Cross-track noise profile measurement for adjacent-track interference study and write-current optimization in perpendicular recording

Abstract

A cross-track noise profile measurement is developed for identifying the source of adjacent-track interference (ATI) fields in perpendicular recording systems. The noise amplitude as a function of cross-track position and write current clearly delineates the extent, magnitude, and polarity of stray fields under different portions of the head. Experimentally obtained stray field strength relative to writing field is in good agreement with finite element modeling. For given head and disk components, the composite picture of noise amplitude for both writing field and stray fields as a function of write current also provides a way of selecting an optimal write current with respect to the medium dynamic coercivity, saturation, and ATI threshold. Further investigation on the asymmetries in the noise profiles have led to two interesting discoveries. The first is an asymmetry in ATI field that can be attributed to the polarity of the radially oriented magnetization in the soft underlayer. The second is an artifact associated with the change in read head sensitivity around track edges due to fields from the dc-erased hard recording layer.