Magnetic Properties Of Fe3O4 Nanoparticles Research Articles

Magnetic properties of Cr doped Fe3O4 porous nanoparticles prepared through a co-precipitation method using surfactant

Magnetic Cr3+xFe3+2 − xFe2+O4 (0 ≦̸ x ≦̸ 0.1) porous nanoparticles were prepared by the aqueous co-precipitation method. The resulting magnetic nanoparticles were characterized by using an x-ray diffraction (XRD), field enhanced scanning electron microscope (FESEM), transmission electron microscope (TEM), and vibrating sampling magnetometer (VSM). The nitrogen gas adsorption/desorption isotherm showed a microporous structure of the obtained magnetic materials. A rod and round shape of Fe3O4 was observed as using polyvinylpyrrolidone (PVP) and cetyltrimethylammonium bromide (CTAB) surfactant, respectively. The Fe3O4 nanoparticles exhibited superparamagnetic properties with easy separation and re-dispersion in solution by using an external magnet. More remarkably, the saturation magnetization (Ms) was enhanced up to 1.2 times for doping Cr3+ into the Fe3O4 lattice. The effect of surfactants and Cr3+ doping concentrations on size and the magnetic properties of Fe3O4 nanoparticles are studied.

High-strength superparamagnetic composite fibers

The polymer composites of magnetic nanoparticles can be possibly used in a bulk form by preserving all the novel characteristics of magnetic nanoparticles such as superparamagnetic behavior. By introducing magnetic properties of Fe3O4 nanoparticles into polymer fibers, novel magnetic properties combine with the advantages of composite fibers such as light-weight and ease-of-use. Using dry-jet-wet fiber spinning technology, we have successfully fabricated iron oxide/polyacrylonitrile (Fe3O4/PAN) composite fibers with 10 wt% nanoparticle in the polymer matrix. Composite fiber with a diameter as small as 15 μm can achieve tensile strength and tensile modulus values as high as 630 MPa and 16 GPa, respectively. Superparamagnetic properties of Fe3O4 nanoparticles were preserved in the composite fibers with saturation magnetization at 80 emu/g and coercivity of 165 G.

Hydrothermal synthesis, off-axis electron holography and magnetic properties of Fe3O4 nanoparticles

The hydrothermal synthesis of Fe3O4 nanoparticles (NPs) (< 50 nm) from mixed FeCl3 / FeCl2 precursor solution at pH ~ 12 has been confirmed using complementary characterisation techniques of transmission electron microscopy and X-ray diffractometry. Off-axis electron holography allowed for visualisation of their single domain (SD) nature, as well as inter-particle interactions, with the latter attributed to explain the pseudo-SD/multi-domain behaviour demonstrated by bulk magnetic measurements.

Magnetic Properties of Fe 3 O 4 Nanoparticles Synthesized by Coprecipitation Method

In this paper, we elucidate several specific magnetic properties of Fe 3O4nanoparticles synthesized by coprecipitation method. The characterizations by X-ray diffraction technique (XRD) and scanning electron microscopy (SEM) showed the particles to be of spinel structure and spherical shapes whose diameter could be controlled in the range from 14 to 22 nm simply by adjusting the precursor salts concentration and coprecipitation temperature. Magnetic properties of the Fe 3O4 nanoparticles measured by using vibration sample magnetometer (VSM) indicated the saturation magnetization and blocking temperature to increase with the particles size. Fe 3O4 nanoparticles with crystal size smaller than 22 nm exhibits superparamagnetic behavior at room temperatures. Characteristic magnetic parameters of the particles including saturation magnetization, effective anisotropy constant, and magnetocrystalline anisotropy constant have been determined. The observed decrease of saturation magnetization was explained on the base of core-shell model. A simple analysis indicated that the shell thickness decreases with an increase in particle size.

