Crystallization of magnetic particles in nNa2O-9SrO-6Fe2O3-8B2O3 (n = 1 and 4) glasses

Magnetic glass-ceramics with composition nNa₂O-9SrO-6Fe₂O₃-8B₂O₃ (n = 1 and 4) were prepared by fast quenching of the molten oxide mixtures and subsequent thermal treatment of the obtained glasses at 450–950 °C. The samples were investigated by differential thermal analysis, x-ray powder diffraction, electron microscopy, and SQIUD magnetometry. Increasing of the sodium oxide content leads to a significant decrease of the glass transition, devitrification, and melting temperatures. Just above the glass transition temperature (525 °C for n = 1 and 430 °C for n = 4) superparamagnetic γ-Fe₂O₃ nanoparticles precipitate, which, at elevating annealing temperature, are substituted by thin hexaferrite nanoplatelets with coercivities of 2000–4000 Oe; the annealing at higher temperatures results in crystallization of the submicron hexaferrite particles with a coercivity of up to 6000 Oe. Thus the glass-ceramics are highly applicable sources of non-sintered nanoparticles with various morphologies and magnetic properties.