JPWO2012137911A1 - Magnetoresistive element and magnetic random access memory - Google Patents

Abstract

The present invention provides an MRAM using a current-driven domain wall motion phenomenon that can be easily manufactured at low cost, and a manufacturing method thereof. A first ferromagnetic layer (10), a second ferromagnetic layer (30) with a fixed magnetization, disposed opposite to the first ferromagnetic layer and sandwiching a nonmagnetic film, and the first ferromagnetic layer A third ferromagnetic layer (40) disposed in contact with one end of the layer, and a fourth ferromagnetic layer (50) disposed in contact with the other end of the first ferromagnetic layer, The first ferromagnetic layer and the third ferromagnetic layer are oxidized at one end in the longitudinal direction of one ferromagnetic material to form the third ferromagnetic layer, and the remaining portion is formed with the first ferromagnetic layer. A magnetoresistive effect element having the structure described above.

Description

(Description of related applications)
The present invention is based on the priority claim of Japanese patent application: Japanese Patent Application No. 2011-086158 (filed on April 8, 2011), the entire contents of which are incorporated herein by reference. Shall.

  The present invention relates to a magnetoresistive effect element, a magnetic random access memory, and an initialization method thereof, and more particularly to a domain wall motion type magnetoresistive effect element, a magnetic random access memory, and a manufacturing method thereof.

  Magnetic Random Access Memory (MRAM) is expected as a non-volatile memory capable of high-speed operation and infinite rewriting, and has been actively developed. In the MRAM, a magnetoresistive effect element is integrated in a memory cell, and data is stored as the magnetization direction of the ferromagnetic layer of the magnetoresistive effect element. Several methods have been proposed as a method for switching the magnetization of the ferromagnetic layer, all of which are common in that current is used. In putting MRAM into practical use, it is very important how much the write current can be reduced. According to Non-Patent Document 1, a reduction to 0.5 mA or less, more preferably a reduction to 0.2 mA or less. It has been demanded.

  The most common method of writing information to the MRAM is to arrange wiring for passing a write current around the magnetoresistive effect element, and to strengthen the magnetoresistive effect element by a current magnetic field generated by passing the write current. This is a method of switching the magnetization direction of the magnetic layer. This method can be written in 1 nanosecond or less in principle, and is suitable for realizing a high-speed MRAM. For example, Patent Document 1 discloses a structure in which the magnetization of the end portion of the magnetization fixed layer is directed in the film thickness direction for an MRAM in which data is written by a current magnetic field.

  However, the magnetic field for switching the magnetization of a magnetic material that has ensured thermal stability and disturbance magnetic field resistance is generally about several tens (Oe). In order to generate such a magnetic field, a large number of about several mA is required. Write current is required. When the write current is large, the chip area is inevitably increased, and the power consumption required for writing increases, so that it is inferior in competitiveness compared to other random access memories. In addition to this, when the memory cell is miniaturized, the write current further increases, which is not preferable in terms of scaling.

  In recent years, the following two methods have been proposed as means for solving such problems. The first method is to use spin injection magnetization reversal. In an MRAM using spin injection magnetization reversal, the magnetoresistive effect element of the memory cell includes a first ferromagnetic layer having a reversible magnetization (often referred to as a free layer) and a second magnetization fixed. It is composed of a laminate including a ferromagnetic layer (often referred to as a pinned layer) and a tunnel barrier layer provided between these ferromagnetic layers. In such MRAM data writing, the interaction between spin-polarized conduction electrons and local electrons in the free layer when a current is passed between the free layer and the pinned layer is used. Magnetization is reversed. The presence or absence of spin injection magnetization reversal depends on the current density (not the absolute value of the current). Therefore, when spin injection magnetization reversal is used for data writing, if the size of the memory cell is reduced, writing is performed. The current is also reduced.

