetite (hematite) and magnetite (non-oxidized) phases are vital. Rates of these processes not only depend on the thermal and gaseous environment the pellet gets exposed in the induration reactor but also interdependent on each other. Therefore, a systematic study should involve understanding these processes in isolation to the extent possible and quantify them seeking the physics. With this motivation, the present paper focusses on investigating the sintering kinetics of oxidized magnetite pellet. For the current investigation, sintering experiments were carried out on pellets containing more than 95 pct magnetite concentrate from LKAB's mine, dried and oxidized to completion at sufficiently low temperature to avoid sintering. The sintering behavior of this oxidized pellet is quantified through shrinkage captured by Optical Dilatometer. The extent of sintering characterized by sintering ratio found to follow a power law with time i.e., Kt n . The rate constant K for sintering was determined for different temperatures from isothermal experiments. The rate constant, K, varies with temperature as ln left( {TK^{(1/n)} } right) = ln K' - Q/RT, and the activation energy (Q) and reaction rate constant (K') are estimated. Further, the sintering kinetic equation was also extended to a non-isothermal environment and validated using laboratory experiments.

Sandeep Kumar, T. K.; Viswanathan, Neelakantan Nurni; Ahmed, Hesham M.; Andersson, Charlotte; Björkman, Bo

2014-12-01

335

The effect of polymer adsorption on the wetting properties of partially hydrophobized magnetite.  

PubMed

Upon reverse flotation of iron ore, the surface of the iron ore concentrate may become partially hydrophobized due to adsorption of flotation collector, which is facilitated by the calcium ions present in the process water. Hydrophobic areas on the concentrate surface may introduce problems in subsequent pelletization of the concentrate. A possible way to restore the wettability of the surface could be by modifying the surface with a hydrophilic polymer. The effect of hydrophilic polymers of different types, viz. cationic, anionic, and non-ionic, on the wettability of the magnetite surface after adsorption of a surfactant was investigated. Although all the polymers could adsorb on magnetite at pH 8.5, the contact angle measurements revealed that only anionic ammonium polyacrylate could decrease the contact angle of synthetic magnetite after surfactant adsorption to a level close to that of as-synthesized magnetite. Such effect was probably achieved due to shielding of the hydrophobic surfactant chains from the aqueous phase by hydrophilic polyacrylate molecules. The fact that polyacrylate adsorption on magnetite occurred via calcium ions makes polyacrylate suitable for application in calcium-rich process water. The results presented in this work illustrate that ammonium polyacrylate could be successfully used to improve the wettability of magnetite after adsorption of surfactants. PMID:22047916

Potapova, E; Grahn, M; Holmgren, A; Hedlund, J

2012-02-01

336

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

NASA Astrophysics Data System (ADS)

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. %.

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

2011-06-01

337

New effects in absorption of ultrasound in intermediate state of high pure type I superconductor  

E-print Network

The research on the longitudinal ultrasound absorption in an intermediate state of the high pure Gallium single crystal at the frequency of 50-190MHz at the temperatures of 0,37-0,75 K, using the impulse method, is conducted. The new effects in the absorption of ultrasound in an intermediate state of the high pure type I superconductor are discovered. The big oscillations in the dependence of the ultrasound absorption on the magnetic field in an intermediate state of the high pure Gallium single crystal are experimentally observed at the magnitudes of magnetic field below the critical magnetic field. The maximum of the monotonic absorption of longitudinal ultrasound in an intermediate state of the high pure type I superconductor is also obtained. The possible original theoretical mechanisms to explain the nature of big oscillations in the dependence of the ultrasound absorption on the magnetic field in an intermediate state of the high pure type I superconductor are proposed.

Shepelev, Anatoly G; Filimonov, Genady D

2012-01-01

338

Isolation and pure culture of a freshwater magnetic spirillum in chemically defined medium.  

PubMed Central

A bipolarly flagellated magnetotactic spirillum containing intracellular chains of single domain-sized magnetite crystals was isolated by applying a magnetic field to sediments from a freshwater swamp. The organism was cultured in a chemically defined medium containing ferric quinate and succinate as sources of iron and carbon, respectively. Nonmagnetic variants of this isolate were maintained in chemically defined medium lacking ferric quinate. In contrast to magnetic cells, these had less iron and lacked measurable magnetic remanence and the intracytoplasmic crystals. In other respects, including moles percent guanine plus cytosine content, growth characteristics, nutrition, and physiology, the two types were similar. The isolate reduced nitrate without accumulating nitrite and produced ammonia during growth. Nitrate or ammonium ions served as a nitrogen source. The organism was microaerophilic and did not grow anaerobically with nitrate in the medium. In chemically defined medium, cells synthesized magnetite only if the initial O2 concentration in the atmosphere of sealed cultures was 6% (vol/vol) or less. Images PMID:500569

Blakemore, R P; Maratea, D; Wolfe, R S

1979-01-01

339

Pure iron and other magnetic minerals in meteorites  

NASA Astrophysics Data System (ADS)

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.

Pechersky, D. M.; Markov, G. P.; Tsel'movich, V. A.

2015-01-01

340

Platinum-group element geochemistry of the Zhuqing Fe-Ti-V oxide ore-bearing mafic intrusions in western Yangtze Block, SW China: control of platinum-group elements by magnetite  

NASA Astrophysics Data System (ADS)

Platinum-group element (PGE) geochemistry combined with elemental geochemistry and magnetite compositions are reported for the Mesoproterozoic Zhuqing Fe-Ti-V oxide ore-bearing mafic intrusions in the western Yangtze Block, SW China. All the Zhuqing gabbros display extremely low concentrations of chalcophile elements and PGEs. The oxide-rich gabbros contain relatively higher contents of Cr, Ni, Ir, Ru, Rh, and lower contents of Pt and Pd than the oxide-poor gabbros. The abundances of whole-rock concentrations of Ni, Ir, Ru, and Rh correlate well with V contents in the Zhuqing gabbros, implying that the distributions of these elements are controlled by magnetite. The fractionation between Ir-Ru-Rh and Pt-Pd in the Zhuqing gabbros is mainly attributed to fractional crystallization of chromite and magnetite, whereas Ru anomalies are mainly due to variable degrees of compatibility of PGE in magnetite. The order of relative incompatibility of PGEs is calculated to be Pd < Pt < Rh < Ir < Ru. The very low PGE contents and Cu/Zr ratios and high Cu/Pd ratios suggest initially S-saturated magma parents that were highly depleted in PGE, which mainly formed due to low degrees of partial melting leaving sulfides concentrating PGEs behind in the mantle. Moreover, the low MgO, Ni, Ir and Ru contents and high Cu/Ni and Pd/Ir ratios for the gabbros suggest a highly evolved parental magma. Fe-Ti oxides fractionally crystallized from the highly evolved magma and subsequently settled in the lower sections of the magma chamber, where they concentrated and formed Fe-Ti-V oxide ore layers at the base of the lower and upper cycles. Multiple episodes of magma replenishment in the magma chamber may have been involved in the formation of the Zhuqing intrusions.

Fan, Hong-Peng; Zhu, Wei-Guang; Zhong, Hong; Bai, Zhong-Jie; He, De-Feng; Ye, Xian-Tao; Chen, Cai-Jie; Cao, Chong-Yong

2014-06-01

341

Titaniferous magnetite–ilmenite thermometry and titaniferous magnetite–ilmenite–orthopyroxene–quartz oxygen barometry in granulite facies gneisses, Bamble Sector, SE Norway: implications for the role of high-grade CO 2 -rich fluids during granulite genesis  

Microsoft Academic Search

Oxygen fugacities have been estimated for a wide distribution of samples from the granulite facies terrane (region C) of\\u000a the Bamble Sector, SE Norway using both the titaniferous magnetite–ilmenite and orthopyroxene–titaniferous magnetite–quartz\\u000a oxygen barometers. These oxygen fugacities are estimated using temperatures calculated from the titaniferous magnetite–ilmenite\\u000a thermometer of Ghiorso and Sack (1991) and are both internally consistent with each other

Daniel E. Harlov

2000-01-01

342

Pure thalamic infarctions: Clinical findings  

Microsoft Academic Search

Our purpose in this study was to evaluate and review the risk factors, clinical profiles, and neuropsychologic abnormalities in patients with pure thalamic infarctions and to describe the clinical syndromes according to the thalamic arterial territory involved. We studied all patients with acute thalamic stroke admitted to our stroke unit over a 5-year period. We performed magnetic resonance imaging (MRI)

Emre Kumral; Dilek Evyapan; Süleyman Kutluhan

2000-01-01

343

Magnetite-sulfide chondrules and nodules in CK carbonaceous chondrites - Implications for the timing of CK oxidation  

NASA Astrophysics Data System (ADS)

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.

Rubin, A. E.

1993-03-01

344

Magnetite (U–Th)\\/He dating and its application to the geochronology of intermediate to mafic volcanic rocks  

Microsoft Academic Search

We present a new approach to dating intermediate to mafic volcanic rocks using magnetite (U–Th)\\/He geochronology. Magnetite is common in volcanic rocks that typically do not contain easily datable minerals such as sanidine or zircon. Analytical procedures for producing magnetite (U–Th)\\/He ages have been developed, including mineral separation, sample air-abrasion to correct for ?-ejection effects, He extraction\\/measurement, sample dissolution, and

Terrence J. Blackburn; Daniel F. Stockli; J. Douglas Walker

2007-01-01

345

Enhanced thermal stability of phosphate capped magnetite nanoparticles  

SciTech Connect

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.

