JP2004146821A - Memory device and memory - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a spin injection type memory device and memory that can be increased easily in density and degree of integration. <P>SOLUTION: A magnetic memory device MM1 is a spin injection type magnetic memory device which performs writing by causing magnetization inversion by injecting spin-polarized electrons. In both end sections of the memory device MM1, a fixed layer 1, the direction of magnetization fixed in one direction, and a free layer 2 with changeable, the direction of magnetizing orientation when the spin-polarized electrons flow in, are respectively included by using a carbon nanotube 10 as one constituent unit and the central part of the tube 10 in the axial direction as a spin conductive layer 3. <P>COPYRIGHT: (C)2004,JPO

Description

{Circle over (1)} The present invention relates to a memory element for writing data using spin polarization injection and a nonvolatile memory device using the same.

(4) With the advent of the high-speed network society, mobile media such as mobile phones and laptop computers, which are rapidly spreading, are required to develop nonvolatile memories. Since the nonvolatile memory can hold data even when power is not always supplied, a device using the nonvolatile memory can be operated immediately after power is turned on, and power consumption can be reduced.

Magnetic Random Access Memory (MRAM), which has been attracting attention in recent years, is designed to reduce the speed of SRAM (Static RAM), the high density of DRAM (Dynamic RAM), the low cost, and the non-volatility of flash memory. It has both and is promising as a future de facto standard. The MRAM is a memory using a magnetic effect, and a MRAM using a spin valve type using a giant magnetoresistance effect and a type using a spin-dependent tunnel effect are known. In these MRAMs, a switching current is applied to a wiring corresponding to a target memory cell, and the generated magnetic field changes the magnetization state of a recording layer in the cell to write bit information. Reading of information is performed by detecting the magnetization state of the cell using a magnetic effect. As described above, since the MRAM is a solid-state memory, there is no danger of damage as in a magnetic recording medium that mechanically writes and reads using a magnetic head, and the MRAM has a feature of being resistant to repeated writing and reading. I have.

However, the practical use still had problems that had arisen with the increase in memory density. The magnetic field strength required for writing is inversely proportional to the width of the recording layer, that is, the cell size. Therefore, when the memory cell is miniaturized, power consumption becomes extremely large. In addition, there is a possibility that crosstalk may occur due to a proximity leakage magnetic field between adjacent cells. For example, for a memory cell having a width of 0.2 μm, the current at the time of writing becomes several mA. In a memory in which the distance between cells is reduced to about 0.1 μm, when a magnetic field is induced in a target cell, a magnetic field of 80% of the magnetic field is applied to an adjacent cell.

Ｍ As a technique for overcoming such a problem, an MRAM using a novel writing method called a polarized spin injection method to a recording layer has been proposed (see Patent Document 1). In this case, the memory element is configured as shown in FIG. That is, the ferromagnetic layer (fixed layer) 111 whose magnetization direction is always fixed and the ferromagnetic layer (free layer) 112 whose magnetization direction is changed according to bit information are separated by the paramagnetic layer 113. The paramagnetic metal layers 114 and 115 are electrode layers for passing a current through the ferromagnetic layers 111 and 112 in the stacking direction. In the polarized spin injection method, polarized electrons are injected into the ferromagnetic layers 111 and 112 by flowing a spin-polarized current in the stacking direction to transmit spin angular momentum. Thereby, in the ferromagnetic layer 112, the magnetic moment is reversed by the interaction. This mechanism is called spin conversion. In the writing method in which the magnetization is switched by injecting the spin current, there is no need to apply an external magnetic field, so that there is no interference between memory cells and power consumption can be suppressed.

