Spin injection magnetic domain wall displacement device and element thereof

A spin injection magnetic domain wall displacement wall displacement device has a plurality of spin injection magnetic domain wall displacement elements. Each element includes a magnetic domain wall displacement layer having a magnetic domain wall, a first magnetic layer group having at least one ferromagnetic layer, and a second magnetic layer group having at least one ferromagnetic layer. The first magnetic layer group is disposed at one end or side of the magnetic domain wall displacement layer and the second magnetic layer group disposed at the other end or side thereof. The magnetic domain wall in the magnetic domain wall displacement layer is displaced by flowing electrons between the first magnetic layer group and the second magnetic layer group. Part of the magnetic domain wall displacement layer can be in antiferromagnetic coupling with the first magnetic layer group, and the other part of the magnetic domain wall displacement layer can be in antiferromagnetic or ferromagnetic coupling with the second magnetic layer group. The element enables detection of the displacement of the magnetic domain wall by measuring the change in the electric resistance. Moreover, the magnetic domain wall displacement at a high speed with a low level current and thermal stability of the recorded magnetic domain wall can be made compatible.

BACKGROUND

FIG. 18schematically shows a cross sectional structure for explaining an example of an arrangement of a previously proposed GMR (Giant Magneto-Resistance) element making use of a GMR effect. For example, on a silicon substrate200, a first electrode201, a first ferromagnetic layer203(with a thickness of approximately 40 nm and a diameter of approximately 100 nm) made of a material such as Co, a nonmagnetic metal layer204(with a thickness of approximately 6 nm and a diameter of approximately 100 nm), a second ferromagnetic layer205(with a thickness of approximately 2.5 nm and a diameter of approximately 100 nm) made of a material such as Co, and a second electrode206are formed in this order. Further, a bit line207is formed on the first electrode201. It is known that such a GMR element can reverse the direction of magnetization of the second ferromagnetic layer205by spin current injection from the second electrode206side, that is, injection of electrons with polarized spins from the first electrode201side. See for example JP-A-2004-207707 and J. A. Katine, et al.,Current-Driven Magnetization Reversal and Spin-Wave Excitations in Co/Cu/Co Pillars, Physical Review Letters, Vol. 84, No. 14, pp. 3149-3152 (2000).

The operation principle of the element is explained as follows. First, a magnetic field with a sufficient strength is applied to the element to align the directions of magnetization of the first ferromagnetic layer203and the second ferromagnetic layer205in the same direction.FIG. 19Aschematically show a cross sectional view of the element shown inFIG. 18in which the direction of magnetization in the ferromagnetic layers are aligned rightwardly (arrows in the figure showing the direction of magnetization) in each ferromagnetic layer. In the following drawings, arrows have the same meaning. The state is to be referred to as the parallel state (P-state). In this state, an electric current flowing in the direction from the second electrode206side to the first electrode201side causes electrons to be injected from the first electrode201to the first ferromagnetic layer203. In the first electrode201, the electron spins are in a state in which the distribution of up-spins corresponds to that of down-spins. In the ferromagnetic layers, however, due to interaction (s-d interaction) between the electron spins and the spins of ferromagnetic metal atoms, the directions of the electron spins are aligned with the direction of magnetization of the first ferromagnetic layer. This is referred to as polarization of spin. Injection of electrons with thus polarized spins into the second ferromagnetic layer205through the nonmagnetic metal layer204exerts a torque on the magnetization of the ferromagnetic layer205in the direction expressed by following Equation (1):
j·M(ferromagnetic layer 205)×M(ferromagnetic layer 203)×M(ferromagnetic layer 205)  (1),
where j is a current (a scalar quantity), M(ferromagnetic layer205) is a unit vector in the direction of the magnetization of the ferromagnetic layer205, and M(ferromagnetic layer203) is a unit vector in the direction of the magnetization of the ferromagnetic layer203.

The torque expressed by Equation (1) is also exerted to the magnetization of ferromagnetic layer203. The ferromagnetic layer203, however, has a thickness sufficiently larger than the thickness of the ferromagnetic layer205, so that the magnetization of the ferromagnetic layer203is unaffected. Therefore, a current exceeding a certain level of a critical current causes only the direction of the magnetization of the ferromagnetic layer205to rotate by the exerted torque, by which the state of the magnetization between the ferromagnetic layer205and the ferromagnetic layer203changes from the P-state shown inFIG. 19Ato an anti-parallel state (AP state) shown inFIG. 19B.

An explanation is made when a current flows from the first electrode201to the second electrode206in the element in the AP-state. In this case, the sign of the current in Equation (1) expressing the direction of torque becomes negative, so that a torque in the direction opposite to the above is exerted on the magnetization of the ferromagnetic layer205. As a result, a current exceeding a certain level of a critical current causes the direction of the magnetization of the ferromagnetic layer205to be inverted, by which the state of the magnetization in the element returns from the AP-state to the P-state shown inFIG. 19A. The electric resistance of a GMR element is known to be small in the p-state and large in the AP-state with the rate of change being several tens of percent. By using the GMR effect, a reading head can be manufactured for a hard disk.FIG. 20is a schematic view showing a planar structure of an MRAM (Magnetic Random Access Memory) in which a plurality of the GMR elements shown inFIG. 18are connected to use the inversion of magnetization of GMR elements by current injection. With the use of the arrangement as shown inFIG. 20, writing (inversion of magnetization) and reading (detection of electric resistance values corresponding to states of magnetization of recording cells209) of bit information to and from the recording cells209are principally possible by a group of laterally running word lines208and a group of longitudinally running bit lines207.

FIGS. 21,22A, and22B schematically illustrate cross sectional views each for explaining a phenomenon of displacement of a magnetic domain wall formed in a ferromagnetic wire in a related magnetic domain wall displacement element by a current flowing in the ferromagnetic wire. See for example A. Yamaguchi, et al.,Real-Space Observation of Current-Driven Domain Wall Motion in Submicron Magnetic Wires, Physical Review Letters, Vol. 92 No. 7, 077205 (2004).FIG. 21is a schematic cross sectional view showing an arrangement of the element, in which a ferromagnetic layer221(10 nm in thickness and several micrometers in length) is formed on an insulator substrate220. On the ferromagnetic layer221, a first electrode222and a second electrode223are formed. For the ferromagnetic layer221, a material such as a permalloy (Ni81Fe19) thin film is used. For the first and second electrodes222and223, a material such as copper (Cu), gold (Au), or platinum (Pt) is used.FIGS. 22A and 22Bare schematic cross sectional views for explaining the principle of displacement of a magnetic domain wall224when a current flows between the first electrode222and the second electrode223. In each of the views, the directions of magnetization in the magnetic layer are shown with arrows like in the above explanation.

First, as shown inFIG. 22A, consider the case in which there is one magnetic domain wall224in the region of the ferromagnetic layer221between two electrodes and the direction of magnetization on the right side of the magnetic domain wall224is opposite to the direction of magnetization on the left side. When flowing a current in this state from the second electrode223to the first electrode222, the current crosses the magnetic domain wall224. At that time, electrons are injected from the first electrode222into the ferromagnetic layer221to flow into the second electrode223. The directions of spins of electrons injected into the ferromagnetic layer221are considered to be aligned by s-d interaction in the same direction as the direction of magnetization in the region on the left side of the magnetic domain wall224in the ferromagnetic layer221(also referred to as polarization). The magnetization due to spins of the polarized electrons is taken as Sl (a rightward vector). Then, when the spin-polarized electrons pass through the magnetic domain wall224and are injected into the region on the right-hand side of the magnetic domain wall224of the ferromagnetic layer221, the directions of spins of electrons is to be aligned this time by s-d interaction in the same direction as the direction of magnetization opposite to the direction before the electrons pass through the magnetic domain wall224. The magnetization due to spins of the electrons polarized on the right-hand side of the magnetic domain wall224is taken as Sr (a leftward vector). Moreover, the magnetization on the left-hand side of the ferromagnetic layer224and the magnetization on the right-hand side are taken as Ml (a rightward vector) and Mr (a leftward vector), respectively.

As was explained above, with the direction of Sr considered to be positive, in the process in which electrons move from the left-hand side to the right-hand side of the magnetic domain wall224, magnetization Sr due to electron spin changes to Sl to result in an increase in electron spins in the negative direction. Before and after electrons cross the magnetic domain wall, the total sum (Ml+Sl+Mr+Sr) of spin angular momentum of magnetization of the magnetic material and conduction electrons is conserved to be constant. In a process in which conduction electrons on the left-hand side of the magnetic domain wall cross the magnetic domain wall, the total sum of whole spin angular momentum of electrons (Sl+Sr) increases by 2Sr (decreases by 2Sl). That is, by the conduction electrons crossing the magnetic domain wall224from the left-hand side to the right-hand side, the magnetization M1of the magnetic domain wall is to go on increasing (the magnetic domain wall224is to go on moving in the same direction as the direction in which electrons flow).

FIGS. 22A and 22Bshow the difference in position of the magnetic domain wall224between the state before a current is made to flow from the electrode223and the state after a current is made to flow from the electrode223. In this way, it is known that the magnetic domain wall224moves in the direction opposite to the direction in which the current flows. It is reported that the current density enabling the displacement of the magnetic domain wall is of the order of 108A/cm2in the case of metallic magnetic material such as permalloy and of the order of 8×104A/cm2in the case of ferromagnetic semiconductor and that, by increasing a current density, the displacement speed of the magnetic domain wall becomes of the order of 3 m/s. See for example Yamaguchi's paper and Michihiko Yamanouchi, Abstract for 60th Annual Meeting Phys. Soc. Jpn., p. 27aYP-5, Mar. 27 (2005).

Each of the above-explained two technologies inverts the magnetization direction by flowing a current in the element. Its operation principle is based on the fact that, when spin-polarized electrons are injected into a ferromagnet, a torque due to electron spin is exerted on the magnetization of the ferromagnet. At this time, the total of the magnetization due to spins of the injected free electrons and the magnetization of the ferromagnet is conserved. Thus, for bringing about inversion of magnetization with a slight amount of injected electrons (or an injected current), the volume and the magnitude of saturation magnetization of the ferromagnet subjected to inversion of magnetization must be made small.

For example, in the case of the MRAM shown inFIG. 20, when its volume and its saturation magnetization are made small, a problem arises in that thermal stability of recording bit, namely thermal stability of magnetization of the recording cell209, becomes low, causing thermal fluctuation of magnetization by thermal disturbance, even at room temperature, and making it impossible to keep the magnetization of the recording cell. Also in the arrangement shown inFIG. 21, for carrying out high speed displacement of the magnetic domain wall by a slight current, saturation magnetization must be lowered. However, lowering the magnetization saturation increases thermal fluctuation of magnetization forming the magnetic domain wall. Thus, it can be easily supposed that a problem arises in which the position of the magnetic domain wall is randomly displaced by thermal agitation.

Furthermore, with the structure shown inFIG. 21, although it is possible to induce a change in a state of magnetization, i.e., displacement of the magnetic domain wall, by supplying a current, it is difficult to detect a state of magnetization. This is because, in the case of the arrangement shown inFIG. 20, only the position of the magnetic domain wall changes without change in the length of the magnetic layer in which a current flows. Although the ratio of the length of the region magnetized rightward and the length of the region magnetized leftward changes in the ferromagnet221, it is considered that the rightward resistivity and the leftward resistivity are the same. Therefore, the difference in the electric resistance due to change in the ratio of the lengths is in a negligible level. Hence, only with such displacement of the magnetic domain wall, there is no large change in the electric resistance between both of the electrodes.

Accordingly, there remains a need for an element in which the magnetized state of the element can be changed by flowing a current between two electrodes and changing the electric resistance between the two electrodes depending on the magnetized state of the element, to provide the element as one in which thermal stability of the magnetized state of the element is improved, while a critical current necessary for changing the magnetized state remains small. Also, there remains a need for an element in which a magnetic domain wall is displaced by flowing a current between two electrodes of a magnetic material, to provide the element as one in which the electric resistance between the two electrodes is changed by displacement of the magnetic domain wall. The present invention addresses these needs.

SUMMARY OF THE INVENTION

The present invention relates to a basic structure element forming a magnetic sensor or a magnetic memory and a device incorporating the element. More specifically, the present invention relates to an element in which electron spin injection is controlled to form a magnetic random access memory having a large capacity and including no mechanical driving section or to an element that detects electron spin injection to form a faint electric current sensor, and a device using the element.

One aspect of the present invention is a spin injection magnetic domain wall displacement element. The element can include a magnetic domain wall displacement layer having a magnetic domain wall, a first magnetic layer group having at least one ferromagnetic layer, and a second magnetic layer group having at least one ferromagnetic layer. The first magnetic layer group is disposed at one end of the magnetic domain wall displacement layer and the second magnetic layer group disposed at the other end of the magnetic domain wall displacement layer. The magnetic domain wall in the magnetic domain wall displacement layer is displaceable by flowing electrons between the first magnetic layer group and the second magnetic layer group.

At least part of the magnetic domain wall displacement layer is in contact with the first magnetic layer group and is in antiferromagnetic coupling with the first magnetic layer group, and at least part of the magnetic domain wall displacement layer is in contact with the second magnetic layer group and is in antiferromagnetic or ferromagnetic coupling with the second magnetic layer group.

In one embodiment, the first magnetic layer group and the second magnetic layer group can be disposed on different surfaces of the magnetic domain wall displacement layer and positioned opposing each other while holding the magnetic domain wall displacement layer therebetween. In another embodiment, the first magnetic layer group and the second magnetic layer group can be disposed on the same surface of the magnetic domain wall displacement layer.

The first magnetic layer group can comprise a nonmagnetic first exchange coupling control layer and a first ferromagnetic layer laminated together, with the first exchange coupling control layer in contact with the magnetic domain wall displacement layer. The first magnetic layer group can comprise a nonmagnetic first exchange coupling control layer and a first ferromagnetic layer laminated together, with the first exchange coupling control layer in contact with the magnetic domain wall displacement layer.

The second magnetic layer group can comprise a nonmagnetic intermediate exchange coupling control layer, an intermediate ferromagnetic layer, a nonmagnetic second exchange coupling control layer, and a second ferromagnetic layer laminated in this order, with the intermediate exchange coupling control layer in contact with the magnetic domain wall displacement layer.