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

346

Magnetite nanoparticles as reporters for microcarrier processing in cytoplasm  

NASA Astrophysics Data System (ADS)

The development and therapeutic application of drug delivery systems based on colloidal microcarriers layer-by-layer coated with biopolyelectrolytes requires the investigation of their processing inside the cell for the successful and efficient transport and release of the active agents. The present study is focused on the time-dependent multilayer decomposition and the subsequent release of active agents to the cytoplasm. Magnetite nanoparticles (MNP) were used as reporter agents integrated into the protamine sulfate/dextran sulfate basis multilayer on colloidal SiO2 cores. This functionalization allows the monitoring of the multilayer decomposition due to the detection of the MNP release, visualized by means of proton-induced X-ray emission (PIXE) by elemental distribution of Si and Fe. The direct correlation between the microcarrier localization in endolysosomes and cytoplasm of HEK293T/17 cells via confocal laser scanning microscopy (CLSM) and the elemental distribution (PIXE) allows tracing the fate of the MNP-coated microcarriers in cytoplasm, and thus the processing of the multilayer. Microcarrier/cell co-incubation experiments of 6 h, 24 h, 48 h, and 72 h show that a MNP release and a slight expansion into the cytoplasm occurs after a longer co-incubation of 72 h.

Reibetanz, Uta; Jankuhn, Steffen

2011-10-01

347

Optimizing Magnetite Nanoparticles for Mass Sensitivity in Magnetic Particle Imaging  

SciTech Connect

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.

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

2011-03-01

348

Novel hybrid nanostructured materials of magnetite nanoparticles and pectin  

NASA Astrophysics Data System (ADS)

A novel hybrid nanostructured material comprising superparamagnetic magnetite nanoparticles (MNPs) and pectin was synthesized by crosslinking with Ca2+ ions to form spherical calcium pectinate nanostructures, referred as MCPs, which were typically found to be 100-150 nm in size in dried condition, confirmed from transmission electron microscopy and scanning electron microscopy. The uniform size distribution was revealed from dynamic light scattering measurement. In aqueous medium the MCPs showed swelling behavior with an average size of 400 nm. A mechanism of formation of spherical MCPs is outlined constituting a MNP-pectin interface encapsulated by calcium pectinate at the periphery, by using an array of characterization techniques like zeta potential, thermogravimetry, Fourier transformed infrared and X-ray photoelectron spectroscopy. The MCPs were stable in simulated gastrointestinal fluid and ensured minimal loss of magnetic material. They exhibited superparamagnetic behavior, confirmed from zero field cooled and field cooled profiles and showed high saturation magnetization (Ms) of 46.21 emu/g at 2.5 T and 300 K. Ms decreased with increasing precursor pectin concentrations, attributed to quenching of magnetic moments by formation of a magnetic dead layer on the MNPs.

Sahu, Saurabh; Dutta, Raj Kumar

2011-04-01

349

Lipolytic biocatalyst based on recyclable magnetite-polysiloxane nanoparticles  

NASA Astrophysics Data System (ADS)

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.

Durdureanu-Angheluta, Anamaria; Ignat, Maurusa-Elena; Maier, Stelian Sergiu; Pricop, Lucia; Coroaba, Adina; Fifere, Adrian; Pinteala, Mariana; Chiriac, Anca

2014-02-01

350

Magnetization and susceptibility of ion-irradiated granular magnetite films  

NASA Astrophysics Data System (ADS)

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 and irradiated films. The in-phase alternating current magnetic susceptibility of the unirradiated film shows a blocking temperature of ˜150 K, depending on frequency. A broadened Verwey transition for the irradiated film occurs at ˜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.

Jiang, W.; McCloy, J. S.; Lea, A. S.; Sundararajan, J. A.; Yao, Q.; Qiang, Y.

2011-04-01

351

Magnetization and susceptibility of ion-irradiated granular magnetite films  

SciTech Connect

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.

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

352

Magnetization and susceptibility of ion irradiated granular magnetite films  

SciTech Connect

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.

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

2011-04-26

353

Low-temperature formation of pyrrhotite from magnetite sup + pyrite: Evidence from low-grade metamorphism and implications for magnetite preservation during deep burial  

SciTech Connect

Early magnetite in sedimentary rocks must be preserved to retain a paleomagnetic signature; however, reactions such as Fe{sub 3}O{sub 4} + 3 FeS{sub 2} + CH{sub 4}' = (organic matter) = 6 FeS' (pyrr.) + CO{sub 2} + 2 H{sub 2}O tend to the right for temperatures less than {approximately}200C. Such low temperatures strongly imply that magnetite can be destroyed merely by deep burial. Such pyrrhotite formation is illustrated by very low-grade metamorphism in a contact aureole surrounding the Jurassic Notch Peak stock in the central House Range of western Utah. The stock invades a Cambrian sedimentary sequence containing miogeoclinal limestones with intercalated siltstones. Limestones in the aureole yield a scattered, two-polarity remagnetization, residing in pyrrhotite, which extends into rocks that appear unmetamorphosed (temperatures {approximately}250C). The pyrrhotite could not have been precipitated from externally derived fluids because oxygen isotopic data from the limestones show no influence of magmatic or phreatic water; hence, it must have formed in situ, as in the above equation. Outside the aureole, a characteristic magnetization is preserved that apparently reflects late Paleozoic remagnetization and that probably resides in authigenic magnetite. Hence, it appears that this relatively late magnetite was in turn destroyed by modest reheating from the pluton. In general, thermal remagnetization of sedimentary rocks is probably rare: chemical changes probably have a much more profound effect on the paleomagnetic signatures.

Gillett, S.L. (Univ. of Nevada, Reno (United States))

1991-03-01

354

Epitaxial Fe3-xTixO4 films from magnetite to ulvöspinel by pulsed laser deposition  

SciTech Connect

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.

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

355

Epitaxial Fe3-xTixO4 films from magnetite to ulvöspinel by pulsed laser deposition  

NASA Astrophysics Data System (ADS)

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(001) substrates. 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 alteration to a titanomaghemite-like composition and structure. The surfaces 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.

Droubay, T. C.; Pearce, C. I.; Ilton, E. S.; Engelhard, M. H.; Jiang, W.; Heald, S. M.; Arenholz, E.; Shutthanandan, V.; Rosso, K. M.

2011-09-01

356

Microwave resonant and zero-field absorption study of doped magnetite prepared by a co-precipitation method.  

PubMed

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

Aphesteguy, Juan Carlos; Jacobo, Silvia E; Lezama, Luis; Kurlyandskaya, Galina V; Schegoleva, Nina N

2014-01-01

357

Magnetite magnetosome and fragmental chain formation of Magnetospirillum magneticum AMB-1: transmission electron microscopy and magnetic observations  

NASA Astrophysics Data System (ADS)

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.

Li, Jinhua; Pan, Yongxin; Chen, Guanjun; Liu, Qingsong; Tian, Lanxiang; Lin, Wei

2009-04-01

358

Magnetite biomineralization in Magnetospirillum gryphiswaldense: time-resolved magnetic and structural studies.  

PubMed

Magnetotactic bacteria biosynthesize magnetite nanoparticles of high structural and chemical purity that allow them to orientate in the geomagnetic field. In this work we have followed the process of biomineralization of these magnetite nanoparticles. We have performed a time-resolved study on magnetotactic bacteria Magnetospirillum gryphiswaldense strain MSR-1. From the combination of magnetic and structural studies by means of Fe K-edge X-ray absorption near edge structure (XANES) and high-resolution transmission electron microscopy we have identified and quantified two phases of Fe (ferrihydrite and magnetite) involved in the biomineralization process, confirming the role of ferrihydrite as the source of Fe ions for magnetite biomineralization in M. gryphiswaldense. We have distinguished two steps in the biomineralization process: the first, in which Fe is accumulated in the form of ferrihydrite, and the second, in which the magnetite is rapidly biomineralized from ferrihydrite. Finally, the XANES analysis suggests that the origin of the ferrihydrite could be at bacterial ferritin cores, characterized by a poorly crystalline structure and high phosphorus content. PMID:23530668

Fdez-Gubieda, M Luisa; Muela, Alicia; Alonso, Javier; García-Prieto, Ana; Olivi, Luca; Fernández-Pacheco, Rodrigo; Barandiarán, José Manuel

2013-04-23

359

Facile one-step fabrication of magnetite particles under mild hydrothermal conditions  

NASA Astrophysics Data System (ADS)

Hydrophilic magnetite particles for biological applications were synthesized by hydrothermal method in the presence of D-Glucose as both reducing and capping agent in a facile, one-step, low energy and environmentally friendly route. The role of D-Glucose as a reducing agent in the formation of magnetite particles under mild hydrothermal conditions has been investigated. The absence of D-Glucose results in the formation of hematite. The magnetite particles synthesized were characterized using powder X-ray Diffraction (XRD), Fourier Transform Infrared (FTIR) Spectroscopy, High Resolution Scanning Electron Microscopy (HR-SEM), Dynamic Light Scattering (DLS) and Vibrating Sample Magnetometery (VSM). The influence of the quantity of D-Glucose used and the reaction duration on the formation of magnetite were studied. DLS and HR-SEM results show that the size of the particles was in nano- to micron range. The antioxidant potency of the particles was confirmed using DPPH assay, where 2,2- Diphenyl-1-picrylhydrazyl was used as a source of free radicals. Hence the magnetite particles obtained could be considered for the use in various biological applications.

Keerthana, D. Shanthini; Namratha, K.; Byrappa, K.; Yathirajan, H. S.

2015-03-01

360

The Use of Magnetite as a Polarisable Anode in the Electrolysis of Water  

NASA Astrophysics Data System (ADS)

We have studied the oxidation of magnetite to Fe2O3 in an electrolytic cell in which the cathode is magnetite and the anode is platinum. We report cyclic voltammogram data consistent with the hypothesis that magnetite, without oxygen gas production but with hydrogen gas production at the anode, is occurring. The reaction occurs at a potential at the cathode of about 0.3V vs SCE in 1M NaOH electrolyte, consistent with colloid experiments which also estimated the equilibrium potential of the hypothesized reaction. We find currents on the order of a milliamp per gram of magnetite electrode with the pelletized magnetite powder electrodes which we are using. Electrode characterization results using BET, XDS and macroscopic volume and mass measurements are reported, as well measurements of the amount of hydrogen gas generated per unit current. The quantity of gas generated is also consistent with our hypothesis concerning the electrode chemistry. Some samples exhibit evidence of two oxidation reactions occurring at the cathode and a possible interpretation of these is also discussed.