Another characteristic of the polarized spin injection method is that the writing time depends only on the spin conduction speed, so that the response speed can be improved.
JP-A-11-120758 Japanese Patent No. 2546114

However, this technology also had a problem for practical use. The paramagnetic layer 113 disposed between the ferromagnetic layers 111 and 112 has a side surface as a spin conduction layer that conducts electrons without relaxing polarized spin, in addition to serving as a magnetic spacer. Therefore, the paramagnetic layer 113 needs to be a material having a long spin coherence length and having a very small spin scattering with respect to the ferromagnetic layers 111 and 112. Since such a combination of (ferromagnetic material / paramagnetic material) is extremely limited, the paramagnetic layer 113 has been required to be made of a material more suitable as a spin conduction layer.

On the other hand, apart from such research and development of MRAM technology, research on the physical properties of carbon nanotubes and application development as functional materials have been promoted. A carbon nanotube is a carbon material having a one-dimensional structure (tubular structure) ordered on a nanoscale, and easily forms an aggregate called a bundle.

Patent Literature 2 discloses a technique of encapsulating various foreign substances in a hollow hole at the center of a carbon nanotube. For a carbon nanotube encapsulating a magnetic substance, (1) tube inner diameter (5 to 10 nm) ) Is smaller than the size of the magnetic domain of a normal magnetic substance, and is considered to be a single domain fine particle. (2) If the long axis of the tube is arranged vertically, the perpendicular magnetic recording medium having extremely high density It is described that it is thought that it can be done. However, the above publication does not describe at all the application of the carbon nanotube to the memory. Although application to transistors has been announced very recently, no concrete progress has been made in memory application until now. The reason is that the cell size is much smaller than in the past, and it is difficult to achieve this by following the conventional structure in terms of how to apply an external magnetic field to each cell. Conceivable. In other words, simply packing elements in nanotubes cannot be a practical MRAM.

The present invention has been made in view of such a problem, and an object of the present invention is to provide a memory device and a memory device of a spin injection type which can easily realize high density and high integration.

The memory element of the present invention includes a holding unit that holds a state in which electrons are spin-polarized, and a spin conductive layer including at least a part of a hollow cylindrical molecule and conducting spin-polarized electrons. The information is written into the holding unit as a spin-polarized state of the electrons by the injection of the polarized electrons. Specifically, the stacking direction of the first and second ferromagnetic layers, in which at least one change in the magnetization direction is induced by the injection of the spin-polarized electrons, and the stacking direction of the first and second ferromagnetic layers, are set in the axial direction. And is provided between the first ferromagnetic layer and the second ferromagnetic layer to interrupt the magnetic interaction and to dispose the spin-polarized electrons. And a spin-conducting layer for conduction. Further, a memory device of the present invention has a plurality of the memory elements of the present invention arranged therein.

メ モ リ The memory element of the present invention is a memory element which is a structural unit of a spin injection random access memory. The memory device of the present invention is a device including a memory main body composed of the memory element. Spin-polarized electrons are conducted between the first ferromagnetic layer and the second ferromagnetic layer by the flow of current in the axial direction of a hollow cylindrical molecule functioning as a spin conduction layer. In this spin conduction layer, electrons are conducted without spin relaxation according to the spin coherence length of the cylindrical molecule or the substance contained in the hollow part, and the angular momentum of the electrons is changed to the first ferromagnetic layer and the second ferromagnetic layer. Provided to the magnetic layer.

As described above, according to the memory device of the present invention, the spin conduction layer is made to be at least part of the hollow cylindrical molecule, so that the spin relaxation of the polarized electrons in the spin conduction layer is performed by the spin coherence or the hollow coherence. This is prevented according to the spin coherence of the substance included in the portion, and current consumption during writing can be suppressed.

In particular, the central part in the axial direction of the cylindrical molecule functions as a spin conduction layer, and a first ferromagnetic layer is provided at one end of the cylindrical molecule and a second ferromagnetic layer is provided at the other end. By enclosing each, the element body is housed in the hollow portion of the cylindrical molecule. Therefore, by selecting nano-sized cylindrical molecules, a nano-sized spin-injection memory device can be realized without using a conventional fine processing technique. In other words, an element whose dimensions are well controlled can be obtained by a simple manufacturing method despite its small size. In this case, the first and second ferromagnetic layers are considered to have a single magnetic domain structure due to the size of the diameter of the cylindrical molecule, and the inclusion of the cylindrical molecule prevents external magnetic disturbance. Due to the interruption, the magnetization orientation can always be kept stable. In addition, thanks to the magnetic shielding effect, integration can be actually performed even in a small size.

