JP2007095765A - Multiple-value recording spin injection magnetization inverting element and device using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multiple-value recording element wherein an increase in resistance is suppressed and the allowable width of magnetization inversion current density is large, and to provide a magnetic recording device. <P>SOLUTION: The spin injection magnetization inverting element is provided with two or more nonmagnetic isolation layers and a ferromagnetic free layer on the same surface of a ferromagnetic fixed layer, or it is provided with two or more ferromagnetic free layers on the same surface of the nonmagnetic isolation layer formed on the ferromagnetic fixed layer. It is preferable to drive each of elements by one FET. The recording device is formed by connecting a plurality of spin injection magnetization inverting elements which are provided with two ferromagnetic free layers, respectively. A bit line is wired in one ferromagnetic free layer; a word line is wired in the other ferromagnetic free layer, and a writing word line is wired in the ferromagnetic fixed layer. When any two lines among the three lines are selected, the spin injection magnetization inverting element is 1 or less as conducting between the two lines. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a basic structural element constituting a magnetic memory and an apparatus using the same. More specifically, the present invention relates to an element and an apparatus constituting a magnetic random access memory capable of multi-value recording by controlling injection of electron spin.

Recently, giant magnetoresistive (GMR) effect elements composed of ferromagnetic layers / nonmagnetic metal layers / ferromagnetic layers or ferromagnetic spin tunnel junction (MTJ) elements composed of ferromagnetic layers / insulator layers / ferromagnetic layers have been developed. The application is expected as a novel magnetic field sensor and magnetic memory. These utilize the fact that the electrical resistance varies depending on the combination of the magnetization directions of the opposing ferromagnetic layers. Recording is performed by changing the combination of the magnetization directions by reversing the magnetization of one of the ferromagnetic layers.
As a method for causing magnetization reversal, a current magnetic field driving method was originally proposed. A metal conductor is provided in the vicinity of the ferromagnetic layer, a current is passed through the conductor to generate a magnetic field, and the direction and strength of the magnetic field are adjusted to reverse the magnetization of one of the ferromagnetic layers of the recording element. However, with this method, only one bit of information can be recorded / reproduced with one recording element, which is not sufficient for future demands for higher density. Furthermore, since a magnetic field is generated by an electric current, there is a problem that power consumption is large for writing information.

As a method for solving this problem, a proposal has been made to write information by direct injection of spin-polarized electrons instead of a current magnetic field, and currently attracting attention (see, for example, Non-Patent Document 1).
FIG. 6 shows a configuration example of a recording element 100 that records and reproduces binary information using spin injection (see, for example, Patent Document 1). A ferromagnetic pinned layer 103, a nonmagnetic separation layer 104, a ferromagnetic free layer 107, and a free layer electrode 109 are formed on the substrate 101 via the pinned layer electrode 102. The ferromagnetic pinned layer 103 is strongly magnetized by, for example, a method of increasing the film thickness, so that magnetization reversal due to an external magnetic field is difficult to occur. In addition, the ferromagnetic free layer is likely to undergo magnetization reversal by, for example, a method of thinning it. FIG. 6 shows an example in which the magnetization of the ferromagnetic pinned layer is directed leftward in the drawing. In the figure, the white arrow indicates the magnetization direction of each magnetic layer, and the layer indicated by the arrow in both directions is the magnetization direction. It indicates that the orientation can take both directions. The notation in the following figures is the same. In the following description, the direction of magnetization will be referred to as rightward and leftward in correspondence with the direction of the white arrow in the figure. Similarly, the direction of the electron spin is also referred to as rightward and leftward.

