Perpendicular magnetic recording medium and method for manufacturing same

Abstract

A perpendicular magnetic recording medium is disclosed in which each magnetic crystal grain in the magnetic recording layer has a multilayer structure and has a configuration like a truncated cone shape, in which the crystal grain of the final layer deposited in the film surface side at the final stage is smaller than the diameter of the crystal grain in the initial layer deposited on the substrate side at the initial stage. The invention improves S/N (signal output to noise ratio) by enhancing signal output and reducing noises. The medium is produced by a simple manufacturing method suitable for mass production, and provides a medium of high recording density by improving recording resolution.

1 . A perpendicular magnetic recording medium comprising a magnetic recording layer that includes a plurality of magnetic crystal grains formed on a nonmagnetic substrate, wherein each magnetic crystal grain has a laminated multilayer structure, layers of which vary in diameter such that layers at the nonmagnetic substrate side of the magnetic recording layer have a larger diameter than layers at the opposite side of the magnetic recording layer.  
   
   
       2 . The medium according to  claim 1 , wherein the magnetic crystal grains are formed in a truncated cone shape that is smaller at a top face of the magnetic recording layer than at a bottom face of the magnetic recording layer that faces the nonmagnetic substrate.  
   
   
       3 . The medium according to  claim 1 , wherein the magnetic recording layer comprises magnetic materials containing ferromagnetic particles that are dispersed in oxides or nitrides.  
   
   
       4 . The medium according to  claim 3 , wherein the magnetic recording layer is composed of a granular structure including a CoCrPt alloy dispersed in SiO 2 .  
   
   
       5 . The medium according to  claim 1 , wherein the magnetic crystal grains exhibit saturation magnetization that varies from the layer that faces the nonmagnetic substrate side towards the layer at the opposite side of the magnetic recording layer.  
   
   
       6 . The medium according to  claim 5 , wherein the magnetic crystal grains exhibit saturation magnetization that increases from the layer that faces the nonmagnetic substrate side towards the layer at the opposite side of the magnetic recording layer.  
   
   
       7 . The medium according to  claim 1 , comprising a soft magnetic backing layer, a nonmagnetic intermediate layer, and the magnetic recording layer comprising the magnetic crystal grains sequentially laminated on the nonmagnetic substrate.  
   
   
       8 . A method for manufacturing a perpendicular magnetic recording medium that comprises a magnetic recording layer formed on a nonmagnetic substrate, the magnetic recording layer including a plurality of magnetic crystal grains, the method including a process for forming the magnetic recording layer that comprises: 
 conducting a plurality of film depositions, from a first deposition conducted at an initial stage of the process at a substrate side to a final deposition conducted at a film surface side, and    varying concentration of oxygen or nitrogen that is contained in a gas used in the film deposition steps, during the plurality of film depositions,    wherein the plurality of film depositions while concentration is varied produces a plurality of magnetic crystal grains each having a laminated multilayer structure, in which each layer corresponds to one of the film depositions, and a diameter of the magnetic crystal grain deposited in the final deposition is less than a diameter of the magnetic crystal grain deposited in the first deposition.    
   
   
       9 . The method according to  claim 8 , wherein the concentration of oxygen or nitrogen increases with progression of the film depositions.  
   
   
       10 . A method for manufacturing a perpendicular magnetic recording medium that comprises a magnetic recording layer formed on a nonmagnetic substrate, the magnetic recording layer including a plurality of magnetic crystal grains, the method comprising a process for forming the magnetic recording layer that comprises: 
 conducting a plurality of film depositions, from a first deposition conducted at an initial stage of the process at a substrate side to a final deposition conducted at a film surface side, and    exposure of a surface formed during each of said film depositions to a gas containing oxygen or nitrogen before conducting the next film deposition,    wherein the plurality of film depositions and intervening exposures to oxygen or nitrogen produces a plurality of magnetic crystal grains each having a laminated multilayer structure, in which each layer corresponds to one of the film depositions, and a diameter of the magnetic crystal grain deposited in the final deposition is less than a diameter of the magnetic crystal grain deposited in the first deposition.    
   
   
       11 . The method according to  claim 10 , wherein the concentration of oxygen or nitrogen increases with progression of the exposures.  
   
   
       12 . The method according to  claim 8 , wherein each film deposition from the first to the final is conducted in a gas containing oxygen using a granular material including a CoCrPt alloy dispersed in SiO 2 .  
   
   
       13 . The method according to  claim 10 , wherein each film deposition from the first to the final is conducted in a gas containing the oxygen using a granular material including a CoCrPt alloy dispersed in SiO 2 .