MAGNETIC POWDER AND ITS MANUFACTURE AND APPLICATION

摘要

A magnetic powder which contains MnBi and has a mean particle diameter of 0.1-20 mu m. The coercive force is 3,000-15,000 Oe measured at 300 K in a magnetic field of 16 KOe and 50-1,000 Oe measured at 80 K in the same magnetic field. The magnetic susceptibility is 20-60 emu/g measured at 300 K in a magnetic field of 16 KOe. The rate of decrease of the magnetic susceptibility is below 40 % and the generated amount of metallic Bi satisfies the relation, metallic Bi/(MnBi + metallic Bi) < 0.5 (where metallic Bi represents the peak area from (012) face at the X-ray diffraction peak of Bi and MnBi represents the peak area from (101) face at the X-ray diffraction peak of the MnBi) when the magnetic powder is left as it is for seven days in an environment of 60 DEG C temperature and 90 % relative humidity. The magnetic powder has an excellent corrosion resistance and hardly deteriorates in saturation magnetization. Therefore, when a magnetic recording medium is manufactured by using this magnetic powder, falsification of records can be prevented.