Substrate for magnetic disk

Abstract

A method for manufacturing a substrate for a magnetic disk, including the steps of (a) polishing a substrate with a polishing composition A containing alumina abrasives having an average particle size of from 0.05 to 0.5 μm, and an oxidizing agent, and (b) polishing the substrate with a polishing composition B containing silica particles having an average particle size of from 0.005 to 0.1 μm; a substrate for a magnetic disk, obtainable by the method for manufacturing a substrate for a magnetic disk; and a substrate for a magnetic disk having the following surface properties of a long-wavelength waviness of 0.05 nm or more and 0.3 nm or less, and an AFM surface roughness of 0.03 nm or more and 0.2 nm or less. The substrate for a magnetic disk may be suitably used in the manufacture of a hard disk having a high recording density. Especially, a hard disk having a recording density of 50 G bits or more per square inch may be industrially manufactured.

1 . A method for manufacturing a substrate for a magnetic disk, comprising the steps of: 
 (a) polishing a substrate with a polishing composition A comprising alumina abrasives having an average particle size of from 0.05 to 0.5 μm, and an oxidizing agent; and    (b) polishing the substrate with a polishing composition B comprising silica particles having an average particle size of from 0.005 to 0.1 μm.    
     
     
         2 . The method according to  claim 1 , wherein the alumina abrasives comprise an α-alumina and an intermediate alumina, wherein the weight ratio of the α-alumina to the intermediate alumina, α-alumina/intermediate alumina, is from 99/1 to 30/70.  
     
     
         3 . The method according to  claim 1 , wherein the oxidizing agent is a peroxide.  
     
     
         4 . The method according to  claim 1 , wherein the polishing composition A further comprises an acid.  
     
     
         5 . The method according to  claim 3 , wherein the polishing composition A further comprises an acid.  
     
     
         6 . The method according to  claim 1 , wherein the substrate obtained after step (a) has surface properties of a long-wavelength waviness of 0.05 nm or more and 0.4 nm or less.  
     
     
         7 . The method according to  claim 4 , wherein the substrate obtained after step (a) has surface properties of a long-wavelength waviness of 0.05 nm or more and 0.4 nm or less.  
     
     
         8 . The method according to  claim 1 , wherein the polished amount of the substrate that has been polished before step (b) is performed is 0.8 μm or more, and the polished amount of the substrate that has been polished during step (a) is 0.2 μm or more, wherein the polished amount is expressed in terms of the polished-off thickness of the substrate.  
     
     
         9 . The method according to  claim 4 , wherein the polished amount of the substrate that has been polished before step (b) is performed is 0.8 μm or more, and the polished amount of the substrate that has been polished during step (a) is 0.2 μm or more, wherein the polished amount is expressed in terms of the polished-off thickness of the substrate.  
     
     
         10 . The method according to  claim 1 , wherein the substrate obtained after step (b) has surface properties of a long-wavelength waviness of 0.05 nm or more and 0.3 nm or less, and an AFM surface roughness of 0.03 nm or more and 0.2 nm or less.  
     
     
         11 . The method according to  claim 4 , wherein the substrate obtained after step (b) has surface properties of a long-wavelength waviness of 0.05 nm or more and 0.3 nm or less, and an AFM surface roughness of 0.03 nm or more and 0.2 nm or less.  
     
     
         12 . The method according to  claim 6 , wherein the substrate obtained after step (b) has surface properties of a long-wavelength waviness of 0.05 nm or more and 0.3 nm or less, and an AFM surface roughness of 0.03 nm or more and 0.2 nm or less.  
     
     
         13 . The method according to  claim 1 , wherein the substrate that is to be subjected to step (b) has surface properties of a long-wavelength waviness of 0.05 nm or more and 0.4 nm or less.  
     
     
         14 . The method according to  claim 4 , wherein a substrate that is to be subjected to step (b) has surface properties of a long-wavelength waviness of 0.05 nm or more and 0.4 nm or less.  
     
     
         15 . A substrate for a magnetic disk obtained by the method of  claim 1 .  
     
     
         16 . The substrate according to  claim 15 , wherein the substrate has the following surface properties: 
 a long-wavelength waviness of 0.05 nm or more and 0.3 nm or less, and    an AFM surface roughness of 0.03 nm or more and 0.2 nm or less.    
     
     
         17 . The substrate according to  claim 15 , wherein the substrate after step (a) has surface properties of a long-wavelength waviness of 0.05 nm or more and 0.4 nm or less.  
     
     
         18 . The substrate according to  claim 15 , wherein the substrate that is to be subjected to step (b) has surface properties of a long-wavelength waviness of 0.05 nm or more and 0.4 nm or less.  
     
     
         19 . A substrate for a magnetic disk having the following surface properties: 
 a long-wavelength waviness of 0.05 nm or more and 0.3 nm or less, and    an AFM surface roughness of 0.03 nm or more and 0.2 nm or less.    
     
     
         20 . The substrate according to  claim 19 , wherein the substrate is used for a hard disk having a recording density of 50 G bits or more per square inch.