Effect of aluminum substitution on microstructure and magnetic properties of electrospun BaFe₁₂O₁₉ nanofibers

BaFe_12−x Al _x O₁₉ nanofibers (x = 0–2.0) with average diameter 110 nm have been prepared via the electrospinning and subsequent heat treatment at 1100 °C for 2 h. Individual BaFe₁₂O₁₉ nanofibers were composed of numerous nanocrystallites stacking alternatively along the long axis of fiber and the single crystallites on each nanofibers had random orientations. With increasing Al³⁺ ions substitution contents from 0 to 2.0, the diameter and morphology of nanofibers were almost no change. However, the lattice parameters decreased due to Fe³⁺ ions substituted by smaller Al³⁺ ions and the average grain size calculated by the Scherrer’s equation reduced from 47 to 42 nm. The crystallites possessed a hexagonal plate-like shape at x = 0 while they became rod-like with various Al³⁺ ions substitution. The X-ray diffraction patterns show that single-phase barium hexaferrite was formed when Al³⁺ ions substitution contents were less than and equal to 1.0, while other impurity phases were detected when they were more than 1.0. The chemical analysis shows that the element Al was all incorporated into the lattice of BaFe₁₂O₁₉ and evenly distributed throughout the BaFe_12−x Al _x O₁₉ nanofibers. The magnetic testing shows that the saturation magnetization (M _s) decreased obviously from 63.92 to 29.70 A m²/kg, while coercivity (H _c) increased significantly from 288.2 to 740.7 kA/m with increasing Al³⁺ ions substitution.