Effect of precursor solutions with different composition on synthesis of ultrafine BaLa_0.3Fe_11.7O₁₉ using sol-gel auto-combustion technique

Hexagonal BaLa_0.3Fe_11.7O₁₉ ultrafine powders with a magnetoplumbite type (M-type) structure were synthesized by a sol-gel auto-combustion method. Precursor solutions with different composition were investigated to clarify the forming conditions of the ferrites. The crystal structure, grain size, form and magnetic properties were studied by means of X-ray diffraction (XRD), transmission electronic microscopy (TEM) and vibrating sample magnetometry (VSM). On the basis of analysing the effect of ammonia, citric acid and glycol on phase structure and magnetic properties, it was demonstrated that adjusting the pH value of the precursor solution with ammonia and adding an appropriate amount of citric acid and glycol are key steps in synthesis of ultrafine powders with single BaFe₁₂O ₁₈ phase and excellent magnetic properties. In the presence of chelate agent (citric acid) and dispersant (glycol), under the conditions of pH about 7.0, nitrate/citric acid molar ratio of 1:3 and calcination temperature of 850°C (1 h), M-type BaLa_0.3Fe_11.7O₁₉ ultrafine powders with a particle size of about 36 nm, a specific magnetization 6 s of 65.54 A · m²/kg and a coercive force He of 433 kA/m, were obtained.