Magnetite particles with an average size of 39 nm and good monodispersity have been synthesized by coprecipitation at 70 °C from ferrous Fe2+ and ferric Fe3+ ions by a (N(CH3)4OH) solution, followed by hydrothermal treatment at 250 °C. The magnetite nanoparticles before the hydrothermal step display an average size of 12 nm and are highly oxidized when they are in contact with air. Complementary microstructural and magnetic characterizations of nanoparticles after hydrothermal treatment show unambiguously that they consist of magnetite with only a slight deviation from stoichiometry (δ ≈ 0.05), leading to Fe2.95O4.

Hydrothermal synthesis of monodisperse magnetite nanoparticles

A solid solution can exist of magnetite (Fe3O4) and maghemite (γ-Fe2O3), which is commonly referred to as nonstoichiometric or partially oxidized magnetite. The degree of stoichiometry in magnetite is quantitatively measured by determining the ratio of Fe2+ to Fe3+. Magnetite stoichiometry ( x = Fe2+/Fe3+) strongly influences several physical properties, including the coercitivity, sorption capacity, reduction potential, and crystalline structure. Magnetite stoichiometry has been extensively studied, although very little work exists examining the stoichiometry of nanoparticulate samples (<<100 nm); when the stoichiometry was measured for nanoparticulate samples, it was not validated with a secondary technique. Here, we review the three most common techniques to determine magnetite stoichiometry: (1) acidic dissolution; (2) Mossbauer spectroscopy; and (3) powder X-ray diffraction (pXRD), specifically with nanoparticulate samples in mind. Eight samples of nonstoichiometric magnetite were synthesized with x ranging from 0 to 0.50 and with the particle size kept as similar as possible (BET specific surface area = 63 ± 7 m2/g; particle size ≈ 20 nm). Our measurements indicate excellent agreement between stoichiometries determined from Mossbauer spectra and by acidic dissolution, suggesting that Mossbauer spectroscopy may be a useful means for estimating magnetite stoichiometry in nanoparticulate, multi-phases samples, such as those found in the environment. A significant linear correlation was also observed between the unit-cell length ( a ) of magnetite measured by pXRD and magnetite stoichiometry, indicating that pXRD may also be useful for determining particle stoichiometry, especially for mixed phased samples.

/pdf/determination-of-nanoparticulate-magnetite-stoichiometry-by-17577rkr9u.pdf

Determination of nanoparticulate magnetite stoichiometry by Mössbauer spectroscopy, acidic dissolution, and powder X-ray diffraction: A critical review

We observed Verwey transition in very small (6–14 nm) amine-coated octahedral magnetite (Fe3O4) nanoparticles that is not present in spherical similarly sized (4–13 nm) nanoparticles. Electron microscopy shows that octahedral nanoparticles have {111} facets with better cationic coordination symmetry as their surface. Spherical shape illustrates conventional superparamagnetic behavior; on the contrary, a characteristic Verwey transition near 120 K is prominent in field-cooled/zero-field-cooled curves of octahedral nanoparticles. Higher saturation magnetization in octahedral nanoparticles indicates lesser surface spin disorder and well-established anisotropy. Better surface coordination offers a reduced number of oxygen vacancies at the surface and, therefore, better stoichiometry results in a Verwey transition in octahedral nanoparticles. Electrical resistivity measurements show a sharp change in resistance for octahedral particles below the Verwey transition temperature which is completely hindered in sph...

Verwey Transition in Ultrasmall-Sized Octahedral Fe3O4 Nanoparticles

We present a facile surfactant-free solvothermal method for the fabrication of nearly monodispersed Fe3O4 submicroparticles with tunable particle sizes ranging from 130 to 420 nm by varying the concentration of single iron source FeCl3·6H2O in initial solutions. The morphology and crystal structure of the as-prepared Fe3O4 submicroparticles have been well characterized by using SEM/TEM/HRTEM, XRD, FT-IR, Raman spectroscopy, and XPS methods. It is found that the Fe3O4 particles present single-crystal nature and strong ferromagnetic property with magnetization saturation values ranged in 54.3–88.7 emu·g–1. A complexation–aggregation–phase transformation formation mechanism was first proposed for the nearly monodispersed single-crystal Fe3O4 submicroparticles based upon the quasi-in situ monitoring of the morphology and structure evolution of the samples during the synthesis process. These size-tunable nearly monodispersed Fe3O4 submicroparticles are expected to have promising applications in wide research f...

