Application die heavily the powder for the substratum of formation magnetic recording medium and being the powder which consists of

摘要

Being the powder which consists of the needle-shaped nonmagnetic iron oxide particle, average extended shaft length of the said particle: The specific surface which is calculated 20 - 200nm, by BET method: To be 30 - 100m2/g, at the same time phosphorus: 0.1 - 5 weight % to contain, the solubility phosphorus compound: To be below 100ppm with P conversion, desirably powder body pH value: Under 8, solubility sodium content: With Na conversion below 100ppm, solubility sulfate: The application type which is below 100ppm with SO₄ conversion heavily it is the powder for the lower stratum of layer magnetic recording medium.