  That is, it can be said that the spin injection magnetization reversal method is excellent in scaling. However, when data is written, a write current must be passed through the tunnel barrier layer having a small film thickness, and rewriting durability and reliability become problems. In addition, since the current path for writing and the current path for reading are the same, there is a concern about erroneous writing during reading. Thus, although spin transfer magnetization reversal is excellent in scaling, there are some barriers to practical use.

  The second method is to use a current-driven domain wall motion phenomenon. The magnetization reversal method using the current-driven domain wall motion phenomenon can solve the above-described problems of spin injection magnetization reversal. For example, Patent Document 2, Patent Document 3, and Patent Document 4 disclose MRAMs that use the current-driven domain wall motion phenomenon. In the most general configuration of an MRAM using a current-driven domain wall motion phenomenon, a ferromagnetic layer (often called a magnetic recording layer) that holds data is provided with a magnetization reversal unit having reversible magnetization and both ends thereof. It is comprised by the two magnetization fixed parts which have the fixed magnetization connected. The data is stored as the magnetization of the magnetization switching unit. The magnetizations of the two magnetization fixed portions are fixed so as to be substantially antiparallel to each other. When the magnetization is arranged in this way, a domain wall is introduced into the magnetic recording layer.

  As reported in Non-Patent Document 2, when a current is passed in the direction penetrating the domain wall, the domain wall moves in the direction of conduction electrons, so that data can be written by passing a current through the magnetic recording layer. Since the presence or absence of current-driven domain wall movement also depends on the current density, it can be said that there is scaling as with spin injection magnetization reversal. In addition, in an MRAM memory cell using current-driven domain wall motion, the write current does not flow through the insulating layer, and the write current path and the read current path are different from each other. The above-mentioned problems that can be solved will be solved.

JP 2005-150303 A JP 2005-191032 A JP 2006-73930 A JP 2006-270069 A JP 2009-252909 A

2006 Symposium on VLSI Circuits, Digest of Technical Papers, p. 136. Physical Review Letters, vol. 92, number 7, p. 077205, (2004). Japan Journal of Applied Physics, vol. 45, no. 5A, pp. 3850-3853 (2006)

  The disclosures of the above patent documents and non-patent documents are incorporated herein by reference. The following analysis is given from the perspective of the present invention.

However, the MRAM using current-driven domain wall motion has a problem that the absolute value of the write current becomes relatively large. Although many observations of current-induced domain wall movement have been reported, a current density of about 1 × 10 ⁸ [A / cm ² ] is generally required for domain wall movement. In this case, for example, when the width of the ferromagnetic film in which the domain wall motion occurs is 100 nm and the film thickness is 10 nm, the write current is 1 mA. In order to reduce the write current below this, the width of the ferromagnetic film may be reduced and the film thickness may be reduced. However, it has been reported that when the film thickness is reduced, the current density required for writing further increases (for example, see Non-Patent Document 3). Moreover, reducing the width of the ferromagnetic film to 100 nm or less is accompanied by great difficulty in terms of processing technology.

In addition, when writing is performed using a current density close to 1 × 10 ⁸ [A / cm ² ], there is a concern about the effects of electron migration and temperature rise.

  In addition to this, in the MRAM using current-driven domain wall motion, as described above, the magnetizations of the two magnetization fixed portions of the magnetic recording layer need to be fixed so as to be antiparallel to each other. As a method for fixing the magnetization, for example, an antiferromagnetic film is used as disclosed in Patent Document 2, and a magnetization fixed region is created separately from the domain wall motion layer as disclosed in Patent Document 5. There are methods.

  However, in order to realize these, a complicated manufacturing process is required. A complicated manufacturing process causes an increase in manufacturing cost.

  An object of the present invention is to provide an MRAM using a current-driven domain wall motion phenomenon that can be easily manufactured at low cost, and a manufacturing method thereof.

