The present work aims to prepare barium hexaferrite (BaFe₁₂O₁₉) particles by a single microemulsion technique and to study the possibility to control their sizes. One of the advantages of the single microemulsion technique is considerably lower cost compared to the other microemulsion methods. We use a water-in-oil microemulsion system, where cetyltrimethylammonium bromide (CTAB) acts as a cationic surfactant, n-butanol as a co-surfactant, n-hexanol as a continuous oil phase, and an aqueous phase contains FeCl₃ and Ba(NO₃)₂ (with the Ba/Fe ratio was 1/10). The co-precipitation was performed by a concentrated solution of NaOH at pH = 12. The second step of the synthesis includes calcination of the precursor at low temperature (900°C) in air ambient.

Since the technological synthesis conditions posses a significant influence on the chemical, structural and physical properties of the obtained materials, we investigated the relation between the experimental conditions of BaFe₁₂O₁₉ synthesis and their properties. We studied the influence of the stirring time, the water/surfactant ratio (W₀) and metallic ions (Ba²⁺ and Fe³⁺) concentration on the particle size distribution and crystallinity of BaFe₁₂O₁₉. The correlation among the microstructure, the magneto-crystalline structure, and the magnetic properties of the barium hexaferrite powders thus prepared was examined as well. The microscopy investigations show a narrower grain size distribution and the average particle size is between 115 and 180 nm depending on the synthesis conditions. These sizes are well below the critical mono-domain diameter for barium hexaferrite (460 nm). We also measured the magnetization-versus-magnetic field at 4.2 K and room temperature. The coercive force is 4.3 kOe for the two temperatures. A saturation magnetization value (M_s) of 43 emu/g was obtained from the magnetization curves in high magnetic fields up to 130 kOe. The magnetic properties may be attributed to the mono-domain structure.

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1. Structural and magnetic properties of nanosized barium hexaferrite powders obtained by microemulsion techniques
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