JP2006196708A - Magnetic-information recording element, method for generating magnetic domain wall thereof and magnetic-information recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable an increase in a capacity and an increase in an integration degree in a high-density magnetic-information recording medium in the next generation. <P>SOLUTION: A magnetic-information recording element 1 is constituted having a constrictor 5 at approximately a central section in the longitudinal direction of a ferromagnetic structure in a nano-scale order. In the recording of a magnetic information, a magnetic domain wall is generated in the constrictor by making a current higher than a specified critical current density j<SB>1</SB>flow through the magnetic-information recording element 1. In the erasing of the magnetic information, the magnetic domain wall is expelled by making the current higher than a magnetic-domain wall moving current density j<SB>2</SB>flow. In the reading of the magnetic information, a reading current density j<SB>3</SB>in the relationship of j<SB>3</SB><j<SB>2</SB><j<SB>1</SB>is made to flow. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a magnetic information recording element, a magnetic information recording medium, and a magnetic wall generating method for a magnetic information recording element using a domain wall generation mechanism by current drive.

  Recently, various information recording elements based on a new principle have been developed. For example, an information recording element called an MRAM (Magnetic Resistive Random Access Memory) in which a tunnel type magnetoresistive element (hereinafter referred to as “TMR element”) is arranged in a memory cell in a lattice arrangement. (For example, refer nonpatent literature 1).

  This MRAM is a kind of non-volatile memory that uses a magnetic material similar to a hard disk as an information recording element, and has a structure in which an insulating thin film having a thickness of several atoms is sandwiched between two ferromagnetic thin films. A three-layer structure is adopted.

  Information writing in the MRAM is performed as follows. In the TMR element constituting the MRAM, the direction of the electron spin in one ferromagnetic thin film is fixed, and the direction of the electron spin in the other ferromagnetic thin film can be changed. For example, the case where both electron spin directions are parallel is made to correspond to “0”, while the case where both electron spin directions are antiparallel is made to correspond to “1” to record information. Yes. The direction of electron spin is controlled by a magnetic field applied from the outside.

  In addition, the reading of information in the MRAM utilizes the characteristic that the electric resistance of the TMR element changes depending on the direction of the electron spin. In the TMR element, when the directions of the electron spins in one and the other ferromagnetic thin films are parallel, the electric resistance value becomes small. Conversely, when the directions of the electron spins are antiparallel, the electric resistance value is low. Becomes larger. Therefore, by detecting the change in the electric resistance value, the spin state of the TMR element can be known, and the bit information stored in the TMR element can be extracted.

  The MRAM has an address access time in the 10 ns range and a cycle time in the 20 ns range, which is about five times faster than a DRAM and can be read and written as fast as an SRAM. In addition, the flash memory has an advantage that low power consumption and high integration can be achieved.

  Furthermore, with the announcement of an MRAM chip having a capacity of 256 kbit by Motorola in February 2001, expectations for the next generation memory technology are increasing.

Roy Scheuerlein et. al. “A 10 ns Read and Write Non-Volatile Memory Array Using a Magnetic Tunnel Junction and FET Switch in search Cell”, ISSCC 2000 Technical Digg. 128-pp. 129

  However, the conventional MRAM disclosed in Non-Patent Document 1 and the like has a configuration in which 1-bit data is stored by two MOS transistors and two TMR elements, so that it is difficult to increase the capacity and the integration. was there.

  In addition, in the conventional MRAM, an externally applied magnetic field is used as described above in writing information. Therefore, when TMR elements are arranged at a high density, a write magnetic field generated at an arbitrary lattice point is adjacent to the TMR. There has been a problem of causing mutual interference that disturbs the magnetization state of the element. Therefore, there is a problem that it is necessary to ensure a constant element spacing in relation to the strength of the writing magnetic field, and it is difficult to achieve high integration in this respect.

  The present invention has been made in view of the above, and an object of the present invention is to provide a magnetic information recording element and a magnetic information recording medium that are excellent in large capacity and high integration. It is another object of the present invention to provide a domain wall generation method for the magnetic information recording element.

