[1] Univ Calif San Diego, Dept Elect & Comp Engn, San Diego, CA 92103 USA
[2] Univ Calif San Diego, Ctr Magnet Recording Res, San Diego, CA 92103 USA
[3] Hitachi GST, Hitachi San Jose Res Ctr, San Jose, CA USA
[4] Fujitsu Labs Ltd, Storage & Intelligent Syst Labs, Tokyo, Japan