JP6967259B2 - High-sensitivity surface direct energization giant magnetoresistive element and its applications - Google Patents

Description

The present invention relates to a magnetoresistive element having a structure in which ferromagnetic layers and non-magnetic layers are alternately laminated on a substrate, and more specifically, by having a specific structure (number of layers, layer thickness). It relates to a surface direct current giant magnetoresistive element exhibiting excellent sensitivity (high MR ratio).

The surface direct current giant magnetoresistive (CPP-GMR) element has a structure in which a laminated film of a ferromagnetic layer / a non-magnetic layer / a ferromagnetic layer is pillared to a size of sub μm or less. When a current is passed through the pillars, the electrical resistance changes depending on the relative angle of magnetization of the two ferromagnetic layers, so the magnetic field can be detected electrically. However, when a general ferromagnet such as CoFe is used, the magnetic resistance (MR) ratio is about 3% (see, for example, Non-Patent Document 1), and the problem is that the sensitivity as a sensor is low. rice field. However, in recent years, Co-based _{Whistler alloys (Co 2} MnSi, Co ₂ (Fe _0.4 Mn _0.6 ) Si, Co ₂ Fe (Ga _0.5 Ge _0.5 ), etc.) having high spin polarization have been strengthened. The (001) oriented Hoisler / Ag / Hoisler epitaxial CPP-GMR element using an Ag non-magnetic layer with good lattice consistency as the magnetic layer realizes an ^{MR ratio of 30-60% and a resistance change area ΔRA = 10Ωμm 2.} (See, for example, Non-Patent Documents 2 to 4).
When a magnetoresistive element is used for a current sensor, a geomagnetic sensor, or the like, the linear response of the sensor element to an external magnetic field is important. Further, in order to realize a sensor with high sensitivity, a large electrical response from the sensor element to an external magnetic field, that is, a large MR ratio is required. Using a tunnel magnetoresistive element, a laminated film is created so that the magnetic moments of the upper and lower ferromagnetic layers are orthogonal, and an external magnetic field perpendicular to the free layer is applied to provide a linear response and a high MR ratio (110). %) Is possible (see, for example, Non-Patent Document 5), but its detectable magnetic field range is as narrow as about ± 10 mT, and its heat resistance is as low as about 250 ° C. Further, according to Non-Patent Document 6, using a tunnel magnetoresistive element, a laminated film is formed so that the magnetic moments of the upper and lower ferromagnetic layers are orthogonal to each other, and the free layer thickness is reduced to improve the linear responsiveness. However, there is a drawback that the MR ratio decreases as the linear response is improved.
On the other hand, in a face-to-face current giant magnetoresistive (CPP-GMR) element using a _{Whistler alloy (Co 2} Fe (Al _0.5 Si _{0.5)) and Ag, by changing the thickness of the Ag layer,} It has been reported that the strength of the correlation exchange bond between the upper and lower ferromagnetic layers changes (see, for example, Non-Patent Document 7), and a detectable magnetic field is used when an Ag film thickness that forms an antiferromagnetic bond is used. The range can be widened to about ± 40 mT, and good heat resistance of the element of 450 ° C. can be realized.
However, there is a demand for a magnetic sensor having higher sensitivity, and further improvement in sensitivity (improvement of MR ratio) is required.

Yuasa et al. , J. Apple. Phys. , 92, 2646 (2002) Y. Sakuraba et al. , Apple. Phys. Let. , 101, 252408 (2012) Li et al. , Apple. Phys. Let. , 103,042405 (2013) Du et al. , Apple. Phys. Let. , 107, 112405 (2015) D. C. Leitao et al. , J. Apple. Phys. , 115, 17E526 (2014) T. Nakano et al. , IEEE Trans. Magn. , Vol. 52, No. 7,4001304 (2016). T. M. Nakatani, Appl. Phys. Let. , 99,182505 (2011)

In view of the above background art, has a higher MR ratio than the prior art, has high sensitivity, to provide a surface direct electrostatic giant magnetoresistive element (CPP-GMR), and develop related technologies The challenge is to do.

As a result of diligent studies, the present inventors have found that a surface-directed giant magnetoresistive element having a specific structure, more specifically, an odd number of magnetic free layers and a specific non-magnetic layer thickness. By using (CPP-GMR ), it was found that a high MR ratio could be realized and the above-mentioned problems could be solved, and the present invention was completed.
That is, the present invention
[1] The substrate and
A laminated portion provided on the substrate and formed by alternately laminating n-layer magnetic free layers and n-1 non-magnetic layers.
It is a surface direct energization giant magnetoresistive element having
n is an odd number
The surface direct energization giant magnetoresistor having a thickness at which at least one non-magnetic layer forms an antiferromagnetic interlayer exchange bond between a pair of magnetic free layers in contact with both sides thereof and having no magnetic fixing layer. The element .