Study on Formation Mechanism by Monitoring the Morphology and Structure Evolution of Nearly Monodispersed Fe3O4 Submicroparticles with Controlled Particle Sizes

Based on chelation effect between iron ions and amino groups of chitosan, in situ mineralization of magnetite nanoparticles in chitosan hydrogel under ambient conditions was proposed. The chelation effect between iron ions and amino groups in CS–Fe complex, which led to that chitosan hydrogel exerted a crucial control on the magnetite mineralization, was proved by X-ray photoelectron spectrum. The composition, morphology and size of the mineralized magnetite nanoparticles were characterized by X-ray diffraction, Raman spectroscopy, transmission electron microscopy and thermal gravity. The mineralized nanoparticles were nonstoichiometric magnetite with a unit formula of Fe2.85O4and coated by a thin layer of chitosan. The mineralized magnetite nanoparticles with mean diameter of 13 nm dispersed in chitosan hydrogel uniformly. Magnetization measurement indicated that superparamagnetism behavior was exhibited. These magnetite nanoparticles mineralized in chitosan hydrogel have potential applications in the field of biotechnology. Moreover, this method can also be used to synthesize other kinds of inorganic nanoparticles, such as ZnO, Fe2O3and hydroxyapatite.

/pdf/in-situ-mineralization-of-magnetite-nanoparticles-in-30jseb8lwb.pdf

In Situ Mineralization of Magnetite Nanoparticles in Chitosan Hydrogel.

Stoichiometric and cation-deficient magnetite Fe3−δO4 and γ-Fe2O3 particles have been prepared by the chemical method followed by heat treatments The magnetic and structural properties were studied using neutron diffraction, magnetic measurements, and Mossbauer spectroscopy Charge ordering of Fe3+ and Fe2+ and lattice distortion are not observed below the Verwey transition temperature in the stoichiometric and cation-deficient magnetite It is found that the lattice parameter and the Verwey transition temperature decrease as the cation vacancy increases The Verwey transition almost disappears in the Fe3−δO4 sample with δ=0066 Mossbauer spectra show that the ratio of Fe3+/Fe25+ in stoichiometric magnetite can be modified by heat treatment The Fe vacancies on the B sites change the nature of the Verwey transition No cation vacancy ordering is observed for γ-Fe2O3, due to the small amount of cation vacancies in the compound

Magnetic and structural studies of the Verwey transition in Fe3−δO4 nanoparticles

Handle everyday research tasks with reliable, citation-backed results

Your personal Research Agent to handle research tasks with citation-backed results

Popular Tasks used by Researchers

How can I help with your research?

Meet SciSpace

Get more enhanced response by uploading the PDFs you want me to reference.

No relevant PDFs in your library

SciSpace is the AI research assistant for academics. Run systematic literature reviews on 280M+ papers, and write papers with cited sources. Trusted by 1M+ students, PhDs & researchers.

SciSpace | AI for Research

Analyze PDFs

Code & Manuscripts

Funding & Grants

Literature & Patents

Medical & Clinical Data

Systematic Review

Visualize & Present

Web & Data

Build a Google Scholar-like website for your research.

Build a website

Create charts and images for your research

Create a Chart

Write a paper for submission to a journal

Draft a manuscript

Patent Search

Design eye-catching scientific posters in minutes.

Scientific Poster Generation

Systematic Literature Review

One task is running at the moment. Your messages will be shown right after.

Drag and drop or click here to browse

Loved by <highlight>1 million+</highlight> researchers

Extract a list of specific topics and their sources from unstructured text

Topics

Compare and analyze relevant papers that matches with your search

Papers

Get insights from PDFs and bookmarked papers from your library

My library

Recent searches

Try searching for:

Catch AI-generated content in scholarly and non-scholarly content

{ai} Detector

Ai Writer

Get PDF Summaries, highlighted text explanations 

Chat with PDF

Effortlessly create in-text citations and bibliographies in APA and 2,500 other formats

Citation generator

Get explanations, summaries, and answers on academic papers

Ease up your research workflow with {scispace}'s cohort of exciting AI tools

Elevate your academic writing skills and convey your ideas the way you want

Paraphraser

Explore our range of reading and writing tools

Your file is being prepared and should be ready in a few minutes. If it's a large file, it might take a bit longer. You can close this window, and we'll email you the file when it's done.

You have reached a maximum limit of <strong>{limit}</strong> columns in the table. Remove at least <strong>1</strong> column to add or create another one.

D. E. Nikles

Author Tools

Chat about Author

Papers

Magnetic and structural studies of the Verwey transition in Fe3−δO4 nanoparticles