Extraordinary magnetoresistance sensor with perpendicular magnetic biasing by a ferromagnetic multilayer

1. An extraordinary magnetoresistance (EMR) sensor comprising:

a substrate;

an EMR active film on the substrate, the active film comprising a nonmagnetic semiconductor material responsive to a magnetic field generally perpendicular to the active film;

an electrically conductive shunt in contact with the active film;

a pair of current leads in contact with the active film;

a pair of voltage leads in contact with the active film; and

a ferromagnetic multilayer on the substrate and having its magnetic moment oriented generally perpendicular to the planes of the ferromagnetic multilayer and active film, said multilayer comprising a plurality of like bilayers, said bilayer comprising a first film of Co, Fe or an alloy consisting essentially of Co and Fe and a second film of Pt, Pd or an alloy consisting essentially of Pt and Pd.

2. The sensor of claim 1 wherein the multilayer comprises a plurality of like bilayers selected from the group consisting of a cobalt-platinum (Co/Pt) bilayer and a cobalt-palladium (Co/Pd) bilayer.

3. The sensor of claim 2 wherein the thickness of the cobalt layer in each bilayer is in the range of approximately 0.1 to 2.0 nm.

4. The sensor of claim 2 wherein the cobalt layer in each bilayer comprises a Co—Y alloy, wherein Y is selected from the group consisting of B, Ta, Cr, O, Cu, Ag, Pt and Pd.

5. The sensor of claim 2 wherein the plurality of bilayers are located above the EMR active film, and further comprising an initial film of Pt between the EMR active film and the first bilayer.

6. The sensor of claim 1 wherein the ferromagnetic multilayer is located above the EMR active film.

7. The sensor of claim 6 further comprising a diffusion barrier between the EMR active film and the ferromagnetic multilayer.

8. The sensor of claim 7 wherein the diffusion barrier is selected from the group consisting of aluminum oxides, aluminum nitrides, silicon oxides, and silicon nitrides.

9. The sensor of claim 1 wherein the ferromagnetic multilayer is located between the substrate and the EMR active film.

10. An extraordinary magnetoresistance (EMR) sensor comprising:

a substrate;

an EMR active film on the substrate, the active film comprising a nonmagnetic semiconductor material responsive to a magnetic field generally perpendicular to the active film;

an electrically conductive shunt in contact with the active film;

a pair of current leads in contact with the active film;

a pair of voltage leads in contact with the active film; and

a ferromagnetic multilayer on the active film and having its magnetic moment oriented generally perpendicular to the planes of the ferromagnetic multilayer and active film, said multilayer comprising a plurality of alternating first and second films, said first film consisting essentially of Co and said second film consisting essentially of an element selected from the group consisting of Pt and Pd.

11. The sensor of claim 10 wherein the thickness of said essentially cobalt film is in the range of approximately 0.1 to 2.0 nm.

12. The sensor of claim 10 wherein said first film comprises an alloy of Co and Y, wherein Y is selected from the group consisting of B, Ta, Cr, O, Cu, Ag, Pt and Pd.

13. The sensor of claim 10 further comprising an initial film of Pt between the EMR active film and the first Co film.

14. The sensor of claim 10 further comprising a diffusion barrier between the EMR active film and the ferromagnetic multilayer.

15. The sensor of claim 14 wherein the diffusion barrier is selected from the group consisting of aluminum oxides, aluminum nitrides, silicon oxides, and silicon nitrides.