Berntson, Bjorn; Woods Halley, J.; Schofield, Andy

2012-02-01

361

Control of nanoparticle size, reactivity and magnetic properties during the bioproduction of magnetite by Geobacter sulfurreducens  

SciTech Connect

The bioproduction of nano-scale 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 has been investigated by X-ray magnetic circular dichroism and indicates 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, optimised biogenic magnetite is able to reduce and sequester the toxic hexavalent chromium very efficiently in the less harmful trivalent form.

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

2011-08-02

362

Small magnetite antiretroviral therapeutic nanoparticle probes for MRI of drug biodistribution  

PubMed Central

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

Guo, Dongwei; Li, Tianyuzi; McMillan, JoEllyn; Sajja, Balasrinivasa R; Puligujja, Pavan; Boska, Michael D; Gendelman, Howard E; Liu, Xin-Ming

2013-01-01

363

Magneto-transport study of magnetite (Fe3O4) nanoparticles between Au nanogap electrodes on surface-oxidized Si substrate  

NASA Astrophysics Data System (ADS)

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.

Kobori, H.; Takata, N.; Fukutome, N.; Yamasaki, A.; Sugimura, A.; Taniguchi, T.; Horie, T.; Naitoh, Y.; Shimizu, T.

2013-04-01

364

Synthesis of magnetite-porphyrin nanocomposite and its application as a novel magnetic adsorbent for removing heavy cations  

SciTech Connect

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.

Bakhshayesh, Sara, E-mail: s_bakhshayesh@yahoo.com; Dehghani, Hossein, E-mail: dehghani@kashanu.ac.ir

2013-07-15

365

Particle characteristics and reduction behavior of synthetic magnetite  

NASA Astrophysics Data System (ADS)

Two samples (S1 and S2) of magnetite were synthesized, using two different methods, and characterized by means of X-ray powder diffractometry, infrared and Mössbauer spectroscopy, N2 sorptiometry and electron microscopy. Particles of sample-S1 were found to be loosely agglomerated, micro-sized spheroids (200-350 nm) composed almost solely of highly aggregated (fused) crystallites (size averaged at 35 nm) of cubic-Fe3O4. In contrast, particles of sample-S2 were strongly agglomerated, nano-sized spheroids (25-30 nm) composed of slightly aggregated crystallites (size averaged at 11 nm) of cubic-Fe3O4 and noncrystalline domains made-up of FeO(OH) species. Temperature-programed reduction (TPR) profiles obtained for the two samples were similar in monitoring two peaks at >450 °C assignable to a two-step reduction of Fe3O4 (?FeO?Fe), but different in monitoring a peak at<450 °C only for the reduction of FeO(OH) (?Fe3O4) contained in sample-S2. However, curve fitting analysis of the TPR profiles and molecular stoichiometry calculations based on amounts of hydrogen consumed revealed that the two-step reduction of Fe3O4 is not straightforward. That is by resolving two consecutive pathways for each step and, hence, nonstoichiometric intermediate products whose composition was found to be critically controlled by the composition of the reducing gas atmosphere (5 or 80% H2/N2) and characteristics of the starting sample particles (chemical and phase composition, and, but to lesser extents, the agglomeration and average size).

Ramadan, Wegdan; Zaki, Mohamed I.; Fouad, Nasr E.; Mekhemer, Gamal A. H.

2014-04-01

366

Fayalite Oxidation Processes: Experimental Evidence for the Stability of Pure Ferric Fayalite?  

NASA Technical Reports Server (NTRS)

Olivine is one of the most important minerals in Earth and planetary sciences. Fayalite Fe2(2+)SiO4, the ferrous end-member of olivine, is present in some terrestrial rocks and primitive meteorites (CV3 chondrites). A ferric fayalite (or ferri-fayalite), Fe(2+) Fe2(3+)(SiO4)2 laihunite, has been reported in Earth samples (magnetite ore, metamorphic and volcanic rocks...) and in Martian meteorites (nakhlites). Laihunite was also synthesized at 1 atmosphere between 400 and 700 C. We show evidence for the stability of a pure ferrifayalite end-member and for potential minerals with XFe(3+) between 2/3 and 1.

Martin, A. M.; Righter, K.; Keller, L. P.; Medard, E.; Devouard, B.; Rahman, Z.

2011-01-01

367

Metastable growth of pure wurtzite InGaAs microstructures.  

PubMed

III-V compound semiconductors can exist in two major crystal phases, namely, zincblende (ZB) and wurtzite (WZ). While ZB is thermodynamically favorable in conventional III-V epitaxy, the pure WZ phase can be stable in nanowires with diameters smaller than certain critical values. However, thin nanowires are more vulnerable to surface recombination, and this can ultimately limit their performances as practical devices. In this work, we study a metastable growth mechanism that can yield purely WZ-phased InGaAs microstructures on silicon. InGaAs nucleates as sharp nanoneedles and expand along both axial and radial directions simultaneously in a core-shell fashion. While the base can scale from tens of nanometers to over a micron, the tip can remain sharp over the entire growth. The sharpness maintains a high local surface-to-volume ratio, favoring hexagonal lattice to grow axially. These unique features lead to the formation of microsized pure WZ InGaAs structures on silicon. To verify that the WZ microstructures are truly metastable, we demonstrate, for the first time, the in situ transformation from WZ to the energy-favorable ZB phase inside a transmission electron microscope. This unconventional core-shell growth mechanism can potentially be applied to other III-V materials systems, enabling the effective utilization of the extraordinary properties of the metastable wurtzite crystals. PMID:24988280

Ng, Kar Wei; Ko, Wai Son; Lu, Fanglu; Chang-Hasnain, Connie J

2014-08-13

368

Preparation of hollow magnetite microspheres and their applications as drugs carriers  

PubMed Central

Hollow magnetite microspheres have been synthesized by a simple process through a template-free hydrothermal approach. Hollow microspheres were surface modified by coating with a silica nanolayer. Pristine and modified hollow microparticles were characterized by field-emission electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, FT-IR and Raman spectroscopy, and VSM magnetometry. The potential application of the modified hollow magnetite microspheres as a drug carrier was evaluated by using Rhodamine B and methotrexate as model drugs. The loading and release kinetics of both molecules showed a clear pH and temperature dependent profile. Graphical abstract Hollow magnetite microspheres have been synthesized. Load-release experiments with Rhodamine-B as a model drug and with Methotrexate (chemotherapy drug used in treating certain types of cancer) demonstrated the potential applications of these nanostructures in biomedical applications. PMID:22490731

2012-01-01

369

Mechanism of formation of magnetite from ferrous hydroxide in aqueous corrosion processes  

NASA Astrophysics Data System (ADS)

The stoichiometric conditions for the formation of ferrous hydroxide Fe(OH)2, by mixing Fe2+ ions with caustic soda NaOH, leads by oxidation to magnetite, irrelevant of the foreign anions, e.g. Cl- or SO4 2-, as demonstrated from Mössbauer spectroscopy. The electrochemical potential Eh and pH value of the initial conditions correspond to the drastic change from basic to acidic medium, observed when varying the initial Fe2+/OH- ratio. Mössbauer analysis of the end products of oxidation at various temperatures shows that magnetite is only obtained at stoichiometry at very low temperature, but extends off stoichiometry at higher temperatures. The mechanism of formation of magnetite through an intermediate compound is discussed.

Olowe, A. A.; Rezel, D.; Génin, J. M. R.

1989-03-01

370

Reflective and magnetic properties of photonic polymer composite materials based on porous silicon and magnetite nanoparticles.  

PubMed

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

Kim, Jihoon; Koh, Youngdae; Jang, Seunghyun; Jung, Kyoungsun; Woo, Hee-Gweon; Kim, Sungsoo; Sohn, Honglae

2010-05-01

371

Magnetic field dependence of the nonequilibrium metal-insulator transition in magnetite nanostructures  

NASA Astrophysics Data System (ADS)

At low temperatures magnetite undergoes a Verwey transition from a comparatively conducting state to a strongly correlated, ordered, more insulating state, the detailed nature of which remains under active debate. Recent experiments using nanostructures based on epitaxial magnetite films have shown that an applied dc electric field can lead to a nonequilibrium transition out of the insulating state. The kinetics of this nonequilibrium transition are nontrivial, with switching taking place over a distribution of applied voltages in a particular device at a given temperature below the Verwey transition. An externally applied magnetic field is observed to alter the kinetics of the nonequilibrium transition as the magnetization of the magnetite film is coerced out of plane. We present this data and discuss what it implies about the nature of the ordered, insulating ground state.

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

2011-03-01

372

Reordering between tetrahedral and octahedral sites in ultrathin magnetite films grown on MgO(001)  

NASA Astrophysics Data System (ADS)

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.

Bertram, F.; Deiter, C.; Schemme, T.; Jentsch, S.; Wollschläger, J.

2013-05-01

373

Reordering between tetrahedral and octahedral sites in ultrathin magnetite films grown on MgO(001)  

SciTech Connect

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.

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

374

Toxicological evaluation of pure hydroxytyrosol.  

