Structure and magnetic properties of strontium ferrite anisotropic powder with nanocrystalline structure

The phase composition, nanocrystallite size, lattice microstrain and particles morphology of a SrFe₁₂O₁₉ powder subjected to milling and subsequent annealing were studied by various methods. The investigations showed that the high-temperature annealing of the preliminarily milled powder resulted in the increase in the coercive force (μ_0i) of the SrFe₁₂O₁₉ powder up to 0.4 T owing to the formation of nanocrystalline structure (D ∼ 10 ³ nm) with low lattice microstrains. However, the annealed powder cannot be textured in an applied magnetic field because of random orientations of the crystallites in powder particles. A processing technique, which includes the low-temperature annealing of powder in an applied magnetic field, was suggested. It allowed us to produce the anisotropic powder of the strontium ferrite with the nanocrystalline structure that ensures the high coercive force of the powder (∼0.4 T) and possibility of the powder texturing in the magnetic field. The prepared samples textured in a magnetic field exhibit the higher both remanence (by a factor of 1.4) and energy product (by a factor of 2.1) as compared to those of isotropic SrFe₁₂O₁₉ samples.