JP2008192712A - Tunnel magnetic resistance element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a tunnel junction magnetic resistance element that has a novel structure wherein tunnel junction is formed without lamination structure. <P>SOLUTION: The tunnel magnetic resistance element includes a first electrode 12 made of ferromagnetic material, a second electrode 13 made of ferromagnetic material and nanoparticles 14 arranged between the first and second electrodes 12 and 13, and the nanoparticles 14 have insulative and protective groups 14b on the outer periphery of ferromagnetic metal nanoparticles 14a. First tunnel junction 15a is formed between the ferromagnetic metal nanoparticles 14a and the first electrode 12, and second tunnel junction 15b is formed between the ferromagnetic metal nanoparticles 14a and the second electrode 13. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a tunnel magnetoresistive element used in a magnetic sensor, an MRAM (Magnetoresistive Random Access Memory), and the like, and more particularly to a tunnel magnetoresistive element in which a tunnel junction is formed without using a laminated structure.

  A tunnel magnetoresistive element generally includes three layers of a magnetic pinned layer (pinned layer) / insulating layer / magnetic free layer (free layer). Since this insulating layer is very thin with a thickness of about 2 nm or less, a part of electrons is present. Tunnel through the insulating layer. The magnetization direction of the magnetic pinned layer in the tunnel magnetoresistive element is fixed in a direction perpendicular to the direction of the current flowing through the tunnel magnetoresistive element, whereas the magnetization direction of the magnetic free layer is determined by the external magnetic field to be detected. Depending on the direction, the direction is the same as or opposite to the magnetization direction of the magnetic pinned layer. When the magnetization direction of the magnetic free layer is the same as the magnetization direction of the magnetic pinned layer, a large tunnel current flows, so that the resistance value of the tunnel magnetoresistive element becomes small. On the other hand, when the magnetization direction of the magnetic free layer is opposite to the magnetization direction of the magnetic pinned layer, only a small tunnel current flows, so that the resistance value of the tunnel magnetoresistive element increases. Therefore, an external magnetic field can be sensed by the magnitude of the resistance value of the tunnel magnetoresistive element (Patent Documents 1 and 2, Non-Patent Documents 1 to 3).

  In a Coulomb blockade anisotropic magnetoresistive element employing a single electron transistor structure made of a gallium / manganese / arsenic thin film, it has been reported that the tunnel magnetoresistance changes more than 100 times (Non-Patent Document 4). .

  On the other hand, the present inventors synthesized an electron shuttle as an electrode of an SPM probe by synthesizing a metal nanoparticle designed with a core particle size and an organic ligand material, and tunneled an organic ligand in a single metal nanoparticle. We have succeeded in estimating the resistance and measuring single electrons on single metal nanoparticles. In addition, single nanometer metal nanoparticles having a particle size of 10 nm or less are attracting great attention as structural units of next-generation nanoelectronic devices and nanomagnetic devices because they exhibit size-specific electronic and magnetic properties. .

  By the way, as a method of producing a nanogap electrode, for example, mechanical break junction method (Non-patent document 5), electromigration method (Non-patent document 6), oblique deposition method using an air bridge mask (Non-patent documents 7 and 8). Various methods such as a direct drawing method (Non-Patent Document 9) by an electron beam exposure method (Electron Beam Lithography, EBL method) and a plating method (Non-Patent Documents 10 and 11) have been proposed. Among them, gaps of several tens of nm are formed by EBL or photolithography, and gaps between these gaps are narrowed by plating, so that gap widths of 3.3 nm ± 1.4 nm and 5 nm or less can be reproducibly and with a 90% yield. It has been reported that a gap electrode is produced (Non-patent Document 12).

