# US 6,721,145 B2 · Method for initializing antiferromagnetic layers in a spin valve magnetic sensor

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- Number: US 6,721,145 B2
- Document ID: US6721145B2
- Status: Granted
- Kind: B2
- Application number: 10/037,269
- Filed: 2002-01-02
- Published: 2003-07-03
- Granted: 2004-04-13
- Earliest claimed: 2002-01-02
- Assignees: International Business Machines Corporation
- Inventors: Robert S. Beach
- Web page: https://patentgrep.com/patent/US6721145B2

## CPC

- G11B 5/3909: {Arrangements using a magnetic tunnel junction}
- B82Y 10/00: Nanotechnology for information processing, storage or transmission, e.g. quantum computing or single electron logic
- B82Y 25/00: Nanomagnetism, e.g. magnetoimpedance, anisotropic magnetoresistance, giant magnetoresistance or tunneling magnetoresistance
- B82Y 40/00: Manufacture or treatment of nanostructures
- H01F 10/3218: {Exchange coupling of magnetic films via an antiferromagnetic interface (H01F10/3268 takes precedence)}
- H01F 41/304: {using temporary decoupling, e.g. involving blocking, Néel or Curie temperature transitions by heat treatment in presence/absence of a magnetic field}
- G11B 5/012: Recording on, or reproducing or erasing from, magnetic disks (G11B17/00, G11B19/00 take precedence)
- G11B 2005/0008: {Magnetic conditionning of heads, e.g. biasing}
- G11B 2005/0016: {of magnetoresistive transducers}
- Y10T 29/49034: Treating to affect magnetic properties
- 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)
- B82Y: SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
- H01F: MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- Y10T: TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION

## Abstract

A method of initializing a magnetic sensor having two antiferromagnetic layers is described. The method takes advantage of the spin flop effect such that the two antiferromagnetic layers may be orthogonally initialized. The signal polarity of the sensor is well controlled.

## Claims

### Claim 1

A method of initializing a first and a second antiferromagnetic layer in a magnetic sensor, said magnetic sensor having an antiparallel pinned substructure, said antiparallel pinned substructure having a first and a second ferromagnetic film, said first antiferromagnetic layer exchanged coupled to said first ferromagnetic film, said method comprising:
performing a first thermal treatment of said magnetic sensor in a first magnetic field to pre-initialize said first antiferromagnetic layer; and,
performing a second thermal treatment of the magnetic sensor in an optimal value magnetic field to initialize said second antiferromagnetic layer,
wherein the magnitude and direction of said optimal value magnetic field is chosen to maintain the pre-initialized direction of magnetization in said first ferromagnetic film.

### Claim 2 (depends on 1)

A method as in claim 1, wherein the direction of said optimal value magnetic field is approximately 90 degrees relative to the direction of said first magnetic field.

### Claim 3 (depends on 1)

A method as in claim 1, wherein said first thermal treatment includes heating from about 1 to 20 hours at a temperature of about 150 to 400 degrees C.

### Claim 4 (depends on 1)

A method as in claim 1, wherein said second thermal treatment is performed by heating from about 1 to 20 hours at a temperature of about 150 to 400 degrees C.

### Claim 5 (depends on 1)

A method as in claim 1, wherein said first magnetic field is above 4000 Oe.

### Claim 6 (depends on 1)

A method as in claim 1, wherein said first magnetic field is below 500 Oe.

### Claim 7

A method of initializing a first and a second antiferromagnetic layer, each being of substantially the same material as the other, in a magnetic sensor, said magnetic sensor having an antiparallel pinned substructure, said antiparallel pinned substructure having a first and a second ferromagnetic film, said first antiferromagnetic layer exchanged coupled to said first ferromagnetic film, said method comprising:
performing a first thermal treatment of said magnetic sensor in a first magnetic field to pre-initialize said first antiferromagnetic layer; and,
performing a second thermal treatment of said magnetic sensor in an optimal value magnetic field to initialize said second antiferromagnetic layer,
wherein the magnitude and direction of said optimal value magnetic field is chosen to maintain the pre-initialized direction of magnetization in said first ferromagnetic film.

### Claim 8 (depends on 7)

A method as in claim 7, wherein the direction of said optimal value magnetic field is approximately 90 degrees relative to the direction of said first magnetic field.

### Claim 9 (depends on 7)

A method as in claim 7, wherein said first thermal treatment is performed by heating from about 1 to 20 hours at a temperature of about 150 to 400 degrees C.

### Claim 10 (depends on 7)

A method as in claim 7, wherein said second thermal treatment is performed by heating from about 1 to 20 hours at a temperature of about 150 to 400 degrees C.

### Claim 11 (depends on 7)

A method as in claim 7, wherein said first magnetic field is above 4000 Oe.

### Claim 12 (depends on 7)

A method as in claim 7, wherein said first magnetic field is below 500 Oersteds.

### Claim 13

A method of initializing a first and a second antiferromagnetic layer in a magnetic sensor, said sensor having an antiparallel pinned substructure, said antiparallel pinned substructure having a first and a second ferromagnetic film, said first antiferromagnetic layer exchanged coupled to said first ferromagnetic film, said method comprising:
inducing a preferred orientation of magnetization in at least one of said first or second ferromagnetic films in said antiparallel substructure during the deposition of said first and second ferromagnetic films;
placing the sensor in a weak magnetic field;
increasing the magnitude of said magnetic field to the optimal value such that the direction of magnetization in said first ferromagnetic film is approximately 90 degrees relative to said magnetic field; and,
performing a thermal treatment in said magnetic field having said optimal value.

### Claim 14 (depends on 13)

A method as in claim 13, wherein said thermal treatment is performed by heating from about 1 to 20 hours at a temperature of about 150 to 400 degrees C.

### Claim 15

A method of initializing a first and a second antiferromagnetic layer, each being of substantially the same material as the other, in a magnetic sensor, said magnetic sensor having an antiparallel pinned substructure, said antiparallel pinned substructure having a first and a second ferromagnetic film, said first antiferromagnetic layer exchanged coupled to said first ferromagnetic film, said method comprising:
inducing a preferred orientation of magnetization in at least one of said first or second ferromagnetic films in the antiparallel substructure during the deposition of said first and second ferromagnetic films;
placing the sensor in a weak magnetic field;
increasing the magnitude of said magnetic field to the optimal value such that the direction of magnetization in said first ferromagnetic film is approximately 90 degrees relative to the magnetic field; and,
performing a thermal treatment in said magnetic field having said optimal value.

### Claim 16 (depends on 15)

A method as in claim 15, wherein said first thermal treatment is performed by heating from about 1 to 20 hours at a temperature of about 150 to 400 degrees C.