Further, by using the carbon nanotubes as the cylindrical molecules, in the spin conduction layer, the polarized electrons are conducted with little spin relaxation due to the good spin coherence of the carbon nanotubes, and the first ferromagnetic layer or the second To the ferromagnetic layer. Therefore, it is possible to realize a nano-sized spin injection memory element with high writing efficiency.

According to the memory device of the present invention, since the plurality of memory elements of the present invention are arranged, writing can be performed efficiently and low power consumption driving is possible. In addition, since each memory element is configured using cylindrical molecules at least in part, unlike a device formed two-dimensionally by a conventional thin film manufacturing technique, it has a columnar three-dimensional structure. , And can be integrated in a vertical orientation. Furthermore, since this memory element is of a spin injection type and is hardly affected by a near magnetic field as compared with other magnetic memories, the pitch of the memory cells can be narrowed. Therefore, high-density integration becomes possible.

FIG. 1 shows a configuration of a memory element according to an embodiment of the present invention. The magnetic memory element MM1 is a "spin injection type" in which writing is performed by causing magnetization reversal by injecting polarized spin electrons. The basic structure is such that a spin conduction layer is provided between two ferromagnetic layers, that is, a fixed layer 1 in which the magnetization orientation is fixed in a fixed direction and a free layer 2 in which the magnetization orientation changes due to the inflow of polarized spin electrons. 3 is provided.

Each of these layers is formed as a layer inside one molecule of the carbon nanotube 10. In other words, the carbon nanotube 10 has a spin conduction layer 3 at the center in the axial direction, and includes the fixed layer 1 and the free layer 2 at both ends to form one unit of the memory. The fixed layer 1 and the free layer 2 are provided with electrode layers 4A and 4B, respectively. Each magnetic memory element MM1 is connected to the wiring layers 5A and 5B via the electrode layers 4A and 4B.

The spin conduction layer 3 is composed of a part of the hollow carbon nanotube 10. The spin conduction layer 3 is made of a non-magnetic material to block magnetic interaction between the fixed layer 1 and the free layer 2. Further, in order to conduct polarized spin electrons between the fixed layer 1 and the free layer 2, the spin coherence length must be at least longer than its own layer thickness. There have been numerous reports suggesting the ballistic conduction of carbon nanotubes, and in recent years, it has been experimentally confirmed that the spin coherence length is 200 nm or more (K. Tsukagoshi, BW Alphenaar and H. Ago " Spin coherent transport in a ferromagnetically contacted carbon nanotube "Nature 401, 572-574 (1999)). On the other hand, the thickness of the spin conductive layer 3 (the length of the carbon nanotube) is approximately 0.5 nm to 5 μm as a practical range. Therefore, the spin conduction layer 3 satisfies the above two conditions at the same time.

As described above, in the present embodiment, a part of the carbon nanotubes 10 is used as (1) the spin conduction layer 3 and (2) constitutes the outer shell of the entire device.

The greatest effect of using the carbon nanotubes 10 as the outer shell of the element is that the magnetic shielding effect by the π electron cloud can prevent the influence of the near magnetic field from being applied to the inside. The magnetic memory element MM1 of the present embodiment is characterized in that it is of a current-driven type. However, when the size (cell size) is on the order of nanometers, the leakage magnetic field generated by the read current causes the magnetization of the adjacent cell to change. May disturb. However, since the carbon nanotubes 10 cover the magnetic layer inside the element and block magnetic disturbance from the outside, the magnetization orientation of the fixed layer 1 and the free layer 2 is always kept stable. Thus, the magnetic memory element MM1 is a small-sized element that can be actually integrated and driven.

