SPIN VALVE DESIGN WITH BIAS POINT INDEPENDENT OF STRIPE HEIGHT
Original Publication Date: 2000-Jan-01
Included in the Prior Art Database: 2003-Jun-18
Stripe height has major effect on the performance of all prior art spin valve designs. The bias point (the FREE layer magnetization angle relative to the pinned layer magnetization) varies significantly with stripe height due to variation in the pinned film demagnetizing field and due to variable current for constant voltage bias operation. For tall stripe height, demagnetizing field decreases and current increases, both make head read back signal asymmetry more postive, i.e., positive signal increases and negative signal decreases. For short stripe height, demagnetizing field increases and current decreases, both make head read signal asymmetry more negative. Thus large variation in the read signal asymmetry is normally observed with varying stripe height. We disclose the following design to overcome the above problems: substrate/30 A Ta/7 A Co/22 A Cu/45 A NiFe/22 A Cu/24 A Co/6 A Ru/24 A Co/10 A NiFe/250 A NiMn/30 A Ta Demagnetizing field of 7 A Co layer underneath the FREE NiFe layer balances with 10 A NiFe which is underneath the NiMn antiferromagnet. The demagnetizing field of antiparallel coupled Co layers (layers around "Ru" spacer) is zero due to flux closed structure. The variable current effect is also negligible in this structure because the field from the current flowing in layers underneath the FREE layer balances with the field from the current flowing in layers above the FREE layer. Thus the net field acting on the FREE layer magnetization from the variable current can be made less important.