Showing papers on "Magnetite published in 2001"

Biogenic Magnetite Formation through Anaerobic Biooxidation of Fe(II)

Abstract: 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.

Synthesis and Characterization of Spherical Magnetite/Biodegradable Polymer Composite Particles

Abstract: A method for preparing colloidal particles formed by a magnetite nucleus and a biodegradable poly(DL-lactide) polymer coating is first described. The method is based on the so-called double-emulsion technique, employed to obtain polymeric spheres loaded with therapeutic drugs, to be used as drug delivery vectors. The aim of this work was to obtain, in a reproducible and rather simple way, colloidal particles that were both magnetic field responsive, and useful as drug delivery systems. In order to investigate to what extent is this target achieved, we compare the structure, chemical composition, and surface properties of the composite particles with those of the nucleus and the coating material. Although the surface properties of the magnetite core are not completely masked, this preliminary study shows that the synthetic new material displays a behavior intermediate between that of magnetite and poly(DL-lactide) spheres. Thus, electrophoresis measurements as a function of pH shows that the isoelectric point (pH(iep)=5.2) of core/shell colloids is in between those of magnetite (pH(iep)=7) and polymer (pH(iep)<2). A similar conclusion is reached when a surface thermodynamic study is performed on the three types of particles: the electron-donor component of the surface free energy of the solids is the quantity that appears to be most sensitive to the surface composition. The fact that poly(DL-lactide) is close to being a nonpolar material gives rise to a measurable decrease in the electron-donor component of the surface free energy, although the effect of coating is also observable in the electron-acceptor and the apolar van der Waals component. Copyright 2001 Academic Press.

Synthesis of Fe3O4 nanoparticles from emulsions

Abstract: A unique oil-in-water emulsion route has been devised to synthesize nanosized magnetite (Fe3O4) particles using a small amount of cyclohexane as the oil phase, NP5 + NP9 as the surfactant phase, and a Fe(II)/Fe(III) salt solution as the aqueous phase. The Fe3O4 powder thus derived from the emulsion containing 88 wt% 0.3 M FeSO4 + Fe(NO3)3 in the aqueous phase possesses an equiaxial morphology and an average particle size of <10 nm. Studies on the electrical conductivity of the emulsions as a function of Fe2+/Fe3+ concentration in the aqueous phase revealed the complexation effect of the NP5 + NP9 surfactant towards Fe2+/Fe3+ ions. The resulting particle size and morphology are therefore dependent on the amounts of surfactant and aqueous phase in the emulsion. A strongly alkaline aqueous phase favors the formation of Fe3O4, while a low alkalinity favors the formation of α-FeOOH. Magnetic property measurements and Mossbauer spectroscopic studies indicate that the emulsion-derived iron oxide powder is superparamagnetic, which becomes ferrimagnetic with decreasing measurement temperature.

The continuous hydrothermal synthesis of nano-particulate ferrites in near critical and supercritical water

Abstract: Magnetic spinel type oxides such as magnetite, Fe3O4, cobalt, nickel, and zinc ferrites, MFe2O4 (M = Co, Ni, Zn) and the mixed nickel and cobalt ferrite, NixCo1 − xFe2O4 have been synthesised continuously by the hydrolysis and simultaneous oxidation of mixtures of Fe(II) acetate and different M(II) acetates in near-critical and supercritical water using a flow reactor. The materials have been characterised by powder X-ray diffraction (PXD) and, in selected cases, by transmission electron microscopy (TEM). The bulk composition of the samples was determined by Atomic Absorption analysis (AA). Additionally, Energy-dispersive Detection X-ray analysis (EDX) was carried out on some of the samples. TEM pictures showed a “bimodal” particle size distribution: small particles of ca. 10 nm and larger particles of up to 100 nm, both of which are highly crystalline. Possible reaction mechanisms are discussed, which may be responsible for the observed morphology. The effects of temperature and residence time on the reaction have been studied.