Furthermore, the inner diameter of the carbon nanotube 10 is extremely small, about 1 to 10 nm. That is, such a fine element can be formed without using a conventional semiconductor processing technique. At the same time, since this size is considerably smaller than the size of the magnetic domain of a normal magnetic material, it is considered that the magnetic material has a single magnetic domain structure inside the carbon nanotube 10. Therefore, since the magnetic domain does not move with respect to the magnetization, it is expected that the coercive force of the magnetic body is increased.

The ferromagnetic materials used for the fixed layer 1 and the free layer 2 include, for example, simple substances of Fe and Co, and their binary alloys, NiFe alloys, MnFeCo, FeCoNi, and the like. Among them, a ferromagnetic material effective for obtaining a high electron polarization rate is an FeCo alloy having a high Fe content. The itinerant d-electron of the 3d ferromagnet has an isotropic free electron-like wave vector, so that it is not necessary to consider the crystal orientation much. The fixed layer 1 may be selected from a hard magnetic material containing Ni, Co, etc., and the free layer 2 may be selected from a soft magnetic material, such as pure iron or permalloy (Ni ₇₉ Fe ₂₁ ). In addition, iron oxide-based spinel-type ferrimagnetic fine particles (crystal grain diameter φ ~ 30 nm, coercive force HcJ ~ 6 kOe), which recently became known to have a high coercive force, Metal nano-particle materials such as FeO ₂ fine particles (calcination temperature 1023K, crystal particle diameter φ-5 nm, HcJ-1 kOe) can also be used.

In order to keep the magnetization orientation constant, the fixed layer 1 may be made of a material whose Gilbert damping coefficient is much larger than that of the free layer 2 or by adjusting the composition or the layer thickness (to be larger than the free layer 2). A uniaxial magnetic anisotropy greater than 2 may be provided. Alternatively, an antiferromagnetic layer may be brought into contact with the fixed layer 1 to pin the magnetization. When the antiferromagnetic layer is a metal, it also has a function as the electrode layer 4A. Such antiferromagnetic metal materials include FeMn, IrMn, NiMn and RhMn.

On the other hand, in order to prevent the magnetization direction (memory state) from fluctuating under the influence of heat or a magnetic field, the composition, thickness, cross-sectional area (diameter of the carbon nanotube 10), and the like are optimized in the free layer 2 to make the anisotropic magnetic field Hu A uniaxial magnetic anisotropy of> 100 Oe may be provided. The magnetization direction of the free layer 2 may change in two directions in the plane, or may change in an in-plane direction and a direction perpendicular to the plane. In the latter case, in order to obtain sufficient perpendicular magnetic anisotropy, it is preferable that the thickness of the free layer 2 be 5 atomic layers or less, that is, about 1 nm.

The electrode layers 4A and 4B may be made of any conductive paramagnetic metal. The thickness and shape are not particularly limited. By the way, the magnetic memory element MM1 has a shape that is encapsulated in a sheath of carbon nanotubes, has a smaller size than a normal memory element, and has a higher thickness ratio than a cross section. Therefore, the electrode layers 4A and 4B and the wiring layers 5A and 5B may be formed by using a conventional semiconductor processing technique, but may be formed by a molecular wire such as a carbon nanotube.

(4) In the magnetic memory element MM1, writing and reading are performed by passing currents as described later, so that writing and reading wiring can be shared, and only two wiring layers 5A and 5B are required. One of the advantages is that the wiring structure is simple.

磁 気 Further, the magnetic memory element MM1 has a feature in integration since the carbon nanotubes 10 are arranged outside the element. Usually, carbon nanotubes easily form aggregates called bundles. Since the outer periphery of the magnetic memory element MM1 is formed of the carbon nanotubes 10, the magnetic memory element MM1 is easily integrated by aggregation. For example, as shown in FIG. 2, when arranged in a matrix, this regular arrangement is maintained by the dispersing force (the force for aggregating the carbon nanotubes 10), and the magnetic memory device MM1 is integrated with the magnetic memory device MM1. Is configured. Thus, a high-density and highly reliable memory device in which one carbon nanotube is used as a unit memory cell can be manufactured.

