Magnetic recording assisted by spin torque oscillator with a radio frequency current bias

• US 8,582,240 B1
• Filed: 08/29/2012
• Issued: 11/12/2013
• Est. Priority Date: 08/29/2012
• Status: Active Grant

• Current Assignee: Headway Technologies Incorporated
• Original Assignee: Headway Technologies Incorporated
• Inventors: Chen, Wenyu, Smyth, Joe
• Primary Examiner(s): Castro, Angel
• Application Number:
  US13/597,472
• Time in Patent Office: 440 Days
• Field of Search: 360/119.04, 360/125.03, 360/125.3
• US Class Current: 360/125.3
• CPC Class Codes: G11B 2005/0024 Microwave assisted recording
• CPC Class Codes: G11B 5/1278 specially adapted for magnetisations perpendicular to the surface of the record carrier
• CPC Class Codes: G11B 5/314 where the layers are extra layers normally not provided in the transducing structure, e.g. optical layers G11B5/3196 takes precedence
• CPC Class Codes: G11B 5/3146 magnetic layers
• CPC Class Codes: G11B 5/399 with intrinsic biasing, e.g. provided by equipotential strips

Abstract

A design is disclosed for a microwave assisted magnetic recording device wherein direct current and rf current are simultaneously injected from a bias tee into a spin transfer oscillator (STO) between a main pole and write shield to improve the assist process. The STO oscillation layer (OL) has a large angle magnetization oscillation frequency that is locked to a magnetic medium bit resonance frequency f0 when the rf current has a frequency f=f0 and a threshold current density is applied. Alternatively, the OL magnetization oscillation frequency may be adjusted closer to f0 to improve the assist process. A third advantage is lowering the threshold current density when both direct current and rf current are injected into the STO during a write process. The main pole is grounded when direct current and rf current are injected into a write shield.

Claims

1. A microwave assisted magnetic recording (MAMR) structure that includes a write head, comprising:

(a) a main pole that generates a magnetic flux field which is directed through a pole tip at an air bearing surface (ABS) and into a magnetic medium comprised of a plurality of bits, the magnetic flux has a gap field component that is directed across a spin torque oscillator (STO) and into a write shield;

(b) the write shield with a side along the ABS that collects magnetic flux which has passed through the magnetic medium and written one or more bits;

(c) the STO that is formed along the ABS and generates a rf field on the magnetic medium and thereby assists the writing to one or more bits; and

(d) a bias tee (T) that is electrically connected by a lead to the main pole and by a lead to the write shield, and combines dc from a dc source and rf current from a rf current source and injects the dc and rf current combination into the STO to provide a dc bias, and a rf bias to the STO.

2. A microwave assisted magnetic recording (MAMR) structure that includes a write head, comprising:

(a) a main pole that generates a magnetic flux field which is directed through a pole tip at an air bearing surface (ABS) and into a magnetic medium comprised of a plurality of bits, the magnetic flux has a gap field component that is directed across a spin torque oscillator (STO) and into a write shield;

(b) the write shield with a side along the ABS that collects magnetic flux which has passed through the magnetic medium and written one or more bits;

(c) the STO that is formed along the ABS and has a NM1/SP/NM3/OL/NM2 configuration wherein a first non-magnetic layer (NM1) adjoins the main pole, a second non-magnetic layer (NM2) contacts the write shield, SP is a layer with perpendicular magnetic anisotropy that spin polarizes direct current (dc) and radio frequency (rf) current passing there through, NM3 is a third non-magnetic layer between SP and OL layers, and OL is a layer with a magnetization that reaches a large angle oscillation state with an oscillation frequency when a threshold current with density (j_c) that is spin polarized by the SP layer exerts a spin transfer torque on the OL layer such that the large angle OL oscillation generates a rf field on the magnetic medium and assists the writing to one or more bits; and

(d) a bias tee (T) that is electrically connected by a lead to the main pole and by a lead to the write shield, and combines dc from a dc source and rf current from a rf current source and injects the dc and rf current combination into the STO through a main pole terminal or a write shield terminal to provide a dc bias, and a rf bias to the STO.

3. The MAMR structure of claim 2 wherein the bias T has a dc terminal that is an inductor with impedance from about 0.1 to 10 milli-Henry.

4. The MAMR structure of claim 2 wherein the bias T has a rf terminal that is a capacitor with a capacitance from about 1 nanofarad to 500 nanofarad.

5. The MAMR structure of claim 2 wherein a terminal of the rf current source is connected to ground, and the leads to the main pole and write shield are electrically floating.

6. The MAMR structure of claim 2 wherein the lead to the main pole is connected to ground, a terminal of the rf current source is connected to ground, and the dc and rf current are injected by the bias T into the write shield terminal, the rf current has a frequency from about 0.1 to 50 GHz.

7. The MAMR structure of claim 2 wherein the lead to the write shield is connected to ground, a terminal of the if current source is connected to ground, and the dc and rf current are injected by the bias T into the main pole terminal.

8. The MAMR structure of claim 2 wherein a frequency and amplitude of the if current are tuned to reduce the threshold current density (j_c) and thereby provide better MAMR reliability and a higher device yield.

9. The MAMR structure of claim 2 wherein a frequency and amplitude of the rf current are tuned to lock the OL oscillation frequency of the large angle oscillation state to provide improved writing assist efficiency.

10. The MAMR structure of claim 2 wherein a frequency and amplitude of the rf current are tuned to pull and mix the OL oscillation frequency of the large angle oscillation state to provide improved writing assist efficiency.

11. The MAMR structure of claim 2 wherein a frequency and amplitude of the rf current are tuned to lock the OL oscillation frequency into a small angle in-plane precession state to prevent return field partial erasure of magnetic medium bits.