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IP.com Disclosure Number: IPCOM000014513D
Original Publication Date: 1999-Dec-01
Included in the Prior Art Database: 2003-Jun-19

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Harry Gill


Tunnel junction type structures exhibit large ferromagnetic coupling between the FREE and the PINNED layers due to thin AlOx junction layer (ony 10 to 20A thick). The large (>20 Oe) ferromagnetic coupling at the FREE layer causes the FREE layer to get into undesired magnetic states which results in undesired biasing and magnetic instability of the sensor. We disclose a new sensor design which eliminates the ferromagnetic coupling at the FREE layer. The sensor has following structure: S1/AFM/FM(1)/Ru/FM(2)/AlOx/FM(3)/AlOx/FM(4)/AFM/S2 S1: First ferromagnetic shield also serves as the first electrode AFM: antiferromagnet for pinning the FM(1)/Ru/FM(2) structure, and pinning FM(4) S1: Second shield also serves as the second electrode FM(3): FREE ferromagnetic layer which is embedded within two AlOx junctions The key features of the design are that FM(2) and FM(4) are pinned 180 degree out of phase and that FM(3) serves as the 3rd common electrode. The ferromagnetic coupling at the FM(3) from FM(2) and FM(4) cancels due to 180 degree phase difference between the pinned orientation of FM(2) and FM(4) providing FREE layer with zero net ferromagnetic coupling. The FREE layer FM(3) is connected to ground terminal of the differential amplifier. Since the signals at the S1 and S2 are 180 out of phase, the differential amplifier adds these signals to provide total signal from the sensor. This detection scheme in-addition to providing zero ferromagnetic coupling at the FREE layer also eliminates the common mode noise such as arising from the Head/Disk contacts in magnetic recording systems.