Extraordinary magnetoresistance sensor with perpendicular magnetic biasing by an antiferromagnetic/ferromagnetic exchange-coupled structure
View Patent ↗An extraordinary magnetoresistance (EMR) sensor has an antiferromagnetic/ferromagnetic exchange-coupled bilayer structure on top of the EMR active film. The ferromagnetic layer in the bilayer structure has perpendicular magnetic anisotropy and is exchange-biased by the antiferromagnetic layer. The antiferromagnetic/ferromagnetic bilayer structure provides a magnetic field perpendicular to the plane of the EMR active film to bias the magnetoresistance vs. field response of the EMR sensor. The ferromagnetic layer may be formed of any of the ferromagnetic materials useful for perpendicular magnetic recording, and is prepared in a way that its anisotropy axis is significantly out-of-plane. The antiferromagnetic layer is formed of any of the known Mn alloys, such as PtMn, NiMn, FeMn, IrMn, PdMn, PtPdMn and RhMn, or any of the insulating antiferromagnetic materials, such as those based on the cobalt oxide and nickel oxide antiferromagnetic materials.
1. An extraordinary magnetoresistance (EMR) sensor comprising:
a semiconductor 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;
a ferromagnetic layer on the substrate and having its magnetic moment oriented generally perpendicular to the planes of the ferromagnetic layer and active film; and
an antiferromagnetic layer in contact with the ferromagnetic layer, the magnetic moment of the ferromagnetic layer being perpendicularly biased by the antiferromagnetic layer.
2. The sensor of claim 1 wherein the material of the ferromagnetic layer is selected from the group consisting of a cobalt-platinum-chromium alloy, an iron-platinum alloy, one or more cobalt-platinum bilayers, one or more cobalt-palladium bilayers, one or more iron-platinum bilayers, and one or more iron-palladium bilayers.
3. The sensor of claim 2 wherein the material of the ferromagnetic layer is a multilayer selected from the group of Co/Pt, Co/Pd, Fe/Pt and Fe/Pd multilayers.
4. The sensor of claim 1 wherein the material of the ferromagnetic layer is selected from the group consisting of (a) one or more bilayers of a Co—Y alloy and Pt and (b) one or more bilayers of a Co—Y alloy and Pd, wherein Y is selected from the group consisting of B, Ta, Cr, O, Cu, Ag, Pt and Pd.
5. The sensor of claim 1 wherein the material of the ferromagnetic layer is the chemically ordered L 1 0 phase of a material selected from the group consisting of FePt, CoPt and (FeCo)Pt.
6. The sensor of claim 1 wherein the material of the ferromagnetic layer is an electrically insulating ferrite.
7. The sensor of claim 1 wherein the ferromagnetic layer is located between the EMR active film and the antiferromagnetic layer.
8. The sensor of claim 1 wherein the antiferromagnetic layer is located between the EMR active film and the ferromagnetic layer.
9. The sensor of claim 1 wherein the EMR active film is located between the substrate and the ferromagnetic layer.
10. The sensor of claim 1 wherein the antiferromagnetic layer is selected from the group consisting of a cobalt oxide, a nickel oxide, and an oxide of an alloy of cobalt and nickel.
11. The sensor of claim 1 wherein the antiferromagnetic layer is an alloy comprising Mn and at least one element selected from the group consisting of Pt, Rh, Ni, Fe, Ir and Pd.
12. The sensor of claim 1 further comprising a diffusion barrier between the EMR active film and the ferromagnetic layer.
13. The sensor of claim 1 wherein the diffusion barrier is selected from the group consisting of aluminum oxides, aluminum nitrides, silicon oxides, and silicon nitrides.
14. An extraordinary magnetoresistance (EMR) sensor comprising:
a semiconductor 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
an antiferromagnetic/ferromagnetic exchange-coupled bilayer on the active film providing a biasing magnetic field substantially perpendicular to the plane of the active film, said bilayer comprising (a) a ferromagnetic layer formed of a material selected from the group consisting of a cobalt-platinum-chromium alloy, an iron-platinum alloy, one or more cobalt-platinum bilayers, and one or more cobalt-palladium bilayers; and (b) an antiferromagnetic layer exchange-coupled with the ferromagnetic layer and formed of a material selected from the group consisting of a cobalt oxide, a nickel oxide, an oxide of an alloy of cobalt and nickel, and an alloy comprising Mn and an element selected from the group consisting of Pt, Ni, Fe, Ir and Pd.
15. The sensor of claim 14 wherein the material of the ferromagnetic layer is one or more bilayers of cobalt and platinum or one or more bilayers of cobalt and palladium, and wherein the cobalt layers in said bilayers include an element selected from the group consisting of B, Ta, Cr, O, Cu, Ag, Pt and Pd.
16. The sensor of claim 14 wherein the material of the ferromagnetic layer is a cobalt-platinum-chromium alloy that includes an element selected from the group consisting of B, Nb and Ta.
17. The sensor of claim 14 wherein the antiferromagnetic layer provides an exchange field H E to the ferromagnetic layer, wherein the ferromagnetic layer has an intrinsic coercivity H C0 that is enhanced by H E to a coercivity H C greater than H C0 , and wherein the sum of H E and H C is greater than the magnetic field to be sensed by the sensor.
18. The sensor of claim 17 wherein the intrinsic coercivity H C0 of the ferromagnetic layer is less than the magnetic field to be sensed.
19. The sensor of claim 14 wherein the ferromagnetic layer is located between the EMR active film and the antiferromagnetic layer.
20. The sensor of claim 14 wherein the antiferromagnetic layer is located between the EMR active film and the ferromagnetic layer.
21. The sensor of claim 14 further comprising a diffusion barrier between the EMR active film and the antiferromagnetic/ferromagnetic bilayer.
22. The sensor of claim 21 wherein the diffusion baffler is selected from the group consisting of aluminum oxides, aluminum nitrides, silicon oxides, and silicon nitrides.