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Strongly coupled anti-parallel layers in CPP GMR structures

IP.com Disclosure Number: IPCOM000014470D
Original Publication Date: 2002-Jan-27
Included in the Prior Art Database: 2003-Jun-19

Publishing Venue

IBM

Abstract

GMR stacks for Current Perpendicular to the Plane (CPP) applications may become practical as the recording density increases and the sensor size deceases dramatically. Such a device was described by Rottmayer and Zhu in US patent US5784224. This design, shown schematically in Figure 1, requires that the moments of the ferromagnetic layers are antiparallel. This is largely accomplished through magnetostatics--i.e. the magnetic layers align antiferromagnetically to reduce stray fields. This can also be accomplished using oscillatory coupling through an appropriate spacer material such as described in Parkin et. al., Phys. Rev. Lett. 66, p. 2152 (1991). However, the coupling could be too large to allow the sensor to respond in a small applied field It is critical that the moments of the ferromagnetic layers on each side of a spacer layer are antiparallel. Below, it will be shown how to use AP trilayers to obtain this alignment even when large magnetic fields are present (as in the case of large sense currents). Figure 1: CPP GMR stack with simple ferromagnetic layers