Surface effects on magnetic properties of superparamagnetic magnetite nanoparticles
TL;DR: In this article, the authors used a theoretical formalism based on a distribution of diameters or volumes of the nanoparticles, and interpreted each single-domain nanoparticle as a core-shell system with magnetocrystalline anisotropy on the core and surface anisotropic on the shell.
Abstract: Superparamagnetic nanoparticles of magnetite (Fe 3 O 4 ) 2 nm in size were produced by a co-precipitation method. Superparamagnetic resonance (SPR) spectra at room temperature show a broad line with a Lande g-factor, g eff ≈ 2. It was observed that, as the temperature decreased to 24 K, the apparent resonance field decreases while the line width considerably increases. We used a theoretical formalism based on a distribution of diameters or volumes of the nanoparticles. The nanoparticles behave as single magnetic domains with random orientations of magnetic moments which are subject to thermal fluctuations. A Landau-Lifshitz line shape function presents adequate results which are in good agreement with the experimental ones. A single set of parameters provides good fits to the spectra recorded at different temperatures. At high T the SPR line shape is governed by the core anisotropy and the thermal fluctuations. By decreasing the temperature, the magnetic susceptibility of shell spins increases. As a result of this, the surface spins produce an effective field on the core leading to a decrease of resonance field, B r . Also, the effective anisotropy increases as the shell spins begin to order. So, the results are interpreted by a simple model, in which each single-domain nanoparticle is considered as a core-shell system, with magnetocrystalline anisotropy on the core and surface anisotropy on the shell.
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TL;DR: A series of Mn doped cobalt ferrite compounds with the formula Mn x Co 1− x Fe 2 O 4 where x ǫ = 0.0, 0.2, 0.4, 0., 0.8 and 1.0 were successfully synthesized by polyethylene glycol-assisted hydrothermal method as discussed by the authors.
269 citations
Cites background from "Surface effects on magnetic propert..."
...This behavior has been explained as due to the large volume fractions of the atoms in the grain boundary area with unusual properties like spin canting, surface anisotropy, dislocations and superparamagnetic behavior [1–19]....
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...Therefore, since the blocking temperature is measured on the entire nanoparticles ensemble, it has to be considered as mean value [5,10,12,16,17,19]....
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...Manganese doped cobalt ferrites are promising ones for magnetic stress sensors, noncontact torque sensing, magnetoptical, magnetomechanical, and high magnetostriction applications [12–15]....
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TL;DR: In this article, superparamagnetic iron oxide nanoparticles were synthesized by a simple and cost-effective gel-to-crystalline method by alkalizing ferrous chloride with ammonium hydroxide at 80-100 degrees.
229 citations
TL;DR: The magnetic polymer nanocomposites are of particular interest because of the combination of excellent magnetic properties, stability, and good biocompatibility as discussed by the authors, and they have been exploited for in vivo imaging, as superparamagnetic or negative contrast agents, drug carriers, heavy metal adsorbents and magnetically recoverable photocatalysts for degradation of organic pollutants.
Abstract: Hybrid nanomaterials have received voluminous interest due to the combination of unique properties of organic and inorganic component in one material. In this class, magnetic polymer nanocomposites are of particular interest because of the combination of excellent magnetic properties, stability, and good biocompatibility. Organic–inorganic magnetic nanocomposites can be prepared by in situ, ex situ, microwave reflux, co-precipitation, melt blending, and ceramic–glass processing and plasma polymerization techniques. These nanocomposites have been exploited for in vivo imaging, as superparamagnetic or negative contrast agents, drug carriers, heavy metal adsorbents, and magnetically recoverable photocatalysts for degradation of organic pollutants. This review article is mainly focused on fabrication of magnetic polymer nanocomposites and their applications. Different types of magnetic nanoparticles, methods of their synthesis, properties, and applications have also been reviewed briefly. The review also provides detailed insight into various types of magnetic nanocomposites and their synthesis. Diverse applications of magnetic nanocomposites including environmental and biomedical uses have been discussed.
218 citations
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TL;DR: In this article, the structural, morphological and magnetic properties of the products were determined by X-ray powder diffractometry (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), vibrating sample magnetometer (VSM), respectively.
210 citations
TL;DR: In this paper, the properties of Co x Zn 1− x Fe 2 O 4 (x = 0.0-1.0) nanoparticles synthesized by a polyethylene glycol (PEG)-assisted hydrothermal route were investigated.
190 citations
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TL;DR: In this paper, the authors measured the electronic conductivity of a number of iron oxides of the homogeneous "Fe3O4" phase, especially as a function of the exact stoichiometrie composition of the material.
Abstract: WE have measured the electronic conductivity, down to liquid nitrogen temperature, of a number of iron oxides of the homogeneous ‘Fe3O4’ phase, especially as a function of the exact stoichiometrie composition of the material. This seemed of theoretical interest for several reasons:
1,520 citations
TL;DR: In this article, an einigen gesinterten Stabchen aus Magnetit (Fe 3 O 4 ) wird festgestellt dass sich der elektrische Widerstand bei Uberschreitung eines Umwandlungpunktes in der Umgebung von 100-200°K sprunghaft andert.
761 citations
TL;DR: In this article, the synthesis and coating of superparamagnetic monodispersed iron oxide nanoparticles was carried out by chemical solution method and controlled co-precipitation technique was used to prevent undesirable critical oxidation of Fe.
716 citations
TL;DR: A review of recent advances in ferrofluid technology both in the conventional and in new market areas is presented in this article, where a number of new applications have emerged such as ferro-fluid steppers, gauges and sensors.
616 citations
TL;DR: In this paper, the relationship between the electronic conductivity of certain spinels and the arrangement of the cations in the crystal structure was studied, and it was shown that the activation energy of the spinels is lowest for those cases in which the electrons can travel along the Fe of the 16-fold position.
Abstract: The relations between the electronic conductivity of certain spinels and the arrangement of the cations in the crystal structure (see preceding paper) are studied. Several arguments favor the assumption that Fe3O4 contains both divalent and trivalent iron in the 16‐fold position. The transition point in the neighborhood of liquid‐air temperature is probably associated with an increased degree of order at low temperature in the distribution of the 8 electrons between the 16 Fe‐lattice points per unit cell. The considerably increased conductivity below the transition points shows tetragonal anisotropy when the crystal is cooled in a magnetic field. The possible distributions of the electrons in the crystal at low temperature are discussed. In more complicated spinels, containing other metal atoms as well as iron in both the divalent and the trivalent state, the electronic interchange is more or less inhibited by the foreign metal atoms. The higher values of their resistance in comparison to that of Fe3O4 can be roughly described by an increased activation energy. The investigation of a number of substances with different arrangements of the cations shows that the activation energy (and therefore the electrical resistance) is lowest for those cases in which the electrons can travel, as in Fe3O4, along the Fe of the 16‐fold position.
569 citations