Bulk and surface phases of iron oxides in an oxygen and water atmosphere at low pressure

Abstract: Thermodynamic stability ranges of different iron oxides were calculated as a function of the ambient oxygen or water gas phase pressure (p⩽1 bar) and temperature by use of the computer program EquiTherm. The phase diagram for Fe–H2O is almost completely determined by the O2 pressure due to the H2O dissociation equilibrium. The formation of epitaxially grown iron oxide films on platinum and ruthenium substrates agrees very well with the calculated phase diagrams. Thin films exhibit the advantage over single crystals that bulk diffusion has only limited influence on the establishment of equilibrium phases. Near the phase boundary Fe3O4–Fe2O3, surface structures are observed consisting of biphase ordered domains of FeO(111) on both oxides. They are formed due to kinetic effects in the course of the oxidation to hematite or reduction to magnetite, respectively. Annealing a Fe3O4(111) film in 5 × 10−5 mbar oxygen at 920–1000 K results in a new γ-Fe2O3(111)-like intermediate surface phase during the oxidation to α-Fe2O3(0001). A model is suggested for the growth of iron oxides and for redox processes involving iron oxides. The formation of several equilibrium surface phases is discussed.

Fabrication of magnetite nanorods by ultrasound irradiation

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

A simple inorganic process for formation of carbonates, magnetite, and sulfides in Martian meteorite ALH84001

Abstract: We show experimental evidence that the zoned Mg-Fe-Ca carbonates, magnetite, and Fe sulfides in Martian meteorite ALH84001 may have formed by simple, inorganic processes. Chemically zoned carbonate globules and Fe sulfides were rapidly precipitated under low-temperature (150 °C), hydrothermal, and non-equilibrium conditions from multiple fluxes of Ca-Mg-Fe-CO2-S-H2O solutions that have different compositions. Chemically pure, single-domain, defect-free magnetite crystals were formed by subsequent decomposition of previously precipitated Fe-rich carbonates by brief heating to 470 °C. The sequence of hydrothermal precipitation of carbonates from flowing CO2-rich waters followed by a transient thermal event provides an inorganic explanation for the formation of the carbonate globules, magnetite, and Fe sulfides in ALH84001. In separate experiments, kinetically controlled 13C enrichment was observed in synthetic carbonates that is similar in magnitude to the 13C enrichment in ALH84001 carbonates.

Adsorption of Cesium, Strontium, and Cobalt Ions on Magnetite and a Magnetite−Silica Composite

Abstract: Constant pH adsorption isotherms for nonradioactive Cs+, Sr2+, and Co2+ on pure magnetite and a 80% (w/w) magnetite−silica composite were measured at 25 °C over a wide range of metal ion concentrations. The adsorption studies were carried out at four different pH's: 6, 7, 8, and 9 for Cs+ and Sr2+ and 5, 6, 7, and 8 for Co2+. All of the constant pH isotherms exhibited type I behavior with a saturation capacity that was pH-dependent and increased with increasing pH. The corresponding distribution coefficients increased with increasing pH but decreased with increasing metal ion concentration; they were also 10−1000 times lower than those reported in the literature for more selective but more expensive adsorbents. These two magnetite-based adsorbents also exhibited moderate regeneration conditions, with nearly 90−100% regeneration achieved in most cases at pH values between 1 and 3. A Langmuir model with pH-dependent parameters was also fitted successfully to all of the constant pH adsorption isotherms. Thi...

Oxide-Scale Structures Formed on Commercial Hot-Rolled Steel Strip and Their Formation Mechanisms

Abstract: The oxide-scale structure developed on commercial hot-rolled steel strip at the mid-coil position was examined. The initial oxide scale after rolling and cooling on the run-out table had a three-layer (hematite, magnetite, and wustite) structure; the thickness was found to be a function of the finishing temperature. From this initial structure, various final scale structures developed after coiling, depending on the coiling temperature, oxygen availability, and cooling rate. For relatively low coiling temperatures (e.g., at 520°C), the final scale structure comprised an inner magnetite/iron mixture layer, an outer magnetite layer, and, at regions away from the center, a very thin outermost hematite layer. For higher coiling temperatures (e.g., in the range of 610 to 720°C), a two-layer hematite/magnetite structure was observed at the edge regions, whereas at the center regions, these two layers were absent and the entire scale layer comprised a mixture of the wustite-transformation products, i.e., a mixture of proeutectoid magnetite, magnetite+iron eutectoid, and a certain amount of retained wustite. At regions between the edges and the center, the oxide structures were similar to those developed at low coiling temperatures (<570°C), i.e., an inner layer comprising a mixture of the wustite-transformation products, an intermediate magnetite layer and at regions near the edges, an outermost hematite layer. In addition, two distinct structures were observed on strips with a coiling temperature of 720°C. One structure comprised a very thick hematite layer (3–5 μm) formed near the edges (within 10–20 mm from the edges), while the other structure comprised a substantial amount of retained wustite formed at the center regions. The formation mechanisms of various oxide scale structures are discussed.