Hereinafter, [2] to [12] are each one of the preferred embodiments of the present invention.
[2] The surface direct conduction giant magnetoresistor according to [1] , wherein all of the non-magnetic layers have a thickness at which an antiferromagnetic interlayer exchange bond is formed between a pair of magnetic free layers in contact with both sides thereof. Element .
[3] When the ratio of residual magnetization / saturation magnetization measured in the in-plane direction for one non-magnetic layer on which an antiferromagnetic interlayer exchange bond is formed and a pair of magnetic free layers in contact with both sides thereof is 0.8 or less. The surface direct current enormous magnetoresistive element according to [1] or [2].
[4] Any one of [1] to [3], wherein the pair of the magnetic free layers forming the antiferromagnetic interlayer exchange bond via the non-magnetic layer has the same or substantially the same total magnetic moment. The surface direct energization giant magnetoresistive element described in 1.
[5] The surface direct energization giant magnetoresistive element according to any one of [1] to [4], wherein the magnetic free layer contains a Co-based Hoisler alloy-based half metal material.
[6] The Co-based Whistler alloy-based half-metal material is Co ₂ YZ (where Y is at least one element selected from the group consisting of Ti, V, Cr, Mn, and Fe, and Z is , Al, Si, Ga, Ge, In, and Sn), which is at least one element selected from the group.). The surface direct energization giant magnetic resistance element according to [5].
[7] The surface direct energization giant magnetoresistive element according to any one of [1] to [6], wherein the non-magnetic layer is composed of a material system having a spin diffusion length of 30 nm or more.
[8] The surface direct energization according to any one of [1] to [7], wherein the non-magnetic layer contains at least one element selected from the group consisting of Cu, Al, Ag, and Zn. Giant magnetoresistive element .
[9] The surface direct energization giant magnetoresistive element according to any one of [1] to [8], further comprising a buffer / electrode layer and a cap layer.
[10] A geomagnetic sensor, a current sensor, or a magnetic head comprising the surface direct energization giant magnetoresistive element according to any one of [1] to [9].

According to the surface direct energization giant magnetoresistive element of the present invention, a high MR ratio that could not be realized by the prior art can be obtained, so that a surface direct energization giant magnetoresistive element (CPP-GMR) having high sensitivity can be realized. The surface direct energization giant magnetoresistive element of the present invention can improve the linearity between the external magnetic field and the resistance value relatively easily by increasing the number of layers of the laminated portion, and thus has high sensitivity and linearity. It is possible to realize a surface direct energization giant magnetoresistive element that achieves both.

It is a schematic diagram which shows the layer structure of Example 1. FIG. It is a schematic diagram which shows the element structure of Example 1. FIG. (A) is a graph showing the evaluation result of the magnetoresistive effect of the element of Example 1, and (b) is a graph showing the evaluation result of the magnetoresistive effect of the element of Comparative Example 1. (A) is a schematic diagram showing an example of a measurement region in the element thickness direction in smoothness evaluation by cross-sectional element analysis by TEM (transmission electron microscope), and (b) is an elemental analysis result and arithmetic mean roughness. It is a graph of a virtual case which shows the relationship with Ra schematically.

With the substrate
A laminated portion provided on the substrate and formed by alternately laminating n-layer magnetic free layers and n-1 non-magnetic layers.
It is a surface direct energization giant magnetoresistive element having
n is an odd number
The surface direct energization giant magnetoresistive element , wherein the at least one non-magnetic layer has a thickness at which an antiferromagnetic interlayer exchange bond is formed between a pair of magnetic free layers in contact with both sides thereof.

Substrate In the present invention, a laminated portion formed by alternately laminating a plurality of magnetic free layers and a plurality of non-magnetic layers is provided on the substrate.
The substrate is not particularly limited as long as it can be laminated with a magnetic free layer usually made of a ferromagnetic material and a non-magnetic material made of a non-magnetic material, but for example, a single crystal MgO substrate is preferably used. can. Alternatively, Si, a metal, an alloy, or the like, which preferably forms a polycrystal in the magnetic free layer containing a Whistler alloy, may be used as the substrate. From the viewpoint of cost, the surface oxide Si substrate is preferable as a substrate because it is inexpensive, but a silicon substrate for semiconductor production may be used, or a glass substrate or a metal substrate may be used. Regardless of which of these materials is used as the substrate, a surface having the configuration of the present invention and having high sensitivity while exhibiting excellent linearity between the external magnetic field and the resistance value by appropriately designing the substrate. A laminated film for a directly energized giant magnetoresistive element (CPP-GMR) can be obtained.
The thickness of the substrate is not particularly limited and may be appropriately set by those skilled in the art as long as it does not contradict the object of the present invention. .1 to 1 mm is preferable, and 0.2 to 0.5 mm is particularly preferable.