Orbital and spin moments of 5 to 11 nm Fe3O4 nanoparticles measured via x-ray magnetic circular dichroism

The orbital and spin contributions to the magnetic moment of Fe in Fe3O4 nanoparticles were measured using X-ray magnetic circular dichroism (XMCD). Nanoparticles of different sizes, ranging from 5 to 11 nm, were fabricated via organic methods and their magnetic behavior was characterized by vibrating sample magnetometry (VSM). An XMCD signal was measured for three different samples at 300 K and 80 K. The extracted values for the orbital and spin contributions to the magnetic moment showed a quenching of the orbital moment and a large spin moment. The calculated spin moments appear somewhat reduced compared to the value expected for bulk Fe3O4. The spin moments measured at 80 K are larger than at 300 K for all the samples, revealing significant thermal fluctuations effects in the nanoparticle assemblies. The measured spin moment is reduced for the smallest nanoparticles, suggesting that the magnetic properties of Fe3O4 nanoparticles could be altered when their size reaches a few nanometers.

Directly aqueous synthesis of well-dispersed superparamagnetic Fe3O4 nanoparticles using ionic liquid-assisted co-precipitation method

In this paper, well-dispersed superparamagnetic Fe3O4 nanoparticles have been successfully synthesized in aqueous phase by a simple co-precipitation method using ionic liquid of 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIN]BF4) as templates. As we studied, the microstructures and magnetic properties of the Fe3O4 nanoparticles were strongly influenced by the addition of ionic liquid. The possible formation mechanisms of Fe3O4 nanoparticles were proposed. It was found that the nanoparticle surface was modified with ionic liquid during the growth of the Fe3O4 nanoparticles, which could prevent the nanoparticles from aggregating effectively. In addition, ionic liquid can be easily removed using deionized water. As a result, well-dispersed Fe3O4 nanoparticles without organic cover can be obtained. Besides, the particle size and magnetic properties of Fe3O4 nanoparticles were strongly depended on the amount of ionic liquid [BMIN]BF4.

Effect of Temperature on Fe&lt;sub&gt;3&lt;/sub&gt;O&lt;sub&gt;4&lt;/sub&gt; Magnetic Nanoparticles Prepared by Coprecipitation Method

The Fe3O4 magnetic nanoparticles obtained by the aqueous coprecipitation method are characterized systematically using scanning electron microscope, X-ray diffraction and vibrating sample magnetometer. These magnetic nanoparticles are spheric, dispersive, and have average grain size of 50 nm. The size and magnetic properties of Fe3O4 nanoparticles can be tuned by the reaction temperature. All samples exhibit high saturation magnetization (Ms=53.4 emu·g-1) and superparamagnetic behavior with a block temperature (TB) of 215K. These properties make such Fe3O4 magnetic nanoparticles worthy candidates for the magnetic carriers of targeted-drug or gene therapy in future.

A facile synthetic pathway of monodisperse Fe3O4 nanocrystals

A facile approach was used for synthesize size-controlled monodisperse magnetite (Fe3O4) nanoparticles. In this method, precursors were obtained only using iron (III) chloride though a simple non-alkoxide sol–gel method. Meanwhile, this operation is without the need for inert gas atmosphere and refluxing conditions and without the strict control of high temperature and pressure. The phase structures, morphologies, particle sizes and magnetic properties of Fe3O4 nanoparticles were characterized by X-ray diffraction, transmission electron diffraction, fourier-transform infrared spectroscopy, near-edge X-ray absorption fine structure and vibrating sample magnetometer. Although this approach is a small modification to other methods, the synthetic pathway includes the advantages of several other methods. In addition, this method may offer a feasible strategy for those reaction which need more moderate reaction conditions.

Structural, optical and magnetic properties of Fe3O4 nanoparticles prepared by a facile microwave combustion method

Iron oxide (Fe3O4) nanoparticles were synthesized by a facile microwave combustion method. X-ray diffraction and energy dispersive X-ray spectroscopy results showed that the as-prepared product was pure Fe3O4 without any impurity. The mechanism for the formation of Fe3O4 by microwave combustion method is also discussed. Microwave combustion produced sufficient energy for the formation of Fe3O4, because of its homogeneous distribution within the raw materials. This results in the formation of nanoparticles, early phase formation and different morphologies within few minutes. Magnetic analysis revealed that the Fe3O4 nanoparticles had ferromagnetic behavior at room temperature with saturation magnetization of 66.12emu/g

Effect of synthesis route on the structural, optical and magnetic properties of Fe3O4 nanoparticles