JP 2006-147605 A JP 2003-086863 A Nano Letters 6, p.123, 2006 Phys. Rev. Lett. 93, p.136601, 2004 Science 306, p.86, 2004 J. Wunderlich and 12 others, “Coulomb Blockade Anisotropic Magnetoresistance Effect in a (Ga, Mn) As Single-Electron Transistor”, Phys. Rev. Lett. 97, p.077201, 2006 M.A.Reed and 4 others, "Conductance of a Molecular Junction", Science, 278, p.252, 1997 H. Park, 5 others, "Nanomechanical Oscillations in a single-C60 Transistor", Nature, 407, p57, 2000 Kazuki Sasao and five others, "Observation of Current Modulation thorough Self-Assembled Monolayer Molecule in Transistor Structure", Jpn. J. Appl. Phys., 43, pp. L337-L339, 2004 J.O.Lee and 8 others, "Absence of Strong Gate Effects in Electrial Measurements on Pheneylene-Based Conjugated Molecules", Nano Lett. 3, pp.113-117, 2003 M.S.M.Saifullah and three others, "A reliable scheme for reducing sub-5nm co-planar junctions for single-molecule electronics", Nanotechnology, 13, pp.659-662, 2002 Y.V.Kervannic and 4 others, "Nanometer-spaced electrodes with calibrated separation", Appl.phys.Lett., 80, pp.321, 2002 B.Liu and 7 others, "Controllable nanogap fabrication on microchip by chronopotentionmetry", Electrochimica Acta, 50, pp.3041-3047, 2005 C.S.Ah and 5 others, "Fabrication of integrated nanogap electrodes by surface-catalyzed chemical deposition", Appl.Phys.Lett., 88, pp.133116, 2006

  However, a general magnetoresistive element has a laminated structure of a magnetic fixed layer / insulating layer / magnetic free layer, and it is difficult to stably obtain the insulating performance of the insulating layer, which adversely affects the operation stability. The Coulomb blockade anisotropic magnetoresistive element has a laminated structure having a two-dimensional electron gas structure of a gallium / manganese / arsenic thin film.

  Accordingly, an object of the present invention is to provide a tunnel junction magnetoresistive element having a novel structure in which a tunnel junction is formed without having a laminated structure.

In order to achieve the above object, a tunnel magnetoresistive element of the present invention includes a first electrode made of a ferromagnetic material, a second electrode, and nanoparticles disposed between the first electrode and the second electrode. The nanoparticle has a protective group having an insulating property on the outer periphery of the ferromagnetic metal nanoparticle, and a tunnel junction is formed between the ferromagnetic metal nanoparticle and the first electrode. And
The tunnel magnetoresistive element of the present invention includes a first electrode made of a ferromagnetic material, a second electrode made of a ferromagnetic material, nanoparticles arranged between the first electrode and the second electrode, The nanoparticle has a protective group having insulating properties on the outer periphery of the ferromagnetic metal nanoparticle, and a first tunnel junction is formed between the ferromagnetic metal nanoparticle and the first electrode. A second tunnel junction is formed between the magnetic metal nanoparticles and the second electrode.

  According to the above configuration, since a tunnel junction is formed between the ferromagnetic metal nanoparticles and the electrode, it is not necessary to employ a laminated structure, and it is possible to operate stably. Further, it can be manufactured with a higher yield than conventional general tunneling magnetoresistive elements.

In the above configuration, the ferromagnetic metal nanoparticle has a smaller coercive force with respect to the external magnetic field than the electrode connected by the tunnel junction, the spin direction of the ferromagnetic metal nanoparticle is controlled by the external magnetic field, and the first electrode and the first electrode A switching function may be provided depending on the magnitude of the current flowing between the two electrodes. In particular, a ferromagnetic metal nanoparticle is used as a Coulomb island and has a switching function having a high magnetoresistance ratio due to the Coulomb blockade phenomenon.
The ferromagnetic metal nanoparticles have a smaller coercive force with respect to the external magnetic field than the electrodes connected by the tunnel junction, and the spin direction of the ferromagnetic metal nanoparticles changes with the external magnetic field, so that the first electrode and the second electrode It is preferable to detect the magnetic field based on the magnitude of the current flowing between the electrodes.
The ferromagnetic metal nanoparticles have a larger coercive force with respect to an external magnetic field than an electrode connected by a tunnel junction, and the spin direction of the first electrode or the second electrode is changed by the external magnetic field. The magnetic field may be detected based on the magnitude of the current flowing between the first electrode and the second electrode.
Furthermore, it is preferable to provide a gate electrode in a direction intersecting with the arrangement direction of the first electrode and the second electrode.

