Abstract:
As a technique for attaining a reduction in power consumption, there is a technique for reducing power consumption using a spin wave. No specific proposal concerning spin wave generation, spin wave detection, and a latch technique for information has been made. 
     A device applies an electric field to a first electrode of a nonmagnetic material using a thin line-shaped stacked body including a first ferromagnetic layer and a nonmagnetic layer to thereby generate a spin wave in the first ferromagnetic layer, and detects a phase or amplitude of the spin wave propagated in the first ferromagnetic layer using a second electrode of a ferromagnetic material with a magnetoresistance effect.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a spin wave device including spin wave generation, spin wave propagation, spin wave detection, and a latch technique for information and further relates to an ultra-low power consumption logic integrated circuit using the spin wave device. 
       BACKGROUND ART 
       [0002]    It is said that a reduction in power consumption in an LSI for a trunk network router is essential to cope with a global increase in an amount of information communication. There are increasing needs for analyzing and processing, at high speed and low costs, a large amount of indefinite dynamic data accumulated in a server. However, a logic integrated circuit that takes on the analysis and the processing has limits in a reduction in power consumption through element refining of a conventional COMS and operation optimization. 
         [0003]    As means for solving these problems, there is a method of using a spin wave described in NPL 1. The spin wave means spatial and temporal changes in magnetization direction in a ferromagnetic material like a wave. There is no loss of energy in propagation of the spin wave. An arithmetic circuit using spin wave having an interference effect of a characteristic of the wave has been proposed. Ultra-low power consumption of a logic circuit is enabled by making use of the method and the arithmetic circuit. 
       CITATION LIST 
     Non Patent Literature 
       [0000]    
       
         NPL 1: A. Khitun, M. Bao, and K. L. Wang, “Spin Wave Magnetic NanoFabric: A New Approach to Spin-Based Logic Circuitry”, IEEE Trans. Mag 44, 2141 (2008). 
         NPL 2: S. Ikeda, J. Hayakawa, Y. Ashizawa, Y. M. Lee, K. Miura, H. Hasegawa, M. Tsunoda, F. Matsukura, and H. Ohno, “Tunnel Magnetoresistance of 604% at 300 K by suppression of Ta diffusion in CoFeB/MgO/CoFeB pseudo-spin-valves annealed at high temperature”, Appl. Phys. Lett. 93, 082508 (2008). 
         NPL 3: S. Ikeda, K. Miura, H. Yamamoto, K. Mizunuma, H. D. Gan, M. Endo, S. Kanai, J. Hayakawa, F. Matsukura, and H. Ohno, “A perpendicular-anisotropy CoFeB—MgO magnetic tunnel junction”, Nature Mater. 9, 721 (2010). 
       
     
       SUMMARY OF INVENTION 
     Technical Problem 
       [0007]    In a logic circuit using a spin wave, in addition to ultra-low power consumption, possibilities of miniaturization and high speed are also indicated. However, no specific proposal concerning spin wave generation, spin wave detection, and a latch technique for information has been made. 
         [0008]    It is an object of the invention to provide a spin wave device including forms capable of realizing spin wave generation, spin wave detection, and a latch technique for information in the spin wave device. 
       Solution to Problem 
       [0009]    In the invention, a modulation effect of magnetization by an electric field is used for spin wave generation. When an electric field is applied to a ferromagnetic material, the direction of magnetization locally changes. However, when the magnetization direction locally changes, the ferromagnetic material becomes energetically unstable. Therefore, in order to relax the instability, the local change in the magnetization tends to spread to the entire ferromagnetic material. At this point, the change in the magnetization direction in the ferromagnetic material spatially and temporally spreads like a wave. This is excitation of a spin wave by an electric field in the invention. 
         [0010]    On the other hand, a magnetoresistance effect is used for detection of a spin wave. The magnetoresistance effect is a resistance change in an element including a three-layer structure of a ferromagnetic layer/a nonmagnetic layer/a ferromagnetic layer as a basic structure. As a general example, one of the ferromagnetic layers is set as a free layer in which magnetization is variable and the other of the ferromagnetic layers is set as a fixed layer in which magnetization is fixed. When the magnetizations of the two ferromagnetic layers are parallel, element resistance is a minimum value. When the magnetizations are antiparallel, the resistance is a maximum value. When a magnetization direction of the free layer continuously changes, the resistance also continuously changes according to the change in the magnetization direction. In a spin wave device, a ferromagnetic layer in which a spin wave propagates is set as a free layer in which a magnetization direction is variable. In this case, when the spin wave propagates to a detection portion (a structure showing the magnetoresistance effect) of the spin wave device, a magnetization direction of a portion equivalent to the free layer changes. Since the resistance changes according to the change in the magnetization direction, it is possible to detect the spin wave by measuring the resistance at timing when the spin wave propagates. 
