| 摘要 |
PROBLEM TO BE SOLVED: To provide a magnetic recording medium combining excellent electromagnetic conversion properties and coating film durability.SOLUTION: Provided is ferromagnetic hexagonal ferrite powder in which the average particle size is 20 nm or lower and including oval hexagonal ferrite particles satisfying formula (1) by 50% or higher based on particle number. In the method for producing a magnetic recording medium having high electromagnetic conversion properties and excellent in the coating film strength of a magnetic layer, an iron salt and a bivalent metal salt are mixed in a base-containing aqueous solution 6 to obtain a hexagonal ferrite precursor, the aqueous solution including the precursor is subjected to heating and pressurizing 4, the water included therein is made of subcritical to supercritical, thus the powder can be obtained as hexagonal ferrite particles. In the ferromagnetic hexagonal ferrite powder, the average particle size is 20 nm or lower: 1.2<long axial length/short axial length<2.0 (1). |