Fe3O4 nanoparticles were prepared by the co-precipitation as well as combustion method. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–Visible spectroscopy and vibrating sample magnetometer (VSM) were used to study the physical properties. XRD pattern revealed the formation of single magnetite phase in the compound. TEM micrographs confirmed the uniform distribution of nanoparticles. UV–Visible spectroscopy measurement exhibited that the shifting of λmax with the variation of particle size which indicated that band gap is dependent on particle size. Development of well saturated magnetization loop indicated the magnetic nature of the samples. The as prepared Fe3O4 nanoparticles exhibited superparamagnetic behavior. The band gap as well saturation magnetization (Ms) was found to be strongly dependent on the particle size. The saturated magnetization of the superparamagnetic Fe3O4 nanoparticles prepared by the co-precipitation and combustion methods were found to be ∼63.5 emu/g and 44.2 emu/g, respectively at room temperature which enables them to be recycled from the solution by applying a small magnet.

Controlling magnetic properties of iron oxide nanoparticles using post-synthesis thermal treatment

Changes in morphological and magnetic properties of Fe3O4 nanoparticles before and after annealing are investigated in the present work. The nanoparticles are synthesized in a standard capacitively coupled plasma enhanced chemical vapour deposition system with two electrodes using ferrocene as the source compound. Post annealing, due to the sintering process, the particles fuse along with recrystallization. This results in increased size of the nanoparticles and the interparticle interaction, which play a major role in deciding the magnetic properties. X-ray diffraction patterns of the samples before and after annealing indicate a phase change from Fe3O4 to Fe2O3. Annealing at 200 ∘C causes the apparent saturation magnetization to increase from 6 emu g−1 to 15 emu g−1. When annealed at 500 ∘C, the magnetic properties of the nanoparticles resemble those of the bulk material. The evidence for the transition from a superparamagnetic state to a collective state is also observed when annealed at 500 ∘C. Variation of the magnetic relaxation data with annealing also reflects the change in the magnetic state brought about by the annealing. The correlation between annealing temperature and the magnetic properties can be used to obtain nanocrystallites of iron oxide with different sizes and magnetic properties.

Correlation of structural and magnetic properties of Fe3O4 nanoparticles with their calorimetric and magnetorheological performance

Magnetic particles based on Fe3O4 were prepared by means of the microwave solvothermal method under different reaction conditions with the intention of their utilization as a mediator in magnetic hyperthermia and material for reducing blood flow in the tumor area. The synthesized particles were characterized in terms of their structure, size, shape, and magnetic properties with an emphasis on the correlation between particle morphology and magnetic properties. Most importantly, their heat development when exposed to an alternating magnetic field was determined, as well as the rheological behavior of their suspensions under static magnetic field. Reasonable heat development and substantial flow resistance under the effect of magnetic field indicate their potential for applications such as hyperthermia mediators or substances for temporary embolization.

Effect of a SiO2 coating on the magnetic properties of Fe3O4 nanoparticles

In this work the effect of a SiO2 coating on the magnetic properties of Fe3O4 nanoparticles obtained by the sol–gel method is analyzed. Two sets of samples were prepared: Fe3O4 nanoparticles and Fe3O4@SiO2 core–shell composites. The samples display the characteristic spinel structure associated with the magnetite Fe3O4 phase, with the majority of grain sizes around 5–10 nm. At room temperature the nanoparticles show the characteristic superparamagnetic behavior with mean blocking temperatures around 160 and 120 K for Fe3O4 and Fe3O4@SiO2, respectively. The main effect of the SiO2 coating is reflected in the temperature dependence of the high field magnetization (μ0H = 6 T), i.e. deviations from the Bloch law at low temperatures (T < 20 K). Such deviations, enhanced by the introduction of the SiO2 coating, are associated with the occurrence of surface spin disordered effects. The induction heating effects (magnetic hyperthermia) are analyzed under the application of an AC magnetic field. Maximum specific absorption rate (SAR) values around 1.5 W g−1 were achieved for the Fe3O4 nanoparticles. A significant decrease (around 26%) is found in the SAR values of the SiO2 coated nanocomposite. The different heating response is analyzed in terms of the decrease of the effective nanoparticle magnetization in the Fe3O4@SiO2 core–shell composites at room temperature.

