# US 10,121,500 B2 · Magnetic tunnel junction (MTJ) free layer damping reduction

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- Number: US 10,121,500 B2
- Document ID: US10121500B2
- Status: Granted
- Kind: B2
- Application number: 16/005,835
- Filed: 2018-06-12
- Published: 2018-10-11
- Granted: 2018-11-06
- Earliest claimed: 2016-06-28
- Assignees: Western Digital Technologies, Inc.
- Applicants: Western Digital Technologies, Inc.
- Inventors: Zheng Gao; James Mac Freitag
- Web page: https://patentgrep.com/patent/US10121500B2

## CPC

- G11B 5/3909: {Arrangements using a magnetic tunnel junction}
- G11C 11/161: {details concerning the memory cell structure, e.g. the layers of the ferromagnetic memory cell}
- H10B 61/00: Magnetic memory devices, e.g. magnetoresistive RAM [MRAM] devices
- H10N 50/10: Magnetoresistive devices
- H10N 50/80: Constructional details
- H10N 50/85: Materials of the active region
- G11B: INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER (recording measured values in a way that does not require playback through a transducer G01D9/00; recording or playback apparatus using mechanically marked tape, e.g. punched paper tape, or using unit records, e.g. punched or magnetically marked cards G06K; transferring data from one type of record carrier to another G06K1/18; circuits for coupling output of reproducer to radio receiver H04B1/20; gramophone pick-ups or like acoustic electromechanical transducers or circuits therefor H04R)
- G11C: STATIC STORES (semiconductor memory devices H10B)
- H10B: ELECTRONIC MEMORY DEVICES
- H10N: ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR

## Abstract

In one embodiment, a system includes a sensor, the sensor having a free layer, a ferromagnetic spin sink layer spaced from the free layer, the spin sink layer being operative to reduce a spin-induced damping in the free layer during operation of the sensor, and a nonmagnetic spacer layer positioned between the free layer and the spin sink layer, the spacer layer having a long spin-diffusion length.

## Claims

### Claim 1

A magnetic sensor comprising:
a spin sink layer to reduce damping in a free layer of the magnetic sensor;
a spacer layer between the free layer and the spin sink layer; and
a spin reflective layer separated from the spacer layer by the spin sink layer.

### Claim 2 (depends on 1)

The magnetic sensor of claim 1, further comprising a cap layer separated from the spin sink layer by the spin reflective layer.

### Claim 3 (depends on 1)

The magnetic sensor of claim 1, wherein the spin reflective layer comprises ones of magnesium oxide, tantalum oxide, ruthenium oxide, and hafnium oxide.

### Claim 4 (depends on 1)

The magnetic sensor of claim 1, wherein the spin reflective layer comprises an oxidized portion of the spin sink layer.

### Claim 5 (depends on 1)

The magnetic sensor of claim 1, wherein a deposition thickness of the spin reflective layer is at least one tenth of a nanometer and not more than one nanometer.

### Claim 6 (depends on 1)

The magnetic sensor of claim 1, wherein the spacer layer is nonmagnetic and comprises a spin diffusion length that is greater than a deposition thickness of the spacer layer.

### Claim 7 (depends on 6)

The magnetic sensor of claim 6, wherein the spin diffusion length of the spacer layer is about one hundred nanometers and the deposition thickness of the spacer layer is about four nanometers.

### Claim 8 (depends on 1)

The magnetic sensor of claim 1, wherein the spacer layer magnetically decouples the spin sink layer from the free layer.

### Claim 9 (depends on 1)

The magnetic sensor of claim 1, wherein the spacer layer comprises at least one of copper, silver, tin, and gold.

### Claim 10 (depends on 1)

The magnetic sensor of claim 1, wherein the spacer layer comprises a nonmagnetic conductive metal having a spin diffusion length that permits electrons to travel across the spacer layer without scattering or flipping.

### Claim 11 (depends on 1)

The magnetic sensor of claim 1, wherein the magnetic sensor is part of a hard disk drive.

### Claim 12 (depends on 1)

The magnetic sensor of claim 1, wherein the magnetic sensor is part of a magnetic random access memory device.

### Claim 13 (depends on 1)

The magnetic sensor of claim 1, wherein the spin sink layer comprises a ferromagnetic material.

### Claim 14 (depends on 1)

The magnetic sensor of claim 1, wherein the spin sink layer reduces damping in the free layer via the spacer layer without modification of the free layer.

### Claim 15 (depends on 1)

The magnetic sensor of claim 1, wherein the spin sink layer has a deposition thickness of at least one nanometer.

### Claim 16

A magnetic sensor comprising:
a spin sink layer to reduce damping in a free layer of the magnetic sensor;
a nonmagnetic spacer layer between the spin sink layer and the free layer;
a cap layer separated from the nonmagnetic spacer layer by the spin sink layer; and
a top shield separated from the spin sink layer by the cap layer.

### Claim 17 (depends on 16)

The magnetic sensor of claim 16, wherein the nonmagnetic spacer layer magnetically decouples the spin sink layer from the free layer, and wherein the cap layer magnetically decouples the spin sink layer from the top shield.

### Claim 18 (depends on 16)

The magnetic sensor of claim 16, wherein the nonmagnetic spacer layer comprises a spin diffusion length that is greater than a deposition thickness of the nonmagnetic spacer layer.

### Claim 19

A magnetic recording device comprising:
a magnetic sensor comprising:
a free layer;
a spin sink layer;
a nonmagnetic spacer layer between the spin sink layer and the free layer; and
a spin reflective layer separated from the spacer layer by the spin sink layer.

### Claim 20 (depends on 19)

The magnetic recording device of claim 19, wherein the magnetic recording device is at least one of a magnetic random access memory and a hard disk drive.