scholarly journals Controlled cobalt doping in biogenic magnetite nanoparticles

2013 ◽  
Vol 10 (83) ◽  
pp. 20130134 ◽  
Author(s):  
J. M. Byrne ◽  
V. S. Coker ◽  
S. Moise ◽  
P. L. Wincott ◽  
D. J. Vaughan ◽  
...  
Keyword(s):  
Quantum Interference ◽  
Magnetic Circular Dichroism ◽  
Cobalt Content ◽  
Microbial Reduction ◽  
Geobacter Sulfurreducens ◽  
Cobalt Doping ◽  
Effective Anisotropy ◽  
Cobalt Iron ◽  
Potential Use ◽  
Ferrite Spinel

Cobalt-doped magnetite (Co x Fe 3 − x O 4 ) 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.

scholarly journals Bacterial production of vanadium ferrite spinel (Fe,V)3O4 nanoparticles

2020 ◽  
Vol 84 (4) ◽  
pp. 554-562
Author(s):  
Victoria S Coker ◽  
Gerrit van der Laan ◽  
Neil D Telling ◽  
Jonathan R Lloyd ◽  
James M Byrne ◽  
...  
Keyword(s):  
Absorption Spectra ◽  
Magnetite Nanoparticles ◽  
Bacterial Production ◽  
Magnetic Circular Dichroism ◽  
Microbial Reduction ◽  
Geobacter Sulfurreducens ◽  
X Ray ◽  
Redox Boundary ◽  
X Ray Absorption ◽  
Ferrite Spinel

AbstractBiogenic nanoscale vanadium magnetite is produced by converting V(V)-bearing ferrihydrites through reductive transformation using the metal-reducing bacterium Geobacter sulfurreducens. With increasing vanadium in the ferrihydrite, the amount of V-doped magnetite produced decreased due to V-toxicity which interrupted the reduction pathway ferrihydrite–magnetite, resulting in siderite or goethite formation. Fe L2,3 and V L2,3 X-ray absorption spectra and data from X-ray magnetic circular dichroism analysis revealed the magnetite to contain the V in the Fe(III) Oh site, predominately as V(III) but always with a component of V(VI), present a consistent V(IV)/V(III) ratio in the range 0.28 to 0.33. The bacteriogenic production of V-doped magnetite nanoparticles from V-doped ferrihydrite is confirmed and the work reveals that microbial reduction of contaminant V(V) to V(III)/V(IV) in the environment will occur below the Fe-redox boundary where it will be immobilised in biomagnetite nanoparticles.

scholarly journals Magnetic spectroscopy of nanoparticulate greigite, Fe3S4

2017 ◽  
Vol 81 (4) ◽  
pp. 857-872 ◽  
Author(s):  
Richard A. D. Pattrick ◽  
Victoria S. Coker ◽  
Masood Akhtar ◽  
M. Azad Malik ◽  
Edward Lewis ◽  
...  
Keyword(s):  
Absorption Spectra ◽  
Oxidation State ◽  
Magnetic Circular Dichroism ◽  
Covalent Character ◽  
X Ray ◽  
Positive Feature ◽  
A Site ◽  
Intermediate Oxidation ◽  
X Ray Absorption ◽  
Ferrite Spinel

AbstractSynthesis of Ni and Zn substituted nano-greigite, Fe3S4, is achieved from single source diethyldithiocarbamato precursor compounds, producing particles typically 50–100 nm in diameter with plate-like pseudohexagonal morphologies. Up to 12 wt.% Ni is incorporated into the greigite structure, and there is evidence that Zn is also incorporated but Co is not substituted into the lattice. The FeL3X-ray absorption spectra for these materials have a narrow single peak at 707.7 eV and the resulting main X-ray magnetic circular dichroism (XMCD) has the same sign at 708.75 eV. All XMCD spectra also have a broad positive feature at 711 eV, a characteristic of covalent mixing. The greigite XMCD spectra contrast with the three clearly defined XMCD site specific peaks found in the ferrite spinel, magnetite. The FeL2,3X-ray absorption spectra and XMCD spectra of the greigite reflect and reveal the high conductivity of greigite and the very strong covalency of the Fe–S bonding. The electron hopping between Fe3+and Fe2+on octahedral sites results in an intermediate oxidation state of the Fe in the Ohsite of Fe2.5+producing an effective formula of [Fe3+↑]A-site[2Fe2.5+↓]B-siteS42–]. The NiL2,3X-ray absorption spectra and XMCD reveal substitution on the Ohsite with a strongly covalent character and an oxidation state <Ni1.5+in a representative formula [Fe3+↑]A[[(2 – x)Fe2.5+↓][Nix1.5+]]BS42–.