  In a first aspect, a magnetoresistive effect element according to the present invention includes a first ferromagnetic layer, a second magnetization layer arranged opposite to the first ferromagnetic layer and sandwiching a nonmagnetic film and having a fixed magnetization. A ferromagnetic layer, a third ferromagnetic layer disposed in contact with one end of the first ferromagnetic layer, a fourth ferromagnetic layer disposed in contact with the other end of the first ferromagnetic layer, The first ferromagnetic layer and the third ferromagnetic layer are oxidized at one end in the longitudinal direction of one ferromagnetic material to form the third ferromagnetic layer, and the remaining portion is the first ferromagnetic layer. The structure is a ferromagnetic layer.

  In a second aspect, the magnetoresistive effect element manufacturing method according to the present invention includes a first ferromagnetic layer and a magnetization that is disposed opposite to the first ferromagnetic layer and sandwiching a nonmagnetic film therebetween. A second ferromagnetic layer, a third ferromagnetic layer disposed in contact with one end of the first ferromagnetic layer, and a fourth ferromagnetic layer disposed in contact with the other end of the first ferromagnetic layer. And forming a first ferromagnetic layer that is long in the longitudinal direction, and oxidizing one end of the first ferromagnetic layer in the longitudinal direction. And a step of forming the third ferromagnetic layer.

  In a third aspect, the magnetoresistive effect element according to the present invention is a magnetoresistive effect element including a domain wall moving layer and a structure in which one magnetization fixed layer is disposed on each side thereof, A second ferromagnetic layer having a degree of oxidation different from that of the first ferromagnetic layer is disposed on one side of the magnetic layer, and the first ferromagnetic layer is used as a domain wall motion layer. The ferromagnetic layer is one of the two magnetization fixed layers.

  The magnetoresistive effect element according to the present invention increases the coercive force by oxidizing at least one end of the domain wall motion layer to form a magnetization fixed layer. By doing so, it is not necessary to create the magnetization fixed layer separately from the domain wall motion layer, so that the manufacturing process is simplified and the manufacturing cost can be reduced.

It is the cross section and plane schematic diagram of one Example of the magnetoresistive effect element of this invention. It is the figure which showed the change of the magnitude | size of the reversal magnetic field by the grade of oxidation. It is the figure which showed the magnetization reversal characteristic in each area | region of the magnetoresistive effect element shown in FIG. It is the figure which showed the manufacturing process flow of one Example of the magnetoresistive effect element of this invention. It is the figure which showed the initialization method of one Example of the magnetoresistive effect element of this invention. It is the figure which showed the writing method of one Example of the magnetoresistive effect element of this invention. It is the figure which showed the manufacturing process flow of the modification of the magnetoresistive effect element of this invention.

In the following, the various possible forms are outlined.
In the first aspect, the other end portion of the one ferromagnetic material in the longitudinal direction is also oxidized to form the fourth ferromagnetic layer, and the remaining central portion is configured to be the first ferromagnetic layer. Is preferred.

  In addition, it is preferable that the third ferromagnetic layer and the fourth ferromagnetic layer have different degrees of oxidation, that is, oxygen content (particularly, such that the domain wall moves).

  The magnitudes of the reversal magnetic fields of the first ferromagnetic layer, the third ferromagnetic layer, and the fourth ferromagnetic layer are as follows: first ferromagnetic layer <third ferromagnetic layer <fourth ferromagnetic layer It is preferable that the first ferromagnetic layer <the fourth ferromagnetic layer <the third ferromagnetic layer (particularly, such that the domain wall moves to a certain extent).

  The first ferromagnetic layer, the second ferromagnetic layer, the third ferromagnetic layer, and the fourth ferromagnetic layer are all magnetic anisotropy in the thickness direction (direction of a specific easy axis). It is preferable to have.

  Further, at least one of the first ferromagnetic layer, the second ferromagnetic layer, the third ferromagnetic layer, and the fourth ferromagnetic layer includes at least one of Fe, Co, and Ni, and Pt, Pd, B, C, N, O, Al, Si, P, Ti, V, Cr, Mn, Cu, Zn, Zr, Nb, Mo, Tc, Ru, Rh, Ag, Hf, Ta, W, It is preferable to include at least one of Re, Os, Ir, Au, and Sm.