  According to the above configuration, a switching element, a magnetic sensor, or the like can be realized with a single tunnel junction magnetoresistive element or a double tunnel junction magnetoresistive element. In addition, since the structure having a gate electrode adopts a single electron transistor structure including a double tunnel junction resistance element, a Coulomb blockade anisotropic magnetoresistive element can be realized, the magnitude of magnetoresistive effect and signal change The positive / negative of can also be controlled by the gate electrode.

  According to the present invention, nanoparticles are arranged between a pair of electrodes, at least one of which is made of a ferromagnetic material, and the nanoparticles have an insulating layer as a protective group on the outer periphery of the ferromagnetic metal nanoparticles. A tunnel junction is formed between the ferromagnetic metal nanoparticles. Therefore, since there is no conventional magnetic pinned layer / insulating layer / magnetic free layer laminated structure, it can operate stably. A switching element or a magnetic field detection element can be realized by a single tunnel junction magnetoresistive element or a double tunnel magnetoresistive element.

Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings. In each figure, the same or corresponding members are denoted by the same reference numerals.
FIG. 1 is a diagram schematically showing the structure of a tunnel magnetoresistive element 10 of the present invention. As shown in FIG. 1, the tunnel magnetoresistive element 10 of the present invention includes a first electrode 12 and a second electrode 13 which are arranged to face each other with a predetermined gap on a substrate 11, It is configured to include nanoparticles 14 arranged in a gap with the second electrode 13. The substrate 11 is formed, for example, by forming an insulating layer 11a on a conductor substrate or a semiconductor substrate 11b.

FIG. 2 is a diagram showing the nanoparticles 14 in the tunnel resistance magnetoresistive element 10 shown in FIG. FIG. 3 is a diagram schematically showing L1 ₀ -FePt nanoparticles having a protecting group as a specific example of FIG. In FIG. 3, the white sphere represents Pt, and the hatched sphere represents Fe. As shown in FIGS. 2 and 3, the nanoparticle 14 is provided with a protective group 14 b having an insulating property on the outer periphery of a metal nanoparticle 14 a made of a ferromagnetic material. Here, the metal nanoparticles made of a ferromagnetic material, that is, the ferromagnetic metal nanoparticles 14a are soft magnetic materials such as Fe, Co, γ-Fe ₂ O _3, and hard magnetic materials such as FePt, CoPt, FePd, and MnAl. These are monodisperse nanoparticles. Monodisperse nanoparticles are nanoparticles with a standard deviation in particle size distribution of 10% or less. The ferromagnetic metal nanoparticles 14a have a predetermined particle size, shape, composition, crystal structure, and yield (g / batch). For example, the predetermined particle size is 3 to 10 nm, and the predetermined shape is a cubo-octahedron or a cube.

The ferromagnetic metal nanoparticles 14a have a predetermined coercive force by controlling any one or more of a predetermined particle size, a metal composition, and a firing temperature. For example, the coercivity when nanoparticles formed from FePt having a particle size of 3.1 nm are fired at 600 ° C. is about 2.8 kOe for Fe ₄₉ Pt ₅₁ , about 6.4 kOe for Fe ₅₅ Pt ₄₅ , Fe ₆₄ Pt. It becomes about 4 kOe at ₃₆ , and the coercive force increases as the composition ratio of iron increases. Furthermore, since the degree of ordering from the fcc (face-centered cubic) to the fct (face-centered cubic) structure increases as the firing temperature increases, the coercive force also increases.
In a nanoparticle having a single magnetic domain structure, the magnetization reversal due to thermal disturbance is suppressed as the particle size increases up to a particle size of about 20 nm, so that the coercive force also increases.

