Acicular gamma -Fe/sub 2/O/sub 3/ particles surface-coated with barium ferrite

Acicular gamma -Fe/sub 2/O/sub 3/ particles surface-coated with barium ferrite (BF) have been prepared by reacting acicular alpha -FeOOH and surface-absorbed Ba/sup ++/ at 810 to 890 degrees C followed by reduction-oxidation. The BF-coated gamma -Fe/sub 2/O/sub 3/ has a diameter of 100 to 200 nm and aspect ratio of 3 to 8, a coercivity of 330 to 3600 Oe, and a saturation and residual magnetization of 47 to 70 and 23 to 34 emu/g, respectively, by controlling the Ba/sup ++/ concentration and heat treatment temperatures. They have an extremely low temperature coefficient of coercivity of -0.07 to -0.1%/ degrees C. These particles are potentially useful for high-density recording purposes.<
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