The hydrothermal synthesis of super-paramagnetic barium hexaferrite particles

Superparamagnetic Ba-hexaferrite nanoparticles were prepared using modified hydrothermal synthesis. The precursor and hydroxide [OH−] concentrations were optimized and the synthesis temperature and time were drastically reduced. The size and the morphology of synthesized nanoparticles was confirmed by transmission electron microscopy (TEM) images. The crystal structure of the nanoparticles was characterized by X-ray diffraction data. Powders synthesized at 160 °C exhibit a bimodal particle size distribution while those synthesized at TS = 150 °C show a monomodal particle size distribution. Zero-field-cooling (ZFC) and field-cooling (FC) magnetization measurements were performed using a superconducting quantum interference device magnetometer from 2 to 300 K to investigate the magnetic properties of nanoparticles. The FC/ZFC magnetization measurements showed a typical superparamagnetic behavior. The synthesized superparamagnetic particles exhibit a disc-like shape, in average 11 nm wide and 3 nm thick with a room temperature magnetization of approximately 10 Am2/kg at 5 T.

Research highlights
► Relatively simple modified hydrothermal synthesis was used to prepare Ba-hexaferrite nanoparticles which are widely used permanent magnetic material.
► The synthesis was carried out in aqueous solution with optimized molar ratios of precursors at relatively low temperatures or even without a soaking time.
► The particles show the superparamagnetic behavior.
► For Ba-hexaferrite nanoparticles the structural properties, magnetic properties, temperature dependence, were investigated.