The first magnetic layer group can comprise a nonmagnetic layer and a first ferromagnetic layer laminated together. The nonmagnetic layer can comprise a first exchange coupling control layer and a first nonmagnetic metal layer. Both the first exchange coupling control layer and the first nonmagnetic metal layer can be in contact with the magnetic domain wall displacement layer.

The second magnetic layer group can comprise a nonmagnetic layer, an intermediate ferromagnetic layer, a nonmagnetic second exchange coupling control layer and a second ferromagnetic layer being laminated in this order. The nonmagnetic layer can comprise an intermediate exchange coupling control layer and an intermediate nonmagnetic metal layer. Both the intermediate exchange coupling control layer and the intermediate nonmagnetic metal layer can be in contact with the magnetic domain wall displacement layer.

The first magnetic layer group can comprise a first exchange coupling control layer and a first ferromagnetic layer laminated together, with the first exchange coupling control layer in contact with the magnetic domain wall displacement layer.

The second magnetic layer group can comprise a nonmagnetic third exchange coupling control layer and a third ferromagnetic layer laminated together, with the third exchange coupling control layer in contact with the magnetic domain wall displacement layer.

The nonmagnetic layer of the second magnetic layer group can comprise a third exchange coupling control layer and a third nonmagnetic metal layer. Both the third exchange coupling control layer and the third nonmagnetic metal layer are in contact with the magnetic domain wall displacement layer.

The second magnetic layer group can comprise a fourth ferromagnetic layer.

The film thickness of the intermediate ferromagnetic layer can be smaller than the spin relaxation length of electrons in the intermediate ferromagnetic layer.

Another aspect of the present invention is a spin injection magnetic domain wall displacement device comprising a plurality of the spin injection magnetic domain wall displacement elements described above. The device can carry out writing and reading based on the difference in electric resistance.

DETAILED DESCRIPTION

FIG. 1is a schematic cross sectional view for explaining an example of the basic arrangement of a first embodiment of a spin injection magnetic domain wall displacement element according to the invention. On a substrate4, there are formed in the order a first electrode5, a first magnetic layer group100, a magnetic domain wall displacement layer8, a second magnetic layer group101and a second electrode2. Further, a bit line1is formed on the first electrode5. The first magnetic layer group100is formed of a first ferromagnetic layer6and a first exchange coupling control layer7. The second magnetic layer group101is formed of an intermediate exchange coupling control layer9, an intermediate ferromagnetic layer10, a second exchange coupling control layer11and a second ferromagnetic layer12. The arrangement shown inFIG. 1is the minimum unit of the element and the necessary number of the elements are disposed on the same substrate to form a desired device. Circuits and driving elements for driving the elements according to the invention can be also arranged on the same substrate.

FIGS. 2A and 2BillustrateFIG. 1in different states for explaining the operation principle of the first embodiment. In each of the magnetic layers in the element shown inFIG. 1, the direction of magnetization thereof is shown with an arrow. The magnetic domain wall displacement layer8is divided by a magnetic domain wall13into a magnetic domain wall displacement layer8aon the first electrode5side and a magnetic domain wall displacement layer8bon the second electrode2side.

The material for the substrate4can be selected as required depending on the desired flatness when the material has an insulation property for individually controlling a plurality of the elements arranged on the substrate and has sufficient rigidity for holding the elements. For example, an insulating substrate of sapphire or silicon oxide with a thickness of several hundreds of micrometers or a semiconductor substrate whose surface is oxidized to ensure insulating property can be used.

The material of the first electrode5can be selected as required when it is a conductive material. The thickness thereof is preferably within the range from several tens of nanometers to several hundreds of nanometers and its area is preferably within the range from 50 nm×50 nm to 1000 nm×1000 nm. Moreover, the shape thereof is preferably a rectangle, but can be a circle or an oval as desired.

The first ferromagnetic layer6and the first exchange coupling control layer7are for providing antiferromagnetic coupling between the first ferromagnetic layer6and the magnetic domain wall displacement layer8aon the first electrode5side in part of the magnetic domain wall displacement layer8. By the antiferromagnetic coupling thus provided, the direction of magnetization of the magnetic domain wall displacement layer8aon the first electrode5side is fixed in the direction opposite to the direction of the magnetization of the first ferromagnetic layer6.

The material of the first ferromagnetic layer6can be selected as necessary from materials having ferromagnetism. For example, alloys such as a Co alloy, a CoPt alloy, a CoPtCr alloy, and a CoCr alloy can be used. During the operation of the element, the magnetization of the first ferromagnetic layer6is preferably fixed in one direction. Thus, the first ferromagnetic layer6has preferably a high coercive force and a large film thickness. The coercive force is preferably from 2000 to 4000 Oe and the thickness is preferably from 50 nm to 200 nm. Moreover, for the material thereof, an ordered alloy such as Co50Pt50is particularly preferable. This is because some ordered alloys are known to have magnetic anisotropy constants Ku exceeding 1×107erg/cm2. With such alloys, the direction of magnetization can be kept stably.

The first exchange coupling control layer7is a nonmagnetic layer for separating the first ferromagnetic layer6and the magnetic domain wall displacement layer8with a specified clearance to control an exchange coupling constant in the exchange coupling between the first ferromagnetic layer6and the magnetic domain wall displacement layer8aon the first electrode5side. The material thereof is preferably Ru, V, C, Nb, Mo, Rh, Ta, W, Re, Ir, Pt, or Pd, or an alloy with the main ingredient being any one of the elements. The exchange coupling constant changes from positive value to negative value depending on the thickness of the first exchange coupling control layer7. Consequently, the thickness of the first exchange coupling control layer7is selected so that antiferromagnetic coupling is provided between the first ferromagnetic layer6and the magnetic domain wall displacement layer8aon the first electrode5side. However, an excessive thickness of the first exchange coupling control layer7creates a weak exchange coupling. Therefore, the thickness is preferably determined as being from 0.5 to 3 nm. For example, in the case in which the first ferromagnetic layer6is made of a CoPt alloy, the first exchange coupling control layer7is made of Ru and the magnetic domain wall displacement layer8is made of a CoHfTa alloy, an antiferromagnetic coupling can be provided with the film thickness of Ru made at 0.8 nm and a ferromagnetic coupling can be provided with the film thickness of Ru made at 1.8 nm.

The magnetic domain wall displacement layer8is a layer that makes the electric resistance of the whole element shown inFIG. 1change depending on the position of the magnetic domain wall13formed in the layer and brings about hysteresis. The detailed explanation of the operation thereof will be given later. The material can be any magnetic material with a magnetic domain wall presented therein, for which a material such as magnetic metal, ferromagnetic semiconductor or ferromagnetic oxide can be used. This is preferably a material such as permalloy, a CoFe alloy, a CoFeB alloy, a NiCoFe alloy, a CoCrFeAl alloy, Fe, a FePt alloy, a NiMnSb alloy, a CoMn group alloy, Sr2FeMoO6, Fe2O3, or CoHfTa. Particularly preferable is permalloy, Co90Fe10, Co2MnAl, Co2MnSi, or Co2MnGe. The film thickness thereof is preferably from 50 nm to 500 nm. It is necessary for the direction of magnetization of the magnetic domain wall displacement layer8aon the first electrode5side to be easily controlled depending on the direction of magnetization of the first ferromagnetic layer6, or for the direction of magnetization of the magnetic domain wall displacement layer8bon the second electrode2side to be easily controlled depending on the direction of magnetization of the second ferromagnetic layer12. Therefore, the coercive force of the magnetic domain wall displacement layer8is preferably equal to 10 Oe or less.

The intermediate exchange coupling control layer9, the intermediate ferromagnetic layer10, the second exchange coupling control layer11, and the second ferromagnetic layer12are for providing antiferromagnetic coupling between the second ferromagnetic layer12and the intermediate ferromagnetic layer10, and between the intermediate ferromagnetic layer10and the magnetic domain wall displacement layer8bon the second electrode2side. By the antiferromagnetic coupling thus provided, the direction of magnetization of the magnetic domain wall displacement layer8bon the second electrode2side is fixed in the same direction as the direction of the magnetization of the second ferromagnetic layer12. Furthermore, by adequately controlling the film thickness of the intermediate ferromagnetic layer10, spins of injected electrons can be controlled.

The intermediate exchange coupling control layer9is a nonmagnetic layer for separating the intermediate ferromagnetic layer10and the magnetic domain wall displacement layer8with a specified clearance to control an exchange coupling constant in the exchange coupling between the intermediate ferromagnetic layer10and the magnetic domain wall displacement layer8bon the second electrode2side. The material and the film thickness of the intermediate exchange coupling control layer9is determined similarly to those for the first exchange coupling control layer7.

The intermediate ferromagnetic layer10is for providing the above antiferromagnetic coupling as well as for injecting electrons into the adjacent layer with the spins of injected electrons being conserved. For example, electrons injected from the intermediate exchange coupling control layer9pass through the intermediate ferromagnetic layer10and are injected into the second exchange coupling control layer11with respective polarized states of electron spins almost being conserved. The directions of polarized electron spins are conserved for a length of several times the mean free path of the electrons. The polarized states of electron spins, however, are soon relaxed and the directions of electron spins are to become aligned in the direction of magnetization of the magnetic layer through which the electrons are passing. Therefore, the film thickness of the intermediate ferromagnetic layer10must be made smaller compared with the relaxation length of electron spin. Since the relaxation length of electron spin is from 100 to 200 nm in metal, the film thickness of the intermediate ferromagnetic layer10is then preferably 50 nm or less. For well conserving the polarized state of electron spin, the film thickness between 5 nm and 20 nm is particularly preferable. Moreover, the direction of magnetization of the intermediate ferromagnetic layer10must be easily controlled by the magnetization of the second ferromagnetic layer12. Thus, the material of the intermediate ferromagnetic layer10is preferably provided as a material having a smaller coercive force compared with the material of the second ferromagnetic layer12. Thus, materials such as a CoHfTa alloy, a CoZrNb alloy, a CoFe alloy, a FeCoN alloy, a FeAlN alloy, a Ni45Fe55alloy, a Ni81Fe19alloy, a NiFeMo alloy, and a FeTaN alloy are preferable. Furthermore, the coercive force is preferably provided as 20 Oe or less.

The second exchange coupling control layer11is a nonmagnetic layer for separating the intermediate ferromagnetic layer10and the second ferromagnetic layer12with a specified clearance to control an exchange coupling constant in the exchange coupling between the intermediate ferromagnetic layer10and the second ferromagnetic layer12. The material and the film thickness of the second exchange coupling control layer11is determined similarly to those for the first exchange coupling control layer7.

The material of the second ferromagnetic layer12can be selected as necessary from materials having ferromagnetism. For example, alloys such as a Co alloy, a CoPt alloy, a CoPtCr alloy and a CoCr alloy can be used. During the operation of the element, the magnetization of the second ferromagnetic layer12is preferably fixed in one direction. Thus, the second ferromagnetic layer12has preferably a high coercive force and a large film thickness. The coercive force is preferably from 2000 to 4000 Oe and the thickness is preferably from 50 nm to 200 nm. Moreover, for the material thereof, an ordered alloy such as Co50Pt50is particularly preferable.

The material of the second electrode2can be selected as required when it is a conductive material. The thickness thereof is preferably within the range from several tens of nanometers to several hundreds of nanometers and its area is preferably within the range from 50 nm×50 nm to 1000 nm×1000 nm. Moreover, the shape thereof is preferably a rectangle, but can be a circle or an oval as desired.

The bit line1is a wire for supplying a desired voltage to the first electrode5for which commonly used wiring materials, such as Al and Cu, can be used.

The area of each of the layers from the first ferromagnetic layer6to the second ferromagnetic layer12is preferably made a little smaller than the area of each of the electrodes to be preferably within the range from 50 nm×50 nm to 300 nm×300 nm.

Each of the layers from the first electrode5to the second electrode2and the bit line1can be formed by a known deposition method for which methods such as sputtering, CVD, and evaporation can be used.

With the element disposed as a vertical element at each position of the recording cell209inFIG. 20and connected to the word line208and the bit line207, an integrated magnetic memory can be formed.

The operation principle of the element according to the first embodiment now follows, referring toFIGS. 2A and 2B. First, the operation principle for carrying out writing or recording in the element will be explained. Referring toFIG. 2A, the element is initialized first. Here, the element is in a magnetized state when a strong leftward magnetic field equivalent to a saturation magnetic field is applied to the element to provide leftward magnetization of all of the first ferromagnetic layer6and the second ferromagnetic layer12before the magnetic field is removed. Antiferromagnetic coupling is provided between the first ferromagnetic layer6and the magnetic domain wall displacement layer8aon the first electrode5side, and the coercive force of the first ferromagnetic layer6is higher than the coercive force of the magnetic domain wall displacement layer8. This causes rightward magnetization, becoming opposite to the direction of magnetization of the first ferromagnetic layer6, to be induced in the magnetic domain wall displacement layer8aon the first electrode5side. Moreover, an antiferromagnetic coupling is provided between the second ferromagnetic layer12and the intermediate ferromagnetic layer10, and the coercive force of the second ferromagnetic layer12is higher than the coercive force of the intermediate ferromagnetic layer10. This causes rightward magnetization, opposite to the direction of magnetization of the second ferromagnetic layer12, to be induced in the intermediate ferromagnetic layer10. Furthermore, an antiferromagnetic coupling is provided between the intermediate ferromagnetic layer10and the magnetic domain wall displacement layer8bon the second electrode2side. This causes leftward magnetization, becoming opposite to the direction of magnetization of the intermediate ferromagnetic layer10, to be induced in the magnetic domain wall displacement layer8bon the second electrode2side. Therefore, the directions of magnetization induced in the magnetic domain wall displacement layers8aand8bare to be invariably opposite to each other. Since the coercive force of the magnetic domain wall displacement layer8is small, a plurality of magnetic domain walls are produced in some cases. However, by letting a current flow from the first electrode5to the second electrode2on the basis of the principle explained with reference toFIGS. 21,22A, and22B, the magnetic domain walls can be concentrated to the position of the magnetic wall13shown inFIG. 2A. Moreover, in the magnetic domain wall displacement layer8aon the first electrode5side, by the antiferromagnetic coupling with the first ferromagnetic layer6, magnetization in the direction opposite to the direction of magnetization of the first ferromagnetic layer6is invariably induced. Thus, even in the case of letting a current continuously flow from the first electrode5to the second electrode2, one stable magnetic domain wall can be formed in the magnetic domain wall displacement layer8.

