Magnetic recording medium underlayer and method for obtaining a desired lattice parameter therefor

Abstract

An underlayer ( 8 A) of a magnetic recording medium ( 16 ) includes first and second non-magnetic, chromium-based layers ( 18, 20 ), at least one of the first and second chromium-based layers being a chromium alloy. The lattice parameter of the composite underlayer is between the lattice parameters of the first and second chromium-based layers. Recognizing this permits one to predictably adjust the lattice parameter of the composite underlayer to be close to the lattice parameter of the magnetic layer ( 10 ) so to optimize magnetic and parametric properties.

What is claimed is:  
     
         1 . A magnetic recording medium comprising: 
 a substrate;    an underlayer supported by the substrate, the underlaying comprising first and second non-magnetic, chromium-based layers, at least one of the first and second chromium-based layers being a chromium alloy, the compositions of the first and second chromium-based layers being different, the lattice parameter of the underlayer being between the lattice parameters of the first and second chromium-based layers; and    a magnetic layer deposited on the underlayer.    
     
     
         2 . The magnetic recording medium according to  claim 1  wherein the substrate is a chosen one of a NiP or a ceramic glass substrate, and the magnetic layer comprises a cobalt alloy.  
     
     
         3 . The magnetic recording medium according to  claim 1  further comprising a protective layer deposited on the magnetic layer, a lubricant deposited on the protective layer and a non-magnetic seedlayer between the substrate and the underlayer.  
     
     
         4 . The magnetic recording medium according to  claim 1  wherein the at least one of the chromium-based layers comprises an alloy chosen from the following group: C, Mg, Al, Si, Ti, V, Co, Ni, Cu, Zr, Mo, Nb, La, Ce, Nd, Gd, Tb, Dy, Er, Ta, W and Mn.  
     
     
         5 . The magnetic recording medium according to  claim 1  wherein the thickness of the underlayer is about 180-200Å.  
     
     
         6 . The magnetic recording medium according to  claim 1  wherein the thickness of the underlayer is less than about 350Å.  
     
     
         7 . The magnetic recording medium according to  claim 1  wherein said first and second chromium-based layers are each between about 10 to 340Å.  
     
     
         8 . The magnetic recording medium according to  claim 1  wherein the first-chromium-based layer is an all-chromium layer and the second chromium-based layer is a Cr/20% Mo alloy.  
     
     
         9 . A non-magnetic underlayer for a magnetic recording medium comprising: 
 first and second non-magnetic, chromium-based layers, at least one of the first and second chromium-based layers being a chromium alloy, the compositions of the first and second chromium-based layers being different, the lattice parameter of the underlayer being between the lattice parameters of the first and second chromium-based layers.    
     
     
         10 . A method for obtaining a desired lattice parameter for a non-magnetic underlayer in the manufacture of a magnetic recording medium of the type comprising a substrate, a non-magnetic underlayer on the substrate and a magnetic layer on the underlayer, comprising: 
 determining a desired lattice parameter for the underlayer, the underlayer having a thickness;    selecting a plurality of non-magnetic, chromium-based layers for the underlayer, at least one of said chromium-based layers being a chromium alloy; and    choosing a fractional thickness for each of the chromium-based layers according to the desired lattice parameter, the sum of the fractional thicknesses for each of the chromium-based layers being equal to the underlayer thickness.    
     
     
         11 . The magnetic recording medium according to  claim 10  wherein the selecting step selects two said chromium-based layers.  
     
     
         12 . The magnetic recording medium according to  claim 11  wherein the choosing step is carried out using a ratio of the two fractional thickness of said two chromium-based layers versus corresponding (002) interplanar spacing as the lattice parameter.  
     
     
         13 . The magnetic recording medium according to  claim 12  wherein the choosing step is carried out using a plot of said ratio versus (002) interplanar spacing.  
     
     
         14 . The magnetic recording medium according to  claim 10  wherein the choosing step is carried out so that the difference between the lattice parameter of the underlayer and the desired lattice parameter is optimized.  
     
     
         15 . The magnetic recording medium according to  claim 11  wherein the selecting and choosing steps are carried out so the lattice parameter of the underlayer is between the lattice parameters of the chromium-based layers.  
     
     
         16 . The magnetic recording medium according to  claim 11  wherein the determining step is carried out with the desired lattice parameter being the same as the lattice parameter of the magnetic layer.  
     
     
         17 . A method for obtaining a desired lattice parameter of a non-magnetic underlayer in the manufacture of a magnetic recording medium of the type comprising a substrate, a non-magnetic underlayer on the substrate and a magnetic layer on the underlayer, comprising: 
 determining a desired lattice parameter for the underlayer, the underlayer having a thickness, the desired lattice parameter being the same as the lattice parameter of the magnetic layer;    selecting first and second non-magnetic, chromium-based layers for the underlayer, at least one of said chromium-based layers being a chromium-based alloy; and    choosing a fractional thickness for each of the chromium-based layers according to the desired lattice parameter using a ratio of the fractional thicknesses for said layers versus the lattice parameter, the sum of the fractional thicknesses for each of the chromium-based layers being equal to the underlayer thickness.