Hexaferrite particles prepared by a novel flux method with δ-FeOOH as a precursor

Abstract

δ-FeOOH precursor, precipitated by NaOH from an aqueous solution containing both barium and ferrous ions, was used to grow barium and strontium ferrites in a flux of NaCl. Differential thermal analysis, thermo-electrical analysis and magnetic measurements were employed to study the formation of barium ferrite (BF). Fe M (M = Ba or Sr) ratios of 8–10 and flux ratios ( Na Fe ) of 3.5–7 were found to be optimal. BF formation starts at temperatures as low as 600 °C and has a greatly enhanced reaction rate at elevated temperatures; both observations are attributed to the use of δ-FeOOH precursor. Doping of (Co,Ti) or (Zn,Ti) in place of Fe is possible in this technique and leads to reduced particle size and coercivity. Hence the modified barium and strontium ferrite particles have coercivities of 600–2000 Oe, and saturation and residual magnetizations of 57–67 and 24–29 emu g −1, respectively; the particles are 30–200 nm in size, with a fine platelet shape. They are thus potential candidates as high-density recording media. This novel method provides a more economical and less polluting way to mass produce barium (strontium) ferrite powders for recording purposes.