Such a magnetic memory element MM1 and its magnetic memory device are oriented using, for example, an oriented carbon nanotube generation method (Jeong et al: Chem. Mater., Vol 14, No. 4, pp1859-1862 (2002)). Carbon nanotubes can be produced by producing a carbon nanotube, filling a hollow portion of the tube with a magnetic metal, and electrically joining at the end. A specific description of this method will be described later as an example.

Next, the operation method will be described. In the magnetic memory element MM1, the state where the magnetization direction of the free layer 2 with respect to the fixed layer 1 is parallel magnetization matching and the state where antiparallel magnetization matching is performed correspond to binary data such as "0" and "1". By doing so, information is recorded. Data writing is performed by reversing the magnetization direction of the free layer 2 by a pulse current flowing in a direction perpendicular to the layer surface (CPP: Current Perpendicular to Plane). For example, when the magnetization of the free layer 2 with respect to the fixed layer 1 is changed from parallel magnetization matching to antiparallel magnetization matching, a current density pulse is applied from the fixed layer 1 to the free layer 2 so that the spin-polarized electrons are removed. , From the free layer 2 toward the fixed layer 1. The magnitude of the current at this time must be larger than the critical current density value at which the magnetization reversal occurs in the free layer 2. During this pulse application, the direction of magnetization of the free layer 2 is reversed, and the state in which the free layer 2 and the fixed layer 1 are parallel-magnetized changes to the antiparallel magnetization-matched state.

Conversely, when changing from the antiparallel magnetization matching state to the parallel magnetization matching, a current may be passed in the opposite direction. That is, a current flows from the free layer 2 toward the fixed layer 1, and spin-polarized electrons are injected from the fixed layer 1 toward the free layer 2.

Here, since the spin conduction layer 3 is made of carbon nanotubes, polarized electrons are conducted in the layer without spin relaxation. Therefore, electrons are injected into the fixed layer 1 and the free layer 2 while maintaining the spin angular momentum, and writing can be performed efficiently.

Reading of data, that is, discrimination of the above two magnetization states can be performed by using, for example, a giant magnetoresistive (CPP-GMR) in a direction perpendicular to the layer surface. In addition, there is a method using the magnetic Kerr effect.

As described above, in the spin injection magnetic memory element MM1 of the present embodiment, the two ferromagnetic layers, the fixed layer 1, and the free layer 2 are filled at both ends of one molecule of the carbon nanotube 10, and the central hollow portion itself is used. Is the spin conduction layer 3. Therefore, the spin conduction layer 3 has good spin coherence of the carbon nanotube, and polarized electrons are injected into the fixed layer 1 and the free layer 2 without spin relaxation. Therefore, writing can be performed efficiently and low power consumption driving can be performed.

Further, since the main body of the memory element is configured to be housed inside the sheath of the carbon nanotube 10, a nano-sized element can be realized without using the conventional fine processing technology. Therefore, a very high-density memory device can be obtained using the magnetic memory element MM1. In this case, the fixed layer 1 and the free layer 2 are considered to have a single magnetic domain structure, and can maintain a stable magnetization orientation. Also, the magnetization orientation is always kept stable even when the π electron cloud of the carbon nanotube 10 covers the fixed layer 1 and the free layer 2 to block external magnetic disturbance. Further, the carbon nanotubes 10 have a one-dimensional shape, and a dispersing force acts between the tubes, so that the carbon nanotubes 10 are aligned in the axial direction and aggregate. Therefore, the magnetic memory element MM1 can be stably and easily oriented with high orientation, and a highly integrated magnetic memory device can be obtained.