PubMed

Of all the phenolic constituents of olives and extra virgin olive oil, hydroxytyrosol is currently being actively exploited as a potential supplement or preservative to be employed in the nutraceutical, cosmeceutical, and food industry. In terms of safety profile, hydroxytyrosol has only been investigated as the predominant part of raw olive mill waste water extracts, due to the previous unavailability of appropriate quantities of the pure compound. We report the toxicological evaluation of hydroxytyrosol and, based on the results, propose a No Observed Adverse Effects Level (NOAEL) of 500mg/kg/d. PMID:23380205

Auñon-Calles, David; Canut, Lourdes; Visioli, Francesco

2013-05-01

375

Synthesis of Enantiomerically Pure Anthracyclinones  

NASA Astrophysics Data System (ADS)

The anthracycline antibiotics are among the most important clinical drugs used in the treatment of human cancer. The search for new agents with improved therapeutic efficacy and reduced cardiotoxicity stimulated considerable efforts in the synthesis of new analogues. Since the biological activity of anthracyclines depends on their natural absolute configuration, various strategies for the synthesis of enantiomerically pure anthracyclinones (aglycones) have been developed. They comprise: resolution of racemic intermediate, incorporation of a chiral fragment derived from natural and non-natural chiral pools, asymmetric synthesis with the use of a chiral auxiliary or a chiral reagent, and enantioselective catalysis. Synthetic advances towards enantiopure anthracyclinones reported over the last 17 years are reviewed.

Achmatowicz, Osman; Szechner, Barbara

376

Ruthenium pure quadrupole resonance spectroscopy  

NASA Astrophysics Data System (ADS)

The unique chemistry of ruthenium and consequent potential importance of the quadrupole coupling constants and asymmetry parameters of 99Ru and 101Ru has prompted us to initiate an apparently original investigation of the pure nuclear quadrupole resonance spectroscopy of these two isotopes. A means for prediction of the expected resonance frequencies based on Mossbauer data is given and detailed circuit diagrams of a spectrometer which has been constructed primarily for ruthenium studies are presented. Preliminary searches carried out for ruthenium tris-acetylacetonate and bis-ruthenium tetroxide have so far failed to yield signals. Possible explanations for this are discussed and the value of continuing the work defended.

Carter, J. C.; Good, M. L.

377

Arsenate and Arsenite Sorption on Magnetite: Relations to Groundwater Arsenic Treatment Using Zerovalent Iron and Natural Attenuation  

EPA Science Inventory

Magnetite (Fe3O4) is a zerovalent iron corrosion product; it is also formed in natural soil and sediment. Sorption of arsenate (As(V)) and arsenite (As(III)) on magnetite is an important process of arsenic removal from groundwater using zerovalent iron-based permeable reactive ba...

378

ccsd-00105476,version1-11Oct2006 Finite size effects in the Verwey transition of magnetite thin films  

E-print Network

size effects in the Verwey transition of stress-free magnetite (Fe3O4 ) thin films. A limit thicknessccsd-00105476,version1-11Oct2006 Finite size effects in the Verwey transition of magnetite thin films A.M. Bataille,1, E. Vincent,2 S. Gota,1, and M. Gautier-Soyer1 1 DRECAM/SPCSI, CEA Saclay, 91191

Paris-Sud XI, Université de

379

Crystallization Stages of the Bishop Tuff Magma Body Recorded in Crystal Textures in Pumice Clasts  

SciTech Connect

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.

Pamukcu, Ayla; Gualda, Guilherme A.R.; Anderson, Jr. , Alfred T. (Vanderbilt); (UC)

2012-07-25

380

Multiple pure tone noise prediction  

NASA Astrophysics Data System (ADS)

This paper presents a fully numerical method for predicting multiple pure tones, also known as “Buzzsaw” noise. It consists of three steps that account for noise source generation, nonlinear acoustic propagation with hard as well as lined walls inside the nacelle, and linear acoustic propagation outside the engine. Noise generation is modeled by steady, part-annulus computational fluid dynamics (CFD) simulations. A linear superposition algorithm is used to construct full-annulus shock/pressure pattern just upstream of the fan from part-annulus CFD results. Nonlinear wave propagation is carried out inside the duct using a pseudo-two-dimensional solution of Burgers' equation. Scattering from nacelle lip as well as radiation to farfield is performed using the commercial solver ACTRAN/TM. The proposed prediction process is verified by comparing against full-annulus CFD simulations as well as against static engine test data for a typical high bypass ratio aircraft engine with hardwall as well as lined inlets. Comparisons are drawn against nacelle unsteady pressure transducer measurements at two axial locations as well as against near- and far-field microphone array measurements outside the duct. This is the first fully numerical approach (no experimental or empirical input is required) to predict multiple pure tone noise generation, in-duct propagation and far-field radiation. It uses measured blade coordinates to calculate MPT noise.

Han, Fei; Sharma, Anupam; Paliath, Umesh; Shieh, Chingwei

2014-12-01

381

Novel protocol for the solid-state synthesis of magnetite for medical practices  

NASA Astrophysics Data System (ADS)

It is reported a novel approach to prepare nanoparticles of magnetite (Fe3O4) by heating a mixture of synthetic commercial maghemite (?Fe2O3) with sucrose. This solid-state reaction leads to the chemical reduction of part of the Fe3+ of the precursor oxide to render Fe2+ and Fe3+ in octahedral and Fe3+ in tetrahedral sites of the Fe-O coordination framework. Powder X-ray diffraction patterns, FTIR and 298 K Mössbauer spectra confirm the conversion of maghemite into magnetite. Based on these results, the optimal sucrose:maghemite rate was found to be 4.

Paiva, D. L.; Andrade, A. L.; Pereira, M. C.; Fabris, J. D.; Domingues, R. Z.; Alvarenga, M. E.

2015-01-01

382

Ligand effects on the electronic structure and magnetism of magnetite surfaces  

NASA Astrophysics Data System (ADS)

We address the effect of functionalization on the electronic and magnetic properties of magnetite surface as an indicator of the same properties in nanoparticles too big for a direct ab-initio approach. Using well-established methods and references (namely LDA+U on magnetite surfaces) we could verify the validity of our approach, and using two typical ligands, dopamine and citrate, namely ? and ? electron donors, we could predict that those ligands would induce a different change in the electronic properties of the systems, but in both cases an enhancement of magnetization.

Brymora, Katarzyna; Calvayrac, Florent

2013-03-01

383

Magnetite (Fe3O4): a new variant of relaxor multiferroic?  

PubMed

The electric polarization, dielectric permittivity, magnetoelectric effect, heat capacity, magnetization and ac susceptibility of magnetite films and polycrystals were investigated. The electric polarization of magnetite films with saturation values between 4 and 8 ?C cm(-2) was found to vanish between 32 and 38 K, but in polycrystals no phase transition was detected in this range by heat capacity. Both types of samples showed magnetoelectric effects at low temperatures below a frequency-dependent crossover. This is interpreted as arising from multiferroic relaxor behavior. PMID:22314835

Ziese, M; Esquinazi, P D; Pantel, D; Alexe, M; Nemes, N M; Garcia-Hernández, M

2012-02-29

384

Thin magnetite films on an oxidized silicon surface: Raman spectroscopy study  

NASA Astrophysics Data System (ADS)

Polycrystalline films of magnetite (Fe3O4) formed by the reactive sputtering of iron in oxygen on Si(001) substrates covered by thin (1.4 nm) or thick (1200 nm) SiO2 layers have been studied by Raman spectroscopy. It is established that (i) the ?-Fe2O3 phase is formed due to the laser-induced heating in magnetite films synthesized on thick SiO2 layers and (ii) the formation of ?-Fe2O3 phase depends on the thickness of the buffer SiO2 layer.

Vikulov, V. A.; Balashev, V. V.; Pisarenko, T. A.; Dimitriev, A. A.; Korobtsov, V. V.

2012-08-01

385

Magnetite (Fe3O4): a new variant of relaxor multiferroic?  

NASA Astrophysics Data System (ADS)

The electric polarization, dielectric permittivity, magnetoelectric effect, heat capacity, magnetization and ac susceptibility of magnetite films and polycrystals were investigated. The electric polarization of magnetite films with saturation values between 4 and 8 µC cm-2 was found to vanish between 32 and 38 K, but in polycrystals no phase transition was detected in this range by heat capacity. Both types of samples showed magnetoelectric effects at low temperatures below a frequency-dependent crossover. This is interpreted as arising from multiferroic relaxor behavior.

Ziese, M.; Esquinazi, P. D.; Pantel, D.; Alexe, M.; Nemes, N. M.; Garcia-Hernández, M.

2012-02-01

386

Protein crystallization: from purified protein to diffraction-quality crystal  

Microsoft Academic Search

Determining the structure of biological macromolecules by X-ray crystallography involves a series of steps: selection of the target molecule; cloning, expression, purification and crystallization; collection of diffraction data and determination of atomic positions. However, even when pure soluble protein is available, producing high-quality crystals remains a major bottleneck in structure determination. Here we present a guide for the non-expert to

Emmanuel Saridakis; Naomi E Chayen

2008-01-01

387

Deterministic transformations of bipartite pure states  

NASA Astrophysics Data System (ADS)

We propose an explicit protocol for the deterministic transformations of bipartite pure states in any dimension using deterministic transformations in lower dimensions. As an example, explicit solutions for the deterministic transformations of 3 ? 3 pure states by a single measurement are obtained, and an explicit protocol for the deterministic transformations of n ? n pure states by three-outcome measurements is presented.

Torun, Gokhan; Yildiz, Ali

2015-01-01

388

Thermal and dielectric properties of sweetpotato puree  

Technology Transfer Automated Retrieval System (TEKTRAN)

Pureeing of sweetpotato (SP) is carried out to enhance the conversion of the roots into value-added products. During processing, production and home utilization, the puree is often heated (conventional cooking or microwaved), hence the need to measure these properties of SP puree. Thermal (specific ...

389

One-pot solvothermal synthesis of highly water-dispersible size-tunable functionalized magnetite nanocrystal clusters for lipase immobilization.  