When electrons flow between the ferromagnetic free layer and the ferromagnetic fixed layer while the magnetization of the ferromagnetic fixed layer is fixed, the magnetization of the ferromagnetic free layer is reversed by the spin of the electrons. This is called spin injection magnetization reversal.
Considering the case where electrons flow from the fixed layer electrode to the free layer electrode, the distribution of electron spins in the fixed layer electrode is rightward and leftward, but in the ferromagnetic fixed layer, electron spin and magnetism are the same. Since the interaction with the metal atom spin (sd interaction) works and the ferromagnetic pinned layer is thick, the electron spin is aligned in the magnetization direction (leftward) of the ferromagnetic pinned layer. When the spin-polarized electrons are injected into the ferromagnetic free layer through the separation layer, the magnetization of the ferromagnetic free layer receives a torque in a direction parallel to the magnetization direction of the ferromagnetic fixed layer. It is understood that when the electron density to be injected is sufficiently increased, the ferromagnetic free layer undergoes magnetization reversal and transitions to a state parallel to the magnetization of the ferromagnetic fixed layer. Hereinafter, the critical current density at which the magnetization direction of the ferromagnetic free layer is reversed is referred to as a magnetization reversal current density.

  On the other hand, when electrons are injected from the ferromagnetic free layer into the ferromagnetic pinned layer with the current direction reversed, electrons with a rightward spin that is opposite to the ferromagnetic pinned layer are electrons with a leftward spin. The potential barrier when injected into the ferromagnetic pinned layer is higher than. For this reason, electrons with rightward spin are reflected at the interface with the ferromagnetic pinned layer, and the reflected electrons give a rightward torque to the magnetization of the ferromagnetic free layer and attempt to align the magnetization to the right. As a result, the magnetization of the ferromagnetic free layer becomes antiparallel to the ferromagnetic pinned layer by flowing electrons having a magnetization reversal current density or higher. Therefore, in the spin-injection magnetization reversal element having this three-layer structure, the magnetization of the ferromagnetic fixed layer and the ferromagnetic free layer are made parallel or antiparallel by passing a current higher than the magnetization reversal current density and changing the direction of the current. It is possible. These two states are maintained below the magnetization reversal current density. In addition, since the electric resistance of the element is different between the two states, it can be used as a binary recording element by corresponding to “0” and “1”, respectively.

A large-capacity magnetic recording apparatus can be constructed by integrating a large number of binary recording elements. FIG. 8 shows an example of the configuration, in which a plurality of recording elements 100 are arranged in a matrix and connected by bit lines 121 and word lines 122, and each recording element 100 is connected to an FET (field effect transistor) or the like. The drive element 120 is used for selection or operation.
However, in the case of a binary recording element, since one driving element is required for binary information, the area occupied by the driving element and the power consumption increase as the recording capacity is increased to constitute a recording apparatus. It becomes an obstacle.
In order to overcome this obstacle, a method of performing multilevel recording is being sought. FIG. 7 is proposed in Patent Document 2 and performs multi-value recording by stacking a large number of binary recording elements. In terms of terms of the present application, the ferromagnetic first pinned layer 131, the first separation layer 141, the ferromagnetic first free layer 151, the second separation layer 142, the ferromagnetic second pinned layer 132, and the third separation layer 143. , A ferromagnetic second free layer 152, a fourth separation layer 144, and a ferromagnetic third fixed layer 133. Although it has a configuration in which the ferromagnetic free layer is sandwiched between ferromagnetic fixed layers, it is basically a stack of the elements shown in FIG. 6, and the magnetic properties of the ferromagnetic first free layer 151 and the ferromagnetic second free layer 152 are the same. By changing the material and film thickness, and changing the magnetization reversal current density of each layer, multi-value can be realized.
JP 2004-207707 A JP 2004-193595 A (paragraphs 0095-0096, FIG. 18) Katine, “Current-Driven Magnetic Reversal and Spin-Wave Excitation in Co / Cu / Co Pillars”, Physical Review. Letters (Physical Review Letters), USA, 2000, Vol. 84, No. 14, p. 3149-3152.