Laminated portion In the present invention, the laminated portion provided on the substrate is formed by alternately laminating n layers of magnetic free layers and n-1 layers of non-magnetic layers.
Here, n is an odd number, and the non-magnetic layer is sandwiched between a pair of magnetic free layers in contact with both sides thereof, so that there are a plurality of free layers. Therefore, at least three magnetic free layers are provided. As a result, at least two non-magnetic layers sandwiched between the two magnetic free layers are provided.
It is more preferable that the number of magnetic free layers is 5 or more. As the number of magnetic free layers increases, the surface direct energization giant magnetoresistive element using the laminated film for the surface direct energization giant magnetoresistive element of the present invention tends to have excellent linearity between the external magnetic field and the resistance value. Is.

In the laminated portion provided on the substrate in the present invention, the number of layers of the magnetic free layer is an odd number. Since the number of magnetic free layers is an odd number, a high reluctance (MR) ratio can be obtained. The mechanism by which a high reluctance (MR) ratio is obtained due to the odd number of layers of the magnetic free layer is not always clear, but when the number of layers of the magnetic free layer is odd, the adjacent magnetic free layers are connected to each other. It is thermally stable when the directions of magnetization are completely reversed from each other, and it has something to do with this thermally stable state when the external magnetic field is zero and showing high electrical resistance. It is presumed to be.

In the laminated portion constituting the laminated film for the surface direct energization giant magnetoresistive element of the present invention, at least one pair of magnetic free layers composed of two adjacent magnetic free layers via a non-magnetic layer. An antiferromagnetic interlayer exchange bond is formed between them. Whether or not an antiferromagnetic interlayer exchange bond is formed can be determined by the ratio of residual magnetization / saturation magnetization measured in the in-plane direction for one non-magnetic layer and a pair of magnetic free layers in contact with both sides thereof. .. That is, by forming an antiferromagnetic interlayer exchange bond between the pairs of magnetic free layers, the saturated magnetic field in the in-plane direction of the pair of magnetic free layers and the non-magnetic layer between them increases, and remains accordingly. Since the ratio of magnetization / saturation magnetization is reduced as compared with the case where the antiferromagnetic interlayer exchange bond is not formed, by measuring this, the antiferromagnetic interlayer exchange bond is formed between the pair of the magnetic free layers. It is possible to judge whether or not it is formed.
Whether or not an antiferromagnetic layer exchange bond is formed between a pair of magnetic free layers depends on the thickness of the non-magnetic layer, if the material of the magnetic free layer and the non-magnetic layer is specified. The formation of an anti-ferrometric layer exchange bond between a pair of magnetic free layers means that the non-magnetic layer forms an anti-ferrometric interlayer exchange bond between the pair of magnetic free layers in contact with both sides thereof. Means to have a thickness. The thickness of the non-magnetic layer is such that the strength of the ferromagnetic exchange bond between the pair of magnetic free layers is the minimum and the strength of the antiferromagnetic interlayer exchange bond between them is the maximum. Is preferable.
The low strength of the ferromagnetic exchange coupling is also preferable from the viewpoint of noise reduction.

An antiferromagnetic interlayer exchange bond is formed between a pair of magnetic free layers composed of two adjacent magnetic free layers via a non-magnetic layer, so that a surface direct current giant magnetoresistive element having high sensitivity can be obtained. It can be realized. It is also relatively easy to improve the linearity between the external magnetic field and the resistance value.
In the laminated portion constituting the laminated film for the surface direct energization giant magnetic resistance element of the present invention, at least one pair of magnetic free layers composed of two adjacent magnetic free layers via a non-magnetic layer. Anti-ferrometric interlayer exchange bonds are formed between them, but it is preferable that anti-ferrometric interlayer exchange bonds are formed between all the pairs of magnetic free layers existing in the laminated portion, in other words, they are present in the laminated portion. It is preferable that all of the non-magnetic layers to be magnetized have a thickness at which an anti-ferrometric interlayer exchange bond is formed between a pair of magnetic free layers in contact with both sides thereof. In the embodiment adopting such a configuration, the reluctance (MR) ratio becomes further excellent.

The pair of magnetic free layers forming an antiferromagnetic interlayer exchange bond via a non-magnetic layer preferably has the same or substantially the same total magnetic moment. By having the same or substantially the same total magnetic moment in the pair of magnetic free layers, the magnetic moments of the pair as a whole are canceled out, and the influence on the magnetic free layers other than the magnetic free layers constituting the pair is reduced. Therefore, it is preferable because it can contribute to the improvement of the linearity between the external magnetic field and the resistance value.

Magnetic-free layer The magnetic-free layer that constitutes the laminated portion of the laminated film for the surface-directed magnetoresistive element of the present invention is a layer containing a ferromagnetic material, and is common with a so-called fixed layer, but its magnetization direction. Is not fixed, which distinguishes it from the so-called fixed layer.
That is, the so-called fixed layer has its magnetization direction fixed by another ferromagnetic layer (also called a pinning layer) adjacent to or adjacent to it, whereas the magnetic free layer has its magnetization direction fixed. However, the direction of magnetization is responsive to an external magnetic field.