Crystallization phenomena in iron-rich glasses

Abstract: In this study, results of the crystallization of iron-rich glasses are summarized. Thermogravimetry (TG)–differential thermal analysis (DTA) were utilized to explain the phase formations and the surface oxidation of FeO to yield Fe2O3. The crystal phases fraction was evaluated utilizing X-ray diffraction analysis (XRD). Low angle XRD technique was used to investigate the distribution of the crystal phases on the surface and in the bulk as a function of the heat treatment. Transmission electron microscopy (TEM) was employed to detect the evolution of the crystalline structure and to determine the variation of the residual glass composition. The crystallization kinetics were investigated in isothermal conditions by measuring the variation of the density. The activation energy of crystal growth was calculated using isothermal and non-isothermal methodologies. The values of 377 and 298 kJ/mol were obtained for the temperature ranges 620–660°C and 720–780°C, respectively. Similar values, 368 and 321 kJ/mol, were estimated for the energy of viscous flow in the same temperature ranges. The results indicate that magnetite and pyroxene are the main crystal phases and that the kinetics of pyroxene formation can be explained as growth on a fixed number of magnetite nuclei. In powder samples, heat-treated in air, the crystallization is inhibited by the surface oxidation of Fe2+ to yield Fe3+ and a layer of haematite is formed on the surface.

The dry oxidation of tetragonal FeS 1- x mackinawite

Abstract: The gradual oxidation of dry mackinawite (tetragonal FeS1− x ) has been studied using X-ray diffraction (XRD), transmission electron microscopy (TEM), transmission Mossbauer spectroscopy (TMS) and X-ray photoelectron spectroscopy (XPS). The initial material and samples exposed to the air (5 min to 6 months) have been analysed. Diffraction patterns showed the slow disappearance of mackinawite with time with concomitant appearance of greigite (Fe3S4) and elemental sulphur (S(0)) as well as iron (oxyhydr)oxides, i.e. magnetite (Fe3O4) and probably goethite (α-FeOOH). After 6 months' air exposure, mackinawite and also greigite were entirely converted into elemental sulphur and iron (oxyhydr)oxide(s), indicating that greigite was an intermediate reaction product. Mossbauer spectra of samples oxidized in air appeared rather complex for interpreting what was easily conceivable in view of the association of several phases, as revealed by the diffraction patterns. The low-temperature Mossbauer spectrum obtained after 6 months air exposure was attributed to magnetite, although a mixture of magnetite and goethite was not completely excluded. XPS iron and oxygen data confirmed the formation of Fe(III) (oxyhydr)oxides at the surface after an induction period. Sulphur spectra demonstrated various oxidation states from S(-II) (monosulphide) to S(VI) (sulphate) for the longest experiments. Mackinawite in these experiments reacted mainly with adsorbed O2 to form elemental sulphur and magnetite. Additionally, sufficient sulphur was generated to react stoichiometrically with mackinawite to produce greigite. Finally, greigite, in the longest experiments, was transformed into elemental sulphur and magnetite.

Coercivity analysis of magnetic phases in sapropel S1 related to variations in redox conditions, including an investigation of the S ratio

