Spherical Magnetite Nanoparticles Research Articles

Effects of Temperature and Precursor Concentration on the Morphological and Optical Properties of Iron Oxide Nanoparticles

Iron oxide nanoparticles are inexpensive materials that are environmentally friendly and have properties that render them suitable for wide range of applications. A facile and time-effective coprecipitation method was used to prepare iron oxide nanoparticles in a 1:1 molar ratio of Fe2+ and Fe3+ ions in solution. Iron oxide nanoparticles obtained at 18 and 60 °C yielded spherical magnetite nanoparticles with particle sizes of 7.63 and 8.5 nm respectively while comprising a mixture of magnetite and hematite nanorods, with a mean width of 9.5 nm and a mean length of 75 nm were obtained at 90 °C. Iron oxide nanoparticles synthesized at 18 °C have energy band gap of 4.16 eV while those synthesized at 60 and 90 °C have the same band gap of 4.66 eV. Precursor concentrations of 0.042, 0.08 and 0.0126 M yielded spherical magnetite nanoparticles with particle sizes of 7.94, 8.5 and 8.5 nm respectively and the particle size range increased with increasing concentration. Magnetite nanoparticles synthesized with concentrations of 0.042, 0.08 and 0.126 M have optical band gaps of 4.65, 4.88 and 5.19 eV respectively. The magnetite crystalline phase was produced regardless of concentration at temperatures of 18 and 60 °C while a temperature of 90 °C yielded a mixture of magnetite and hematite phases. The band optical band gap showed direct proportionality with temperature and concentration in an inert environment.

Magnetite Reduced Graphene Oxide/Ordered Mesoporous Carbon Nanocomposite as Effective Adsorbent for Removal of 2-Naphthol in Wastewater

Background: The wastewater released from various industries contains substantial amounts of organic compounds such as dyes and naphthols. However, naphthols are toxic to the environment and human health. So, it is essential to eliminate them, which will contribute to manufacturing and environmental management. Methods: In the work, an eco-friendly method is adapted to synthesize reduced graphene oxide (rGO) using Equisetum arvense plant extract as a strong reducing and stabilizing agent. Then, a hybrid nano adsorbent based on rGO and ordered mesoporous carbon (CMK-3) decorated with iron oxide nanoparticles (Fe3O4@rGO/CMK-3) was prepared as an adsorbent. We investigate the performance of Fe3O4@rGO/CMK-3 to remove 2-naphthol (2-NP). Results: The FE-SEM images exhibited spherical magnetite nanoparticles with sizes ranging from 31 to 47 nm on composite. Efficient removal (90%) of 2-NP from aqueous solution is demonstrated using high surface area Fe3O4@rGO/CMK-3 (initial concentration of 2-NP: 10 mg mL-1, pH: 5.0, time: 30 min, and amount of adsorbent dosage: 3 mg mL-1). The high surface area of Fe3O4@rGO/CMK-3, hydrogen binding, π-π stacking interaction between the benzene rings of 2-NP and graphitic skeleton of hybrid adsorbent facilitate the adsorption of 2-NP on the Fe3O4@rGO/CMK-3. The 2NP removal capacity by (Fe3O4@rGO/CMK-3) showed a significant decrease during five successive cycles. Conclusions: These results promise the potential of high surface area (Fe3O4@rGO/CMK-3) for efficient removal of 2-NP for wastewater treatment.

A facile route to synthesis NixFe1−xFe2O4 ferrofluids with optimal rheological and magneto‐optical properties

AbstractThis study presents an easy method for synthesizing ultrafine NixFe1–xFe2O4 nanoparticles with adjustable composition (x = 0–.8), followed by their stabilization into ferrofluids. Structural identification of the crystalline structure, lattice points, and grain boundaries from the broadened diffraction peaks reveal an average crystalline size of the nanoparticles as 10–16.5 nm. Transmission electron microscopy images reveal spherical magnetite nanoparticles with a particle size ranging from 6 to 13 nm, consistent with diffraction studies. In ferrofluids, the NixFe1–xFe2O4 nanoparticles are stabilized in kerosene with oleic acid, a surfactant. Absorbance data of the ferrofluids is seen in the 200–400 nm wavelength region of UV–vis spectra. The magnetic properties of the samples are probed using a Superconducting Quantum Interference Device. The synthesized samples exhibit superparamagnetic behavior at room temperature (300 K). The saturation magnetization of the samples decreases with an increase in Ni composition (x = 0–.8), ranging from 54 to 28 emu/g. This study explores the magnetic and magneto‐optical properties of NixFe1–xFe2O4 ferrofluids. Magneto‐viscosity of ferrofluids is also studied, and the final application of such ferrofluids in data storage, catalysis, and biomedical applications is discussed.

