Production and Magnetic Properties of Nanocomposites made of Ferrites and Ceramic Matrices
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PRODUCTION AND MAGNETIC PROPERTIES OF NANOCOMPOSITES MADE OF FERRITES AND CERAMIC MATRICES H. A. CALDERON1, A. HUERTA1, M. UMEMOTO2, K. CORNETT3 1 Depto. Ciencia de Materiales ESFM-IPN, Apdo. Postal 75-707, México D.F. 07300 2 Dept. Production Systems, Technical Univesity of Toyohashi, Japan 3 Motorola Inc. Fort Lauderdale FLA, USA.
ABSTRACT This investigation deals with the production of materials containing a dispersion of magnetic nanoparticles in an insulating matrix. Such a distribution of magnetic centers is expected to absorb electromagnetic radiation in a range of wavelengths. Wüstite-magnetite and magnesiamagnesioferrite nanocrystalline ceramics have been prepared by mechanical milling and spark plasma sintering. As-milled powders have a nanocrystalline structure in both systems. Low energy milling gives rise to an increasingly higher volume fraction of wüstite as a function of milling time in the Fe1-xO-Fe3O4 system. Similar results are obtained in the MgO-MgFe2O4 system with increasingly larger amounts of MgFe2O4 produced by milling. Composites of magnetic particles (Fe3O4 or MgFe2O4) in a nonconductive matrix (FeO or MgO, respectively) are found in the sintered samples. Measurement of magnetic properties can be used to determine conclusively the nature of the developed phases and the effect of grain size. INTRODUCTION Materials for absorption of electromagnetic waves can be divided into basically two types. One of them consists of pure materials such as ferrites and the other is typically a composite including a polymeric supporting phase and a magnetic material in dispersion or forming a characteristic arrangement. Ferrites have high potential for electromagnetic wave absorption since they have frequency dependent physical properties such as permittivity and permeability. There are several investigations on the frequency dispersion of complex permeability in polycrystralline ferrite [13]. Such properties depend on the chemical composition of the ferrite and on the postsintering density, grain size, porosity and inter or intragranular porosity [3]. On the other hand, composite wave absorbers are also commonly produced. Takada et al. [4] report the properties of a Ferrite/SiC sintered composite showing a dependence between the volume fraction of ferrite and the absorption properties. Arrangements of aligned thin magnetic metal particles in polymers have also been successfully used as electromagnetic wave absorbers [5]. Nevertheless few efforts have been made to evaluate the effect of a nanostructure (including grain size and scale of the magnetic centers) on the wave absorbing properties of this type of materials. This investigation deals with the production of a wave absorber by using mechanical milling. Such an experimental method produces nanostructured materials usually in a non stable condition but proper heat treatment can be used to achieve the desired dispersion of nanomagnetic particles in the insulating matrix. This report summarizes the production, magnetic properties and characterization of m
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