Nanophase BaFe 12 O 19 synthesized from a nonaqueous microemulsion with Ba- and Fe-containing surfactants
- PDF / 704,527 Bytes
- 4 Pages / 576 x 792 pts Page_size
- 39 Downloads / 188 Views
Pushan Ayyub Materials Research Group, Tata Institute of Fundamental Research, Homi Bhabha Road, Bombay 400 005, India (Received 25 April 1995; accepted 10 July 1995)
Ultrafine BaFe^Oig with uniform particle size was synthesized from an alcohol-in-oil (nonaqueous) microemulsion system where the metal ions were supplied by the surfactant (metal di-2-ethylhexylsulfosuccinate) molecules themselves. A monodisperse, fine-grained precipitate (Ba-Fe oxalate) was ensured by the steric barrier provided by the surfactant monolayer, while the nonaqueous environment promoted stoichiometric coprecipitation. Pure BaFe ]2 Oi9 was obtained by calcining the oxalate precursor at or above 950 °C. Structural and magnetic properties of the resulting ultrafine magnetic material are reported.
The hexagonal ferrite BaFei 2 Oi 9 (and modifications resulting from Co and Ti doping) has been extensively used as permanent magnets, and, more recently, as high density magnetic recording media. Its use as a permanent magnet is based on a relatively large coercive field, which usually still falls far short of the theoretically predicted value of 6.7 kOe, obtained for an unoriented assembly of uniaxial single-domain particles.1 Conventional synthesis techniques involve solid-state reaction at —1200 °C, followed by repeated grinding (to reduce the multidomain structure to single domain) and annealing (to remove the strain introduced while grinding). Some of the problems associated with solid-state reaction (large multidomain particles, broad particle size distribution, presence of impurity phases) can be reduced, and the coercivity increased, by using co-precipitation-based techniques. 23 Among the other synthesis techniques used in an attempt to improve the magnetic properties of this material are glass crystallization,4 organometallic route,5 colloidal route,6 and aerosol route.7 For magnetic recording applications, however, both the anisotropy and the coercive force need to be reduced. Here we report a new technique for the synthesis of nominally single phase, ultrafine, BaFe^Oig particles. The technique makes use of the dispersed cores of a microemulsion as chemical reaction media. A microemulsion 89 is generally defined as a thermodynamically stable, optically isotropic dispersion of two immiscible liquids (usually water and a hydrocarbon), one or both of which are dispersed as microdomains which are 10-50 nm in dimension. This type of fluid microstructure is stabilized by the presence of one or more species of surfactant molecules that reside as a monomolecular layer at the liquid-liquid interface and J. Mater. Res., Vol. 10, No. 11, Nov 1995 http://journals.cambridge.org
Downloaded: 28 Mar 2015
drastically reduce the interfacial tension. A soluble metal salt may be incorporated within the dispersed cores of a microemulsion and subsequently reduced or oxidized and thermally treated to produce nanoparticles of metals (such as Pt10) or metal oxides (such as Fe 3 O 4 "). It is possible to encapsulate both the reactants (e.g., metal salt and p
Data Loading...
