US Patent 7773331 Thermally assisted magnetic recording system

The optimum head-field intensity for saturation recording is assumed to be 560×103 A/m or more. Under a condition where the recording track width of an information recording medium is equal to or less than 60 nm, the optimum head-field intensity Y satisfies the following inequalities (1) and (2):Y≧(X2−119×X+4135)×1000  (1)Y≦(X2−119×X+const)×1000  (2)where X denotes the nondimensional value of the recording track width divided by 10−9 m, and Y denotes a magnetic field (expressed in units of A/m) which a magnetic pole for head-field application applies to the center of the information recording medium in the direction of the thickness thereof. Note that const=−0.8×v2+33.7×v+4250 if the relative velocity v between the head and the medium at the position of the head is less than 20 m/sec, or const=4600 if the velocity v is equal to or more than 20 m/sec.