The magnetic properties of aligned M hexa-ferrite fibres

Aligned and random fibres of strontium hexaferrite (SrM, SrFe 12O19) and barium hexaferrite (BaM, BaFe 12O19) were manufactured by blow spinning from an aqueous inorganic sol-gel precursor, which was then fired to give the hexagonal ferrite fibre. Their magnetic properties were studied by VSM, investigating the evolution of these properties with firing and measurement temperature, and in particular the effects of fibre alignment. It has been predicted that aligned ferrite fibres will demonstrate an enhanced magnetisation along the axis of alignment with respect to perpendicular to the axis, and this has been demonstrated here for the first time. The optimum firing temperature was 1000 °C, at which point they still had submicron grains. In BaM random fibres Ms=63.8 emu g-1 and Hc=428.1 kA m-1, and in SrM random fibres Ms=63.3 emu g-1 and H c=452.8 kA m-1, high values for polycrystalline materials. Fibres aligned parallel to the applied field had saturation magnetisation (Ms) values equal to those of the random fibres, whilst fibres aligned perpendicular to the field had Ms values 62% and 75% lower, for BaM and SrM, respectively. There was no change in coercivity (Hc) between random or aligned fibres of any orientation, and fibres aligned 45° and parallel to H appeared identical. Therefore, properties along the axis of alignment were superior when compared to measurements perpendicular to the axis of alignment, giving a directionality to the magnetisation in an otherwise randomly oriented ferrite material. © 2005 Elsevier B.V. All rights reserved.