Method of producing magnetic powder

Abstract

A fine magnetic powder suitable for magnetic tape capable of high-density magnetic recording is provided that helps to prevent degradation of tape surface property and durability with increasing fineness of the magnetic powder particles, which magnetic powder consists of particles composed chiefly of Fe whose surface layer contains an oxide of at least one of Al, Si and Ra (where Ra represents one or more rare earth elements, defined as including Y), has an average particle diameter of less than 70 nm, the number of basic sites on the particle surface of not greater than 0.85 sites/nm 2 , and the number of acid sites on the particle surface of not greater than 0.75 sites/nm 2 .

1 . A magnetic powder consisting of particles composed chiefly of Fe whose surface layer contains an oxide of at least one of Al, Si and Ra (where Ra represents one or more rare earth elements, defined as including Y), which magnetic powder has an average particle diameter of less than 70 nm, the number of basic sites on the particle surface of not greater than 0.85 sites/nm 2 , and the number of acid sites on the particle surface of not greater than 0.75 sites/nm 2 .  
     
     
         2 . A magnetic powder according to  claim 1 , wherein the Ra content expressed as Ra/Fe atomic percent is less that 10 at. %.  
     
     
         3 . A method of producing the magnetic powder of  claim 1 , comprising: subjecting magnetic powder consisting of particles composed chiefly of Fe whose surface layer contains an oxide of at least one of Al, Si and Ra (where Ra represents one or more rare earth elements, defined as including Y) and whose average particle diameter is less than 70 nm to heat treatment at a temperature exceeding 180° C. followed by a gentle oxidation.  
     
     
         4 . A method of producing the magnetic powder of  claim 1 , comprising: subjecting magnetic powder consisting of particles composed chiefly of Fe whose surface layer contains an oxide of at least one of Al, Si and Ra (where Ra represents one or more rare earth elements, defined as including Y) and whose average particle diameter is less than 70 nm to surface treatment with a silane coupling agent.  
     
     
         5 . A method of producing the magnetic powder of  claim 1 , comprising: subjecting magnetic powder consisting of particles composed chiefly of Fe whose surface layer contains an oxide of at least one of Al, Si and Ra (where Ra represents one or more rare earth elements, defined as including Y) and whose average particle diameter is less than 70 nm to surface treatment with an alcohol and/or polyalcohol.  
     
     
         6 . A magnetic recording medium comprising a magnetic layer formed from the magnetic powder of  claim 1  or  2 .