WO2010024201A1

WO2010024201A1 - Magnetoresistive element having multi-layered ferry structure, magnetic memory, and magnetic random access memory

Info

Publication number: WO2010024201A1
Application number: PCT/JP2009/064661
Authority: WO
Inventors: 大野英男; 池田正二; 長谷川晴弘; 三浦勝哉; 早川純
Original assignee: 株式会社日立製作所; 国立大学法人東北大学
Priority date: 2008-08-28
Filing date: 2009-08-21
Publication date: 2010-03-04
Also published as: JP5351894B2; JPWO2010024201A1

Abstract

A high thermal stability constant is achieved in a magnetoresistive element applied to a memory cell of a magnetic memory. A free layer (415) of a magnetoresistive element (304) performs write-in by using a current magnetization inversion by spin transfer torque. The free layer (415) is formed by three or more ferromagnetic layers (403, 405, 407, 409) layered via non-magnetic antiparallel coupling layers (404, 406, 408). The ferromagnetic layers constituting the free layer have magnetization directions (411 - 414) parallel or antiparallel to the magnetization direction (410) of a fixed layer. The two ferromagnetic layers arranged to sandwich the antiparallel coupling layers have magnetization directions antiparallel to each other. Moreover, the sum of the volume of the ferromagnetic layer having a single magnetization direction and the magnetization product is set substantially identical to the sum of the volume of the ferromagnetic layer having a magnetization direction antiparallel to the aforementioned direction and the magnetization product.

Description

Magnetoresistive effect element, magnetic memory and magnetic random access memory having multilayer laminated ferri structure

The present invention relates to a magnetoresistive effect element, a magnetic memory using the same, and a magnetic random access memory.

Currently, in the memory field represented by dynamic random access memory (DRAM), research and development of new memories that satisfy the three requirements of high speed, high integration, and low power consumption are being performed all over the world. Magnetic random access memory (MRAM) is highly expected as a candidate for a memory that satisfies these conditions and has non-volatility.

MRAM records bit information in the magnetoresistive effect element. The magnetoresistive effect element has a basic structure of a three-layer structure in which a nonmagnetic layer is sandwiched between two ferromagnetic layers. One (fixed layer) of the ferromagnetic layer has a fixed magnetization direction, and the other (free layer) has a variable magnetization direction. When the magnetization directions of the ferromagnetic layers are parallel to each other, the resistance is low, and when the magnetization directions are antiparallel, the resistance is high. In the MRAM, this resistance change is made to correspond to “0” and “1” of the bit information.

JP 2007-294737 A

In an MRAM using a magnetoresistive element as a memory cell, writing is performed using current magnetization reversal by spin transfer torque according to bit information of “0” and “1” to be written. When rewriting “0” to “1”, a current is applied in a direction in which electrons move from the free layer toward the fixed layer. In this case, electrons that have passed through the free layer and reached the pinned layer pass only through the pinned layer in the same direction as the magnetization direction of the pinned layer, and the electrons spin-polarized in the opposite direction are reflected. . When the reflected electrons give a torque to the free layer and the current exceeds a certain threshold value, the magnetization of the free layer is reversed so as to be opposite to the fixed layer. Therefore, the magnetoresistive element has a high resistance. Conversely, when rewriting “1” to “0”, a current is applied in a direction in which electrons move from the fixed layer toward the free layer. The electrons that have passed through the fixed layer are spin-polarized in the same direction as the fixed layer. Since the electrons give torque to the free layer, the magnetization of the free layer is reversed so as to be in the same direction as the fixed layer. Therefore, the magnetoresistive effect element has a low resistance. The threshold value of this current is 200 μA or less from the characteristics of the cell transistor. Therefore, it is necessary to reduce the write current density of the magnetoresistive effect element.

On the other hand, in reading, it is necessary to distinguish the resistance value of the magnetoresistive element corresponding to the information of “0” or “1”. In general, a voltage is applied to the magnetoresistive effect element, and a distinction is made from the difference in voltage attenuation when the voltage is extracted at a certain time. That is, the voltage attenuates slowly when the resistance is high, whereas the voltage decreases rapidly when the resistance is low. Therefore, a current flows through the magnetoresistive effect element at the time of reading as well as at the time of writing. For this reason, even in the read current, the magnetization of the free layer receives torque, and a read disturb occurs in which writing is erroneously performed during reading.