A molecular dynamics study on the size effects of Fe3O4 nanoparticles on the mechanical characteristics of polypyrrole/Fe3O4 nanocomposite

ABSTRACT Nanoparticle size effects on elastic properties of polymeric bio-nanocomposites were studied using atomistic molecular dynamics (MD) simulations. Spherical magnetite nanoparticles (MNPs) were placed at the centre of amorphous polypyrrole (PPy) polymer in three models with different sizes. Three models of nanocomposites with the same particle volume fractions with different sizes were considered. The Lennard-Jones 6-12 potential modelled the interface interaction between polymer and particles. Initially, the obtained mechanical properties for pristine PPy and magnetite in the bulk state showed an acceptable agreement with experimental data. Subsequently, simulation results illustrated that incorporating MNP into the PPy matrix improves the elastic modulus of the matrix by 28-58%, and more importantly, decreasing the size of the nanoparticle from 2.40 to 1.80 nm in the system leads to increasing Young's modulus of the nanocomposite from a 3.20 to 3.94 GPa. Furthermore, the atomic investigation demonstrated that this change in elastic modulus is due to the change in interatomic interaction between nanoparticle and polymer when the nanoparticle size changes. Finally, the comparison between the results of MD and micromechanical analysis shows that as the size of the nanoparticle in nanocomposites increases, the elastic properties of nanocomposites converge with the results obtained by the micromechanical approach.

Ferromagnetic resonance spectra of linear magnetosome chains.

The ferromagnetic resonance (FMR) spectra of oriented and non-oriented assemblies of linear magnetosome chains are calculated by solving the stochastic Landau-Lifshitz equation. The dependence of the shape of the FMR spectrum of a dilute assembly of chains on the particle diameter, the number of particles in a chain, the distance between the centers of neighboring particles, the mutual orientation of the cubic axes of particle anisotropy, and the value of the magnetic damping constant is studied. It is shown that FMR spectra of non-oriented chain assemblies depend on the average particle diameter at a fixed thickness of the lipid magnetosome membrane, as well as on the value of the magnetic damping constant. At the same time, they are practically independent of the number Np of particles in the chain under the condition Np ≥ 10. The FMR spectra of non-oriented assemblies of magnetosome chains are compared with that of random clusters of interacting spherical magnetite nanoparticles. The shape of FMR spectra of both assemblies is shown to differ appreciably even at sufficiently large values of filling density of random clusters.

Influence of size, volume concentration and aggregation state on magnetic nanoparticle hyperthermia properties versus excitation conditions.

Treatment planning in magnetic hyperthermia requires a thorough knowledge of specific loss power of magnetic nanoparticles as a function of size and excitation conditions. Moreover, in biological tissues the magnetic nanoparticles can aggregate into clusters, making the evaluation of their heating performance more challenging because of the magnetostatic dipole-dipole interactions. In this paper, we present a comprehensive modelling analysis of 10-40 nm sized spherical magnetite (Fe3O4) nanoparticles, investigating how their heating properties are influenced by magnetic field parameters (peak amplitude and frequency), and by volume concentration and aggregation state. The analysis is performed by means of an in-house micromagnetic numerical model, which solves the Landau-Lifshitz-Gilbert equation under the assumption of single-domain nanoparticles, including thermal effects via a Langevin approach. The obtained results provide insight into how to tune hyperthermia properties by varying magnetic nanoparticle size, under different excitation magnetic fields fulfilling the Hergt-Dutz limit (frequency between 50 kHz and 1 MHz, and peak amplitude between 1 kA m-1 and 50 kA m-1). Special attention is finally paid to the role of volume concentration and aggregation order, putting in evidence the need for models able to account for stochasticity and clustering in spatial distribution, to accurately simulate the contribution of magnetostatic dipole-dipole interactions in real applications.

