MgO based perpendicular spin polarizer in microwave assisted magnetic recording (MAMR) applications

• US 9,230,571 B1
• Filed: 08/26/2014
• Issued: 01/05/2016
• Est. Priority Date: 08/26/2014
• Status: Active Grant

• Current Assignee: Headway Technologies Incorporated (TDK Corporation)
• Original Assignee: Headway Technologies Incorporated (TDK Corporation)
• Inventors: Chen, Wenyu, Wu, Yan
• Primary Examiner(s): Klimowicz, Will J
• Application Number:
  US14/468,399
• Time in Patent Office: 497 Days
• Field of Search: 360/125.3, 360/128
• US Class Current: 1/1
• 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 5/147 with cores being composed of metal sheets, i.e. laminated cores with cores composed of isolated magnetic layers, e.g. sheets in thin films G11B5/31
• 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 5/315 Shield layers on both sides of the main pole, e.g. in perpendicular magnetic heads
• CPC Class Codes: G11B 5/3909 Arrangements using a magnetic tunnel junction

Abstract

A design for a microwave assisted magnetic recording device is disclosed wherein a spin torque oscillator (STO) between a main pole and write shield has a spin polarization (SP) layer less than 30 Angstroms thick and perpendicular magnetic anisotropy (PMA) induced by an interface with one or two metal oxide layers. Back scattered spin polarized current from an oscillation layer is used to stabilize SP layer magnetization. One or both of the metal oxide layers may be replaced by a confining current pathway (CCP) structure. In one embodiment, the SP layer is omitted and spin polarized current is generated by a main pole/metal oxide interface. A direct current or pulsed current bias is applied across the STO. Rf current may also be injected into the STO to reduce critical current density. A write gap of 25 nm or less is achieved while maintaining good STO performance.

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 to write one or more 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 the one or more bits;

(c) an external current source that produces a direct current bias or pulsed current bias between the main pole and write shield, and across the STO; and

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

(1) a spin polarization (SP) layer which is selected from CoFeB, CoFe, CoFeNi, CoB, or FeB with perpendicular magnetic anisotropy (PMA) that spin polarizes the bias current in a direction perpendicular to a top surface of the SP layer and towards an oscillation layer (OL);

(2) the oscillation layer (OL) wherein the spin polarized bias current of a critical current density from the SP layer causes magnetization in the OL to oscillate with a sufficiently large angle and frequency to generate the if field on the magnetic medium to assist the writing to one or more bits;

(3) a non-magnetic spacer between the SP layer and OL, the non-magnetic spacer comprises one or more metal oxides;

(4) a seed layer formed between the main pole and the SP layer, the seed layer is a metal oxide layer consisting of AlOx, TaOx, or RuOx, a laminate of one or more of AlOx, TaOx, and RuOx, or a laminate of MgO with one or more of AlOx, TaOx, and RuOx; and

(5) a capping layer formed between the OL and the write shield wherein the seed layer and the non-magnetic spacer induce the PMA in the SP layer.

2. The MAMR structure of claim 1 wherein the SP layer has a thickness less than 30 Angstroms.

3. The MAMR structure of claim 2 wherein the PMA in the SP layer may be increased by decreasing a thickness of the SP layer.

4. The MAMR structure of claim 1 wherein back scattered spin polarized current from the OL works with a damping torque to stabilize the SP layer against undesired magnetization switching in the SP layer.

5. The MAMR structure of claim 1 wherein a thickness of the STO in a down-track direction between the main pole and write shield represents a write gap (WG) distance, and the WG distance is about 25 nm or less.

6. The MAMR structure of claim 1 wherein the seed layer has a thickness from 10 to 20 Angstroms.

7. The MAMR structure of claim 1 wherein the non-magnetic spacer is a metal oxide layer or a laminate that is comprised of one or more of AlOx, MgO, AlTiOx, MgZnOx, and ZnOx.

8. The MAMR structure of claim 1 wherein the non-magnetic spacer has a thickness from 10 to 20 Angstroms.

9. The MAMR structure of claim 1 wherein the OL is comprised of a Co alloy, a Fe alloy, or is a laminate with an (A1/A2)_n stack of layers where n is a lamination number, A1 is one of Co, Fe, CoFe, CoFeR in which R is a non-magnetic element, and A2 is one of Ni, NiCo, and NiFe.

10. The MAMR structure of claim 1 wherein a rf current bias may be combined with the direct current bias or the pulsed current bias across the STO to reduce the critical current density.

11. A method to form a microwave assisted magnetic recording (MAMR) write head, comprising:

(a) providing a main pole that generates magnetic flux which is directed through a main 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) forming the STO on the main pole, the STO comprises;

(1) a seed layer that contacts a surface of the main pole that faces a down-track direction, the seed layer is a metal oxide layer consisting of AlOx, TaOx, or RuOx, a laminate of one or more of AlOx, TaOx, and RuOx, or a laminate of MgO with one or more of AlOx, TaOx, and RuOx;

(2) a spin polarization (SP) layer which is selected from CoFeB, CoFe, CoFeNi, CoB, or FeB having a bottom surface contacting the seed layer, the SP layer has perpendicular magnetic anisotropy (PMA) and spin polarizes a bias current from an external current source in a direction perpendicular to a top surface of the SP layer and towards an oscillation layer (OL);

(3) a non-magnetic spacer that contacts the top surface of the SP layer and a bottom surface of the OL, the non-magnetic spacer comprises one or more metal oxides;

(4) the oscillation layer (OL) wherein the spin polarized current from the SP layer has a critical current density that causes magnetization in the OL to oscillate with a sufficiently large angle and frequency to generate a rf field on the magnetic medium to assist the writing to one or more bits; and

(5) a capping layer formed on a top surface of the OL, and wherein the seed layer and the non-magnetic spacer induce the PMA in the SP layer;

(d) forming the write shield on the capping layer; and

(e) connecting the external current source by a lead to the main pole and with a lead to the write shield.

12. The method of claim 11 wherein the SP layer is has a thickness less than about 30 Angstroms.

13. The method of claim 12 wherein the PMA in the SP layer may be increased by decreasing a thickness of the SP layer.

14. The method of claim 11 wherein a thickness of the STO in the down-track direction between the main pole and the write shield represents a write gap (WG) distance, and the WG distance is about 25 nm or less.

15. The method of claim 11 wherein the seed layer has a thickness from 10 to 20 Angstroms.

16. The method of claim 11 wherein the non-magnetic spacer is a metal oxide layer or a laminate that is comprised of one or more of AlOx, MgO, AlTiOx, MgZnOx, and ZnOx.

17. The method of claim 11 wherein the OL is comprised of a Co alloy, a Fe alloy, or is a laminate with an (A1/A2)_n stack of layers where n is a lamination number, A1 is one of Co, Fe, CoFe, CoFeR in which R is a non-magnetic element, and A2 is one of Ni, NiCo, and NiFe.