In the element in the state as shown inFIG. 2A, a current made to continuously flow from the second electrode2toward the first electrode5causes the magnetic domain wall13to displace in the direction opposite to the direction of the current, by which the magnetic domain wall disposition as shown inFIG. 2Bis presented. When the current flow is stopped, the antiferromagnetic coupling between the intermediate ferromagnetic layer10and the magnetic domain wall displacement layer8bon the second electrode2side causes magnetization in the direction opposite to the direction of magnetization of the intermediate ferromagnetic layer10to be invariably induced in the magnetic domain wall displacement layer8bon the second electrode2side. Therefore, one stable magnetic domain wall is formed in the magnetic domain wall displacement layer8without disappearance. Moreover, by letting a sufficient amount of current flow, the thickness of the magnetic domain wall displacement layer8bon the second electrode2side can be made sufficiently smaller compared with electron spin relaxation length. For example, the thickness can be made on the order of 20 nm.

In the element in the state as shown inFIG. 2B, a current made to continuously flow from the first electrode5toward the second electrode2causes an operation carried out in reverse to the foregoing, by which the element is brought to the state as shown inFIG. 2A. Moreover, by letting a sufficient amount of current flow, the thickness of the magnetic domain wall displacement layer8aon the first electrode5side can be made sufficiently smaller compared with electron spin relaxation length. For example, the thickness can be made on the order of 20 nm.

In this way, by reversing the direction of current, the magnetic domain wall13can be freely positioned at either end section of the magnetic domain wall displacement layer8.

The operation principle for reading out a record or detecting a state of magnetization in the element follows below. The operation principle is based on the fact that the behavior of electron spin differs depending on the relative relation between the thickness of a magnetic layer and an electron spin relaxation length. More specifically, the principle is based on the following understanding. When the thickness of a magnetic layer is sufficiently smaller compared with the electron spin relaxation length, electrons pass through the magnetic layer with most of their spins being conserved. While, when the thickness of the magnetic layer is equivalent to or more than the electron spin relaxation length, electrons pass through the magnetic layer with their spins made polarized by the magnetization of the magnetic layer.

In the following, a method of detecting difference in electric resistance of an element will be explained by flowing a detecting current from the second electrode2to the first electrode5(namely, the case of injecting electrons from the first electrode5toward the second electrode2) for the element shown inFIG. 1taken as an example. In the state shown inFIG. 2A, electrons flow in the following path (Electron path1): the first electrode5—the thick first ferromagnetic layer6in the leftward magnetized state—the nonmagnetic first exchange coupling control layer7—the thin magnetic domain wall displacement layer8awith the leftward magnetized state being induced therein—the thick magnetic domain wall displacement layer8bin the leftward magnetized state—the nonmagnetic intermediate exchange coupling control layer9—the thin intermediate ferromagnetic layer10in the rightward magnetized state—the nonmagnetic second exchange coupling control layer11—the thick second ferromagnetic layer12in the leftward magnetized state—the second electrode2. Here, the case where a film thickness is equivalent to or greater compared with the electron spin relaxation length is expressed as being “thick”, and the case where a film thickness is sufficiently smaller compared with the electron spin relaxation length is expressed as being “thin”. A thin film thickness is that of the order of 20 nm, for example, and a thick film thickness is that of the order of 200 nm, for example.

In the state shown inFIG. 2B, electron flows in the following path (Electron path2) (the meaning of the expressions of “thick” and “thin” are the same as that in the foregoing): the first electrode5—the thick first ferromagnetic layer6in the leftward magnetized state—the nonmagnetic first exchange coupling control layer7—the thick magnetic domain wall displacement layer8ain the rightward magnetized state—the thin magnetic domain wall displacement layer8bwith the leftward magnetized state being induced therein—the nonmagnetic intermediate exchange coupling control layer9—the thin intermediate ferromagnetic layer10in the rightward magnetized state—the nonmagnetic second exchange coupling control layer11—the thick second ferromagnetic layer12in the leftward magnetized state—the second electrode2.

The spin-polarized electrons are scattered or reflected at an interface with a magnetic material magnetized in the direction different from the direction of the spins of the electrons to cause an increase in electric resistance. Moreover, when the electrons pass through a thick magnetic layer, the directions of the spins of electrons are to be polarized in the direction of the magnetization of the magnetic material.

Comparison will be made between the electron path2and the electron path1. In the electron path2, electrons with their spins polarized in the direction of the leftward magnetization (here, this is considered as the down-spin) in the first ferromagnetic layer6by s-d interaction are largely scattered or reflected at the interface with the thick magnetic domain wall displacement layer8ato thereby cause an increase in electric resistance. However, the electrons with down-spins injected into the magnetic domain wall displacement layer8aare this time brought to be polarized by s-d interaction to be electrons with up-spins, spins in the direction of the magnetization of the thick magnetic domain wall displacement layer8a. The electrons with the up-spins, when injected into the thin magnetic domain wall displacement layer8b, are to be weakly scattered or reflected at the interface. Since the magnetic domain wall displacement layer8bis thin, the electrons with up-spins injected into the thin magnetic domain wall displacement layer8b, with their spins being kept polarized in up-spins, reach the intermediate ferromagnetic layer10whose direction of magnetization is the same as the direction of the up-spin. As a result, at the interface with the intermediate ferromagnetic layer10, the electrons are subjected to no large scattering and reflection. Furthermore, the electrons pass through the thin intermediate ferromagnetic layer10with up-spins being kept unchanged and are to be largely reflected and scattered at the interface with the thick second ferromagnetic layer12.

While, in the electron path1, electrons with their spins polarized in the down-spin, in the direction of the leftward magnetization, in the first ferromagnetic layer6by s-d interaction are subjected to weak scattering or reflection at the interface with the thin magnetic domain wall displacement layer8a. However, since the magnetic domain wall displacement layer8a, having the direction of magnetization being different from the direction of the down-spin, is thin, the electrons are allowed to keep their down-spins and pass through the magnetic domain wall displacement layer8bwith their down-spins being kept to reach the intermediate ferromagnetic layer10with the direction of magnetization being different from the direction of the down-spin. At the interface with the intermediate ferromagnetic layer10, the electrons are subjected to weak scattering or reflection. However, the thin intermediate ferromagnetic layer10allows the electrons to reach up to the second ferromagnetic layer12having the direction of magnetization being the same as the direction of the down-spin with the down-spins of the electrons being kept unchanged.

When electrons are injected into a magnetic film, to electrons having spins with the directions different from the direction of magnetization in the magnetic film, there exists a potential barrier at the interface of the magnetic film. Therefore, the electrons are scattered or reflected by the potential barrier. The case in which electrons are largely scattered or reflected by a potential barrier at an interface to largely increase electric resistance is the case in which sufficiently spin-polarized electrons are injected into a thick magnetic material magnetized in the direction different from the directions of spin angular momentum of the electrons. That is, a combination of directions of magnetization of thick magnetic layers largely contributes to spin-dependent conduction. More specifically, electric resistance of the element largely changes depending on whether the directions of magnetization of thick magnetic layers are in an antiparallel state or in a parallel state. However, influence that the direction of magnetization of a thin magnetic layer between thick magnetic layers has on electric resistance is small.

A comparison with only combinations of the directions of magnetization of thick magnetic layers extracted from the electron paths1and2is as follows. In electron path1: the thick first ferromagnetic layer6in the leftward magnetized state—the thick magnetic domain wall displacement layer8bin the leftward magnetized state—the thick second ferromagnetic layer12in the leftward magnetized state. In electron path2: the thick first ferromagnetic layer6in the leftward magnetized state—the thick magnetic domain wall displacement layer8ain the rightward magnetized state—the thick second ferromagnetic layer12in the leftward magnetized state.

In the electron path2, electrons with their spins polarized leftward in the first ferromagnetic layer6by s-d interaction are injected into the thick magnetic domain wall displacement layer8amagnetized rightward. Furthermore, electrons with their spins polarized rightward in the magnetic domain wall displacement layer8aby s-d interaction are to be injected into the second ferromagnetic layer12magnetized leftward. Thus, the electrons are injected two times into layers with directions of magnetization different from each other. While, in the electron path1, electrons with their spins polarized leftward in the first ferromagnetic layer6by s-d interaction are injected into the thick magnetic domain wall displacement layer8aand second ferromagnetic layer12both being similarly magnetized leftward. Thus, the electrons are not subjected to so large scattering or reflection. Therefore, the electric resistance of the electron path2becomes higher than the electric resistance of the electron path1. Consequently, by measuring electric resistance across the electrodes, the state of internal magnetization of the element can be easily detected.

In the foregoing, the explanation related to a method of separately detecting two magnetized states, which method becomes effective particularly in a memory element. However, continuous detection of magnetized state is also possible. When electrons pass through a magnetic layer with the direction of magnetization different from the directions of electron spins, the electron spins continuously change until the directions of electron spins are aligned with the direction of magnetization of the magnetic layer. Namely, the degree of polarization of electron spins differs depending on the length along which the electrons pass, and the electric resistance in a magnetic layer into which the electrons are injected next is to change depending on the degree of polarization of electron spins. More specifically, depending on the position of the magnetic domain wall13in the magnetic domain wall displacement layer8, the electric resistance from the first electrode5to the second electrode2changes continuously. Since the position of the magnetic domain wall13depends on the value of a current flowed in the element, by detecting the electric resistance of the element, realization of detection of a flowed current becomes possible. Moreover, stepwise classification of the change in electric resistance also enables multi-value recording of the resistance.

The arrangement shown inFIG. 1can be modified as necessary within the range without departing from the gist of the invention. For example, antiferromagnetic coupling can be changed to ferromagnetic coupling. In the following, more specific explanations will be presented.

FIG. 3is a schematic cross sectional view for explaining an example of another arrangement of the first embodiment of the spin injection magnetic domain wall displacement element according to the invention. On a substrate4, there are formed in the order a first electrode5, a first magnetic layer group100, a magnetic domain wall displacement layer8, a second magnetic layer group101, and a second electrode2. Further, a bit line1is formed on the first electrode5. The first magnetic layer group100is formed of a first ferromagnetic layer6and a first exchange coupling control layer7. The second magnetic layer group101is formed of a third exchange coupling control layer121and a third ferromagnetic layer122.

FIGS. 4A and 4Bare for explaining the operation principle of the element ofFIG. 3. In each of the magnetic layers in the element shown inFIG. 3, the direction of magnetization thereof is shown with an arrow. The magnetic domain wall displacement layer8is divided by a magnetic domain wall13into a magnetic domain wall displacement layer8aon the first electrode5side and a magnetic domain wall displacement layer8bon the second electrode2side. The substrate4, the first electrode5, the first ferromagnetic layer6, the first exchange coupling control layer7, the second electrode2and the bit line1are arranged similarly to those in the element shown inFIG. 1.

The magnetic domain wall displacement layer8differs from that in the element shown inFIG. 1in a method of controlling the magnetic domain wall displacement layer8bon the second electrode2side. However, the material, the film thickness and the magnetic characteristic thereof are provided similarly to those of the element shown inFIG. 1.

The third exchange coupling control layer121and the third ferromagnetic layer122are for providing ferromagnetic coupling between the third ferromagnetic layer122and the magnetic domain wall displacement layer8bon the second electrode2side. By the ferromagnetic coupling thus provided, the direction of magnetization of the magnetic domain wall displacement layer8bon the second electrode2side is fixed in the same direction as the direction of the magnetization of the third ferromagnetic layer122.

The third exchange coupling control layer121is a nonmagnetic layer for separating the magnetic domain wall displacement layer8and the third ferromagnetic layer122with a specified clearance to control an exchange coupling constant in the exchange coupling between the magnetic domain wall displacement layer8bon the second electrode2side and the third ferromagnetic layer122. The material of the third exchange coupling control layer121is determined similarly to that for the first exchange coupling control layer7. Moreover, the film thickness thereof is determined so that ferromagnetic coupling is provided between the magnetic domain wall displacement layer8bon the second electrode2side and the third ferromagnetic layer122.

The material of the third ferromagnetic layer122can be selected as necessary from materials having ferromagnetism. For example, alloys such as a Co alloy, a CoPt alloy, a CoPtCr alloy, and a CoCr alloy can be used. During the operation of the element, the magnetization of the third ferromagnetic layer122is preferably fixed in one direction. Thus, the third ferromagnetic layer122has preferably a high coercive force and a large film thickness. The coercive force is preferably from 2000 to 4000 Oe and the thickness is preferably from 50 nm to 200 nm.

The area of each of the layers from the first ferromagnetic layer6to the third ferromagnetic layer122is preferably made a little smaller than the area of each of the electrodes to be preferably within the range from 50 nm×50 nm to 300 nm×300 nm.

Each of the layers from the first electrode5to the second electrode2and the bit line1can be formed by a known deposition method for which methods such as sputtering, CVD, and evaporation can be used.

The operation principle is the same as that of the element shown inFIG. 1. Writing is carried out on the basis that the magnetic domain wall13can be displaced to positions such as those shown inFIGS. 4A and 4Bdepending on the direction of the current supplied between the first electrode5and the second electrode2. When a sufficient amount of the current is made to flow from the first electrode5to the second electrode2, the magnetized state becomes as that shown inFIG. 4A, in which the thickness of the magnetic domain wall displacement layer8aon the first electrode5side can be made sufficiently smaller than the electron-spin relaxation length to be on the order of, for example, 20 nm. Conversely, when the current is made to flow from the second electrode2to the first electrode5, the magnetized state becomes as that shown inFIG. 4B, in which the thickness of the magnetic domain wall displacement layer8bon the second electrode2side can be made sufficiently smaller than the electron-spin relaxation length to be on the order of, for example, 20 nm.

Reading is carried out on the basis that the electric resistance of the element is largely changed depending on whether the states of magnetization of the thick magnetic layers are in antiparallel or in parallel and an influence of the magnetization of the thin magnetic layer between the thick magnetic layers on the electric resistance is small. In the case of the magnetized state shown inFIG. 4A, all of the directions of magnetization in the first ferromagnetic layer6, the magnetic domain wall displacement layer8bon the second electrode2side and the third ferromagnetic layer122as thick magnetic layers are the same. Compared with this, in the case of the magnetized state shown inFIG. 4B, in the first ferromagnetic layer6, the magnetic domain wall displacement layer8aon the first electrode5side and the third ferromagnetic layer122as thick magnetic layers, the directions of magnetization in the magnetic layers adjacent to each other are opposite to each other. Consequently, the electric resistance in the state shown inFIG. 4Bbecomes larger than the electric resistance in the state shown inFIG. 4A.

