JP6614002B2 - Magnetic sensor, magnetic head, and magnetic recording apparatus - Google Patents

Description

  The present invention relates to a magnetic sensor, a magnetic head, and a magnetic recording apparatus.

  A magnetoresistive element is known as a magnetic sensor used in a thin film magnetic recording / reproducing head. In general, in a magnetoresistive element, a high output is obtained because a current flows between the magnetization fixed layer and the magnetization free layer. However, in the magnetic sensor using the magnetoresistive element, an unnecessary signal resulting from the movement of the domain wall due to the spin torque given by the current is obtained.

  On the other hand, there is known a spin accumulation (SA) magnetic sensor in which a magnetization free layer and a magnetization fixed layer are formed on the same horizontal plane (channel layer for accumulating spin) (for example, Patent Document 1, Patent) Reference 2).

  When a spin accumulation type magnetic sensor is used for a thin film magnetic recording / reproducing head, it is not necessary to pass a current through a magnetization free layer for sensing an external magnetic field such as a magnetic recording medium. That is, in the spin accumulation type magnetic sensor, it is possible to detect the magnetic state as the output voltage by using only the pure spin current. Therefore, an unnecessary signal that is observed by the magnetoresistive element is less likely to be observed by the spin accumulation type magnetic sensor.

  In the spin accumulation type magnetic sensor, the position where the magnetization fixed layer is installed is not limited. Therefore, the magnetization fixed layer can be installed at a position that is not easily affected by the external magnetic field. By suppressing the influence of an external magnetic field on the magnetization fixed layer, noise can be reduced and spatial resolution can be increased.

Japanese Patent No. 5338264 JP 2015-26741 A

  For example, Patent Document 1 describes a spin accumulation type magnetic sensor that reads a change in resistance value depending on the relative angle between the magnetization of a channel layer and the magnetization of a magnetization free layer with a voltmeter connected to the channel layer and the magnetization free layer. Has been.

  However, the voltmeter in the magnetic sensor described in Patent Document 1 is connected to the channel layer and the magnetization free layer at positions close to each other. Therefore, a portion serving as a reference for the potential difference (portion connected to the voltmeter in the channel layer) exists at a position affected by the external magnetic field. If the potential difference reference is affected by an external magnetic field, the spatial resolution cannot be sufficiently increased.

  For example, Patent Document 2 describes a spin accumulation type magnetic sensor having a three-terminal structure. It is described that the three-terminal structure can reduce the size of the magnetic sensor and the influence of an external magnetic field.

  However, in the magnetic sensor described in Patent Document 2, a path for detecting a pure spin current as a voltage and a path for injecting a spin into the channel layer are partially common. Therefore, the voltage drop in the spin injection path becomes the background of the output voltage of the pure spin current. Therefore, a sufficient background / output ratio cannot be obtained, and high spatial resolution cannot be exhibited.

  The present invention has been made in view of the above problems, and an object thereof is to provide a magnetic sensor with high spatial resolution.

  The present invention provides the following means in order to solve the above problems.

(1) A magnetic sensor according to one aspect of the present invention includes a channel layer, a magnetization free layer that is provided in a first portion of the channel layer, and detects an external magnetic field, and the first portion of the channel layer. A first magnetization fixed layer that is provided in a different second portion and injects spins into the channel layer; a current source that supplies a current for injecting spin current into the channel layer to the first magnetization fixed layer; A voltage is measured between a reference electrode provided on a third portion located on the opposite side of the first portion across the second portion of the channel layer, and the magnetization free layer and the reference electrode. A voltmeter.

(2) In the magnetic sensor according to (1), the current is configured to flow in a direction intersecting the extending surface of the channel layer in the channel layer, and the channel layer is equipotential. But you can.

(3) In the magnetic sensor according to any one of (1) and (2), the channel layer is provided on a surface opposite to the surface on which the first magnetization fixed layer is formed, and the first magnetization fixed A second magnetization fixed layer that injects spins in the same direction as spins injected from the layer into the channel layer may be further provided.

(4) In the magnetic sensor according to (3), at least a part of the first magnetization fixed layer and the second magnetization fixed layer may be provided at a position overlapping in the extending direction of the channel layer. .

(5) In the magnetic sensor according to (4), the current source is electrically connected to the first magnetization fixed layer and the second magnetization fixed layer, and the first magnetization fixed layer and the second magnetization are A configuration in which a current flows in the stacking direction of the fixed layer may be used.

(6) The magnetic sensor according to any one of (1) to (5) may further include a barrier layer between the first magnetization fixed layer and the channel layer.

(7) In the magnetic sensor according to any one of (3) to (6), the barrier layer may be further provided between the second magnetization fixed layer and the channel layer.

(8) In the magnetic sensor according to any one of the above (3) to (7), the reference electrode has a spin diffusion length of the channel layer from the first magnetization fixed layer and the second magnetization fixed layer. It may be in a position farther away.

(9) In the magnetic sensor according to any one of (3) to (8), the magnetization free layer includes spin diffusion of the first magnetization fixed layer or the second magnetization fixed layer and the channel layer. It may be in a position closer than the length.

(10) In the magnetic sensor according to any one of the above (3) to (9), the first magnetization fixed layer and the second magnetization fixed layer are respectively formed on a surface opposite to the channel layer. A configuration in which a magnetic layer and a ferromagnetic layer are sequentially provided, and the magnetization directions of the first magnetization fixed layer and the second magnetization fixed layer are fixed by the laminated ferromagnetic layers, respectively. But you can.

