MAGNETIC POWDER, ITS MANUFACTURE, AND MAGNETIC RECORDING MEDIUM

摘要

PROBLEM TO BE SOLVED: To manufacture magnetic powder which can suppress an increase in noise after a magnetic recording medium using this magnetic powder is run for a long time and has higher durability and a higher corrosion resistance by forming a ferrite layer composed mainly of iron and cobalt on the surface of each acicular particle containing iron and cobalt. SOLUTION: In a method for manufacturing magnetic powder, acicular particles containing iron and cobalt are first reduced. Then a ferrite layer composed mainly of iron and cobalt is formed on the surface of each particle by oxidizing the reduced particles in a high-temperature atmosphere higher than a room temperature. In the acicular alloy magnetic powder, the mixing ratio of the cobalt against the iron is adjusted to about 5-50 wt.%. The major- axis and aspect ratio of each particle are respectively adjusted to about <=0.25 μm and about 4-8 respectively. Moreover, the ferrite layer is coated with at least either one of Si and Al. Therefore, the occurrence of such a phenomenon that dropout or noise increases can be suppressed when a magnetic recording medium using the magnetic powder is kept in a corrosive environment and the output is high.