  In a second aspect, it is preferable that the method further includes a step of forming the fourth ferromagnetic layer by oxidizing the other end portion in the longitudinal direction of the one ferromagnetic material.

  Moreover, it is preferable that the step of oxidizing both ends of the first ferromagnetic layer in the longitudinal direction is a step of oxidizing each end with different degrees of oxidation, that is, oxygen content.

  In a third aspect, a third ferromagnetic layer having an oxidation degree different from any of the first ferromagnetic layer and the second ferromagnetic layer is disposed on the other side of the first ferromagnetic layer. Therefore, it is preferable to use another magnetization fixed layer. At this time, the magnitudes of the reversal magnetic fields of the first ferromagnetic layer, the third ferromagnetic layer, and the fourth ferromagnetic layer are as follows: first ferromagnetic layer <third ferromagnetic layer <fourth ferromagnetic layer, It is preferable to set the respective oxidation degrees so as to satisfy the following formula, or to set the respective oxidation degrees so that the first ferromagnetic layer <the fourth ferromagnetic layer <the third ferromagnetic layer.

  The first ferromagnetic layer, the third ferromagnetic layer, and the fourth ferromagnetic layer preferably all have magnetic anisotropy in the thickness direction.

  In addition, at least one of the first ferromagnetic layer, the third ferromagnetic layer, and the fourth ferromagnetic layer includes at least one of Fe, Co, and Ni, and further includes Pt, Pd, B, and C. N, O, Al, Si, P, Ti, V, Cr, Mn, Cu, Zn, Zr, Nb, Mo, Tc, Ru, Rh, Ag, Hf, Ta, W, Re, Os, Ir, Au , Sm is preferably included.

  Next, several embodiments of a magnetic random access memory according to the present invention will be described with reference to the accompanying drawings. In one embodiment, the magnetic random access memory has a plurality of memory cells arranged in an array, and each memory cell has a magnetoresistive element. Hereinafter, an embodiment based on the configuration of the magnetoresistive effect element and the memory cell will be described. In the following description, an xyz orthogonal coordinate system as shown in the accompanying drawings is introduced, and the structure of the magnetoresistive effect element and the magnetic random access memory will be described using the xyz orthogonal coordinate system.

(Example 1) (Configuration of magnetoresistive element)
1A is a cross-sectional view showing the structure of the main part of the magnetoresistive effect element 80 according to the first embodiment of the present invention, and FIG. 1B is a plan view showing the configuration of the magnetoresistive effect element 80. (Shown excluding the spacer layer 20). The magnetoresistive element 80 includes a first ferromagnetic layer 10 that is provided extending in the x-axis direction, a nonmagnetic spacer layer 20, and a second ferromagnetic layer 30. The spacer layer 20 is sandwiched between the first ferromagnetic layer 10 and the second ferromagnetic layer 30. The first ferromagnetic layer 10 and the second ferromagnetic layer 30 are formed of a ferromagnetic material. The spacer layer 20 is preferably formed of an insulator. In this case, a magnetic tunnel junction (MTJ) is formed by the first ferromagnetic layer 10, the spacer layer 20, and the second ferromagnetic layer 30. The spacer layer 20 is preferably made of an insulator, but may be made of a nonmagnetic conductor or semiconductor.

  A third ferromagnetic layer 40 and a fourth ferromagnetic layer 50 are formed on both ends of the first ferromagnetic layer 10. The first ferromagnetic layer 10, the third ferromagnetic layer 40, and the fourth ferromagnetic layer 50 are continuous films, and the lower surface and the upper surface thereof have the same height (or thickness). That is, they are formed flush with each other.

  For the first ferromagnetic layer 10, the second ferromagnetic layer 30, the third ferromagnetic layer 40, and the fourth ferromagnetic layer 50, perpendicular magnetization films are used. That is, the first ferromagnetic layer 10, the second ferromagnetic layer 30, the third ferromagnetic layer 40, and the fourth ferromagnetic layer 50 are all magnetic anisotropy in the film thickness direction (direction perpendicular to the film surface). have. The magnetization of the second ferromagnetic layer 30 is fixed in one direction substantially parallel to the z axis.