Abstract: [1] Abstract: The most recent sapropel (S1) in the eastern Mediterranean has been extensively investigated with geochemical and rock-magnetic techniques. Different redox conditions prevailed in different zones of the sediment through time. The oxidized sapropel zone is particularly interesting, because earlier studies indicated that new magnetic material was formed, including possible magnetosomes. Here we utilize component analyses of isothermal remanent magnetization (IRM) acquisition curves and the analysis of first-order reversal curves (FORC) to further investigate the magnetic mineralogy. In the entire box core ABC26, the original input of eolian dust consisted of both magnetite and hematite. In the oxidized sapropel and in the active oxidation zone, an additional magnetite component is present. This magnetite component has a higher coercivity than the eolian magnetite and a very small coercivity dispersion, suggesting a narrow grain size distribution. This is a strong indication that magnetosomes, which are formed in the active oxidation zone, are the magnetic carriers of this coercivity fraction. FORC diagrams support these findings. The S ratio is forwardly modeled for mixed magnetic mineralogies with varying coercivity distributions to explain the down core S ratio behavior: close to 1 in the top sediment and in the oxidized sapropel, a drop in values in the active oxidation zone, and again close to 1 in the (syn)sapropel. The observed S ratio pattern in the oxidized sapropel and in the active oxidation zone can be explained by the recovered IRM components. Whereas both oxidized sapropel and active oxidation zone contain the extra magnetite component, their S ratios are different because of the differences in coercivity characteristics (coercivity and dispersion) of the two magnetites in these zones. Thus, in these zones the S ratio does not reflect variations in the relative contributions of hematite to magnetite but variations in the characteristics of the individual magnetite assemblages. Also in the rest of the core, the S ratio depends on the coercivity characteristics of the magnetite component rather than on the relative contributions of high- versus low-coercivity minerals. The S ratio thus appears to be an unsuitable parameter to describe variations in the magnetic mineralogy, especially when more than two components are present. Therefore the classical interpretation of the S ratio should be treated with caution.

Phyllosilicate-poor palagonitic dust from Mauna Kea Volcano (Hawaii): A mineralogical analogue for magnetic Martian dust?

Abstract: The mineralogical and elemental composition of dust size fractions (<2 and <5 μm) of eight samples of phyllosilicate-poor palagonitic tephra from the upper slopes of Mauna Kea Volcano (Hawaii) were studied by X-ray diffraction (XRD), X-ray fluorescence (XRF), visible and near-IR reflectance spectroscopy, Mossbauer spectroscopy, magnetic properties methods, and transmission electron microscopy (TEM). The palagonitic dust samples are spectral analogues of Martian bright regions at visible and near-IR wavelengths. The crystalline phases in the palagonitic dust are, in variable proportions, plagioclase feldspar, Ti-containing magnetite, minor pyroxene, and trace hematite. No basal reflections resulting from crystalline phyllosilicates were detected in XRD data. Weak, broad XRD peaks corresponding to X-ray amorphous phases (allophane, nanophase ferric oxide (possibly ferrihydrite), and, for two samples, hisingerite) were detected as oxidative alteration products of the glass; residual unaltered glass was also present. Mossbauer spectroscopy showed that the iron-bearing phases are nanophase ferric oxide, magnetite/titanomagnetite, hematite, and minor glass and ferrous silicates. Direct observation by TEM showed that the crystalline and X-ray amorphous phases observed by XRD and Mossbauer are normally present together in composite particles and not normally present as discrete single-phase particles. Ti-bearing magnetite occurs predominantly as 5–150 nm particles embedded in noncrystalline matrix material and most likely formed by crystallization from silicate liquids under conditions of rapid cooling during eruption and deposition of glassy tephra and prior to palagonitization of glass. Rare spheroidal halloysite was observed in the two samples that also had XRD evidence for hisingerite. The saturation magnetization Js and low-field magnetic susceptibility for bulk dust range from 0.19 to 0.68 Am2/kg and 3.4×10−6 to 15.5×10−6 m3/kg at 293 K, respectively. Simulation of the Mars Pathfinder Magnet Array (MA) experiment was performed on Mauna Kea Volcano in areas with phyllosilicate-poor palagonitic dust and with copies of the Pathfinder MA. On the basis of the magnetic properties of dust collected by all five MA magnets and the observation that the Pathfinder MAs collected dust on the four strongest magnets, the value for the saturation magnetization of Martian dust collected in the MA experiments is revised downward from 4±2 Am2/kg to 2.5±1.5 Am2/kg. The revised value corresponds to 2.7±1.6 wt % magnetite if the magnetic mineral is magnetite (using Js = 92 Am2/kg for pure magnetite, Fe3O4) or to 5.0±3.0 to 3.4±2.0 wt % maghemite if the magnetic mineral is pure maghemite (using Js = 50 to 74 Am2/kg for pure maghemite, γ-Fe2O3). Comparison of the magnetic properties of bulk Mauna Kea palagonitic dust to those for dust collected by MA magnets shows that the MA magnets extracted (culled) a subset (25–34 wt %) of composite magnetic particles from bulk dust. The extent of culling of Martian dust is not well constrained. Because the Mauna Kea palagonitic dust satisfies the essential constraints of the Pathfinder magnetic properties experiment (composite and magnetic particles capable of being collected by five MA magnets), a working hypothesis for the strongly magnetic mineral present in Martian dust and soil is magnetite (possibly Ti-bearing) formed by rapid crystallization from silicate liquids having volcanic and/or impact origins. Subsequent palagonitization of the glass produces the nanophase ferric oxide phases that dominate the spectral properties of Martian bright regions at visible and near-IR wavelengths. Magnetic and phyllosilicate-poor palagonitic dust from Mauna Kea Volcano is thus a spectral and magnetic analogue for magnetic Martian dust.