The above-described multi-value recording method assumes that a plurality of elements for performing binary recording are stacked. Accordingly, since it is necessary to dispose at least one ferromagnetic pinned layer for each ferromagnetic free layer that records magnetization reversal, as the number of multilevel recordings increases, the layers of the ferromagnetic pinned layer increase. The number increases. However, the ferromagnetic pinned layer is required to have a sufficient thickness in order to fix the magnetization and not easily fluctuate. As a result, when a plurality of ferromagnetic pinned layers are provided, the element resistance increases and the power consumption during operation increases.
In addition, since the number of ferromagnetic free layers is required as the number for setting the magnetization reversal current density, the variation width allowed for each magnetization reversal current density is limited, and the number of layers increases. The tolerance is reduced, and the difficulty in manufacturing the recording element is increased. Since the ferromagnetic free layer is preferably a thin layer in order to facilitate the reversal of magnetization, the difficulty in manufacturing increases in addition to the difficulty in forming a thin layer.

  The present invention has been made paying attention to such points, and an object of the present invention is to provide a recording element capable of multi-value recording by suppressing an increase in resistance. It is another object of the present invention to provide a recording element that enables multi-value recording without reducing the allowable width of the magnetization reversal current density. Furthermore, the present invention provides a magnetic recording apparatus in which an increase in the number of elements that drive the recording element is suppressed by a spin-injection magnetization reversal element capable of multilevel recording.

In order to achieve the above object, the present invention provides a spin-injection magnetization switching device including a ferromagnetic pinned layer, a nonmagnetic separation layer, and a ferromagnetic free layer in this order, wherein the separation layers are separated from each other. It is divided into regions and arranged on the same plane of the ferromagnetic pinned layer, and a ferromagnetic free layer is provided on each region of the separation layer.
Alternatively, in a spin-injection magnetization reversal element including a ferromagnetic pinned layer, a nonmagnetic separation layer, and a ferromagnetic free layer in this order, the ferromagnetic free layer is divided into two or more regions that are separated from each other. May be arranged on the same plane.
It is preferable to provide a free layer electrode on the main surface of the ferromagnetic free layer opposite to the separation layer side.
Moreover, it is preferable to provide a fixed layer electrode on the main surface of the ferromagnetic fixed layer opposite to the separation layer side.

Further, it is preferable that the number of the regions separated from each other is two.
The present invention is characterized in that in the recording apparatus, a plurality of the above-described spin-injection magnetization switching elements are connected.
It is preferable that one spin injection magnetization switching element is driven by one FET.
Further, in a recording apparatus in which a plurality of spin-injection magnetization reversal elements having two regions separated from each other are connected, a wiring for one of the ferromagnetic free layers is a bit line and a wiring for the other ferromagnetic free layer And the wiring to the ferromagnetic pinned layer as a write word line, and when any two of the bit line, the word line, and the write word line is selected, the spin that conducts between the two lines The injection magnetization reversal element is 1 or less.

  By configuring the spin-injection magnetization switching element as described above, multi-value recording can be performed while suppressing the number of ferromagnetic fixed layers having a high resistance value and suppressing an increase in resistance. Further, since the magnetization reversal operation of each ferromagnetic free layer can be controlled independently, it is not necessary to reduce the permissible width of the magnetization reversal current density, and therefore it is possible to provide a multi-value recording element that is easy to manufacture. . Furthermore, it is possible to provide a magnetic recording apparatus in which an increase in the number of elements that drive the recording element is suppressed by a spin-injection magnetization reversal element capable of multilevel recording.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view for explaining a configuration example of a recording element 20 of the present invention. A fixed layer electrode 2 and a ferromagnetic fixed layer 3 are formed on a nonmagnetic substrate 1. Are formed with a first separation layer 5 and a second separation layer 6, respectively. Further, a ferromagnetic first free layer 7 and a first free layer electrode 9 are formed in this order on the first separation layer 5, and the ferromagnetic second free layer 8 and the second free layer electrode 9 are formed on the second separation layer 6. Free layer electrodes 10 are formed in this order. Hereinafter, the ferromagnetic first free layer 7 and the ferromagnetic second free layer 8 together are also simply referred to as a ferromagnetic free layer, and the first free layer electrode 9 and the second free layer electrode 10 are both simply free. It is also referred to as a layer electrode, and both the first separation layer 5 and the second separation layer 6 are also simply referred to as a separation layer.
(Operating principle)
First, the operation principle of this element will be described.