  In order to solve the above-described problems and achieve the object, the magnetic information recording element according to claim 1 is characterized by having a constricted portion at a substantially central portion in the longitudinal direction of a ferromagnetic structure of nanoscale order.

  The magnetic information recording element according to claim 2 is characterized in that the ferromagnetic structure is a columnar structure.

  The magnetic information recording element according to claim 3 is characterized in that the ferromagnetic structure is a substantially gourd-type structure.

  Further, in the magnetic information recording element according to claim 4, the length of the constricted portion in the short direction is uniform, and the length in the short direction is long-short-length for the entire element. It is formed by such a three-layer structure.

  The magnetic information recording element according to claim 5, wherein the nanoscale-order ferromagnetic structure has a three-layer structure, and the magnetic material at both ends of the three-layer structure is different from the magnetic material at the center. It is characterized by comprising.

  The magnetic information recording element according to claim 6 is characterized in that each of the magnetic bodies at both ends is made of a different magnetic material.

  A magnetic information recording medium according to claim 7 uses the magnetic information recording element according to any one of claims 1 to 6 as a magnetic information recording element applied to an MRAM. .

  The magnetic information recording medium according to claim 8 uses the magnetic information recording element according to any one of claims 1 to 6 as a magnetic information recording element applied to a patterned medium. And

  The domain wall generating method for a magnetic information recording element according to claim 9 is a domain wall generating method for a magnetic information recording element having a constricted portion at a substantially central portion in a longitudinal direction of a ferromagnetic structure of a nanoscale order. A step of bringing the magnetic information recording element into a uniform magnetization state, and a step of passing a current equal to or higher than a predetermined critical current density to the magnetic information recording element.

  The magnetic information recording element according to the present invention has a structure having a constricted portion at a substantially central portion in the longitudinal direction of a nanoscale-order ferromagnetic structure, so that the domain wall can be easily generated. Play.

  Further, according to the magnetic information recording medium according to the present invention, since the magnetic information recording elements according to the present invention as described above can be arranged discontinuously and with high density, magnetic information such as MRAM and patterned media can be obtained. There is an effect that the recording density can be improved by simply applying to a recording medium.

  According to the magnetic wall generating method of the magnetic information recording element according to the present invention, the magnetic wall is generated by flowing a current having a predetermined critical current density or higher without using a magnetic field. When used in an information recording medium, it is possible to prevent the occurrence of mutual interference that disturbs the magnetization state (recording state) of adjacent recording elements, and the recording density can be improved.

  Hereinafter, embodiments of a magnetic information recording element, a magnetic information recording medium, and a domain wall generating method of the magnetic information recording element of the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to these embodiments.

(Structure of magnetic information recording element)
First, the structure of the magnetic information recording element will be described. FIG. 1 is a schematic diagram showing the structure of a magnetic information recording element according to the present invention. A magnetic information recording element 1 shown in FIG. 1 is a nanoscale microferromagnetic material having a columnar structure. As shown in the figure, in the magnetic information recording element 1 which is a microferromagnetic material, constrictions 2 are formed at both ends of a substantially central portion in the longitudinal direction. As a result, the magnetic information recording element 1 has a form as a columnar structure having a constricted portion 5 such that the length in the short direction of the magnetic information recording element 1 is shortened at a substantially central portion in the longitudinal direction. Further, in the longitudinal direction of the figure, for example, magnetization 3 is generated from the bottom to the top of the figure by a magnetic field applied from the outside.