(11) In the magnetic sensor according to any one of (1) to (10), at least a part of the magnetization free layer may be magnetically shielded.

(12) A magnetic head according to an aspect of the present invention includes the magnetic sensor according to any one of (1) to (11).

(13) A magnetic recording apparatus according to one aspect of the present invention is a magnetic recording medium for recording data by magnetization, and the above-mentioned (12), wherein the magnetization free layer is disposed facing a recording layer of the magnetic recording medium. And a magnetic head described in 1. above.

  According to the present invention, a magnetic sensor with high spatial resolution can be provided.

1 is a schematic cross-sectional view schematically showing a magnetic recording apparatus according to a first embodiment of the present invention. It is the cross-sectional schematic diagram which showed typically the detection part of the magnetic-recording apparatus concerning 1st Embodiment of this invention. It is a cross-sectional schematic diagram for demonstrating operation | movement of the magnetic-recording apparatus concerning 1st Embodiment of this invention. It is the cross-sectional schematic diagram which showed typically the magnetic-recording apparatus concerning a comparative example. It is the cross-sectional schematic diagram which showed typically the magnetic-recording apparatus concerning 2nd Embodiment of this invention. It is the cross-sectional schematic diagram which showed typically the magnetic-recording apparatus concerning 3rd Embodiment of this invention. It is the cross-sectional schematic diagram which showed typically the magnetic-recording apparatus concerning 4th Embodiment of this invention.

  Hereinafter, the present invention will be described in detail with appropriate reference to the drawings. In the drawings used in the following description, in order to make the characteristics of the present invention easier to understand, there are cases where the characteristic parts are enlarged for the sake of convenience, and the dimensional ratios of the respective components are different from actual ones. is there. The materials, dimensions, and the like exemplified in the following description are merely examples, and the present invention is not limited to these, and can be implemented with appropriate modifications within the scope of the effects of the present invention.

“First Embodiment”
FIG. 1 is a schematic cross-sectional view schematically showing the magnetic recording apparatus according to the first embodiment of the present invention. The magnetic recording apparatus according to the first embodiment includes a magnetic head 200 and a magnetic recording medium W.

  Here, the direction is defined as shown in FIG. A direction in which the magnetic recording medium W extends is defined as an x direction, a direction perpendicular to the x direction is defined as a y direction, and the xy plane is parallel to the main surface of the magnetic recording medium W. A direction connecting the magnetic recording medium W and the magnetic head 200 and perpendicular to the xy plane is defined as a z direction.

  The magnetic recording medium W records magnetic information as the direction of magnetization. The magnetic recording medium W has a recording layer W1 and a backing layer W2. The recording layer W1 is a portion for performing magnetic recording, and the backing layer W2 is a magnetic path (flux path) for returning the magnetic flux for writing from the magnetic head 200 to the magnetic head 200 again. The backing layer W2 enables the perpendicular recording of the recording layer W1.

  The magnetic head 200 records and reads magnetic information on the magnetic recording medium W. The magnetic head 200 has an air bearing surface (medium facing surface) S opposed to the magnetic recording medium W, and flies at a position away from the magnetic recording medium W by a certain distance in the z direction. In FIG. 1, the magnetic head 200 moves relative to the magnetic recording medium W in the y direction.

The magnetic head 200 includes a magnetic recording unit 110 and a magnetic sensor 100.
The magnetic recording unit 110 applies a magnetic field to the recording layer W1 of the magnetic recording medium W, and determines the magnetization direction of the recording layer W1. That is, the magnetic recording unit 110 performs magnetic recording on the magnetic recording medium W.
The magnetic sensor 100 reads the information on the magnetization of the recording layer W1 written by the magnetic recording unit 110.

<Magnetic recording part>
The magnetic recording unit 110 includes a main magnetic pole 111, a contact unit 112, a return yoke 113, and a coil 114. The main magnetic pole 111 is provided on the return yoke 113 with the contact portion 112 interposed therebetween. A coil 114 is disposed around the contact portion 112 so as to surround the contact portion 112.

  When a write current is passed through the coil 114, a magnetic flux is emitted from the lower end of the main magnetic pole 111 in the z direction. The emitted magnetic flux passes through the recording layer W1 of the magnetic recording medium W and returns to the magnetic head 200 side along the magnetic path of the backing layer W2. The magnetic flux returned to the magnetic head 200 side is collected by the return yoke 113. When the magnetic flux passes through the recording layer W1, the direction of magnetization of the recording layer W1 is determined, and a write operation is performed.

<Magnetic sensor>
The magnetic sensor 100 is a spin accumulation type magnetic sensor as shown in FIG.
The magnetic sensor 100 includes a channel layer 10, a detection unit 20 that detects an external magnetic field, a first spin injection unit 30 that injects spins into the channel layer 10, a reference electrode 40 that serves as a potential reference, and a reference electrode 40. A voltmeter 50 for measuring a potential difference. Further, in FIG. 1, a current source 60 for supplying a current to the first spin injection unit 30 is provided.

(Channel layer)
The channel layer 10 is a layer that accumulates the spins injected from the first spin injection unit 30 and is a flow path of a pure spin current due to the injected spins. The channel layer 10 extends from the air bearing surface S of the magnetic head 200 in the z direction.

