Magnetic properties of acicular BaFe/sub 12/O/sub 19/ 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 BaFe/sub 12/O/sub 19/ particles by a plasma reaction. The fine acicular particles has an aspect ratio of about 13 and a magnetization of 43.5 emu/g and contained small amounts of alpha -Fe/sub 2/O/sub 3/ and BaFe/sub 2/O/sub 4/. The particles were mixed with a binder, and the resulting mixture was formed into a coating under a magnetic field of 7 kOe applied vertically to the surface of the film. The squareness ratio in the direction perpendicular to the surface of the coating film was 0.83 without any correction for the demagnetizing field. Transmission electron microscopy (TEM) showed that the long axes of the BaFe/sub 12/O/sub 19/ particles all were aligned parallel to the film base. The cross-sections of the particles were rectangular when observed by TEM. It follows that the easy axes of the particles are perpendicular to their long axes.<
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