Crystallisation of W-type hexagonal ferrites in an oxide glass with As₂O₃ as nucleation catalyst

Abstract

Magnetic glass-ceramics with the W-type (BaFe₁₈O₂₇) hexagonal Ba-ferrite as a prominent crystalline phase have been prepared from glasses in the system BaO-Fe₂O₃-B₂O₃ by subjecting the latter to a two stage heat-treatment. The magnetic phases due to M-type (BaFe₁₂O₁₉) hexagonal ferrite and iron oxide have also precipitated in some of the samples. An incorporation of ≈1 mol% As₂O₃ in the glass particularly favours the nucleation and growth of the W-type ferrite microcrystals in the shape of hexagonal platelets. Detailed X-ray diffraction, magnetic and EPR measurements have been carried out for all the glass-ceramic samples. The results are explained on the basis of the microstructure. The glass-ceramic products obtained show a maximum magnetisation of ≈79 emu/g in the ferrite particles with coercivity H_c = 5350 Oe at room temperature (≈ 300 K) and T_c≈820 K.