Magnetic recording medium

Abstract

A magnetic recording medium includes a substrate, a seed layer, an under layer, and a perpendicular recording layer having a granular structure. (Ms·α·δ 1.5 (1−Rs) 0.33 ), Ms, and α satisfy (Ms·α·δ 1.5 (1−Rs) 0.33 )≦0.1 [μ·emu·(mm) −1.5 ], Ms≧450 [emu/cc], and α≧1.2. In the above formulas, Ms indicates a saturated magnetization amount, α indicates the gradient of a M-H loop around a coercive force Hc, δ indicates the thickness of the perpendicular recording layer, and Rs indicates a squareness ratio.

What is claimed is: 
     
         1 . A magnetic recording medium comprising:
 a substrate;   a seed layer;   an under layer; and   a perpendicular recording layer having a granular structure,   wherein (Ms·α·δ 1.5 (1−Rs) 0.33 ), Ms, and α satisfy the following relations:
   (Ms·α·δ 1.5 (1−Rs) 0.33 )≦0.1 [μ·emu·(mm) −1.5 ],
 
     Ms≧ 450 [emu/cc], and 
   α≧1.2, and
 
   wherein in the above formulas, Ms indicates a saturated magnetization amount, α indicates the gradient of a M-H loop around a coercive force Hc, δ indicates the thickness of the perpendicular recording layer, and Rs indicates a squareness ratio.   
     
     
         2 . The magnetic recording medium according to  claim 1 ,
 wherein the seed layer has an amorphous state and includes a metal having a melting point of 2,000° C. or less.   
     
     
         3 . The magnetic recording medium according to  claim 1 ,
 wherein the seed layer has an amorphous state and includes an alloy containing Ti and Cr.   
     
     
         4 . The magnetic recording medium according to  claim 1 ,
 wherein (Ku·V/k B ·T) satisfies the following relation:
   ( Ku·V/k   B   ·T )≧65, and
 
   wherein in the above formula, Ku indicates magnetic anisotropy energy, V indicates an activation volume, k B  indicates Boltzmann constant, and T indicates the absolute temperature.   
     
     
         5 . The magnetic recording medium according to  claim 1 ,
 wherein the under layer includes Ru.   
     
     
         6 . The magnetic recording medium according to  claim 1 ,
 wherein the perpendicular recording layer has a granular structure in which grains containing Co, Pt, and Cr are separated from each other with oxides provided therebetween.   
     
     
         7 . The magnetic recording medium according to  claim 6 ,
 wherein the perpendicular recording layer has an average composition represented by the following formula (1):
   (Co x Pt y Cr 100-x-y ) 100-z —(SiO 2 ) z   (1), and
 
   wherein in the formula (1), x, y, and z satisfy 69≦x≦72, 12≦y≦16, 9≦z≦12, respectively.   
     
     
         8 . The magnetic recording medium according to  claim 1 ,
 wherein the substrate is a flexible non-magnetic substrate.