         [0011]    Movement of a magnetic domain wall is used for latching the spin wave. In this case, the magnetic domain wall is introduced into the ferromagnetic layer in which the spin wave propagates. When the spin wave propagates and reaches the magnetic domain wall, the magnetic domain wall moves according to the amplitude of the spin wave. This is due to transfer of an angular momentum between the spin wave and the magnetic domain wall. With this, it is possible to detect the spin wave by detecting the position of the magnetic domain wall. After the magnetic domain wall moves, even if the spin wave attenuates, the magnetic domain wall stays in a place to which the magnetic domain wall has moved. This makes it possible to keep information and function as latch. 
         [0012]    It is possible to realize a logic integrated circuit by the spin wave by using these means. The logic integrated circuit by the spin wave is made of a material substantially the same as the material of a tunnel magnetic resistance effect element (TMR element), which is a recording element of a magnetic memory (a Magnetoresistance Random Access Memory; MRAM). Therefore, it is possible to manufacture a spin wave device in a layer same as a layer of the TMR element in a manufacturing process same as a manufacturing process of the TMR element in a semiconductor manufacturing process. 
       Advantageous Effect of Invention 
       [0013]    By applying the logic circuit using the spin wave, it is possible to realize ultra-low power consumption, miniaturization, and high speed that cannot be realized by the conventional logic circuit using the CMOS. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  is a conceptual diagram of a spin wave device described in a first embodiment. 
           [0015]      FIG. 2  is a conceptual diagram showing operation timings of a clock signal, a write pulse (WP) applied from a first electrode  103 , and a read pulse (RP) applied from a second electrode  104  in the spin wave device described in the first embodiment and a magnetization direction of the spin wave device. 
           [0016]      FIG. 3  is a circuit configuration of the spin wave device described in the first embodiment. 
           [0017]      FIG. 4  is a circuit configuration of the spin wave device described in the first embodiment. 
           [0018]      FIG. 5  is a schematic diagram of a spin wave having information of [0] and [1] in the spin wave device described in the first embodiment. 
           [0019]      FIG. 6  is a schematic diagram showing the spin wave having the information of [0] and [1] propagated to an output portion  106  in the spin wave device described in the first embodiment and a magnetization direction of a first ferromagnetic layer  101  at that point. 
           [0020]      FIG. 7  is a diagram showing a temporal change of an output signal obtained by measuring, via a reference resistor, as a voltage, the magnitude of an output current at the time when a micro-voltage is applied in a film surface perpendicular direction of the output portion  106  in the spin wave device described in the first embodiment. 
           [0021]      FIG. 8  is a diagram showing a temporal change of an output signal obtained by measuring, via a reference resistor, as a voltage, the magnitude of an output current at the time when a micro-voltage is applied in a film surface perpendicular direction of the output portion  106  in a spin wave device described in a second embodiment. 
           [0022]      FIG. 9  is a schematic diagram showing a spin wave having information of [0] and [1] propagated to the output portion  106  in a spin wave device described in a third embodiment and a magnetization direction of the first ferromagnetic layer  101  at that point. 
           [0023]      FIG. 10  is a diagram showing a temporal change of an output signal obtained by measuring, via a reference resistor, as a voltage, the magnitude of an output current at the time when a micro-voltage is applied in a film surface perpendicular direction of the output portion  106  in a spin wave device described in the third embodiment. 
           [0024]      FIG. 11  is a conceptual diagram of a spin wave device into which a magnetic domain wall is introduced described in a fourth embodiment. 
           [0025]      FIG. 12  is a conceptual diagram showing operation timings of a clock signal, a write pulse WP applied from the first electrode  103 , and a read pulse RP applied from the second electrode  104  in the spin wave device described in the fourth embodiment and a magnetization direction of the spin wave device. 
