Magnetic recording medium and method for manufacturing same

Abstract

A magnetic recording medium has a non-magnetic under-layer, a magnetic layer, a protective film and a liquid lubricant layer sequentially laminated on a non-magnetic substrate. The magnetic layer has a multi-layer structure laminated with two or more magnetic layer components, each of the magnetic layer components having ferromagnetic grains and non-magnetic grain boundaries surrounding the grain. The resulting magnetic recording medium has a granular magnetic layer exhibiting very high Hc accompanying high density of magnetic recording, while decreasing the amount of platinum needed for attaining the high Hc, and reducing media noise accompanying the high recording density.

What is claimed is:  
     
         1 . A magnetic recording medium comprising: 
 a non-magneticmagnetic under-layer, a magnetic layer, a protective film, and a liquid lubricant layer sequentially laminated on a non-magneticmagnetic substrate, wherein    said magnetic layer has a layered structure including at least two magnetic layer components, each of said magnetic layer components having ferromagnetic grains and non-magneticmagnetic grain boundaries surrounding said ferromagnetic grains.    
     
     
         2 . The magnetic recording medium according to  claim 1 , wherein said at least two magnetic layer components have a composition different from one another.  
     
     
         3 . The magnetic recording medium according to  claim 1 , wherein said non-magneticmagnetic grain boundaries are composed of an oxide or a nitride of at least one element selected from the group consisting of Cr, Co, Si, Al, Ti, Ta, Hf and Zr.  
     
     
         4 . The magnetic recording medium according to  claim 1 , wherein said under-layer is composed of chromium or chromium alloy.  
     
     
         5 . The magnetic recording medium according to  claim 1 , wherein said substrate is composed of one of a crystallized glass, a chemically strengthened glass and a plastic.  
     
     
         6 . A magnetic recording medium comprising: 
 a non-magneticmagnetic under-layer, a magnetic layer, a protective film, and a liquid lubricant layer sequentially laminated on a non-magneticmagnetic substrate, wherein    said magnetic layer includes at least two magnetic layer components and at least three oxide layers; and    said magnetic layer components and said oxide layers are alternately disposed such that a top layer and a bottom layer in said magnetic layer are two of said at least three oxide layers.    
     
     
         7 . The magnetic recording medium according to  claim 6 , wherein each of said magnetic layer components having ferromagnetic grains and non-magneticmagnetic grain boundaries surrounding said ferromagnetic grains.  
     
     
         8 . The magnetic recording medium according to  claim 7 , wherein said non-magneticmagnetic grain boundaries are composed of an oxide or nitride of at least one element selected from the group consisting of Cr, Co, Si, Al, Ti, Ta, Hf and Zr.  
     
     
         9 . The magnetic recording medium according to  claim 6 , wherein said under-layer is composed of chromium or chromium alloy.  
     
     
         10 . The magnetic recording medium according to  claim 6 , wherein said substrate is composed of one of a crystallized glass, a chemically strengthened glass and a plastic.  
     
     
         11 . A method for manufacturing a magnetic recording medium comprising: 
 laminating a non-magneticmagnetic under-layer on a non-magneticmagnetic substrate;    laminating a magnetic layer on said under-layer by depositing a plurality of magnetic layer components, each of said magnetic layer components comprising ferromagnetic grains and grain boundaries surrounding said grains;    laminating a protective film on said magnetic layer; and    laminating a liquid lubricant layer on said protective film.    
     
     
         12 . The method for manufacturing a magnetic recording medium according to  claim 11 , wherein said step for laminating said magnetic layer is a step of depositing a plurality of magnetic layer components, each component having different composition from one another.  
     
     
         13 . The method for manufacturing a magnetic recording medium according to  claim 11 , wherein each step is performed without heating said substrate in advance.  
     
     
         14 . A method for manufacturing a magnetic recording medium comprising: 
 laminating a non-magneticmagnetic under-layer on a non-magneticmagnetic substrate;    laminating a magnetic layer on said under-layer by 
 (i)exposing to an atmosphere of oxygen-containing gas and forming an oxide layer on a surface,  
 (ii) depositing a magnetic layer component comprising ferromagnetic grains and grain boundaries surrounding said grains,  
 (iii) repeating the procedures (i) and (ii) predetermined times, and  
 (iv) exposing to said atmosphere of oxygen-containing gas and forming an oxide layer on a surface;  
   laminating a protective film on said magnetic layer; and    laminating a liquid lubricant layer on said protective film.    
     
     
         15 . The method for manufacturing a magnetic recording medium according to  claim 14 , wherein each step is performed without heating said substrate in advance.