  FIG. 2 is a schematic cross-sectional view for explaining the operation when writing to this element. FIG. 2a shows a case where the magnetization directions of the ferromagnetic pinned layer 3, the ferromagnetic first free layer 7, and the ferromagnetic second free layer 8 are all in the same direction. Show. The state in this state is set to “0”. The write operation is performed by flowing a current equal to or higher than the magnetization reversal current density from each free layer electrode to the fixed layer electrode. That is, electrons flow from the fixed layer electrode toward each free layer electrode. The electrons injected from the fixed layer electrode 2 into the ferromagnetic fixed layer 3 are spin-polarized in the direction of magnetization of the ferromagnetic fixed layer when moving through the ferromagnetic fixed layer 3. Electrons continue to be injected into each ferromagnetic free layer through each separation layer, and the density of electrons injected into each ferromagnetic free layer is higher than the density necessary for magnetization reversal. The magnetization is aligned in the same direction as the magnetization of the ferromagnetic pinned layer 3.

FIG. 2b shows an example in which the magnetization of one ferromagnetic free layer is reversed from the state of FIG. 2a. FIG. 2b shows an example of the state in which the magnetization of the ferromagnetic second free layer 8 is reversed. The write operation is performed by flowing a current equal to or higher than the magnetization reversal current density from the fixed layer electrode 2 toward the second free layer electrode 10. In this case, the spin polarization of electrons injected from the free layer electrode 10 into the ferromagnetic free layer 8 is slightly limited due to the fact that the ferromagnetic free layer 8 is a thin film. When injected, electrons having a spin opposite to that of the ferromagnetic fixed layer 3 are reflected toward the ferromagnetic free layer 8, and the magnetization of the ferromagnetic free layer 8 is opposite to the magnetization of the ferromagnetic fixed layer 3. Magnetization is reversed in the right direction. Assume that the state of FIG.
FIG. 2c shows a state in which both ferromagnetic free layers have undergone magnetization reversal, and the write operation is performed by flowing a current equal to or higher than the magnetization reversal current density from the fixed layer electrode 2 to each free layer electrode. The principle of magnetization reversal is the same as in the example of FIG. Assume that the state of FIG.

As described above, the magnetization state of the recording element 20 can be changed and held in three different states. In addition, it is possible to reverse the magnetization of each ferromagnetic free layer independently by passing a current between the fixed layer electrode 2 and each free layer electrode. Therefore, the magnetization reversal current density of each ferromagnetic free layer can be set independently. For example, it is possible to operate even if both magnetization reversal current densities are exactly the same, and there is a manufacturing margin when forming a recording element. Can be kept high.
Next, reading or reproduction of recorded information will be described. Reading is performed by flowing a current less than the magnetization reversal current density between the first free layer electrode 9 and the second free layer electrode 10 to determine the resistance value. When the separation layer is a nonmagnetic metal layer, the GMR effect is used, and when the separation layer is an insulating layer, the MTJ effect is used. Both effects use the fact that the resistance between the adjacent ferromagnetic layers across the separation layer varies depending on the magnetization direction of both, and the resistance is small when the magnetization directions of both are parallel, and the anti-parallel case Resistance increases. For example, when a current is passed from the first free layer electrode 9 to the second free layer electrode 10, the current is the ferromagnetic first free layer 7, the first separation layer 5, the ferromagnetic fixed layer 3, the second The path of the separation layer 6 and the ferromagnetic second free layer 8 is followed, and the flow between the adjacent ferromagnetic layers sandwiching the separation layer occurs twice. The states of FIGS. 2a to 2c have different resistance values because the combinations of adjacent magnetization directions are different. FIG. 3 is a diagram for explaining the relationship between the current and the voltage when a current is passed between the first free layer electrode 9 and the second free layer electrode 10, and each state is discriminated as shown in FIG. Is possible. In the case of the state “0” in FIG. 2 a, the magnetizations of the ferromagnetic layers are in the same direction and have the smallest resistance. In the case of the state “2” in FIG. 2c, the magnetization directions of the adjacent ferromagnetic layers are antiparallel to each other, and the resistance becomes the largest. In the case of the state “1” in FIG. 2b, the magnetization directions of the adjacent ferromagnetic layers are antiparallel at one place, and the resistance is intermediate.