           [0026]      FIG. 13  is a schematic diagram of a spin wave having information of [0] and [1] in the spin wave device described in the fourth embodiment. 
           [0027]      FIG. 14  is a schematic diagram showing movement of a magnetic domain wall  1101  at the time when a spin wave having a signal “ 0 ” reaches the magnetic domain wall  1101  in the spin wave device described in the fourth embodiment. 
           [0028]      FIG. 15  is a schematic diagram showing movement of the magnetic domain wall  1101  at the time when a spin wave having a signal “ 1 ” reaches the magnetic domain wall  1101  in the spin wave device described in the fourth embodiment. 
           [0029]      FIG. 16  is a conceptual diagram of a spin wave device into which a magnetic domain wall including magnetization fixed layers  1601  and  1602  is introduced described in a fifth embodiment. 
           [0030]      FIG. 17  is a conceptual diagram of a spin wave device operating as an AND gate described in the fifth embodiment. 
           [0031]      FIG. 18  is a conceptual diagram showing operation timings of a clock signal, a write pulse WP applied from a first electrode  1703  and a second electrode  1704 , and a read pulse RP applied from a third electrode  1708  in the spin wave device operating as the AND gate described in the fifth embodiment. 
           [0032]      FIG. 19  is a schematic diagram showing a spin wave detected by an output portion  1709  with respect to signals input in a first input portion  1705  and a second input portion  1706  in the spin wave device operating as the AND gate described in the fifth embodiment. 
           [0033]      FIG. 20  is a schematic diagram showing an FPGA basic configuration using a spin wave device. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
     First Embodiment 
       [0034]    A spin wave device is a device that converts an input signal (“ 0 ” or “ 1 ”) into a spin wave corresponding to “ 0 ” or “ 1 ”, propagates the spin wave to an output unit present in a place apart from an input unit, and read out. Major characteristics are that consumption of electric power is extremely small in a portion that generates the spin wave corresponding to the input signal, a portion that propagates the spin wave, and a portion that outputs the spin wave. It is possible to convert two input signals respectively into spin waves, cause the two spin waves to interfere with each other to cause the spin waves to operate like a logic gate, and output logic. By disposing the logic gate by the spin wave device in multiple stages, it is possible to form a logic circuit. In the following explanation, an operation principle of the spin wave device is explained with reference to the figures. 
         [0035]    According to a viewpoint of the invention, as shown in  FIG. 1 , a spin wave device  100  includes a thin line-shaped stacked body in which a first ferromagnetic layer  101  and a first nonmagnetic layer  102  are stacked in this order, includes a first electrode  103  on the first nonmagnetic layer  102 , and includes a second electrode  104  in a position different from the position of the first electrode  103  on the first nonmagnetic layer  102 . The second electrode  104  is a ferromagnetic material. A magnetization direction of the second electrode  104  is fixed. A part of the first nonmagnetic layer  102  and the first ferromagnetic layer  101  present right under the first electrode  103  configures an input portion  105  including the first electrode  103 . A part of the first nonmagnetic layer  102  and the first ferromagnetic layer  101  present right under the second electrode  104  configures an output portion  106  including the second electrode  104 . 
         [0036]    Electrodes are provided at both ends of the first ferromagnetic layer  101 . Consequently, it is possible to apply a voltage between the first electrode  103  and an end portion of the first ferromagnetic layer  106  on a side closer to the first electrode  103 . The spin wave device  100  includes a mechanism for reading resistance in a film surface perpendicular direction of the output portion  106  (a mechanism for applying a micro-voltage of a degree not affecting magnetization of the second electrode  104  and the first ferromagnetic layer  101  and reading an electric current or a mechanism for applying a micro-current and reading a voltage). Therefore, the output portion  106  is formed in a three-layer structure of a ferromagnetic layer/a nonmagnetic layer/a ferromagnetic layer and shows a so-called magnetoresistance effect. The spin wave device  100  includes, on the outside, a mechanism for generating a clock signal. 
         [0037]      FIG. 2  is a diagram showing an example of operation timings of a clock signal, a write pulse (WP) applied from the first electrode  103 , and a read pulse (RP) applied from the second electrode  104 . In the example shown in  FIG. 2 , CoFeB is used in the first ferromagnetic layer  101 , MgO is used in the first nonmagnetic layer  102 , Au is used in the first electrode  103 , and CoFeB is used in the second electrode  104 . 