scholarly journals Nanosized Iron Oxide Colloids Strongly Enhance Microbial Iron Reduction

2009 ◽  
Vol 76 (1) ◽  
pp. 184-189 ◽  
Author(s):  
Julian Bosch ◽  
Katja Heister ◽  
Thilo Hofmann ◽  
Rainer U. Meckenstock
Keyword(s):  
Iron Oxide ◽  
Iron Oxides ◽  
Iron Reduction ◽  
Colloidal Suspension ◽  
Microbial Reduction ◽  
Geobacter Sulfurreducens ◽  
Hydrodynamic Diameter ◽  
Colloidal Iron ◽  
Surface Areas ◽  
Microbial Iron Reduction

ABSTRACT Microbial iron reduction is considered to be a significant subsurface process. The rate-limiting bioavailability of the insoluble iron oxyhydroxides, however, is a topic for debate. Surface area and mineral structure are recognized as crucial parameters for microbial reduction rates of bulk, macroaggregate iron minerals. However, a significant fraction of iron oxide minerals in the subsurface is supposed to be present as nanosized colloids. We therefore studied the role of colloidal iron oxides in microbial iron reduction. In batch growth experiments with Geobacter sulfurreducens, colloids of ferrihydrite (hydrodynamic diameter, 336 nm), hematite (123 nm), goethite (157 nm), and akaganeite (64 nm) were added as electron acceptors. The colloidal iron oxides were reduced up to 2 orders of magnitude more rapidly (up to 1,255 pmol h− 1 cell− 1) than bulk macroaggregates of the same iron phases (6 to 70 pmol h− 1 cell− 1). The increased reactivity was not only due to the large surface areas of the colloidal aggregates but also was due to a higher reactivity per unit surface. We hypothesize that this can be attributed to the high bioavailability of the nanosized aggregates and their colloidal suspension. Furthermore, a strong enhancement of reduction rates of bulk ferrihydrite was observed when nanosized ferrihydrite aggregates were added.

scholarly journals Microbial Reduction of Fe(III) under Alkaline Conditions Relevant to Geological Disposal

2013 ◽  
Vol 79 (11) ◽  
pp. 3320-3326 ◽  
Author(s):  
Adam J. Williamson ◽  
Katherine Morris ◽  
Sam Shaw ◽  
James M. Byrne ◽  
Christopher Boothman ◽  
...  
Keyword(s):  
Magnetic Circular Dichroism ◽  
Microbial Reduction ◽  
Geological Disposal ◽  
X Ray ◽  
Electron Shuttles ◽  
Disposal Facility ◽  
Transmission Electron ◽  
Alkaline Conditions ◽  
Set Up ◽  
Final Extent

ABSTRACTTo determine whether biologically mediated Fe(III) reduction is possible under alkaline conditions in systems of relevance to geological disposal of radioactive wastes, a series of microcosm experiments was set up using hyperalkaline sediments (pH ∼11.8) surrounding a legacy lime working site in Buxton, United Kingdom. The microcosms were incubated for 28 days and held at pH 10. There was clear evidence for anoxic microbial activity, with consumption of lactate (added as an electron donor) concomitant with the reduction of Fe(III) as ferrihydrite (added as the electron acceptor). The products of microbial Fe(III) reduction were black and magnetic, and a range of analyses, including X-ray diffraction, transmission electron microscopy, X-ray absorption spectroscopy, and X-ray magnetic circular dichroism confirmed the extensive formation of biomagnetite in this system. The addition of soluble exogenous and endogenous electron shuttles such as the humic analogue anthraquinone-2,6-disulfonate and riboflavin increased both the initial rate and the final extent of Fe(III) reduction in comparison to the nonamended experiments. In addition, a soluble humic acid (Aldrich) also increased both the rate and the extent of Fe(III) reduction. These results show that microbial Fe(III) reduction can occur in conditions relevant to a geological disposal facility containing cement-based wasteforms that has evolved into a high pH environment over prolonged periods of time (>100,000 years). The potential impact of such processes on the biogeochemistry of a geological disposal facility is discussed, including possible coupling to the redox conditions and solubility of key radionuclides.

