Abstract: The present invention provides a method for mixing a raw material powder for powder metallurgy that allows efficient mixing at a low cost with a simple measure and easy adjustment of the apparent density by performing first agitation mixing in which a powder mixture obtained by adding, to an iron powder, one or two or more members selected from lubricant powders, free-machining agent powders, and lubricant powders for sliding surface, an alloying powder, and a binding agent is agitated while increasing the temperature to a temperature TK equal to or higher than the melting point TM of the binding agent, the resultant is agitated while maintaining the temperature TK, and the resultant is further agitated while reducing the temperature from the temperature TK, and performing second agitation mixing in which the obtained powder mixture is agitated while cooling.

Abstract: The present invention provides a method for mixing a raw material powder for powder metallurgy that allows efficient mixing at a low cost with a simple measure and easy adjustment of the apparent density by performing first agitation mixing in which a powder mixture obtained by adding, to an iron powder, one or two or more members selected from lubricant powders, free-machining agent powders, and lubricant powders for sliding surface, an alloying powder, and a binding agent is agitated while increasing the temperature to a temperature TK equal to or higher than the melting point TM of the binding agent, the resultant is agitated while maintaining the temperature TK, and the resultant is further agitated while reducing the temperature from the temperature TK, and performing second agitation mixing in which the obtained powder mixture is agitated while cooling.

Abstract: Because of its characteristics, a perpendicular magnetic recording medium has the inconvenience that since sections with low signal stability due to magnetic defects are not easily detectible in advance, these sections are detected after mounting of the medium in a magnetic disk device or after product shipping. According to one embodiment, in the manufacturing processes for the perpendicular magnetic recording medium, a DC-erase process step for direct-current demagnetizing the medium is performed after a magnetic film deposition process step and a lubricating-agent application process step. This maximizes the effects of a demagnetizing field and intentionally increases directional instability of magnetization. After the above processes, the medium is further provided with a heating process to accelerate the reversal of magnetization in latent defective sections.