The channel layer 10 is preferably made of a material having a long spin diffusion length and a relatively low conductivity. The channel layer 10 is preferably made of a non-ferromagnetic material.
For example, as the material used for the channel layer 10, a material containing one or more elements selected from the group consisting of B, C, Mg, Ag, Al, Cu, and Zn can be used. Cu and Al have a long spin diffusion length and are particularly preferable among these material types.

  Further, as a material used for the channel layer 10, a semiconductor compound such as Si, ZnO, or GaAs can be used. These semiconductor compounds have a longer spin diffusion length than the above materials and a relatively low conductivity. Therefore, it is more suitable as a spin accumulation layer that transmits only pure spin current. In addition, the potential output can be increased compared to the case of using a metal or alloy.

(Detection unit)
The detection unit 20 is a part that reads information recorded on the recording layer W1 of the magnetic recording medium W. The detection unit 20 is provided in a first portion that is an end of the channel layer 10 on the air bearing surface S side of the magnetic head 200.

  FIG. 2 is a schematic cross-sectional view of the detection unit cut along the A-A ′ plane of FIG. 1. That is, FIG. 2 corresponds to a view of the detection unit 20 viewed from the air bearing surface S side.

  As shown in FIGS. 1 and 2, the detection unit 20 includes a magnetization free layer 21, a first insulating layer 22, a second insulating layer 23, a first magnetic shield 24, a second magnetic shield 25, and a permanent magnet. And a magnet 26.

  The magnetization free layer 21 is provided on one surface of the first portion of the channel layer 10. The first insulating layer 22 is provided on the side surfaces of the channel layer 10 and the magnetization free layer 21 and covers the magnetization free layer 21 and the channel layer 10. The second insulating layer 23 is provided on the surface of the channel layer 10 opposite to the magnetization free layer 21 and covers the channel layer 10. The first magnetic shield 24 and the second magnetic shield 25 are provided at positions sandwiching the magnetization free layer 21 via the first insulating layer 22 and the second insulating layer 23. The permanent magnets 26 are disposed on both sides of the magnetization free layer 21 in the x direction via the first insulating layer 22.

  The magnetization free layer 21 is a part that detects an external magnetic field to be detected. One surface of the magnetization free layer 21 is exposed to the air bearing surface S. Although the specific operation will be described later, the direction of magnetization recorded on the recording layer W1 of the magnetic recording medium W is detected sharply by making the air bearing surface S where the magnetization free layer 21 is exposed face the magnetic recording medium W. To do.

  The material used for the magnetization free layer 21 includes a ferromagnetic material, and a soft magnetic material is particularly preferable. For example, the material used for the magnetization free layer 21 can be a metal or alloy containing one or more elements selected from the group consisting of Cr, Mn, Co, Fe, and Ni. More specifically, for example, CoFeB, NiFe or the like can be used.

The first insulating layer 22 and the second insulating layer 23 are layers for preventing the pure spin current in the channel layer 10 from flowing out to a portion other than the magnetization free layer 21. Specifically, it is a layer that prevents the first magnetic shield 24, the second magnetic shield 25, and the permanent magnet 26 from directly contacting the channel layer 10. For the first insulating layer 22 and the second insulating layer 23, for example, SiO ₂ or the like can be used.

  The first magnetic shield 24 and the second magnetic shield 25 are layers that prevent unnecessary magnetic fields from entering the magnetization free layer 21. When an unnecessary magnetic field is prevented from entering the magnetization free layer 21, noise when the magnetization free layer 21 reads the magnetic information of the recording layer W1 of the magnetic recording medium W is reduced. That is, the spatial resolution of the magnetization free layer 21 is increased, and the detection sensitivity of necessary magnetic information is increased.

  In FIG. 2, the first magnetic shield 24 and the second magnetic shield 25 are arranged so as to sandwich the magnetization free layer 21. However, a magnetic shield may be provided so as to cover the magnetization free layer 21.

  As a material used for the first magnetic shield 24 and the second magnetic shield 25, a known material having a high magnetic shielding property can be used. For example, a soft magnetic material such as an alloy containing Ni and Fe, Sendust, an alloy containing FeCo, an alloy containing Fe, Co, and Ni can be used.

  The permanent magnet 26 stabilizes (uniaxially) the magnetic domain structure of the magnetization free layer 21. The leakage magnetic flux from the permanent magnet 26 applies a bias magnetic field to the magnetization free layer 21. This bias magnetic field stabilizes the magnetic domain structure of the magnetization free layer 21. By stabilizing the magnetic domain structure, Barkhausen noise caused by the movement of the domain wall can be suppressed.

(First spin injection part)
The first spin injection part 30 is a part for injecting spin into the channel layer 10 as described above. The first spin injection section 30 is stacked in the y direction on a second portion different from the first portion of the channel layer 10.

  A distance L1 between the first spin injection unit 30 and the detection unit 20 is equal to or shorter than the spin diffusion length of the channel layer 10. Here, the distance between the first spin injection unit 30 and the detection unit 20 is detected in the z direction of the magnetization free layer 21 in the z direction of the end of the first spin injection unit 30 and the first magnetization fixed layer 31. It is the distance from the end on the part 20 side. The spin diffusion length is a constant specific to the substance and is a distance at which the magnitude of the spin current is 1 / e. The magnitude of the spin current decays exponentially according to exp (−d / λ) depending on the ratio of the distance d and the spin diffusion length λ. The spin diffusion length of a material can be estimated by various methods. For example, a non-local method, a method using the spin pumping effect, a method using the Hanle effect, and the like are known.

