Substrate for perpendicular magnetic recording hard disk medium and method for producing the same

Abstract

Proposed are a substrate that comprises an easily producible soft magnetic backing film and can reduce spike noise from the soft magnetic backing film, and a method for producing the substrate. More specifically, provided are a substrate for a perpendicular magnetic recording hard disk medium, comprising an Si single crystal substrate ( 1 ) having a diameter of 65 mm or less, a thickness of 1 mm or less and an average surface roughness (Rms) of 1 nm or more and 1000 nm or less; an under-plated layer ( 2 ) formed on the substrate, the layer ( 2 ) comprising one or more metals selected from a group consisting of Ni, Cu and Ag and having a thickness of 1 nm to 300 nm; and a plated soft magnetic layer ( 3 ) formed on the under-plated layer, the layer ( 3 ) having a thickness of 50 nm or more and less than 1000 nm, a coercivity of 20 Oe(oersteds) or less and a saturation magnetization of 1T or more, wherein the average surface roughness (Rms) of the plated soft magnetic layer is 0.1 nm or more and 5 nm or less.

1 . A substrate for a perpendicular magnetic recording hard disk medium, comprising 
 an Si single crystal substrate having a diameter of 65 mm or less, a thickness of 1 mm or less and an average surface roughness (Rms) of 1 nm or more and 1000 nm or less;    an under-plated layer formed on said substrate, the under-plated layer comprising one or more metals selected from a group consisting of Ni, Cu and Ag and having a thickness of 1 nm to 300 nm;    and a plated soft magnetic layer formed on said under-plated layer, the plated soft magnetic layer having a thickness of 50 nm or more and less than 1000 nm, coercivity of 20 Oe(oersteds) or less and a saturation magnetization of 1T or more,    wherein the average surface roughness (Rms) of said plated soft magnetic layer is 0.1 nm or more and 5 nm or less.    
     
     
         2 . The substrate for a perpendicular magnetic recording hard disk medium according to  claim 1 , having induced anisotropy on the surface thereof.  
     
     
         3 . A method for producing a substrate for a perpendicular magnetic recording hard disk medium, comprising steps of 
 carrying out under-plating to form an under-plated layer comprising one or more metals selected from a group consisting of Ni, Cu and Ag on an Si single crystal substrate having a diameter of 65 mm or less, a thickness of 1 mm or less and an average surface roughness (Rms) of 1 nm or more and 1000 nm or less;    forming a plated soft magnetic layer having coercivity of 20 Oe(oersteds) or less and a saturation magnetization of 1T or more on said under-plated layer;    and polishing said plated soft magnetic layer so as to have an average surface roughness (Rms) of 0.1 nm or more and 5 nm or less.    
     
     
         4 . The method for producing a substrate for a perpendicular magnetic recording hard disk medium according to  claim 3 , comprising a pretreatment step of etching said Si single crystal substrate preceding the step of carrying out the under-plating.  
     
     
         5 . The method for producing a substrate for a perpendicular magnetic recording hard disk medium according to  claim 3 , wherein the step of carrying out the under-plating comprises electroless plating.  
     
     
         6 . The method for producing a substrate for a perpendicular magnetic recording hard disk medium according to  claim 3 , wherein the pretreatment step comprises chemically etching the Si single crystal substrate.  
     
     
         7 . The method for producing a substrate for a perpendicular magnetic recording hard disk medium according to  claim 4 , wherein the pretreatment step comprises etching in an alkaline aqueous solution comprising one or more selected from the group consisting of NaOH, KOH and ammonia.  
     
     
         8 . The method for producing a substrate for a perpendicular magnetic recording hard disk medium according to  claim 4 , wherein the pretreatment step comprises etching in an acidic aqueous solution comprising one or more selected from the group consisting of hydrofluoric acid, hydrochloric acid and nitric acid.  
     
     
         9 . The method for producing a substrate for a perpendicular magnetic recording hard disk medium according to  claim 3 , wherein said substrate has induced anisotropy on the surface thereof.  
     
     
         10 . The method for producing a substrate for a perpendicular magnetic recording hard disk medium according to  claim 3 , wherein said step of forming said plated soft magnetic layer is carried out in a magnetic field having an intensity of 10 G or more and 1000 G or less.  
     
     
         11 . The method for producing a substrate for a perpendicular magnetic recording hard disk medium according to  claim 3 , preceding the step of carrying out the under-plating, comprising a step of mirror-polishing said Si single crystal substrate and a subsequent pretreatment step of etching in a mixed aqueous solution of ammonia and hydrogen peroxide.  
     
     
         12 . The method for producing a substrate for a perpendicular magnetic recording hard disk medium according to  claim 3 , wherein the sep of forming said plated soft magnetic layer comprises electroless plating.