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

摘要

Well scattered strontium hexaferrites (SrFe_(12)O_(19)) 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. Fe_2O_3, 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.