Effect of pH on single phase BaFe12O19 nanoparticles and their improved magnetic properties

Room temperature ferromagnetic measurements were made on BaFe 12 O 19 nanoparticles that had been synthesized via a co-precipitation method at various pH values between 9 and 14 and then calcined at temperatures between 800 and 1000 °C. The synthesized samples were characterized using X-ray diffraction (XRD), transmission electron microscopy, X-ray absorption near edge structure, X-ray photoelectron spectroscopy and vibrating sample magnetometry. The samples, prepared starting from pH 13 and calcined at temperatures between 800 and 1000 °C, exhibited XRD peaks corresponding to a single phase hexagonal BaFe 12 O 19 . The crystallite sizes increased from 60 ± 6 to 77 ± 8 nm with increasing calcination temperature. Their nanoparticle morphology showed rod-like shapes with diameters of 81 ± 13 and 94 ± 15 nm and lengths of 207 ± 25 and 254 ± 40 nm for samples calcined at 900 and 1000 °C, respectively. The presence of Ba 2+ and Fe 3+ in all samples was confirmed. All synthesized samples showed hard ferromagnetic behavior at room temperature, but a single phase BaFe 12 O 19 at pH 13 achieved a maximal saturation magnetization ( M S ), 67 emu/g, which was higher than samples prepared at other pH values. The highest M S value, 68 emu/g, was on the sample calcined at 1000 °C. M S values are related to size effects and the O 2− /Fe 3+ ion ratio. The origin of these phenomena is discussed.