Spin valve sensor having a nonmagnetic enhancement layer adjacent an ultra thin free layer
View Patent ↗A spin valve device includes a non-magnetic enhancement layer adjacent an ultra thin free layer. The thickness of the free layer may be less than the mean free path of a conduction electron through the free layer. The GMR ratio is significantly improved for free layer thicknesses below 50 Å. The enhancement layer allows electrons to travel longer in their spin state before encountering scattering sites. The electronic properties of the enhancement layer material can be matched with the adjacent free layer without creating a low resistance shunt path. Because the free layer may be made ultra thin and the enhancement layer is formed of a nonmagnetic material, less magnetic field is required to align the free layer, allowing for improved data density. Also, the enhancement layer allows for effective bias point control by shifting sensor current density distribution.
1. A spin valve sensor comprising:
a) a first pinned layer;
b) a free layer;
c) a spacer layer located between the pinned layer and the free layer; and
d) a non-magnetic enhancement layer immediately adjacent to the free layer, the enhancement layer comprising NiFeCr;
wherein the free layer has a thickness in a range about 10 Angstroms to about 25 Angstroms.
2. The spin valve sensor of claim 1 wherein the free layer and the enhancement layer have a combined thickness equal to about a mean free path length of a conduction electron through the free layer.
3. The spin valve sensor of claim 1 wherein the free layer and the enhancement layer have a combined thickness within a range about 20 Angstroms to about 80 Angstroms.
4. The spin valve sensor of claim 1 wherein the enhancement layer further comprises at least one of Cu, Ru, or copper alloy.
5. The spin valve sensor of claim 1 wherein the free layer comprises at least one of NiFe, CoFe, Ni alloy, or Fe alloy.
6. The spin valve sensor of claim 5 wherein the enhancement layer further comprises at least one of Cu, Ru, or copper alloy.
7. The spin valve sensor of claim 6 wherein the enhancement layer comprises Cu and the free layer comprises CoFe, and wherein the layers are arranged in a bottom spin valve structure.
8. The spin valve sensor of claim 7 wherein the enhancement layer is about 10 Angstroms to about 20 Angstroms in thickness and the free layer is about 10 Angstroms to about 25 Angstroms in thickness.
9. The spin valve sensor of claim 6 wherein the free layer comprises about 20 Angstroms of CoFe, and the enhancement layer comprises about 30 Angstroms of NiFeCr in a top spin valve structure.
10. The spin valve sensor of claim 1 wherein the free layer consists of CoFe, and wherein the enhancement layer comprises a material capable of lowering the coercivity of the CoFe free layer.
11. The spin valve sensor of claim 1 further comprising a second pinned layer and an antiparallel coupling layer between the first pinned layer and the second pinned layer, wherein the spacer layer is between the second pinned layer and the free layer.
12. The spin valve sensor of claim 1 wherein the layers are arranged in a top spin valve structure, and wherein the enhancement layer comprises a material capable of providing good crystallographic texture to the free layer.
13. The spin valve sensor of claim 1 wherein the enhancement layer is a multi-layer structure comprising layers of NiFeCr and copper.
14. The spin valve sensor of claim 1 wherein the enhancement layer is a multi-layer structure comprising a NiFeCr layer having a thickness about 30 Å and a copper layer having a thickness of about 20 Å.
15. The spin valve sensor of claim 1 , further comprising a seed layer.
16. The spin valve sensor of claim 1 wherein the non-magnetic enhancement layer comprises two or more layers.