Spin transfer torque device with oxide layer beneath the seed layer
A spin transfer torque (STT) device is formed on an electrically conductive substrate and includes a ferromagnetic polarizer layer near the substrate, a ferromagnetic free layer, and a nonmagnetic spacer layer between the ferromagnetic polarizer layer and the ferromagnetic free layer. A multilayer structure is located between the substrate and the ferromagnetic polarizer layer. The multilayer structure includes a metal or metal alloy seed layer for the ferromagnetic polarizer layer and an intermediate oxide layer below and in contact with the seed layer. The intermediate oxide layer reflects spin current from the write pole and thus reduces undesirable spin pumping of the ferromagnetic polarizer layer.
1. A spin transfer torque (STT) device, comprising:
an electrically conductive substrate;
a ferromagnetic polarizer layer;
an intermediate oxide layer between the substrate and the polarizer layer and comprising an oxide of one or more of Mg, Al, Ti and Ta;
a metal or metal alloy seed layer for the polarizer layer on and in contact with the intermediate oxide layer, wherein the polarizer layer is on and in contact with the seed layer;
a ferromagnetic free layer;
a nonmagnetic spacer layer between the polarizer layer and the free layer, wherein the polarizer layer is located between the substrate and the free layer; and
an electrically conductive layer on the free layer.
2. The STT device of claim 1 , wherein the intermediate oxide layer consists of MgO.
3. The STT device of claim 1 , wherein the intermediate oxide layer has a thickness greater than or equal to 0.1 nm and less than or equal to 0.5 nm.
4. The STT device of claim 1 , wherein the seed layer comprises one or more films selected from one or more of Cu, Cr, Ta, Ru, Hf, Nb and NiAl.
5. The STT device of claim 1 , wherein the seed layer comprises a film selected from a Ru film and a NiAl film.
6. The STT device of claim 1 , wherein the seed layer has a thickness greater than or equal to 1 nm and less than or equal to 9 nm.
7. A spin torque oscillator (STO) comprising:
a first electrically conductive electrode;
a ferromagnetic polarizer layer;
an intermediate oxide layer between the first electrode and the polarizer layer and comprising an oxide of one or more of Mg, Al, Ti and Ta;
a metal or metal alloy seed layer for a ferromagnetic free layer on and in contact with the intermediate oxide layer, wherein the polarizer layer is on and in contact with the seed layer;
the ferromagnetic free layer;
a nonmagnetic spacer layer between the polarizer layer and the free layer, wherein the polarizer layer is located between the first electrode and the free layer; and
a second electrically conductive electrode.
8. The STO of claim 7 , wherein the intermediate oxide layer consists of MgO.
9. The STO of claim 7 , wherein the intermediate oxide layer has a thickness greater than or equal to 0.1 nm and less than or equal to 0.5 nm.
10. The STO of claim 7 , wherein the seed layer comprises one or more films selected from one or more of Cu, Cr, Ta, Ru, Hf, Nb and NiAl.
11. The STO of claim 7 , wherein the seed layer has a thickness greater than or equal to 1 nm and less than or equal to 9 nm.
12. The STO of claim 7 , further comprising a buffer layer between the first electrode and the intermediate oxide layer, wherein the buffer layer is on and in contact with the first electrode and the intermediate oxide layer is on and in contact with the buffer layer.
13. The STO of claim 12 , wherein the buffer layer comprises one or more films selected from one or more of Cu, Cr, Ta, Ru, Hf and Nb and their alloys.
14. The STO of claim 7 , wherein the second electrically conductive electrode is formed of a ferromagnetic material.
15. A magnetic recording write head for magnetizing regions in a magnetic recording layer, the write head comprising:
a write pole;
a spin torque oscillator (STO) comprising a ferromagnetic polarizer layer, a free layer, and a nonmagnetic spacer layer between the ferromagnetic polarizer layer and the free layer, wherein the ferromagnetic polarizer layer is located between the write pole and the free layer; and
a multilayer between the write pole and the ferromagnetic polarizer layer, the multilayer comprising:
a buffer layer in contact with the write pole;
an intermediate oxide layer on and in contact with the buffer layer and comprising an oxide of one or more of Mg, Al, Ti and Ta; and
a metal or metal alloy seed layer for the ferromagnetic polarizer layer on and in contact with the intermediate oxide layer, wherein the ferromagnetic polarizer layer is on and in contact with the seed layer.
16. The head of claim 15 , wherein the intermediate oxide layer consists of MgO.
17. The head of claim 15 , wherein the seed layer comprises a film selected from a Ru film and a NiAl film.
18. The head of claim 15 , wherein the buffer layer comprises one or more films selected from one or more of Cu, Cr, Ta, Ru, Hf and Nb and their alloys.
19. The head of claim 15 , further comprising a trailing shield and a nonmagnetic capping layer between the free layer and the trailing shield.
20. The head of claim 15 , further comprising an electrically conductive coil coupled to the write pole, the write pole adapted to generate a magnetic write field in the presence of electrical write current through the coil, and STO electrical circuitry between the write pole and the free layer for directing electron flow from the write pole to the free layer, whereby the free layer is adapted to provide microwave-assisted magnetic recording to the recording layer in the presence of current through the STO electrical circuitry.