Spin-torque oscillator, a magnetic sensor and a magnetic recording system

• US 8,174,798 B2
• Filed: 09/08/2009
• Issued: 05/08/2012
• Est. Priority Date: 09/30/2008
• Status: Active Grant

• Current Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Original Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Inventors: Nagasawa, Tazumi, Kudo, Kiwamu, Mizushima, Koichi, Sato, Rie
• Primary Examiner(s): Evans, Jefferson
• Application Number:
  US12/555,272
• Publication Number:
  US 20100079919A1
• Time in Patent Office: 973 Days
• Field of Search: 360/313, 360/324.1, 360/324.11, 360/324.12, 360/324.2
• US Class Current: 360/313
• CPC Class Codes: B82Y 25/00 Nanomagnetism, e.g. magnetoimpedance, anisotropic magnetoresistance, giant magnetoresistance or tunneling magnetoresistance
• CPC Class Codes: G01R 33/093 using multilayer structures, e.g. giant magnetoresistance sensors thin magnetic films H01F10/00
• CPC Class Codes: G01R 33/098 comprising tunnel junctions, e.g. tunnel magnetoresistance sensors
• CPC Class Codes: G01R 33/1284 Spin resolved measurements; Influencing spins during measurements, e.g. in spintronics devices G01R33/093 takes precedence; semiconductor devices using spin polarized carriers H01L29/66984
• CPC Class Codes: G11B 2005/0002 Special dispositions or recording techniques
• CPC Class Codes: G11B 5/3903 using magnetic thin film layers or their effects, the films being part of integrated structures
• CPC Class Codes: H01F 10/3254 the spacer being semiconducting or insulating, e.g. for spin tunnel junction [STJ]
• CPC Class Codes: H01F 10/3277 by use of artificial ferrimagnets [AFI] only
• CPC Class Codes: H01F 10/329 Spin-exchange coupled multilayers wherein the magnetisation of the free layer is switched by a spin-polarised current, e.g. spin torque effect
• CPC Class Codes: H10N 50/10 Magnetoresistive devices

Abstract

In a spin-torque oscillator, a first ferromagnetic layer, a non-magnetic layer and a second ferromagnetic layer are stacked. A pair of electrodes perpendicularly applies a current onto each plane of the first ferromagnetic layer, the non-magnetic layer and the second ferromagnetic layer. The current induces a precession of a magnetization of at least one of the first ferromagnetic layer and the second ferromagnetic layer. The at least one of the first ferromagnetic layer and the second ferromagnetic layer is formed by an in-plane magnetization film having a uniaxial magnetic anisotropy. A magnetic field generator generates a magnetic field to control a direction of the magnetization so that a non-linearity frequency shift of the precession by the uniaxial magnetic anisotropy cancels a non-linearity frequency shift of the precession by a demagnetizing field on the in-plane magnetization film.

Claims

1. A spin-torque oscillator comprising:

a first ferromagnetic layer;

a non-magnetic layer stacked on the first ferromagnetic layer;

a second ferromagnetic layer stacked on the non-magnetic layer;

a pair of electrodes configured to perpendicularly apply a current onto each plane of the first ferromagnetic layer, the non-magnetic layer and the second ferromagnetic layer, the current inducing a precession of a magnetization of at least one of the first ferromagnetic layer and the second ferromagnetic layer, the at least one of the first ferromagnetic layer and the second ferromagnetic layer being formed by an in-plane magnetization film having a uniaxial magnetic anisotropy; and

a magnetic field generator configured to generate a magnetic field to control a direction of the magnetization so that a non-linearity frequency shift of the precession by the uniaxial magnetic anisotropy cancels a non-linearity frequency shift of the precession by a demagnetizing field on the in-plane magnetization film.

2. The spin-torque oscillator according to claim 1, wherein the magnetic field generator generates the magnetic field along a direction larger than 45°

from the uniaxial magnetic anisotropy on a plane of the at least one of the first ferromagnetic layer and the second ferromagnetic layer.

3. The spin-torque oscillator according to claim 1, wherein the magnetic field generator is a permanent magnet or a line to generate a magnetic field.

4. A magnetic sensor comprising:

the spin-torque oscillator described in claim 1; and

a detection circuit configured to detect change of an amplitude or an oscillation frequency of a high-frequency oscillation voltage induced by an external magnetic field, the high-frequency oscillation voltage being occurred at the spin-torque oscillator by the precession of the magnetization of at least one of the first ferromagnetic layer and the second ferromagnetic layer.

5. A magnetic recording system comprising:

a magnetic head having the magnetic sensor described in claim 4; and

a magnetic recording medium.