In order to suppress read disturb, it is necessary to increase the thermal stability constant of the free layer of the magnetoresistive element. The thermal stability constant is a physical constant defined by the ratio E / k _B T between the energy E required for magnetization reversal and the external thermal energy k _B T (k _B is Boltzmann's constant, T is temperature). It is. When the MRAM recording retention time is 10 years required for the nonvolatile memory and the error rate of the dynamic RAM (DRAM) is suppressed to the same level, the thermal stability constant needs to be 40 to 60 or more.

A magnetoresistive element applied to an MRAM must satisfy these conditions at the same time. However, a reduction in write current density and an increase in thermal stability constant are basically in a trade-off relationship. For this reason, it has been considered a very difficult task to satisfy both of these conditions.

In the present invention, the free layer of the magnetoresistive effect element that performs writing using current magnetization reversal by spin transfer torque is composed of three or more ferromagnetic layers stacked via a nonmagnetic antiparallel coupling layer. The magnetization directions of the plurality of ferromagnetic layers constituting the free layer are parallel or antiparallel to the magnetization direction of the fixed layer, and the magnetization directions of the two ferromagnetic layers provided across the antiparallel coupling layer are antiparallel to each other. is there. The sum of the product of the volume and magnetization of the ferromagnetic layer whose magnetization direction is directed to one side is substantially equal to the sum of the product of the volume and magnetization of the ferromagnetic layer whose magnetization direction is antiparallel to it.

A magnetic memory cell according to the present invention includes the magnetoresistive element and a switching element that controls on / off of a current flowing through the magnetoresistive element.

The magnetic random access memory includes a plurality of magnetic memory cells and means for selecting a desired magnetic memory cell.

According to the present invention, a magnetic memory having improved thermal stability can be realized without greatly increasing the write current.

The schematic diagram which showed the writing principle of the magnetoresistive effect element to which this invention is applied. The schematic diagram which showed the coercive force increase of the magnetoresistive effect element to which this invention is applied. The memory cell sectional view of a magnetic memory. The cross-sectional schematic diagram which shows the example of the magnetoresistive effect element by this invention. The schematic diagram of a magnetic random access memory. The figure which shows the relationship between the write-in current density of a magnetoresistive effect element, and a thermal stability constant using the number of layers of the ferromagnetic layer which comprises a free layer as a parameter. The cross-sectional schematic diagram which shows the example of the magnetoresistive effect element by this invention. The cross-sectional schematic diagram which shows the example of the magnetoresistive effect element by this invention. The cross-sectional schematic diagram which shows the example of the magnetoresistive effect element by this invention. The cross-sectional schematic diagram which shows the example of the magnetoresistive effect element by this invention.

Hereinafter, a magnetic memory and a magnetoresistive effect element to which the present invention is applied will be described in detail with reference to the drawings.

First, the principle of realizing a reduction in write current density and an increase in thermal stability constant by the magnetoresistive effect element of the present invention will be described below. Here, a case where the free layer is constituted by four ferromagnetic layers laminated via a nonmagnetic antiparallel coupling layer will be described as an example. The four ferromagnetic layers have the same thickness and are made of the same material, and the first ferromagnetic layer, the second ferromagnetic layer, the third ferromagnetic layer, from the side close to the fixed layer, This is called a fourth ferromagnetic layer.

In the case of a conventional so-called laminated ferrimagnetic structure, there are two ferromagnetic layers. As in Patent Document 1, in the case of two layers, current magnetization reversal by spin transfer torque has been experimentally verified. In the case of four layers, since the volume is larger than that of the two layers, it has been considered that magnetization reversal due to spin transfer torque hardly occurs. However, as described below, it has been clarified that when the spin passes through the four ferromagnetic layers having magnetizations coupled substantially antiparallel to each other, the angular momentum is transferred by the spin transfer torque in each layer.

