Patent ID: 7862917

Claim:
A perpendicular magnetic recording medium including a perpendicular magnetic recording layer between a lower layer and an upper layer, wherein a thickness t2 of the perpendicular magnetic recording layer is determined by an expression of 8 â¢ n â¢ A K < t2 < 16 â¢ n â¢ A K , here, K > 10 5 â¢ â¢ erg â¢ â¢ / â¢ cm 3 , n > 30 â¢ k B â¢ T Ï€ â¢ â¢ D 2 â¢ AK , D â‰¤ ( 30 â¢ k B â¢ T Ï€ â¢ KA ) 1 / 2 , D denotes an average grain diameter of the recording layer, and A denotes an exchange constant of the material of the recording layer, wherein D=2 nm and 19.7 nmâ‰¦t2<39.4 nm or D=1 nm and 49.3 nm<t2<98.6 nm.