In the effort toward achieving higher data density on recording media, spin filters have become of interest for use in magnetoresistive (MR) read heads. FIG. 1 is a diagram of a conventional spin filter 10. In general, the conventional spin filter 10 would be incorporated into a MR read head (not explicitly shown), which would include leads electrically connected to other electronics to drive current through the conventional spin filter 10 during reading. In such an application, current is generally driven in the current perpendicular to the plane (CPP) configuration. The CPP configuration is in the z-direction depicted in FIG. 1.
The conventional spin filter 10 includes a seed layer 12, an antiferromagnetic (AFM) layer 14, a pinned layer 16, a nonmagnetic spacer layer 24, a free layer 26, a filter layer 28, a specular oxide layer 30, and a capping layer 32. The seed layer 12 is used to provide the appropriate surface for growing the AFM layer 14 with the desired crystal structure. The AFM layer 14 is used in pinning the magnetization of the pinned layer 16. The pinned layer 16 may be a synthetic pinned layer, including ferromagnetic layers 18 and 22 separated by an electrically conductive spacer layer 20 that is typically Ru. The electrically conductive spacer layer 20 has a thickness configured to ensure that the ferromagnetic layers 18 and 22 are antiferromagnetically coupled. Thus, the magnetization of the ferromagnetic layer 18 is pinned by the AFM layer 14. The magnetization of the ferromagnetic layer 22 is set because it is strongly antiferromagnetically coupled to the magnetization of the ferromagnetic layer 18. The nonmagnetic spacer layer 24 is typically electrically conductive, for example Cu. The free layer 26 is ferromagnetic and typically includes materials such as CoFe.
The filter layer 28 has a high electrical conductivity and typically includes materials such as Cu. The specular oxide layer 30 may be a nano-oxide and typically includes materials such as alumina. The combination of the filter layer 28 and the specular oxide layer 30 has been used to provide adequate specularity of scattering of electrons from the free layer 26 that are incident on the specular oxide layer 30. In particular, the filter layer 28 has been utilized in the conventional spin filter 10 to provide a region, or filter, for specular reflection between the free layer 26 and specular layer 30. Thus, the magnetoresistance of the conventional spin filter 10 is improved. Consequently, the magnetoresistance of the conventional spin filter 10 is adequate. The capping layer 32 is typically oxidized Ta.
Although the conventional spin filter 10 functions, there are drawbacks to the use of the conventional spin filter 10. Insertion of the specular oxide layer 30 can increase the coercivity of the free layer 26, which is undesirable. Furthermore, the specular oxide layer 30 is generally a nano-oxide that can continue to oxidize during processing. The signal may degrade during the lifetime of the conventional spin filter 10. The conventional spin filter 10 thus suffers thermal instabilities and may have reduced reliability.
Analogous conventional spin filters are described in U.S. Pat. No. 6,795,279 B2; U.S. Pat. No. 6,556,390 B1; U.S. Pat. No. 5,898,612; U.S. Pat. No. 6,407,890 B1; U.S. Pat. No. 6,764,778 B2; U.S. Pat. No. 6,700,753 B2; U.S. Pat. No. 6,775,111 B2; U.S. Pat. No. 6,591,481; U.S. Pat. No. 6,613,380 B1; U.S. Pat. No. 6,636,398 B2.
Accordingly, what is needed is a system and method for providing a spin filter having improved thermal stability, signal sensitivity, and/or reliability.