FIG. 1 schematically shows how one electron transfers angular momentum to the magnetization of each layer when the electron moves from bottom to top. FIG. 1A shows that electrons pass through the fixed layer 101 and have a spin in the same direction as the magnetization of the fixed layer 101. In FIG. 1B, the electrons try to direct the magnetization of the first ferromagnetic layer of the free layer 102 in the same direction as the spin of electrons, and exchange angular momentum. At this time, since the angular momentum is conserved, the electron spin receives a reverse torque. In FIG. 1C, electrons exchange angular momentum with the second ferromagnetic layer of the free layer 102. In the magnetoresistive effect element of the present invention, there are four ferromagnetic layers constituting the free layer, and electrons transfer angular momentum to each of them. For this reason, when the thickness of the four ferromagnetic layers composing the free layer is equal to that of the four layers, considering the conservation of angular momentum, as shown in FIG. The momentum is in principle the same as the electrons shown in FIG. In other words, since the angular momentum of electrons does not change between the first and last states, electrons can efficiently apply torque to each of the four ferromagnetic layers constituting the free layer, and the write current density increases in volume. However, it will not increase. The same effect can be obtained when electrons move in the opposite direction.

Also, the thermal stability constant is proportional to the coercivity of the free layer. The coercive force is an amount expressed by the magnitude of the magnetic field to stop the magnetization in one direction. As shown in FIG. 2A, a magnetic field is applied in the same direction as the magnetization direction of the first ferromagnetic layer (the ferromagnetic layer closest to the fixed layer 101) of the free layer 102 of the magnetoresistive effect element to which the present invention is applied. Consider the case where it takes. At this time, as shown in FIG. 2B, the magnetization of the second ferromagnetic layer and the magnetization of the fourth ferromagnetic layer of the free layer 102 tend to go in the direction of the magnetic field, and the directions are inclined. Accordingly, the magnetization of the first ferromagnetic layer and the magnetization of the third ferromagnetic layer, which are coupled antiparallel to the magnetization of the second ferromagnetic layer and the magnetization of the fourth ferromagnetic layer, are also obtained. The direction is changed (FIG. 2 (c)). Here, since the magnetization of the first ferromagnetic layer and the magnetization of the third ferromagnetic layer tend to go in the direction of the magnetic field again (FIG. 2D), the magnetization of the second ferromagnetic layer and the fourth The magnetization of the ferromagnetic layer is returned to the original direction (FIG. 2 (e)). Because of this balance relationship, the coercivity increases.

Also, it is known that the thermal stability constant is reduced by an external magnetic field, and this is also affected by the leakage magnetic field of the magnetoresistive effect element itself. However, since the magnetizations of the first, second, third, and fourth ferromagnetic layers of the free layer are coupled substantially antiparallel to each other, the lines of magnetic force emitted from the respective ferromagnetic layers are closed. Therefore, a magnetic field is not applied to the fixed layer from these ferromagnetic layers, and the thermal stability is improved compared to other structures.

Furthermore, the thermal stability constant is proportional to the volume of the free layer of the magnetoresistive element. In the magnetoresistive effect element, there are four ferromagnetic layers constituting the free layer, which is larger than that of the conventional two-layer structure, and the thermal stability constant is increased.

Hereinafter, the present invention will be described in more detail with reference to examples.

FIG. 3 shows a memory cell 300 of a magnetic memory using the magnetoresistive effect element of the present invention. The memory cell 300 includes a plurality of bit lines 301 arranged in parallel to each other, a plurality of source lines 302 parallel to the bit lines 301 and arranged in parallel to each other, and intersecting the bit lines 301 and parallel to each other. A plurality of word lines 303 arranged in a row. A magnetoresistive effect element 304 is disposed at a portion where the bit line 301 and the word line 303 intersect. The upper part of the magnetoresistive effect element 304 is electrically connected to the bit line 301. The lower part of the magnetoresistive effect element 304 is electrically connected to the drain electrode 306 of the transistor through the first metal wiring layer 305. The source line 302 is electrically connected to the source electrode 308 of the transistor through the second metal wiring layer 307. The word line 303 is electrically connected to the gate electrode of the transistor.

