Magnetic recording medium

Abstract

A magnetic recording medium for perpendicular magnetic recording system includes a nonmagnetic substrate and layers sequentially laminated on the substrate. The layers include a seed layer comprised of a metal or an alloy with a face centered cubic crystal structure, a nonmagnetic underlayer of a metal or an alloy with a hexagonal closest packed crystal structure, a magnetic layer having a granular structure including ferromagnetic crystalline grains with a hexagonal closest packed structure and nonmagnetic grain boundary region of mainly oxide surrounding the crystalline grains, a protective layer, and a liquid lubricant layer.

1 . A magnetic recording medium for a perpendicular magnetic recording system comprising a nonmagnetic substrate and layers sequentially laminated on the substrate, the layers including 
 a nonmagnetic underlayer comprising a metal or an alloy with a hexagonal closest packed crystal structure,    a magnetic layer having a granular structure comprised of ferromagnetic crystalline grains with a hexagonal closest packed structure and nonmagnetic grain boundary region of mainly oxide surrounding the ferromagnetic crystalline grains,    a protective layer, and    a liquid lubricant layer.    
     
     
         2 . A magnetic recording medium according to  claim 1 , wherein a degree of mismatching between an a-axis lattice constant of the nonmagnetic underlayer and an a-axis lattice constant of the magnetic layer is not larger than 10%.  
     
     
         3 . A magnetic recording medium according to  claim 2 , wherein a proportion of crystalline grains larger than 8 nm in the nonmagnetic underlayer is not larger than 10% of whole crystalline grains in the nonmagnetic underlayer, and a standard deviation of the grain sizes of the crystalline grains is at most 1.4 nm.  
     
     
         4 . A magnetic recording medium according to  claim 1 , wherein the underlayer is comprised of a metal selected from Re, Ru, and Os, or an alloy mainly comprised of one or more metals selected from Ru, Os, and Re.  
     
     
         5 . A magnetic recording medium according to  claim 2 , wherein the underlayer is comprised of a metal selected from Re, Ru, and Os, or an alloy mainly comprised of one or more metals selected from Ru, Os, and Re.  
     
     
         6 . A magnetic recording medium according to  claim 3 , wherein the underlayer is comprised of a metal selected from Re, Ru, and Os, or an alloy mainly comprised of one or more metals selected from Ru, Os, and Re.  
     
     
         7 . A magnetic recording medium according to  claim 1 , wherein the oxide is comprised of an oxide of at least an element selected from Cr, Co, Si, Al, Ti, Ta, Hf, and Zr.  
     
     
         8 . A magnetic recording medium according to  claim 2 , wherein the oxide is comprised of an oxide of at least an element selected from Cr, Co, Si, Al, Ti, Ta, Hf, and Zr.  
     
     
         9 . A magnetic recording medium according to  claim 3 , wherein the oxide is comprised of an oxide of at least an element selected from Cr, Co, Si, Al, Ti, Ta, Hf, and Zr.  
     
     
         10 . A magnetic recording medium according to  claim 4 , wherein the oxide is comprised of an oxide of at least an element selected from Cr, Co, Si, Al, Ti, Ta, Hf, and Zr.  
     
     
         11 . A magnetic recording medium according to  claim 5 , wherein the oxide is comprised of an oxide of at least an element selected from Cr, Co, Si, Al, Ti, Ta, Hf, and Zr.  
     
     
         12 . A magnetic recording medium according to  claim 6 , wherein the oxide is comprised of an oxide of at least an element selected from Cr, Co, Si, Al, Ti, Ta, Hf, and Zr.  
     
     
         13 . A magnetic recording medium according to  claim 1 , wherein the ferromagnetic crystalline grains are comprised of a CoPt alloy containing an additive element selected from Cr, Ni, and Ta.  
     
     
         14 . A magnetic recording medium according to  claim 2 , wherein the ferromagnetic crystalline grains are comprised of a CoPt alloy containing an additive element selected from Cr, Ni, and Ta.  
     
     
         15 . A magnetic recording medium according to  claim 3 , wherein the ferromagnetic crystalline grains are comprised of a CoPt alloy containing an additive element selected from Cr, Ni, and Ta.  
     
     
         16 . A magnetic recording medium according to  claim 4 , wherein the ferromagnetic crystalline grains are comprised of a CoPt alloy containing an additive element selected from Cr, Ni, and Ta.  
     
     
         17 . A magnetic recording medium according to  claim 5 , wherein the ferromagnetic crystalline grains are comprised of a CoPt alloy containing an additive element selected from Cr, Ni, and Ta.  
     
     
         18 . A magnetic recording medium according to  claim 6 , wherein the ferromagnetic crystalline grains are comprised of a CoPt alloy containing an additive element selected from Cr, Ni, and Ta.  
     
     
         19 . A magnetic recording medium according to  claim 7 , wherein the ferromagnetic crystalline grains are comprised of a CoPt alloy containing an additive element selected from Cr, Ni, and Ta.  
     
     
         20 . A magnetic recording medium according to  claim 8 , wherein the ferromagnetic crystalline grains are comprised of a CoPt alloy containing an additive element selected from Cr, Ni, and Ta.  
     
     
         21 . A magnetic recording medium according to  claim 9 , wherein the ferromagnetic crystalline grains are comprised of a CoPt alloy containing an additive element selected from Cr, Ni, and Ta.  
     
     
         22 . A magnetic recording medium according to  claim 10 , wherein the ferromagnetic crystalline grains are comprised of a CoPt alloy containing an additive element selected from Cr, Ni, and Ta.  
     
     
         23 . A magnetic recording medium according to  claim 11 , wherein the ferromagnetic crystalline grains are comprised of a CoPt alloy containing an additive element selected from Cr, Ni, and Ta.  
     
     
         24 . A magnetic recording medium according to  claim 12 , wherein the ferromagnetic crystalline grains are comprised of a CoPt alloy containing an additive element selected from Cr, Ni, and Ta.