  On the other hand, the magnetization of the first ferromagnetic layer 10 can be reversed. The magnetization of the portion is directed in a direction parallel or antiparallel to the magnetization of the second ferromagnetic layer 30 according to stored data.

  About the 1st ferromagnetic layer 10 and the 2nd ferromagnetic layer 30, in order to implement | achieve magnetic anisotropy in a film thickness direction, the single layer film | membrane formed from the material which has perpendicular magnetic anisotropy, or several film | membrane It is preferable that each of the laminates formed in (1) is formed. The laminated body in this case may be a laminated body composed of a plurality of ferromagnetic films or a laminated body composed of a ferromagnetic film and a nonmagnetic film.

On the other hand, the third ferromagnetic layer 40 and the fourth ferromagnetic layer 50 also have perpendicular magnetic anisotropy. The magnitude of the reversal field is as follows: the reversal field of the first ferromagnetic layer <the reversal field of the third ferromagnetic layer <the reversal field of the fourth ferromagnetic layer, or
The reversal magnetic field of the first ferromagnetic layer <the reversal magnetic field of the fourth ferromagnetic layer <the reversal magnetic field of the third ferromagnetic layer.

  The third ferromagnetic layer 40 and the fourth ferromagnetic layer 50 have a function of pinning the domain wall at a desired position of the first ferromagnetic layer 10. The third ferromagnetic layer 40 is magnetically coupled to a portion near one end in the x-axis direction of the first ferromagnetic layer 10, and the fourth ferromagnetic layer 50 is in the x-axis direction of the first ferromagnetic layer 10. Magnetically coupled to a portion in the vicinity of the other end. When the first ferromagnetic layer 10, the third ferromagnetic layer 40, and the fourth ferromagnetic layer 50 are in the magnetization arrangement as described above, the region of the first ferromagnetic layer 10 that faces the second ferromagnetic layer 30. Depending on the magnetization direction, a domain wall is formed in the first ferromagnetic layer 10.

  The third ferromagnetic layer 40 and the fourth ferromagnetic layer 50 have a switching magnetic field larger than that of the first ferromagnetic layer. For this reason, hereinafter, the third ferromagnetic layer 40 may be referred to as the first magnetization pinned portion 40. Similarly, the fourth ferromagnetic layer 50 may be referred to as the second magnetization fixed unit 50. In the section of the first ferromagnetic layer 10 between the third ferromagnetic layer 40 and the fourth ferromagnetic layer 50, the domain wall can move. For this reason, hereinafter, the first ferromagnetic layer 10 may be referred to as a domain wall motion unit 10.

  The second ferromagnetic layer 30, the third ferromagnetic layer 40, and the fourth ferromagnetic layer 50 are electrically connected to different external wirings. As will be understood from this, the magnetoresistive effect element 80 is a three-terminal element. Although not shown in FIG. 1, an electrode layer for obtaining electrical connection with the wiring is joined to each of the second ferromagnetic layer 30, the third ferromagnetic layer 40, and the fourth ferromagnetic layer 50. Is desirable.

  Below, the material of the 1st ferromagnetic layer 10, the spacer layer 20, the 2nd ferromagnetic layer 30, the 3rd ferromagnetic layer 40, and the 4th ferromagnetic layer 50 is demonstrated. Note that all the materials shown here are examples, and in practice, any material may be used as long as a desired magnetization state can be realized.

  The first ferromagnetic layer 10 (and the ferromagnetic layer obtained by oxidizing this) and the second ferromagnetic layer 30 contain at least one material selected from Fe, Co, and Ni. Is desirable.