Ni Doped Fe3O4 Magnetic Nanoparticles

In this work, the effect of nickel doping on the structural and magnetic properties of Fe3O4 nanoparticles is analysed. Ni(x)Fe(3-x)O4 nanoparticles (x = 0, 0.04, 0.06 and 0.11) were obtained by chemical co-precipitation method, starting from a mixture of FeCl2 x 4H2O and Ni(AcO)2 x 4H2O salts. The analysis of the structure and composition of the synthesized nanoparticles confirms their nanometer size (main sizes around 10 nm) and the inclusion of the Ni atoms in the characteristic spinel structure of the magnetite Fe3O4 phase. In order to characterize in detail the structure of the samples, X-ray absorption (XANES) measurements were performed on the Ni and Fe K-edges. The results indicate the oxidation of the Ni atoms to the 2+ state and the location of the Ni2+ cations in the Fe2+ octahedral sites. With respect to the magnetic properties, the samples display the characteristic superparamagnetic behaviour, with anhysteretic magnetic response at room temperature. The estimated magnetic moment confirms the partial substitution of the Fe2+ cations by Ni2+ atoms in the octahedral sites of the spinel structure.

Effect of Cobalt Doping Concentration on the Crystalline Structure and Magnetic Properties of Monodisperse CoxFe3–xO4 Nanoparticles within Nonpolar and Aqueous Solvents

In this work, we investigate the effect of cobalt substitution on the size evolution, crystal structure, and magnetic properties of Fe3O4 nanoparticles. Monodisperse CoxFe3–xO4 nanoparticles were prepared, using a one-step method, by direct heating process of iron(III) and cobalt(II) acetylacetonates in high-boiling-point inert organic solvent. The quantities of precursors added were based on stoichiometric Fe/Co ratio of desired ferrite. Elemental analyses ICP-AES evidenced successful cobalt doping. The doped particles showed a cobalt-deficient composition. Transmission electron microscopy demonstrated the large changes of particle size as a function of cobalt doping. The magnetization measurements showed an unchanged saturation magnetization only up to x = 0.24, beyond which it significantly decreased. To make the as-synthesized nanoparticles suitable for biomedical applications, oleic acid ligands are exchanged with caffeic acid molecules leading to stable nanoparticles in physiological conditions.

Efficient removal of arsenate by versatile magnetic graphene oxide composites

The magnetic graphene oxide (MGO) composites were prepared by coprecipitation of FeCl3·6H2O and FeCl2·4H2O on graphene oxide (GO) nanosheets and characterized in detail. The Fe3O4 was uniformly deposited on the surface of GO. The synthesized MGO composites were used as a versatile adsorbent for As(V) removal from aqueous solutions. The results showed that the adsorption of As(V) on MGO is an endothermic process and the adsorption kinetic fitted the pseudo-second-order model well. The MGO composites had a good adsorption capability for As(V) removal and the adsorption isotherms were described by the Langmuir model better than by the Freundlich model. The adsorption of As(V) on MGO decreased with ascending pH due to the electrostatic interaction. In addition, the adsorption of As(V) on MGO was greatly affected by the nature and concentration of coexisting cations and anions. The presence of coexisting anions showed an inhibiting effect on As(V) adsorption, which was more efficient at low pH, whereas the presence of coexisting cations showed an enhancing effect on As(V) adsorption, which was more efficient at high pH. The results of this work indicated that the combination of the excellent adsorption capacity of GO and the magnetic properties of Fe3O4 nanoparticles is very important in drinking water treatment due to the easy magnetic separation of MGO from aqueous solutions.

Strongly interacting superspins in Fe3O4 nanoparticles

In this paper we report structural and magnetic properties of Fe3O4 nanoparticles synthesized by thermal decomposition of ball milled iron nitrate and citric acid in N2 and air ambient. The XRD pattern of samples which are prepared in air shows some impurity phases, while the samples synthesized in the N2 atmosphere are almost pure Fe3O4 phase. The result shows that by increasing the particle size, the magnetization of the samples increases. The increase of magnetization by increasing the particle size could be attributed to the lower surface spin canting and surface spin disorder of the larger magnetic nanoparticles. The results of ac magnetic susceptibility measurements show that the susceptibility data are not in accordance with the Néel -Brown model for superparamagnetic relaxation, but fit well with conventional critical slowing down model which indicates that the dipole-dipole interactions are strong enough to cause superspin-glass like phase in these samples.