In addition, as shown in FIG. 3, a spin array layer 11 containing a dilute magnetic alloy may be provided in addition to the spin conductive layer 3. The diluted magnetic alloy is obtained by doping a semiconductor with a magnetic metal and has a magnetic order while maintaining the characteristics of the semiconductor. At the junction interface between a diluted magnetic material and a ferromagnetic metal, the magnetization becomes non-equilibrium and spin-polarized electrons can be generated (Source: R. FIEDERLING, M. KEIM, G. REUSCHER, W. OSSAU, G. SCHMIDT, A. WAAG & LW MOLENKAMP Nature 402, 787-790 (1999) "Injection and detection of a spin-polarized current in a light-emitting diode"). Therefore, a higher spin polarization can be obtained by using the diluted magnetic alloy as the spin alignment layer 11 also serving as the spin conduction layer.

Examples of the diluted magnetic material alloy include (In, Mn) As, (Ga, Mn) As, (Cd, Mn) Te, (Zn, Mn) Te, and (Zn, Cr) Te.

The position of the spin alignment layer 52 containing the diluted magnetic alloy may be between the two ferromagnetic layers (the fixed layer 1 and the free layer 2), and more preferably, the reference fixed layer 1 and the reference spin transfer layer (Paramagnetic layer) 3, whereby the degree of polarization of conduction spin in spin injection can be increased.

Furthermore, specific examples of the present invention will be described in detail.

(Example 1)
First, a high-purity aluminum sheet (99.999%) was degreased with acetone and washed with an ethanol solution. This was electropolished in a mixed solution of perchloric acid and ethanol. Subsequently, it was anodized in a 0.3 M oxalic acid at 15 ° C. for 12 hours at a voltage of 40 V. Thus, an anodized alumina substrate having pores was obtained. These pores are self-organized as a nano-order regular porous structure, and have a regular arrangement over a long distance. The pores actually obtained penetrated the alumina substrate (that is, the pores were open at both ends), had a diameter of 80 nm, and a density of 1.0 × 10 ¹⁰ pores / cm ² .

Then, precipitated alumina substrate CoSO ₄ · 7H ₂ O solution was added an AC voltage of 18V 1 minute. Thus, the Co catalyst was electrochemically precipitated on the bottom of the pores of the substrate. The Co particles on the surface were reduced by exposing the substrate to a mixed gas of 10% H ₂ and 90% Ar at 500 ° C. for 1 hour. The Co catalyst is a catalyst for generating carbon nanotubes and, at the same time, serves as a magnetic layer (fixed layer) of a magnetic memory element.

Next, an Ar carrier gas containing 10% of C ₂ H _{2 and} 20% of H ₂ was supplied, and carbon nanotubes were grown in the pores of the substrate by a thermal decomposition method.

カ ー ボ ン Excessively grown carbon nanotubes were cut together with the substrate by ultrasonic treatment at 40 kHz in an acetone solution. Thus, axially oriented nanotubes having uniform lengths were obtained.

Next, the carbon nanotubes were immersed together with the substrate in an acid bath containing iron ions and hypophosphite as a reducing agent, and pure iron was packed into the carbon nanotubes using an electroless plating method until a metallic color appeared. Was. As a result, each carbon nanotube has the basic structure of the spin injection magnetic memory element. That is, a Co layer, which is a hard magnetic material, is formed as the fixed layer, a hollow nanotube is formed as the spin conductive layer 3, and an Fe layer is formed as the free layer.

(4) A thinner nanotube was bonded to both ends of the magnetic substance-encapsulated nanotube as an electrode and a lead-out wiring by an atom manipulation method.

Further, the nanotubes were placed together with the alumina substrate on an insulating substrate made of SiO ₂ and immersed in 0.1 M NaOH at 70 ° C. for 3 hours to decompose and remove the alumina substrate. At this time, the bundle structure of the magnetic substance-containing nanotubes and the tubes serving as electrodes and wirings remained on the insulating substrate.

(4) Next, a signal wiring was bonded to the lead wiring, and this was used as a two-dimensional grid wiring to take an address. Finally, the insulating substrate was fixed to a Cu heat sink to complete the magnetic memory device.