FIG. 5is a schematic cross sectional view for explaining an example of yet another arrangement of the first embodiment of the spin injection magnetic domain wall displacement element according to the invention. On a substrate4, there are formed in the order a first electrode5, a first magnetic layer group100, a magnetic domain wall displacement layer8, a second magnetic layer group101, and a second electrode2. Further, a bit line1is formed on the first electrode5. The first magnetic layer group100is formed of a first ferromagnetic layer6and a first exchange coupling control layer7. The second magnetic layer group101is formed of a fourth ferromagnetic layer142.

FIGS. 6A and 6Bare for explaining the operation principle of the example of the arrangement of the element shown inFIG. 5. In each of the magnetic layers in the element shown inFIG. 5, the direction of magnetization thereof is shown with an arrow. The magnetic domain wall displacement layer8is divided by a magnetic domain wall13into a magnetic domain wall displacement layer8aon the first electrode5side and a magnetic domain wall displacement layer8bon the second electrode2side.

The substrate4, the first electrode5, the first ferromagnetic layer6, the first exchange coupling control layer7, the second electrode2and the bit line1are arranged similarly to those in the element shown inFIG. 1explained in the foregoing.

The magnetic domain wall displacement layer8differs from that in the element shown inFIG. 1in a method of controlling the magnetic domain wall displacement layer8bon the second electrode2side. However, the material, the film thickness and the magnetic characteristic thereof are provided similarly to those of the element shown inFIG. 1.

The fourth ferromagnetic layer142and the magnetic domain wall displacement layer8are in direct contact with each other to provide ferromagnetic coupling between the fourth ferromagnetic layer142and the magnetic domain wall displacement layer8bon the second electrode2side, by which the direction of magnetization of the magnetic domain wall displacement layer8bon the second electrode2side is fixed in the same direction as the direction of the magnetization of the fourth ferromagnetic layer142.

The material of the fourth ferromagnetic layer142can be selected as necessary from materials having ferromagnetism. For example, alloys such as a Co alloy, a CoPt alloy, a CoPtCr alloy, and a CoCr alloy can be used. During the operation of the element, the magnetization of the fourth ferromagnetic layer142is preferably fixed in one direction. Thus, the fourth ferromagnetic layer142has preferably a high coercive force and a large film thickness. The coercive force is preferably from 2000 to 4000 Oe and the thickness is preferably from 50 nm to 200 nm.

The area of each of the layers from the first ferromagnetic layer6to the fourth ferromagnetic layer142is preferably made a little smaller than the area of each of the electrodes to be preferably within the range from 50 nm×50 nm to 300 nm×300 nm.

Each of the layers from the first electrode5to the second electrode2and the bit line1can be formed by a known deposition method for which methods such as sputtering, CVD, and evaporation can be used.

The operation principle is the same as that of the element shown inFIG. 1. Writing is carried out on the basis that the magnetic domain wall13is made displaced to positions such as those shown inFIGS. 6A and 6Bdepending on the direction of the current supplied between the first electrode5and the second electrode2. When a sufficient amount of the current is made to flow from the first electrode5to the second electrode2, a magnetized state becomes as that shown inFIG. 6A, in which the thickness of the magnetic domain wall displacement layer8aon the first electrode5side can be made sufficiently smaller than the electron-spin relaxation length to be on the order of, for example, 20 nm. Conversely, when the current is made to flow from the second electrode2to the first electrode5, the magnetized state becomes as that shown inFIG. 6B, in which the thickness of the magnetic domain wall displacement layer8bon the second electrode2side can be made sufficiently smaller than the electron-spin relaxation length to be on the order of, for example, 20 nm.

Reading is carried out on the basis that the electric resistance of the element is largely changed depending on whether the states of magnetization of the thick magnetic layers are in antiparallel or in parallel and an influence of the magnetization of the thin magnetic layer between the thick magnetic layers on the electric resistance is small. In the case of the magnetized state shown inFIG. 6A, all of the directions of magnetization in the first ferromagnetic layer6, the magnetic domain wall displacement layer8bon the second electrode2side and the fourth ferromagnetic layer142as thick magnetic layers are the same. Compared with this, in the case of the magnetized state shown inFIG. 6B, in the first ferromagnetic layer6, the magnetic domain wall displacement layer8aon the first electrode5side and the fourth ferromagnetic layer142as thick magnetic layers, the directions of magnetization in the magnetic layers adjacent to each other are opposite to each other. Consequently, the electric resistance in the state shown inFIG. 6Bbecomes larger than the electric resistance in the state shown inFIG. 4A.

The arrangements of the first embodiment can be used in which the order of the layers from the first electrode5to the second electrode2is just reversed in each of the foregoing arrangements.

FIG. 7is a schematic cross sectional view for explaining an example of the basic arrangement of a second embodiment of the spin injection magnetic domain wall displacement element according to the invention. On a substrate20, a magnetic domain wall displacement layer22is formed, on the one end of which a first magnetic layer group100and a first electrode25are formed in the order. On the other end of the magnetic domain wall displacement layer22, a second magnetic layer group101, and a second electrode30are formed in the order. In the first magnetic layer group100, a first exchange coupling control layer23and a first ferromagnetic layer24are formed in the order. In the second magnetic layer group101, an intermediate exchange coupling control layer26, an intermediate ferromagnetic layer27, a second exchange coupling control layer28and a second ferromagnetic layer29are formed in the order.

FIGS. 8A and 8Bare for explaining the operation principle of the example of the arrangement of the element ofFIG. 7. In each of the magnetic layers in the element shown inFIG. 7, the direction of magnetization thereof is shown with an arrow. The magnetic domain wall displacement layer22is divided by a magnetic domain wall33into a magnetic domain wall displacement layer22aon the first electrode25side and a magnetic domain wall displacement layer22bon the second electrode30side. The arrangement shown inFIG. 7is the minimum unit of the element and the necessary number of the elements are disposed on the same substrate to form a desired device. Circuits and driving elements for driving the elements according to the invention can be also arranged on the same substrate.

The material for the substrate20can be selected as required depending on the desired flatness when the material has an insulation property for individually controlling a plurality of the elements arranged on the substrate and has sufficient rigidity for holding the elements. For example, there can be used an insulating substrate of such a material as sapphire or silicon oxide with a thickness of several hundreds of micrometers or a semiconductor substrate whose surface is oxidized to ensure insulating property.

The material of the first electrode25can be selected as required when it is a conductive material. The thickness thereof is preferably within the range from several tens of nanometers to several hundreds of nanometers and its area is preferably within the range from 50 nm×50 nm to 1000 nm×1000 nm. Moreover, the shape thereof is preferably a rectangle, but can be a circle or an oval as desired.

The first ferromagnetic layer24and the first exchange coupling control layer23are for providing antiferromagnetic coupling between the first ferromagnetic layer24and the magnetic domain wall displacement layer22aon the first electrode25side in a part of the magnetic domain wall displacement layer22. By the antiferromagnetic coupling thus provided, the direction of magnetization of the magnetic domain wall displacement layer22aon the first electrode25side is fixed in the direction opposite to the direction of the magnetization of the first ferromagnetic layer24.

The material of the first ferromagnetic layer24can be selected as necessary from materials having ferromagnetism. For example, alloys such as a Co alloy, a CoPt alloy, a CoPtCr alloy, and a CoCr alloy can be used. During the operation of the element, the magnetization of the first ferromagnetic layer24is preferably fixed in one direction. Thus, the first ferromagnetic layer24has preferably a high coercive force and a large film thickness. The coercive force is preferably from 2000 to 4000 Oe and the thickness is preferably from 50 nm to 200 nm.

The first exchange coupling control layer23is a nonmagnetic layer for separating the first ferromagnetic layer24and the magnetic domain wall displacement layer22with a specified clearance to control an exchange coupling constant in the exchange coupling between the first ferromagnetic layer24and the magnetic domain wall displacement layer22aon the first electrode25side. The material thereof is preferably Ru, V, C, Nb, Mo, Rh, Ta, W, Re, Ir, Pt, or Pd, or an alloy with the main ingredient being any one of the elements. The exchange coupling constant changes from positive value to negative value depending on the thickness of the first exchange coupling control layer23. Consequently, the thickness of the first exchange coupling control layer23is selected so that antiferromagnetic coupling is provided between the first ferromagnetic layer24and the magnetic domain wall displacement layer22aon the first electrode25side. However, an excessive thickness of the first exchange coupling control layer23causes weak exchange coupling. Therefore, the thickness is preferably determined as being from 0.5 to 3 nm.

The magnetic domain wall displacement layer22is a layer that makes the electric resistance of the whole element shown inFIG. 7change depending on the position of the magnetic domain wall33formed in the layer and brings about hysteresis. The detailed explanation of the operation thereof will be given later. The material can be any magnetic material with a magnetic domain wall presented therein, for which a material such as magnetic metal, ferromagnetic semiconductor or ferromagnetic oxide can be used. This is preferably a material such as permalloy, a CoFe alloy, a CoFeB alloy, a NiCoFe alloy, a CoCrFeAl alloy, Fe, a FePt alloy, a NiMnSb alloy, a CoMn group alloy, Sr2FeMoO6, Fe2O3, or CoHfTa. Particularly preferable is permalloy, Co90Fe10, Co2MnAl, Co2MnSi, or Co2MnGe. The film thickness thereof is preferably from 50 nm to 500 nm. It is necessary that the direction of magnetization of the magnetic domain wall displacement layer22aon the first electrode25side can be easily controlled depending on the direction of magnetization of the first ferromagnetic layer24, or that the direction of magnetization of the magnetic domain wall displacement layer22bon the second electrode30side can be easily controlled depending on the direction of magnetization of the second ferromagnetic layer29. Therefore, the coercive force of the magnetic domain wall displacement layer22is preferably equal to 10 Oe or less. The size thereof only needs to be a size with which the first magnetic layer group100and the second magnetic layer group101are formed while being separated with a desired distance and, for integrating a plurality of elements with a high density, a rectangular shape with a width from 30 to 200 nm and a length from 50 to 1000 nm is preferable.

The intermediate exchange coupling control layer26, the intermediate ferromagnetic layer27, the second exchange coupling control layer28and the second ferromagnetic layer29are for providing antiferromagnetic coupling between the second ferromagnetic layer29and the intermediate ferromagnetic layer27, and between the intermediate ferromagnetic layer27and the magnetic domain wall displacement layer22bon the second electrode30side. By the antiferromagnetic coupling thus provided, the direction of magnetization of the magnetic domain wall displacement layer22bon the second electrode30side is fixed in the same direction as the direction of the magnetization of the second ferromagnetic layer29. Furthermore, by adequately controlling the film thickness of the intermediate ferromagnetic layer27, spins of injected electrons can be controlled.

The intermediate exchange coupling control layer26is a nonmagnetic layer for separating the intermediate ferromagnetic layer27and the magnetic domain wall displacement layer22with a specified clearance to control an exchange coupling constant in the exchange coupling between the intermediate ferromagnetic layer27and the magnetic domain wall displacement layer22bon the second electrode30side. The material and the film thickness of the intermediate exchange coupling control layer26is determined similarly to those for the first exchange coupling control layer23.

The intermediate ferromagnetic layer27is for providing the above antiferromagnetic coupling and, along with this, for injecting electrons into the adjacent layer with the spins of injected electrons being conserved. For example, electrons injected from the intermediate exchange coupling control layer26pass through the intermediate ferromagnetic layer27and are injected into the second exchange coupling control layer28with respective polarized states of electron spins almost being conserved. The film thickness of the intermediate ferromagnetic layer27must be made smaller compared with the relaxation length of electron spin. Thus, the film thickness of the intermediate ferromagnetic layer27is preferably 50 nm or less. For well conserving the polarized state of electron spin, the film thickness between 5 nm and 20 nm is particularly preferable. Moreover, the direction of magnetization of the intermediate ferromagnetic layer27must be easily controlled by the magnetization of the second ferromagnetic layer29. Thus, the material of the intermediate ferromagnetic layer27is preferably provided as a material having a smaller coercive force compared with the material of the second ferromagnetic layer29. Thus, materials such as a CoHfTa alloy, a CoZrNb alloy, a CoFe alloy, a FeCoN alloy, a FeAlN alloy, a Ni45Fe55alloy, a Ni81Fe19alloy, a NiFeMo alloy, and a FeTaN alloy are preferable. Furthermore, the coercive force is preferably provided as 20 Oe or less.

The second exchange coupling control layer28is a nonmagnetic layer for separating the intermediate ferromagnetic layer27and the second ferromagnetic layer29with a specified clearance to control an exchange coupling constant in the exchange coupling between the intermediate ferromagnetic layer27and the second ferromagnetic layer29. The material and the film thickness of the second exchange coupling control layer28is determined similarly to those for the first exchange coupling control layer23.

The second ferromagnetic layer29can be selected as necessary from materials having ferromagnetism. For example, alloys such as a Co alloy, a CoPt alloy, a CoPtCr alloy, and a CoCr alloy can be used. During the operation of the element, the magnetization of the second ferromagnetic layer29is preferably fixed in one direction. Thus, the second ferromagnetic layer29has preferably a high coercive force and a large film thickness. The coercive force is preferably from 2000 to 4000 Oe and the thickness is preferably from 50 nm to 200 nm.

The material of the second electrode30can be selected as required when it is a conductive material. The thickness thereof is preferably within the range from several tens of nanometers to several hundreds of nanometers and its area is preferably within the range from 50 nm×50 nm to 300 nm×300 nm. Moreover, the shape thereof is preferably a rectangle, but can be a circle or an oval as desired.

The area of each of the first ferromagnetic layer24and the first exchange coupling control layer23is preferably made equivalent to the area of the first electrode25. Moreover, the area of each of the layers from the intermediate exchange coupling control layer26to the second ferromagnetic layer29is preferably made equivalent to the area of the second electrode30.

Each of the layers on the substrate20can be formed by a known deposition method for which methods such as sputtering, CVD, and evaporation can be used.