  Further, the perpendicular magnetic anisotropy is stabilized when the first ferromagnetic layer 10 (and the ferromagnetic layer obtained by oxidizing this) and the second ferromagnetic layer 30 contain Pt and / or Pd. be able to. The first ferromagnetic layer 10 and the second ferromagnetic layer 30 have B, C, N, O, Al, Si, P, Ti, V, Cr, Mn, Cu, Zn, Zr, Nb, Mo, Tc, Ru, By adding Rh, Ag, Hf, Ta, W, Re, Os, Ir, Au, Sm, etc., it is possible to adjust so that desired magnetic properties are expressed.

  Specifically, Co, Co—Pt, Co—Pd, Co—Cr, Co—Pt—Cr, Co—Cr—Ta, Co—Cr—B, Co—Cr—Pt—B, Co—Cr—Ta— B, Co-V, Co-Mo, Co-W, Co-Ti, Co-Ru, Co-Rh, Fe-Pt, Fe-Pd, Fe-Co-Pt, Fe-Co-Pd, Sm-Co, Examples include Gd—Fe—Co, Tb—Fe—Co, and Gd—Tb—Fe—Co.

  In addition, magnetic anisotropy in the vertical direction is expressed by laminating a film containing any one material selected from Fe, Co, and Ni and a film formed of a material different from the film. It can also be made. Specifically, a laminated film of Co / Pd, Co / Pt, Co / Ni, Fe / Au, and the like are exemplified, but other magnetic anisotropic films having various compositions and layer structures can be used.

  In the present embodiment, the third ferromagnetic layer 40 and the fourth ferromagnetic layer 50 are formed by oxidizing both end portions of the first ferromagnetic layer 10. As shown in FIG. 2, the switching magnetic field increases in proportion to the time for oxidizing the first ferromagnetic layer. Therefore, three regions having different reversal magnetic fields can be created by changing the oxidation time between the left and right regions of the first ferromagnetic layer facing the second ferromagnetic layer, that is, by changing the oxidation degree.

  FIG. 3 shows the reversal magnetization curve of each region. By appropriately selecting the oxidation time, the magnitude of the reversal magnetic field can be set as region 1 <region 2 <region 3. Here, the region 1 represents the first ferromagnetic layer 10, the region 2 represents the fourth ferromagnetic layer 50, and the region 3 represents the third ferromagnetic layer 40.

  The spacer layer 20 is preferably made of an insulator. Specifically, the material of the spacer layer 20 may be an oxide or nitride of metal such as Mg—O, Al—O, Al—N, Ni—O, Hf—O, or oxynitride. . However, it should be noted that the present invention can be implemented even if a semiconductor or a metal material is used for the spacer layer 20. Specific examples of semiconductors and metal materials that can be used as the spacer layer 20 include Cr, Al, Cu, and Zn.

(Production method)
FIG. 4 shows an example of a method for manufacturing this element. First, a DW (Domain Wall) layer 15 (a portion that becomes a first ferromagnetic layer, a third ferromagnetic layer, and a fourth ferromagnetic layer), a barrier layer 25 (a portion that becomes a nonmagnetic spacer layer), and a Ref layer 35. (A portion to become the second ferromagnetic layer) is formed on the substrate 1 (FIG. 4A), and junction separation is performed by a known method (FIG. 4B). Next, either one of the left and right regions of the bonded and separated Ref layer is covered with a photoresist 36 (FIG. 4C). Then, after exposing the substrate to a gas containing oxygen for a predetermined time, the photoresist is removed (FIG. 4D). Finally, the DW layer is patterned (that is, formed in a predetermined pattern) (FIG. 4E).

  Regions not covered by the photoresist and Ref layer are exposed to oxygen plasma from the beginning, so the oxygen exposure time is long and regions covered only by the photoresist are relatively short in oxygen exposure time. Also, the DW layer below the region covered by the Ref layer is not exposed to oxygen. The change in the magnetic properties of the DW layer increases the coercive force (Hc) in proportion to the oxygen exposure time (oxidation degree). As a result, a plurality (three in this example) of regions having different Hc can be formed on the DW element, and antiparallel initialization can be performed.