Next, a method for writing and reading information when a large number of the elements are integrated will be described. FIG. 5 is a diagram for explaining an example of the configuration of a circuit in the case where this element is integrated to constitute a large-capacity magnetic recording apparatus. In this example, a plurality of recording elements 20 are arranged in an n × n square matrix. Show. Each recording element 20 is connected by a bit line 31, a word line 32, and a writing word line 33, and each recording element 20 is selected or operated using a driving element 30 such as an FET. In the figure, BL _k represents the k-th bit line, WL _k represents the k-th word line, and WWL _k represents the k-th write word line. Further, (i, j) represents the number of the recording element, and represents that the recording element is connected to the i-th bit line BL _i and the j-th word line WL _j . Connected to either the first free layer electrode 9 or the second free layer electrode 10. Hereinafter, for the sake of clarity, a case where the driving element 30 is connected to the first free layer electrode 9, that is, a case where wiring is made to the ferromagnetic first free layer 7 will be described as an example.

Bit line 31 is connected to second free layer electrode 10, and word line 32 is connected to first free layer electrode 9 via drive element 30. More specifically, the word line 32 is connected to a control unit of the drive element 30, for example, a gate in the case of an FET. The write word line 33 is connected to the fixed layer electrode 2 of the recording element 20. That is, the bit line 31 is wired to the ferromagnetic second free layer 8, the word line 32 is wired to the ferromagnetic first free layer 7, and the write word line 33 is wired to the ferromagnetic fixed layer 3.
By connecting in this way, the magnetization directions of the ferromagnetic first free layer 7 and the ferromagnetic second free layer 8 of any recording element can be reversed. When reversing the magnetization of the ferromagnetic first free layer 7, a word line and a write word line connected to the recording element to be written are selected, and a current equal to or higher than the magnetization reversal current density is passed between both lines. When the magnetization is reversed in the same direction as the ferromagnetic pinned layer 3, a current is passed in the direction from the word line toward the write word line. When the magnetization is reversed in the direction opposite to that of the ferromagnetic pinned layer 3, a current may be passed in the direction from the write word line toward the word line. When reversing the magnetization of the ferromagnetic second free layer 8, a bit line and a write word line connected to the recording element to be written are selected, and a current equal to or higher than the magnetization reversal current density is passed between both lines. When the magnetization is reversed in the same direction as the ferromagnetic fixed layer 3, a current is passed in the direction from the bit line to the write word line. When the magnetization is reversed in the direction opposite to that of the ferromagnetic pinned layer 3, a current may be passed in the direction from the write word line toward the bit line.

When reading the state of the recording element, a word line and a bit line connected to the recording element to be read out are selected, and the resistance is determined using a current less than the magnetization reversal current density.
Note that, when any two of the word lines WL _i , bit lines BL _j , and write word lines WWL _k are selected, the number of recording elements that operate or conduct with the same combination of wirings is one or less. It is necessary. In other words, any combination of any two of the numbers i, j, k, specifically, the same number in any of (i, j), (i, k) or (j, k) It is necessary to connect so that the number of recording elements connected to the combination is 1 or less. This is because, for example, when there are two recording elements connected to both BL ₁ and WWL ₁ , rewriting of the ferromagnetic second free layer 8 is performed simultaneously by the two recording elements. . In the example of FIG. 5, there is a combination that is not wired to the recording element, such as a combination of WL ₁ and WWL _n .

For this purpose, the write word line has no more than one recording element from the i-th row and no more than one recording element from the j-th column with respect to the matrix arrangement (i, j) of the recording elements. Select and connect.
The write word line WWL _k and the recording element 20 are connected as follows, for example.
1) When k is 1 to n Connect to the recording element group with the number (α, α + k−1).
However, 1 ≦ α ≦ n−k + 1
2) When k is n + 1 to 2n−1 Connect to the recording element group with the number (β, β−k + n).
However, k−n + 1 ≦ β ≦ n
By connecting in this manner, only one recording element among the integrated recording elements can be selected for writing or reading. In addition, ternary recording can be performed with one driving element.