An example of a magnetoresistive effect element is shown in FIG. The magnetoresistive effect element 304 shown in FIG. 4 has a structure in which a fixed layer (ferromagnetic layer) 401 whose magnetization direction is fixed with a non-magnetic 402 interposed therebetween and a free layer 415 are laminated. The free layer 415 includes first to fourth

ferromagnetic layers

403, 405, 407, and 409 whose magnetization directions are variable, and nonmagnetic antiparallel coupling layers 404, 406, and 408 formed therebetween. The magnetization direction of the ferromagnetic layer was limited to two directions (+ direction and-direction) by imparting magnetic anisotropy. The magnetization direction 411 of the first ferromagnetic layer 403 and the magnetization direction 412 of the second ferromagnetic layer 405 are substantially antiparallel, and the magnetization direction 412 and the magnetization direction 413 of the third ferromagnetic layer 407 are substantially antiparallel. The magnetization direction 413 and the magnetization direction 414 of the fourth ferromagnetic layer 409 are substantially antiparallel. The free layer 415 is a so-called laminated ferri structure having four layers.

FIG. 5 shows a schematic diagram of a memory array. A plurality of magnetoresistive elements 304 constituting the memory cell are arranged in an array. At the time of writing, a voltage corresponding to bit information to be written is applied between the selected bit line 301 and the source line 302 and a voltage is applied to the word line 303 to turn on the cell transistor of the memory cell. When the transistor is turned on, a current in a direction corresponding to the bit information to be written to the magnetoresistive effect element 304 flows, so that the spin transfer torque acts on the free layer 415 of the magnetoresistive effect element 304 and magnetization reversal occurs.

In the magnetoresistive effect element 304 of this example, the ferromagnetic layers in the free layer are all four layers of the same thickness made of the same material. For this reason, there are two types of magnetization directions of the ferromagnetic layer constituting the free layer, but the number of ferromagnetic layers having the magnetization direction in the + direction and the number of ferromagnetic layers having the − direction are the same. Since the ferromagnetic layers have the same film thickness, the volume of the ferromagnetic layer having the positive magnetization direction is the same as the volume of the ferromagnetic layer having the negative direction. Therefore, the coercivity of the free layer determined by the amount of magnetization in different directions increases. In addition, since the magnetic field lines are closed by the free layer, there is no leakage magnetic field from the end face of the magnetoresistive effect element, and a reduction in thermal stability can be suppressed. Furthermore, since there are four ferromagnetic layers, the conventional ferromagnetic layer has a larger volume than a two-layer laminated ferrimagnetic structure, and thermal stability can be improved.

FIG. 6 shows experimental data on the distribution of the thermal stability constant and the write current density when the ferromagnetic layers constituting the free layer are three layers, four layers, five layers, and six layers. The ferromagnetic layers constituting the free layer are all the same material and have the same thickness. Focusing on the thermal stability constant, the thermal stability constant in the case of applying the present invention was 50 or more, 52 in the case of 4 layers and 78 in the case of 6 layers. In the case of 3 layers and 5 layers, the thermal stability constants were 38 and 35, respectively. This is because when the number of layers is an odd number, the volume of the ferromagnetic layer whose magnetization direction is in the + direction and the volume of the ferromagnetic layer that is in the − direction are not the same, and the magnetic field lines are not closed by the free layer. It is considered that the thermal stability constant was reduced. Even when the number of layers was increased, no increase in the write current was observed.

On the other hand, as the volume of the free layer increases, the write current density increases. The write current density is also proportional to the magnitude of the free layer magnetization. However, as described above, the spin transfer torque works efficiently in the magnetoresistive effect element to which the present invention is applied. Among the ferromagnetic layers constituting the free layer, when the volumes of the ferromagnetic layers having different magnetization directions are the same, the spin transfer torque works most efficiently. Therefore, in the magnetoresistive effect element 304 to which the present invention is applied, even if the volume is increased, the write current density is hardly increased to 6 × 10 ⁶ A / cm ² , and the volume is small as shown in FIG. It was found that there was almost no difference from the case of 3 layers.