On the other hand, the protecting group 14b is an organic substance such as an organic acid or an organic amine. Examples of organic acids include oleic acid represented by chemical formula (1), fatty acids such as stearic acid, palmitic acid, myristic acid, lauric acid and capric acid, oleylamine represented by chemical formula (2) as organic amine, and stearyl. Aliphatic amines such as amine, myristylamine, laurylamine, caprylamine and adamantylamine are preferred.
The organic acid and the organic amine are attached as protective groups 14b around the ferromagnetic metal nanoparticles 14a in an approximately equimolar ratio, that is, in a molar ratio of 4/6 to 6/4, particularly preferably in a molar ratio of 5/5. ing.

  The first electrode 12 and the second electrode 13 are made of a ferromagnetic material such as Ni, Fe, Co, NiFe (permalloy), CoPtCr, BaFeO, MnAl, FePd, CoPt, FeNdB, FePt, and SmCo. Therefore, the first tunnel junction 15a is formed between the ferromagnetic metal nanoparticles 14a and the first electrode 12, and the second tunnel is formed between the ferromagnetic metal nanoparticles 14a and the second electrode 13. A junction 15b is formed, the first electrode 12 and the ferromagnetic metal nanoparticles 14a are connected by a first tunnel junction 15a, and the second electrode 13 and the ferromagnetic metal nanoparticles 14a are connected by a second tunnel junction 15b. Connected with.

  Here, the first electrode 12 and the second electrode 13 are made of different electrode materials, and the electrode-shaped structure such as the electrode width and the electrode length is made symmetric structure or asymmetric structure. The coercive force of can be changed. That is, when the electrode structure is symmetric, the magnetic moments of the first electrode 12 and the second electrode 13 are parallel in a constant external magnetic field, but in the constant external magnetic field, the first and second electrodes 12 and 13 have a parallel magnetic moment. The magnetic moments of the first electrode 12 and the second electrode 13 can be brought into an antiparallel state.

  As described above, the tunnel junction magnetoresistive element 10 shown in FIG. 1 is arranged such that the first and second electrodes 12 and 13 have a gap on the substrate 11 having an insulating surface, and the protective group 14b is made ferromagnetic. Since the nanoparticle 14 provided on the outer periphery of the metal nanoparticle 14a is arranged, the first and second tunnel junctions 15a and 15b have a double tunnel junction without having a laminated structure. Yes. Therefore, unlike the conventional case, there is no laminated structure of magnetic fixed layer / insulating layer / magnetic free layer in order to form a tunnel junction.

Here, the gap between the first electrode 12 and the second electrode 13, that is, the gap is preferably nano-order of 1 to 10 nm, particularly 3 to 5 nm. This is to reduce leakage current due to unnecessary tunneling processes. The tunnel current decreases exponentially with respect to the tunnel distance, and the current changes by one digit at 0.1 nm in a vacuum or the atmosphere. Therefore, when the gap is 1 nm or less, tunneling between the first electrode 12 and the second electrode 13 without interposing the ferromagnetic metal nanoparticles 14a causes a leakage current due to an unnecessary tunneling process to flow. Therefore, it is not preferable.
In particular, in the case of a Coulomb blockade anisotropic magnetoresistive element, the smaller the capacitance between the ferromagnetic metal nanoparticles 14a and the first electrode 12 and the second electrode 13, the better the temperature characteristics. It is preferable that the particle size of the ferromagnetic metal nanoparticles is small, and as a result, it is preferable that the gap is narrow.

  FIG. 4 is a diagram schematically showing a circuit configuration for operating the tunnel junction magnetoresistive element 10 shown in FIG. As shown in FIG. 4, a variable DC power source 21 is connected to the first electrode 12 side of the tunnel junction magnetoresistive element 10 and a current flowing through the tunnel junction magnetoresistive element 10 is measured on the second electrode 13 side. The ammeter 22 is connected. Thus, the current flowing through the tunnel junction magnetoresistive element 10 can be measured by the ammeter 22 and a change in the current can be detected.

