Method for producing nanoparticle layer having uniform easy axis of magnetization, magnetic recording medium having such layer, its production method, and its production apparatus

Abstract

The magnetic recording medium provided is produced by forming a substrate having a nanoparticle layer comprising an array of nanoparticles, and an organic compound between said array of nanoparticles; irradiating the nanoparticle layer with an infrared beam to magnetize the nanoparticles; applying a magnetic field to the nanoparticle layer to orient easy axis of magnetization of the magnetic nanoparticles in a substantially uniform direction; and irradiating the nanoparticle layer with an ultraviolet beam to bind said organic compound to thereby produce a magnetic recording medium wherein easy axis of magnetization of the nanoparticles has been oriented in a direction substantially parallel to a direction at a particular angle with the substrate. The resulting magnetic recording medium experiences no deterioration of the underlying layer or the soft magnetic layer, and exhibits good magnetic properties.

1 . A method for producing a magnetic recording medium comprising: 
 forming a nanoparticle layer on a substrate having a surface, or on an underlying layer or a soft magnetic layer formed on said substrate by arranging particles in a substantially ordered array,    forming the nanoparticles by making each of said particles comprise a nanoparticle and an organic compound coating said nanoparticle, wherein said nanoparticles having an average particle size of at least 1 nm and not more than 20 nm, and containing at least one element selected from the group consisting of Fe, Co, Ni, Mn, Sm, Pt, and Pd;    irradiating said nanoparticle layer with an infrared beam to magnetize said nanoparticles and produce magnetic nanoparticles;    applying a magnetic field to said nanoparticle layer to orient an easy axis of magnetization of said magnetic nanoparticles in a substantially uniform direction; and    irradiating said nanoparticle layer with an ultraviolet beam to bind said organic compound.    
   
   
       2 . A method for producing a magnetic recording medium according to  claim 1  wherein said step of forming the nanoparticle layer is accomplished by employing a Langmuir-Blodgett method wherein a colloid solution of the nanoparticles coated with the organic compound is added dropwise onto a water surface to form a monolayer film, and the thus formed film is compressed to obtain a film wherein nanoparticles are densely arranged.  
   
   
       3 . A method for producing a magnetic recording medium according to  claim 1  wherein said step of forming the nanoparticle layer is accomplished by employing spin coating wherein a colloid solution of the nanoparticles coated with the organic compound is added dropwise onto the substrate and the substrate is rotated to form a thin film.  
   
   
       4 . A method for producing a magnetic recording medium according to  claim 1  wherein said infrared beam has a wavelength longer than 600 nm.  
   
   
       5 . A method for producing a magnetic recording medium according to  claim 1  wherein said ultraviolet beam has a wavelength shorter than 400 nm.  
   
   
       6 . A method for producing a magnetic recording medium according to  claim 1  wherein said infrared beam or said ultraviolet beam used, is a laser beam.  
   
   
       7 . A method for producing a magnetic recording medium according to  claim 1  wherein said magnetic field is a static magnetic field wherein direction and intensity of the magnetic field do not change with time.  
   
   
       8 . A method for producing a magnetic recording medium according to  claim 1  wherein when applying a magnetic field, said magnetic field is a pulse magnetic field wherein direction of the magnetic field applied is constant, and intensity of the magnetic field varies with time.  
   
   
       9 . A method for producing a magnetic recording medium according to  claim 1  wherein the magnetic field is applied in a direction substantially parallel to said substrate surface.  
   
   
       10 . A method for producing a magnetic recording medium according to  claim 1  wherein the magnetic field is applied in a direction which is substantially parallel to a direction at 45 degrees to said substrate surface.  
   
   
       11 . A method for producing a magnetic recording medium according to  claim 1  wherein the magnetic field is applied in a direction substantially parallel to a direction which is perpendicular to said substrate surface.