Magnetic and structural properties of a silica/SrFe12O19 nanocomposite subjected to different heat-treatments

This study reports on the preparation of a silica composite containing strontium hexaferrite nanoparticles. We investigated its structural and magnetic properties, examining the influence of both the magnetic nanoparticle concentration and various heat treatment conditions. This work addresses the critical need for precise control over the structure and magnetic properties of silica-based composites with magnetic nanoparticles for biomedical applications. The magnetic nanocomposite was fabricated using strontium hexaferrite (SrFe₁₂O₁₉) nanoparticles, incorporated into the silica during the hydrolysis/condensation reaction of the sol-gel process to obtain a homogeneous mix. To understand the impact of heat treatment, we investigated the structural and magnetic properties of the nanocomposite after thermal processing through two different heating routes: using an electrical furnace and by means of microwave hybrid heating using low power microwave oven. The heat treatment was carried out at 850 and 1050 °C, while the microwave processing lasted for 20- and 30-min. Results showed high tuneability of the structural and magnetic properties. The silica matrix can range from amorphous to crystalline, whereas the magnetic properties can be adjusted from hard-magnetic to soft-magnetic. The samples processed using microwave hybrid heating show marked differences in their structural and magnetic properties compared to those obtained via conventional heating. Specifically, the sample obtained at 20 min retains the amorphous structure and induces a drop in coercive field from 2.0 to 0.28 kOe, while the squareness ratio decreased from 0.5 to 0.1. This behavior is attributed to a phase evolution of the hexaferrite nanoparticles embedded in the amorphous quartz matrix.