Magnetic enhancement of carbon-encapsulated magnetite nanoparticles
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Ferrimagnetism
Superparamagnetism
Coprecipitation
Carbon fibers
Maghemite
Amorphous carbon
Maghemite
Ferrimagnetism
Superparamagnetism
Biomagnetism
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Characterization
Magnetite Nanoparticles
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Iron oxides that exhibit magnetic properties have been widely studied not only from an academic standpoint, but also for numerous applications in different fields of knowledge, such as biomedical and technological research. In this work, magnetite and maghemite nanoparticles were synthesized by chemical coprecipitation of FeCl 2 ·4H 2 O and FeCl 3 ·6H 2 O (proportion of 1 : 2) in three different cases using two bases (sodium hydroxide and hydroxide ammonium) as precipitants. The chemical coprecipitation method was selected for its simplicity, convenience, reproducibility, and low cost in the use of glassware. The nanostructured materials were characterized by transmission electron microscopy (TEM), X‐ray diffraction (XRD) and magnetometry (VSM). The objective of this work is to study the variation in the morphological characteristics and physical properties of nanoparticles magnetic as a function of the different production processes. As observed by TEM, the materials obtained from the precipitating agent NH 4 OH are more uniform than those obtained with NaOH. From XRD pattern analysis, it appears that the obtained materials correspond to magnetite and maghemite and, from magnetometry VSM analysis, show high magnetization as a function of the magnetic field at room temperature, indicating that these materials are superparamagnetic.
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Magnetite Nanoparticles
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To analyze the decomposition of siderite during thermal treatment, and to characterize the magnetic minerals formed as its alteration products, low‐temperature magnetic measurements were conducted on natural siderite samples that were heated to different temperatures. For the unheated siderite sample, on warming curves remanence sharply decreases at 35–40 K while the in‐phase AC susceptibility peaks, consistent with the Néel temperature ( T N ) at 38 K. The natural siderite can decompose significantly even at relatively low temperature (below 250°C). At this stage, the alteration products are hematite and probably superparamagnetic (SP) maghemite due to the quick oxidization. After 400°C, both susceptibility and SIRM of the thermally treated samples sharply increase, indicating the formation of significant amounts of strongly magnetic minerals. Furthermore, the apparently depressed Verwey transitions at 120 K indicate that most of the ferrimagnetic minerals formed by 490–530°C are either very fine grains or highly oxidized magnetite and/or maghemite.
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Coprecipitation and microemulsion were used to prepare nanosized magnetite. The average particle sizes of samples A and B were calculated by Brunauer–Emmett–Teller analysis and are 8.16 and 2.24 nm, respectively. The saturation magnetization of sample A at 300 K was 57.2 emu/g, but sample B was not saturated even 7.0 T. The blocking temperature for sample B was 17 K and the crystalline anisotropy energy was 1.2×105 J/m3. At 5 K, sample B is ferrimagnetic with σs=7.62 emu/g. This value is much lower than the σs=65.4 emu/g of the crystallized sample A at 50 K. Mössbauer spectra showed that sample A was ferrimagnetic at room temperature, but sample B was superparamagnetic at T>Tb (critical blocking temperature).
Coprecipitation
Ferrimagnetism
Superparamagnetism
Microemulsion
Anisotropy energy
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Ferrimagnetism
Superparamagnetism
Coprecipitation
Carbon fibers
Maghemite
Amorphous carbon
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Studying the magnetic properties of ultrafine nanometer‐scale ferrimagnetic particles (<10 nm) is vital to our understanding of superparamagnetism and its applications to environmental magnetism, biogeomagnetism, iron biomineralization, and biomedical technology. However, magnetic properties of the ultrafine nanometer‐sized ferrimagnetic grains are very poorly constrained because of ambiguities caused by particle magnetostatic interactions and unknown size distributions. To resolve these problems, we synthesized magnetoferritins using the recombinant human H chain ferritin (HFn). These ferrimagnetic HFn were further purified through size exclusion chromatography to obtain monodispersed ferrimagnetic HFn. Transmission electron microscopy revealed that the purified ferrimagnetic HFn are monodispersed and each consists of an iron oxide core (magnetite or maghemite) with an average core diameter of 3.9 ± 1.1 nm imbedded in an intact protein shell. The R value of the Wohlfarth‐Cisowski test measured at 5 K is 0.5, indicating no magnetostatic interactions. The saturation isothermal remanent magnetization acquired at 5 K decreased rapidly with increasing temperature with a median unblocking temperature of 8.2 K. The preexponential frequency factor f 0 determined by AC susceptibility is (9.2 ± 7.9) × 10 10 Hz. The extrapolated M rs / M s and B cr / B c at 0 K are 0.5 and 1.12, respectively, suggesting that the ferrimagnetic HFn cores are dominated by uniaxial anisotropy. The calculated effective magnetic anisotropy energy constant K eff = 1.2 × 10 5 J/m 3 , which is larger than previously reported values for bulk magnetite and/or maghemite or magnetoferritin and is attributed to the effect of surface anisotropy. These data provide useful insights into superparamagnetism as well as biomineralization of ultrafine ferrimagnetic particles.
Ferrimagnetism
Maghemite
Superparamagnetism
Magnetocrystalline anisotropy
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Maghemite
Coprecipitation
Superparamagnetism
Ferrimagnetism
Peptization
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CMS@Fe3O4 magnetic nanoparticles were prepared by chemical coprecipitation.The morphology and properties of the nanoparticles were characterized by SEM,FT-IR,Zeta potential analyzer and VSM.The magnetic nanoparticles are quasi-spherical and with an average diameter of(35±10) nm.The results indicate that the particles have shown superparamagnetism high negative charges at the high pH range.And the stability was also investigated,after 30 d,the CMS@Fe3O4 magnetic nanoparticles remain excellent stability at pH 11.
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Superparamagnetism
Zeta potential
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