Perpendicular magnetic recording write head and system with improved spin torque oscillator for microwave-assisted magnetic recording
View Patent ↗A microwave-assisted magnetic recording (MAMR) write head and system has a spin-torque oscillator (STO) located between the write pole of the write head and a trailing shield that alters the write field from the write pole. The STO is a stack of layers whose planes lie generally parallel to the X-Y plane of an X-Y-Z coordinate system, the stack including a ferromagnetic polarizer layer, a free ferromagnetic layer, and a nonmagnetic electrically conductive spacer between the polarizer layer and the free layer. In the presence of the write field from the write pole the polarizer layer has its magnetization oriented at an angle between 20 and 80 degrees, preferably between 30 and 70 degrees, with the Z-axis. In the presence of a direct electrical current through the STO stack, the free layer magnetization rotates or precesses about the Z-axis with a non-zero angle to the Z-axis.
1. A microwave-assisted magnetic recording (MAMR) write head for magnetizing regions in a perpendicular magnetic recording layer, the write head comprising:
a write pole;
an electrically conductive coil coupled to the write pole, the write pole generating a magnetic write field in the presence of electrical write current through the coil;
a trailing shield of magnetically permeable material for altering the angle of the write field; and
a spin torque oscillator (STO) between the write pole and the trailing shield and comprising a ferromagnetic polarizer, a free ferromagnetic layer having a magnetization that rotationally oscillates in the presence of an electrical current through the free layer to thereby generate an oscillating magnetic field to assist the magnetic field from the write pole, and a nonmagnetic electrically conductive spacer between the polarizer and free layer, the polarizer having a magnetization, in the presence of the write field from the write pole, oriented at an angle greater than 20 degrees and less than 80 degrees from the normal to the plane parallel to the free layer.
2. The head of claim 1 wherein the polarizer is a ferromagnetic polarizer layer having a magnetization, in the presence of the write field from the write pole, oriented at an angle greater than 30 degrees and less than 70 degrees from the normal to the plane of the polarizer layer.
3. The head of claim 1 wherein the polarizer is a ferromagnetic polarizer layer having a net in-plane magnetostatic shape anisotropy greater than 5 kOe.
4. The head of claim 3 wherein the polarizer is a ferromagnetic polarizer layer wherein the ratio of largest lateral in-plane dimension to thickness for the polarizer layer is between 5 and 15.
5. The head of claim 3 wherein the polarizer is a ferromagnetic polarizer layer formed of one or more of Co, Ni and Fe and has a saturation magnetization M s greater than 1500 emu/cc and less than 1800 emu/cc.
6. The head of claim 1 wherein the polarizer is a ferromagnetic polarizer layer located between the write pole and the free layer.
7. The head of claim 1 wherein the polarizer is a ferromagnetic polarizer layer located between the free layer and the trailing shield.
8. The head of claim 1 wherein the polarizer is a ferromagnetic polarizer layer exchange coupled to the write pole.
9. The head of claim 1 wherein the polarizer is a ferromagnetic polarizer layer exchange coupled to the trailing shield.
10. The head of claim 1 wherein the polarizer is the write pole, the magnetization near the surface of the write pole adjacent to the free layer when the write pole is fully magnetized being oriented at an angle greater than 20 degrees and less than 80 degrees from the normal to the plane parallel to the free layer.
11. The head of claim 1 wherein the polarizer is the trailing shield.
12. The head of claim 1 further comprising a ferromagnetic layer exchange coupled to the free layer and having a magnetization substantially perpendicular to the plane of the free layer.
13. The head of claim 1 wherein the STO further comprises two electrodes for the passage of electrical current.
14. The head of claim 13 wherein the write pole comprises a first of said two electrodes and the trailing shield comprises the second of said two electrodes.
15. The head of claim 13 further comprising:
circuitry coupled to the two electrodes of the STO and capable of supplying direct current to the STO when write current is supplied to the coil.
16. A MAMR system comprising:
the write head of claim 1 ; and
a magnetic recording medium having a perpendicular magnetic recording layer.
17. A magnetic recording disk drive perpendicular recording write head for magnetizing regions in data tracks of a perpendicular magnetic recording layer on the disk, the head being formed on a slider having an air-bearing surface (ABS) lying substantially in a plane parallel to the X-Z plane of an X-Y-Z coordinate system and comprising:
a substrate;
a write pole on the substrate and aligned generally parallel to the Y-axis, the write pole having an end substantially at the ABS;
an electrically conductive coil coupled to the write pole, the write pole generating a magnetic write field in the presence of electrical write current through the coil;
a trailing shield on the substrate and formed of magnetically permeable material for altering the angle of the write field, the trailing shield being spaced from the write pole along the Z-axis;
a spin torque oscillator (STO) on the substrate between the write pole and the trailing shield and comprising a stack of layers with planes generally parallel with the X-Y plane, said stack including a ferromagnetic polarizer layer having a magnetization, in the presence of the write field from the write pole, oriented at an angle φ p between 20 degrees and 80 degrees from the Z-axis, a free ferromagnetic layer having a magnetization oriented at a non-zero angle ψ to the Z-axis and free to rotate about the Z-axis in the presence of electrical current through the free layer, and a nonmagnetic electrically conductive spacer between the polarizer layer and the free layer; and
circuitry coupled to the STO and capable of supplying direct current through the stack when write current is supplied to the coil.
18. The head of claim 17 further comprising a first electrode between the STO and the write pole and a second electrode between the STO and the trailing shield and wherein said circuitry is coupled to the first and second electrodes.
19. The head of claim 17 wherein said circuitry is coupled to the write pole and the trailing shield.
20. The head of claim 17 wherein the polarizer layer has a magnetization, in the presence of the write field from the write pole, oriented at an angle greater than 30 degrees and less than 70 degrees from the Z-axis.
21. The head of claim 17 wherein the polarizer layer has a net in-plane magnetostatic shape anisotropy greater than 5 kOe.
22. The head of claim 17 wherein the polarizer layer is located between the write pole and the free layer.
23. The head of claim 17 wherein the polarizer layer is located between the free layer and the trailing shield.
24. The head of claim 17 wherein the polarizer layer is exchange coupled to the write pole.
25. The head of claim 17 wherein the polarizer layer is exchange coupled to the trailing shield.
26. The head of claim 17 further comprising a ferromagnetic layer exchange coupled to the free layer and having a magnetization substantially perpendicular to the plane of the free layer.
27. A microwave-assisted magnetic recording (MAMR) system comprising:
the write head of claim 17 ; and
a magnetic recording disk maintained near the write head and having a perpendicular magnetic recording layer oriented generally parallel to the ABS of the write head.