![X-ray diffractogram of the as-prepared and milled samples. Patterns also look similar to that of 2L-ferrihydrite [9].](https://www.researchgate.net/profile/Leandro-Socolovsky/publication/236238710/figure/fig1/AS:393324314808330@1470787232471/X-ray-diffractogram-of-the-as-prepared-and-milled-samples-Patterns-also-look-similar-to_Q320.jpg)
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Magnetic Properties of γ-Fe 2 O 3 Nanoparticles at the Verge of Nucleation Process
Abstract and Figures
A low-energy new method based in a one-step synthesis at room temperature produces very small maghemite nanoparticles. The fast neutralization reaction (co-precipitation) of a ferric solution (FeCl 3 aqueous) in a basic medium (NH 4 OH concentrated) produces an intermediate phase, presumably two-line ferrihydrite, that in oxidizing conditions is transformed to maghemite nanoparticles. That "primordial soup" is characterized by small atoms arrangements, that are the base for maghemite tiny crystals. The final product of the reaction was characterized by X-Ray Diffraction, High-Resolution Transmission Electron Microscopy, X-ray Absorption Fine Structure, Mössbauer spectroscopy, and magnetometry.
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This work discusses the influence of synthesis conditions on self-assembly capability and morphology of obtained Ag–Fe3O4 nanoheterostructures. Samples were synthesized in two steps: first silver nanoparticles were synthesized and then used as seeds for the growth of iron oxide nanoparticles in a second step. The silver nanoparticle size was tuned, changing the oleylamine (OAm) and oleic acid (OA) ratio, which enables us to study the influence of chemical agents and seed size on the final magnetic nanoparticle morphology. The mechanism during the formation of these heterostructures has been discussed by several authors; however, it remains an open issue. In this paper we extend the discussion and advance on the understanding of synthesis conditions, related to silver sizes, chemical agents, and physical properties on the obtained nanoparticles. In our Ag–Fe3O4 system, two types of heterostructures were obtained: dimer, flower, or combination of the two. We have found that the final shape depends on silver seed size, as well as the polarity of the chemical agents used during the synthesis. We made an exhaustive study of the relationship between magnetic properties and structural features. The morphology and size distributions of the heterostructures were analyzed with transmission electron microscopy (TEM).
A progress report is presented on a selection of scientific, technological and commercial advances in the biomedical applications of magnetic nanoparticles since 2003. Particular attention is paid to (i) magnetic actuation for in vitro non-viral transfection and tissue engineering and in vivo drug delivery and gene therapy, (ii) recent clinical results for magnetic hyperthermia treatments of brain and prostate cancer via direct injection, and continuing efforts to develop new agents suitable for targeted hyperthermia following intravenous injection and (iii) developments in medical sensing technologies involving a new generation of magnetic resonance imaging contrast agents, and the invention of magnetic particle imaging as a new modality. Ongoing prospects are also discussed.
We produced needle-like goethite (alpha-FeOOH) and lepidocrocite (gamma-FeOOH) nanoparticles and investigated their magnetic properties. Both goethite and lepidocrocite nanoparticles were found to have an orthorhombic structure with lattice constants of a 4.642, b = 9.945, and c = 3.059 Angstrom and a = 3.388, b = 12.517, and c = 3.067 Angstrom, respectively, which were consistent with their corresponding bulk values. We observed Neel temperatures at 252 and 53 K for goethite and lepidocrocite nanoparticles, respectively, which were lower than their corresponding bulk values. We found that the magnetic properties of goethite and lepidocrocite nanoparticles were quite different. In addition, we observed unusual magnetic behaviors in both goethite and lepidocrocite nanoparticles. These include an additional phase transition near 12.5 K and unusual temperature dependences of both M-r and H-e in goethite nanoparticles and hysteretic magnetizations, unlike those in antiferromagnetic materials, in lepidocrocite nanoparticles. We think that these unusual magnetic behaviors are related to the defect structures, such as vacancies in goethite nanoparticles and splits and snaps in lepidocrocite nanoparticles, observed in the transmission electron microscope micrographs.
We produced needle-like goethite (α-FeOOH) and lepidocrocite (γ-FeOOH) nanoparticles and investigated their magnetic properties. Both goethite and lepidocrocite nanoparticles were found to have an orthorhombic structure with lattice constants of a = 4.642, b = 9.945, and c = 3.059 Å and a = 3,388, b = 12.517, and c = 3.067 Å, respectively, which were consistent with their corresponding bulk values. We observed Neel temperatures at 252 and 53 K for goethite and lepidocrocite nanoparticles, respectively, which were lower than their corresponding bulk values. We found that the magnetic properties of goethite and lepidocrocite nanoparticles were quite different. In addition, we observed unusual magnetic behaviors in both goethite and lepidocrocite nanoparticles. These include an additional phase transition near 12.5 K and unusual temperature dependences of both M r and H c in goethite nanoparticles and hysteretic magnetizations, unlike those in antiferromagnetic materials, in lepidocrocite nanoparticles. We think that these unusual magnetic behaviors are related to the defect structures, such as vacancies in goethite nanoparticles and splits and snaps in lepidocrocite nanoparticles, observed in the transmission electron microscope micrographs.