Next, as a preferable form of the tunnel junction magnetoresistive element 10 shown in FIG. 1, the form in which the ferromagnetic metal nanoparticles 14a have a smaller or larger coercive force than the first electrode 12 and the second electrode 13 with respect to the external magnetic field. Will be described.
First, the case where the ferromagnetic metal nanoparticles 14a have a smaller coercive force against the external magnetic field than the first electrode 12 and the second electrode 13 will be described. Here, in order to make the ferromagnetic metal nanoparticles 14a have a smaller coercive force against the external magnetic field than the first electrode 12 and the second electrode 13, as described above, the particle size and composition of the ferromagnetic metal nanoparticles 14a. And adjusting the electrode material or the electrode shape of the first electrode 12 and the second electrode 13 can be realized. In this form, the spin direction of the ferromagnetic metal nanoparticles 14a can be controlled by an external magnetic field.

FIG. 5 is an explanatory diagram for illustrating the operation of the tunnel junction magnetoresistive element 10 shown in FIG. In the figure, white arrows indicate the spin state of electrons, and bold arrows indicate the flow of electrons.
When an external magnetic field is applied to the ferromagnetic metal nanoparticles 14a, the spin directions of the ferromagnetic metal nanoparticles 14a are aligned with the spin directions of the first electrode 12 and the second electrode 13 (FIG. 5A). The current flowing between the first electrode 12 and the second electrode 13 through the first tunnel junction 15a, the ferromagnetic metal nanoparticles 14a, and the second tunnel junction 15b can be increased. .
Conversely, when an external magnetic field is applied to the ferromagnetic metal nanoparticles 14a, the spin directions of the ferromagnetic metal nanoparticles 14a are made opposite to the spin directions of the first electrode 12 and the second electrode 13 (FIG. 5 (B)), the current flowing between the first electrode 12 and the second electrode 13 through the first tunnel junction 15a, the ferromagnetic metal nanoparticles 14a and the second tunnel junction 15b. Can be small.
Therefore, the tunnel magnetoresistive element 10 has a switching function for controlling the magnitude of current with an external magnetic field, and a detection function for detecting an external magnetic field by measuring a flowing current.

  On the contrary, even if the ferromagnetic metal nanoparticle 14a is a tunnel junction magnetoresistive element 10 having a larger coercive force with respect to the external magnetic field than the first electrode 12 and the second electrode 13, the first due to the external magnetic field A change in the spin direction of the electrode 12 and the second electrode 13 can be detected, and a magnetic field detection element can be realized.

Furthermore, the tunnel junction magnetoresistive element 10 shown in FIG. 1 has a structure in which metal nanoparticles are embedded between the first electrode 12 and the second electrode 13 made of a ferromagnetic material, that is, a double tunnel junction magnetoresistance. Since it is an element, it is possible to realize a switching function having a high magnetoresistance ratio due to the Coulomb blockade phenomenon by using metal nanoparticles as Coulomb islands.
That is, in the double tunnel junction structure in which the ferromagnetic metal nanoparticle 14 is a Coulomb island, when electrons tunnel from the first electrode 12 or the second electrode 13 to the ferromagnetic metal nanoparticle 14, the intermediate electrode A so-called Coulomb blockade phenomenon is observed in which a single electron is transported on the ferromagnetic metal nanoparticles 14 that play a role, and the current value takes a discontinuous value corresponding to each electron. Such a single electronic element can detect the behavior of a single electron and can operate as a very sensitive sensor. Furthermore, this time, by using a magnetic material as an electrode material, it is affected by spin interaction when electrons tunnel.

On the other hand, the conventionally produced tunnel resistance element has a laminated structure, and even though a double tunnel junction can be formed, the size of the intermediate electrode cannot be controlled. As the size of the intermediate electrode increases, the capacitance between the intermediate electrode and the electrodes 12 and 13 increases, making it difficult to observe the Coulomb blockade phenomenon, increasing the number of electrons tunneling, and thus increasing the noise. .
Therefore, in the structure of the tunnel junction magnetoresistive element 10 shown in FIG. 1, since the intermediate electrode is ideally one ferromagnetic nanoparticle, electrons are tunneled one by one by the Coulomb blockade phenomenon, and noise is reduced. Thus, a higher magnetoresistance ratio can be realized.