(Initialization method)
Next, the initialization method of the magnetoresistive effect element 80 of Example 1 is demonstrated using FIG.

  In the magnetoresistive element 80, it is necessary to introduce a domain wall into the first ferromagnetic layer 10, and FIG. 5 shows the process. In FIG. 5, only the first ferromagnetic layer 10, the nonmagnetic spacer 20, the second ferromagnetic layer 30, the third ferromagnetic layer 40, and the fourth ferromagnetic layer 50 are shown.

  In order to introduce a domain wall into the first ferromagnetic layer 10, first, a uniform and sufficiently large external magnetic field is applied to the magnetoresistive effect element 80 in the z-axis direction. At this time, as shown in FIG. 5A, all the magnetic moments are aligned and saturated in the direction of the external magnetic field. Thereafter, when an external magnetic field is applied in the opposite direction and the external magnetic field is gradually increased, the portion of region 1 is reversed as shown in FIG. 5B. At this time, the magnetizations of region 1 (first ferromagnetic layer 10) and region 2 (fourth ferromagnetic layer 50) and region 1 and region 3 (third ferromagnetic layer 40) are antiparallel to each other. A domain wall is formed at the boundary.

  When the external magnetic field is further increased, as shown in FIG. 5C, the region 2 is reversed in magnetization, and the regions 1 and 2 are magnetized in the same direction. At this time, the portion of the region 3 is held antiparallel to the region 1, and a domain wall exists at the boundary of this region. In this way, a domain wall is formed in the magnetization moving region by making the magnetization fixed regions 40 and 50 antiparallel.

  The above is the first initialization process of the magnetoresistive effect element 80 in the first embodiment.

(Writing method)
FIG. 6 illustrates a writing method of this element. As shown in FIG. 6A, when the magnetization directions of the first ferromagnetic layer 10 and the second ferromagnetic layer 30 are parallel in the initial state, the resistance of the magnetoresistive element 80 is in a low resistance state. That is, the state is “0”.

  Further, it is assumed that the domain wall is introduced between the first ferromagnetic layer 10 and the third ferromagnetic layer 40. As shown in FIG. 6A, when a current is passed, the domain wall moves to the right due to the effect of the spin torque and stops at the boundary between the first ferromagnetic layer 10 and the fourth ferromagnetic layer 50. At this time, the direction of magnetization of the first ferromagnetic layer 10 is reversed and becomes opposite to that of the second ferromagnetic layer 30. That is, the state becomes “1”.

  On the other hand, when the initial state is the “1” state as shown in FIG. 6B, the current can be similarly written to the “0” state by flowing a current in the direction opposite to that in FIG. 6A.

  The magnetoresistive effect element 80 of the present embodiment can be variously modified. Below, the modification of the magnetoresistive effect element 80 of Example 1 is demonstrated.

(Example 2)
In the above embodiment, the third ferromagnetic layer can be composed of another magnetic film. A configuration for this purpose is shown in FIG. In the second embodiment, since the third ferromagnetic layer is formed separately, there is a synergistic (extraordinary) effect that the margin of the magnetic field at the time of initialization is widened.

  The manufacturing method of Example 2 is shown. First, as shown in FIG. 7A, a hard layer 11 serving as a third ferromagnetic layer is formed on a substrate, and then an interlayer film 12 is formed and planarized (FIG. 7B). Next, a DW (Domain Wall) layer 15 (a portion to be a first ferromagnetic layer and a fourth ferromagnetic layer), a barrier layer 25 (a portion to be a nonmagnetic spacer layer), and a Ref layer 35 (to be a second ferromagnetic layer) (Part) is formed (FIG. 7C), and junction separation is performed by a known method (FIG. 7D). Next, either one of the left and right regions of the separated Ref layer is covered with a photoresist 36 (FIG. 7E). Thereafter, the substrate is exposed to a gas containing oxygen for a predetermined time (ashed) (FIG. 7F), and then the photoresist is removed. Finally, the DW layer is patterned (FIG. 7G).