         [0038]    When a combination of the CoFeB and the MgO is used, magnetic anisotropy of the CoFeB can be controlled with a film thickness. Usually, magnetization of a CoFeB thin film aligns in a parallel direction with respect to a film surface. In the case of the CoFeB set in contact with the MgO, when the film thickness of the CoFeB is reduced, the magnetization is in a direction perpendicular to the film surface. A reason for this is explained by conflict of magnetic anisotropy in a perpendicular direction on an interface between the CoFeB and the MgO and CoFeB crystal magnetic anisotropy in an in-plane direction. That is, when the CoFeB film thickness is large, the CoFeB crystal magnetic anisotropy becomes predominant and the magnetization is in the in-plane direction. However, when the CoFeB film thickness is reduced, the interface magnetic anisotropy becomes predominant and the magnetization is in the perpendicular direction. Making use of this principle, the magnetization of the first ferromagnetic layer  101  is set in a perpendicular upward direction with respect to the film surface and the magnetization of the second electrode  104  is set in a parallel rightward direction with respect to the film surface. Therefore, the film thickness of the first ferromagnetic layer  101  is designed to be 1.4 nm such that the crystal magnetic anisotropy of the CoFeB is smaller than the interface magnetic anisotropy between the CoFeB and the MgO. The film thickness of the second electrode  104  is designed to be 3.0 nm such that the crystal magnetic anisotropy of the CoFeB is larger than the interface magnetic anisotropy between the CoFeB and the MgO. The film thickness of the MgO is set to 2.0 nm such that a magnetoresistance effect (in this case, a tunnel magnetoresistance effect) increases in the output portion  106 . 
         [0039]    In the first embodiment, the CoFeB is used in the first ferromagnetic layer  101  and the second electrode  104  and the MgO is used in the first nonmagnetic layer. However, other materials may be used. For example, various ferromagnetic materials can be used in the first ferromagnetic layer  101  and the second electrode  104 . However, a material having a large magnetoresistance effect and large modulation of magnetization by an electric field is desirable. Any material can be used in the first nonmagnetic layer as long as the material is a nonmagnetic material. As combinations of such materials, there are a ferromagnetic material containing at least one or more 3d transition metal elements for a ferromagnetic layer and an oxide insulator containing oxygen for a nonmagnetic layer. A reason for using these materials is that, for example, a large output is easily obtained because a so-called tunnel magnetoresistance effect is obtained. Further, large interface magnetic anisotropy is obtained by bonding of 3d transition metal and oxygen. Therefore, another reason is that, for example, it is easy to control modulation of magnetization by an electric field according to film thickness control of the ferromagnetic layer. 
         [0040]    In particular, as described in Non Patent Literature 2, the magnetoresistance effect is large in the combination of the CoFeB and the MgO. As described in Non Patent Literature 3, it is possible to control the direction of magnetic anisotropy with the film thickness of the CoFeB. Therefore, an electric field effect increases by setting a film thickness near a boundary between a film thickness with which the magnetization is parallel to the film surface and a film thickness with which the magnetization is perpendicular to the film surface. 
         [0041]    At time t WP  synchronizing with a clock signal, when a voltage signal is applied to the first electrode  103 , an electric field is applied to the first ferromagnetic layer  101  via the first nonmagnetic layer  102 . At this point, the direction of magnetization locally changes in a portion of the first ferromagnetic layer  101  included in the input portion  105 . In the example shown in  FIG. 2 , an electric field is applied from the first electrode  103 , whereby magnetization of the first ferromagnetic layer  101  locally becomes parallel to the film surface. This is caused because magnetic anisotropy of a portion right under the first electrode  103  in the first ferromagnetic layer  101  is modulated by the electric field application. What is modulated by the electric field is the interfacial magnetic anisotropy along a direction perpendicular to the film surface. When the interfacial magnetic anisotropy decreases, the crystal magnetic anisotropy of the CoFeB becomes relatively predominant and the magnetization changes to the parallel direction with respect to the film surface. To efficiently modulate the interface magnetic anisotropy with the electric field, the film thickness of the first ferromagnetic layer  101  only has to be designed slightly smaller than the film thickness of the interface where the magnetization becomes parallel. In this example, the film thickness is set to 1.4 nm as explained above. 