Characterization and antitumor effect of doxorubicin-loaded Fe3O4-Au nanocomposite synthesized by electron beam evaporation for magnetic nanotheranostics.

Magnetic nanocomposites (MNC) are promising theranostic platforms with tunable physicochemical properties allowing for remote drug delivery and multimodal imaging. Here, we developed doxorubicin-loaded Fe3O4-Au MNC (DOX-MNC) using electron beam physical vapor deposition (EB-PVD) in combination with magneto-mechanochemical synthesis to assess their antitumor effect on Walker-256 carcinosarcoma under the influence of a constant magnetic (CMF) and electromagnetic field (EMF) by comparing tumor growth kinetics, magnetic resonance imaging (MRI) scans and electron spin resonance (ESR) spectra. Transmission (TEM) and scanning electron microscopy (SEM) confirmed the formation of spherical magnetite nanoparticles with a discontinuous gold coating that did not significantly affect the ferromagnetic properties of MNC, as measured by vibrating-sample magnetometry (VSM). Tumor-bearing animals were divided into the control (no treatment), conventional doxorubicin (DOX), DOX-MNC and DOX-MNC + CMF + EMF groups. DOX-MNC + CMF + EMF resulted in 14% and 16% inhibition of tumor growth kinetics as compared with DOX and DOX-MNC, respectively. MRI visualization showed more substantial tumor necrotic changes after the combined treatment. Quantitative analysis of T2-weighted (T2W) images revealed the lowest value of skewness and a significant increase in tumor intensity in response to DOX-MNC + CMF + EMF as compared with the control (1.4 times), DOX (1.6 times) and DOX-MNC (1.8 times) groups. In addition, the lowest level of nitric oxide determined by ESR was found in DOX-MNC + CMF + EMF tumors, which was close to that of the muscle tissue in the contralateral limb. We propose that the reason for the relationship between the observed changes in MRI and ESR is the hyperfine interaction of nuclear and electron spins in mitochondria, as a source of free radical production. Therefore, these results point to the use of EB-PVD and magneto-mechanochemically synthesized Fe3O4-Au MNC loaded with DOX as a potential candidate for cancer magnetic nanotheranostic applications.

Наночастицы магнетита увеличивают проводимость азолектинового бислоя в неоднородном магнитном поле

In the magnetofection method, magnetic fields and magnetic nanoparticles are used to increase the efficiency of gene delivery into cells. Magnefection enhances the introduction into cells of gene vectors with which magnetic nanoparticles are associated, due to the action of a magnetic field that holds the nanoparticles in the area of their application. It is believed that the magnetic field itself does not change the mechanism of absorption (endocytosis) of nanoparticles. Both the beneficial effect of magnetofection - delivery of the vector into the cell, and its side effect - cytotoxicity are associated with the interaction of particles with cell membranes and, in particular, with lipid bilayers. In our work, we investigated the effect of an applied stationary inhomogeneous magnetic field and spherical superparamagnetic magnetite nanoparticles with a diameter of about 4 nm on the conductivity of azolectin bilayer lipid membranes. The membranes were formed in a stationary magnetic field with a magnetic induction of up to 26 mT. The magnetic field had no effect on the conductivity of the membrane. After monitoring the membrane conductivity, magnetic nanoparticles were added to the solution surrounding the membrane. The addition was carried out on one side of the membrane so that the magnetic field attracted nanoparticles to the membrane surface. After adding nanoparticles in a magnetic field, the conductivity of the membranes increased by one to two orders of magnitude. This effect was observed for all membranes. A smooth increase in conductivity was accompanied in a number of cases (for 25% of the membranes) by the appearance of current jumps, which can be associated with the formation of through conducting pores with a radius of about 0.5 nm. The conductivity increased with increasing magnetic field gradient.