The magnetic free layer may be any one capable of forming an antiferromagnetic interlayer exchange bond with another magnetic free layer, and is usually made of a ferromagnetic material or contains a ferromagnetic material, for example, iron ( Fe), cobalt (Co), nickel (Ni), boron (B), manganese (Mn), chromium (Cr), hafnium (Hf), copper (Cu), zirconium (Zr), tantalum (Ta), titanium ( It can be composed of one or more of Ti) and their alloys.
From the viewpoint of the sensitivity of the giant magnetoresistive element, the magnetic free layer preferably contains a Co-based Rousser alloy-based half-metal material.

The whisler alloy has a composition formula of, for example, Co ₂ XY (X = Mn, Fe, Y = Si, Ge, Al, Ga, Sn, As, Ti, V, Cr).
Co ₂ CrZ (Z = Si, Ge, Al, Ga, Sn, As, Ti, V,),
Co ₂ FeAl _0.5 Si _0.5 ,
Co ₂ FeCr _0.5 Al _0.5
Alloys are known.
_{Taking Co 2} MnGe as an example, the Whisler alloy has an A2 structure in which three elements are randomly arranged, Co is arranged at the four corners of bcc (body-centered cubic lattice), and Mn and Ge are randomly arranged in the center of B2. It has three states: the structure and the L21 structure in which Co is at the four corners and Mn and Ge are arranged alternately. As the degree of regularity progresses from the A2 structure to the B2 structure and from the B2 structure to the L21 structure, the polarization rate indicating the properties of the half metal increases. ₂ YZ (Here, Y is at least one element selected from the group consisting of Ti, V, Cr, Mn, and Fe, and Z is composed of Al, Si, Ga, Ge, In, and Sn. It is an element having a composition represented by at least one element selected from the group).
It has been reported that the interlayer exchange bond is caused by the quantum well state formed between the magnetic free layer and the non-magnetic layer, and it is rational that the same effect can be obtained if the materials have similar electronic states. Is estimated. It is reasonable by those skilled in the art that the above materials have similar electronic states to the Co-based Whistler alloy-based half-metal materials for which the effects of the present invention have been experimentally confirmed, and similar effects will be obtained. Understood by.

The thickness of the magnetic free layer is not particularly limited, and an appropriate thickness may be selected in relation to the object of the present invention according to the material and the number of layers of the magnetic free layer and the non-magnetic layer. It is preferably 5 to 50 nm, and particularly preferably 1 to 20 nm.
As an example, when the magnetic free layer has a CFAS ( _{Whisler alloy having a composition of Co 2} FeAl _0.5 Si _0.5 ) and the non-magnetic layer has a laminated portion having a structure of 4 to 6 layers of Ag, the magnetic free layer has a laminated portion. The thickness is preferably 1 to 50 nm, particularly preferably 1 to 20 nm. A film thickness of 0.5 nm or more, more preferably 1 nm or more facilitates control of film formation, and a film thickness of 50 nm or less, more preferably 20 nm or less facilitates subsequent microfabrication.

Non-magnetic layer The non-magnetic layer constituting the laminated portion of the laminated film for the surface direct energization giant magnetic resistance element of the present invention maintains an antiferromagnetic interlayer exchange bond between two adjacent magnetic-free layers via the non-magnetic layer. It suffices to be made of a material that can be used, and there are no other restrictions, but it is preferably made of a non-magnetic metal element in consideration of measuring the electrical resistance in the direction perpendicular to the plane.
Further, from the viewpoint of ease of manufacturing the laminated portion and suppressing the influence of strain and the like due to lattice mismatch, it is preferable that the non-magnetic layer is made of a material having good lattice consistency with the magnetic free layer.
Further, from the viewpoint of the sensitivity and linearity of the magnetoresistive element, it is preferable that the change in spin scattering due to the change in the magnetization direction of the magnetic free layer can be detected more clearly. For example, it is preferably composed of a material having a spin diffusion length of 30 nm or more. It is more preferable that the material is composed of a material having a spin diffusion length of 100 nm or more.

From the above viewpoint, it is particularly preferable that the non-magnetic layer contains at least one element selected from the group consisting of copper (Cu), aluminum (Al), silver (Ag), and zinc (Zn).
Further, it may contain at least one of gold (Au), ruthenium (Ru) and magnesium (Mg).

An antiferromagnetic (AFM) coupled magnetic field is generated via the non-magnetic layer between two magnetic free layers adjacent to each other via the non-magnetic layer. It is preferable that the non-magnetic layer has a thickness such that the strength of the ferromagnetic bond between the pair of magnetic free layers is minimized and the antiferromagnetic bond is formed between them. The thickness of such a suitable non-magnetic layer may vary depending on the constituent elements, composition, crystal system, etc. of the magnetic free layer and the non-magnetic layer, but is usually in the range of 0.1 to 10 nm.

