Magnetic recording devices and methods using a write-field-enhancement structure and bias current with offset pulses
Disclosed herein are magnetic recording devices and methods of using them. A magnetic recording device comprises a main pole extending to an air-bearing surface (ABS), a trailing shield extending to the ABS, a write-field-enhancing structure disposed between and coupled to the main pole and the trailing shield at the ABS, a write coil configured to magnetize the main pole, a write current control circuit coupled to the write coil and configured to apply a write current to the write coil, wherein the write current comprises a write pulse, and a bias current control circuit coupled to the write-field-enhancing structure and configured to apply a bias current to the write-field-enhancing structure, wherein the bias current comprises a driving pulse offset in time from the write pulse by a delay, wherein the delay substantially coincides with an expected magnetization switch-time lag of a free layer of the write-field-enhancing structure.
1. A magnetic recording device, comprising:
a main pole extending to an air-bearing surface (ABS) of the magnetic recording device;
a trailing shield extending to the ABS of the magnetic recording device;
a write-field-enhancing structure disposed between and coupled to the main pole and the trailing shield at the ABS of the magnetic recording device;
a write coil configured to magnetize the main pole;
a write current control circuit coupled to the write coil and configured to apply a write current to the write coil, wherein the write current comprises a write pulse; and
a bias current control circuit coupled to the write-field-enhancing structure and configured to apply a bias current to the write-field-enhancing structure, wherein the bias current comprises a driving pulse offset in time from the write pulse by a delay, wherein the delay substantially coincides with an expected magnetization switch-time lag of a free layer of the write-field-enhancing structure.
2. The magnetic recording device recited in claim 1 , wherein the bias current control circuit is coupled to the write current control circuit to enable the bias current control circuit to impose the delay.
3. The magnetic recording device recited in claim 1 , wherein the delay is between approximately 50 ps and approximately 500 ps.
4. The magnetic recording device recited in claim 1 , wherein the delay is dependent on a characteristic of the free layer.
5. The magnetic recording device recited in claim 4 , wherein the characteristic is at least one of a free-layer saturation magnetization density (Bst) value or a thickness.
6. The magnetic recording device recited in claim 5 , wherein the Bst value is between approximately 4 Tnm and approximately 7 Tnm.
7. The magnetic recording device recited in claim 1 , wherein the delay is dependent on a characteristic of the bias current.
8. The magnetic recording device recited in claim 7 , wherein the characteristic is at least one of a duty cycle, an amplitude, or a current density.
9. The magnetic recording device recited in claim 1 , wherein the delay is dependent on a characteristic of the write current.
10. The magnetic recording device recited in claim 9 , wherein the characteristic is at least one of a duty cycle, an amplitude, or a current density.
11. The magnetic recording device recited in claim 1 , wherein the write-field-enhancing structure comprises a spin-torque oscillator (STO) comprising a spin-preserving layer (SPL), a field-generating layer (FGL), and a spacer layer disposed between the SPL and FGL.
12. The magnetic recording device recited in claim 1 , wherein the write-field-enhancing structure comprises a DC field generation (DFG) layer, a non-magnetic layer, and a spacer layer disposed between the DFG layer and the non-magnetic layer, the DFG layer being the free layer of the write-field-enhancing structure.
13. The magnetic recording device recited in claim 12 , wherein the DFG layer is the only magnetic layer within a write gap between the main pole and the trailing shield that is not adjacent to the main pole or the trailing shield.
14. The magnetic recording device recited in claim 12 , wherein a write gap between the main pole and the trailing shield does not include any magnetic layer other than the DFG layer.
15. The magnetic recording device recited in claim 1 , wherein the driving pulse has at least two non-zero amplitudes.
16. The magnetic recording device recited in claim 1 , wherein the bias current control circuit is further configured to adjust at least one characteristic of the driving pulse based on the write current or based on an upcoming bit to be recorded.
17. The magnetic recording device recited in claim 16 , wherein the at least one characteristic of the driving pulse comprises an amplitude, the delay, or a duration.
18. The magnetic recording device recited in claim 1 , wherein the bias current further comprises an advance pulse that precedes the driving pulse.
19. The magnetic recording device recited in claim 18 , wherein an amplitude of the advance pulse is less than an amplitude of the driving pulse, or less than or equal to zero.
20. The magnetic recording device recited in claim 18 , wherein the bias current control circuit is further configured to adjust at least one characteristic of the advance pulse based on the write current or based on an upcoming bit to be recorded.
21. The magnetic recording device recited in claim 20 , wherein the at least one characteristic of the driving pulse comprises an amplitude, the delay, or a duration.
22. A method of writing to a magnetic recording media using a magnetic recording device comprising a main pole, a trailing shield, and a write-field-enhancing structure that includes a free layer and is disposed between the main pole and the trailing shield, the method comprising:
a write current control circuit supplying a write current to a write coil coupled to the main pole and to the trailing shield, the write current comprising a write pulse;
a bias current control circuit obtaining a delay value, the delay value being determined based on an expected magnetization switch-time lag of the free layer in response to the write pulse; and
the bias current control circuit supplying, to the write-field-enhancing structure, a bias current comprising a bias pulse, wherein the bias pulse is delayed relative to the write pulse by the delay value.
23. The method recited in claim 22 , wherein the delay value is between approximately 50 ps and approximately 500 ps.
24. The method recited in claim 22 , further comprising the bias current control circuit adjusting at least an aspect of the bias current.
25. The method recited in claim 24 , wherein the aspect is an amplitude of the bias current or the driving pulse, a timing of the bias pulse, a duration of the bias pulse, or a duty cycle of the bias current.
26. The method recited in claim 22 , wherein the bias pulse comprises a driving pulse.
27. The method recited in claim 26 , wherein the bias pulse further comprises an advance pulse that precedes the driving pulse.
28. The method recited in claim 22 , wherein obtaining the delay value comprises calculating the delay value.