The effect of pH value on strontium hexaferrites: microstructure and magnetic properties

Well scattered strontium hexaferrites (SrFe12O19) nanoparticles have been successfully synthesized by coprecipitation method using polyvinyl alcohol (PVA) as a surfactant and calcinated at 850 °C. With the aim of exploring the magnetic properties of powders obtained, pH values ranging from 8 to 12. The resulting particles were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, Ultraviolet–Visible spectroscopy, thermogravimetric analysis, scanning electron microscopy, dynamic light scattering and vibrating sample magnetometer. In the pH value range 8–12 inclusively, there is sharp rise in the coercivity but an evident decline in both the saturation and remanence magnetization. Fe2O3, as a secondary phase, was discovered to reduce and even disappeared in higher pH value. Single phase strontium hexaferrite plates roughly 40 nm in size were synthesized at pH = 12, and the resulting powders present a coercivity being as high as 4321 Oe and a weak saturation magnetization. Comparing magnetic property of as-obtained nanoparticles synthesized at low pH values, the material combined with higher pH and PVA is in pure phase, which may pave a way for large-scale application.