JP2008021882A - Apparatus and method for controlling magnetization state - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology for controlling magnetization state of a magnetic material. <P>SOLUTION: A small magnetic material and a superconductor are disposed closely to each other, and thereby a magnetic field generated from the small magnetic material is caused to enter the superconductor as a vortex magnetic field. Then, the vortex magnetic field is moved by flowing current to the superconductor, thus controlling magnetization state of the small magnetic material. The shape of the small magnetic material to be employed may include a thin line shape, a ring shape, a disk shape and the like. When the small magnetic material is of disk shape and structured to form multiple magnetic domains, the position of a magnetic wall is controlled by current supply. When the small magnetic material is of disk shape and structured to form a single magnetic domain, magnetization direction is controlled by current supply. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a technique for controlling the magnetization state of a magnetic material.

  A hard disk or an MRAM (magnetoresistance memory) is a memory using a minute magnetic material, and stores information according to the magnetization state (spin direction) of each minute magnetic material. In such a storage device, a magnetic field is generated by passing a current through a conducting wire arranged near the micromagnetic material, and the magnetization of the micromagnetic material is reversed by this magnetic field.

In recent years, for the purpose of reducing power consumption, a spin-injection magnetization reversal method for reversing the magnetization of a micromagnetic material by directly flowing a spin-polarized current into the micromagnetic material has been studied (Non-patent Document 1). ).
JA Katine, FJ Albert, RA Buhrman, EB Myers, DC Ralph, "Current-Driven Magnetization Reversal and Spin-Wave Excitations in Co / Cu / Co Pillars", Physical Review Letter Vol.84 No.14, The American Physical Society , pp. 3149-3152, 2000

  Along with the miniaturization of elements and the increase in processing speed, a method for controlling the magnetization state different from the conventional one is required. Therefore, an object of the present invention is to provide a novel technique capable of controlling the magnetization state of a magnetic material.

  In order to achieve the above object, in the present invention, the magnetization state of the magnetic material is controlled by the following means or processing. The magnetization state control device according to the present invention includes a magnetic body, a superconductor, and a magnetization state control means.

  The magnetic body in the present invention is a magnetic body miniaturized on a submicron scale, and takes a characteristic magnetization state corresponding to its shape. For example, depending on the shape and size of the magnetic material, it can have a single magnetic domain structure that is composed of a single magnetic domain and has a constant magnetization direction, and is also composed of two magnetic domains and has a magnetization direction at the boundary between the magnetic domains. It is also possible to take a magnetization state having a domain wall in which is changed. A magnetic field is generated from a magnetic material having such a magnetization state.

  The superconductor is disposed close to the magnetic body, and takes a state where a magnetic field generated from the magnetic body enters the inside as a vortex. That is, the superconductor in the present invention is a type 2 superconductor and takes a mixed state in which a superconducting phase and a normal conducting phase are mixed.

  The magnetization state control means supplies a current to the superconductor. By passing a current through the superconductor, Lorentz force acts on the vortex and the vortex moves. Here, since the magnetization state of the magnetic material and the vortex in the superconductor are magnetically coupled, the magnetization state of the magnetic material changes as the vortex moves. That is, the magnetization state control means can control the magnetization state of the magnetic material by supplying a current to the superconductor. Here, the control of the magnetization state means changing the position of the domain wall in the magnetic material or changing the magnetization direction of the magnetic material. Note that the magnetization state of the magnetic material can be controlled to a desired state by the direction and magnitude of the current to be supplied or the time for supplying the current.

