MAGNETIC-PROPERTIES OF ACICULAR BAFE12O19 PARTICLES PREPARED BY MICROWAVE PLASMA SINTERING

Acicular alpha-FeOOH particles coated with barium ions were irradiated with microwaves under an oxygen pressure of 20 Torr to prepare fine BaFe12O19 particles by a plasma reaction. The fine acicular particles had an aspect ratio of about 13 and a magnetization of 43.5 emu/g and contained small amounts of alpha-Fe2O3 and BaFe2O4 in addition to BaFe12O19. The fine particles were mixed with a binder, and the resulting mixture was formed into a coating film under a magnetic field of 7 kOe applied vertically to the surface of the film. The squareness ratio, when examined in the direction perpendicular to the surface of the coating film, was 0.83 without any correction for the demagnetizing field. When the surface and cross-section of the coating film were observed by TEM, it was found that the long axes of the BaFe12O19 particles were aligned parallel to the film base with none being perpendicular to the film base. The cross-sections of the acicular BaFe12O19 particles were rectangular when observed by TEM. It follows that the easy axes of the acicular BaFe12O19 particles are in the direction perpendicular to their long axes.