PubMed

A facile one-pot synthesis of highly water-dispersible size-tunable magnetite (Fe3O4) nanocrystal clusters (MNCs) end-functionalized with amino or carboxyl groups by a modified solvothermal reduction reaction has been developed. Dopamine and 3,4-dihydroxyhydroxycinnamic acid were used for the first time as both a surfactant and interparticle linker in a polylol process for economical and environment-friendly purposes. Morphology, chemical composition, and magnetic properties of the prepared particles were investigated by several methods, including FESEM, TEM, XRD, XPS, Raman, FTIR, TGA, zeta potential, and VSM. The sizes of the particles could be easily tuned over a wide range from 175 to 500?nm by varying the surfactant concentration. Moreover, ethylene glycol/diethylene glycol (EG/DEG) solvent mixtures with different ratios could be used as reductants to obtain the particles with smaller sizes. The XRD data demonstrated that the surfactants restrained the crystal growth of the grains. The nanoparticles showed superior magnetic properties and high colloidal stability in water. The cytotoxicity results indicated the feasibility of using the synthesized nanocrystals in biology-related fields. To estimate the applicability of the obtained MNCs in biotechnology, Candida rugosa lipase was selected for the enzyme immobilization process. The immobilized lipase exhibited excellent thermal stability and reusability in comparison with the free enzyme. This novel strategy would simplify the reaction protocol and improve the efficiency of materials functionalization, thus offering new potential applications in biotechnology and organocatalysis. PMID:23616374

Zhu, Hao; Hou, Chen; Li, Yijing; Zhao, Guanghui; Liu, Xiao; Hou, Ke; Li, Yanfeng

2013-07-01

390

Pure gauge QCD and holography  

NASA Astrophysics Data System (ADS)

Holographic models for the pure gauge quantum chromodynamics (QCD) vacuum are explored. The holographic renormalization of these models is considered as required by a phenomenological approach that takes the ?-functions of the models as the only input. This approach is done taking the dilaton as the coordinate orthogonal to the border. This choice greatly simplifies the analysis and gives a geometrical interpretation for the fixed points of the renormalization group flow. Examples are constructed that present asymptotic freedom, confinement of static quarks, either with vanishing or nonvanishing gluon condensate G2. The latter models require an extension of the dilaton-gravity models already considered in the literature. This extension is also determined by the only input, i.e. the ?-function. In addition, the restrictions imposed by the trace anomaly equation (TAE) are studied. In doing so, a holographic derivation of this equation is presented.

Trinchero, R. C.

2014-09-01

391

Decryption of pure-position permutation algorithms.  

PubMed

Pure position permutation image encryption algorithms, commonly used as image encryption investigated in this work are unfortunately frail under known-text attack. In view of the weakness of pure position permutation algorithm, we put forward an effective decryption algorithm for all pure-position permutation algorithms. First, a summary of the pure position permutation image encryption algorithms is given by introducing the concept of ergodic matrices. Then, by using probability theory and algebraic principles, the decryption probability of pure-position permutation algorithms is verified theoretically; and then, by defining the operation system of fuzzy ergodic matrices, we improve a specific decryption algorithm. Finally, some simulation results are shown. PMID:15495308

Zhao, Xiao-Yu; Chen, Gang; Zhang, Dan; Wang, Xiao-Hong; Dong, Guang-Chang

2004-07-01

392

Doped TGS crystals for IR detection and sensors  

Microsoft Academic Search

Triglycine sulfate crystals (TGS) doped with l- and d-alanine, respectively, where grown in paraelectric phase at 52°C. They show stable parameters versus pure TGS crystals, lower permittivities and losses, i.e. higher pyroelectric figure of merit. l- and d-alanine-doped crystals show a mirror asymmetry of the growth habit along the ferroelectric axis. Hysteresis loop of pure and doped samples were automatically

H. V. Alexandru; C. Berbecaru; F. Stanculescu; L. Pintilie; I Matei; M Lisca

2004-01-01

393

Magnetoresistance and magnetic properties of epitaxial magnetite thin films  

Microsoft Academic Search

The magnetotransport and magnetic properties of epitaxial Fe3O4 thin films grown on (001)-oriented MgO substrates by pulsed-laser deposition have been investigated. The magnetoresistance (MR) exhibits a peak around the Verwey transition (Tnu) as has also been reported previously for single crystals. Additionally, we have observed that the MR increases monotonically below 100 K with decreasing temperature. MR values as high

G. Q. Gong; A. Gupta; Gang Xiao; W. Qian; V. P. Dravid

1997-01-01

394

Role of magnetite and humic acid in radionuclide migration in the environment.  

PubMed

Sorption of (137)Cs, (90)Sr, (154)Eu and (141)Ce by magnetite has been studied at varying pH (4 to 11) in the presence and absence of humic acid. The sorption studies have also been carried out at varying ionic strength (0.01 to 0.2 M NaClO(4)) and humic acid concentration (2 to 20 mg/L). Percentage sorption of (137)Cs and (90)Sr was found to be pH dependent, with the sorption increasing with increasing pH of the suspension. At any pH, the percentage sorption of (90)Sr was higher than that of (137)Cs. The results have been explained in terms of the electrostatic interaction between the positively charged metal ions and the surface charge of the magnetite which becomes increasingly negative with increasing pH. On the other hand, (154)Eu and (141)Ce were found to be strongly sorbed by the magnetite at all pH values, with the sorption being independent of pH. The strong sorption of trivalent and tetravalent metal ions suggests the role of complexation reactions during sorption, apart from the electrostatic interactions. However, in the case of (141)Ce surface precipitation of Ce(III) formed by reduction of Ce(IV) in the presence of magnetite cannot be ruled out. Presence of humic acid (2 mg/L) was found to have negligible effect on sorption of all metal ions. PMID:19268388

Singh, B K; Jain, Aishwarya; Kumar, Sumit; Tomar, B S; Tomar, Radha; Manchanda, V K; Ramanathan, S

2009-05-12

395

Re-Examination of Anomalous I-Xe Ages: Orgueil and Murchison Magnetites and Allegan Feldspar  

NASA Technical Reports Server (NTRS)

Old I-Xe age for Orgueil (and Murchison) magnetite is not confirmed. New results show closure 2.8 Ma after Shallowater/Bjurbole standard, 10.3 Ma later than previously reported. The anomalously old I-Xe age of Allegan feldspar is attributed to shock.

Hohenberg, Charles M.; Pravdivtseva, Olga V.; Meshik, Alex P.

2000-01-01

396

Self-heating of magnetite nanoparticles for a potential hyperthermia application  

NASA Astrophysics Data System (ADS)

A comparative study of heat generation in superparamagnetic magnetite nanoparticles in aqueous and hexane solutions in the presence of external magnetic field is presented. The field strength dependence of the specific absorption rate (SAR) complies with the power law of second order. The concave-convex change of SAR-H curves substantially illustrates the importance of particle dispersion in the fluid.

Kim, Chang-Yeoul; Xu, Lixing; Lee, Eun-Hee

2014-07-01

397

Interactions between Magnetite Oxidation and Flux Calcination during Iron Ore Pellet Induration  

NASA Astrophysics Data System (ADS)

Many chemical reactions take place simultaneously during the induration of iron ore pellets produced from magnetite concentrates. Two of the most important are magnetite oxidation and calcination of carbonate fluxes. The first reaction consumes oxygen diffusing into the pellet, while the second reaction produces carbon dioxide that must diffuse out of the pellet. A mathematical model combining the two reactions and gaseous diffusion within the pellet has been developed to quantify the interaction between the two reactions. This combined mathematical model showed that current induration plant mathematical models for the mass and energy balance around a pellet furnace are inaccurate in treating magnetite oxidation and flux calcination as separate reactions. Assuming separate reactions can lead to an error of up to 20 pct conversion of magnetite at the end of the preheat stage. This combined mathematical model, confirmed by experiments with single pellets, also demonstrated that calcination of fluxes also tends to follow a “shrinking core” model rather than reacting simultaneously across the pellet, as existing whole plant models assume. Modifying induration plant mathematical models in accordance with the findings of this article could lead to further savings in energy costs for pellet plants.

Firth, Andrew R.; Garden, John F.

2008-08-01

398

Interaction of magma with sedimentary wall rock and magnetite ore genesis in the Panzhihua mafic  

E-print Network

1 Interaction of magma with sedimentary wall rock and magnetite ore genesis in the Panzhihua mafic of large quantities of CO2 as the rocks were converted to marble and skarns during intrusion and close to the liquidus. We propose that CO2-rich fluids released during decarbonatization of sedimentary

Paris-Sud XI, Université de

399

New kind of type 3 chondrite with a graphite-magnetite matrix  

NASA Technical Reports Server (NTRS)

Four clasts in three ordinary-chondrite regolith breccias are discovered which are a new kind of type 3 chondrite. As with ordinary and carbonaceous type 3 chondrites, they have distinct chondrules, some of which contain glass, highly heterogeneous olivines and pyroxenes, and predominantly monoclinic low-Ca pyroxenes. Instead of the usual, fine-grained, Fe-rich silicate matrix, however, the clasts have a matrix composed largely of aggregates of micron- and submicron-sized graphite and magnetite. The bulk compositions of the clasts, as well as the types of chondrules (largely porphyritic), are characteristic of type 3 ordinary chondrites, although chondrules in the clasts are somewhat smaller (0.1-0.5 mm). A close relationship with ordinary chondrites is also suggested by the presence of similar graphite-magnetite aggregates in seven type 3 ordinary chondrites. It is thought that this new kind of chondrite is probably the source of the abundant graphite-magnetite inclusions in ordinary-chondrite regolith breccias and that it may be more common than indicated by the absence of whole meteorites made of chondrules and graphite-magnetite.

Scott, E. R. D.; Rubin, A. E.; Taylor, G. J.; Keil, K.