  The magnetic body can take various shapes. For example, the magnetic body can be formed into a thin line shape. In a thin wire-shaped magnetic body, it is stable that the magnetization direction is the thin wire direction. A domain wall whose magnetization direction changes can be provided by providing a bent portion in a part of the fine-line-shaped magnetic body. In this case, a leakage magnetic field is generated from the domain wall, and the leakage magnetic field penetrates the superconductor as a vortex. Also, the magnetic material can be ring-shaped. In this case, there are two domain walls in the magnetic body, and leakage magnetic fields in opposite directions are generated, and the leakage magnetic field penetrates the superconductor as a vortex. In these cases, when the magnetization state control means supplies a current to the superconductor, the vortex moves by the Lorentz force, and the domain wall magnetically coupled to the vortex moves. In this way, the magnetization state of the magnetic material can be controlled.

  Also, the magnetic material can be disk-shaped. When the disk-shaped magnetic material is sufficiently small, it takes a single domain structure, and the magnetic field generated from the magnetic material penetrates the superconductor as a vortex. Then, when the magnetization state control means supplies a current to the superconductor, the vortex is moved by the Lorentz force, and the magnetization direction of the magnetic material magnetically coupled to the vortex is changed. In this way, the magnetization state of the magnetic material can be controlled.

  In this way, it is possible to control the magnetization state of the magnetic material by supplying a current to the superconductor that is arranged close to the magnetic material and the magnetic field generated from the magnetic material enters the inside as a vortex. . Further, since the superconductor is used, the magnetization state can be controlled with a smaller current than in the conventional method. Therefore, power consumption can be reduced.

  In addition, the shape (thin wire shape, ring shape, disk shape) and the magnetization state of the magnetic material described above are examples, and the magnetization state control device according to the present invention indicates the magnetization state of the magnetic material of any shape. Can be controlled. For example, the magnetization state control apparatus according to the present invention may control the magnetization state of a magnetic material having a shape other than those described above, or a thin wire-shaped magnetic material having a single magnetic domain structure or a disk-shaped magnetic material having a vortex structure. You may control the magnetization state of a body.

  In addition, this invention can also be grasped | ascertained as the magnetization state control method containing the said process. That is, in the magnetization state control method as one aspect of the present invention, a magnetic body and a superconductor are arranged so that a magnetic field generated from the magnetic body enters the superconductor as a vortex, and a current is supplied to the superconductor. By flowing, the vortex is moved to control the magnetization state of the magnetic material.

  According to the present invention, it is possible to control the magnetization state of the magnetic material.

  Exemplary embodiments of the present invention will be described in detail below with reference to the drawings.

(First embodiment)
The first embodiment will be described below with reference to FIGS.

<Configuration>
FIG. 1 is a schematic plan view of a magnetization state control device according to this embodiment, and FIG. 2 is a cross-sectional view taken along line AA in FIG. As shown in the drawing, in the magnetization state control apparatus according to the present embodiment, an insulator 3 and a minute magnetic body 1 are disposed on a superconductor 2. In addition, a pulse current can flow from the pulse generator 4 to the superconductor 2.

[Micro magnetic material]
When a magnetic material is miniaturized to a submicron scale, it takes a characteristic magnetization state according to its shape. In the present embodiment, a fine wire shape is adopted as the shape of the minute magnetic body 1. In the fine magnetic body 1 having a fine line shape, the magnetization is easily oriented in the direction along the fine line direction due to the shape magnetic anisotropy.

  When a magnetic field is applied in the direction of the fine line of a fine magnetic substance having a thin line shape and then the magnetic field is made zero, it is common to adopt a single domain structure in which the direction of magnetization is aligned in the direction of the fine line. The magnetic body 1 has a domain wall introduced by bending a part of the thin wire. As shown in FIGS. 1 and 2, since the magnetization direction of the minute magnetic body 1 in the present embodiment is opposed to the domain wall 1 a, a leakage magnetic field is generated from the domain wall 1 a. Since the minute magnetic body 1 is installed on the superconductor 2, the leakage magnetic field leaking from the domain wall 1a of the minute magnetic body 1 penetrates the superconductor 2 downward as shown in FIG.