Further, characteristics of the manufactured magnetic memory device were measured. The results are shown below.
<Calculated value>
Polarization efficiency: ~ 50%
Effective in-plane anisotropic magnetic field for the free layer: Hu = + 2 Ku / Ms 100100 Oe
Spin number density: ~ 5.0 × 10 ¹⁵ cm ²
Gilbert damping coefficient: 0.01
Critical value Jt: ８8 × 10 ³ A / cm ²
Electric resistance: 16mΩ
Noise voltage (10Hz BW, 77k): 0.2nV
<Measured value>
Experimental switching current density: １1 × 10 ⁴ A / cm ²
Switching time θ (0￣π): ~ 0.05μsec
Peak power consumption during reading: ~ 0.1 pW
Reading current density: ~ 3 × 10 ³ A / cm ²
Read current pulse: ~ 6.4μA, 1Hz
CPP-GMR 4% ΔR / R: ~ (800μΩ / 16mΩ)
Average reading voltage: ~ 5nV
Magnetic recording density: ~ 65Gbit / inch ²

記録 The measured recording density can be improved by controlling the pore diameter of the anodized alumina substrate and optimizing the nanotube diameter, that is, the diameter of the magnetic memory element. When the starting point of pore growth is controlled by a method such as ion sputtering of Ar, Ga or the like on the electropolished aluminum substrate, the pore diameter can be controlled in the range of several tens to several hundreds of nm.

(Example 2)
A carbon nanotube containing a ferromagnetic metal can be obtained by adding a ferromagnetic metal to a graphite electrode used for synthesis by an arc discharge method or the like. In this example, a magnetic memory device was assembled from the carbon nanotubes obtained in this manner.

First, a mixture was prepared by adding Ni, Y, and Permalloy (NiFe alloy) powder to graphite powder at a weight ratio of 4%, 1%, and 4%, and carbon pitch was further added thereto. Fired. Using this as a cathode electrode, arc discharge was performed by a contact arc method in a He atmosphere under a pressure of 200 Torr.

炭素 By dispersing the obtained carbon soot in a magnetic field, magnetically encapsulated nanotubes were selectively taken out. Since Ni functions as a catalyst for forming carbon nanotubes, it is included in one end of almost all tubes. Therefore, it is necessary to selectively take out a tube filled with permalloy at the other end. Next, of the obtained magnetic nanotubes, only a tube containing ferromagnetic Ni at one end and permalloy at the other end was collected while visually recognizing with a scanning electron microscope.

カ ー ボ ン Each of the collected carbon nanotubes has a basic structure as a spin injection magnetic memory element. That is, a Ni layer which is a hard magnetic material is formed as a fixed layer, a hollow nanotube is formed as a spin conduction layer, and a permalloy layer is formed as a free layer. These carbon nanotubes aggregate with each other at a distance of about 0.3 nm by Van der Waals force.

(4) A thinner nanotube was bonded to both ends of the magnetic substance-encapsulated nanotube as an electrode and a lead-out wiring by an atom manipulation method. Thereafter, a magnetic memory device was completed in the same manner as in Example 1.

The present invention is not limited to the above embodiments and examples, and various modifications can be made. For example, in the above-described embodiment, the portion of the spin conductive layer 3 of the carbon nanotube 10 is used in a hollow state, but a conductive paramagnetic material having a long spin coherence length may be included. Examples of the candidate include a carbon material such as fullerene and an antiferromagnetic 3d metal and 4d metal such as Ag and Au.

Further, in the above-described embodiment, the magnetic memory element whose main part is formed inside the carbon nanotube 10 has been described. However, the carbon nanotube 10 may be replaced with other tubular molecules, for example, a boron nitride (BN) tube, a peptide nanotube, or the like. Etc. may be substituted. In this case, the portion corresponding to the spin conductive layer 3 may be filled with the above-described carbon material or metal to improve the characteristics.

