Dynamic Kerr imaging of soft underlayers for perpendicular recording applications (invited)

Abstract

Time-resolved Kerr imaging was used to examine the magnetization dynamics of soft underlayers (SULs) within perpendicular magnetic recording media. Two media configurations were examined with permalloy SULs of 20 and 200 nm thickness. The media in both of these samples were 14 nm thick Co/Pt multilayer films separated from the soft underlayer by a thin exchange decoupling layer of Ta. For comparison, two equivalent SUL samples were examined with no media layer. The media were examined while driven at 80 MHz by one of two types of magnetic recording heads: a 2.5 μm track width longitudinal head, and a 1 μm track width perpendicular recording head. The rise time (10%–90%) of the fields from the heads was ∼1.4 ns. It was observed in the SUL films without media, that the film switching speeds were similar to that of the driving head, for both longitudinal and perpendicular heads. The switching speed of the SUL films with a recording layer was slower due to influence of the recording layer on the magnetic properties of the SUL. In the 200 nm thick SUL-only film, the integration of the normal magnetization at the back surface of the medium indicates that approximately half of the flux generated by the write head passes out through the back of the film. The switching behavior seen in the films with media were significantly different from the films without media. The switching seen on the back surface of the 20 nm SUL with media was confined to the area directly over the pole tips. For the 200 nm with media, the switching was more active past the track edges than directly over the pole tips.