  The first spin injection unit 30 includes a first magnetization fixed layer 31, a first magnetization coupling layer (nonmagnetic layer) 32, a first magnetization opposing layer (ferromagnetic layer) 33, and a first antiferromagnetic layer 34. And a first buffer layer 35. The first spin injection part 30 has a so-called synthetic pind structure.

  The first magnetization fixed layer 31 is provided on one surface of the second portion that is away from the air bearing surface S in the z direction from the first portion of the channel layer 10. In FIG. 1, the surface on which the first magnetization fixed layer 31 is provided in the channel layer 10 and the surface on which the magnetization free layer 21 is provided are the same, but may be different surfaces. A first magnetization coupling layer 32, a first magnetization facing layer 33, a first antiferromagnetic layer 34, and a first buffer layer 35 are sequentially stacked on the surface of the first magnetization fixed layer 31 opposite to the channel layer 10. Yes.

  The first magnetization fixed layer 31 is a layer for injecting spin into the channel layer 10. The magnetization direction of the first magnetization fixed layer 31 is fixed in one direction.

  The first magnetization facing layer 33 is provided to face the first magnetization facing layer 33 with the first magnetization coupling layer 32 interposed therebetween. The first magnetization facing layer 33 has magnetization antiparallel to the first magnetization fixed layer 31. The magnetization of the first magnetization fixed layer 31 is stabilized by the first magnetization facing layer 33. In FIG. 1, the magnetization direction of the first magnetization fixed layer 31 is the −z direction, and the magnetization direction of the first magnetization counter layer 33 is the + z direction.

  The magnetization directions of the first magnetization fixed layer 31 and the first magnetization counter layer 33 are controlled by the thickness of the first magnetization coupling layer 32. When the thickness of the first magnetization coupling layer 32 changes, the magnetization directions of the first magnetization fixed layer 31 and the first magnetization opposing layer 33 become parallel or antiparallel due to the RKKY interaction.

For the first magnetization fixed layer 31 and the first magnetization opposing layer 33, a ferromagnetic metal material having a high spin polarizability can be used. For example, a metal or alloy containing one or more elements selected from the group consisting of Cr, Mn, Co, Fe, and Ni can be used. In addition to these elements, a metal or alloy containing one or more elements selected from the group consisting of B, C, and N can be used. For example, CoFe, CoFeB, or the like can be used.
A material such as Ru can be used for the first magnetic coupling layer 32.

  The first antiferromagnetic layer 34 is a layer for further enhancing the magnetization fixed function of the first magnetization fixed layer 31. The first antiferromagnetic layer 34 is in contact with the first magnetization facing layer 33 and has a magnetization antiparallel to the magnetization direction of the first magnetization facing layer 33. For example, as shown in FIG. 1, when the first antiferromagnetic layer 34 and the first magnetization facing layer 33 are in contact with each other, the magnetization direction of the first magnetization facing layer 33 is fixed in the + z direction, and the first magnetization facing The magnetization direction of the first magnetization fixed layer 31 facing the layer 33 is fixed in the −z direction. Since the magnetization directions of the first antiferromagnetic layer 34, the first magnetization facing layer 33, and the first magnetization fixed layer 31 are sequentially antiparallel to each other, the magnetization direction of the first magnetization fixed layer 31 is more strongly fixed. Is done.

  For the first antiferromagnetic layer 34, an alloy or the like exhibiting antiferromagnetism can be used. For example, an alloy with one or more metals selected from the group consisting of Mn, Pt, Ir, and Fe can be used. Specifically, IrMn, PtMn, or the like can be used.

  The first buffer layer 35 is a layer that improves crystal orientation and magnetic stability. For the first buffer layer 35, for example, a metal material such as Ru or Ta can be used. In the absence of the first antiferromagnetic layer 34, the first buffer layer 35 is in contact with the first magnetization facing layer 33.

  A first upper electrode 36 and a first lower electrode 38 are provided at both ends of the first spin injection part 30 in the y direction. The first upper electrode 36 and the first lower electrode 38 function as electrodes for passing a current to the first spin injection unit 30, and at least the first upper electrode 36 prevents an external magnetic field from entering the first spin injection unit 30. It also functions.

The first upper electrode 36 and the first lower electrode 38 can be made of the same material as the first magnetic shield 24 and the second magnetic shield 25 described above. In addition to these materials, nonmagnetic metals can be used. In consideration of spin conduction, the first lower electrode 38 is preferably a nonmagnetic metal. On the other hand, since the first upper electrode 36 is disposed outside the first magnetization fixed layer 31, it is preferable to have a magnetic shielding effect.
A first tunnel layer 37 is provided between the first lower electrode 38 and the channel layer 10 to prevent the pure spin current in the channel layer 10 from flowing out to a portion other than the magnetization free layer 21. The first tunnel layer 37 may be connected to the second insulating layer 23 to form a single layer.

  The case where the magnetization of the first magnetization fixed layer 31 is fixed by the first magnetization facing layer 33 has been described above. As another magnetization fixing method, a method of fixing magnetization by the shape anisotropy of the first magnetization fixed layer 31 or a method of fixing magnetization by an external magnetic field at the time of forming the first magnetization fixed layer 31 may be used. It is preferable that the magnetization is fixed by at least one of these magnetization fixing methods. By fixing magnetization by these methods, the magnetization direction of the first magnetization fixed layer 31 becomes difficult to react to an external magnetic field.

