Perpendicular magnetic recording medium and a method of manufacturing the same

Abstract

A perpendicular magnetic recording medium has a granular magnetic layer and a nonmagnetic underlayer of a metal or an alloy having a hexagonal close packed (hcp) crystal structure. A seed layer of a metal or an alloy of a face-centered cubic (fcc) crystal structure is provided under the nonmagnetic underlayer. Such a perpendicular magnetic recording medium exhibits excellent magnetic characteristics even when the thickness of the underlayer or the total thickness of the underlayer and the seed layer is very thin. Excellent magnetic characteristics can be obtained even when of the substrate is not preheated. Accordingly, a nonmagnetic substrate, such as a plastic resin can be employed to reduce the manufacturing cost.

1. A perpendicular magnetic recording medium comprising:
 a nonmagnetic substrate; and  
 at least a seed layer, a nonmagnetic underlayer, a magnetic layer, and a protective film sequentially laminated on said substrate,  
 wherein said magnetic layer is composed of ferromagnetic crystal grains and nonmagnetic grain boundaries mainly composed of silicon oxide  an oxide of at least one member selected from the group consisting of Cr, Co, Si, Al, Ti, Ta, Hf and Zr,  
 wherein said nonmagnetic underlayer is composed of a metal or an alloy having a hexagonal close packed crystal structure wherein said metal is selected from a group consisting of Re, Ru, and Os, and said alloy composing said nonmagnetic underlayer contains at least one element selected from a group consisting of Re, Ru, and Os, and  
 wherein the seed layer is composed of a metal or an alloy having a face-centered cubic crystal structure.  
 
     
     
       2. A perpendicular magnetic recording medium according to  claim 1 , wherein said metal composing said seed layer is selected from a group consisting of Cu, Au, Pd, Pt, and Ir, and said alloy composing said seed layer contains at least one element selected from a group consisting of Cu, Au, Pd, Pt, and Ir, or contains at least Ni and Fe. 
     
     
       3. A perpendicular magnetic recording medium according to  claim 1 , further comprising a nonmagnetic alignment-control layer disposed between said seed layer and said nonmagnetic substrate, said alignment control layer being composed of a metal or an alloy that has a body-centered cubic crystal structure or an amorphous structure. 
     
     
       4. A perpendicular magnetic recording medium according to  claim 3 , wherein said metal composing said alignment-control layer is selected from a group consisting of Nb, Mo, Ta, and W, and said alloy composing said alignment-control layer contains at least one element selected from a group consisting of Nb, Mo, Ta, and W. 
     
     
       5. A perpendicular magnetic recording medium according to  claim 1 , wherein said nonmagnetic substrate is composed of a plastic resin. 
     
     
       6. A perpendicular magnetic recording medium according to  claim 3 , wherein said nonmagnetic substrate is composed of a plastic resin. 
     
     
       7. A perpendicular magnetic recording medium according to  claim 1 , wherein said underlayer is at least 2 nm thick. 
     
     
       8. A perpendicular magnetic recording medium according to  claim 1 , wherein said underlayer is at least 5 nm thick. 
     
     
       9. A perpendicular magnetic recording medium according to  claim 7 , wherein said seed layer is at least 3 nm thick. 
     
     
       10. A perpendicular magnetic recording medium according to  claim 7 , wherein said underlayer is at least 5 nm thick. 
     
     
       11. A perpendicular magnetic recording medium according to  claim 8 , wherein said seed layer is at least 3 nm thick. 
     
     
       12. A perpendicular magnetic recording medium according to  claim 8 , wherein said underlayer is at least 5 nm thick. 
     
     
       13. A method of manufacturing perpendicular magnetic recording medium comprising a nonmagnetic substrate and at least a seed layer, a nonmagnetic underlayer, a magnetic layer, and a protective film sequentially laminated on said substrate, wherein said magnetic layer is composed of ferromagnetic crystal grains and nonmagnetic grain boundaries mainly composed of silicon oxide  an oxide of at least one member selected from the group consisting of Cr, Co, Si, Al, Ti, Ta, Hf and Zr, wherein said nonmagnetic underlayer is composed of a metal or an alloy having a hexagonal close packed crystal structure, wherein said metal is selected from a group consisting of Re, Ru, and Os and said alloy composing said nonmagnetic underlayer contains at least one element selected from a group consisting of Re, Ru, and Os, and wherein the seed layer is composed of a metal or an alloy having a face-centered cubic crystal structure, the method comprising the steps of:
 depositing the seed layer on the nonmagnetic substrate;  
 depositing the nonmagnetic underlayer on said seed layer;  
 depositing the magnetic layer on said underlayer; and  
 depositing the protective film on said magnetic layer.  
 
     
     
       14. A method of manufacturing a perpendicular magnetic recording medium according to  claim 13 , wherein each of said depositing steps is conducted while a temperature of said substrate is lower than 80° C. 
     
     
       15. A method of manufacturing a perpendicular magnetic recording medium according to  claim 13 , wherein each of said depositing steps is conducted without preheating said nonmagnetic substrate. 
     
     
       16. A method of manufacturing a perpendicular magnetic recording medium according to  claim 13 , further comprising the step of depositing a nonmagnetic alignment-control layer composed of a metal or an alloy having a body-centered cubic crystal structure or an amorphous structure on said nonmagnetic substrate before depositing said seed layer. 
     
     
       17. A method of manufacturing a perpendicular magnetic recording medium according to  claim 16 , wherein each of said depositing steps is conducted while a temperature of said substrate is lower than 80° C. 
     
     
       18. A method of manufacturing a perpendicular magnetic recording medium according to  claim 16 , wherein each of said depositing steps is conducted without preheating said nonmegnetic  nonmagnetic substrate. 
     
     
       19. A perpendicular magnetic recording medium comprising: a nonmagnetic substrate; and at least a seed layer, a nonmagnetic underlayer, a magnetic layer, and a protective film sequentially laminated on said substrate, wherein said magnetic layer is composed of ferromagnetic crystal grains and nonmagnetic grain boundaries mainly composed of an oxide of at least one member selected from the group consisting of Si, Al, Ti, Ta, Hf and Zr, wherein said nonmagnetic underlayer is composed of a metal or an alloy having a hexagonal close packed crystal structure wherein said metal is selected from a group consisting of Re, Ru, and Os, and said alloy composing said nonmagnetic underlayer contains at least one element selected from a group consisting of Re, Ru, and Os, and wherein the seed layer is composed of a metal or an alloy having a face- centered cubic crystal structure.   
     
     
       20. A method of manufacturing a perpendicular magnetic recording medium comprising a nonmagnetic substrate and at least a seed layer, a nonmagnetic underlayer, a magnetic layer, and a protective film sequentially laminated on said substrate, wherein said magnetic layer is composed of ferromagnetic crystal grains and nonmagnetic grain boundaries mainly composed of an oxide of at least one member selected from the group consisting of Si, Al, Ti, Ta, Hf and Zr, wherein said nonmagnetic underlayer is composed of a metal or an alloy having a hexagonal close packed crystal structure, wherein said metal is selected from a group consisting of Re, Ru, and Os and said alloy composing said nonmagnetic underlayer contains at least one element selected from a group consisting of Re, Ru, and Os, and wherein the seed layer is composed of a metal or an alloy having a face- centered cubic crystal structure, the method comprising the steps of: depositing the seed layer on the nonmagnetic substrate; depositing the nonmagnetic underlayer on said seed layer; depositing the magnetic layer on said underlayer; and depositing the protective film on said magnetic layer.