1981-01-01

400

URANIUM REMOVAL BY CHITOSAN IMPREGNATED WITH MAGNETITE NANOPARTICLES: ADSORPTION AND DESORPTION  

Microsoft Academic Search

A magnetic biosorbent composed of nanoparticles of magnetite covered with chitosan, denominated magnetic chitosan, was prepared. The magnetic chitosan has showed a magnetic response of intense attraction in the presence of a magnetic field without however to become magnetic, a typical behavior of superparamagnetic material. Its adsorption performance was evaluated by the adsorption isotherm models of Langmuir and Freundlich for

Luiz Cláudio; Barbosa Stop; Mitiko Yamaura

401

Using chromate to investigate the impact of natural organics on the surface reactivity of nanoparticulate magnetite.  

PubMed

Chromate was used as a chemical probe to investigate the size-dependent influence of organics on nanoparticle surface reactivity. Magnetite-chromate sorption experiments were conducted with ?90 and ?6 nm magnetite nanoparticles in the presence and absence of fulvic acid (FA), natural organic matter (NOM), and isolated landfill leachate (LL). Results indicated that low concentrations (1 mg/L) of organics had no noticeable impact on chromate sorption, whereas concentrations of 50 mg/L or more resulted in decreased amounts of chromate sorption. The adsorption of organics onto the magnetite surfaces interfered equally with the ability of the 6 and 90 nm particles to sorb chromate from solution, despite the greater surface area of the smaller particles. Results indicate the presence of organics did not impact the redox chemistry of the magnetite-chromate system over the duration of the experiments (8 h), nor did the organics interact with the chromate in solution. Brunauer-Emmett-Teller (BET) and scanning electron microscopy (SEM) results indicate that the organics blocked the surface reactivity by occupying surface sites on the particles. The similarity of results with FA and NOM suggests that coverage of the reactive mineral surface is the main factor behind the inhibition of surface reactivity in the presence of organics. PMID:25607467

Swindle, Andrew L; Cozzarelli, Isabelle M; Elwood Madden, Andrew S

2015-02-17

402

Photo-Fenton oxidation of phenol with magnetite as iron source Marco Minella,1  

E-print Network

Photo-Fenton oxidation of phenol with magnetite as iron source Marco Minella,1 Giulia Marchetti,1 irradiation. Very interestingly, the photo-Fenton degradation of phenol was also observed under neutral to promote photo-Fenton reactions even under circumneutral pH conditions, the limited iron leaching and its

403

The Terminal Oxidase cbb3 Functions in Redox Control of Magnetite Biomineralization in Magnetospirillum gryphiswaldense  

PubMed Central

The biomineralization of magnetosomes in Magnetospirillum gryphiswaldense and other magnetotactic bacteria occurs only under suboxic conditions. However, the mechanism of oxygen regulation and redox control of biosynthesis of the mixed-valence iron oxide magnetite [FeII(FeIII)2O4] is still unclear. Here, we set out to investigate the role of aerobic respiration in both energy metabolism and magnetite biomineralization of M. gryphiswaldense. Although three operons encoding putative terminal cbb3-type, aa3-type, and bd-type oxidases were identified in the genome assembly of M. gryphiswaldense, genetic and biochemical analyses revealed that only cbb3 and bd are required for oxygen respiration, whereas aa3 had no physiological significance under the tested conditions. While the loss of bd had no effects on growth and magnetosome synthesis, inactivation of cbb3 caused pleiotropic effects under microaerobic conditions in the presence of nitrate. In addition to their incapability of simultaneous nitrate and oxygen reduction, cbb3-deficient cells had complex magnetosome phenotypes and aberrant morphologies, probably by disturbing the redox balance required for proper growth and magnetite biomineralization. Altogether, besides being the primary terminal oxidase for aerobic respiration, cbb3 oxidase may serve as an oxygen sensor and have a further role in poising proper redox conditions required for magnetite biomineralization. PMID:24794567

Li, Yingjie; Raschdorf, Oliver; Silva, Karen T.

2014-01-01

404

Effects of magnetite on high-frequency ground-penetrating radar Remke L. Van Dam1  

E-print Network

Effects of magnetite on high-frequency ground-penetrating radar Remke L. Van Dam1 , Jan M. H, paleoclimatology (Maher and Thompson, 1995), soil development (Singer et al., 1996; Van Dam et al., 2008 et al., 2011), the detection of unexploded ordnance (UXO) and land mines (Van Dam et al., 2005

Borchers, Brian

405

A&M. Special shielding materials. Stockpile of magnetite, used for making ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

A&M. Special shielding materials. Stockpile of magnetite, used for making high-density concrete, and loading conveyor near TAN-607 construction site. Date: September 25, 1953. INEEL negative no. 8710 - Idaho National Engineering Laboratory, Test Area North, Scoville, Butte County, ID

406

Arbaret, Launeau, Diot, Sizaret Magnetic and shape fabrics of magnetite in  

E-print Network

strains 20 was performed using a suspension of 1% volume fraction of multidomain magnetite randomly of applied finite strain. For 8, fabric elements, foliation and lineation, stabilised closely parallel, Diot, Sizaret 3 1. Introduction Magmas flowing from their source are usually regarded as suspensions

Paris-Sud XI, Université de

407

Site-Selective Holographic Imaging of Iron Arrangements in Magnetite P. Korecki,1  

E-print Network

Site-Selective Holographic Imaging of Iron Arrangements in Magnetite P. Korecki,1 M. Szymon´ski,1 J of the holograms to real space provided three-dimensional images of local iron arrangements in octahedral pattern into a three-dimensional image of the local structure around detecting atoms. By selection

Korecki, Pawe³

408

Misorientations in [001] magnetite thin films studied by electron backscatter diffraction and magnetic force microscopy  

Microsoft Academic Search

Magnetite thin films grown on [001] oriented MgO substrates are analyzed by means of electron backscatter diffraction (EBSD) analysis and magnetic force microscopy in applied fields. The EBSD technique enables the crystallographic orientation of individual grains to be determined with a high spatial resolution up to 20 nm on such ceramic samples. A high image quality of the recorded Kikuchi

A. Koblischka-Veneva; M. R. Koblischka; J. D. Wei; Y. Zhou; S. Murphy; F. Mücklich; U. Hartmann; I. V. Shvets

2007-01-01

409

Magnetic properties of magnetite thin films close to the Verwey transition  

Microsoft Academic Search

Temperature dependence of the magnetic properties of magnetite thin film across the Verwey transition has been investigated. As the temperature is decreased, the magnetization of the film in a fixed field showed a sharp decrease close to the Verwey transition temperature (Tv). The M–H loops of the film have been recorded at various temperatures below and above Tv. It is

Murtaza Bohra; Shiva Prasad; N. Venketaramani; Naresh Kumar; S. C. Sahoo; R. Krishnan

2009-01-01

410

Structural and magnetic properties of epitaxial magnetite thin films prepared by pulsed laser deposition  

Microsoft Academic Search

Epitaxial magnetite thin films have been prepared on substrates with small (periclase) and large (sapphire) lattice misfits by pulsed laser deposition. 350 nm thick films on both substrates exhibit nearly bulk saturation magnetization. Films on periclase showed a shift in the Verwey transition towards lower temperatures most probably due to strain effects.

C. A. Kleint; H. C. Semmelhack; M. Lorenz; M. K. Krause

1995-01-01

411

Magnetic force microscopy of epitaxial magnetite films through the Verwey transition  

Microsoft Academic Search

Magnetic force microscopy was performed on 300 nm thick magnetite films grown epitaxially on MgO (001) at temperatures ranging from well below to well above the Verwey transition temperature, TV. Frequency shift images were acquired at different locations on the sample as temperature was increased through the Verwey transition. The magnetic domain features are persistent at all temperatures, which indicates

A. K. H. Lee; P. B. Jayathilaka; C. A. Bauer; M. C. Monti; J. T. Markert; A. de Lozanne; Casey W. Miller

2010-01-01

412

Submonolayers of Au/Pd on the hematite (0001) and magnetite (111) surfaces  

NASA Astrophysics Data System (ADS)

Ultra-thin films and nanostructures formed by noble metals on oxide surfaces exhibit enhanced catalytic activity for CO oxidation. We used the spin-polarized density functional theory (DFT) and the DFT+U method, accounting for the strong on-site Coulomb correlations, to study the submonolayer adsorption of Au/Pd atoms on two stable iron-oxide surfaces: hematite (0001) and a magnetite (111). For each surface, adsorption on two terminations has been studied: one terminated with iron and the other with oxygen. Both Au and Pd bind strongly to hematite and magnetite surfaces and induce large changes in their geometry. DFT and DFT+U provide qualitatively similar surface geometries but they differ much in the prediction of the surface energetics and the electronic and magnetic properties of the oxides. Pd binds stronger than Au both to hematite and magnetite surfaces and the Au/Pd bonding to the O-terminated surface is distinctly stronger than that to the Fe-terminated one. For hematite, the DFT+U bonding is by 0.3-0.6 eV weaker than DFT on the Fe-terminated surface and about 2 eV stronger on the O-terminated one. For magnetite, in each case, DFT+U gives stronger bonding than DFT. The differences between DFT and DFT+U results are discussed based on the calculated electronic structure.