(Concept of domain wall generation mechanism in magnetic information recording element)
Next, the domain wall generation mechanism in the magnetic information recording element 1 shown in FIG. 1 will be described with reference to FIG. FIG. 2 is a diagram for explaining the concept of the domain wall generation mechanism in the magnetic information recording element 1 shown in FIG. In FIG. 2, when a high-density current is passed through an arbitrary portion of the uniformly magnetized magnetic information recording element 1, the uniform magnetization state is destabilized at a certain critical current density (j ₁ ) or more. At this time, for example, as shown in the figure, the magnetization of the lower half of the constricted part 5 is reversed to form antiparallel magnetizations 3a and 3b, and the domain wall 6 is generated in the constricted part 5 part. . The generation process of the domain wall 6 has a kind of interface energy (energy per unit area) property. Therefore, if it has a part where interface energy becomes large locally, it will be thought that generation of domain wall 6 becomes easy. The portion of the constricted portion 5 shown in FIG. 1 is a portion formed as a portion where such interfacial energy is locally increased. The domain wall 6 generated in the portion of the constricted portion 5 acts as a bearer of information as will be described later.

  By the way, the above-mentioned domain wall generation mechanism is based on a completely new concept that does not exist in the prior art. This is because, conventionally, when generating such a domain wall, an external magnetic field is used. On the other hand, in the present invention, this is realized by flowing a current of a certain value or more without using an external magnetic field. That is, the present invention is a novel part that does not exist in the prior art in that the domain wall is generated using only the current action regardless of the magnetic field action.

(Basic principle of domain wall generation mechanism)
Next, the basic principle of the domain wall generation mechanism will be described. In general, even if a current is passed through a perfectly uniform ferromagnetic material, the torque due to the spin-polarized current does not work. On the other hand, when the magnetization in a ferromagnet is spatially changing, there is a spin-polarized current (current that flows when the spin angular momentum of electrons carrying the current is adiabatically aligned with the direction of magnetization). By flowing, torque is generated in the magnetization. This torque is generated by the interaction between magnetization and electron spin angular momentum. That is, the spin-polarized current promotes a spatial direction change with respect to the magnetization. As described above, even if a current is passed through a perfectly uniform ferromagnetic material, torque due to the spin-polarized current does not work, but depending on the thermal fluctuation or its shape, the magnetic charge that appears on the boundary surface As a result, the direction of magnetization changes locally. For example, when the current density is locally increased using a point contact or the like, non-uniformity occurs in the current direction in the vicinity of the contact between the point contact and the ferromagnetic material. In other words, even with a uniformly magnetized ferromagnet, by passing a current, the magnetization is locally subjected to torque based on the spin-polarized current, changing its direction, and further flowing a sufficiently large current. The torque based on the spin-polarized current increases and the uniform magnetization state becomes unstable. If the uniform magnetization state becomes unstable, a multi-domain structure is formed as a result of turning it over, and a domain wall is generated at the boundary.

  The above description describes the domain wall generation mechanism from a phenomenological point of view. The domain wall generation mechanism is described from the viewpoint of energy as follows.

  When a current is passed through a uniformly magnetized ferromagnet, the dispersion energy of the spin wave in the uniform magnetization state decreases due to the spin-polarized current, the dispersion energy becomes zero above a certain critical current, and the uniform magnetization state becomes It becomes unstable. On the other hand, when a domain wall is present, the dispersion energy does not become zero even when the critical current is exceeded, and is stable against spin waves. Also, in the case of a uniform magnetization state and one static domain wall, the energy of both of them is lower in the latter case above the critical current. Therefore, when these results are integrated, it means that the uniform magnetization state becomes unstable above the critical current, a multi-domain structure is formed, and a domain wall is generated at the boundary. Note that the number of domain walls to be generated is not limited to one, but is determined based on the shape of the ferromagnetic material, the magnetostatic energy, and the like.

  Next, basic operations when the above-described domain wall generation mechanism is used as a magnetic information recording element, that is, (1) information recording, (2) information erasing, and (3) information reading operations will be described.

