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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
Document File: 5 page(s) / 86K

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

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Strongly coupled anti-parallel layers in CPP GMR structures

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

non-magnetic spacer magnetic layers

antiferromagn though magn

This magnetic structure may be very hard to obtain. The moments of the magnetic layers may align parallel. This could happen when a bias field is applied or when large sense-currents are applied. This is shown in Figure 2. This is bad because the structure can not be properly biased

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and no signal can be obtained from an applied field.

Figure 2: CPP stack with moments aligned

non-magnetic spacer magnetic layers a by current induce

The antiparallel free layer design (Heim and Parkin, US patent 05583725, 1996) has significant advantages in GMR systems. In particular, it allows for the moment of the sense layer(s) to be reduced without the reduction in GMR that happens when one just reduces the physical thickness of the layers. An AP trilayer is shown in Figure 3: 2 ferromagnetic layers coupled by an AP spacer such as ruthenium or rhodium.

This invention suggests using A...