Degradation of Methylene Blue with H2O2 Activated by Peroxidase-Like Fe3O4 Magnetic Nanoparticles

Fe3O4 magnetic nanoparticles (Fe3O4 MNPs) were successfully prepared through an advanced reverse co-precipitation method under the assistance of ultrasound irradiation. The structure and size distribution were characterized by X-ray powder diffraction (XRD), laser particle size analyzer (LPSA), Fourier transform infrared spectroscopy (FT-IR) and Raman spectroscopy. The magnetic properties of Fe3O4 nanoparticles were measured by the vibrating sample magnetometer (VSM). Such Fe3O4 MNPs were used as a peroxidase mimetic to remove the dye pollutant methylene blue (MB) in the presence of H2O2. Some important reaction parameters were optimized to improve the degradation of MB. It was observed that the degradation efficiency of 10 mg L(-1) MB was above 96% over 0.62 g L(-1) Fe3O4 MNPs within 0.30 mmol L(-1) H2O2 at pH 4.85 and temperature 25 degrees C in 15 min, being superior to the previous reports.

Magnetic properties of Fe3O4 nanoparticles coated with oleic and dodecanoic acids

Magnetic nanoparticles (NP) of magnetite (Fe3O4) coated with oleic acid (OA) and dodecanoic acid (DA) were synthesized and investigated through transmission electron microscopy (TEM), magnetization M, and ac magnetic susceptibility measurements. The OA coated samples were produced with different magnetic concentrations (78%, 76%, and 65%) and the DA sample with 63% of Fe3O4. Images from TEM indicate that the NP have a nearly spherical geometry and mean diameter ∼5.5 nm. Magnetization measurements, performed in zero-field cooled (ZFC) and field cooled processes under different external magnetic fields H, exhibited a maximum at a given temperature TB in the ZFC curves, which depends on the NP coating (OA or DA), magnetite concentration, and H. The temperature TB decreases monotonically with increasing H and, for a given H, the increase in the magnetite concentration results in an increase in TB. The observed behavior is related to the dipolar interaction between NP, which seems to be an important mechanism in all samples studied. This is supported by the results of the ac magnetic susceptibility χac measurements, where the temperature in which χ′ peaks for different frequencies follows the Vogel–Fulcher model, a feature commonly found in systems with dipolar interactions. Curves of H versus TB/TB(H=0) for samples with different coatings and magnetite concentrations collapse into a universal curve, indicating that the qualitative magnetic behavior of the samples may be described by the NP themselves, instead of the coating or the strength of the dipolar interaction. Below TB, M versus H curves show a coercive field (HC) that increases monotonically with decreasing temperature. The saturation magnetization (MS) follows the Bloch’s law and values of MS at room temperature as high as 78 emu/g were estimated, a result corresponding to ∼80% of the bulk value. The overlap of M/MS versus H/T curves for a given sample and the low HC at high temperatures suggest superparamagnetic behavior in all samples studied. The overlap of M/MS versus H curves at constant temperature for different samples indicates that the NP magnetization behavior is preserved, independently of the coating and magnetite concentration.

Functionalization-induced improvement in magnetic properties of Fe3O4 nanoparticles for biomedical applications

Fe 3 O 4 were synthesized nanoparticles by thermal decomposition method with oleic acid as the surfactant, and to make them suitable for aqueous environments, dopamine ligand exchange was carried out on the particles. The nanoparticle size and phase was quantified by transmission electron microscopy (TEM) and x-ray diffraction (XRD), respectively. Superconducting quantum interference device magnetometry confirmed superparamagnetic behavior in both nanoparticles. A surprising and significant increase in the remanence MR, saturation magnetization MS, and blocking temperature TB of the particles was found after dopamine functionalization, even though TEM and XRD studies revealed no change in the particles’ size and/or structure. The results are consistent with an increase in the magnetic size of the nanoparticle core induced by the dopamine ligand exchange process. These effects are tentatively attributed to surface bonding effects that alter the canted magnetic state of the Fe3O4 nanoparticles.