  Although any magnetic material can be used as the material of the minute magnetic material 1, it is preferable to use a soft magnetic material that can ignore the magnetocrystalline anisotropy. As a specific example of the material used for the minute magnetic body 1, a NiFe alloy can be cited. The size of the minute magnetic body 1 is about 100 nm in line width and about several tens of nm in thickness.

[Superconductor]
The superconductor 2 is a type 2 superconductor. Since the superconductor 2 which is the second type superconductor is disposed close to the micromagnetic body 1, the magnetic flux of the leakage magnetic field leaking from the domain wall 1 a of the micromagnetic body 1 is quantized into the superconductor 2. Invade as. Around the quantized magnetic flux, the superconducting current circulates, and the magnetic flux that has entered is also called vortex.

The superconductor 2 is a second type superconductor in which vortex exists in this way, and Nb, Nb—Ti, Nb ₃ Sn, NbN or other Nb alloys are used as specific materials. be able to. The shape of the superconductor 2 may be any shape. The thickness of the superconductor 2 is about several tens of nm. In order to prevent the superconducting state from being broken by the proximity effect between the micromagnetic body 1 and the superconductor 2, an insulator 3 of about 10 nm to several tens of nm is sandwiched between the micromagnetic body 1 and the superconductor 2. Yes.

[Pulse generator]
The pulse generator 4 passes a direct current through the superconductor 2. The pulse generator 4 can control the magnitude of the supplied current, the pulse width, and the like. The pulse generator 4 can also control the direction of current supplied to the superconductor 2 (I → II or II → I in FIG. 1).

<Principle of magnetization state control>
As described above, by arranging the minute magnetic body 1 and the superconductor 2 close to each other, the magnetic flux leaking from the domain wall 1a of the minute magnetic body 1 penetrates the superconductor 2 downward as a vortex. When a direct current is supplied to the superconductor 2 by the pulse generator 4 in this state, Lorentz force acts on the vortex.

  As shown in FIG. 3A, when a current flows in the direction of I → II, a left Lorentz force acts on the vortex penetrating the superconductor 2 downward. Conversely, as shown in FIG. 3B, when a current is passed in the direction of II → I, a Lorentz force directed to the right acts on the vortex. The vortex is moved by this Lorentz force.

  Since the domain wall 1a in the minute magnetic body 1 and the vortex in the superconductor 2 are magnetically coupled, the domain wall 1a also moves left and right in response to the movement of the vortex. Even after the supply of current is stopped, the domain wall 1a maintains the moved position.

  Thus, as shown in FIGS. 3A and 3B, the moving direction of the domain wall 1a can be controlled by the direction of the current supplied to the superconductor 2. Further, the amount of movement of the domain wall 1a can also be controlled by controlling the magnitude of the current to be supplied and the time (pulse width) for supplying the current.

<Effect of embodiment>
As described above, when a magnetic field generated from the domain wall 1a of the minute magnetic body 1 flows into the superconductor 2 that has entered the inside as a vortex, the vortex is moved by the Lorentz force, and the domain wall 1a is also moved along with the movement of the vortex. To do. That is, according to the magnetization state control apparatus according to the present embodiment, the position of the domain wall of the minute magnetic body can be controlled.

  At this time, since the current is supplied to the superconductor 2, the magnetization state of the minute magnetic body 1 is controlled with less power consumption compared to the conventional method of changing the magnetization state by supplying an external magnetic field or a spin current. be able to.

(Second Embodiment)
Hereinafter, the second embodiment will be described with reference to FIGS. Since the second embodiment is basically the same as the first embodiment, only different parts will be mainly described.

  4 is a schematic plan view of the magnetization state control apparatus according to the present embodiment, and FIG. 5 is a cross-sectional view taken along the line BB in FIG. As shown in the drawing, in the present embodiment, a ring-shaped minute magnetic body is used as the minute magnetic body 21. Further, the superconductor 22 has a cross shape, and has a structure in which the pulse generator 24 can supply a pulse current in both the vertical and horizontal directions.