Next, a modified example will be described.
As a modification, a double tunnel junction is not formed like the tunnel junction magnetoresistive element 10 shown in FIG. 1, and only one of the first electrode 11 and the second electrode 12 is made of a ferromagnetic material and is single-layered. The tunnel junction may be formed. That is, one of the first electrode 12 and the second electrode 13 is a ferromagnetic material, and the other is a non-magnetic material. In this case, the nonmagnetic electrode is made of Au, Ag, Cu, Al, Pt, Ir, Pd, Mo, W, Ta, Cr, Ru, Rh, Mn, or the like.

  As another modification, even if, for example, the first electrode 11 is tunnel-joined with the ferromagnetic metal nanoparticles 14a and the second electrode 12 is not tunnel-joined with the ferromagnetic metal nanoparticles 14a, the pair of electrodes is not required. Good. In this case, the one electrode 11 or 12 that is not tunnel-junction and the ferromagnetic metal nanoparticle 14a are electrically connected, or the nanoparticle is embedded between the nanogap electrodes.

  As another modification, a gate electrode or a pair of gate electrodes may be arranged in a direction intersecting with the arrangement direction of the first electrode 12 and the second electrode 13. Here, the gate electrode may be magnetic or non-magnetic. For example, Au, Ag, Cu, Al, Pt, Ir, Pd, Mo, W, Ta, Cr, Ru, Rh, Mn, Ni, Fe, Co NiFe, CoPtCr, BaFeO, MnAl, FePd, CoPt, FeNdB, FePt, SmCo, and the like.

  FIG. 6 is a diagram schematically showing a tunnel junction magnetoresistive element 30 of the present invention. The tunnel junction magnetoresistive element 30 of the present invention is configured by providing a gate electrode 31 as a third electrode so as to be orthogonal to the arrangement direction of the first electrode 12 and the second electrode 13 forming a gap.

  FIG. 7 is a diagram schematically showing a tunnel junction magnetoresistive element 40 of the present invention. The tunnel junction magnetoresistive element 40 of the present invention includes a first gate electrode 41 and a fourth electrode as third electrodes so as to be orthogonal to the arrangement direction of the first electrode 12 and the second electrode 13 forming the gap. The second gate electrode 42 is provided.

  Thus, by having the gate electrodes 31, 41 and 42, a single electron transistor structure including a double tunnel junction magnetoresistive element is adopted, whereby the voltage applied to the gate electrodes 31, 41 and 42 ( The magnitude of the magnetoresistive effect and the sign of the signal change can be controlled by the gate voltage. That is, the number of electrons on the ferromagnetic metal nanoparticle 14a serving as the intermediate electrode varies depending on the tunneling of electrons from the first electrode 12 or the second electrode 13 and the control of the gate voltage. When electrons are present on the ferromagnetic metal nanoparticle 14a, there is a repulsive force due to electrostatic force on the next electron to be tunneled on the ferromagnetic metal nanoparticle 14a. It is necessary to apply an extra voltage for the repulsive force compared to the case where there is no. That is, the resistance and positive / negative of the element can be controlled by the gate electrodes 31, 41 and 42. In particular, when the gate electrodes 31, 41, and 42 are made of a magnetic material, the direction of electron spin on the ferromagnetic metal nanoparticles 14a can be controlled by spin injection from the gate electrodes 31, 41, and 42. In addition to the external magnetic field, the magnetoresistive effect due to the gate electrode can be expected.

Next, a method for manufacturing the tunnel magnetoresistive element 10 will be described.
First, the first electrode 12 and the second electrode 13 are formed so as to have a nanogap. At that time, it is preferable to form a gap of several tens of nanometers by electron beam lithography (EBL) or optical lithography, and then narrow the gap by plating to a predetermined distance. This is because reproducibility and process suitability are good, and a large number of elements can be constructed at a time. Further, a gap of about 10 nm may be directly formed by electron beam lithography.
Here, it is preferable that the gap interval is narrow. This is because the capacitance between the ferromagnetic metal nanoparticles 14a as the Coulomb island and the first and second electrodes 12 and 13 is small, and the temperature characteristics of the Coulomb blockade anisotropic magnetoresistive element are excellent.