FIG. 9is a schematic view for explaining a method of arranging a plurality of the elements shown inFIG. 7while being connected with one another. InFIG. 9, the first electrodes25are connected to a plurality of horizontally running word lines32and the second electrodes30are connected to a plurality of vertically running bit lines31, which enables realization of an integrated magnetic memory.

The operation principle of the element according to the second embodiment follows usingFIGS. 8A and 8B. First, the operation principle in the case of carrying out writing or recording in the element will be explained. Referring toFIG. 8A, the element is initialized first. Here, the element is in a magnetized state when a strong rightward magnetic field equivalent to a saturation magnetic field is applied to the element to provide rightward magnetization of all of the first ferromagnetic layer24and the second ferromagnetic layer29before the magnetic field is removed.

Antiferromagnetic coupling is provided between the first ferromagnetic layer24and the magnetic domain wall displacement layer22aon the first electrode25side, and the coercive force of the first ferromagnetic layer24is higher than the coercive force of the magnetic domain wall displacement layer22. This causes leftward magnetization, becoming opposite to the direction of magnetization of the first ferromagnetic layer24, to be induced in the magnetic domain wall displacement layer22aon the first electrode25side. Moreover, antiferromagnetic coupling is provided between the second ferromagnetic layer29and the intermediate ferromagnetic layer27, and the coercive force of the second ferromagnetic layer29is higher than the coercive force of the intermediate ferromagnetic layer27. This causes leftward magnetization, opposite to the direction of magnetization of the second ferromagnetic layer29, to be induced in the intermediate ferromagnetic layer27. Furthermore, antiferromagnetic coupling is provided between the intermediate ferromagnetic layer27and the magnetic domain wall displacement layer22bon the second electrode30side. This causes rightward magnetization, becoming opposite to the direction of magnetization of the intermediate ferromagnetic layer27, to be induced in the magnetic domain wall displacement layer22bon the second electrode30side. Therefore, the directions of magnetization induced in the magnetic domain wall displacement layers22aand22bare to be invariably opposite to each other. Since the coercive force of the magnetic domain wall displacement layer22is small, a plurality of magnetic domain walls are produced in some cases. However, by letting a current flow from the first electrode25to the second electrode30on the basis of the principle explained with reference toFIGS. 21,22A, and22B, the magnetic domain walls can be concentrated to the position of the magnetic wall33shown inFIG. 8A. Moreover, in the magnetic domain wall displacement layer22aon the first electrode25side, by antiferromagnetic coupling with the first ferromagnetic layer24, magnetization in the direction opposite to the direction of magnetization of the first ferromagnetic layer24is invariably induced. Thus, even in the case of letting a current continuously flow from the first electrode25to the second electrode30, one stable magnetic domain wall can be formed in the magnetic domain wall displacement layer22.

In the element in the state as shown inFIG. 8A, a current made to continuously flow from the second electrode30toward the first electrode25causes the magnetic domain wall33to displace in the direction opposite to the direction of the current, by which the magnetic domain wall disposition as shown inFIG. 8Bis presented. When the current is made stopped, the antiferromagnetic coupling between the intermediate ferromagnetic layer27and the magnetic domain wall displacement layer22bon the second electrode30side causes magnetization in the direction opposite to the direction of magnetization of the intermediate ferromagnetic layer27to be invariably induced in the magnetic domain wall displacement layer22bon the second electrode30side. Therefore, one stable magnetic domain wall is formed in the magnetic domain wall displacement layer22without disappearance. Moreover, by letting a sufficient amount of current flow, the thickness of the magnetic domain wall displacement layer22bon the second electrode30side can be made sufficiently smaller compared with electron spin relaxation length. For example, the thickness can be made on the order of 20 nm.

In the element in the state as shown inFIG. 8B, a current made to continuously flow from the first electrode25toward the second electrode30causes an operation carried out in reverse to the foregoing, by which the element is brought to the state as shown inFIG. 8A. Moreover, by letting a sufficient amount of current flow, the thickness of the magnetic domain wall displacement layer22aon the first electrode25side can be made sufficiently smaller compared with electron spin relaxation length. For example, the thickness can be made on the order of 20 nm. In this way, by reversing the direction of current, the magnetic domain wall33can be freely made positioned at either end section of the magnetic domain wall displacement layer22.

The operation principle in the case of reading out a record or detecting a state of magnetization in the element follows. The operation principle is the same as that explained about the first embodiment, which is based on the fact that the behavior of electron spin differs depending on the relative relation between a thickness of a magnetic layer and an electron spin relaxation length. In the following, a method of detecting difference in electric resistance of an element will be explained with the case of letting a detecting current flow from the second electrode30to the first electrode25(namely, the case of injecting electrons from the first electrode25toward the second electrode30) for the element shown inFIG. 7taken as an example. Moreover, the meaning that each layer is “thick” or “thin” is as follows. The case where a distance in which an electron passes through in the layer is equivalent to or more compared with the electron spin relaxation length is expressed as being “thick”, and the case where the distance is sufficiently shorter compared with the electron spin relaxation length is expressed as being “thin”.

As was explained above, the electric resistance of the element is largely changed depending on whether the states of magnetization of the thick magnetic layers are in antiparallel or in parallel and an influence of the magnetization of the thin magnetic layer between the thick magnetic layers on the electric resistance is small. In the case of the magnetized state shown inFIG. 8A, all of the directions of magnetization in the first ferromagnetic layer24, the magnetic domain wall displacement layer22bon the second electrode30side and the second ferromagnetic layer29as thick magnetic layers are the same. Compared with this, in the case of the magnetized state shown inFIG. 8B, in the first ferromagnetic layer24, the magnetic domain wall displacement layer22aon the first electrode25side and the second ferromagnetic layer29as thick magnetic layers, the directions of magnetization in the magnetic layers adjacent to each other are opposite to each other. Consequently, the electric resistance in the state shown inFIG. 8Bbecomes larger than the electric resistance in the state shown inFIG. 8A. Therefore, by measuring electric resistance across both of the electrodes, the state of internal magnetization of the element can be easily detected.

Moreover, detection of a flowed current by continuous detection of the state of magnetization of the element and multi-value recording by stepwise classification of the change in electric resistance can be also brought into realization according to the method explained about the first embodiment.

The arrangement shown inFIG. 7can be modified as necessary within the range without departing from the gist of the invention. For example, antiferromagnetic coupling can be changed to ferromagnetic coupling. In the following, more specific explanations will be presented.

FIG. 10is a schematic cross sectional view for explaining an example of another arrangement of the second embodiment of the spin injection magnetic domain wall displacement element according to the invention. On a substrate20, a magnetic domain wall displacement layer22is formed, on the one end of which a first magnetic layer group100and a first electrode25are formed in the order. On the other end of the magnetic domain wall displacement layer22, a second magnetic layer group101, and a second electrode30are formed in the order. In the first magnetic layer group100, a first exchange coupling control layer23and a first ferromagnetic layer24are formed in the order. In the second magnetic layer group101, a third exchange coupling control layer48, and a third ferromagnetic layer49are formed in the order.

FIGS. 11A and 11Bare for explaining the operation principle of the example of the arrangement of the element ofFIG. 10. In each of the magnetic layers in the element shown inFIG. 10, the direction of magnetization thereof is shown with an arrow. The magnetic domain wall displacement layer22is divided by a magnetic domain wall33into a magnetic domain wall displacement layer22aon the first electrode25side and a magnetic domain wall displacement layer22bon the second electrode30side.

The substrate20, the first electrode25, the first ferromagnetic layer24, the first exchange coupling control layer23and the second electrode30are arranged similarly to those in the element shown inFIG. 7explained in the foregoing.

The magnetic domain wall displacement layer22differs from that in the element shown inFIG. 7in a method of controlling the magnetic domain wall displacement layer22bon the second electrode30side. However, the material, the film thickness, and the magnetic characteristic thereof are provided similarly to those of the element shown inFIG. 7.

The third exchange coupling control layer48and the third ferromagnetic layer49are for providing ferromagnetic coupling between the third ferromagnetic layer49and the magnetic domain wall displacement layer22bon the second electrode30side. By the ferromagnetic coupling thus provided, the direction of magnetization of the magnetic domain wall displacement layer22bon the second electrode30side is fixed in the same direction as the direction of the magnetization of the third ferromagnetic layer49.

The third exchange coupling control layer48is a nonmagnetic layer for separating the magnetic domain wall displacement layer22and the third ferromagnetic layer49with a specified clearance to control an exchange coupling constant in the exchange coupling between the magnetic domain wall displacement layer22bon the second electrode30side and the third ferromagnetic layer49. The material of the third exchange coupling control layer48is determined similarly to that for the first exchange coupling control layer23. Moreover, the film thickness thereof is determined so that a ferromagnetic coupling is provided between the magnetic domain wall displacement layer22bon the second electrode30side and the third ferromagnetic layer49.

The material of the third ferromagnetic layer49can be selected as necessary from materials having ferromagnetism. For example, alloys such as a Co alloy, a CoPt alloy, a CoPtCr alloy, and a CoCr alloy can be used. During the operation of the element, the magnetization of the third ferromagnetic layer49is preferably fixed in one direction. Thus, the third ferromagnetic layer49has preferably a high coercive force and a large film thickness. The coercive force is preferably from 2000 to 4000 Oe and the thickness is preferably from 50 nm to 200 nm.

The area of each of the first ferromagnetic layer24and the first exchange coupling control layer23is preferably made equivalent to the area of the first electrode25. Moreover, the area of each of the third ferromagnetic layer49and the third exchange coupling control layer48is preferably made equivalent to the area of the second electrode30.

Each of the layers on the substrate20can be formed by a known deposition method for which methods such as sputtering, CVD, and evaporation can be used.

The operation principle is the same as that of the element shown inFIG. 7. Writing is carried out on the basis that the magnetic domain wall33is made displaced to positions such as those shown inFIGS. 11A and 11Bdepending on the direction of a current supplied between the first electrode25and the second electrode30. When a sufficient amount of the current is made to flow from the first electrode25to the second electrode30, a magnetized state becomes as that shown inFIG. 11A, in which the thickness of the magnetic domain wall displacement layer22aon the first electrode25side can be made sufficiently smaller than the electron-spin relaxation length to be on the order of, for example, 20 nm. Conversely, when a sufficient amount of the current is made to flow from the second electrode30to the first electrode25, the magnetized state becomes as that shown inFIG. 11B, in which the thickness of the magnetic domain wall displacement layer22bon the second electrode30side can be made sufficiently smaller than the electron-spin relaxation length to be on the order of, for example, 20 nm.

Reading is carried out on the basis that the electric resistance of the element is largely changed depending on whether the states of magnetization of the thick magnetic layers are in antiparallel or in parallel and an influence of the magnetization of the thin magnetic layer between the thick magnetic layers on the electric resistance is small. In the case of the magnetized state shown inFIG. 11A, all of the directions of magnetization in the first ferromagnetic layer24, the magnetic domain wall displacement layer22bon the second electrode30side and the third ferromagnetic layer49as thick magnetic layers are the same. Compared with this, in the case of the magnetized state shown inFIG. 11B, in the first ferromagnetic layer24, the magnetic domain wall displacement layer22aon the first electrode25side and the third ferromagnetic layer49as thick magnetic layers, the directions of magnetization in the magnetic layers adjacent to each other are opposite to each other. Consequently, the electric resistance in the state shown inFIG. 11Bbecomes larger than the electric resistance in the state shown inFIG. 11A.

FIG. 12is a schematic cross sectional view for explaining an example of further another arrangement of the second embodiment of the spin injection magnetic domain wall displacement element according to the invention. On a substrate20, a magnetic domain wall displacement layer22is formed, on the one end of which a first magnetic layer group100and a first electrode25are formed in the order. On the other end of the magnetic domain wall displacement layer22, a second magnetic layer group101, and a second electrode30are formed in the order. In the first magnetic layer group100, a first exchange coupling control layer23, and a first ferromagnetic layer24are formed in the order. The second magnetic layer group101is formed of a fourth ferromagnetic layer109.

FIGS. 13A and 13Bare for explaining the operation principle of the example of the arrangement of the element ofFIG. 12. In each of the magnetic layers in the element shown inFIG. 12, the direction of magnetization thereof is shown with an arrow. The magnetic domain wall displacement layer22is divided by a magnetic domain wall33into a magnetic domain wall displacement layer22aon the first electrode25side and a magnetic domain wall displacement layer22bon the second electrode30side.

The substrate20, the first electrode25, the first ferromagnetic layer24, the first exchange coupling control layer23, the second electrode30are arranged similarly to those in the element ofFIG. 7.

The magnetic domain wall displacement layer22differs from that in the element shown inFIG. 7in a method of controlling the magnetic domain wall displacement layer22bon the second electrode30side. However, the material, the film thickness and the magnetic characteristic thereof are provided similarly to those of the element shown inFIG. 7.

The fourth ferromagnetic layer109and the magnetic domain wall displacement layer22are in direct contact with each other to provide ferromagnetic coupling between the fourth ferromagnetic layer109and the magnetic domain wall displacement layer22bon the second electrode30side, by which the direction of magnetization of the magnetic domain wall displacement layer22bon the second electrode30side is fixed in the same direction as the direction of the magnetization of the fourth ferromagnetic layer109.

The material of the fourth ferromagnetic layer109can be selected as necessary from materials having ferromagnetism. For example, alloys such as a Co alloy, a CoPt alloy, a CoPtCr alloy, and a CoCr alloy can be used. During the operation of the element, the magnetization of the fourth ferromagnetic layer109is preferably fixed in one direction. Thus, the fourth ferromagnetic layer109has preferably a high coercive force and a large film thickness. The coercive force is preferably from 2000 to 4000 Oe and the thickness is preferably from 50 nm to 200 nm.

The area of each of the first ferromagnetic layer24and the first exchange coupling control layer23is preferably made equivalent to the area of the first electrode25. Moreover, the area of the fourth ferromagnetic layer109is preferably made equivalent to the area of the second electrode30.

Each of the layers on the substrate20can be formed by a known deposition method for which methods such as sputtering, CVD, and evaporation can be used.