  The minute magnetic body 21 has a ring shape, a line width of about 100 nm, and a thickness of about several tens of nm. In the ring-shaped minute magnetic body 21, a magnetization state called an onion state having two domain walls of an HH domain wall 21a and a TT domain wall 21b as shown in FIG. 4 is a stable magnetization state. The HH domain wall is a domain wall (Head to Head Domain Wall) in which the heads of magnetization arrows face each other, and the TT domain wall is a domain wall (Tail to Tail Domain Wall) in which the tails of magnetization arrows are facing each other. ). As shown in FIG. 5, a downward magnetic field is generated in the HH domain wall 21a, and an upward magnetic field is generated in the TT domain wall 21b. Therefore, in the superconductor 22 arranged close to the minute magnetic body 21, the quantized magnetic flux penetrates downward in the HH domain wall 21a, and the quantized magnetic flux penetrates upward in the TT magnetic wall 21b.

  Next, a method for supplying a current from the pulse generator 24 to the superconductor 22 to control the magnetization state of the minute magnetic body 21 will be described. Here, the magnetization state control of the minute magnetic body 21 will be described with reference to an example in which a current is passed in the I → II direction (upward) in FIG.

  FIG. 6 is a diagram for explaining the force acting on the domain wall when a current is supplied to the superconductor 22 in the I → II direction. In the HH domain wall 21a, since the vortex penetrates the superconductor 22 downward, a current in the I → II direction causes a left-handed Lorentz force in the figure to move the vortex to the left. Then, the HH domain wall 21a magnetically coupled to the vortex also moves to the left along with this. In the TT domain wall 21b, since the vortex penetrates the superconductor 22 upward, the Lorentz force accompanying the current supply acts to the right and the vortex moves to the right. The TT domain wall 21b that is magnetically coupled to the vortex also moves to the right. That is, the domain wall pair consisting of the HH domain wall 21a and the TT domain wall 21b rotates counterclockwise by supplying a current in the I → II direction.

In the ring-shaped minute magnetic body 21, four magnetization states can be changed depending on the direction of the current supplied to the superconductor 22. FIG. 7 is a diagram for explaining the current supply direction to the superconductor 22 and the magnetization state of the micromagnetic material 21.

  As shown in FIG. 7, when the HH domain wall 21a is in the 12 o'clock direction, by supplying an upward (I → II) current, the domain wall pair rotates counterclockwise, and the HH domain wall 21a is 9 o'clock. Located in the direction of Conversely, when the HH domain wall 21a is in the 12 o'clock direction, by supplying current downward (II → I), the domain wall pair rotates clockwise, and the HH domain wall 21a is positioned in the 3 o'clock direction.

  When the HH domain wall 21a is positioned in the 3 o'clock direction and a current is supplied to the right (III → IV), the domain wall pair rotates counterclockwise and the HH domain wall 21a is positioned in the 12 o'clock direction. Conversely, when a current is supplied to the left (IV → III), the domain wall pair rotates clockwise, and the HH domain wall 21a is positioned in the 6 o'clock direction.

  When the HH domain wall 21a is positioned in the 6 o'clock direction and a current is supplied downward (II → I), the domain wall pair rotates counterclockwise and the HH domain wall 21a is positioned in the 3 o'clock direction. Conversely, when a current is supplied upward (I → II), the domain wall pair rotates clockwise, and the HH domain wall 21a is positioned in the 9 o'clock direction.

  When the HH domain wall 21a is positioned in the 9 o'clock direction and a current is supplied to the left (IV → III), the domain wall pair rotates counterclockwise and the HH domain wall 21a is positioned in the 6 o'clock direction. Conversely, when a current is supplied in the right direction (III → IV), the domain wall pair rotates clockwise, and the HH domain wall 21a is positioned in the 12 o'clock direction.

  Thus, by changing the direction of the current supplied to the superconductor 22, it is possible to control the magnetization state of the minute magnetic body 21 in four ways.