  Further, when adopting a method of fixing the magnetization by giving the first magnetization fixed layer 31 shape anisotropy, the first antiferromagnetic layer 34 can be omitted. For example, the first magnetization fixed layer 31 may be formed in a rectangular shape whose major axis is the x direction when viewed from the y direction.

(Reference electrode)
The reference electrode 40 is a portion that becomes a reference potential of a potential difference measured by a voltmeter 50 described later.
The reference electrode 40 is provided in a third portion located on the opposite side of the first portion across the second portion of the channel layer 10. That is, the reference electrode 40 and the detection unit 20 sandwich the first spin injection unit 30 in the z direction.

  The distance L2 between the reference electrode 40 and the first spin injection part 30 is preferably not less than the spin diffusion length of the channel layer 10. This is because, with this configuration, it is possible to suppress spin absorption by the reference electrode 40 and a decrease in output. Here, the distance L2 between the reference electrode 40 and the first spin injection part 30 is the end of the first magnetization fixed layer 31 on the reference electrode 40 side in the z direction and the first spin injection in the z direction of the reference electrode 40. This is the distance from the end on the part 30 side.

  The material used for the reference electrode 40 is not particularly limited, but it is preferable to use a nonmagnetic metal material. By being non-magnetic, it is possible to avoid the reference electrode 40 from being affected by a magnetic field.

(Voltmeter, current source)
As the voltmeter 50, a known voltmeter can be used. In FIG. 1, the voltmeter 50 has one end side electrically connected to the magnetization free layer 21 via the first magnetic shield 24 of the detection unit 20, and the other end side connected to the reference electrode 40. That is, the voltmeter 50 measures the potential difference of the magnetization free layer 21 with respect to the reference electrode 40. The voltmeter 50 includes a voltage source for measuring a potential difference.

  A known current source can be used as the current source 60. In FIG. 1, a current source 60 is connected at one end to a first upper electrode 36 connected to the first spin injection part 30 and connected at the other end to a first lower electrode 38 connected to the first spin injection part 30. Has been. That is, the current source 60 allows a current to flow in the stacking direction (y direction) of the first spin injection unit 30.

(Operation of magnetic sensor)
The operation of the magnetic sensor 100 will be described. FIG. 3 is a schematic cross-sectional view for explaining the operation of the magnetic recording apparatus according to the first embodiment of the present invention.

  The magnetic sensor 100 flies with the recording layer W1 of the magnetic recording medium W and the air bearing surface S facing each other. At this time, the magnetization direction of the magnetization free layer 21 exposed on the air bearing surface S of the magnetic sensor 100 is affected by the magnetization recorded in the recording layer W 1 of the magnetic recording medium W facing the magnetization free layer 21. For example, in FIG. 3, the magnetization direction of the magnetization free layer 21 is directed to the + z direction due to the influence of the magnetization directed to the + z direction of the recording layer W1.

  On the other hand, when the detection current I is applied from the current source 60 to the first spin injection unit 30, spins are injected from the first magnetization fixed layer 31 of the first spin injection unit 30 into the channel layer 10. The direction of spins injected at this time is the same as the direction of magnetization in the first magnetization fixed layer 31 and is the −z direction.

When spin is injected into the channel layer 10, a pure spin current flows in the channel layer 10. A pure spin current is a spin current with no current. Specifically, the electron flow of the upward spin S ⁺ is defined as J _↑ , the electron flow of the downward spin S ⁻ as J _↓ , and the spin current as J _S , defined as J _S = J _↑ −J _↓. . In FIG. 3, the pure spin current flows in the + z direction and the −z direction, respectively, with respect to the first spin injection part 30. Here, J _S is an electron flow having a polarizability of 100%.

  As described above, the distance L1 between the first spin injection unit 30 and the detection unit 20 is less than the spin diffusion length, and the distance L2 between the first spin injection unit 30 and the reference electrode 40 is more than the spin diffusion length. Therefore, the spin injected from the first spin injection unit 30 hardly reaches the reference electrode 40 but reaches the magnetization free layer 21. As a result, spin diffused as a pure spin current is accumulated in the channel layer 10 in the vicinity of the magnetization free layer 21. At this time, the direction of spin accumulated in the channel layer 10 in the vicinity of the magnetization free layer 21 is the same as the direction of magnetization of the first magnetization fixed layer 31. Therefore, the direction of magnetization of the magnetization free layer 21 and the direction of spin accumulated in the channel layer 10 near the magnetization free layer 21 are antiparallel.

  Here, the magnetization direction of the magnetization free layer 21 changes as the magnetization direction of the recording layer W1 facing the magnetization free layer 21 changes. Therefore, the relative angle between the magnetization direction of the magnetization free layer 21 and the direction of the spin accumulated in the channel layer 10 in the vicinity of the magnetization free layer 21 changes according to the magnetization direction of the recording layer W1. It is known as a magnetoresistive effect that the resistance value changes depending on the relative angle between the magnetizations of each other. The resistance value is small when the magnetization directions are parallel to each other, and the resistance value is large when the magnetization directions are antiparallel. That is, by measuring the potential difference between the reference electrode 40 and the magnetization free layer 21, information on the magnetization of the recording layer W1 is read out as a change in resistance value.