Since the interlayer coupling between the magnetic free layers periodically repeats ferromagnetism and antiferromagnetism with respect to the film thickness of the non-magnetic layer, it is possible to set the optimum film thickness of the non-magnetic layer experimentally. Yes and preferred. When an antiferromagnetic interlayer exchange bond is formed, the saturated magnetic field in the in-plane direction increases. By measuring the ratio of residual magnetization / saturation magnetization in the direction, it is possible to experimentally determine the optimum thickness of the non-magnetic layer. When an antiferromagnetic interlayer exchange bond is formed between a pair of magnetic free layers, the saturated magnetic field in the in-plane direction of the pair of magnetic free layers and the non-magnetic layer between them increases, and the residual magnetization / The ratio of saturation magnetization is reduced as compared to the case where the antiferromagnetic interlayer exchange bond is not formed. If the numerical value of the ratio of residual magnetization / saturation magnetization in the in-plane direction itself is, for example, 0.8 or less, it can be determined that the film thickness is such that an antiferromagnetic interlayer exchange bond is formed. .. The ratio of residual magnetization / saturation magnetization in the in-plane direction is more preferably 0.5 or less, and even more preferably 0.2 or less.
For example, when the magnetic free layer is CFAS ( _{Whisler alloy having a composition of Co 2} FeAl _0.5 Si _0.5 ) and the non-magnetic layer is Ag, it is cyclically ferromagnetic / antiferromagnetic with respect to the film thickness of the Ag layer. The phenomenon of repeating ferromagnetism disappears when the thickness of the Ag layer exceeds, for example, 5 nm. On the other hand, when the film thickness of the Ag layer is, for example, less than 0.5 nm, a ferromagnetic bond may appear due to the discontinuity of the film or the like. Therefore, in the case of this material system, it is preferable to set the optimum film thickness of the Ag layer by experiment or simulation, for example, in the range of 0.5 to 5 nm.

Other Layers The laminated film for the surface direct energization giant magnetoresistive element of the present invention and the surface direct energization giant magnetoresistive element using the same are the above-mentioned substrate, the magnetic free layer, and the magnetic free layer, as long as it does not contradict the object of the present invention. It may have a layer other than the non-magnetic layer.

For example, it is preferable to provide a buffer / electrode layer (base layer), a cap layer, and the like as needed.
The buffer / electrode layer (base layer) referred to here is not a layer that serves as a base for the magnetoresistive (MR) sensor element, but a layer that is included in the sensor configuration, and is provided between the base and the laminated portion. It is a thing.
The buffer / electrode layer has a function of performing lattice matching between the substrate and the laminated portion and / or a function of serving as an electrode for measuring magnetic resistance, and when it has the former function, it is simply referred to as a buffer layer. When it has the latter function, it may be simply referred to as an electrode layer, and both functions may be collectively referred to as a buffer layer / electrode layer. It may also be commonly referred to as a base layer.
The buffer layer / electrode layer may be one layer having both functions, or may be a laminate of a layer having the function of the buffer layer and a layer having the function of the electrode layer, and is a preferable example. A Cr / Ag laminate can be mentioned.
When the buffer / electrode layer has a function as an electrode layer, the buffer / electrode layer serves as an electrode for measuring magnetic resistance, and for example, at least one kind of metal selected from Ag, Al, Cu, Au, Cr and the like, and these. Alloys of metallic elements can be preferably used, but are not limited thereto.
The buffer / electrode layer may have a two-layer structure composed of a plurality of metal / alloy layers or a multi-layer structure having three or more layers.
The thickness of the buffer / electrode layer is not particularly limited and may be appropriately set by those skilled in the art as long as it does not contradict the object of the present invention, but the effect on ensuring conductivity and the magnetic free layer and the non-magnetic layer is limited. From the viewpoint of magnetism and the like, it is preferably 5 to 1000 nm, and particularly preferably 20 to 500 nm.

The buffer layer may be provided on the lower side (base side) of the electrode layer. At this time, the buffer layer can also be referred to as an alignment layer, which has an action of giving a desired orientation to the free magnetic layer, for example, orientation in the (001) direction, and is, for example, an Ag, Al, Cu, Au, Cr alloy. It is preferable to use one containing at least one kind, but the present invention is not limited thereto.
The thickness of the buffer layer (alignment layer) is not particularly limited and may be appropriately set by those skilled in the art as long as it does not contradict the object of the present invention. It is preferably 1 to 100 nm, and particularly preferably 0.1 to 20 nm.
Although the results of the magnetoresistive element oriented in the (001) direction are shown in Examples and the like, if the magnetic free layer and the non-magnetic layer satisfy the requirements specified in claim 1 of the present application, the growth crystal orientation of the element can be set. The same effect can be obtained with the (110) and (211) orientations that do not depend on each other.

The cap layer is a layer containing a metal or alloy for surface protection. The cap layer is also a layer in the sensor configuration and can also be referred to as a ferromagnetic layer lid.
The cap layer may contain at least one kind of metal selected from, for example, Ag, Al, Cu, Au, Cr and the like, or an alloy of these metal elements may be used.
The thickness of the cap layer is not particularly limited and may be appropriately set by those skilled in the art as long as it does not contradict the object of the present invention, but it is preferably 1 to 100 nm from the viewpoint of sufficiently protecting the surface. It is particularly preferably 3 to 20 nm.
As the cap layer, one kind of material may be used, or two or more kinds of materials may be laminated.