         [0042]    When a part of the first ferromagnetic layer  101  has magnetization in the parallel direction with respect to the film surface, the first ferromagnetic layer  101  becomes unstable in terms of energy. In order to stabilize the first ferromagnetic layer  101  in terms of energy, it is attempted to average a magnetization direction in the entire first ferromagnetic layer  101 , then the magnetization temporally and spatially changes like a wave. This is a spin wave, and an angle of the magnetization from the direction perpendicular to the film surface corresponds to amplitude. A wavelength, speed, and the like, which are characteristics of the spin wave, are controlled with the pulse width of WP and the material, the shape, and the like of the first ferromagnetic layer  101 . It is possible to control, with an external magnetic field uniformly applied to the entire spin wave device  100 , a propagation direction of the spin wave. Therefore, the spin wave device  100  may include a mechanism for applying the external magnetic field. The spin wave induced by the electric field applied from the first electrode  103  propagates toward the second electrode  104 . 
         [0043]    A diagram schematically showing a circuit configuration  300  for realizing such an operation of the spin wave device  100  is  FIG. 3 . In  FIG. 3 , the first electrode  103  is electrically connected to a source electrode of a first selection transistor  301 . The second electrode  104  is electrically connected to a source electrode of a second selection transistor  302 . A drain electrode of the first selection transistor  301  is electrically connected to a first bit line  303 . A drain electrode of the second select ion transistor  302  is electrically connected to a second bit line  304 . Electrodes present at both ends of the first ferromagnetic layer  101  are electrically connected to a source line  305 . A gate electrode of the first selection transistor  301  is electrically connected to a first word line  306 . A gate electrode of the second selection transistor  302  is electrically connected to a second word line  307 . One ends of the first bit line  303  and the second bit line  304  are electrically connected to a bit line driver  308 . One end of the source line  305  is electrically connected to a source line driver  309 . The first word line  306  and the second word line  307  are electrically connected to a word line driver  310 . A clock input line  311  is electrically connected to the bit line driver  308 . A clock input line  312  is electrically connected to the source line driver  309 . A clock input line  312  is electrically connected to the word line driver  310 . Timings of voltages applied to the first bit line  303 , the second bit line  304 , the source line  305 , the first word line  306 , and the second word line  307  are controlled according to clock signals input from the respective clock input lines. In the following explanation, the bit line driver  308 , the source line driver  309 , the word line driver  310 , the clock input line  311  of the bit line driver  308 , the clock input line  312  of the source line driver  309 , and the clock input line  313  of the word line driver  310  are not shown in the figures. 
         [0044]    It is desirable to add a mechanism for applying a magnetic field to the entire spin wave device  100 . As the mechanisms, it is conceivable to adopt a method of, for example, disposing a magnetic material around the spin wave device  100  or disposing a wire right under the first ferromagnetic layer  101  of the spin wave device  100  and using a magnetic field induced by an electric current applied to the wire. 
         [0045]    A voltage for exciting a spin wave with an electric field is applied to the first bit line  303 . In this state, when a voltage corresponding to a WP is applied to the first word line  306 , the first selection transistor  301  changes to an ON state and the spin wave is excited. A voltage for reading the resistance of the output portion  106  is applied to the second bit line  304 . In this state, when a voltage corresponding to an RP is applied to the second word line  307 , the second selection transistor  302  changes to the ON state and the resistance can be read. 
         [0046]    In a circuit configuration  400  shown in  FIG. 4 , a positional relation of the first selection transistor  301  and the second selection transistor  302  with the spin wave device  100  is opposite to the positional relation shown in  FIG. 3 . Even with such a configuration, an operation same as the operation of the circuit configuration  300  is possible. Further, since the spin wave device is disposed above the transistors, it is easy to manufacture the spin wave device. 
         [0047]    The generated spin wave has information of a signal “ 0 ” or “ 1 ”. The information of “ 0 ” or “ 1 ” is characterized by a phase of the spin wave. In an example shown in  FIG. 5 , a spin wave phase-shifted by π/2 from the spin wave having the information of the signal “ 0 ” is represented as “ 1 ”. 
         [0048]    In order to generate, according to an input signal, such a spin wave having the phase different by π/2, when the WP is applied, the application of the WP only has to be delayed by time equivalent to π/2. The spin wave device  100  may include such a delay circuit. 
