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Magnetic powders   Print  E-mail
Written by Editor  
Sunday, 21 March 2004

Understanding the correlation between magnetic properties and nanostructure involves collaborative efforts between chemists, physicists, and materials scientists to study both fundamental properties and potential applications. Magnetic nanoparticles of a size of a single magnetic domain possess very interesting properties and they possess the potential to replace many of the conventional magnetic materials.

Ferromagnetic materials, magnetic powders, have been widely used as ferrite magnets, in magnetic recording, as ferrite cores, and as ferrite wave absorbers. Nanoparticles of magnetic materials are used in the industry in magnetic disks, recording tapes, etc. Superparamagnetic nanoparticles also find important medical applications e.g. magnetic cell sorting, magnetocytolysis, drug-targeting experiments etc.

Different types of magnetic nanostructures
The correlation between nanostructure and magnetic properties suggests a classification of nanostructures morphologies:

Type A
Materials include the ideal ultrafine particle system, with interparticle spacing large enough to approximate the particles as noninteracting. The isolated particles with mamoscale diameters.

Subgroup of Type A
Materials in which magnetic particles are surrounded by a surfactant preventing interactions. Ferrofluids, in which long surfactant molecules provide separation of particles.

Type B
Materials include ultrafine particles with a core-shell morphology. In type- B particles, the presence of shell can help prevent particle-particle interaction between core and the shell.

Type C
Nanocomposites are composed of small magnetic particles embedded in chemically dissimilar matrix. The matrix may or may nit be magnetoactive.

Type D
Materials consists of small crystallites dispersed in noncrystalline matrix. The nanostructure may be two-phase, in which nanocrystalites are a distinct phase form the matrix, or the ideal case in which both the crystallites and matrix are made of the same material.

We have laboratory at our disposal ready to syntheses of silica and titania matrices in sol-gel technology. For a some time we lead innovative scientific research to obtained magnetic powders about spherical grains of submicro size. The purity sol-gel material are doped with organometallic compounds Fe2+ and Fe3+ rains magnetic powders obtained for us are spherical and have about 800 nm size diameter.

The spherical powders doped with ferrofluid and other magnetic compounds are prepared by sol-gel process, modified in the part of TEOS hydrolysis technique. Spherical hydrous silica particles with narrow size distribution were previously produced by Stöber, et al. via the hydrolysis/condensation method. Under conditions of constant stirring at room temperature, TEOS (tetraethylorthosilicate) was added to a solution of reagent-grade ethanol and concentrated ammonium hydroxide solution. The TEOS underwent hydrolysis/condensation reaction, forming (poly)silicic acid. Within minutes, precipitation of uniform spherical particles occurred.

Fig. 1. Diagram of the sol-gel preparation procedure for SiO2 powders doped with the magnetic fluid (FF21)

Fig. 2. SEM photographs of spherical magnetic powders.

The coating of these nanoparticles can be made using micelles of biomaterials. We are working on the synthesis of metal compounds and other inorganic materials in biocompatible matrix. Some applications are drug delivery and new biocompatible materials.

Nanostructured materials exhibit unusual chemical and physical properties and this is the fundamental motivation for the fabrication and study of nanoscale magnetic materials.

Last Updated ( Sunday, 21 March 2004 )

Sol-Gel Materials and Nanotechnology Center of Excellence
Institute of Materials Science and Applied Mechanics
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