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Mathew George

Bio: Mathew George is an academic researcher from Cochin University of Science and Technology. The author has contributed to research in topics: Grain size & Coercivity. The author has an hindex of 4, co-authored 4 publications receiving 691 citations.

Papers
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Journal ArticleDOI
TL;DR: In this article, the effect of grain size on NiFe 2 O 4 nanoparticles has been studied in detail using X-ray diffraction (XRD) data and the strain graph and it was found that the specific magnetization of the nanosized NiFe O 4 powders was lower than that of the corresponding coarse-grained counterparts and decreased with a decrease in grain size.

435 citations

Journal ArticleDOI
TL;DR: In this paper, the magnetic properties of Li0.5Fe2.5O4 nanoparticles with grain sizes ranging from 12 to 32 nm were studied. And the as-prepared sample of lithium ferrite showed a maximum saturation magnetization of 75 emu g−1.
Abstract: Fine particles of lithium ferrite were synthesized by the sol-gel method. By subsequent heat treatment at different temperatures, lithium ferrites of different grain sizes were prepared. A structural characterization of all the samples was conducted by the x-ray diffraction technique. A grain size of around 12 nm was observed for Li0.5Fe2.5O4 obtained through the sol-gel method. Magnetic properties of lithium ferrite nanoparticles with grain size ranging from 12 to 32 nm were studied. Magnetization measurements showed that Li0.5Fe2.5O4 fine particles exhibit a deviation from the predicted magnetic behaviour. The as-prepared sample of lithium ferrite showed a maximum saturation magnetization of 75 emu g−1. Variation of coercivity is attributed to the transition from multi-domain to single domain nature. Dielectric permittivity and ac conductivity of all the samples were evaluated as a function of frequency, temperature and grain size. Variation of permittivity and ac conductivity with frequency reveals that the dispersion is due to the Maxwell–Wagner type interfacial polarization.

171 citations

Journal ArticleDOI
TL;DR: In this article, fine particles of cobalt ferrite were synthesized by the sol?gel method and X-ray diffraction studies were carried out to elucidate the structure of all the samples.
Abstract: Fine particles of cobalt ferrite were synthesized by the sol?gel method. Subsequent heat treatment at different temperatures yielded cobalt ferrites having different grain sizes. X-ray diffraction studies were carried out to elucidate the structure of all the samples. Dielectric permittivity and ac conductivity of all the samples were evaluated as a function of frequency, temperature and grain size. The variation of permittivity and ac conductivity with frequency reveals that the dispersion is due to Maxwell?Wagner type interfacial polarization in general, with a noted variation from the expected behaviour for the cold synthesized samples. High permittivity and conductivity for small grains were explained on the basis of the correlated barrier-hopping model.

161 citations

Journal ArticleDOI
TL;DR: In this article, the effect of loading and the grain size of the filler on the cure characteristics and ten-sile properties of rubber ferrite compo- sites (RFCs) were evaluated.
Abstract: Ultra fine nickel ferrite have been synthe- sized by the sol-gel method. By heat treating different por- tions of the prepared powder separately at different temperatures, nano-sized particles of nickel ferrite with varying particle sizes were obtained. These powders were characterised by the X-ray diffraction and then incorpo- rated in the nitrile rubber matrix according to a specific recipe for various loadings. The cure characteristics and the mechanical properties of these rubber ferrite compo- sites (RFCs) were evaluated. The effect of loading and the grain size of the filler on the cure characteristics and ten- sile properties were also evaluated. It is found that the grain size and porosity of the filler plays a vital role in determining the mechanical properties of the RFCs. V C 2010

6 citations


Cited by
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Journal ArticleDOI
TL;DR: In this article, a summary on the physical concepts of ferrofluids, hyperthermia principal, magnetic properties and synthesis methods of nanosized ferrites is given, based on the importance of ferrite particles in ferro-fluids for hyper-thermia treatment.

612 citations

Journal ArticleDOI
TL;DR: Spinel ferrite (SF) magnetic materials are an important class of composite metal oxides containing ferric ions and having the general structural formula M 2+ Fe 2 3+ O 4.

523 citations

Journal ArticleDOI
TL;DR: In this article, the formation of single-phase nickel ferrite nanoparticles in the range 8-28nm depending upon the annealing temperature of the samples during the synthesis was investigated.

390 citations

Journal ArticleDOI
TL;DR: In this paper, a review of microwave ferrites is presented, with a brief discussion of fundamentals of magnetism, particularly ferrimagnetism, and chemical, structural, and magnetic properties of ferrites of interest as they pertain to net magnetization, especially to self biasing.
Abstract: Ferrimagnets having low RF loss are used in passive microwave components such as isolators, circulators, phase shifters, and miniature antennas operating in a wide range of frequencies (1–100 GHz) and as magnetic recording media owing to their novel physical properties. Frequency tuning of these components has so far been obtained by external magnetic fields provided by a permanent magnet or by passing current through coils. However, for high frequency operation the permanent part of magnetic bias should be as high as possible, which requires large permanent magnets resulting in relatively large size and high cost microwave passive components. A promising approach to circumvent this problem is to use hexaferrites, such as BaFe12O19 and SrFe12O19, which have high effective internal magnetic anisotropy that also contributes to the permanent bias. Such a self-biased material remains magnetized even after removing the external applied magnetic field, and thus, may not even require an external permanent magnet. In garnet and spinel ferrites, such as Y3Fe5O12 (YIG) and MgFe2O4, however, the uniaxial anisotropy is much smaller, and one would need to apply huge magnetic fields to achieve such high frequencies. In Part 1 of this review of microwave ferrites a brief discussion of fundamentals of magnetism, particularly ferrimagnetism, and chemical, structural, and magnetic properties of ferrites of interest as they pertain to net magnetization, especially to self biasing, are presented. Operational principles of microwave passive components and electrical tuning of magnetization using magnetoelectric coupling are discussed in Part 2.

362 citations

Journal ArticleDOI
TL;DR: In this paper, an electric enthalpy variational principle for nanosized dielectrics is proposed concerning with the flexoelectric effect, the surface effects and the electrostatic force.
Abstract: The flexoelectric effect is very strong for nanosized dielectrics. Moreover, on the nanoscale, surface effects and the electrostatic force cannot be ignored. In this paper, an electric enthalpy variational principle for nanosized dielectrics is proposed concerning with the flexoelectric effect, the surface effects and the electrostatic force. Here, the surface effects contain the effects of both surface stress and surface polarization. From this variational principle, the governing equations and the generalized electromechanical Young–Laplace equations are derived and can account for the effects of flexoelectricity, surface and the electrostatic force. Moreover, based on this variational principle, both the generalized bulk and surface electrostatic stresses can be obtained and are composed of two parts: the Maxwell stress corresponding to the polarization and strain and the remainder relating to the polarization gradient and the strain gradient. The theory developed in this paper provides the underlying framework for the analyses and computational solutions of electromechanical problems in nanodielectrics.

359 citations