  Next, superparamagnetic nanoparticles are arranged and embedded between the first electrode 12 and the second electrode 13, and then subjected to heat treatment, thereby transforming the superparamagnetic nanoparticles and the ferromagnetic nanoparticles 14a. To do. Taking the case of ferromagnetic FePt nanoparticles as an example, as a first method, superparamagnetic fcc-FePt nanoparticles arranged between the first electrode 12 and the second electrode 13 are set at a predetermined temperature, for example, 300 to 600. Heat treatment at about ℃ to transform to ferromagnetism. Then, the protective group 14b used as a tunnel layer is coordinated to the nanoparticle surface by being immersed in the solution containing the protective group 14b. Here, the nanoparticles 14 can be disposed between the nanogap electrodes by a coating method, a spray jet method, a dipping method, an LB method, or the like.

  As a second method, the superparamagnetic fcc-FePt nanoparticles disposed between the first electrode 12 and the second electrode 13 are heat-treated in a hydrogen atmosphere, so that the protective group 14b remains and is partially ordered. Ferromagnetic ferromagnetic FePt nanoparticles. For example, when heat treatment is performed at 300 ° C. in a 4% hydrogen atmosphere, the coercive force is about 3 kOe. In this case, it is not necessary to immerse in a solution containing the protecting group 14b.

A modification of the method for manufacturing the tunnel magnetoresistive element 10 will be described.
The first electrode 12 and the second electrode 13 are formed so as to have a nanogap, but the previously prepared ferromagnetic metal nanoparticles 14 are placed between the first electrode 12 and the second electrode 13. It differs in that it is embedded in. In the case of ferromagnetic FePt nanoparticles, for example, by preparing metal nanoparticles 14a having protective groups 14b at about 400 ° C. in an autoclave, it is possible to obtain FePt nanoparticles made of a partially ordered ferromagnetic material. it can. Further, after confining superparamagnetic fcc-FePt nanoparticles in a silica shell or NaCl microcrystal, and transforming to ferromagnetic at about 600 ° C., the silica shell or NaCl microcrystal is dissolved, thereby attaching a protective group 14b. Ferromagnetic FePt nanoparticles 14 can be obtained. The ferromagnetic metal nanoparticles 14 thus produced are arranged and embedded between the first electrode 12 and the second electrode 13. At this time, the substrate in which the nanogap is formed is immersed in a solution containing the nanoparticle 14 or the solution containing the nanoparticle 14 is dropped on the substrate in which the nanogap is formed. .

  As described above, the tunnel junction magnetoresistive element 10 shown in FIG. 1 can be manufactured. When the tunnel magnetoresistive elements 30 and 40 are manufactured, the gate electrode 31 as the third electrode or the fourth electrode is formed simultaneously with or after the first electrode 12 and the second electrode 13 are formed. By forming 41 and 42, it can be produced in the same manner as the tunnel junction magnetoresistive element 10.

Next, examples will be described.
First, the first electrode 12 and the second electrode were formed to have a nanogap by using a lithography method.

  Next, a three-necked flask equipped with a thermometer, a reflux condenser and a nitrogen inlet tube, 30.7 mmol of iron acetylacetonate (Fe (acac)), 20.30 mmol of platinum acetylacetonate (Pt (acac)), 5 oleic acid 0.0 mmol, 0.5 mmol of oleylamine and 1.5 mmol of 1,2-hexadecanediol were added, and the temperature was raised to 160 ° C. while flowing nitrogen gas. Subsequently, alloy nanoparticles were synthesized by stirring at 300 ° C. for 30 minutes. The synthesized alloy nanoparticles were heat-treated at 400 to 600 ° C. to transform the nanoparticles into a ferromagnetic material.

  FIG. 8 is a diagram showing a TEM image of the nanoparticles produced in the example. From the figure, it can be seen that FePt nanoparticles of 5.1 nm ± 0.7 nm are formed.