Chains of Magnetite Crystals in the Meteorite ALH84001: Evidence of Biological Origin

Abstract: The presence of magnetite crystal chains, missing evidence for their biological origin, as well as five morphological characteristics incompatible with a nonbiological origin are demonstrated by high-power stereo backscattered scanning electron microscopy. Additional information is contained in the original extended abstract.

Polydisperse fractal aggregate formation in clay mineral and iron oxide suspensions, pH and ionic strength dependence

Abstract: pH- and ionic-strength-dependent aggregation of permanently and conditionally charged clay mineral (montmorillonite) and iron oxide (magnetite) particles was investigated by means of dynamic light scattering and rheology. An indifferent electrolyte (NaCl) was used. The surface charging of solids was determined by acid–base titration. The point of zero charge (PZC) of magnetite seemed to be at pH 8.0 ± 0.1. The permanent negative charges on the basal plane of montmorillonite influence the interfacial distribution of H+ and Na+ ions. The pH dependence of the electrophoretic mobility showed directly the dominance of negative charges on montmorillonite lamellae independently of pH, while for magnetite the sign of the mobility reversed at pH ˜ 8.0. Montmorillonite particles formed stable suspensions; coagulation did not take place below 35 mM 1:1 electrolyte independently of pH. The aggregation of magnetite sol becomes significant near the pH of the PZC even at low ionic strength. Colloidal stability in composite systems was investigated at pH ˜ 4, where oxide and clay mineral particles are oppositely charged. At the lowest NaCl concentrations (1, 5 mM) the mixed systems remained stable and aggregation of oppositely charged particles could not be observed at all. Heterocoagulation of dissimilar particles needed a definite amount of dissolved electrolytes (about 8 mM). Mixed clay mineral and oxide systems are more sensitive to electrolyte under acidic conditions than those separately. Rheological investigation of the mixed clay mineral–oxide suspensions at pH ˜ 4 provided proof for the absence of attractive particle interaction at low ionic strength (2 mM). A physical network of oppositely charged particles could form only at higher salt concentration, for example, in the presence of 10 mM NaCl. The yield value of plastic systems showed a significant maximum at 1:15 magnetite/montmorillonite mass ratio.

Aeromagnetic anomalies, magnetic petrology, and rock magnetism of hemo-ilmenite- and magnetite-rich cumulate rocks from the Sokndal Region, South Rogaland, Norway

Abstract: Aeromagnetic maps of the Egersund Mid-Proterozoic igneous province show a spectacular range of positive and negative magnetic anomalies with a contrast up to 15 600 nT. The positive magnetic anomalies are over magnetite norites and overlying mangerites and quartz mangerites of the Bjerkreim-Sokndal layered intrusion. These rocks are dominated by multi-domain (MD) magnetite. The negative magnetic anomalies are over ilmenite-rich norites of the Bjerkreim-Sokndal layered intrusion, the Tellnes ilmenite norite ore deposit, and massif anorthosites. These rocks are dominated by hemo-ilmenite and/or by silicates containing fine-grained oxide exsolution lamellae. Electron microprobe analyzes of coexisting Fe-Ti oxides in the layered intrusion confirm earlier observations that oxides in early magmatic rocks are dominated by hemo-ilmenite with minor end-member magnetite, followed by more reduced oxides dominated by titanomagnetite with minor near end-member ilmenite. What is not fully understood is the property of ilmenite with hematite exsolution lamellae, or, even more striking, hematite with ilmenite lamellae, to produce strong remanent magnetization of high coercivity and with a Neel temperature equal to or above the Curie temperature of magnetite. This property makes the rhombohedral oxides an important candidate to explain some high-amplitude deep-crustal anomalies on earth, or strong remanent magnetization on other planets. A remarkable feature in the Egersund province is that primitive magmas produced rocks rich in hemo-ilmenite causing negative magnetic anomalies related to magnetic remanence, and more evolved magmas produced rocks rich in magnetite related to positive induced magnetic anomalies, all in the course of crystallization-differentiation.

