Analysis of transition shape and adjacent track aging for 1 Tb/in ² write head designs

This paper analyzes the write field profiles for perpendicular head designs that have been proposed for reaching 1 Tb/in². Designs considered include side shielded poles and high anisotropy poles. A vector Stoner-Wohlfarth writing criteria is used to find the maximum medium anisotropy each head can write on, subject to the constraints that transition curvature and transition jitter do not exceed the bit cell length. Vector fields are also used to assess thermal switching on adjacent tracks. For optimal writing consistent with these assumptions, the number of grains under the read head is 5 for the shielded design (H_κ = 1380 kA/m) with a 20 nm thick medium and a stability coefficient of 40, and is 3.6-4 (H_κ = 930 kA/m) for the high anisotropy designs. The improved downtrack gradient of the shielded design accounts for much of this difference, and suggests that a downtrack shield may improve the high anisotropy design. In all cases, transition curvature suggests the read head width will be limited to around 30% of the track pitch, which is substantially less than current values.