The operation principle is the same as that of the element shown inFIG. 7. Writing is carried out on the basis that the magnetic domain wall33is made displaced to positions such as those shown inFIGS. 13A and 13Bdepending on the direction of a current supplied between the first electrode25and the second electrode30. When a sufficient amount of the current is made to flow from the first electrode25to the second electrode30, a magnetized state becomes as that shown inFIG. 13A, in which the thickness of the magnetic domain wall displacement layer22aon the first electrode25side can be made sufficiently smaller than the electron-spin relaxation length to be on the order of, for example, 20 nm. Conversely, when a sufficient amount of the current is made to flow from the second electrode30to the first electrode25, the magnetized state becomes as that shown inFIG. 13B, in which the thickness of the magnetic domain wall displacement layer22bon the second electrode30side can be made sufficiently smaller than the electron-spin relaxation length to be on the order of, for example, 20 nm.

Reading is carried out on the basis that the electric resistance of the element is largely changed depending on whether the states of magnetization of the thick magnetic layers are in antiparallel or in parallel and an influence of the magnetization of the thin magnetic layer between the thick magnetic layers on the electric resistance is small. In the case of the magnetized state shown inFIG. 13A, all of the directions of magnetization in the first ferromagnetic layer24, the magnetic domain wall displacement layer22bon the second electrode30side and the fourth ferromagnetic layer109as thick magnetic layers are the same. Compared with this, in the case of the magnetized state shown inFIG. 13B, in the first ferromagnetic layer24, the magnetic domain wall displacement layer22aon the first electrode25side and the fourth ferromagnetic layer109as thick magnetic layers, the directions of magnetization in the magnetic layers adjacent to each other are opposite to each other. Consequently, the electric resistance in the state shown inFIG. 13Bbecomes larger than the electric resistance in the state shown inFIG. 13A.

Other arrangements of the second embodiment can be made so that in each of which the order of the layers from the first electrode25to the second electrode30is just reversed in each of the foregoing arrangements.

FIG. 14is a schematic cross sectional view for explaining an example of the basic arrangement of a third embodiment of the spin injection magnetic domain wall displacement element according to the invention. On a substrate60, a magnetic domain wall displacement layer62is formed, on the one end of which a first magnetic layer group100and a first electrode65are formed in the order. On the other end of the magnetic domain wall displacement layer62, a second magnetic layer group101, and a second electrode71are formed in the order. In the first magnetic layer group100, a first exchange coupling control layer63and a first nonmagnetic metal layer66are formed adjacent to each other, on both of which a first ferromagnetic layer64is formed. In the second magnetic layer group101, an intermediate nonmagnetic metal layer67and an intermediate exchange coupling control layer72are formed adjacent to each other, on both of which an intermediate ferromagnetic layer68, a second exchange coupling control layer69and a second ferromagnetic layer70are formed in the order.

FIGS. 15A and 15Bare for explaining the operation principle of the example of the arrangement of the element shown inFIG. 14. In each of the magnetic layers in the element shown inFIG. 14, the direction of magnetization thereof is shown with an arrow. The magnetic domain wall displacement layer62is divided by a magnetic domain wall73into a magnetic domain wall displacement layer62aon the first electrode65side and a magnetic domain wall displacement layer62bon the second electrode71side. The arrangement shown inFIG. 14is the minimum unit of the element and the necessary number of the elements are disposed on the same substrate to form a desired device. Circuits and driving elements for driving the elements according to the invention can be also arranged on the same substrate.

A material for the substrate60can be selected as required depending on the desired flatness when the material has an insulation property for individually controlling a plurality of the elements arranged on the substrate and has sufficient rigidity for holding the elements. For example, there can be used an insulating substrate of such sapphire or silicon oxide with a thickness of several hundreds of micrometers or a semiconductor substrate whose surface is oxidized to ensure insulating property.

The material of the first electrode65can be selected as required when it is a conductive material. The thickness thereof is preferably within the range from several tens of nanometers to several hundreds of nanometers and its area is preferably within the range from 50 nm×50 nm to 300 nm×300 nm. Moreover, the shape thereof is preferably a rectangle, but can be a circle or an oval as desired.

The first ferromagnetic layer64and the first exchange coupling control layer63are for providing antiferromagnetic coupling between the first ferromagnetic layer64and the magnetic domain wall displacement layer22aon the first electrode65side in a part of the magnetic domain wall displacement layer62. By the antiferromagnetic coupling thus provided, the direction of magnetization of the magnetic domain wall displacement layer62aon the first electrode65side is fixed in the direction opposite to the direction of the magnetization of the first ferromagnetic layer64.

The material of the first ferromagnetic layer64can be selected as necessary from materials having ferromagnetism. For example, alloys such as a Co alloy, a CoPt alloy, a CoPtCr alloy, and a CoCr alloy can be used. During the operation of the element, the magnetization of the first ferromagnetic layer64is preferably fixed in one direction. Thus, the first ferromagnetic layer64has preferably a high coercive force and a large film thickness. The coercive force is preferably from 2000 to 4000 Oe and the thickness is preferably from 50 nm to 200 nm.

The first exchange coupling control layer63is a nonmagnetic layer for separating the first ferromagnetic layer64and the magnetic domain wall displacement layer62with a specified clearance to control an exchange coupling constant in the exchange coupling between the first ferromagnetic layer64and the magnetic domain wall displacement layer62aon the first electrode65side. The material thereof is preferably Ru, V, C, Nb, Mo, Rh, Ta, W, Re, Ir, Pt, or Pd, or an alloy with the main ingredient being any one of the elements. The exchange coupling constant changes from positive value to negative value depending on the thickness of the first exchange coupling control layer63. Consequently, the thickness of the first exchange coupling control layer63is selected so that antiferromagnetic coupling is provided between the first ferromagnetic layer64and the magnetic domain wall displacement layer62aon the first electrode65side. However, an excessive thickness of the first exchange coupling control layer63causes weak exchange coupling. Therefore, the thickness is preferably determined as being from 0.5 to 3 nm.

The first nonmagnetic metal layer66is a layer for securing conductivity between the first ferromagnetic layer64and the magnetic domain wall displacement layer62and for cutting off the magnetic coupling between the first ferromagnetic layer64and the magnetic domain wall displacement layer62. Here, to cut off magnetic coupling means that the direction of magnetization is not fixed to a specified relation for a section of the magnetic domain wall displacement layer62which section faces the first ferromagnetic layer64with the first nonmagnetic metal layer66put between. More specifically, this means that, in the section in contact with the first nonmagnetic metal layer66in the magnetic domain wall displacement layer62, the direction of magnetization can be taken as either state of rightward and leftward when the direction magnetization of the first ferromagnetic layer64is rightward. The materials for the first nonmagnetic metal layer66are preferably Cu, Cr, V, Ru, and their alloys. The thickness thereof is preferably made equal to that of the first exchange coupling control layer63.

The area ratio of the first exchange coupling control layer63to the first nonmagnetic metal layer66is determined as necessary depending on the desired size and the electric resistance of the whole element. The ratio is preferably from 0.1:1 to 1:0.1 and, in particular, is preferably from 0.5:1 to 1:0.5. The position of the first nonmagnetic metal layer66is determined to be closer to the second magnetic layer group101than that of the first exchange coupling control layer63with the later explained operation principle taken into consideration.

The magnetic domain wall displacement layer62is a layer that makes the electric resistance of the whole element shown inFIG. 14change depending on the position of the magnetic domain wall73formed in the layer and brings about hysteresis. The detailed explanation of the operation thereof will be given later. The material can be any magnetic material with a magnetic domain wall presented therein, for which a material such as magnetic metal, ferromagnetic semiconductor or ferromagnetic oxide can be used. This is preferably a material such as permalloy, a CoFe alloy, a CoFeB alloy, a NiCoFe alloy, a CoCrFeAl alloy, Fe, a FePt alloy, a NiMnSb alloy, a CoMn group alloy, Sr2FeMoO6, Fe2O3, or CoHfTa. Particularly preferable is permalloy, Co90Fe10, Co2MnAl, Co2MnSi, or Co2MnGe. The film thickness thereof is preferably from 50 nm to 500 nm. It is necessary that the direction of magnetization of the magnetic domain wall displacement layer62aon the first electrode65side can be easily controlled depending on the direction of magnetization of the first ferromagnetic layer64, or that the direction of magnetization of the magnetic domain wall displacement layer62bon the second electrode71side can be easily controlled depending on the direction of magnetization of the second ferromagnetic layer70. Therefore, the coercive force of the magnetic domain wall displacement layer62is preferably equal to 10 Oe or less. The size thereof only needs to be a size with which the first magnetic layer group100and the second magnetic layer group101are formed while being separated with a desired distance and, for integrating a plurality of elements with a high density, a rectangular shape with a width from 30 to 200 nm and a length from 50 to 1000 nm is preferable.

The intermediate exchange coupling control layer72, the intermediate ferromagnetic layer68, the second exchange coupling control layer69and the second ferromagnetic layer70are for providing antiferromagnetic coupling between the second ferromagnetic layer70and the intermediate ferromagnetic layer68, and between the intermediate ferromagnetic layer68and the magnetic domain wall displacement layer62bon the second electrode71side. By the antiferromagnetic coupling thus provided, the direction of magnetization of the magnetic domain wall displacement layer62bon the second electrode71side is fixed in the same direction as the direction of the magnetization of the second ferromagnetic layer70. Furthermore, by adequately controlling the film thickness of the intermediate ferromagnetic layer68, spins of injected electrons is controlled.

The intermediate exchange coupling control layer72is a nonmagnetic layer for separating the intermediate ferromagnetic layer68and the magnetic domain wall displacement layer62with a specified clearance to control an exchange coupling constant in the exchange coupling between the intermediate ferromagnetic layer68and the magnetic domain wall displacement layer62bon the second electrode71side. The material and the film thickness of the intermediate exchange coupling control layer72is determined similarly to those for the first exchange coupling control layer63.

The intermediate nonmagnetic metal layer67is a layer for securing conductivity between the intermediate ferromagnetic layer68and the magnetic domain wall displacement layer62and, along with this, for cutting off the magnetic coupling between the intermediate ferromagnetic layer68and the magnetic domain wall displacement layer62. The meaning of cutting off the magnetic coupling is as was explained before. The materials for the intermediate nonmagnetic metal layer67are preferably Cu, Cr, V, Ru, and their alloys. The thickness thereof is preferably made equal to that of the intermediate exchange coupling control layer72.

The area ratio of the intermediate exchange coupling control layer72to the intermediate nonmagnetic metal layer67is determined as necessary depending on the desired size and the electric resistance of the whole element. The ratio is preferably from 0.1:1 to 1:0.1 and, in particular, is preferably from 0.5:1 to 1:0.5. The position of the intermediate nonmagnetic metal layer67is determined to be closer to the first magnetic layer group100than that of the intermediate exchange coupling control layer72with the later explained operation principle taken into consideration.

The intermediate ferromagnetic layer68is for providing the above antiferromagnetic coupling and for injecting electrons into the adjacent layer with the spins of injected electrons being conserved. For example, electrons injected from the intermediate nonmagnetic metal layer67pass through the intermediate ferromagnetic layer68and are injected into the second exchange coupling control layer69with respective polarized states of electron spins almost being conserved. The film thickness of the intermediate ferromagnetic layer68must be made smaller compared with the relaxation length of electron spin. Thus, the film thickness of the intermediate ferromagnetic layer68is preferably 50 nm or less. For well conserving the polarized state of electron spin, the film thickness between 5 nm and 20 nm is particularly preferable. Moreover, the direction of magnetization of the intermediate ferromagnetic layer68must be easily controlled by the magnetization of the second ferromagnetic layer70. Thus, the material of the intermediate ferromagnetic layer68is preferably provided as a material having a smaller coercive force compared with the material of the second ferromagnetic layer70. Thus, materials such as a CoHfTa alloy, a CoZrNb alloy, a CoFe alloy, a FeCoN alloy, a FeAlN alloy, a Ni45Fe55alloy, a Ni81Fe19alloy, a NiFeMo alloy, and a FeTaN alloy are preferable. Furthermore, the coercive force is preferably provided as 20 Oe or less.

The second exchange coupling control layer69is a nonmagnetic layer for separating the intermediate ferromagnetic layer68and the second ferromagnetic layer70with a specified clearance to control an exchange coupling constant in the exchange coupling between the intermediate ferromagnetic layer68and the second ferromagnetic layer70. The material and the film thickness of the second exchange coupling control layer69is determined similarly to those for the first exchange coupling control layer63.

The material of the second ferromagnetic layer70can be selected as necessary from materials having ferromagnetism. For example, alloys such as a Co alloy, a CoPt alloy, a CoPtCr alloy, and a CoCr alloy can be used. During the operation of the element, the magnetization of the second ferromagnetic layer70is preferably fixed in one direction. Thus, the second ferromagnetic layer70has preferably a high coercive force and a large film thickness. The coercive force is preferably from 2000 to 4000 Oe and the thickness is preferably from 50 nm to 200 nm.

The material of the second electrode71can be selected as required when it is a conductive material. The thickness thereof is preferably within the range from several tens of nanometers to several hundreds of nanometers and its area is preferably within the range from 50 nm×50 nm to 300 nm×300 nm. Moreover, the shape thereof is preferably a rectangle, but can be a circle or an oval as desired.

Each of the total area of the first exchange coupling control layer63and the first nonmagnetic metal layer66and the area of the first ferromagnetic layer64is preferably made equivalent to the area of the first electrode65. Moreover, each of the total area of the intermediate exchange coupling control layer72and the intermediate nonmagnetic metal layer67and the area of each of the layers from the intermediate ferromagnetic layer68to the second ferromagnetic layer70is preferably made equivalent to the area of the second electrode71.

Each of the layers on the substrate60can be formed by a known deposition method for which methods such as sputtering, CVD, and evaporation can be used.

Also in the element shown inFIG. 14, by using the arrangement shown inFIG. 9, the first electrodes65of the element are connected to a plurality of horizontally running word lines32and the second electrodes71are connected to a plurality of vertically running bit lines31, which enables realization of an integrated magnetic memory.

The operation principle of the element according to the third embodiment will be explained usingFIGS. 15A and 15B. First, the operation principle in the case of carrying out writing or recording in the element will be explained. Referring toFIG. 15A, the element is initialized first. Here, the element is in a magnetized state when a strong rightward magnetic field equivalent to a saturation magnetic field is applied to the element to provide rightward magnetization of all of the first ferromagnetic layer64and the second ferromagnetic layer70before the magnetic field is removed.

