Perpendicular magnetic recording system with spin torque oscillator and control circuitry for fast switching of write pole magnetization
View Patent ↗A perpendicular magnetic recording hard disk drive includes a write head with a write pole and an electrically conductive coil coupled to the write pole, a write driver for supplying electrical write current to the coil to generate magnetic flux in the write pole, a spin torque oscillator (STO) that injects auxiliary magnetic flux to the write pole to facilitate magnetization switching of the write pole, and STO control circuitry. Direct electrical current to the STO induces rotation of the magnetization of a free ferromagnetic layer in the STO, which generates the auxiliary magnetic flux. The STO control circuitry may be coupled to the STO via the electrical lines that connect the write driver to the write head, the lines that connect the read amplifier to the read head, or, if the disk drive is one with thermal fly-height control (TFC), the lines that connect the TFC circuitry with the heater.
1. A perpendicular magnetic recording disk drive:
a disk having a perpendicular magnetic recording layer;
a write head for magnetizing regions of the recording layer comprising
a main pole;
a main electrically conductive coil coupled to the main pole for generating magnetic flux in the main pole in the presence of electrical write current; and
a spin torque oscillator (STO) having first and second electrodes and a free ferromagnetic layer between the electrodes, the free layer having a magnetization free to rotate in the presence of an electrical current between the electrodes, the rotation of the free layer magnetization generating an auxiliary magnetic flux directed to the main pole at an angle to the main pole greater than 15 degrees and less than or equal to 90 degrees;
a write driver capable of supplying write current in two directions to the main coil;
a read head for detecting magnetized regions in the recording layer and generating a readback signal;
a read amplifier for amplifying the readback signal from the read head;
an integrated lead suspension (ILS) having electrically conductive traces connecting the write driver to the write head and electrically conductive traces connecting the read amplifier to the read head;
STO control circuitry for supplying direct electrical current to the STO electrodes when write current is supplied to the main coil, the STO circuitry being connected to the STO via traces connecting the write driver to the write head; and
a pair of matched resistors between the write driver and the write head; and wherein the STO control circuitry includes a low-pass filter coupled to the common-mode through the resistors, a voltage source, and a comparator for comparing the output of the low-pass filter to the voltage source.
2. The disk drive of claim 1 further comprising an electrically resistive heater for moving the write head and read head toward the recording layer and heater control circuitry for supplying electrical current to the heater, and wherein the ILS includes electrically conductive traces connecting the heater control circuitry to the heater.
3. The disk drive of claim 2 wherein the STO circuitry directs electrical current to the STO electrodes via said traces connecting the heater control circuitry to the heater.
4. The disk drive of claim 1 further comprising a high-pass filter coupled to the STO for shunting high-frequency signal content away from the STO.
5. A perpendicular magnetic recording disk drive:
a disk having a perpendicular magnetic recording layer;
a write head for magnetizing regions of the recording layer comprising a main pole and a main electrically conductive coil coupled to the main pole for generating magnetic flux in the main pole in the presence of electrical write current;
a write driver for supplying electrical write current in two directions to the main coil of the write head;
electrically conductive traces connecting the write driver to the main coil of the write head;
a spin torque oscillator (STO) comprising first and second electrodes, a pinned ferromagnetic layer having a magnetization fixed in the presence of a direct electrical current between the electrodes, a free ferromagnetic layer having a magnetization free to rotate in the presence of a direct electrical current between the electrodes, and a nonmagnetic spacer layer between the pinned and free layers, wherein the pinned, spacer and free layers are located between the first and second electrodes and an edge of the free layer is magnetically coupled to the main pole of the write head;
STO control circuitry for supplying direct electrical current to the STO electrodes through the traces connecting the write driver to the main when write current is supplied to the main coil by the write driver; and
a pair of matched resistors between the write driver and the main coil of the write head; and wherein the STO control circuitry includes a low-pass filter coupled to the common-mode through the resistors, a voltage source, and a comparator for comparing the output of the low-pass filter to the voltage source.
6. The disk drive of claim 5 further comprising a high-pass filter coupled to the STO for shunting high-frequency signal content away from the STO.
7. The disk drive of claim 5 wherein the STO free layer is oriented substantially orthogonal to the main pole.
8. The disk drive of claim 5 wherein the STO free layer is oriented substantially parallel to the main pole and further comprising a flux guide between the free layer and the main pole for directing magnetic flux from the free layer to the main pole.
9. The disk drive of claim 5 wherein the main coil is a helical coil wrapped around the main pole.