Magnetite nanoparticles obtained by solution combustion synthesis

This research presents a comprehensive investigation into the synthesis and characterization of magnetite nanoparticles through solution combustion reactions ignited by conventional means. In addition to the structural and compositional findings, this study's main investigation results include the specific surface area measurements conducted using the BET method. The analysis revealed specifi c surface area values for the synthesized magnetite nanoparticles at varying propellant-to-oxidant ratios, demonstrating a substantial decrease in specific surface area as the ratio increased. Specifically, specific surface areas of 72.203 m2/g for the 1:1 ratio, 22.240 m2/g for the 1:1.5 ratio, and 9.204 m2/g for the 1:2 ratio were determined. Furthermore, calculations based on the BET results and assuming spherical magnetite nanoparticles provided average particle sizes of 16±1 nm for the 1:1 ratio, 51±2 nm for the 1:1.5 ratio, and 125±4 nm for the 1:2 ratio. These findings highlight the impact of synthesis parameters on the nanoparticles' surface area and size, shedding light on their potential applications in various fields, including nanomedicine and magnetic diagnostics. Overall, this research contributes valuable insights into the synthesis, characterization, and tunable properties of magnetite nanoparticles, offering potential avenues for their utilization across diverse industries.

Iron oxide nanoparticles impact on improving reservoir rock minerals catalytic effect on heavy oil aquathermolysis

The past decade has seen a renewed importance in developing heavy oil reserves due to the rapid raise in energy resources’ demand. The next decade is likely to witness a considerable rise in extracting these resources by thermally enhanced oil recovery methods. However, many hypotheses regarding the influence of reservoir mineral components on aquathermolysis reactions appear to be disputable. This paper outlines a new approach to model the aquathermolysis of Aschalcha’s reservoir rock heavy oil in the presence and absence of iron oxide nanoparticles combined with hydrogen donor in water steam atmosphere at 200, 250, and 300 °C using different physical and chemical methods. X-ray powder diffraction (XRD) and scanning electron microscopy (SEM) have showed adsorbed spherical magnetite (Fe3O4) nanoparticles with less than 100 nm size on the studied rock minerals in hydrothermal conditions. Moreover, SARA (Saturates, Aromatics, Resins and Asphaltenes) analysis, gas analysis, and gas chromatography–mass spectrometry (GC–MS) have revealed that the obtained iron oxide nanoparticles exhibit their highest catalytic activity at 250 °C comparing to 200 and 300 °C respectively. What’s more, the obtained data have indicated a considerable decrease in resins (from 19.6 to 8.9 wt%) and asphaltenes compounds (from 5.1 to 1.5 wt%) in the presence of iron oxide nanoparticles comparing to the non-catalytic aquathermolysis of reservoir rock heavy oil. Contrary to resins and asphaltenes’ content, it has been found that saturates’ content increases significantly from 41.1% to 61.7% wt%. On another hand, the viscosity of the extracted oil has decreased almost 30 times and the gas proportion has doubled more than twice from 0.2 g to 0.43 g per 100 g of the reservoir rock sample. Interestingly, these results have been obtained in the presence of iron oxide nanoparticles at 250 °C, meanwhile, the same results have been found for the non-catalytic experiments at 300 °C. These findings confirm the significant contribution (synergistic effect) of iron oxide nanoparticles to stimulate the catalytic activity of the reservoir rock minerals. What’s more, the evidence from this study suggests that the presence of iron oxide nanoparticles in hydrothermal conditions at higher temperatures leads to the formation and adsorption of heavy coke-like carbenes, carboides, needle coke as well as carbon nanotubes of 100 nm size on the surface of the reservoir rock heavy oil as confirmed by thermal analysis (TG-DSC), SEM, and drop shape analysis (DSA) data.

Superparamagnetic spherical magnetite nanoparticles: synthesis, characterization and catalytic potential

Superparamagnetic spherical magnetite nanoparticles: synthesis, characterization and catalytic potential

Study of the optimization and mechanism for the remediation process of Malachite green dye via hybrid-based Magnetite-date’s stones