(Basic operation-recording magnetic information)
First, recording of magnetic information in the magnetic information recording element 1 will be described with reference to FIG. In the recording of magnetic information, the basic principle of the present invention is used that "if a current exceeding a certain critical current flows through a ferromagnetic material, the uniform magnetization state becomes unstable and a domain wall is generated". . That is, in the uniformly magnetized magnetic information recording element 1 as shown in the left diagram of FIG. 2, when a current of a certain critical current density j ₁ or more is passed, as shown in the right diagram of FIG. A domain wall 6 is generated at 5. The critical current density j ₁ is given by the following equation from theoretical analysis.

j ₁ = ( ² eS ² / η) · √ (J) · [√ (K ₁ + K ₂ )] (1)
(√ (J) in the formula represents the square root of J)
In equation (1), e is elementary charge, S is the magnitude of spin of ferromagnetic magnetization, η is Planck's constant, J [J / m] is exchange interaction constant, and K ₁ [J / m ³ ] is easy magnetization Anisotropic energy density in the magnetic domain, K ₂ [J / m ³ ] is an anisotropic energy density in the hard axis of magnetization.

  The constricted portion 5 is a stabilizing means for stably holding the generated domain wall 6 in the magnetic information recording element 1, and is so-called “pinning”. The constricted portion 5 acting as such a domain wall stabilizing means (pinning) utilizes the property that the anisotropic energy is locally reduced in the narrowed constricted portion.

Note that K ₁ and K ₂ shown in Equation (1) are parameters that depend on the substance used, shape, and the like. Therefore, the magnitude of the critical current density j ₁ can be controlled by adjusting these parameters.

Further, after being generated magnetic wall 6 to the magnetic information recording device 1 once, but the domain wall 6 which is the product must be stabilized, it is only necessary to cut off the critical current density j ₁ This treatment was simply applied. This is because the domain wall 6 once generated is in an energetically stabilized state, and such an energetically stable state is maintained by cutting off the critical current density j ₁ .

(Basic operation-Erase magnetic information)
Next, erasing of magnetic information in the magnetic information recording element 1 will be described with reference to FIG. In erasing magnetic information, the principle that “the generated domain wall is driven out by the current action by passing a predetermined current density j ₂ in the domain wall state” is used. That is, in the magnetic information recording element 1 in which the domain wall 6 as shown in the right diagram of FIG. 4 is generated, when a predetermined current is applied so as to have a certain current density j ₂ (j ₂ <j ₁ ), It returns to the state of uniform magnetization shown in the left figure. This operation corresponds to erasure of magnetic information. If the current density at this time is defined as the domain wall motion current density, this domain wall motion current density j ₂ is given by the following equation.

j ₂ = [4e / (a ³ η)] · (αVλ ² / ξ) (2)

  In equation (2), e is an elementary charge, a is a lattice constant, is a Planck constant, α is a Gilbert damping constant, V is a pinning potential magnitude, λ is a domain wall width, and ξ is an effective range of the pinning potential. It is.

In addition, a, α, V, ξ, and λ shown in the equation (2) are parameters that depend on the substance and shape to be used. Therefore, by adjusting these parameters, the magnitude of the domain wall motion current density j ₂ can be controlled to satisfy j ₂ <j ₁ .

(Basic operation-reading information)
Next, reading of information in the magnetic information recording element 1 will be described. As a general characteristic, when a current is passed through a ferromagnetic material, a phenomenon called a magnetoresistance effect is observed in which the electric resistance varies depending on the spatial configuration of the magnetization. This magnetoresistive effect can be used when reading magnetic information recorded on the magnetic information recording element 1 according to the present invention. In the magnetic information recording element 1, when the uniform magnetization state (state in which the domain wall is not included) and the domain wall state (state in which the domain wall is included) are compared, the electric resistance is lowered in the domain wall state. Therefore, it is possible to cope with reading of magnetic information by using a fact that a predetermined current is passed through the magnetic information recording element 1 and the resistance varies depending on the presence or absence of a domain wall.

For example, “0” can be associated with the resistance value (high resistance) in the uniform magnetization state, and “1” can be associated with the resistance value (low resistance) in the domain wall state. Note that the read current density j ₃ , which is the current density at this time, has a relationship of j ₃ <j ₂ <j _{1 with} the previous j ₁ and j ₂ . If j ₃ having such a relationship is used, the magnetic information recorded in the magnetic information recording element 1 is read without affecting the uniform magnetization state or the domain wall state, that is, without changing each state. be able to.