From the viewpoint of reliably and stably realizing a sufficiently strong antiferromagnetic interlayer exchange bond between the magnetic-free layers, the buffer / electrode layer surface, the interface between the magnetic-free layer and the non-magnetic layer, and the cap layer surface. It is preferable that at least one has high smoothness.
From the viewpoint of the strength and stability of the antiferromagnetic interlayer exchange bond between the magnetic free layers (ferromagnetic layers), the smoothness of the interface between the magnetic free layer and the non-magnetic layer is important, but in order to realize it. The smoothness of the buffer / electrode layer surface is important, and in many cases, the buffer / electrode layer surface needs to have high smoothness. When the smoothness of the interface between the buffer / electrode layer surface and the magnetic free layer / non-magnetic layer is good, the smoothness of the cap layer surface is also improved in most cases, so the smoothness of the cap layer surface is evaluated. By doing so, the smoothness of the interface between the magnetic free layer / non-magnetic layer can be indirectly evaluated.
More specifically, the smoothness Ra of at least one of the buffer / electrode layer surface, the interface between the magnetic free layer and the non-magnetic layer, and the cap layer surface is preferably 0.75 nm or less, preferably 0.5 nm or less. Is more preferable, and 0.25 nm or less is particularly preferable. It is particularly preferable that all the smoothness Ras of these surfaces and interfaces satisfy the above conditions.
There is no particular lower limit to the smoothness Ra of at least one of the buffer / electrode layer surface, the interface between the magnetic free layer and the non-magnetic layer, and the surface of the cap layer, but Ra is the smoothness obtained by a normal process. It is realistic that it is 0.1 nm or more.
In the present application, the arithmetic average roughness Ra measured for an area of 50 nm × 50 nm or more is used as an index of interfacial smoothness. The method for measuring the interfacial smoothness is not particularly limited, and the evaluation method used in the art can be appropriately used. For example, cross-sectional observation by a TEM (transmission electron microscope) or AFM (atomic force) can be used. It can be measured by smoothness evaluation with a force microscope).

That is, in the manufacturing process, the surface smoothness and the interfacial smoothness can be obtained by the smoothness evaluation by AFM or the like on the upper part of the laminated film. At this time, Ra is measured and measured in an area of 50 nm × 50 nm or more. This is because if the area is too small, Ra may become extremely small. Further, in the completed device, the smoothness can be measured by observing the cross section by TEM having atomic resolution.
An example of a method for measuring the arithmetic mean roughness Ra of an interface such as a laminated portion by observing a cross section by TEM will be described below.
By using HAADF-STEM (High-angle Anal Dark Field Scanning TEM) and elemental analysis by EDS (Energy Dispersive X-ray Spectroscopy) in combination to prepare the observation sample, atomic-level component analysis of the sample cross section can be performed. It will be possible. Using this, component analysis near the interface is performed, and the thickness in the element thickness direction of the mixed region where the elemental components of the upper layer and the elemental components of the lower layer are mixed is measured, and then the interface smoothness (arithmetic mean roughness) is measured. S) Ra can be estimated. Due to the unevenness of the interface, both the elemental component of the upper layer and the elemental component of the lower layer are mixed at the same position in the element thickness direction. Therefore, the larger Ra, the larger the thickness of the mixed region in the element thickness direction. This is to become.
More specifically, by observing the cross section of the device and mapping the elements using the above method, the cross section analysis as schematically shown in FIG. 4 becomes possible. The element shown in FIG. 4A has a two-layer structure in which the upper layer is composed of the component a and the lower layer is composed of the component b, and observation / element mapping is performed on the measurement region shown by the solid line ab in the element thickness direction near the interface. And, the component distribution in the element thickness direction as schematically shown in FIG. 4B can be obtained. In FIG. 4B, the horizontal axis is a position (arbitrary scale) in the element thickness direction, and indicates a distance from the substrate. The vertical axis is the component ratio (%), and the solid line represents the ratio of the component a and the dotted line represents the ratio of the component b. The left side near the substrate on the horizontal axis (in the element thickness direction) is the lower layer, and the component b occupies most of it. The right side separated from the substrate on the horizontal axis (in the element thickness direction) is the upper layer, and the component a occupies most of it. In the figure, the portion of the a (upper layer) component of 20 to 80% in the component ratio also has the b (lower layer) component of 20 to 80%, which is defined as a mixed region. As described above, the mixed region can be evaluated as indicating the unevenness of the interface, and the thickness of the mixed region in the element thickness direction is twice the interfacial smoothness Ra. Therefore, the element thickness of the mixed region obtained by the above measurement is obtained. The interfacial smoothness Ra can be specified by dividing the thickness in the direction by 2.
This measuring method indirectly evaluates the interfacial smoothness Ra, and although it includes some errors, it matches the smoothness evaluation by AFM or the like with an accuracy of about 20% or less.
Examples of actual element cross-section observation and element mapping results by the above method are described in Jung et al. , Apple. Phys. Let. , 108, 102408 (2016) FIG. It is described in 4th grade.
The TEM used in the above evaluation method preferably has atomic-level resolution, and for example, Titan G2 manufactured by FEI Company can be preferably used.
The above-mentioned HAADF-STEM (High-angle Anal Dark Field Scanning TEM) image is obtained by applying a finely focused electron beam to a sample while scanning it, and detecting the transmitted electrons scattered at a high angle with an annular detector. It is obtained.
The sample is generally adjusted to a TEM sample thickness of several to several tens of nanometers (the thickness direction of the sample corresponds to the in-plane direction of the interface such as a magnetic free layer / non-magnetic layer). In the case of the Whistler alloy / Ag typical as the magnetic free layer / non-magnetic layer constituting the laminated portion of the present invention, the TEM sample thickness is generally adjusted in the range of 30 nm to 50 nm. At this time, in order to set the analysis area as an area of 50 nm × 50 nm or more required for the interface / surface smoothness measurement in the present application, the interface smoothness is evaluated at the interface having a width of 70 nm or more.

