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Perpendicular Recording Media with AP-Coupled Soft Underlayer Disclosure Number: IPCOM000013991D
Original Publication Date: 2001-Aug-01
Included in the Prior Art Database: 2003-Jun-19

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Perpendicular recording media uses a soft magnetic layer under the main recording layer. The magnetic domain wall jumps in the soft underlayer introducing noise into the head signal, usually referred to as the spike noise. An antiparallel coupled soft underlayer could minimize this noise. The structure of the antiparallel coupled soft layer is CoFe/Ru/CoFe or NiFe/Ru/NiFe. The antiferromagnetic exchange coupling between the ferromagnetic layers through the nonmagnetic spacer layer (Ru) can obtain single domain magnetic state in the underlayer if the exchange coupling energy exceeds the edge demagnetizing energy. Also, it is possible to adjust the magnetic anisotropy field (Hk) of the soft underlayer by selecting proper thicknesses of the layers in the antiparallel coupled system, i.e., CoFe(t1)/Ru/CoFe(t2) yields net Hk which is given by equation: Hk(t1)+Hk(t2)/(t2-t1). Usually, an Hk value between 50 to 100 Oe is required to avoid saturation of the soft underlayer. 1