(Structure of Magnetic Information Recording Element—Modification 1)
FIG. 3 is a diagram showing another structure (modification 1) of the magnetic information recording element. As described above, the main point of the present invention is to destabilize the uniform magnetization state by the applied current, and for that purpose, it is only necessary to provide a constricted portion where the current density increases locally. Therefore, it may have a gourd type (or array type) structure having a constricted portion in the vicinity of the substantially central portion in the longitudinal direction, like the magnetic information recording element 8 shown in FIG.

(Structure of Magnetic Information Recording Element—Modification 2)
FIG. 4 is a diagram showing another structure (modification 2) of the magnetic information recording element. In the magnetic information recording element 10 shown in the figure, the constriction created in the ferromagnetic material has a steeper structure than the magnetic information recording element 1 shown in FIG. 1, and has a small contact portion in the ferromagnetic material. . By adopting such a configuration, a ballistic magnetoresistive effect (hereinafter referred to as “BMR effect”) is expected. This BMR effect can provide a higher resistance ratio than the anisotropic magnetoresistive effect (hereinafter referred to as “AMR effect”), which is a general magnetoresistive effect. It is suitable for. The difference between the effects of the AMR effect and the BMR effect will be described later.

(Structure of Magnetic Information Recording Element—Modification 3)
FIG. 5 is a diagram showing another structure (Modification 3) of the magnetic information recording element. 1, 3, and 4 exemplify the structure of a magnetic information recording element having a constricted portion in the vicinity of the substantially central portion in the longitudinal direction. However, like these constricted portions, the constricted portion is not necessarily short. It is not necessary to have a structure in which the length in the hand direction continuously decreases. For example, as in the magnetic information recording element 20 shown in FIG. 5, the short direction of the constricted portion has a uniform length, and the length in the short direction is long-short-long in the entire magnetic information recording element 20. It is also possible to adopt a structure formed of a ferromagnetic material having a three-layer structure. As the magnetic information reading method, the same method as that of other structures can be used.

(Structure of Magnetic Information Recording Element—Modifications 4 and 5)
FIG. 6 is a diagram showing another structure (Modification 4) of the magnetic information recording element, and FIG. 7 is a diagram showing another structure (Modification 5) of the magnetic information recording element. The difference between FIG. 5 and FIG. 6 is that instead of adopting a structure in which the length in the short direction is the same, the magnetic body (F ₁ ) at both ends and the magnetic body (F ₂ ) at the center in the three-layer structure. ) And different materials are used. As shown in FIG. 6, when the magnetic body at the center is different from the magnetic bodies at both ends, the balance of the spin torque between the two becomes large, and the magnetization reversal becomes easy. Therefore, a predetermined domain wall can be generated in the vicinity of the magnetic body in the central portion by selecting a material suitable for the magnetic body in the central portion and the magnetic body at both ends. In FIG. 6, the same material is used as the ferromagnetic material located at both ends, but the material is not limited to the same material, and different materials (upper part) as shown in FIG. Side: material F ₁ , lower side: material F ₃ ) can be used.

  As described above, according to this embodiment, the domain wall generated in the magnetic information recording element is generated using only the current action regardless of the magnetic field action. Since mutual interference that disturbs the state is not caused, the magnetic information recording elements can be arranged close to each other, and the capacity and integration of the magnetic information recording medium can be easily realized.

  In addition, according to the magnetic information recording element of this embodiment, since the write line (including the erase line) and the read line can be shared, the configuration of the magnetic information recording medium can be realized easily and inexpensively. Can do.