Powder X-ray diffraction (XRD) curves were calculated for the different structural models so far proposed for feroxyhite (δFeOOH). The influence on XRD features of different structural parameters were considered. On the basis of agreement between experimental and simulated curves it is shown that δFeOOH is a mixture of feroxyhite proper and ultradispersed hematite in the 9:1 volume ratio. Nearest Fe-Fe distances calculated for the model proposed (2.88, 3.01, 3.39 and 3.73 Å) practically coincide with those found by EXAFS spectroscopy for the same sample (2.91, 3.04 and 3.7-3.8 Å). -from Authors
In this work we describe the synthesis and characterization of maghemite nanoparticles obtained by a new synthetic route. The material was synthesized using triethylamine as a coprecipitation agent in the presence of the organic ligand N,N′-bis(3,5-di-tert-butyl-catechol)-2,4-diaminotoluene (LCH3). Mössbauer spectrum at 4 K shows typical hyperfine parameters of maghemite and Transmission Electron Microscopy images reveal that the nanoparticles have a mean diameter of 3.9 nm and a narrow size distribution. AC magnetic susceptibility in zero field presents an Arrhenius behavior with unreasonable relaxation parameters due to the strong influence of dipolar interaction. In contrast when the measurements are performed in a 1 kOe field, the effect of dipolar interactions becomes negligible and the obtained parameters are in good agreement with the static magnetic properties. The dynamic energy barrier obtained from the AC susceptibility results is larger than the expected from the average size observed by HRTEM results, evidencing the strong influence of the surface contribution to the anisotropy.
Very small maghemite nanoparticles (∼3 nm) are obtained through a one-step synthesis at room temperature. The fast neutralization reaction of a ferric solution in a basic medium produces an intermediate phase, presumably two-line ferrihydrite, which in oxidizing conditions is transformed to maghemite nanoparticles. The synthesis of maghemite, as final product of the reaction, was characterized by High-Resolution Transmission Electron Microscopy (HR-TEM), X-ray Absorption Fine Structure (XAFS), Mössbauer spectroscopy, and magnetometry. The XAFS technique allowed the analysis of the crystallographic variations into maghemite nanoparticles as a result of modification in its surface/volume ratio. Mössbauer spectroscopy at low temperature (4.2 K) confirms the presence of Fe(III) in tetrahedral and octahedral interstices, in the stoichiometry corresponding to maghemite. The specific magnetization, M vs H (3 K and 300 K, up to 7 T) and temperature dependence of the magnetization (50 Oe by ZFC mode, 2 K ≤ T ≤ 300 K) indicate that maghemite nanoparticles of 3 nm are in superparamagnetic state with a blocking temperature close to 36 K
A truly modern treatment of materials that can hold a magnetic field. * Covers cutting-edge materials with many important technical applications. * Includes examples and problems along with computer solutions.
The synthesis of mono-dispersed γ-Fe2O3 nanoparticles by mechanochemical processing was demonstrated for the first time, via the solid-state exchange reaction Fe2(SO4)3+3Na2CO3→Fe2(CO3)3+3Na2SO4→Fe2O3+3Na2SO4+3CO2(g) and subsequent heat treatment at 673K. The nanoparticles had a volume-weighted mean diameter of 6nm and a narrow size distribution with the standard deviation of 3nm. The particles showed a superparamagnetic nature with the superparamagnetic blocking temperature of 56.6K. The anisotropy constant was 6.0×106erg/cm3, two orders of magnitude larger than the magnetocrystalline anisotropy constant of bulk γ-Fe2O3. The detailed analysis of the magnetic properties indicated that the γ-Fe2O3 nanoparticles had a core–shell structure, consisting of a ferrimagnetic core of ∼4nm in diameter having a collinear spin configuration and a magnetically disordered shell of ∼1.2nm in thickness.
Very small maghemite nanoparticles (�3 nm) are obtained through a one-step synthesis at room temperature. The fast neutralization reaction of a ferric solution in a basic medium produces an intermediate phase, presumably two-line ferrihydrite, which in oxidizing conditions is transformed to maghemite nanoparticles. The synthesis of maghemite, as final product of the reaction, was characterized by High-Resolution Transmission Electron Microscopy (HR-TEM), X-ray Absorption Fine Structure (XAFS), Mo¨ssbauer spectroscopy, and magnetometry. The XAFS technique allowed the analysis of the crystallographic variations into maghemite nanoparticles as a result of modification in its surface/volume ratio. Mo¨ ssbauer spectroscopy at low temperature (4.2 K) confirms the presence of Fe(III) in tetrahedral and octahedral interstices, in the stoichiometry corresponding to maghemite. The specific magnetization, M vs H (3 K and 300 K, up to 7 T) and temperature dependence of the magnetization (50 Oe by ZFC mode, 2 K � T � 300 K) indicate that maghemite nanoparticles of 3 nm are in superparamagnetic state with a blocking temperature close to 36 K.