Dates' stones, a natural, abundant biowaste in Saudi Arabia, was hybridized with magnetite nanoparticles to produce hybrid-based magnetite dates' stones nanoparticles (D-Fe3O4-NPS). The synthesized sorbent was utilized for remediation of dye pollutants. A set oftechniques were used to characterize D-Fe3O4-NPS. Scanning electron microscopy (SEM) showed masses of spherical magnetite nanoparticles dispersed uniformly among the dates' stones bed. The average diameter of the nanoparticles was found to be 8 nm, while BET surface area was 44.174 m2/g. The adsorption capability of the synthesized D-Fe3O4-NPS towards the malachite green (MG) dye was evaluated via optimization factors, isotherm, and kinetics studies. The optimization factors investigated included pH, temperature, contact time, and sorbent mass. It was found that the extent of MG adsorption by D-Fe3O4-NPS increased with initial dye concentration, contact time, the dosage of the sorbent, and pH of solution while temperature effect was not pronounced. Overall, the sorption kinetics of MG was best described by the pseudo-second-order model. Finally, a mechanism for the adsorption behavior of (MG) was suggested to obtain a deeper understanding of the sorption procedure. The results showed that D-Fe3O4-NPS could be very promising as a low-cost sorbent, which easily hooks MG from an aqueous environment.

The effect of surface-modifier of magnetite nanoparticles on electrochemical detection of dopamine and heating efficiency in magnetic hyperthermia

The citric acid (CA), dextran (DEX) and (3-aminopropyl)triethoxysilane (APTES) are frequently used ligands for surface modification of magnetite nanoparticles to improve their colloidal stability and biocompatibility for use in biomedicine. Here we report the synthesis, surface modification of magnetite (Fe3O4) nanoparticles and analysis of the influence of coating materials on heating efficiency in magnetic hyperthermia, as well as on electrochemical sensing toward the detection of neurotransmitter dopamine (DOP). Spherical magnetite nanoparticles (~13 nm) were prepared by co-precipitation and surface-modified with CA, APTES and DEX. The hyperthermia tests revealed that Fe3O4@APTES resulted in the highest specific absorption rate (SAR) of 67.2 W/g. The engineered sensor, by surface modification of screen-printed carbon (SPC) electrodes with Fe3O4@APTES, showed linear response with DOP in the concentration range of 1−200 μM and a low detection limit of 34.3 nM. Besides, the sensor offered remarkable selectivity, repeatability and reproducibility. Application of SPC-, Fe3O4-, Fe3O4@CA- and Fe3O4@DEX-modified SPC electrode resulted in lower electrocatalytic activity compared with Fe3O4@APTES/SPC. The obtained results indicate the effects of a surface modifier especially that Fe3O4@APTES, alone and combining with SPC electrodes, can serve as an agent in various types of biomedical applications, like hyperthermia and electrochemical sensing of biologically active compounds such as DOP.

Mechanism for the formation of magnetite iron oxide nanostructures by Ficus carica dried fruit extract using green synthesis method

The green synthesis of iron oxide nanoparticles is a convenient, inexpensive, rapid, and ecofriendly method compared to traditional synthesis methods. Magnetic iron oxide nanoparticles with appropriate nanosized exhibit many interesting properties that can be exploited in a variety of biomedical applications. In this regard, we have synthesized magnetite iron oxide (Fe3O4) nanostructures from ferric chloride solution in aqueous extracts of Ficus carica dried fruit. Nanostructures were characterized by X-ray diffractometry (XRD), field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectrometry (EDX), and ultraviolet–visible spectrophotometer (UV–Vis). The XRD study revealed the magnetite structure. FE-SEM results showed various nanoshapes (nanoparticles, nanowires and nanoellipsoids) at different volumetric ratios (1:0.5, 1:0.75, and 1:1) of ferric chloride and extract solution, respectively. At higher concentration of solute, the process of agglomeration started, and the amorphous film is formed. UV–Vis spectroscopy showed the absorption peaks at 220 nm and 302 nm. Chemical composition analysis confirmed the presence of magnetite. Mechanism for the formation of various nanostructures was discussed on the basis of classical nucleation theory. The smaller critical nuclei favor the formation of spherical magnetite nanoparticles at lower concentration. By increasing the concentration, size of the critical nuclei increases resulting in the formation of amorphous film.

Poly(ethylene-imine)-Functionalized Magnetite Nanoparticles Derivatized with Folic Acid: Heating and Targeting Properties.

