Abstract: By Using XRD, SEM, TEM, and VSM methods, the shape, micro structure and magnetic property of the barium ferrite powder prepared by hydrothermal synthesized in different magnetic field (reactive temperature: 150℃ and 180℃) were discussed . It was shown that, BaFe2O4 powder can be prepared at the reaction temperature of 150℃ without magnetic field, while at the reactive temperature of 180℃ the powder are composed of BaFe12O19 with sheet shape. While with the magnetic field imposed, all the powder are composed of rod-like BaFe12O19 at the reactive temperature of both 150℃ and 180℃. With the increase of magnetic flux density, the proportion of rod-like BaFe12O19 also increased. When the magnetic flux density reached 10T, single-crystal BaFe12O19 with the diameter of about less than 100nm and length of tens of microns has been obtained. The products obtained by hydrothermal reaction under different magnetic flux are all small size and showed paramagnetic property. Thermodynamic calculation results show that with the application of magnetic field, the magnetic Gibbs free energy of hydrothermal reaction reached hundreds or even thousands of kJ/mol. So it changed the hydrothermal reaction in the thermodynamic aspect, which made the hydrothermal reaction turn to generate the product with higher susceptibility.

Key words: Magnetic field, Hydrothermal reaction, Ba-ferrite, Magnetic properties, Magnetic Gibbs free energy