Structure and magnetic properties of the porous Al-substituted barium hexaferrites

Ion substitution is considered to be one of the efficient approaches to improve the magnetic properties of the barium hexaferrites. In this work, we fabricated BaFe 12− x Al x O 19 ( x  = 0, 1, 2, 4, 6) via a simple auto-combustion method and investigated their structures, morphologies and magnetic properties. The coercivity is greatly affected by annealing temperature and Al 3+ content. In addition, the Al 3+ substitution sites in BaFe 12− x Al x O 19 were further investigated by the Mössbauer spectroscopy and the superparamagnetic components were found in the BaFe 8 Al 4 O 19 and BaFe 6 Al 6 O 19 . The highest coercivity of 13.7 kOe was achieved in the BaFe 8 Al 4 O 19 , which increases by 168.6% compared with that of BaFe 12 O 19 . This work opens up a new and meaningful insight for the understanding of microstructure and coercivity mechanism towards the Al 3+ substituted barium hexaferrites.