  In this embodiment, the configuration example is shown in FIGS. 1 and 3 to 7 as the magnetic information recording element using the domain wall generation mechanism. However, these configuration examples are merely examples, If the basic principle of the present invention is used, the present invention is applicable if the concept of “when a current exceeding a certain critical current is passed through a ferromagnetic material, the uniform magnetization state becomes unstable and a domain wall is generated” is used. It is included in the technical scope of

(Description of Examples)
Prior to describing the configuration and the like of the first embodiment, the problems of the current high-density magnetic recording medium and the next-generation high-density magnetic recording medium will be described. At present, a typical high-density magnetic recording medium is a hard disk. In a general hard disk, a ferromagnetic thin film is used as a continuous magnetic recording medium. However, in a continuous magnetic recording medium using a ferromagnetic thin film, the recording magnetization becomes thermally unstable due to the refinement of crystal grains accompanying the increase in density. For this reason, it is not possible to meet the demand for further increasing the capacity of information recording with the increase in the amount of information in recent years, and it is said that there is a limit to the high density integration of magnetic information.

  As one of new magnetic information recording media for solving this limitation, a magnetic information recording medium called a patterned media has attracted attention. The patterned media is a recording medium in which fine ferromagnets are used as recording bit units, and they are discontinuously and densely arranged. Therefore, the magnetization transition region between bits that has also caused noise in the continuous medium is eliminated, and the problem of thermal fluctuation can be avoided, so that the recording density can be greatly improved.

  Thus, patterned media can be a strong candidate for next-generation high-density magnetic recording media. On the other hand, the magnetic information recording element according to the present invention can be applied as a magnetic information recording element for patterned media. A specific example in which the magnetic information recording element according to the present invention is applied to a patterned medium will be described.

(Example 1)
FIG. 8 is a diagram showing a configuration of a patterned medium configured using the magnetic information recording element 1 shown in FIG. In the patterned medium shown in FIG. 8, a large number of magnetic information recording elements 1 shown in FIG. 1 are arranged on a matrix on a non-magnetic substrate. As a material forming the magnetic information recording element 1, for example, iron (Fe), cobalt (Co), nickel (Ni), an alloy thereof, permalloy (Fe ₂₀ Ni ₃₀ ), or the like can be used. In addition, the magnetic information recording element 1 which is a bearer of individual bit information preferably has a rectangular or oblong structure so that a uniform magnetization state can easily appear without an external element such as a magnetic field. is there.

In FIG. 8, when the area occupied by the magnetic information recording element 1 is about 2 × 10 ⁴ (nm ² ), the recording density is approximately 30 Gbit / in ² , and an ultra-high density magnetic information recording medium can be realized. .

Next, magnetic information recording, erasing and reading procedures in the patterned medium shown in FIG. 8 will be described. In addition, FIG. 9 is a figure for demonstrating the outline. As shown in the lower part of the figure, for example, using a point contact 18, a predetermined current is passed through the magnetic information recording element 1 to destabilize the uniform magnetization state and generate a domain wall. In order to effectively generate the domain wall, for example, it is necessary to flow a current that generates a current density equal to or higher than the critical current density j ₁ described above.

When the material of the magnetic information recording element 1 is, for example, Co, the critical current density calculated based on the equation (1) is estimated to be approximately j ₁ ≈10 ¹³ (A / m ² ). The point contact 18 is made of a non-magnetic metal such as copper and has a needle-like structure so that the current density is increased at the tip. Although it is difficult to directly measure the radius of the tip of the point contact, the tip radius of the point contact is estimated to be several nm to several tens of nm by performing resistance measurement and using the Sharvin formula. Therefore, if the current value flowing through the point contact is 2.5 μA and the tip radius is 5 nm, the current density near the point contact is approximately 10 ¹⁴ (A / m ² ), which satisfies the required critical current density. be able to.

Further, as shown in the lower part of FIG. 9, the generated domain wall is generated and held by passing a predetermined current that satisfies the domain wall moving current density j ₂ shown in equation (2) or the like. The magnetic domain wall is pushed out of the magnetic information recording element 1 to return to a uniform magnetization state.

