Abstract
The structure of SrFe 12O 19 powders, subjected to mechanochemical treatment in a high-energy ball mill and subsequent annealing, were studied by X-ray diffraction technique, high-resolution scanning electron microscopy and sedimentation analysis. The magnetic properties were measured in a vibrating sample magnetometer. As a result of the milling under Ar or air atmosphere an amorphous phase was formed in the powder and its amount rised with increase of the milling time. In addition, the milling resulted in a reduction of powder particles and SrFe 12O 19 crystallite size as well as in increase of microstrain in the SrFe 12O 19 lattice. The milling caused a deterioration of the magnetic properties. The annealing led to a sharp improvement of the magnetic properties due to crystallization and formation of the SrFe 12O 19 phase with fine crystallites. The best properties ( μ 0 H ci≈0.42 T, B r≈0.24 T and ( BH) max≈9.6 kJ/m 3) were reached after the milling and annealing of the powder at 950–1000 °C for 1 hr. In this case, the average particles size was about 1 μm and the average crystallite size was 100–200 nm. The high magnetic properties of the annealed powder may be explained by the formation of SrFe 12O 19 nanocrystallites with a size smaller than the critical dimension of the single-domain particles.
Published Version
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