In applying the present invention, Co ₄₀ Fe ₄₀ B ₂₀ was used as the material of the fixed layer 401 and the first, second, third, and fourth

ferromagnetic layers

403, 405, 407, and 409 of the free layer. Different compositions of this material may be used. As other materials, all ferromagnets are candidates, but materials with high spin polarizability are suitable in view of the efficiency of spin transfer torque and the rate of resistance change. In addition, the nonmagnetic layer 402 plays a role of changing resistance by the magnetization direction 410 of the fixed layer 401 above and below the nonmagnetic layer 402 and the magnetization direction 411 of the first ferromagnetic layer 403 of the free layer 415. As a material for the nonmagnetic layer 402, all nonmagnetic materials are candidates. Further, an insulator may be used for this layer. In this case, the magnetoresistive effect element acts as a tunnel magnetoresistive effect (TMR) element, and its resistance change rate is increased. Similarly, all insulators are candidates as insulators, but for example, MgO or the like can be used. The material of the antiparallel coupling layers 404, 406, and 408 plays a role of coupling the magnetization directions of two ferromagnetic layers sandwiching these layers in antiparallel. As materials, all non-magnetic materials are candidates, but for example, Ru can be used.

In the magnetic memory of the present invention, all the ferromagnetic layers constituting the free layer of the magnetoresistive effect element are made of the same material and have the same film thickness, and the number of layers is an even number of 6 or more (n is a natural number and 2n layers). Good. This is because, as described above, if the volume of the ferromagnetic layer whose magnetization direction is the + direction and the volume of the ferromagnetic layer whose direction is the − direction are the same, the influence of the leakage magnetic field does not appear. Furthermore, as the number of layers increases, the volume increases and the thermal stability constant increases. On the other hand, when the number of layers is equal, when the number of layers is an odd number, the thermal stability constant decreases due to the influence of the leakage magnetic field, and the write current density also increases. FIG. 7 shows a conceptual diagram of a magnetoresistive effect element 700 in which a free layer is composed of six ferromagnetic layers. The free layer 415 is a so-called laminated ferrimagnetic structure having 2n layers. As shown in FIG. 6, in the case of 6 layers, the thermal stability constant was 80, and it was found that the write current density hardly changed although it was larger than that of 4 layers.

In the magnetoresistive element of the present invention, the plurality of ferromagnetic layers constituting the free layer are all made of the same material. However, when the film thickness is not equal, the number of ferromagnetic layers is not limited to an even number. In other words, among the ferromagnetic layers constituting the free layer, the volume of the ferromagnetic layer having the magnetization direction in the + direction may be designed to be equal to the volume of the ferromagnetic layer having the − direction.

Fig. 8 shows an example. The magnetoresistive effect element 800 shown in FIG. 8 has a structure in which a fixed layer (ferromagnetic layer) 401 whose magnetization direction is fixed with a non-magnetic 402 interposed therebetween and a free layer 415 are laminated. The free layer 415 includes first to third

ferromagnetic layers

403, 403, and 407 whose magnetization directions are variable, and nonmagnetic antiferromagnetic coupling layers 404 and 406 disposed between the ferromagnetic layers. The magnetization direction 411 of the first ferromagnetic layer 403 of the free layer and the magnetization direction 412 of the second ferromagnetic layer 405 are substantially antiparallel, and the magnetization direction 412 and the magnetization direction 413 of the third ferromagnetic layer 407 are approximately. Antiparallel. In this case, the free layer 415 has a three-layer structure.

As an example, the first ferromagnetic layer 403 and the third ferromagnetic layer 407 have the same film thickness, and the second ferromagnetic layer 405 has a film thickness that is 2 times the film thickness of the first ferromagnetic layer 403. Is double. Therefore, among the ferromagnetic layers constituting the free layer, the volume of the ferromagnetic layer whose magnetization direction is the + direction is equal to the volume of the ferromagnetic layer whose − direction is the magnetization direction. For this reason, in this structure, there is no influence of the leakage magnetic field from the end surface of the magnetoresistive effect element, and the decrease in the thermal stability constant can be suppressed. Further, it has been found that the increase in the write current density can be suppressed by the fact that the spin transfer torque works efficiently and the effect of spin accumulation in the

nonmagnetic layers

404 and 406 works.

