Magnetic Barium Hexaferrite Nanoparticles with Tunable Coercivity as Potential Magnetic Heating Agents

Using magnetic nanoparticles (MNPs) for extracorporeal heating applications results in higher field strength and, therefore, particles of higher coercivity can be used, compared to intracorporeal applications. In this study, we report the synthesis and characterization of barium hexa-ferrite (BaFe₁₂O₁₉) nanoparticles as potential particles for magnetic heating. Using a precipitation method followed by high-temperature calcination, we first studied the influence of varied synthesis parameters on the particles' properties. Second, the iron-to-barium ratio (Fe/Ba = r) was varied between 2 and 12. Vibrating sample magnetometry, scanning electron microscopy and X-ray diffraction were used for characterization. A considerable influence of the calcination temperature (T_cal) was found on the resulting magnetic properties, with a decrease in coercivity (H_C) from values above 370 kA/m for T_cal = 800-1000 °C to H_C = 45-70 kA/m for T_cal = 1200 °C. We attribute this drop in H_C mainly to the formation of entirely multi-domain particles at high T_cal. For the varying Fe/Ba ratios, increasing amounts of BaFe₂O₄ as an additional phase were detected by XRD in the small r (barium surplus) samples, lowering the particles' magnetization. A decrease in H_C was found in the increased r samples. Crystal size ranged from 47 nm to 240 nm and large agglomerates were seen in SEM images. The reported particles, due to their controllable coercivity, can be a candidate for extracorporeal heating applications in the biomedical or biotechnological field.