Effect of fine-scale microstructures in titanohematite on the acquisition and stability of natural remanent magnetization in granulite facies metamorphic rocks, southwest Sweden: implications for crustal magnetism

Abstract: Mid-Proterozoic granulites in SW Sweden, having opaque minerals hematiteilmenite with minor magnetite, and occurring in an area with negative aeromagnetic anomalies, have strong and stable reversed natural remanent magnetization ∼9.2 A/m, with 100% remaining after demagnetization to 100 mT. Samples were characterized by optical microscopy, electron microprobe (EMP), transmission electron microscopy (TEM), and rock-magnetic measurements. Earliest oxide equilibrium was between grains of titanohematite and ferri-ilmenite at 650°–600°C. Initial contacts were modified by many exsolution cycles. Hematite and ilmenite (Ilm) hosts and lamellae by EMP are Ilm 24–25, ILm 88–93, like titanohematite, and ilmenite above 520°C on Burton's diagram [1991]. Finer hosts and lamellae by TEM are Ilm16 ±3 and Ilm 88±4, like coexisting antiferromagnetically ordered (AF) hematite and ilmenite below 520°C on Burton's diagram. This may be the first example of analytical identification, in one sample, of former hematite, now finely exsolved, and AF hematite. TEM microstructures consist of gently curving semicoherent ilmenite lamellae within hematite, flanked by precipitate-free zones and abundant ilmenite disks down to unit cell scale (1–2 nm). Strain contrast of disks suggests full coherence with the host, and probable formation at the reaction titanohematite ---> AF hematite + ilmenite at 520°C. Magnetic properties are a consequence of chemical and magnetic evolution of hematite and ilmenite with bulk compositions ilmenite-richer than Ilm 28, that apparently exsolved without becoming magnetized, down to 520°C where hematite broke down to AF hematite plus ilmenite, producing abundant AF hematite below its Neel temperature. Intensity of magnetization is greater than possible with hematite alone, and TEM work suggests that ultrafine ilmenite disks in AF hematite are associated with a ferrimagnetic moment due to local imbalance of up and down spins at coherent interfaces.

Off-axis electron holography of magnetotactic bacteria: magnetic microstructure of strains MV-1 and MS-1

Abstract: Off-axis electron holography in the transmission electron microscope is used to characterize the magnetic microstructure of magnetotactic bacteria. The practical details of the technique are illustrated through the examination of single cells of strains MV-1 and MS-1, which contain crystals of magnetite (Fe 3 O 4 ) that are ∼50 nm in size and are arranged in chains. Electron holography allows the magnetic domain structures within the nanocrystals to be visualized directly at close to the nanometer scale. The crystals are shown to be single magnetic domains. The magnetization directions of small crystals that would be superparamagnetic if they were isolated are found to be constrained by magnetic interactions with adjacent, larger crystals in the chains. Magnetization reversal processes are followed in situ , allowing a coercive field of between 30 and 45 mT to be measured for the MV-1 cell. To within experimental error, the remanent magnetizations of the chains are found to be equal to the saturation magnetization of magnetite (0.60T). A new approach is used to determine that the magnetic moments of the chains are 7 and 5×10 −16 Am 2 for the 1600-nm long MV-1 and 1200-nm long MS-1 chains examined, respectively. The degree to which the observed magnetic domain structure is reproducible between successive measurements is also addressed.

Magnetic behavior of coated superparamagnetic iron oxide nanoparticles in ferrofluids

Abstract: We present a study on the magnetic behavior of nanosized iron oxide particles coated with different surfactants (sodium oleate, PVA and starch) in a ferrofluid. The effect of the coating material, and different particle concentrations in the ferrofluid have been magnetically investigated to determine the effective magnetic particle size and possible interaction. The superparamagnetic iron oxide particles, synthesized by a controlled co-precipitation technique, are found to contain magnetite (Fe3O4) as a main phase with a narrow physical particle size distribution between 6 and 8 nm. The mean effective magnetic size of the particles in different ferrofluid systems are estimated to be around 4-5 nm which is smaller than the physical particle size. On a 10% dilution in the starch coated ferrofluid we observe a decrease in the blocking temperature.