Further, the relationship between the film thicknesses of the

ferromagnetic films

403, 405, and 407 constituting the free layer is not limited to the above case, and the volume of the ferromagnetic layer whose magnetization direction is the + direction and the strongness that is the − direction. What is necessary is just to design so that the volume of a magnetic layer may become equal.

In the magnetoresistive element of the present invention, the material or film thickness of the ferromagnetic layer constituting the free layer may be different for each layer. In this case, among the ferromagnetic layers constituting the free layer, the sum of the product of the volume of the ferromagnetic layer whose magnetization direction is the + direction and the magnetization of each layer of the ferromagnetic layer is the ferromagnetic layer whose magnetization direction is the-direction. May be designed to be equal to the sum of the products of the volume of the magnetic layer and the magnetization product of each ferromagnetic layer.

The magnetoresistive effect element may include an antiferromagnetic layer for fixing the magnetization of the fixed layer. FIG. 9 shows an example of a magnetoresistive effect element 900 including an antiferromagnetic layer 901 in the case where the number of ferromagnetic layers constituting the free layer is four. In this configuration, since the magnetization direction of the fixed layer 401 is strongly fixed by the antiferromagnetic layer 901, the operation during writing is stabilized.

In the magnetoresistive element of the present invention, the fixed layer may have a laminated ferri structure. FIG. 10 shows an example of a magnetoresistive effect element 1000 that employs a laminated ferrimagnetic structure as a fixed layer when the free layer 415 includes four ferromagnetic layers. In this configuration, the magnetization direction 1003 of the ferromagnetic layer 1001 is strongly fixed by the first antiferromagnetic layer 901. The magnetization direction 410 of the ferromagnetic layer 401 and the magnetization direction 1003 of the ferromagnetic layer 1001 are coupled approximately antiparallel via the nonmagnetic antiparallel coupling layer 1002. For this reason, the ferromagnetic layer 1001, the nonmagnetic layer 1002, and the ferromagnetic layer 401 act as a fixed layer, and the leakage magnetic field in this portion is suppressed. The product of the film thickness and magnetization of the ferromagnetic layer 1001 and the product of the film thickness and magnetization of the ferromagnetic layer 401 are preferably the same.

In the free layer of the magnetoresistive effect element described above, the nonmagnetic antiparallel coupling layer has an action of coupling the magnetization directions of the upper and lower ferromagnetic layers in a substantially antiparallel manner. This coupling is very sensitive to the film thickness of the antiparallel coupling layer. When the material of the antiparallel coupling layer is Ru, the optimum value is about 1 nm. However, the antiparallel coupling layer may diffuse due to heat. Therefore, in the magnetoresistive effect element described above, new layers for suppressing this diffusion may be applied above and below the antiparallel coupling layer. When Ru was used for the antiparallel coupling layer, Ru diffusion could be suppressed by applying Ta layers above and below the Ru layer. All non-magnetic materials are candidates for the material of the layer that suppresses diffusion. The film thickness of the diffusion preventing layer is preferably about 0.1 nm to 1 nm. In the case of the magnetoresistive effect element shown in FIG. 10, a layer that suppresses diffusion may also be applied to the antiparallel coupling layer 1002 in the fixed layer.

