Magnetic recording medium and magnetic storage apparatus

Abstract

A magnetic recording medium is constructed to include at least one exchange layer structure and a magnetic layer provided on the exchange layer structure. The exchange layer structure includes a ferromagnetic layer and a non-magnetic coupling layer provided on the ferromagnetic layer. At least one of the ferromagnetic layer and the magnetic layer has a granular layer structure in which ferromagnetic crystal grains are uniformly distributed within a non-magnetic base material.

What is claimed is:  
     
         1 . A magnetic recording medium comprising: 
 at least one exchange layer structure; and    a magnetic layer provided on the exchange layer structure,    said exchange layer structure including a ferromagnetic layer and a non-magnetic coupling layer provided on the ferromagnetic layer,    at least one of said ferromagnetic layer and said magnetic layer having a granular layer structure in which ferromagnetic crystal grains are uniformly distributed within a non-magnetic base material.    
     
     
         2 . The magnetic recording medium as claimed in  claim 1 , wherein said ferromagnetic crystal grains are made of a material selected from a group of Co, Ni, Fe, Ni-based alloys, Fe-based alloys, and Co-based alloys including CoCrTa, CoCrPt and CoCrPt—M, where M=B, Mo, Nb, Ta, W, Cu and alloys thereof.  
     
     
         3 . The magnetic recording medium as claimed in  claim 1 , wherein said non-magnetic base material is made of a material selected from a group of ceramic materials and oxide materials.  
     
     
         4 . The magnetic recording medium as claimed in  claim 1 , wherein said non-magnetic coupling layer is made of a material selected from a group of Ru, Rh, Ir, Ru-based alloys, Rh-based alloys. and Ir-based alloys.  
     
     
         5 . The magnetic recording medium as claimed in  claim 1 , wherein magnetization directions of the ferromagnetic layer and the magnetic layer are mutually antiparallel.  
     
     
         6 . The magnetic recording medium as claimed in  claim 5 , wherein said non-magnetic coupling layer is made of a material selected from a group of Ru, Rh, Ir, Ru-based alloys, Rh-based alloys and Ir-based alloys, and has a thickness in a range of approximately 0.4 to 1.0 nm.  
     
     
         7 . The magnetic recording medium as claimed in  claim 1 , wherein magnetization directions of the ferromagnetic layer and the magnetic layer are mutually parallel.  
     
     
         8 . The magnetic recording medium as claimed in  claim 7 , wherein said non-magnetic coupling layer is made of a material selected from a group of Ru, Rh, Ir, Ru-based alloys, Rh-based alloys and Ir-based alloys, and has a thickness in a range of approximately 0.2 to 0.4 nm and 1.0 to 1.7 nm.  
     
     
         9 . The magnetic recording medium as claimed in  claim 1 , wherein said non-magnetic coupling layer is added with a ceramic material or an oxide material.  
     
     
         10 . The magnetic recording medium as claimed in  claim 1 , which further comprises: 
 an underlayer provided above said substrate;    a ferromagnetic layer having a granular layer structure and provided on the underlayer; and    a non-magnetic intermediate layer provided between the underlayer and the ferromagnetic layer,    said non-magnetic intermediate layer being made of a CoCr—M alloy having a hcp structure and having a thickness of approximately 1 to 5 nm, where M=B, Mo, Nb, Ta, W, Cu or alloys thereof.    
     
     
         11 . The magnetic recording medium as claimed in  claim 10 , which further comprises: 
 a NiP layer provided between said substrate and said underlayer,    said NiP layer being mechanically textured or oxidized.    
     
     
         12 . The magnetic recording medium as claimed in  claim 10 , wherein said underlayer is made of an alloy having a B 2  structure and selected from a group of NiAl and FeAl.  
     
     
         13 . The magnetic recording medium as claimed in  claim 1 , which comprises at least a first exchange layer structure and a second exchange layer structure provided between the first exchange layer structure and the magnetic layer, 
 said first and second exchange layer structures having a granular layer structure,    said second exchange layer structure having a granular layer with a magnetic anisotropy smaller than that of a granular layer of the first exchange layer structure, and the granular layers of said first and second exchange layer structures having magnetization directions which are mutually antiparallel.    
     
     
         14 . The magnetic recording medium as claimed in  claim 1 , which comprises at least a first exchange layer structure and a second exchange layer structure provided between the first exchange layer structure and the magnetic layer, 
 said first and second exchange layer structures having a granular layer structure,    said second exchange layer structure having a granular layer with a remanence magnetization and thickness product smaller than that of a granular layer of the first exchange layer structure, and the granular layers of said first and second exchange layer structures having magnetization directions which are mutually antiparallel.    
     
     
         15 . A magnetic storage apparatus comprising: 
 at least one magnetic recording medium including at least one exchange layer structure, and a magnetic layer provided on the exchange layer structure,    said exchange layer structure including a ferromagnetic layer and a non-magnetic coupling layer provided on the ferromagnetic layer,    at least one of said ferromagnetic layer and said magnetic layer having a granular layer structure in which ferromagnetic crystal grains are uniformly distributed within a non-magnetic base material.