Perpendicular magnetic recording medium and method of manufacturing the same and product thereof

Abstract

The quantity of oxide contained in a magnetic layer is controlled to control the crystal grains and the segregation structure for ensuring low noise characteristic in a granular magnetic layer of a perpendicular magnetic recording medium. The granular magnetic layer consists of ferromagnetic crystal grains and a nonmagnetic grain boundary region mainly of an oxide surrounding the ferromagnetic crystal grains. The perpendicular magnetic recording medium has a nonmagnetic underlayer composed of a metal or alloy having hexagonal closest-packed crystal structure. The ferromagnetic crystal grain is composed of an alloy containing at least cobalt and platinum. The volume proportion of the nonmagnetic grain boundary region mainly of the oxide falls within a range of 15% to 40% of the volume of the total magnetic layer.

1 . A perpendicular magnetic recording medium comprising: 
 a nonmagnetic substrate; and    at least a nonmagnetic underlayer, a magnetic layer, and a protective film sequentially laminated on the substrate,    wherein the nonmagnetic underlayer is composed of a metal or alloy having a hexagonal closest-packed (hcp) crystal structure,    wherein the magnetic layer consists essentially of ferromagnetic crystal grains and a nonmagnetic grain boundary region, the nonmagnetic grain boundary region being composed of an oxide surrounding the ferromagnetic crystal grains,    wherein the ferromagnetic crystal grains are composed of an alloy containing at least cobalt and platinum,    wherein the oxide in the magnetic layer is an oxide of Mg, Ti, Zr, or Si, and    wherein a volume occupied by the grain boundary region falls within a range of 15% to 40% of a total volume of the magnetic layer.    
   
   
       2 . A perpendicular magnetic recording medium according to  claim 1 , wherein the magnetic layer has a thickness falling within a range of 5 nm to 20 nm.  
   
   
       3 . A perpendicular magnetic recording medium according to  claim 1 , wherein the substrate is composed of a plastic resin.  
   
   
       4 . A perpendicular magnetic recording medium according to  claim 2 , wherein the substrate is composed of a plastic resin.  
   
   
       5 . A method of manufacturing a perpendicular magnetic recording medium, comprising steps of: 
 depositing a nonmagnetic underlayer composed of a metal or an alloy having a hexagonal closest-packed (hcp) crystal structure on a nonmagnetic substrate;    depositing a magnetic layer consisting essentially of ferromagnetic crystal grains and a nonmagnetic grain boundary region surrounding the ferromagnetic crystal grains by sputtering using a composite target containing a ferromagnetic alloy and an oxide on the underlayer,    wherein the ferromagnetic crystal grains are composed of an alloy containing at least cobalt and platinum, and    wherein a volume occupied by the oxide contained in the composite target falls within a range of 20% to 35% of a total volume of the target.    
   
   
       6 . A method of manufacturing a perpendicular magnetic recording medium according to  claim 5 , wherein the oxide in the target is an oxide of Mg, Cr, Ti, Zr, or Si.  
   
   
       7 . A method of manufacturing a perpendicular magnetic recording medium according to  claim 5 , wherein the oxide in the target is SiO 2 .  
   
   
       8 . A method of manufacturing a perpendicular magnetic recording medium according to  claim 6 , wherein the oxide in the magnetic layer is an oxide of Mg, Cr, Ti, Zr, or Si.  
   
   
       9 . A method of manufacturing a perpendicular magnetic recording medium according to  claim 7 , wherein the oxide in the magnetic layer is SiO 2 .  
   
   
       10 . A method of manufacturing a perpendicular magnetic recording medium according to  claim 5 , wherein a volume of the grain boundary region falls within a range of 15% to 40% of a total volume of the magnetic layer.  
   
   
       11 . A method of manufacturing a perpendicular magnetic recording medium according to  claim 8 , wherein a volume of the grain boundary region falls within a range of 15% to 40% of a total volume of the magnetic layer.  
   
   
       12 . A method of manufacturing a perpendicular magnetic recording medium according to  claim 9 , wherein a volume of the grain boundary region falls within a range of 15% to 40% of a total volume of the magnetic layer.