  Within the scope of the entire disclosure (including claims and drawings) of the present invention, the embodiments and examples can be changed and adjusted based on the basic technical concept. Further, various combinations or selections of various disclosed elements (including each element of each claim, each element of each embodiment, each element of each drawing, etc.) are possible within the scope of the claims of the present invention. It is. That is, the present invention of course includes various variations and modifications that could be made by those skilled in the art according to the entire disclosure including the claims and the technical idea.

1 substrate 10 first ferromagnetic layer 11 hard layer 12 interlayer film 15 DW layer 20 (nonmagnetic) spacer (layer)
25 Barrier layer 30 Second ferromagnetic layer 35 Ref layer 36 Photoresist 40 Third ferromagnetic layer 50 Fourth ferromagnetic layer 80 Magnetoresistive element

Claims (9)

A first ferromagnetic layer;
A second ferromagnetic layer having a fixed magnetization, disposed opposite to the first ferromagnetic layer and sandwiching a nonmagnetic film;
A third ferromagnetic layer disposed in contact with one end of the first ferromagnetic layer;
A fourth ferromagnetic layer disposed in contact with the other end of the first ferromagnetic layer,
The first ferromagnetic layer and the third ferromagnetic layer are oxidized at one end in the longitudinal direction of one ferromagnetic material to form the third ferromagnetic layer, and the remaining portion is formed with the first ferromagnetic layer. A magnetoresistive effect element having the structure described above.   The other end portion of the one ferromagnetic material in the longitudinal direction is also oxidized to form the fourth ferromagnetic layer, and the remaining central portion is configured to be the first ferromagnetic layer. Item 2. The magnetoresistive effect element according to Item 1.   3. The magnetoresistive element according to claim 2, wherein the third ferromagnetic layer and the fourth ferromagnetic layer have different degrees of oxidation, that is, oxygen content. The magnitudes of the reversal magnetic fields of the first ferromagnetic layer, the third ferromagnetic layer, and the fourth ferromagnetic layer are:
The first ferromagnetic layer <the third ferromagnetic layer <the fourth ferromagnetic layer, or the first ferromagnetic layer <the fourth ferromagnetic layer <the third ferromagnetic layer, Item 4. The magnetoresistive element according to Item 3.   2. The first ferromagnetic layer, the second ferromagnetic layer, the third ferromagnetic layer, and the fourth ferromagnetic layer all have a magnetic anisotropy in a thickness direction. The magnetoresistive effect element as described in any one of -4.   At least one of the first ferromagnetic layer, the second ferromagnetic layer, the third ferromagnetic layer, and the fourth ferromagnetic layer includes at least one of Fe, Co, and Ni, and further includes Pt, Pd, B, C, N, O, Al, Si, P, Ti, V, Cr, Mn, Cu, Zn, Zr, Nb, Mo, Tc, Ru, Rh, Ag, Hf, Ta, W, Re, The magnetoresistive effect element according to claim 1, comprising at least one of Os, Ir, Au, and Sm. A first ferromagnetic layer;
A second ferromagnetic layer having a fixed magnetization, disposed opposite to the first ferromagnetic layer and sandwiching a nonmagnetic film;
A third ferromagnetic layer disposed in contact with one end of the first ferromagnetic layer;
A fourth ferromagnetic layer disposed in contact with the other end of the first ferromagnetic layer, and a method of manufacturing a magnetoresistive element,
Forming a first ferromagnetic layer that is long in the longitudinal direction;
Forming the third ferromagnetic layer by oxidizing one end of the first ferromagnetic layer in the longitudinal direction;
The manufacturing method characterized by including.   The manufacturing method according to claim 7, further comprising forming the fourth ferromagnetic layer by oxidizing the other end of the one ferromagnetic material in the longitudinal direction.   9. The step of oxidizing each of both ends in the longitudinal direction of the first ferromagnetic layer is a step of oxidizing each end with a different degree of oxidation, that is, oxygen content, respectively. The manufacturing method as described.

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