  As described above, according to the magnetic sensor 100 of the present embodiment, information recorded on the magnetic recording medium W can be read as a resistance value change. Here, what is read out as a change in resistance value is a change in chemical potential of a pure spin current flowing through the channel layer 10 with respect to the magnetization free layer 21. Therefore, the reference potential is stabilized by providing the reference electrode 40 at a position not affected by the pure spin current. That is, the change in chemical potential of the pure spin current can be read without being affected by noise associated with the fluctuation of the reference potential. That is, the spatial resolution of the magnetic sensor 100 can be increased.

  Further, by separating the reference electrode 40 from the air bearing surface S facing the magnetic recording medium W, the magnetic field resolution of the magnetic head 200 can be reduced. In order to reduce the magnetic field resolution of the magnetic head 200, it is necessary to reduce the structure near the air bearing surface S of the magnetic head 200. Therefore, by providing the reference electrode 40 at a position away from the air bearing surface S, the magnetic head 200 can be reduced in magnetic field resolution. Further, in the vicinity of the air bearing surface S, it is necessary to provide a magnetic shield around the reference electrode 40 in order to avoid the influence of the external magnetic field and maintain high spatial resolution. On the other hand, by separating the reference electrode 40 from the air bearing surface S, this magnetic shield becomes unnecessary. That is, the amount of the structure other than the reference electrode is also reduced, and the magnetic field resolution can be further reduced.

  In the magnetic sensor 100 according to the first embodiment, the direction of the current passed by the current source 60 and the extending surface of the channel layer 10 intersect. In terms of structure, the stacking direction of the stacked body in the first spin injection unit 30 intersects the extending surface of the channel layer 10. That is, the detection current I supplied from the current source 60 flows in the stacking direction from the first upper electrode 36 toward the first lower electrode 38 and returns to the current source 60. As a result, a current for spin injection does not flow along the channel layer 10, and the channel layer 10 becomes equipotential. That is, the current for spin injection can be prevented from becoming noise, and the magnetic sensor 100 with high spatial resolution can be obtained.

  If only the viewpoint of increasing the distance between the magnetization free layer 21 and the reference electrode 40 is considered, the arrangement of FIG. 4 seems to be acceptable, but the configuration of FIG. 4 cannot increase the spatial resolution. FIG. 4 is a schematic cross-sectional view schematically showing a magnetic recording apparatus according to a comparative example.

  The magnetic sensor 100 ′ in the magnetic head 200 ′ according to the comparative example shown in FIG. 4 is related to the first example in that a reference electrode 40 is disposed between the detection unit 20 and the first spin injection unit 30. Different from the magnetic sensor 100. The magnetization free layer 21 and the reference electrode 40 are separated from each other by a spin diffusion length or more, and the influence of the magnetization free layer 21 can be sufficiently blocked. However, in the case of the magnetic sensor 100 ′ according to the comparative example, the distance L1 ′ between the first spin injection unit 30 and the detection unit 20 is increased, and spins can be sufficiently accumulated in the channel layer 10 in the vicinity of the magnetization free layer 21. Can not. Further, it is assumed that a part of the pure spin current flows to the voltmeter 50 side, so that a sufficient output cannot be obtained and a sufficient spatial resolution cannot be obtained.

“Second Embodiment”
FIG. 5 is a schematic cross-sectional view schematically showing a magnetic recording apparatus according to the second embodiment of the present invention. The magnetic head 201 constituting the magnetic recording apparatus according to the second embodiment is different from the magnetic head 200 according to the first embodiment in that the magnetic sensor 101 includes the second spin injection unit 70. In the following description, description of common parts is omitted. Moreover, in each drawing used for description, the same code | symbol shall be attached | subjected to the same component as FIGS. 1-4.

  The second spin injection part 70 is provided at a position overlapping the first spin injection part 30 in the z direction so as to face the first spin injection part 30 with the channel layer 10 interposed therebetween. The second spin injection unit 70 injects spins in the same direction as the spins injected from the first spin injection unit 30 into the channel layer 10.

  The second spin injection unit 70 includes a second magnetization fixed layer 71, a second magnetization coupling layer (nonmagnetic layer) 72, a second magnetization opposing layer (ferromagnetic layer) 73, and a second antiferromagnetic layer 74. And a second buffer layer 75. The second magnetization fixed layer 71 is provided on the opposite side of the surface of the channel layer 10 on which the first magnetization fixed layer 31 is provided. A second magnetization coupling layer 72, a second magnetization facing layer 73, a second antiferromagnetic layer 74, and a second buffer layer 75 are sequentially stacked on the surface of the second magnetization fixed layer 71 opposite to the channel layer 10. Yes.

  Each of the second magnetization fixed layer 71, the second magnetization coupling layer 72, the second magnetization facing layer 73, the second antiferromagnetic layer 74, and the second buffer layer 75 in the second spin injection part 70 is a first spin injection part. 30 corresponding to each of the first magnetization fixed layer 31, the first magnetization coupling layer 32, the first magnetization opposing layer 33, the first antiferromagnetic layer 34, and the first buffer layer 35, the same material can be used. . A second lower electrode 76 is provided on the opposite side of the second spin injection part 70 from the first spin injection part 30.

  The magnetization direction of the second magnetization fixed layer 71 is antiparallel to the magnetization direction of the first magnetization fixed layer 31. In FIG. 5, the magnetization direction of the first magnetization fixed layer 31 is the −z direction, and the magnetization direction of the second magnetization fixed layer 71 is the + z direction.