In the present invention, as a layer exhibiting ferromagnetism, an odd number of magnetic free layers having three or more layers is provided, and the desired effect is realized by an odd number of magnetic free layers having three or more layers. that it does not require.

Manufacturing Method There is no particular limitation on the manufacturing method of the laminated film for the surface direct energization giant magnetoresistive element of the present invention and the surface direct energization giant magnetoresistive element provided with the same, and a method capable of precisely laminating a metal thin film or a metal compound thin film can be used. It may be appropriately selected by a person skilled in the art, but it is preferably produced by a sputtering method.

It is possible to appropriately perform annealing after forming a part or all of the laminated film for the surface direct energization giant magnetoresistive element of the present invention. The timing of annealing is not particularly limited, and it is preferable to perform annealing at an appropriate timing according to the annealing temperature, heat resistance of each layer, and the like. In the present embodiment, the buffer / electrode layer, the laminated portion (alternately magnetic-free layer and non-magnetic layer), and the cap layer are formed on the substrate, so that at least the laminated portion is formed. It is preferable to perform annealing later. Further, annealing may be performed after forming the cap layer, or when the annealing temperature is high, for example, 600 ° C. or higher, the film is formed up to the laminated portion and then annealed, and then the cap layer is formed. May be good.
The temperature of annealing is not particularly limited, but the crystallinity can be improved by performing the annealing at a temperature of, for example, 300 ° C. or higher, preferably 350 ° C. or higher, more preferably 400 ° C. or higher.

Applications The magnetoresistive element using the laminated film for the surface direct current enormous magnetic resistance element of the present invention can realize high sensitivity and it is relatively easy to improve the linearity between the external magnetic field and the resistance value. It can be particularly preferably used in HDD lead heads, high-sensitivity current sensors, etc., which require high sensitivity, and geomagnetic sensors, current sensors, etc., which require linearity between an external magnetic field and a resistance value.

Although the present invention has been described above by taking a specific embodiment as an example, the present invention is not limited to the embodiments described in the above-described embodiment, and various modifications can be made as long as it does not deviate from the gist of the present invention. Is.

Hereinafter, the present invention will be specifically described with reference to Examples / Comparative Examples. The present invention is not limited to the following examples in any sense.

(Example 1)
As Example 1 of a laminated film having 5 magnetic free layers and 4 non-magnetic layers (Ag, thickness: 2 nm), _{Co 2} Fe (Al _0.5 Si _0.5 )) (hereinafter, also referred to as “CFAS”. ) And Ag were used to prepare a laminated film for surface direct current giant magnetic resistance (CPP-GMR). The number n of the magnetic free layers was set to 5 which is an odd number. The film thickness of the Ag layer (non-magnetic layer) was 2 nm, which is a thickness indicating an antiferromagnetic interlayer exchange bond, and the number of layers (n-1) was four.
FIG. 1 shows the layer structure (CFAS: 5 layers) of the produced laminated film for a surface direct energization giant magnetoresistive element. MgO substrate / Cr (10 nm) / Ag (100 nm) / CFAS (3 nm) / (Ag (2 nm) / CFAS (3 nm)) _n-2 / Ag (2 nm) / CFAS (3 nm) / Ag (5 nm) / Ru ( A laminated film for single crystal CPP-GMR oriented at 8 nm) and (001) was prepared.
The number of magnetic free layers was 5 (n = 5).
The heat treatment of the laminated film was performed at 400 ° C. for 30 minutes after laminating the upper Ru layer. Furthermore, using photolithography, pillars having a size of 200 × 100 nm were created. FIG. 2 shows the cross-sectional structure of the pillar.
The magnetic resistance was measured by measuring the electrical resistance by the DC 4-terminal method while changing the magnetic field applied in the minor axis direction of the rectangular shape obtained by photolithography. The measurement result of the magnetic resistance is shown in FIG. In FIG. 3, the portion showing a linear response was approximated to a straight line, and the non-linearity, which is the deviation from the approximate straight line of the portion, was calculated according to the following (formula). It showed good linearity.