In the magnetic domain wall displacement layer62, the relation between the direction of magnetization in the section in contact with the first exchange coupling control layer63and the direction of magnetization in the first ferromagnetic layer64is the same as the relation in the element shown inFIG. 7. Moreover, in the magnetic domain wall displacement layer62, the relation among the direction of magnetization in the section in contact with the intermediate exchange coupling control layer72, the direction of magnetization in the intermediate ferromagnetic layer68and the direction of magnetization in the second ferromagnetic layer70is also the same as the relation in the element shown inFIG. 7. In the magnetic domain wall displacement layer62, the direction of magnetization in the section in contact with the first nonmagnetic metal layer66and the direction of magnetization in the section in contact with the intermediate nonmagnetic metal layer67are not fixed as explained in the foregoing. Therefore, inFIG. 15A, for example, the magnetic domain wall displacement layer62bon the second electrode71side extends to a position under the first ferromagnetic layer64. In this case, electrons can move in the path through the first ferromagnetic layer64, the first nonmagnetic metal layer66, and the magnetic domain wall displacement layer62b. When the film thickness of the magnetic domain wall displacement layer62is large, the magnetic domain wall displacement layer62aon the first electrode65side is to localize in the vicinity of the first exchange coupling control layer63as shown inFIG. 8A.

In the element in the state as shown inFIG. 15A, a current made to continuously flow from the second electrode71to the first electrode65causes the magnetic domain wall73to displace in the direction opposite to the direction of the current, by which the magnetic domain wall disposition as shown inFIG. 15Bis presented. When the current is made stopped, the antiferromagnetic coupling between the intermediate ferromagnetic layer68and the magnetic domain wall displacement layer62bon the second electrode71side causes magnetization in the direction opposite to the direction of magnetization of the intermediate ferromagnetic layer68to be invariably induced in the magnetic domain wall displacement layer62bon the second electrode71side. Therefore, one stable magnetic domain wall is formed in the magnetic domain wall displacement layer62without disappearance.

In the element in the state as shown inFIG. 15B, a current made to continuously flow from the first electrode65toward the second electrode71causes an operation carried out in reverse to the foregoing, by which the element is brought to the state as shown inFIG. 15A. The antiferromagnetic coupling between the first ferromagnetic layer64and the magnetic domain wall displacement layer62aon the first electrode65side causes magnetization in the direction opposite to the direction of magnetization of the first ferromagnetic layer64to be invariably induced in the magnetic domain wall displacement layer62aon the first electrode65side. Therefore, one stable magnetic domain wall is formed in the magnetic domain wall displacement layer62without disappearance. In this way, by reversing the direction of current, the magnetic domain wall73can be freely made positioned at either end section of the magnetic domain wall displacement layer62.

The operation principle in the case of reading out a record or detecting a state of magnetization in the element will be explained. The operation principle is the same as that explained regarding the first embodiment, which is based on the fact that the behavior of electron spin differs depending on the relative relation between a thickness of a magnetic layer and an electron spin relaxation length. In the following, a method of detecting difference in electric resistance of an element will be explained with the case of letting a detecting current flow from the second electrode71to the first electrode65(namely, the case of injecting electrons from the first electrode65toward the second electrode71) for the element shown inFIG. 14taken as an example. Moreover, the meaning that each layer is “thick” or “thin” is as follows. The case where a distance in which an electron passes through in the layer is equivalent to or more compared with the electron spin relaxation length is expressed as being “thick”, and the case where the distance is sufficiently shorter compared with the electron spin relaxation length is expressed as being “thin”.

As was explained above, the electric resistance of the element is largely changed depending on whether the states of magnetization of the thick magnetic layers are in antiparallel or in parallel and an influence of the magnetization of the thin magnetic layer between the thick magnetic layers on the electric resistance is small. In the case of the magnetized state shown inFIG. 15A, all of the directions of magnetization in the first ferromagnetic layer64, the magnetic domain wall displacement layer62bon the second electrode71side and the second ferromagnetic layer70as thick magnetic layers are the same. Compared with this, in the case of the magnetized state shown inFIG. 15B, in the first ferromagnetic layer64, the magnetic domain wall displacement layer62aon the first electrode65side, and the second ferromagnetic layer70as thick magnetic layers, the directions of magnetization in the magnetic layers adjacent to each other are opposite to each other. Consequently, the electric resistance in the state shown inFIG. 15Bbecomes larger than the electric resistance in the state shown inFIG. 15A. Therefore, by measuring electric resistance across both of the electrodes, the state of internal magnetization of the element can be easily detected.

Moreover, detection of a flowed current by continuous detection of the state of magnetization of the element and multi-value recording by stepwise classification of the change in electric resistance can be also brought into realization according to the method explained about the first embodiment.

The arrangement shown inFIG. 14can be modified as necessary within the range without departing from the gist of the invention. For example, antiferromagnetic coupling can be changed to ferromagnetic coupling. In the following, more specific explanations will be presented.

FIG. 16is a schematic cross sectional view for explaining an example of another arrangement of the third embodiment of the spin injection magnetic domain wall displacement element according to the invention. On a substrate60, a magnetic domain wall displacement layer62is formed, on the one end of which a first magnetic layer group100and a first electrode65are formed in the order. On the other end of the magnetic domain wall displacement layer62, the second magnetic layer group101and a second electrode71are formed in the order. In the first magnetic layer group100, a first exchange coupling control layer63and a first nonmagnetic metal layer66are formed adjacent to each other, on both of which a first ferromagnetic layer64is formed. In the second magnetic layer group101, a third nonmagnetic metal layer87and a third exchange coupling control layer90are formed adjacent to each other, on both of which a third ferromagnetic layer88is formed.

FIGS. 17A and 17Bare for explaining the operation principle of the element with the arrangement shown inFIG. 16. In each of the magnetic layers in the element shown inFIG. 16, the direction of magnetization thereof is shown with an arrow. The magnetic domain wall displacement layer62is divided by a magnetic domain wall73into a magnetic domain wall displacement layer62aon the first electrode65side and a magnetic domain wall displacement layer62bon the second electrode71side.

The substrate60, the first electrode65, the first ferromagnetic layer64, the first exchange coupling control layer63, the first nonmagnetic metal layer66and the second electrode71are arranged similarly to those in the element ofFIG. 14.

The magnetic domain wall displacement layer62differs from that in the element shown inFIG. 14in a method of controlling the magnetic domain wall displacement layer62bon the second electrode71side. However, the material, the film thickness and the magnetic characteristic thereof are provided similarly to those of the element shown inFIG. 14.

The third exchange coupling control layer90and the third ferromagnetic layer88are for providing ferromagnetic coupling between the third ferromagnetic layer88and the magnetic domain wall displacement layer62bon the second electrode71side. By the ferromagnetic coupling thus provided, the direction of magnetization of the magnetic domain wall displacement layer62bon the second electrode71side is fixed in the same direction as the direction of the magnetization of the third ferromagnetic layer88.

The third exchange coupling control layer90is a nonmagnetic layer for separating the magnetic domain wall displacement layer62and the third ferromagnetic layer88with a specified clearance to control an exchange coupling constant in the exchange coupling between the magnetic domain wall displacement layer62bon the second electrode71side and the third ferromagnetic layer88. The material of the third exchange coupling control layer90is determined similarly to that for the first exchange coupling control layer63. Moreover, the film thickness thereof is determined so that ferromagnetic coupling is provided between the magnetic domain wall displacement layer62bon the second electrode71side and the third ferromagnetic layer88.

The third nonmagnetic metal layer87is a layer for securing conductivity between the third ferromagnetic layer88and the magnetic domain wall displacement layer62and, along with this, for cutting off the magnetic coupling between the third ferromagnetic layer88and the magnetic domain wall displacement layer62. The meaning of cutting off the magnetic coupling is as was explained before. The materials for the third nonmagnetic metal layer87are preferably Cu, Cr, V, Ru, and their alloys. The thickness thereof is preferably made equal to that of the third exchange coupling control layer90.

The area ratio of the third exchange coupling control layer90to the third nonmagnetic metal layer87is determined as necessary depending on the desired size and the electric resistance of the whole element. The ratio is preferably from 0.1:1 to 1:0.1 and, in particular, is preferably from 0.5:1 to 1:0.5. The position of the third nonmagnetic metal layer87is determined to be closer to the first magnetic layer group100than that of the third exchange coupling control layer90with the later explained operation principle taken into consideration.

The material of the third ferromagnetic layer88can be selected as necessary from materials having ferromagnetism. For example, alloys such as a Co alloy, a CoPt alloy, a CoPtCr alloy, and a CoCr alloy can be used. During the operation of the element, the magnetization of the third ferromagnetic layer88is preferably fixed in one direction. Thus, the third ferromagnetic layer88has preferably a high coercive force and a large film thickness. The coercive force is preferably from 2000 to 4000 Oe and the thickness is preferably from 50 nm to 200 nm.

Each of the total area of the third exchange coupling control layer90and the third nonmagnetic metal layer87and the area of the third ferromagnetic layer88is preferably made equivalent to the area of the second electrode71.

Each of the layers on the substrate60can be formed by a known deposition method for which methods such as sputtering, CVD, and evaporation can be used.

The operation principle is the same as that of the element shown inFIG. 14. Writing is carried out on the basis that the magnetic domain wall73is made displaced to positions such as those shown inFIGS. 17A and 17Bdepending on the direction of a current supplied between the first electrode65and the second electrode71. When a sufficient amount of the current is made to flow from the first electrode65to the second electrode71, a magnetized state becomes as that shown inFIG. 17A, in which the magnetic domain wall displacement layer62bon the second electrode71side extends to a position under the first ferromagnetic layer64. Conversely, when a sufficient amount of the current is made to flow from the second electrode71to the first electrode65, the magnetized state becomes as that shown inFIG. 17B, in which the magnetic domain wall displacement layer62aon the first electrode65side extends to a position under the third ferromagnetic layer88.

Reading is carried out on the basis that the electric resistance of the element is largely changed depending on whether the states of magnetization of the thick magnetic layers are in antiparallel or in parallel and an influence of the magnetization of the thin magnetic layer between the thick magnetic layers on the electric resistance is small. In the case of the magnetized state shown inFIG. 17A, all of the directions of magnetization in the first ferromagnetic layer64, the magnetic domain wall displacement layer62bon the second electrode71side and the third ferromagnetic layer88as thick magnetic layers are the same. Compared with this, in the case of the magnetized state shown inFIG. 17B, in the first ferromagnetic layer64, the magnetic domain wall displacement layer62aon the first electrode65side and the third ferromagnetic layer88as thick magnetic layers, the directions of magnetization in the magnetic layers adjacent to each other are opposite to each other. Consequently, the electric resistance in the state shown inFIG. 17Bbecomes larger than the electric resistance in the state shown inFIG. 17A.

Other arrangement of the third embodiment can be made where the order of the layers from the first electrode65to the second electrode71is just reversed in each of the foregoing arrangements.

More detailed explanations will be made with specific examples. Example 1 is one in which an element with the arrangement shown inFIG. 1is fabricated and operated. For the substrate4, a quartz plate with a thickness of 500 μm was used, on which the following layers were formed by sputtering. The first electrode5of Cu was formed with a thickness of 200 nm and an area of 500 nm×500 nm. Thereafter, the first ferromagnetic layer6of a CoPt alloy was formed with a thickness of 200 nm, an area of 100 nm×100 nm and a coercive force of 2500 Oe. Then, the first exchange coupling control layer7of Ru was formed with a thickness of 0.8 nm and an area of 100 nm×100 nm. Next, the magnetic domain wall displacement layer8of Ni80Fe20was formed with a thickness of 200 nm, an area of 100 nm×100 nm and a coercive force of 5 Oe. Subsequently, the intermediate exchange coupling control layer9of Ru was formed with a thickness of 0.8 nm and an area of 100 nm×100 nm. Next, the intermediate ferromagnetic layer10of CoHfTa was formed with a thickness of 15 nm, an area of 100 nm×100 nm and a coercive force of 5 Oe. Thereafter, the second exchange coupling control layer11of Ru was formed with a thickness of 0.8 nm and an area of 100 nm×100 nm. Next, the second ferromagnetic layer12of a CoPt alloy was formed with a thickness of 200 nm, an area of 100 nm×100 nm, and a coercive force of 2500 Oe. Then, the second electrode2of Au was formed with a thickness of 200 nm and an area of 500 nm×500 nm. Finally, the bit line1of Al was formed to provide Example 1.

By using the element, an evaluation was carried out with the following procedures. At the beginning, a magnetic field of 5000 Oe was applied to initialize the element into the state shown inFIG. 2A. Following this, as a first procedure, a driving current of 10 mA (with a current density of 1×108A/cm2) was made to flow from the second electrode2toward the first electrode5to bring the element into the state shown inFIG. 2B. Then, electric resistance between the first electrode5and the second electrode2at this time was measured with a detecting current at 300 μA. Next, as a second procedure, a driving current of 10 mA (with a current density of 1×108A/cm2) was made to flow from the first electrode5toward the second electrode2to bring the element into the state shown inFIG. 2A. Then, the electric resistance between the first electrode5and the second electrode2at this time was measured with a detecting current at 300 μA. With the direction of the current alternately reversed, each of the first and second procedures was carried out ten times, by which an average of the electric resistance values in each procedure was obtained. The average of electric resistance values in the state shown inFIG. 2Awas 1.4 Ω and the average of electric resistance values in the state shown inFIG. 2Bwas 1.6 Ω. Stable measured values were obtained in each of the procedures, by which the memory operation of the element can be confirmed.

Example 2 is one in which an element with the arrangement shown inFIG. 3is fabricated and operated. For the substrate4, a silicon substrate with a thickness of 500 μm with a 500 nm thick oxide film formed thereon was used, on which the following layers were formed by using sputtering. The first electrode5of Cu was formed with a thickness of 200 nm and an area of 500 nm×500 nm. Thereafter, the first ferromagnetic layer6of a CoPt alloy was formed with a thickness of 200 nm, an area of 100 nm×100 nm and a coercive force of 2500 Oe. Then, the first exchange coupling control layer7of Ru was formed with a thickness of 0.8 nm and an area of 100 nm×100 nm. Next, the magnetic domain wall displacement layer8of Ni80Fe20was formed with a thickness of 200 nm, an area of 100 nm×100 nm, and a coercive force of 5 Oe. Subsequently, the third exchange coupling control layer121of Ru was formed with a thickness of 0.8 nm and an area of 100 nm×100 nm. Next, the third ferromagnetic layer122of a CoPt alloy was formed with a thickness of 200 nm, an area of 100 nm×100 nm, and a coercive force of 2500 Oe. Then, the second electrode2of Au was formed with a thickness of 200 nm and an area of 500 nm×500 nm. Finally, the bit line1of Al was formed to provide Example 2.