scholarly journals Room-temperature intrinsic ferromagnetism in epitaxial CrTe2 ultrathin films

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Xiaoqian Zhang ◽  
Qiangsheng Lu ◽  
Wenqing Liu ◽  
Wei Niu ◽  
Jiabao Sun ◽  
...  
Keyword(s):  
Quantum Interference ◽  
Large Scale ◽  
Room Temperature ◽  
Magnetic Circular Dichroism ◽  
Room Temperature Ferromagnetism ◽  
Perpendicular Magnetic Anisotropy ◽  
Interlayer Coupling ◽  
Angle Resolved Photoemission Spectroscopy ◽  
Device Applications ◽  
Intrinsic Ferromagnetism

AbstractWhile the discovery of two-dimensional (2D) magnets opens the door for fundamental physics and next-generation spintronics, it is technically challenging to achieve the room-temperature ferromagnetic (FM) order in a way compatible with potential device applications. Here, we report the growth and properties of single- and few-layer CrTe2, a van der Waals (vdW) material, on bilayer graphene by molecular beam epitaxy (MBE). Intrinsic ferromagnetism with a Curie temperature (TC) up to 300 K, an atomic magnetic moment of ~0.21 $${\mu }_{{\rm{B}}}$$ μ B /Cr and perpendicular magnetic anisotropy (PMA) constant (Ku) of 4.89 × 105 erg/cm3 at room temperature in these few-monolayer films have been unambiguously evidenced by superconducting quantum interference device and X-ray magnetic circular dichroism. This intrinsic ferromagnetism has also been identified by the splitting of majority and minority band dispersions with ~0.2 eV at Г point using angle-resolved photoemission spectroscopy. The FM order is preserved with the film thickness down to a monolayer (TC ~ 200 K), benefiting from the strong PMA and weak interlayer coupling. The successful MBE growth of 2D FM CrTe2 films with room-temperature ferromagnetism opens a new avenue for developing large-scale 2D magnet-based spintronics devices.

scholarly journals Structural, Magnetic and Mechanical Properties of Nd16 (Fe76−xCox)B8 0 ≤ x ≤ 25 Alloys

2020 ◽  
Vol 10 (16) ◽  
pp. 5656
Author(s):  
Juan Sebastián Trujillo Hernández ◽  
Ahmed Talaat ◽  
Jesús Tabares ◽  
Dagoberto Oyola Lozano ◽  
Humberto Bustos Rodríguez ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Cobalt Content ◽  
Magnetic Behavior ◽  
Ferromagnetic Behavior ◽  
General Tendency ◽  
Cobalt Doping ◽  
X Ray Diffraction ◽  
Soft Magnetic ◽  
Magnetically Hard ◽  
Hard Magnetic Properties

In this work, the structural, magnetic and mechanical properties of Nd16Fe76−xCoxB8 alloys with a varying Co content of x = 0, 10, 20 and 25 were experimentally investigated by X-ray diffraction (XRD), Mössbauer spectrometry (MS) and vibrating sample magnetometry (VSM) at room temperature (RT), and microhardness tests were performed. The system presented hard Nd2Fe14B and the Nd1.1Fe4B4 phases for samples with x = 0; when the concentration increased to x = 20 and 25, the CoO phase appeared. All MS data showed ferromagnetic behavior (eight sextets: sites 16k1, 16k2, 8j1, 8j2, 4c, 4e, sb) associated with the hard and soft magnetic phases, and one paramagnetic component (doublet: site d) associated with the minority Nd1.1Fe4B4 phase, which was not identified by XRD. All samples were magnetically hard and presented hard magnetic behavior. The increase of Co content in these samples did not improve the hard magnetic properties but increased the critical temperature of the system and decreased the crystallite size of the hard phase. There was a general tendency towards increased microhardness with cobalt content that was attributable to cobalt doping, which reduces the lattice parameters and porosities within the sample, improving its hardness.