Kiejna, Adam; Pabisiak, Tomasz; Ossowski, Tomasz

2012-02-01

413

Magnesium outdiffusion through magnetite films grown on magnesium oxide (001) (abstract)  

E-print Network

Magnesium outdiffusion through magnetite films grown on magnesium oxide (001) (abstract) K. A. Shaw of magnesium in the uppermost layers of the film, and indicate a concentration gradient, with the highest concentrations of magnesium in the surface layer. X-ray fluorescence in scanning electron microscopy

Diebold, Ulrike

414

M. Bahrami ENSC 388 (F09) Properties of Pure Substances Properties of Pure Substances  

E-print Network

pressure, the temperature at which a pure substance starts boiling is called the saturation temperature, Tsat. Likewise, at a given temperature, the pressure at which a pure substance starts boiling composition throughout is called a pure substance such as water, air, and nitrogen. A pure substance does

Bahrami, Majid

415

6.2. Pure death processes 6.2.1. Postulates of pure death processes.  

E-print Network

45 6.2. Pure death processes 6.2.1. Postulates of pure death processes. {X(t) : t [0, )} is called a pure death process with parameters µ0 = 0, µ1, ..., µN , and state space {0, 1, ..., N are equivalent, but Postulate 2 is incomplete and cannot be considered as a definition for pure death process. 6

Chen, Kani

416

Geochronology and stable isotope signature of alteration related to hydrothermal magnetite ores in Central Anatolia, Turkey  

NASA Astrophysics Data System (ADS)

Hydrothermal iron ores at Divri?i, east Central Anatolia, are contained in two orebodies, the magnetite-rich A-kafa and the limonitic B-kafa (resources of 133.8 Mt with 56% Fe and 0.5% Cu). The magnetite ores are hosted in serpentinites of the Divri?i ophiolite at the contact with plutons of the Murmano complex. Hydrothermal biotite from the Divri?i A-kafa yield identical weighted mean plateau ages of 73.75 ± 0.62 and 74.34 ± 0.83 Ma (2?). This biotite represents a late alteration phase, and its age is a minimum age for the magnetite ore. Similar magnetite ores occur at Hasançelebi and Karakuz, south of Divri?i. There, the iron ores are hosted in volcanic or subvolcanic rocks, respectively, and are associated with a voluminous scapolite ± amphibole ± biotite alteration. At Hasançelebi, biotite is intergrown with parts of the magnetite, and both minerals formed coevally. The weighted mean plateau ages of hydrothermal biotite of 73.43 ± 0.41 and 74.92 ± 0.39 Ma (2?), therefore, represent mineralization ages. Hydrothermal biotite from a vein cutting the scapolitized host rocks south of the Hasançelebi prospect has a weighted mean plateau age of 73.12 ± 0.75 Ma (2?). This age, together with the two biotite ages from the Hasançelebi ores, constrains the minimum age of the volcanic host rocks, syenitic porphyry dikes therein, and the scapolite alteration affecting both rock types. Pyrite and calcite also represent late hydrothermal stages in all of these magnetite deposits. The sulfur isotope composition of pyrite between 11.5 and 17.4‰ ?34S(VCDT) points towards a non-magmatic sulfur source of probably evaporitic origin. Calcite from the Divri?i deposit has ?18O(VSMOV) values between +15.1 and +26.5‰ and ?13C(VPDB) values between -2.5 and +2.0‰, which are compatible with an involvement of modified marine evaporitic fluids during the late hydrothermal stages, assuming calcite formation temperatures of about 300°C. The presence of evaporite-derived brines also during the early stages is corroborated by the pre-magnetite scapolite alteration at Divri?i, and Hasançelebi-Karakuz, and with paleogeographic and paleoclimatic reconstructions. The data are compatible with a previously proposed genetic model for the Divri?i deposit in which hydrothermal fluids leach and redistribute iron from ophiolitic rocks concomitant with the cooling of the nearby plutons.

Marschik, Robert; Spikings, Richard; Ku?cu, Ilkay

2008-01-01

417

Methane production from hydrothermal transformation of siderite to magnetite  

NASA Astrophysics Data System (ADS)

Mumma et al. (2009) observed a methane (CH4) plume above the Nili Fossae region on Mars, a region rich in carbonate minerals. Morris et al. (2010) suggest this to be (Mg,Fe)-carbonate. McCollom (2003) demonstrated that the hydrothermal transformation of siderite (FeCO3), to magnetite (Fe3O4) produces CH4. This reaction may thus contribute to the formation of methane on Mars, but is also relevant in the context of such diverse topics as diagenesis of Precambrian banded iron formations, sources of prebiotic organic compounds on early Earth, oil and gas accumulations in Earth's crust, or geological sequestration and storage of CO2. However, neither the thermodynamics of this reaction nor the conditions of maximum CH4 yield have been investigated to date. In order to estimate how pressure and temperature influence CH4 yield we derived a thermodynamic model with a numerical solution implemented in MATLAB. We used the equation 12FeCO3 + 2H2O ? 4Fe3O4 + 11CO2 + CH4 (Frost et al. 2007) and thermodynamic calculations of the stability field of FeCO3 by Thoms-Keprta et al. (2009) as a template. At 1 bar pressure, the Gibbs energy turns negative (favorable reaction conditions) at a temperature of 200°C. Increasing pressure to 1000 bar changes that temperature to 250°C. An increase in temperature has a larger effect on shifting the Gibbs energy to more negative values. We therefore chose ambient pressure and temperatures of 300°C, 400°C, and 500°C as experimental conditions. We added 100 mg of either natural or synthetic FeCO3 and 25 ?L of MilliQ water into long tip Pasteur pipettes inside an anoxic glove box to avoid contamination by free oxygen. The Pasteur pipettes were sealed with butyl stoppers and then melted shut outside of the glove box. The glass capsules were heated for 48 hours in a muffle furnace at 300°C, 400 0C or 5000C. The composition of the gas phase and the formation of methane in particular were analyzed using gas chromatography with a flame ionization detector. We used Mössbauer spectroscopy, X-ray diffraction, X-ray fluorescence, and scanning electron microscopy with Energy-Dispersive X-ray spectroscopy to investigate changes in the solid phase. Synthetic FeCO3 was completely transformed to Fe3O4 and sometimes the further oxidized phases maghemite (?-Fe2O3) and hematite (?-Fe2O3). Natural FeCO3 was not completely transformed, which can be explained by its larger particle size and therefore reduced reactivity. Methane yield was consequently higher from synthetic siderite. Our results show that hydrothermal activity invoked by either impact or volcanic activity could have transformed siderite and thereby released at least some of the CH4 observed on Mars. On Earth, long-term underground storage of CO2 as carbonate minerals has to avoid hydrothermal conditions. Otherwise not only CO2 will be released again, but some of it will potentially be transformed into the more potent greenhouse gas methane. References Frost et al., Contrib. Mineral. Pet. 153 (2006) 211; McCollom, Geochim. Cosmochim. Ac. 67 (2003) 311; Morris et al., Science 329 (2010), 421; Mumma et al., Science 323 (2009) 1041; Thomas-Keprta et al., Geochim. Cosmochim. Ac. 73 (2009) 6631, EA-4

Muratbayev, T.; Schroeder, C.; Kappler, A.; Haderlein, S.

2012-12-01

418

Synthesis of Environmentally Friendly Highly Dispersed Magnetite Nanoparticles Based on Rosin Cationic Surfactants as Thin Film Coatings of Steel  

PubMed Central

This work presents a new method to prepare monodisperse magnetite nanoparticles capping with new cationic surfactants based on rosin. Core/shell type magnetite nanoparticles were synthesized using bis-N-(3-levopimaric maleic acid adduct-2-hydroxy) propyl-triethyl ammonium chloride (LPMQA) as capping agent. Fourier transform infrared spectroscopy (FTIR) was employed to characterize the nanoparticles chemical structure. Transmittance electron microscopies (TEM) and X-ray powder diffraction (XRD) were used to examine the morphology of the modified magnetite nanoparticles. The magnetite dispersed aqueous acid solution was evaluated as an effective anticorrosion behavior of a hydrophobic surface on steel. The inhibition effect of magnetite nanoparticles on steel corrosion in 1 M HCl solution was investigated using potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS). Results obtained from both potentiodynamic polarisation and EIS measurements reveal that the magnetite nanoparticle is an effective inhibitor for the corrosion of steel in 1.0 M HCl solution. Polarization data show that magnetite nanoparticles behave as a mixed type inhibitor. The inhibition efficiencies obtained from potentiodynamic polarization and EIS methods are in good agreement. PMID:24758936

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

2014-01-01

419

Synthesis of environmentally friendly highly dispersed magnetite nanoparticles based on rosin cationic surfactants as thin film coatings of steel.  

PubMed

This work presents a new method to prepare monodisperse magnetite nanoparticles capping with new cationic surfactants based on rosin. Core/shell type magnetite nanoparticles were synthesized using bis-N-(3-levopimaric maleic acid adduct-2-hydroxy) propyl-triethyl ammonium chloride (LPMQA) as capping agent. Fourier transform infrared spectroscopy (FTIR) was employed to characterize the nanoparticles chemical structure. Transmittance electron microscopies (TEM) and X-ray powder diffraction (XRD) were used to examine the morphology of the modified magnetite nanoparticles. The magnetite dispersed aqueous acid solution was evaluated as an effective anticorrosion behavior of a hydrophobic surface on steel. The inhibition effect of magnetite nanoparticles on steel corrosion in 1 M HCl solution was investigated using potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS). Results obtained from both potentiodynamic polarisation and EIS measurements reveal that the magnetite nanoparticle is an effective inhibitor for the corrosion of steel in 1.0 M HCl solution. Polarization data show that magnetite nanoparticles behave as a mixed type inhibitor. The inhibition efficiencies obtained from potentiodynamic polarization and EIS methods are in good agreement. PMID:24758936

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

2014-01-01

420

Coating of magnetite with mercapto modified rice hull ash silica in a one-pot process.  

PubMed

In this research, mercapto-silica coated magnetite (Fe3O4-SiO2-SH) has been prepared in aqueous solution through a simple approach so called a one-pot process. The Fe3O4-SiO2-SH was prepared in nitrogen condition by mixing magnetite, 3-mercaptopropyltrimethoxysilane (MPTMS), and sodium silicate (Na2SiO3) solution extracted from rice hull ash, and adjusting the pH of 7.0 using hydrochloric acid. The residue was washed with deionized water, dried at 150°C and separated with an external magnetic field. In that work, the volume of MPTMS and Na2SiO3 was varied and the total amount of Si represented as silica was kept constant. Characters of the material including the functional group presence, the structure, the porosity, the morphology and stability toward various solvents were identified and evaluated. Results of characterization indicated that mercapto-silica has been coated magnetite particle with a simple one-pot process. Coating mercapto-silica on magnetite increases particle size, surface area, and chemical stability. Additionally, Fe3O4-SiO2-SH also shows high stability toward various organic solvents. The magnetic property of magnetite does not change after coating and the addition of nonmagnetic material still gives high value of maximum saturation magnetization. The presence of mercapto groups effective for interaction with heavy metal ions, the high chemical stability without removing the magnetic property promises the prospective application of Fe3O4-SiO2-SH in the future such as for separation and removal of heavy metal ions from aquatic environments. PMID:25279307

Nuryono, Nuryono; Mutia Rosiati, Nur; Rusdiarso, Bambang; Sakti, Satya Candra Wibawa; Tanaka, Shunitz

2014-01-01

421

Crystal Creations.  