Magnetite nanoparticles (MNPs) coated by branched poly (ethylene-imine) (PEI) were synthesized in a one-pot. Three molecular weights of PEI were tested, namely, 1.8 kDa (sample MNP-1), 10 kDa (sample MNP-2), and 25 kDa (sample MNP-3). The MNP-1 particles were further functionalized with folic acid (FA) (sample MNP-4). The four types of particles were found to behave magnetically as superparamagnetic, with MNP-1 showing the highest magnetization saturation. The particles were evaluated as possible hyperthermia agents by subjecting them to magnetic fields of 12 kA/m strength and frequencies ranging between 115 and 175 kHz. MNP-1 released the maximum heating power, reaching 330 W/g at the highest frequency, in the high side of reported values for spherical MNPs. In vitro cell viability assays of MNP-1 and MNP-4 against three cell lines expressing different levels of FA receptors (FR), namely, HEK (low expression), and HeLa (high expression), and HepG2 (high expression), demonstrated that they are not cytotoxic. When the cells were incubated in the presence of a 175 kHz magnetic field, a significant reduction in cell viability and clone formation was obtained for the high expressing FR cells incubated with MNP-4, suggesting that MNP-4 particles are good candidates for magnetic field hyperthermia and active targeting.

A New Systematic Approach to the Morphology and Magnetic Properties of Spherical, Cubic, and Rod-like Magnetite Nanoparticles

In this study, a new and systematic approach was taken to study the effect of morphology on the magnetic properties of magnetite nanoparticles. A simple hydrothermal method was used to synthesize spherical, cubic, and rod-shaped nanoparticles. For this purpose, homogeneous solutions of heptahydrate ferro sulfate, deionized water, polyethylene glycol, ammonia, hydrogen peroxide, and alcohol were first made in different proportions. The resulting solutions were heated in an autoclave at 160°C for 5 h to allow the nucleation and growth of the magnetite nanoparticles. The resulting precipitates were then filtered, washed, and dried at 80°C. XRD was utilized to study the phase formation of the synthesized samples and their crystallite size. The morphology of the samples and the particle size were studied using SEM. VSM was used to investigate the magnetic properties. The results showed that spherical, cubic, and rod-shaped magnetite nanoparticles were successfully synthesized without any XRD detectable impurities with the present scan conditions. The crystallite size of the spherical, cubic, and rod-like powders was calculated to be about 17, 22, and 8 nm, respectively, while the average particle size was about 25, 63, and 12 nm, respectively, indicating the polycrystalline nature of the particles, i.e., the particles consisted of many crystallites. All the samples, regardless of the morphology, showed superparmagnetic properties. Magnetite nanoparticles with cubic morphology showed a higher Ms value than the others, while the rod-like nanoparticles exhibited the lowest Ms value. The magnetic saturation values were 60.74, 66.36, and 35.11 emu g−1 for the spherical, cubic, and rod-like particles, respectively.

A Fast and Robust Approach for the Green Synthesis of Spherical Magnetite (Fe3O4) Nanoparticles byTilia tomentosa(Ihlamur) Leaves and its Antibacterial Studies

Background:In the past few years, Magnetite (Fe3O4) nanoparticles have gained a significant research interest in the field of biology, chemistry, metallurgy due to their wide range of applications. Some of their important applications include drug delivery, chemotherapy, low-friction seals, magnetic fluid, adsorbent, recovery of hazardous wastes, etc.Methods:In the present paper, we reported an eco-friendly route of preparing magnetite nanoparticles by using leaves of Tilia Tomentosa (Ihlamur) followed by calcination at 400 ˚C for 15 minutes.Results:The bandgap energy of the prepared Fe3O4nanoparticles was studied by UV–Visible spectroscopy and the value was found to be 3.31 eV. The scanning electron microscopy (SEM) image showed the spherical magnetite nanoparticles with an average size of 25 nm. The phases and thermal properties of Fe3O4nanoparticles were studied by using X-ray diffraction, thermogravimetric (TG) and differential thermal analysis (DTA). The enthalpy change of Fe3O4nanoparticles was calculated by using the DTA curve and the value was found to be 4.97 kJ/mol at 8˚C/min heating rate. The antimicrobial activity of Fe3O4nanoparticles was carried out by the minimum inhibition concentration (MIC) assay method. Except for B. subtilis, Fe3O4nanoparticles demonstrated significant antibacterial property.Conclusion:The prepared magnetite nanoparticles showed excellent thermal stability and less weight loss over a 30–1000 ˚C temperature range. The size of the prepared magnetite nanoparticles is very less therefore they interacted effectively with the organelle, enzymes, and cells of bacteria and inhibited bacterial growth by killing them.