By using the element, an evaluation was carried out similarly to that for Example 1. With the magnetic field strength for initialization given at 5000 Oe, the current density of the driving current given at 1×108A/cm2and the detecting current given at 300 μA, the electric resistance value in each of the first and second procedures was measured ten times. The average of electric resistance values in the state shown inFIG. 4Awas 3.2 Ω and the average of electric resistance values in the state shown inFIG. 4Bwas 3.6 Ω. Stable measured values were obtained in each of the procedures, by which the memory operation of the element can be confirmed.

Example 3 is one in which an element with the arrangement shown inFIG. 5is fabricated and operated. For the substrate4, a silicon substrate with a thickness of 500 μm with a 500 nm thick oxide film formed thereon was used, on which the following layers were formed by using sputtering. The first electrode5of Cu was formed with a thickness of 200 nm and an area of 500 nm×500 nm. Thereafter, the first ferromagnetic layer6of a CoPt alloy was formed with a thickness of 200 nm, an area of 100 nm×100 nm, and a coercive force of 2500 Oe. Then, the first exchange coupling control layer7of Ru was formed with a thickness of 0.8 nm and an area of 100 nm×100 nm. Next, the magnetic domain wall displacement layer8of Ni80Fe20was formed with a thickness of 200 nm, an area of 100 nm×100 nm, and a coercive force of 5 Oe. Subsequently, the fourth ferromagnetic layer142of a CoPt alloy was formed with a thickness of 200 nm, an area of 100 nm×100 nm, and a coercive force of 2500 Oe. Then, the second electrode2of Au was formed with a thickness of 200 nm and an area of 500 nm×500 nm. Finally, the bit line1was formed to provide Example 3.

By using the element, an evaluation was carried out similarly to that for Example 1. With the magnetic field strength for initialization given at 5000 Oe, the current density of the driving current given at 1×108A/cm2and the detecting current given at 300 μA, the electric resistance value in each of the first and second procedures was measured ten times. The average of electric resistance values in the state shown inFIG. 6Awas 3.2 Ω and the average of electric resistance values in the state shown inFIG. 6Bwas 3.6Ω. Stable measured values were obtained in each of the procedures, by which the memory operation of the element can be confirmed.

Example 4 is one in which an element with the arrangement shown inFIG. 7is fabricated and operated. For the substrate20, a silicon substrate with a thickness of 500 μm with a 500 nm thick oxide film formed thereon was used, on which the following layers were formed by using sputtering. The magnetic domain wall displacement layer22of Ni80Fe20was formed with a thickness of 100 nm, a width of 200 nm, a length of 1000 nm, and a coercive force of 5 Oe. Thereafter, the first exchange coupling control layer23of Ru was formed with a thickness of 0.8 nm and an area of 100 nm×100 nm. Then, the first ferromagnetic layer24of a CoPt alloy was formed with a thickness of 200 nm, an area of 100 nm×100 nm, and a coercive force of 2500 Oe. Next, the first electrode25of Au was formed with a thickness of 200 nm and an area of 100 nm×100 nm. Subsequently, the intermediate exchange coupling control layer26of Ru was formed with a thickness of 0.8 nm and an area of 100 nm×100 nm. Next, the intermediate ferromagnetic layer27of CoHfTa was formed with a thickness of 15 nm, an area of 100 nm×100 nm, and a coercive force of 5 Oe. Thereafter, the second exchange coupling control layer28of Ru was formed with a thickness of 0.8 nm and an area of 100 nm×100 nm. Next, the second ferromagnetic layer29of a CoPt alloy was formed with a thickness of 200 nm, an area of 100 nm×100 nm, and a coercive force of 2500 Oe. Then, the second electrode30of Au was formed with a thickness of 200 nm and an area of 100 nm×100 nm to provide Example 4.

By using the element, an evaluation was carried out similarly to that for Example 1. With the magnetic field strength for initialization given at 5000 Oe, the current density of the driving current given at 1×108A/cm2and the detecting current given at 300 μA, the electric resistance value in each of the first and second procedures was measured ten times. The average of electric resistance values in the state shown inFIG. 8Awas 3.2 Ω and the average of electric resistance values in the state shown inFIG. 8Bwas 3.6 Ω. Stable measured values were obtained in each of the procedures, by which the memory operation of the element can be confirmed.

Example 5 is one in which an element with the arrangement shown inFIG. 10is fabricated and operated. For the substrate20, a silicon substrate with a thickness of 500 μm with a 500 nm thick oxide film formed thereon was used, on which the following layers were formed by using sputtering. The magnetic domain wall displacement layer22of Ni80Fe20was formed with a thickness of 100 nm, a width of 200 nm, a length of 1000 nm, and a coercive force of 5 Oe. Thereafter, the first exchange coupling control layer23of Ru was formed with a thickness of 0.8 nm and an area of 100 nm×100 nm. Then, the first ferromagnetic layer24of a CoPt alloy was formed with a thickness of 200 nm, an area of 100 nm×100 nm, and a coercive force of 2500 Oe. Next, the first electrode25of Au was formed with a thickness of 200 nm and an area of 100 nm×100 nm. Subsequently, the third exchange coupling control layer48of Ru was formed with a thickness of 1.8 nm and an area of 100 nm×100 nm. Next, the third ferromagnetic layer49of a CoPt alloy was formed with a thickness of 200 nm, an area of 100 nm×100 nm, and a coercive force of 2500 Oe. Then, the second electrode30of Au was formed with a thickness of 200 nm and an area of 100 nm×100 nm to provide Example 5.

By using the element, an evaluation was carried out similarly to that for example 1. With the magnetic field strength for initialization given at 5000 Oe, the current density of the driving current given at 1×108A/cm2and the detecting current given at 300 μA, the electric resistance value in each of the first and second procedures was measured ten times. The average of electric resistance values in the state shown inFIG. 11Awas 3.2 Ω and the average of electric resistance values in the state shown inFIG. 11Bwas 3.6 Ω. Stable measured values were obtained in each of the procedures, by which the memory operation of the element can be confirmed.

Example 6 is one in which an element with the arrangement shown inFIG. 12is fabricated and operated. For the substrate20, a silicon substrate with a thickness of 500 μm with a 500 nm thick oxide film formed thereon was used, on which the following layers were formed by using sputtering. The magnetic domain wall displacement layer22of Ni80Fe20was formed with a thickness of 100 nm, a width of 200 nm, a length of 1000 nm, and a coercive force of 5 Oe. Thereafter, the first exchange coupling control layer23of Ru was formed with a thickness of 0.8 nm and an area of 100 nm×100 nm. Then, the first ferromagnetic layer24of a CoPt alloy was formed with a thickness of 200 nm, an area of 100 nm×100 nm, and a coercive force of 2500 Oe. Next, the first electrode25of Au was formed with a thickness of 200 nm and an area of 100 nm×100 nm. Subsequently, the fourth ferromagnetic layer109of a CoPt alloy was formed with a thickness of 200 nm, an area of 100 nm×100 nm, and a coercive force of 2500 Oe. Then, the second electrode30of Au was formed with a thickness of 200 nm and an area of 100 nm×100 nm to provide Example 6.

By using the element, an evaluation was carried out similarly to that for Example 1. With the magnetic field strength for initialization given at 5000 Oe, the current density of the driving current given at 1×108A/cm2and the detecting current given at 300 μA, the electric resistance value in each of the first and second procedures was measured ten times. The average of electric resistance values in the state shown inFIG. 13Awas 3.2 Ω and the average of electric resistance values in the state shown inFIG. 13Bwas 3.6 Ω. Stable measured values were obtained in each of the procedures, by which the memory operation of the element can be confirmed.

Example 7 is one in which an element with the arrangement shown inFIG. 14is fabricated and operated. For the substrate60, a silicon substrate with a thickness of 500 μm with a 500 nm thick oxide film formed thereon was used, on which the following layers were formed by using sputtering. The magnetic domain wall displacement layer62of Ni80Fe20was formed with a thickness of 100 nm, a width of 200 nm, a length of 1000 nm, and a coercive force of 5 Oe. Thereafter, the first exchange coupling control layer63of Ru was formed with a thickness of 0.8 nm and an area of 100 nm×100 nm. Next, the first nonmagnetic metal layer66of Cu was formed with a thickness of 0.8 nm and an area of 100 nm×100 nm. Then, the first ferromagnetic layer64of a CoPt alloy was formed with a thickness of 200 nm, an area of 100 nm×200 nm, and a coercive force of 2500 Oe. Next, the first electrode65of Au was formed with a thickness of 200 nm and an area of 100 nm×200 nm. Subsequently, the intermediate nonmagnetic metal layer67of Cu was formed with a thickness of 0.8 nm and an area of 100 nm×100 nm. Thereafter, the intermediate exchange coupling control layer72of Ru was formed with a thickness of 0.8 nm and an area of 100 nm×100 nm. Next, the intermediate ferromagnetic layer68of CoHfTa was formed with a thickness of 15 nm, an area of 100 nm×200 nm, and a coercive force of 5 Oe. Thereafter, the second exchange coupling control layer69of Ru was formed with a thickness of 0.8 nm and an area of 100 nm×200 nm. Next, the second ferromagnetic layer70of a CoPt alloy was formed with a thickness of 200 nm, an area of 100 nm×200 nm, and a coercive force of 2500 Oe. Then, the second electrode71of Au was formed with a thickness of 200 nm and an area of 100 nm×200 nm to provide Example 7.

By using the element, an evaluation was carried out similarly to that for Example 1. With the magnetic field strength for initialization given at 5000 Oe, the current density of the driving current given at 1×108A/cm2and the detecting current given at 300 μA, the electric resistance value in each of the first and second procedures was measured ten times. The average of electric resistance values in the state shown inFIG. 15Awas 3.4 Ω and the average of electric resistance values in the state shown inFIG. 15Bwas 3.6 Ω. Stable measured values were obtained in each of the procedures, by which the memory operation of the element can be confirmed.

Example 8 is one in which an element with the arrangement shown inFIG. 16is fabricated and operated. For the substrate60, a silicon substrate with a thickness of 500 μm with a 500 nm thick oxide film formed thereon was used, on which the following layers were formed by using sputtering. The magnetic domain wall displacement layer62of Ni80Fe20was formed with a thickness of 100 nm, a width of 200 nm, a length of 1000 nm, and a coercive force of 5 Oe. Thereafter, the first exchange coupling control layer63of Ru was formed with a thickness of 0.8 nm and an area of 100 nm×100 nm. After this, the first nonmagnetic metal layer66of Cu was formed with a thickness of 0.8 nm and an area of 100 nm×100 nm. Then, the first ferromagnetic layer64of a CoPt alloy was formed with a thickness of 200 nm, an area of 100 nm×200 nm, and a coercive force of 2500 Oe. Next, the first electrode65of Au was formed with a thickness of 200 nm and an area of 100 nm×200 nm. Subsequently, the third nonmagnetic metal layer87of Cu was formed with a thickness of 1.8 nm and an area of 100 nm×100 nm. Thereafter, the third exchange coupling control layer90of Ru was formed with a thickness of 1.8 nm and an area of 100 nm×100 nm. Next, the third ferromagnetic layer88of a CoPt alloy was formed with a thickness of 200 nm, an area of 100 nm×200 nm, and a coercive force of 2500 Oe. Then, the second electrode71of Au was formed with a thickness of 200 nm and an area of 100 nm×200 nm to provide Example 8.

By using the element, an evaluation was carried out similarly to that for Example 1. With the magnetic field strength for initialization given at 5000 Oe, the current density of the driving current given at 1×108A/cm2and the detecting current given at 300 μA, the electric resistance value in each of the first and second procedures was measured ten times. The average of electric resistance values in the state shown inFIG. 17Awas 3.2 Ω and the average of electric resistance values in the state shown inFIG. 17Bwas 3.6 Ω. Stable measured values were obtained in each of the procedures, by which the memory operation of the element can be confirmed.

By arranging a ferromagnetic layer with a large coercive force outside a magnetic domain wall displacement layer and providing antiferromagnetic or ferromagnetic coupling between the ferromagnetic layer and the magnetic domain wall displacement layer, it became feasible to record and reproduce a position of a magnetic domain wall as a change in electric resistance.

Furthermore, by providing antiferromagnetic or ferromagnetic coupling between a ferromagnet and the magnetic domain wall displacement layer, it became possible to stabilize the magnetic domain wall and the position of the magnetic domain wall. As a result, even though the volume or the saturation magnetization of the magnetic domain wall displacement layer is brought to be small for making the magnetic domain wall displacement in the magnetic domain wall displacement layer carried out at a high speed and at a low current, it is possible to secure thermal stability of the recorded magnetic domain wall. This enabled realization of high speed operation, operating current reduction and thermal stability in recording magnetization of the element with compatibility among them being assured.

A measure, such as one by which a large number of the elements according to the invention are integrated on a substrate, on which silicon semiconductor CMOS circuits are integrated, while being combined with the circuits, enables realization of a magnetic random access memory having a large recording capacity and including no mechanical driving sections. In addition, the element according to the invention exhibits magnetoresistance effect that changes the state of magnetization in the element depending on the direction of a current flowing between terminals to change electric resistance between the terminals. Thus, the element can be also used as a weak current sensor.

While the present invention has been particularly shown and described with reference to particular embodiments, it will be understood by those skilled in the art that the foregoing and other changes in form and details can be made therein without departing from the spirit and scope of the present invention. All modifications and equivalents attainable by one versed in the art from the present disclosure within the scope and spirit of the present invention are to be included as further embodiments of the present invention. The scope of the present invention accordingly is to be defined as set forth in the appended claims.

This application is based on, and claims priority to, JP PA 2005-107114, filed on 4 Apr. 2005. The disclosure of the priority application, in its entirety, including the drawings, claims, and the specification thereof, is incorporated herein by reference.