Ｒ（ｍｅａｓ）： 抵抗Ｒの測定値
Ｒ（ｆｉｔ）： 抵抗Ｒの近似値
（Ｒ（ｍｅａｓ）−Ｒ（ｆｉｔ））ｍａｘ：
直線近似範囲におけるＲ（ｍｅａｓ）−Ｒ（ｆｉｔ）の最大値
Ｒ（ｍａｘ）： 直線近似範囲における抵抗Ｒの測定値の最大値
Ｒ（ｍｉｎ）： 直線近似範囲における抵抗Ｒの測定値の最少値 (formula)

R (meas): Measured value of resistor R R (fit): Approximate value of resistor R (R (meas) -R (fit)) max:
Maximum value of R (meas) -R (fit) in the linear approximation range R (max): Maximum value of the measured value of resistance R in the linear approximation range R (min): Minimum value of the measured value of resistance R in the linear approximation range

Further, when the magnetic resistance (MR) ratio was calculated from the change in the resistance value of the element with respect to the external magnetic field according to the following formula, the MR ratio was 60%, which was an extremely high value.

(Comparative Example 1)
Laminated film having 6 magnetic free layers and 5 non-magnetic layers (Ag, thickness: 2 nm) The number of layers n of the magnetic free layers is an even number, and the number of Ag layers (non-magnetic layers) (n−). A laminated film for surface direct current giant magnetoresistance (CPP-GMR) using CFAS and Ag was produced in the same manner as in Example 1 except that 1) was made into 5 layers.
FIG. 3B shows the change in the resistance value of the pillar with respect to the external magnetic field. The non-linearity was 0.5% FS, showing good linearity, but the MR ratio was 39%, which was significantly lower than that of Example 1.

The surface direct energization giant magnetoresistive element of the present invention has high sensitivity that could not be realized by the prior art, and can improve the linearity between the external magnetic field and the resistance value relatively easily, so that the sensitivity is high. It has high practical value, such as being able to realize a surface-directed giant magnetoresistive element that achieves both linearity, and is high in various fields of industry such as navigation in electrical and electronic equipment, information communication, and transportation equipment. Has availability.

Claims (10)

With the substrate
A laminated portion provided on the substrate and formed by alternately laminating n-layer magnetic free layers and n-1 non-magnetic layers.
It is a surface direct energization giant magnetoresistive element having
n is an odd number
The at least one non-magnetic layer has a thickness at which an antiferromagnetic interlayer exchange bond is formed between a pair of magnetic free layers in contact with both sides thereof, and has no magnetic fixing layer.
The above-mentioned surface direct energization giant magnetoresistive element . The surface direct energization giant magnetoresistive element according to claim 1, wherein all of the non-magnetic layers have a thickness in which an antiferromagnetic interlayer exchange bond is formed between a pair of magnetic free layers in contact with both sides thereof. Claimed that the ratio of residual magnetization / saturation magnetization measured in the in-plane direction for one non-magnetic layer on which an antiferromagnetic interlayer exchange bond is formed and a pair of magnetic free layers in contact with both sides thereof is 0.8 or less. Item 2. The surface direct current enormous magnetoresistive element according to Item 1 or 2. The surface direct communication according to any one of claims 1 to 3, wherein the pair of the magnetic free layers forming the antiferromagnetic interlayer exchange bond via the non-magnetic layer has the same or substantially the same total magnetic moment. Giant magnetoresistive element . The surface direct conduction giant magnetoresistive element according to any one of claims 1 to 4, wherein the magnetic free layer contains a Co-based Hoisler alloy-based half metal material. The Co-based Whistler alloy-based half-metal material is Co2YZ (where Y is at least one element selected from the group consisting of Ti, V, Cr, Mn, and Fe, and Z is Al, Si, The surface direct energization giant magnetic resistance element according to claim 5, which has a composition represented by at least one element selected from the group consisting of Ga, Ge, In, and Sn). The surface direct conduction giant magnetoresistive element according to any one of claims 1 to 6, wherein the non-magnetic layer is composed of a material system having a spin diffusion length of 30 nm or more. The surface direct conduction giant magnetoresistive element according to any one of claims 1 to 7, wherein the non-magnetic layer contains at least one element selected from the group consisting of Cu, Al, Ag, and Zn. The surface direct energization giant magnetoresistive element according to any one of claims 1 to 8, further comprising a buffer / electrode layer and a cap layer. A geomagnetic sensor, a current sensor, or a magnetic head comprising the surface direct energization giant magnetoresistive element according to any one of claims 1 to 9.

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