By the way, it has been reported that the domain wall moving speed by current driving is about 3 (m / s) when the current density is about 10 ¹² (A / m ² ). Accordingly, it takes about several hundred ns (10 ⁻⁷ s at a distance of 300 nm) for the domain wall to move a distance of several hundred nm (for example, 300 nm) and change to a uniform magnetization state. On the other hand, it is important to obtain the time required for changing from the uniform magnetization state to the domain wall state by the critical current density j ₁ . This is because the generated domain wall may move due to the current that continues to flow. At present, it is difficult to accurately determine the generation time. However, in a ferromagnetic material of this size, the magnetization reversal time due to a magnetic field having a typical strength is on the order of a few ns, and it can be assumed that the domain wall generation by current driving is also this time. Therefore, by generating a domain wall by passing a predetermined current satisfying the critical current density j ₁ through the magnetic information recording element 1 for several ns, the generated domain wall can be pinned. To summarize these results, the information recording time and the erasing time per bit can be estimated to be several ns and several hundred ns, respectively.

  On the other hand, reading of magnetic information recorded on the magnetic information recording element 1 can also use the point contact 18 in the same manner as recording and erasing of magnetic information. Specifically, the point contact 18 and the magnetic information recording element 1 are brought into contact with each other and energized, and “1” and “0” of the magnetic information may be read using the difference in electric resistance depending on the presence or absence of the domain wall. Note that the difference in electric resistance used at this time means the AMR effect. Further, since the electrical resistance ratio based on the AMR effect is less than 1% and the detected value is small, the detection signal may be amplified using an operational amplifier or the like. Further, if the magnetic information recording element 10 having a minute contact as shown in FIG. 4 is used, the above-described BMR effect can be used and a higher electric resistance ratio can be obtained. High-precision magnetic information can be read.

(Example 2)
FIG. 12 is a diagram showing a configuration of the MRAM 30 configured using the magnetic information recording element 20 shown in FIG. In the MRAM 30 shown in FIG. 12, a large number of magnetic information recording elements 20 shown in FIG. 5 are arranged on a matrix on a non-magnetic substrate. From the viewpoint of comparison with the MRAM 30 according to the present invention, the configuration of the MRAM 100 according to the prior art is shown in FIG. 10, and FIG. 11 shows the structure of the TMR element 102 used in the MRAM in FIG.

  As shown in FIG. 10, the MRAM generally includes a TMR element 102 which is a nano-scale order micro magnetoresistive element sandwiched between lattice lines of a writing line or a reading line (101) that runs vertically and horizontally, and both lines. It is a lattice arrangement. Currently, in a configuration that is about to be put into practical use, a TMR element having a three-layer structure of ferromagnetic material / insulator / ferromagnetic material as shown in FIG. 11 is used. The decisive difference from the present invention is that a magnetic field induced by an electromagnetic current is used as a method of writing information to the TMR element. For this reason, when TMR elements are arranged at high density, mutual interference occurs such that a write magnetic field generated at an arbitrary lattice point disturbs the magnetization state (recording state) of adjacent elements. Furthermore, when the change in resistance due to the change in the magnetization state is not sufficiently high, the change is minute compared to the total resistance of the circuit including the lattice points, making it difficult to read information.

On the other hand, in the present invention, the magnetic information recording element according to the present invention as shown in FIG. 1 or FIGS. The example shown in FIG. 12 shows the configuration of the MRAM 30 in which the magnetic information recording elements 20 shown in FIG. 5 are arranged. By using the magnetic information recording element of the present invention, the above two problems can be solved at once. As a material forming the magnetic information recording element 1, for example, iron (Fe), cobalt (Co), nickel (Ni), an alloy thereof, permalloy (Fe ₂₀ Ni ₃₀ ), or the like can be used.

