Stray Field Dependent Reader Noise in Thin-Film Heads

Abstract

The stray field magnitude and distribution, at sensor level, have been investigated as a function of the thickness of the shield, the presence of a domain wall in the shield, the relative position of the vortex accompanying the wall and its proximity to the Air-Bearing-Surface (ABS). Using micromagnetics, the stray fields at the reader sensor have been simulated while a domain wall moves in a shield near the ABS in a magnetic head. For shield thicknesses from 640 nm to 1280 nm, a range of interest for head design, the domain wall shape is C-shaped with a vortex-like structure on either side of the domain wall that provides flux closure inside the film. For a 5 Oe incidental field, the wall exits at the ABS in less than 20 ns when the wall is between the ABS and the vortex. Average stray fields reached 60 Oe while 100 Oe localized stray fields are observed as the wall exits the ABS. The dynamics of wall motion change when the vortex is between the ABS and the domain wall. A 5 Oe incidental field in a 640 nm thick shield drove the wall toward the ABS, compressing the vortex and creating a blocking structure. An incidental 10 Oe field twisted the wall center magnetization enough to change wall chirality accelerating the wall exit, preventing the blocking structure, and flipping the vortex to the other side of the wall. Average stray fields are 55 Oe with a local maximum of 70 Oe. Similar results occur for a 1280 nm thick shield for a 5 Oe field, with average stray fields of 60 Oe and a local maximum of 100 Oe.