Estimation of Magnetic Anisotropy of Individual Magnetite Nanoparticles for Magnetic Hyperthermia.

Ideal interaction-free magnetite nanoparticles were prepared, and their magnetic properties were measured to clarify the true nature of magnetic anisotropy of individual magnetite nanoparticles at the nanoscale and to analyze the shape, surface, and crystalline anisotropy contributions. Spherical (17.7 nm), cubic (10.6 nm), and octahedral-shaped magnetite nanoparticles with average sizes ranging from 7.6 to 23.4 nm were synthesized using solution techniques. Then, these nanoparticles were coated with silica at appropriate shell thicknesses to prepare magnetic interaction-free samples, and their noninteractive nature was confirmed through first-order reversal curve diagrams. For these well-isolated nanoparticles, remanent magnetizations of the hysteresis loops are just equal to a half of the saturation magnetization. This result clearly indicates that uniaxial magnetic anisotropy is predominant in each nanoparticle. In order to clarify the details of the uniaxial magnetic anisotropy, the analysis of blocking temperature-switching field distribution diagrams is constructed based on thermal decay curves of isothermal remanent magnetization at various applied fields. The obtained effective magnetic anisotropy constant Keff is distributed around 10-20 kJ/m3 and has insignificant size dependence. This result seems inconsistent with the inverse proportion relation of Keff with size predicted for surface magnetic anisotropy. The theoretical calculation suggested that the crystalline magnetic anisotropy plays a major role in magnetic properties of the magnetite nanoparticles at lower temperatures. However, it should be noted that Keff seems slightly different for the different shapes. The above study indicates that control size, shape, and interparticle interactions is required to strictly discuss such delicate differences of magnetic anisotropy of individual magnetite nanoparticles for the design of thermal seeds for magnetic hyperthermia.

Slow magnetic relaxation in well crystallized, monodispersed, octahedral and spherical magnetite nanoparticles

Thermally activated relaxation over energy barriers concurrently related to local properties and interparticle interactions constitutes a major contribution to both the coercivity and the applied field frequency dependence of that quantity. We have measured the slow magnetic relaxation of magnetite nanoparticles (NPs), synthetized by using the oxidative precipitation technique, having spherical and octahedral shapes, monodispersed size distributions and similar transverse dimensions. From our relaxation data we evaluated the temperature dependencies of a) the irreversible demagnetization susceptibility, b) the fluctuation field (associated to the thermally induced demagnetization occurring during the measuring time range) and c) the activation volume (corresponding to the demagnetization produced by the fluctuation field). We conclude that i) the irreversible susceptibility peaks in both samples at ca. 135 K (Verwey transition temperature) and ii) the monotonically increasing temperature variation of the activation volume shows the same values in both samples for temperatures below ca. 135 K and at 290 K reaches values corresponding to 10 and 30 times the average particle volume of the spherical and octahedral NPs, respectively. Those large increases of the activation volume are compatible with a transition from local to collective of the thermally activated processes.

Tracking of the electronic re-ordering in Fe3O4/OA nanoparticles using magnetometry

Abstract We performed structural and magnetic investigation of Fe3O4/OA nanoparticles prepared by solvothermal method. Based on XRD, TEM and FTIR examination, investigated sample contained monodisperse, 5 nm-sized spherical magnetite nanoparticles coated with oleic acid. Magnetic measurement of the hysteretic curves at 5 K in zero-field cooled (ZFC) and field-cooled (FC) regime confirmed presence of exchange bias effect. ZFC/FC measurements were performed in applied magnetic fields: 10 Oe, 100 Oe, 200 Oe, 500 Oe and 1000 Oe. Zero-field cooled magnetization curves recorded in 10 Oe and 100 Oe exhibited behavior characteristic for low coercivity Nanomaterials. Same sample exposed to the ZFC/FC measurement protocol in 200 Oe, 500 Oe and 1000 Oe showed increase in ZFC magnetization in the certain temperature range. The observed feature is attributed to the local changes in the magnetite electronic structure, occurred through the spin reorientation process.