High frequency dynamics of the soft underlayer in perpendicular recording system

In this study, we present time-resolved Kerr microscopy of the magnetization dynamics in response to the reversal of the write current in the soft magnetic underlayers (SULs) films used in dual layer perpendicular recording media. 20-nm-thick FeCoB films with a 5 nm Pd cap layer are positioned in contact with a single-pole-type high-speed perpendicular magnetic write head. The temporal responses of both in-plane and out-of-plane magnetization components of the SUL were simultaneously measured using the time-resolved Kerr effect. Precessional effects were observed in both magnetization components during the SUL switching, using a driving pulse current with rise-time of about 0.8 ns. The precessional frequencies range from 3 to 7 GHz, depending on the distance (x) away from the main pole. The present results highlight the importance of soft magnetic underlayer dynamics for high data rate perpendicular magnetic recording technology.