  Thereafter, the substrate on which the nanogap is formed is immersed in a solution containing the nanoparticles, so that the nanoparticles 14 are arranged between the gaps of the first electrode 12 and the second electrode 13, and the tunnel junction magnetoresistance An element was obtained.

  The tunnel junction magnetoresistive element 10 of the present invention is expected to expand to a nm-scale memory sensor, which is expected to increase in the future, and is expected to play an important role in the field of molecular nanoelectronics.

It is a figure which shows typically the structure of the tunnel magnetoresistive element of this invention. It is a figure which shows typically the nanoparticle in the tunnel resistance magnetoresistive element shown in FIG. It is a figure which shows typically the L1 ₀ -FePt nanoparticle which has a protecting group. It is a figure which shows typically the circuit structure for operating the tunnel junction magnetoresistive element shown in FIG. FIG. 5 is an explanatory diagram for illustrating the operation of the tunnel junction magnetoresistive element shown in FIG. 1. It is a figure which shows typically the tunnel junction magnetoresistive element of this invention. It is a figure which shows typically the tunnel junction magnetoresistive element of this invention. It is a figure which shows the TEM image of the nanoparticle produced in the Example.

Explanation of symbols

10, 30, 40: Tunnel resistance magnetoresistive element 11: Substrate 11a: Insulating layer 11b: Conductor substrate or semiconductor substrate 12: First electrode 13: Second electrode 14: Nanoparticle 14a: Ferromagnetic metal nanoparticle 14b: Protective group 15a: first tunnel junction 15b: second tunnel junction 21: variable DC power supply 22: ammeter 31, 41, 42: gate electrode

Claims (7)

A first electrode made of a ferromagnetic material, a second electrode, and nanoparticles disposed between the first electrode and the second electrode,
The nanoparticles have an insulating protective group on the outer periphery of the ferromagnetic metal nanoparticles,
A tunnel magnetoresistive element, wherein a tunnel junction is formed between the ferromagnetic metal nanoparticles and the first electrode. A first electrode made of a ferromagnetic material, a second electrode made of a ferromagnetic material, and nanoparticles arranged between the first electrode and the second electrode,
The nanoparticles have an insulating protective group on the outer periphery of the ferromagnetic metal nanoparticles,
A first tunnel junction is formed between the ferromagnetic metal nanoparticles and the first electrode;
A tunnel magnetoresistive element, wherein a second tunnel junction is formed between the ferromagnetic metal nanoparticles and the second electrode.   The ferromagnetic metal nanoparticles have a smaller coercive force with respect to an external magnetic field than electrodes connected by the tunnel junction, and the spin direction of the ferromagnetic metal nanoparticles is controlled by an external magnetic field. The tunnel magnetoresistive element according to claim 1, wherein the tunnel magnetoresistive element has a switching function depending on a magnitude of a current flowing between the second electrode and the second electrode.   4. The tunnel magnetoresistive element according to claim 3, wherein the ferromagnetic metal nanoparticles are a Coulomb island and have a switching function having a high magnetoresistance ratio due to a Coulomb blockade phenomenon. 5.   The ferromagnetic metal nanoparticles have a smaller coercive force with respect to an external magnetic field than an electrode connected by the tunnel junction, and the spin direction of the ferromagnetic metal nanoparticles is changed by the external magnetic field, whereby the first electrode The tunnel magnetoresistive element according to claim 1, wherein a magnetic field is detected based on a magnitude of a current flowing between the first electrode and the second electrode.   The ferromagnetic metal nanoparticles have a larger coercive force against an external magnetic field than the electrodes connected by the tunnel junction, and the spin direction of the first electrode or the second electrode changes in the external magnetic field, The tunnel magnetoresistive element according to claim 1, wherein a magnetic field is detected based on a magnitude of a current flowing between the first electrode and the second electrode.   The tunnel magnetoresistive element according to claim 2, further comprising a gate electrode in a direction intersecting with an arrangement direction of the first electrode and the second electrode.