101 pinned layer 102 free layer 300 magnetic memory 301 bit line 302 source line 303 word line 304 magnetoresistive effect element 306 transistor drain electrode 308 transistor source electrode 401 pinned layer 402 nonmagnetic layer 403 first ferromagnetic layer 404 antiparallel Coupling layer 405 Second ferromagnetic layer 406 Antiparallel coupling layer 407 Third ferromagnetic layer 408 Antiparallel coupling layer 409 Fourth ferromagnetic layer 415 Free layer 700 Magnetoresistive element 800 Magnetoresistive element 900 Magnetoresistive effect Element 901 Antiferromagnetic layer 1000 Magnetoresistive element 1001 Ferromagnetic layer 1002 Antiparallel coupling layer

Claims

A fixed layer with a fixed magnetization direction, a nonmagnetic layer formed on the fixed layer, a free layer with a variable magnetization direction formed on the nonmagnetic layer, and a direction perpendicular to the film thickness In a magnetoresistive effect element that has a pair of electrodes for flowing current and performs writing using current magnetization reversal by spin transfer torque,
The free layer includes three or more ferromagnetic layers stacked via a nonmagnetic antiparallel coupling layer, and the magnetization directions of the plurality of ferromagnetic layers are parallel or antiparallel to the magnetization direction of the fixed layer. The magnetization directions of the two ferromagnetic layers provided across the antiparallel coupling layer are antiparallel to each other, and the sum of the product of the volume and magnetization of the ferromagnetic layer with the magnetization direction facing one side is the magnetization direction Is substantially equal to the sum of the product of volume and magnetization of a ferromagnetic layer oriented in an antiparallel direction.
2. The magnetoresistive effect element according to claim 1, wherein the number of ferromagnetic layers provided in the free layer is an even number.
2. The magnetoresistive element according to claim 1, wherein the free layer includes four ferromagnetic layers made of the same material having the same thickness.
2. The magnetoresistive element according to claim 1, wherein the three or more ferromagnetic layers include ferromagnetic layers having different thicknesses.
2. The magnetoresistive effect element according to claim 1, wherein the three or more ferromagnetic layers include ferromagnetic layers made of different materials.
2. The magnetoresistive element according to claim 1, wherein an antiferromagnetic layer is provided in contact with the fixed layer.
2. The magnetoresistive element according to claim 1, further comprising a diffusion prevention layer above and below the antiparallel coupling layer.
2. The magnetoresistive effect element according to claim 1, wherein the nonmagnetic layer formed on the fixed layer is an insulating layer.
A fixed layer with a fixed magnetization direction, a nonmagnetic layer formed on the fixed layer, a free layer with a variable magnetization direction formed on the nonmagnetic layer, and a direction perpendicular to the film thickness A pair of electrodes for flowing current, and the free layer includes three or more ferromagnetic layers stacked via a nonmagnetic antiparallel coupling layer, and the magnetization directions of the plurality of ferromagnetic layers Is parallel or anti-parallel to the magnetization direction of the fixed layer, the magnetization directions of the two ferromagnetic layers provided across the anti-parallel coupling layer are anti-parallel to each other, and the magnetization direction is one direction ferromagnetic. The sum of the volume and magnetization product of the layer is approximately equal to the sum of the volume and magnetization product of the ferromagnetic layer whose magnetization direction is antiparallel to the direction, and writing is performed using current magnetization reversal by spin transfer torque. A magnetoresistive element;
A magnetic memory cell comprising: a switching element that controls on / off of a current flowing through the magnetoresistive element.
In a magnetic random access memory comprising a plurality of magnetic memory cells and means for selecting a desired magnetic memory cell,
The magnetic memory cell is
A fixed layer with a fixed magnetization direction, a nonmagnetic layer formed on the fixed layer, a free layer with a variable magnetization direction formed on the nonmagnetic layer, and a direction perpendicular to the film thickness A pair of electrodes for flowing current, and the free layer includes three or more ferromagnetic layers stacked via a nonmagnetic antiparallel coupling layer, and the magnetization directions of the plurality of ferromagnetic layers Is parallel or anti-parallel to the magnetization direction of the fixed layer, the magnetization directions of the two ferromagnetic layers provided across the anti-parallel coupling layer are anti-parallel to each other, and the magnetization direction is one direction The sum of the volume of the layer and the product of magnetization is approximately equal to the sum of the product of the volume and magnetization of the ferromagnetic layer whose direction of magnetization is antiparallel, and writing is performed using current magnetization reversal by spin transfer torque. A magnetoresistive element;
And a switching element that controls on / off of a current flowing through the magnetoresistive element.