(Configuration of each layer)
Next, the structure of each layer constituting this element will be described.
The material of the substrate 1 has an insulating property for independently controlling a plurality of elements arranged on the substrate, and has a desired flatness as long as the material has sufficient rigidity to hold the elements. It can be appropriately selected depending on the situation. For example, an insulating substrate having a thickness of several hundreds μm, such as sapphire or silicon oxide, or a semiconductor substrate whose surface is oxidized to ensure insulation can be used.
The fixed layer electrode 2 can be appropriately selected as long as it is a conductive material, and preferably has a thickness of several tens of nm to several hundreds of nm and an area of 20 nm × 20 nm to 10 μm × 10 μm. The shape is preferably a square shape, but may be a round shape, an oval shape, or the like as desired.
The ferromagnetic pinned layer 3 and each ferromagnetic free layer preferably have a magnetization orientation direction in a specific direction parallel to the substrate surface (for example, the left-right direction in FIG. 1). In order to orient the magnetization in such a direction, it is effective to give the ferromagnetic layer shape anisotropy. Therefore, when the thickness of the ferromagnetic layer is T, the direction in which the ferromagnetic layer is oriented is the length (L), and the direction perpendicular to this is the width (W), L / W ≧ 2, L / T It is preferable that ≧ 2. Therefore, it is preferable that the fixed layer electrode 2 is provided on the main surface of the ferromagnetic fixed layer 3 and each free layer electrode is also provided on the main surface of each ferromagnetic free layer.

As the magnetic material of the ferromagnetic pinned layer 3, a material having a large magnetic anisotropy constant and a coercive force is preferable. A lattice film, a CoPtCr—SiO ₂ granular film, and the like are particularly preferable. The film thickness of the ferromagnetic pinned layer is preferably thick in order to sufficiently fix the magnetization and align the electron spin, and specifically, it is preferably 50 nm or more.
The first separation layer 5 and the second separation layer 6 are layers for ensuring magnetic separation between the ferromagnetic layers, and are provided between the ferromagnetic fixed layer and the ferromagnetic free layer, and use a nonmagnetic material. It is necessary. The material is preferably a nonmagnetic metal or an oxide. In the case of a nonmagnetic metal, it is preferable to use at least one of Cu, V, Nb, Mo, Rh, Ta, W, Re, Ir, Pt and Pd. Or MgO is preferable. Further, a two-layer laminated film of these nonmagnetic metal film and oxide can be used. The thickness of each separation layer is preferably 3 nm or more in order to ensure magnetic separation between the ferromagnetic layers, and is preferably 10 nm or less in order to reduce electrical resistance.

As the magnetic material of the ferromagnetic first free layer 7 and the ferromagnetic second free layer 8, a magnetic metal, a ferromagnetic semiconductor, or a ferromagnetic oxide can be used. For example, Co, CoCr alloy, CoPtCr alloy, CoPtCrB alloy, CoPtCrTaB alloy, permalloy alloy (eg, Ni ₈₀ Fe ₂₀ , NiFeMo alloy, etc.), Fe, FeCo alloy (eg, CoFeB, NiCoFe, FeCoN, etc.), NiMnSb alloy Co ₂ MnAl alloy, Co ₂ MnSi alloy, Co ₂ MnGe alloy, CoCrFeAl alloy, FePt alloy, Sr ₂ FeMoO ₆ alloy, Fe ₂ O ₃ alloy, CoHfTa alloy, CoZrNb alloy, FeAlN alloy, FeTaN alloy, etc. it can.
Among these, a CoCr alloy, a CoPt alloy, or a CoPtCr alloy is particularly preferable. This is because the uniaxial magnetic anisotropy constant (Ku) and coercive force (Hc) can be adjusted over a wide range by adjusting the concentration of Pt or Cr. This is because the current density can be easily set to a desired value. The thickness of each ferromagnetic free layer needs to be thinner than the relaxation distance of electron spin. Since the relaxation distance of electron spin is about 100 to 200 nm for metal, the thickness of each ferromagnetic free layer is preferably 50 nm or less. In order to suitably control the polarization state of electron spin, it is 5 nm or more and 20 nm. The following are particularly preferred:

The first free layer electrode 9 and the second free layer electrode 10 can be appropriately selected as long as they are conductive materials. The thickness is preferably several tens of nm to several hundreds of nm, and the shape is the same as that of the ferromagnetic free layer. It is preferable that
(Other embodiments)
The configuration of FIG. 1 shows the basic configuration of the element of the present invention, and each component can be appropriately changed and modified according to the purpose. Hereinafter, a modification is illustrated.
FIG. 4 shows an example in which the nonmagnetic separation layer 4 is composed of a single layer. In the case where an insulating layer is used as the separation layer, it is particularly preferable that the separation layer is composed of a single layer because the manufacturing process becomes simple. Even when the separation layer is made of a nonmagnetic metal, since the separation layer is a thin layer, its electric resistance is high, and it can operate even if it is made of a single layer.

Since the ferromagnetic pinned layer is required not to easily reverse its magnetization by an external magnetic field, it has a multilayer structure for the purpose of forming known antiferromagnetic coupling, ferromagnetic coupling, etc. in order to strengthen the pinning of magnetization. It can also be.
In the above description, the case where there are two ferromagnetic free layers has been described. Needless to say, multi-value recording can be performed using three or more ferromagnetic free layers. In this case as well, conduction between the ferromagnetic free layers needs to be performed via the ferromagnetic fixed layer. That is, the ferromagnetic free layers are arranged on the same surface of the separation layer by being divided into a plurality of regions separated from each other so that the ferromagnetic free layers do not directly conduct with each other. Alternatively, the separation layer is divided into a plurality of regions separated from each other and arranged on the same surface of the ferromagnetic pinned layer, and then a ferromagnetic free layer is formed on each separation layer. Here, the plurality of regions of the ferromagnetic free layer or the separation layer are separated from each other, such as an arrangement in which a gap is provided between the plurality of areas or an arrangement in which an insulator is provided between the plurality of areas. Means an arrangement that does not conduct directly. Writing is performed by passing a current equal to or higher than the magnetization reversal current density between the ferromagnetic fixed layer and the ferromagnetic free layer to be written, as in the case of two ferromagnetic free layers. Each ferromagnetic free layer can perform magnetization reversal independently, and the fluctuation range allowed for the magnetization reversal current density is equivalent to that of a single ferromagnetic free layer. Therefore, even if the degree of multi-value is increased, the manufacturing difficulty level does not change greatly. The material, size, etc. of each layer can use what was mentioned above.

Hereinafter, it demonstrates in detail using an Example.
A GMR type magnetic memory element was fabricated using the configuration of FIG. 1 and using a non-magnetic metal as a separation layer.
A Si substrate was used as the non-magnetic substrate 1, and a Cu film having a thickness of 1 μm and a length of 10 μm was formed as a fixed layer electrode 2 on the Si substrate to a thickness of 200 nm. Subsequently, the ferromagnetic fixed layer 3 was formed on the fixed layer electrode 2 to a thickness of 100 nm using Co ₇₀ Cr ₂₀ Pt ₁₀ (where the subscript number represents atomic%; the same applies hereinafter). . Subsequently, a first separation layer 5 and a second separation layer 6 made of Cu and having a thickness of 6 nm were formed on the ferromagnetic fixed layer 3 in a shape having a width of 500 nm and a length of 1 μm, respectively. Subsequently, a ferromagnetic first free layer 7 made of Co ₉₆ Pt ₃ Cr ₁ having the same length and width as the first separation layer 5 and having a thickness of 10 nm is formed on the first separation layer 5, and a layer having a thickness of 200 nm made of Cu is formed. The first free layer electrode 9 is sequentially formed, and the second free layer having the same length and width as the second separate layer 6 and made of Co ₉₆ Pt ₃ Cr ₁ and having a thickness of 10 nm is formed on the second separate layer 6. 8. A second free layer electrode 10 made of Cu and having a layer thickness of 200 nm was sequentially formed. The above layers were formed using a sputtering method. In this way, a ternary recording element having a GMR effect was obtained.