  The operation of the magnetic sensor 101 according to the second embodiment is almost the same as that of the magnetic sensor 100 according to the first embodiment, but spins are injected into the channel layer 10 from the first spin injection unit 30 and the second spin injection unit 70. Is different.

  The current source 60 is connected to the first upper electrode 36 stacked on the first spin injection unit 30 and the second lower electrode 76 stacked on the second spin injection unit 70. Therefore, the detection current I applied from the current source 60 flows in the stacking direction of the first spin injection unit 30 and the second spin injection unit 70. The process in which spins in the −z direction are injected from the first spin injection unit 30 is the same as in the first embodiment.

  On the other hand, some of the spins in the −z direction injected from the first spin injection unit 30 are also injected into the second magnetization fixed layer 71 through the channel layer 10. Here, the channel layer 10 and the second magnetization fixed layer 71 have different spin resistances. The spin resistance is an amount that quantitatively indicates the ease of spin current flow (difficulty of spin relaxation). Reflection (return) of spin current occurs at the interface of materials having different spin resistances.

  Further, when spin in the −z direction is injected into the second magnetization fixed layer 71 whose magnetization is oriented in the + z direction, the direction of magnetization of the second magnetization fixed layer 71 is opposite to that of the second magnetization fixed layer 71 due to the conductivity mismatch. Spins in the directions are injected into the channel layer 10. That is, spins magnetically polarized in the same direction are respectively injected from the first spin injection unit 30 and the second spin injection unit 70.

  According to this embodiment, the amount of spin accumulated in the vicinity of the magnetization free layer 21 is increased by injecting spins magnetically polarized in the same direction from the first spin injection unit 30 and the second spin injection unit 70, respectively. can do. Therefore, the potential output of the magnetic sensor can be increased, and the spatial resolution of the magnetic sensor can be increased.

  The direction of the detection current I is not limited to the direction from the first spin injection unit 30 to the second spin injection unit 70, and may be the opposite direction.

“Third Embodiment”
FIG. 6 is a schematic cross-sectional view schematically showing a magnetic recording apparatus according to the third embodiment of the present invention. The magnetic head 202 constituting the magnetic recording apparatus according to the third embodiment is different from the magnetic head 201 according to the second embodiment in that the magnetic sensor 102 has a barrier layer 80. In the following description, description of common parts is omitted. In the drawings used for the description, the same reference numerals are given to the same components as those in FIG.

  As described above, the reflection (return) of the pure spin current occurs at the interface between substances having different spin resistances. That is, when there is no barrier layer 80, part of the spins injected from the first magnetization fixed layer 31 of the first spin injection unit 30 into the channel layer 10 returns to the first magnetization fixed layer 31. Similarly, in the second spin injection unit 70, part of the spins injected from the second magnetization fixed layer 71 of the second spin injection unit 70 into the channel layer 10 returns to the second magnetization fixed layer 71.

  On the other hand, by providing the barrier layer 80, it is possible to suppress the injected spins from returning to the first magnetization fixed layer 31 and the second magnetization fixed layer 71. Since the barrier layer 80 has a high energy barrier, the spin at the time of injection receiving external force due to the detection current I can pass through, but the injected spin can pass through the first magnetization fixed layer 31 or the second magnetization fixed layer 71. Can't go back to As a result, spins can be efficiently injected, and the injected spins can be efficiently accumulated in the channel layer 10 in the vicinity of the magnetization free layer 21. That is, the potential output of the magnetic sensor can be increased, and the spatial resolution of the magnetic sensor can be increased.

  The barrier layer 80 causes electrical resistance. However, the barrier layer 80 is provided in a direction crossing the extending direction of the channel layer 10. That is, it does not affect the detection circuit connecting the reference electrode 40, the extending channel layer 10, the magnetization free layer 21, and the voltmeter 50, and does not cause noise.

  When the barrier layer 80 is included, the definitions of the distance L1 between the first spin injection unit 30 and the detection unit 20 and the distance L2 between the reference electrode 40 and the first spin injection unit 30 are different from the definitions in the first embodiment. .

  When the barrier layer 80 is included, the distance L1 between the first spin injection unit 30 and the detection unit 20 is the center of the first magnetization fixed layer 31 in the z direction in the first spin injection unit 30 and the magnetization free layer 21 in the detection unit 20. It means the distance from the center in the z direction. Further, the distance L2 between the first spin injection part 30 and the reference electrode 40 when the barrier layer 80 is provided is the z-direction center of the first magnetization fixed layer 31 and the z-direction center of the reference electrode 40 in the first spin injection part 30. Means distance.

“Fourth Embodiment”
FIG. 7 is a schematic cross-sectional view schematically showing a magnetic recording apparatus according to the fourth embodiment of the present invention. The magnetic head 203 constituting the magnetic recording apparatus according to the fourth embodiment is such that the first spin injection unit 30 and the second spin injection unit 70 are not located in the position overlapping in the y-axis direction. 202. In the following description, description of common parts is omitted. In the drawings used for the description, the same reference numerals are given to the same components as those in FIG.

  The magnetic sensor 103 in the magnetic head 203 is not in a position where the first spin injection unit 30 and the second spin injection unit 70 overlap in the z-axis direction. Therefore, a current source 60 that applies a detection current to the first spin injection unit 30 and a second current source 90 that applies a detection current to the second spin injection unit 70 are provided.

  The first tunnel layer 37 and the second tunnel layer 77 are provided so that the current source 60 and the second current source 90 are not in direct contact with the channel layer 10. In addition, a first lower electrode 38 and a second upper electrode 78 are provided on the outside of each.