(Third embodiment)
Hereinafter, the third embodiment will be described with reference to FIGS. The third embodiment basically changes only the shape of the minute magnetic body in the second embodiment.

  FIG. 8 is a schematic plan view of the magnetization state control apparatus according to the present embodiment, and FIG. 9 is a CC cross-sectional view in FIG. As shown in the figure, in the present embodiment, a disk-shaped minute magnetic body is used as the minute magnetic body 31. Permalloy is used as the minute magnetic body 31 and has a diameter of about 100 nm and a thickness of about several tens of nm. The micro magnetic material 31 having a sufficiently small disk shape as described above has a single magnetic domain structure composed of one magnetic domain as shown in FIG. Then, as shown in FIG. 9, the upward and downward magnetic flux pairs penetrate the superconductor 22 due to the magnetic field leaking from the minute magnetic material.

  A method for controlling the magnetization direction of the disk-shaped minute magnetic body 31 by supplying a current from the pulse generator 24 to the superconductor 22 will be described. As shown in FIG. 10, when a current is supplied to the superconductor 22 in the same direction as the magnetization direction, Lorentz forces are applied in opposite directions to the vortex penetrating the superconductor downward and the vortex penetrating upward. Working, these vortexes move. As the vortex moves, the magnetization direction of the minute magnetic body 31 that is magnetically coupled to the vortex changes. In the example of FIG. 10, the direction of magnetization moves counterclockwise.

  In the present embodiment, similarly to the second embodiment, the four magnetization states can be changed according to the magnetization direction and the current supply direction. FIG. 11 is a diagram for explaining the current supply direction to the superconductor 22 and the magnetization state of the minute magnetic body 31.

1 is a schematic plan view of a magnetization state control device according to a first embodiment. It is sectional drawing of the magnetization state control apparatus which concerns on 1st Embodiment. It is a figure explaining the principle of the magnetization state control in 1st Embodiment. It is a schematic plan view of the magnetization state control apparatus which concerns on 2nd Embodiment. It is sectional drawing of the magnetization state control apparatus which concerns on 2nd Embodiment. It is a figure explaining the principle of the magnetization state control in 2nd Embodiment. It is a figure which shows the relationship between the supply direction of the electric current in 2nd Embodiment, and the transition of a magnetization state. It is a schematic plan view of the magnetization state control apparatus which concerns on 3rd Embodiment. It is sectional drawing of the magnetization state control apparatus which concerns on 3rd Embodiment. It is a figure explaining the principle of the magnetization state control in 3rd Embodiment. It is a figure which shows the relationship between the supply direction of the electric current in 3rd Embodiment, and the transition of a magnetization state.

Explanation of symbols

1,21,31 Micro magnetic material 2,22 Superconductor 3 Insulator 4,24 Pulse generator

Claims (5)

Magnetic material,
A superconductor disposed close to the magnetic body so that a magnetic field generated from the magnetic body enters the inside as a vortex,
A magnetization state control means for controlling the magnetization state of the magnetic body by moving the vortex by passing a current through the superconductor;
A magnetized state control device. The magnetic body has a thin wire shape and has a domain wall whose magnetization direction changes,
The magnetization state control apparatus according to claim 1, wherein the magnetization state control unit moves the position of the domain wall in the magnetic body by passing a current through the superconductor. The magnetic body has an annular shape and has two domain walls whose magnetization directions change,
The magnetization state control device according to claim 1, wherein the magnetization state control unit moves the positions of the two domain walls in the magnetic body by passing a current through the superconductor. The magnetic body is disk-shaped and consists of a single magnetic domain,
The magnetization state control device according to claim 1, wherein the magnetization state control unit changes a magnetization direction of the magnetic body by passing a current through the superconductor. A magnetic body and a superconductor are arranged so that a magnetic field generated from the magnetic body enters the superconductor as a vortex,
By passing a current through the superconductor, the vortex is moved to control the magnetization state of the magnetic body.
A magnetization state control method characterized by the above.

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