Using the device of the example, ternary recording and reading were performed by the method described in FIGS. The write current density is 6 × 10 ⁻⁷ A / cm when the free layer is semi-parallel to the fixed layer, and 4 × 10 ⁻⁷ A / cm when the free layer and the fixed layer are parallel. I went there. Reading is performed at a voltage of 10 V, and the read current density is 12.5 mA in state “0”, 12.3 mA in state “1”, 12.1 mA in state “2”, and three values are recorded. Was identifiable.

It is a cross-sectional schematic diagram for demonstrating the structural example of the recording element of this invention. It is a cross-sectional schematic diagram for demonstrating the write-in operation | movement of the recording element of this invention. It is a schematic diagram for explaining a reading operation of the recording element of the present invention. It is a cross-sectional schematic diagram for demonstrating the other structural example of the recording element of this invention. FIG. 6 is a circuit diagram for explaining a configuration example when a large number of recording elements of the present invention are integrated. It is a cross-sectional schematic diagram for demonstrating the structural example of the conventional binary recording element. It is a cross-sectional schematic diagram for demonstrating the structural example of the conventional multi-value recording element. It is a circuit diagram for demonstrating the structural example in the case of integrating the conventional binary recording element.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,101 Substrate 2,102 Fixed layer electrode 3,103 Ferromagnetic fixed layer 4,104 Separation layer 5 First separation layer 6 Second separation layer 7 Ferromagnetic first free layer 8 Ferromagnetic second free layer 9 First free Layer electrode 10 Second free layer electrode 20 Recording element 30 Drive element 31 Bit line 32 Word line 33 Write word line 100 Binary recording element 107 Ferromagnetic free layer 109 Free layer electrode 120 Drive element 121 Bit line 122 Word line 131 Ferromagnetic First Fixed Layer 132 Ferromagnetic Second Fixed Layer 133 Ferromagnetic Third Fixed Layer 141 First Separation Layer 142 Second Separation Layer 143 Third Separation Layer 144 Fourth Separation Layer 151 Ferromagnetic First Free Layer 152 Ferromagnetic Second Free layer

Claims (8)

In the spin-injection magnetization reversal element comprising a ferromagnetic pinned layer, a nonmagnetic separation layer, and a ferromagnetic free layer in this order,
The separation layer is divided into two or more regions separated from each other and disposed on the same plane of the ferromagnetic pinned layer;
A spin injection magnetization reversal element, wherein a ferromagnetic free layer is provided on each region of the isolation layer. In the spin-injection magnetization reversal element comprising a ferromagnetic pinned layer, a nonmagnetic separation layer, and a ferromagnetic free layer in this order,
The spin injection magnetization reversal element, wherein the ferromagnetic free layer is divided into two or more regions separated from each other and arranged on the same surface of the separation layer.   3. The spin injection magnetization reversal element according to claim 1, wherein a free layer electrode is provided on the main surface of the ferromagnetic free layer opposite to the separation layer side.   4. The spin injection magnetization reversal element according to claim 1, wherein a pinned layer electrode is provided on the main surface of the ferromagnetic pinned layer opposite to the separation layer side.   5. The spin injection magnetization reversal element according to claim 1, wherein the number of the regions separated from each other is two.   6. A recording apparatus comprising a plurality of spin-injection magnetization reversal elements according to claim 1 connected together.   7. The recording apparatus according to claim 6, wherein one spin injection magnetization reversal element is driven by one FET. In a recording apparatus in which a plurality of spin injection magnetization reversal elements according to claim 5 are connected,
The wiring for one of the ferromagnetic free layers is a bit line, the wiring for the other ferromagnetic free layer is a word line, and the wiring for the ferromagnetic fixed layer is a write word line,
The recording apparatus, wherein when any two of the bit line, the word line, and the write word line is selected, the spin-injection magnetization switching element that conducts between the two lines is 1 or less.

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