Magnetic properties of nanocrystalline BaFe12O19 prepared by hydrothermal method

Barium ferrite nanoparticles were synthesized by hydrothermal method. The grain size of BaFe12O19 produced chemically at temperatures between 150 and 200 °C with a reaction time of 12 h varies from 9 to 15 nm. At 4.2 K a grain size independent coercive field of about 1.2 kOe was found. However, at 300 K, the coercivity changes from 230 Oe up to 590 Oe. The magnetization at 4.2 and 300 K increases linearly with grain size. In TEM images it can be seen, that the materials are composed of plate-like and stick-like particles. The amount of the stick-like particles increases with synthesis temperature. The low values of the coercivity at 300 K are discussed in terms of demagnetising field and the nearness of the blocking temperature. The increase of the magnetization with reaction temperature may be attributed to the increase of grain size.