MICROSTRUCTURAL EVALUATION OF NANOCRYSTALLINE COBALT-IRON-NICKEL THIN FILMS ELECTRODEPOSITED FROM CITRATE-FREE AND CITRATE-ADDED BATHS

2012 ◽  
Vol 05 ◽  
pp. 712-719
Author(s):  
SAEED MEHRIZI ◽  
M. HYDARZADEH SOHI ◽  
S. A. SEYYED EBRAHIMI
Keyword(s):  
Thin Films ◽  
Sodium Citrate ◽  
Cobalt Content ◽  
Film Composition ◽  
Nickel Thin Films ◽  
Morphological Studies ◽  
Cobalt Iron ◽  
Microstructural Evaluation ◽  
Iron Nickel ◽  
Scherrer Formula

The microstructures of nanocrystalline CoFeNi thin films in direct current electrodeposition, under various processing conditions, have comparatively been investigated. Morphological studies by SEM showed that CoFeNi films plated from the sodium citrate-added baths were more uniform and denser than those deposited from the conventional citrate-free baths. Energy dispersive spectroscopy (EDS) showed the anomalous behaviors in electrodeposition of CoFeNi films from both citrate-added and citrate-free baths. It was also noticed that addition of 10g/L sodium citrate in the bath strongly decreases the iron content and increases nickel contents of the deposit. Addition of citrate up to 50g/L in the bath has reverse effect on the film composition. Further addition of sodium citrate appears to have no or little effect on the film composition. Addition of sodium citrate to the bath has no significant affect on the cobalt content of the deposit. XRD analyses showed that all CoFeNi films were nanocrystalline and their average grain sizes, estimated by Scherrer formula, were below 80nm. It was also noticed that FCC and BCC phases could be co-deposited in electroplated CoFeNi films by controlling the bath composition and/or the plating conditions.

Anisotropy Enhancement in Co Granular Multilayers by Capping

2008 ◽  
Vol 570 ◽  
pp. 1-9 ◽  
Author(s):  
Juan Bartolomé ◽  
F. Luis ◽  
L.M. García ◽  
F. Bartolomé ◽  
F. Petroff ◽  
...  
Keyword(s):  
Thin Films ◽  
Circular Dichroism ◽  
Magnetic Circular Dichroism ◽  
Magnetic Surface ◽  
Surface Anisotropy ◽  
Dominant Contribution ◽  
Effective Anisotropy ◽  
X Ray ◽  
Co Nanoparticles ◽  
Circular Dichroïsm

The effect of capping with Cu, Au and Pt of an array of Co nanoparticles is revised. The magnetic surface anisotropy KS was found to be the dominant contribution to the effective anisotropy Keff of the particles. Recent X-ray Magnetic Circular Dichroism (XMCD) measurements show that there is hybridization between the 3d Co electrons and the d and 4p electrons of the capping metal. By comparison to the mechanisms which give rise to the surface anisotropy in thin films, it is argued that this hybridization governs the modification of KS, and hence, of Keff.

scholarly journals Structural, Magnetic, and Mechanical Properties of Nd16(Fe76-xCox)B8 0 ≤ x ≤ 25 Alloys

2020 ◽  
Author(s):  
Juan Sebastián Trujillo Hernández ◽  
Ahmed Talaat ◽  
Jesus A. Tabares ◽  
Dagoberto Oyola Lozano ◽  
Humberto Bustos Rodriguez ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Cobalt Content ◽  
Magnetic Behavior ◽  
Ferromagnetic Behavior ◽  
General Tendency ◽  
Cobalt Doping ◽  
X Ray Diffraction ◽  
Soft Magnetic ◽  
X Ray ◽  
Magnetically Hard

In this work, the structural, magnetic, and mechanical properties of Nd16Fe76-xCoxB8 alloys varying the Co content at x = 0, 10, 20 and 25, were experimentally investigated by X-Ray Diffraction (XRD), M&ouml;ssbauer Spectrometry (MS), Vibrating Sample Magnetometry (VSM) at room temperature (RT), and microhardness test were performed too. The system presents the hard Nd2Fe14B and the Nd1.1Fe4B4 phases for samples with x = 0 and 10. When concentration increases to x= 20 and 25, the CoO phase appears. All MS show the ferromagnetic behavior (eight sextets: sites 16k1, 16k2, 8j1, 8j2, 4c, 4e, sb) associated to the hard and soft magnetic phases, and one paramagnetic component (doublet: site d) associated to the minority Nd1.1Fe4B4 phase, which was not identified by XRD. All samples are magnetically hard present a hard magnetic behavior. The increase of Co content in these samples did not improve the hard magnetic behavior, but increased the critical temperature of the system and decrease the crystallite size of the hard phase. The hysteresis loop showed that predominates the Nd2Fe14B hard magnetic phase. There is a general tendency to increase microhardness with cobalt content, attributable to cobalt doping reduces the lattice parameters and porosities in the sample improving it hardness.

Sign in / Sign up

Export Citation Format

Share Document