Next, the operation principle of the MRAM using the magnetic information recording element of the present invention will be described with reference to FIGS. First, a lattice point for recording information is selected and two write lines 32 are selected (FIG. 12). Next, when a current having a critical current density j ₁ is applied, a domain wall is generated inside the magnetic information recording element 20 (left diagram → right diagram in FIG. 5). At this time, the generated domain wall is captured by a constricted portion that is a stable position (the right diagram in FIG. 5). Further, when a current having a domain wall moving current density j ₂ is applied, the domain wall is swept out from the inside of the element (the right diagram → the left diagram in FIG. 5). In the reading of the information, the determination of the bit information by utilizing a difference in electrical resistance between the high resistance state of not containing the low-resistance state and the magnetic domain wall enclosing the domain walls by using a current read current density j ₃ Perform (FIG. 5).

  Even in the case of MRAM, magnetic information can be read with high accuracy by using the BMR effect as in the case of patterned media. For example, by using the BMR effect, an electric resistance change reaching 10,000% is expected, and an improvement effect of 100 times or more can be obtained as compared with the TMR element of the current method.

  As described above, the magnetic information recording element according to the present invention is useful as a magnetic information recording element applicable to an ultra-high density magnetic information recording medium, and in particular, a magnetic information recording medium such as a patterned medium or an MRAM. It is suitable as a magnetic information recording element capable of improving the problem and improving the recording capacity.

It is a schematic diagram which shows the structure of the magnetic information recording element concerning this invention. It is a figure for demonstrating the concept of the domain wall production | generation mechanism in the magnetic information recording element of this invention shown in FIG. It is a figure which shows the structure (modification 1) of the magnetic information recording element concerning this invention. It is a figure which shows the structure (modification 2) of the magnetic information recording element concerning this invention. It is a figure which shows the structure (modification 3) of the magnetic information recording element concerning this invention. It is a figure which shows the structure (modification 4) of the magnetic information recording element concerning this invention. It is a figure which shows the structure (modification 5) of the magnetic information recording element concerning this invention. It is a figure which shows the structure of the patterned media comprised using the magnetic information recording element of this invention shown in FIG. It is a figure for demonstrating the recording, erasure | elimination, and read-out point of the magnetic information in the patterned medium of this invention shown in FIG. It is a figure which shows the structure of MRAM concerning a prior art. It is a figure which shows the structure of MRAM comprised using the magnetic information recording element of the prior art shown in FIG. It is a figure which shows the structure of MRAM comprised using the magnetic information recording element of this invention shown in FIG.

Explanation of symbols

1, 8, 10, 20 Magnetic information recording element 3, 3a, 3b Magnetization 6 Domain wall 18 Point contact 30 MRAM
32 writing lines

Claims (9)

  A magnetic information recording element comprising a constricted portion at a substantially central portion in the longitudinal direction of a nanoscale-order ferromagnetic structure.   The magnetic information recording element according to claim 1, wherein the ferromagnetic structure is a columnar structure.   The magnetic information recording element according to claim 1, wherein the ferromagnetic structure is a substantially gourd-type structure.   The constricted portion has a uniform length in the short direction, and is formed in a three-layer structure in which the length in the short direction is long-short-length throughout the device. The magnetic information recording element according to claim 1.   A magnetic information recording element comprising a nanoscale-order ferromagnetic structure having a three-layer structure, wherein the magnetic material at both ends of the three-layer structure and the magnetic material at the center are made of different magnetic materials. .   6. The magnetic information recording element according to claim 5, wherein each of the magnetic bodies at both ends is made of a different magnetic material.   7. A magnetic information recording medium using the magnetic information recording element according to claim 1 as a magnetic information recording element applied to an MRAM.   7. A magnetic information recording medium using the magnetic information recording element according to claim 1 as a magnetic information recording element applied to a patterned medium. A magnetic domain generating method for a magnetic information recording element having a constricted portion at a substantially central portion in the longitudinal direction of a nanoscale-order ferromagnetic structure,
Bringing the magnetic information recording element into a uniform magnetization state;
Passing a current equal to or higher than a predetermined critical current density to the magnetic information recording element;
A domain wall generating method for a magnetic information recording element, comprising:

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