  The magnetization directions of the first magnetization fixed layer 31 and the second magnetization fixed layer 71 are parallel to each other. Since the magnetization directions are parallel to each other, the directions of spins injected into the channel layer 10 are the same.

  As described above, according to the present embodiment, spins magnetically polarized in the same direction are injected from the first spin injection unit 30 and the second spin injection unit 70, respectively, and accumulated in the vicinity of the magnetization free layer 21. The amount of spin can be increased. Therefore, the potential output of the magnetic sensor can be increased, and the spatial resolution of the magnetic sensor can be increased.

DESCRIPTION OF SYMBOLS 10 ... Channel layer, 20 ... Detection part, 21 ... Magnetization free layer, 22 ... 1st insulating layer, 23 ... 2nd insulating layer, 24 ... 1st magnetic shield, 25 ... 2nd magnetic shield, 26 ... Permanent magnet, 30 ... 1st spin injection part, 31 ... 1st magnetization fixed layer, 32 ... 1st magnetization coupling layer, 33 ... 1st magnetization opposing layer, 34 ... 1st antiferromagnetic layer, 35 ... 1st buffer layer, 36 ... 1st DESCRIPTION OF SYMBOLS 1 Upper electrode, 37 ... 1st tunnel layer, 38 ... 1st lower electrode, 40 ... Reference electrode, 50 ... Voltmeter, 60 ... Current source, 70 ... 2nd spin injection part, 71 ... 2nd magnetization fixed layer, 72 ... 2nd magnetization coupling layer, 73 ... 2nd magnetization opposing layer, 74 ... 2nd antiferromagnetic layer, 75 ... 2nd buffer layer, 76 ... 2nd lower electrode, 77 ... 2nd tunnel layer, 78 ... 2nd upper part Electrode, 80 ... barrier layer, 90 ... second current source, 100, 100 ', 101, 102, 103 ... magnetic sensor, 1 DESCRIPTION OF SYMBOLS 0 ... Magnetic recording part, 111 ... Main magnetic pole, 112 ... Contact part, 113 ... Return yoke, 114 ... Coil, 200, 200 ', 201, 202, 203 ... Magnetic head, W ... Magnetic recording medium, W1 ... Recording layer, W2 ... backing layer, S ... air bearing surface

Claims (14)

A channel layer;
A magnetization free layer provided in a first portion of the channel layer and detecting an external magnetic field;
A first magnetization pinned layer provided in a second portion different from the first portion of the channel layer and injecting spin into the channel layer ;
Sandwiching the second portion of the prior SL channel layer, and a reference electrode provided in the third portion located on the opposite side of the first portion,
A lower electrode connected to a surface of the channel layer opposite to a surface with which the first magnetization fixed layer is in contact with the second layer;
A voltmeter for measuring a voltage between the magnetization free layer and the reference electrode;
A current source for passing a current between the first magnetization fixed layer and the lower electrode;
A magnetic sensor comprising: The magnetization free layer is exposed on the air bearing surface;
2. The magnetic sensor according to claim 1, wherein the reference electrode is located farther from the air bearing surface than the first magnetization fixed layer. The current is configured to flow in a direction intersecting the extending surface of the channel layer in the channel layer, a magnetic sensor according to claim 1 or 2 wherein the channel layer is an equipotential. Provided on the surface of the channel layer opposite to the surface on which the first magnetization fixed layer is formed, spins in the same direction as the spins injected from the first magnetization fixed layer are injected into the channel layer. The magnetic sensor according to any one of claims 1 to 3 , further comprising a second magnetization fixed layer. 5. The magnetic sensor according to claim 4 , wherein at least a part of the first magnetization fixed layer and the second magnetization fixed layer is provided at a position where the channel layer extends in the extending direction. Said current source, said first magnetization pinning layer and is connected to the second magnetization pinned layer and the electrically, according to claim 5, a current flows in the stacking direction of the first magnetization pinned layer and the second magnetization pinning layer Magnetic sensor. The magnetic sensor according to any one of claims 4 to 6 , further comprising a barrier layer between the second magnetization fixed layer and the channel layer. Said reference electrode, said from the first magnetization fixed layer and the second magnetization pinned layer, a magnetic sensor according to any one of claims 4-7 which is in position apart than the spin diffusion length of the channel layer. The magnetization free layer, said a first magnetization fixing layer or the second magnetization pinned layer, a magnetic sensor according to any one of claims 4-8 which is closer than the spin diffusion length of the channel layer. Each of the first magnetization fixed layer and the second magnetization fixed layer has a nonmagnetic layer and a ferromagnetic layer in order on the surface opposite to the channel layer,
The magnetic sensor according to any one of claims 4 to 9 , wherein the magnetization directions of the first magnetization fixed layer and the second magnetization fixed layer are respectively fixed by the ferromagnetic layers stacked on each other. . The magnetic sensor according to any one of claims 1 to 10, further comprising a barrier layer between the channel layer and the first magnetization pinning layer. The magnetic sensor according to any one of claims 1 to 11, at least part of the magnetization free layer is magnetically shielded. A magnetic head comprising a magnetic sensor according to any one of claims 1 to 12. A magnetic recording medium for recording data by magnetization;
A magnetic recording apparatus comprising: the magnetic head according to claim 13 , wherein the magnetic free layer is disposed so as to face the recording layer of the magnetic recording medium.

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