Further, in the above-described embodiment, the carbon nanotubes 10 include the fixed layer 1 and the free layer 2, but a part of the electrode layers 4A and 4B may be included to further improve the bonding property. In the magnetic memory device of the present invention, it is sufficient that at least the spin conductive layer provided between the fixed layer and the free layer is composed of cylindrical molecules represented by carbon nanotubes. Is optional. However, as described above, since a conductive cylindrical molecule can be expected to have a magnetic shielding effect, it is preferable to adopt a structure in which the molecule is included as necessary.

FIG. 1 is a diagram illustrating a configuration of a magnetic memory element according to an embodiment of the present invention. FIG. 2 is a schematic configuration diagram of a memory device in which the magnetic memory elements shown in FIG. 1 are integrated. FIG. 9 is a diagram illustrating a configuration of a magnetic memory element according to another embodiment of the present invention. FIG. 2 is a configuration diagram of a conventional spin injection magnetic memory element.

Explanation of reference numerals

MM1: magnetic memory element, 1: fixed layer, 2: free layer, 3: spin conductive layer, 4A, 4B: electrode layer, 5A, 5B: wiring layer, 10: carbon nanotube, 11: spin array layer.

Claims (14)

A holding unit that holds a state in which electrons are spin-polarized,
A spin-conducting layer comprising at least a portion of a hollow cylindrical molecule and conducting spin-polarized electrons,
A memory element, wherein information is written into the holding unit as spin-polarized state of electrons by injection of spin-polarized electrons. First and second ferromagnetic layers in which at least one change in magnetization direction is induced by injection of spin-polarized electrons;
It is formed of at least a part of hollow cylindrical molecules arranged with the stacking direction of the first and second ferromagnetic layers as an axial direction, and is provided between the first ferromagnetic layer and the second ferromagnetic layer. And a spin conductive layer for blocking magnetic interaction and conducting spin-polarized electrons. In the cylindrical molecule, a central portion in the axial direction functions as the spin conduction layer, and includes a first ferromagnetic layer at one end and a second ferromagnetic layer at the other end. The memory device according to claim 2, wherein: The memory device according to claim 2, wherein one of the cylindrical molecules is a constituent unit of the device. The memory device according to claim 2, wherein the spin conductive layer made of the cylindrical molecule has an axial length shorter than its own spin coherence length at an operating temperature. The memory device according to claim 2, wherein the spin conductive layer formed of the cylindrical molecule includes another molecule or atom in a hollow portion. The memory device according to claim 2, further comprising a spin alignment layer between the first ferromagnetic layer and the second ferromagnetic layer. The memory element according to claim 7, wherein the spin array layer includes a diluted magnetic material. The diluted magnetic material comprises at least one of (In, Mn) As, (Ga, Mn) As, (Cd, Mn) Te, (Zn, Mn) Te, and (Zn, Cr) Te. The memory device according to claim 8, wherein The memory element according to claim 6, wherein a spin coherence length of the molecule or atom included in the hollow portion at an operating temperature is longer than an axial length of the cylindrical molecule in the spin conductive layer. The memory element according to claim 2, wherein the cylindrical molecule is a carbon nanotube. A memory device in which a plurality of memory elements are arranged,
The memory element includes a holding unit that holds a state in which electrons are spin-polarized, and a spin conductive layer that is formed of at least a part of a hollow cylindrical molecule and that conducts spin-polarized electrons, and is spin-polarized. A memory device, wherein information is written into the holding unit by spin injection of electrons by injection of electrons, and / or the information is read from the holding unit. A memory device in which a plurality of memory elements are arranged,
The memory element may include a first and a second ferromagnetic layer in which at least one change in magnetization direction is induced by injection of spin-polarized electrons, and a stacking direction of the first and the second ferromagnetic layers. The first ferromagnetic layer and the second ferromagnetic layer are provided between the first ferromagnetic layer and the second ferromagnetic layer to interrupt the magnetic interaction and to be spin-polarized. A memory device, comprising: a spin conduction layer that conducts electrons. 14. The memory device according to claim 13, wherein the memory elements are integrated by arranging the cylindrical molecules in the same axial direction.

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