ERIC Educational Resources Information Center

Presents a many-faceted learning approach to the study of crystals. Provides instructions for performing activities including crystal growth and patterns, creating miniature simulations of crystal-containing rock formations, charcoal and sponge gardens, and snowflakes. (RT)

Whipple, Nona; Whitmore, Sherry

1989-01-01

422

Bringing Planctomycetes into pure culture.  

PubMed

Planctomycetes have been known since the description of Planctomyces bekefii by Gimesi at the beginning of the twentieth century (1924), although the first axenic cultures were only obtained in the 1970s. Since then, 11 genera with 14 species have been validly named and five candidatus genera belonging to the anaerobic ammonium oxidation, anammox bacteria have also been discovered. However, Planctomycetes diversity is much broader than these numbers indicate, as shown by environmental molecular studies. In recent years, the authors have attempted to isolate and cultivate additional strains of Planctomycetes. This paper provides a summary of the isolation work that was carried out to obtain in pure culture Planctomycetes from several environmental sources. The following strains of planctomycetes have been successfully isolated: two freshwater strains from the sediments of an aquarium, which were described as a new genus and species, Aquisphaera giovannonii; several Rhodopirellula strains from the sediments of a water treatment recycling tank of a marine fish farm; and more than 140 planctomycetes from the biofilm community of macroalgae. This collection comprises several novel taxa that are being characterized and described. Improvements in the isolation methodology were made in order to optimize and enlarge the number of Planctomycetes isolated from the macroalgae. The existence of an intimate and an important relationship between planctomycetes and macroalgae reported before by molecular studies is therefore supported by culture-dependent methods. PMID:23335915

Lage, Olga M; Bondoso, Joana

2012-01-01

423

Method for solid state crystal growth  

DOEpatents

A novel method for high quality crystal growth of intermetallic clathrates is presented. The synthesis of high quality pure phase crystals has been complicated by the simultaneous formation of both clathrate type-I and clathrate type-II structures. It was found that selective, phase pure, single-crystal growth of type-I and type-II clathrates can be achieved by maintaining sufficient partial pressure of a chemical constituent during slow, controlled deprivation of the chemical constituent from the primary reactant. The chemical constituent is slowly removed from the primary reactant by the reaction of the chemical constituent vapor with a secondary reactant, spatially separated from the primary reactant, in a closed volume under uniaxial pressure and heat to form the single phase pure crystals.

Nolas, George S.; Beekman, Matthew K.

2013-04-09

424

Growth and properties of triglycine sulfate (TGS) crystals: Review  

Microsoft Academic Search

The present status of data on growth and properties of pure and doped single crystals of triglycine sulfate (TGS) is reviewed. The results of growth and characteristics of TGS crystals grown in the low-gravity environment of the space shuttle for infrared detector applications are presented. Applications of crystals in various devices are also described.

R. B. Lal; A. K. Batra

1993-01-01

425

The pure spinor formulation of superstrings  

NASA Astrophysics Data System (ADS)

In this paper we outline the construction of pure spinor superstrings. We consider both the open and closed pure spinor superstrings in critical and noncritical dimensions and on flat and curved target spaces with RR flux. We exhibit the integrability properties of pure spinor superstrings on curved backgrounds with RR fluxes. These lectures have been given at the RTN Winter School on Strings, Supergravity and Gauge Theories, CERN (2008).

Oz, Yaron

2008-11-01

426

Polarized ensembles of random pure states  

NASA Astrophysics Data System (ADS)

A new family of polarized ensembles of random pure states is presented. These ensembles are obtained by linear superposition of two random pure states with suitable distributions, and are quite manageable. We will use the obtained results for two purposes: on the one hand we will be able to derive an efficient strategy for sampling states from isopurity manifolds. On the other, we will characterize the deviation of a pure quantum state from separability under the influence of noise.

Deelan Cunden, Fabio; Facchi, Paolo; Florio, Giuseppe

2013-08-01

427

In Vitro Cell Uptake of Biocompatible Magnetite\\/Chitosan Nanoparticles with High Magnetization: A Single-Step Synthesis Approach for In-Situ-Modified Magnetite by Amino Groups of Chitosan  

Microsoft Academic Search

Current attempts for synthesizing chitosan-modified magnetite nanoparticles (CS-MNPs) as drug carrier involve use of surfactants, which brings potential cytotoxicity and decrease of saturated magnetization (Ms). To address this, we developed a facile single-step method for synthesizing CS-MNPs. The developed method offers several advantages. No surfactant was involved and the magnetite nanoparticles were in-situ-coated with a chitosan (CS) layer, which endows

Yongliang Wang; Baoqiang Li; Feng Xu; Dechang Jia; Yujie Feng; Yu Zhou

2012-01-01

428

Electrochemical discharge of nanocrystalline magnetite: structure analysis using X-ray diffraction and X-ray absorption spectroscopy.  

PubMed

Magnetite (Fe3O4) is an abundant, low cost, environmentally benign material with potential application in batteries. Recently, low temperature coprecipitation methods have enabled preparation of a series of nanocrystalline magnetite samples with a range of crystallite sizes. Electrochemical cells based on Li/Fe3O4 show a linear increase in capacity with decreasing crystallite size at voltages ?1.2 V where a 2× capacity improvement relative to commercial (26.2 nm) magnetite is observed. In this report, a combination of X-ray powder diffraction (XRD) and X-ray absorption spectroscopy (XAS) is used to measure magnetite structural changes occurring upon electrochemical reduction, with parent Fe3O4 crystallite size as a variable. Notably, XAS provides evidence of metallic iron formation at high levels of electrochemical reduction. PMID:24077019

Menard, Melissa C; Takeuchi, Kenneth J; Marschilok, Amy C; Takeuchi, Esther S

2013-11-14

429

Structure, composition and crystallinity of epitaxial magnetite thin films  

NASA Astrophysics Data System (ADS)

Epitaxially-grown Fe 3O 4(0 0 1) thin films by reactive deposition on MgO(1 0 0) substrates were studied using low-energy electron diffraction (LEED), conversion electron Mössbauer spectroscopy (CEMS), Rutherford backscattering spectrometry (RBS), channeling (RBS-C) experiments and X-ray reflectometry (XRR). No visible influence from the ion irradiation of the samples on the CEMS spectra was found, while surface oxidation of the samples was observed after exposure to the atmospheric pressure. RBS analysis indicated the presence of magnesium with an average amount of 3% in the films. RBS-C experiments yielded a value of 22% for the minimum yield of Fe and a value of 0.62° for the half-angle for Fe in the film indicating a good crystal quality of the films. The value for film-thickness obtained from XRR is in a good agreement with that from RBS and the nominal value.

Kim-Ngan, N.-T. H.; Balogh, A. G.; Meyer, J. D.; Brötz, J.; Hummelt, S.; Zaj?c, M.; ?l?zak, T.; Korecki, J.

2008-07-01

430

Study of a possible magnetite biosignature in Martian meteorite ALH84001: Implications for the biological toxicology of Mars  

NASA Astrophysics Data System (ADS)

"Why do we have such a longstanding fascination with Mars? Very simply put, it's about life. The search for life elsewhere in our Solar System has been a major driver for exploring Mars, pretty much since we began seriously looking at that planet."1 The major objective of this work is to describe signs of possible life, that is biosignatures, in rocks from Mars if indeed they are present. Biosignatures are specific identifiable properties that result from living things; they may be implanted in the environment and may persist even if the living thing is no longer present. Over 100 mineral biosignatures have been discussed in the literature; however, only one, magnetite, is addressed by this study. Magnetite is found in many rock types on earth and in meteorites. Previous studies of terrestrial magnetite have used few properties, such as size and chemical composition, to determine one of the modes of origins for magnetite (e.g., biogenic, inorganic). This study has established a rigorous set of six criteria for the identification of intracellularly precipitated biogenic magnetite. These criteria have been applied to a subpopulation of magnetites embedded within carbonates in Martian meteorite ALH84001. These magnetites are found to be chemically and physically indistinguishable from those produced by magnetotactic bacteria strain MV-1, hence, they were likely formed by biogenic processes on ancient Mars. These criteria may be also used to distinguish origins for magnetites from terrestrial samples with complex or unknown histories. The presence of purported past life on early Mars suggests that, if life once began it may still exist today, possibly in oases in the Martian subsurface. Future manned missions should consider potential hazards of an extant biological environment(s) on Mars. 1 Quote attributed to Jack Farmer of Arizona State University in discussing NASA's program of Mars Exploration (see "Deciphering Mars: Follow the Water," Astrobiology Magazine Sept. 12, 2005)

Thomas-Keprta, Kathie Louise

431

Magnetoresistance Enhancement Of Half-metal Magnetite (Fe3O4) Thin Film On SiO2Glass Substrate  

Microsoft Academic Search

We present the magneto-resistance study of magnetite thin film on SiO2-glass substrate prepared by RF-magnetron sputtering method, as functions of magnetic field, temperature and film thickness. The magneto- and electrical-resistance, SEM, AFM, XRD and magnetization measurements have been performed. We have found that the magnetite thin film deposited by the RF-magnetron sputtering consists of nano-sized grains and the magneto-resistance of

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

2008-01-01