         [0049]    Alternatively, when the spin wave of “ 1 ” is generated with respect to the spin wave of “ 0 ”, a voltage only has to be applied to the first electrode  103  at timing delayed by one clock signal. In this case, a characteristic of the spin wave only has to be controlled such that a cycle of the clock signal is equivalent to ¼ of a spin wave cycle. 
         [0050]    When the spin wave propagates in the first ferromagnetic layer  101  and reaches the output portion  106 , a voltage (an electric current) is applied at time t RP  in synchronization with the clock signal in the second electrode  104 . An electric current (a voltage) flowing in the film surface perpendicular direction of the output portion  106  is read. A magnetization direction of a part of the first ferromagnetic layer  101  included in the output portion  106  changes by a generated spin wave. Therefore, the resistance in the film surface perpendicular direction of the output portion  106  changes with the magnetoresistance effect. 
         [0051]      FIG. 6  schematically shows spin waves having the information of “ 0 ” and “ 1 ” propagated to the output portion  106  and the magnetization direction of the first ferromagnetic layer  101  at that point. The spin wave having the information of “ 0 ” reaches the output portion  106  at time t 0 , and its amplitude is maximized at time t 1 . On the other hand, the spin wave having the information of “ 1 ” reaches the output portion at time t 1 . Therefore, when t RP =t 1 , the resistance in the film surface perpendicular direction of the output portion  106  at the time when the spin wave of the signal “ 0 ” reaches is low because of the magnetoresistance effect. On the other hand, the resistance in the film surface perpendicular direction of the output portion  106  at the time when the spin wave of the signal “ 1 ” reaches is high compared with the resistance at the time when the spin wave of the signal “ 0 ” reaches. Consequently, in the output portion, the different spin waves of “ 0 ” or “ 1 ” can be detected and output. Similarly, the spin waves can be detected when t RP =t 2 . 
         [0052]      FIG. 7  is a diagram showing a temporal change of an output signal obtained by measuring, via a reference resistor, as a voltage, the magnitude of an output current at the time when a micro-voltage is applied in the film surface perpendicular direction of the output portion  106 . In  FIG. 7 , a magnetization direction of the first ferromagnetic layer  101  at the time when the amplitude is plus is defined as a parallel right direction with respect to a film surface. Therefore, in an output voltage waveform of the signal “ 0 ” in  FIG. 7 , at t 1 , a magnetization direction in a portion of the first ferromagnetic layer  101  included in the output portion  106  is a parallel right direction with respect to a film surface and is parallel to magnetization of the second electrode  104 . 
         [0053]    Therefore, the resistance in the film surface perpendicular direction of the output portion  106  at t 1  decreases and an output current increases. Therefore, an output signal in  FIG. 7  increases. In an output signal waveform of the signal “ 1 ” in  FIG. 7 , magnetization is in a perpendicular upward direction with respect to the film surface at t 1 . Therefore, the output signal does not change. When time elapses from t 1 , an output waveform starts to increase. It is seen from the figure that a waveform delayed by π/2 from the spin wave of the signal “ 1 ” can be detected. In this example, t RP =t 1 . However, timing when it is possible to distinguish which of the spin waves of “ 0 ” and “ 1 ” propagates is not limited to t RP =t 1 . Characteristics such as the cycle of the clock signal, the speed, the wavelength of the spin wave, t WP  and t RP  only have to be controlled such that it is possible to distinguish which of the spin waves “ 0 ” and “ 1 ” propagates in the output portion  106 . 
         [0054]    By controlling a voltage applied to the second electrode  104 , it is possible to control the spin wave not to propagate from the first electrode  103  passing over a portion right under the second electrode  104 . The principle of this operation is that a magnetization direction can be controlled by applying an electric field. When an electric field is applied to the second electrode  104 , a magnetization direction of a portion of the first ferromagnetic layer  101  included in the output portion  106  locally changes to a parallel direction. The spin wave is a spatial and temporal change of magnetization. However, when the spin wave reaches a region of magnetization locally strongly fixed and directed in a parallel direction, the spin wave cannot spatially change the magnetization. Therefore, the spin wave cannot propagate passing over a portion right under the second electrode  104 . 
         [0055]    In the spin wave device manufactured as explained above, in the input portion  105 , since the spin wave is generated by the electric field, ideally, there is no consumption of electric power. In the spin wave propagation as well, since the spin wave is the temporal and spatial change in the magnetization direction, electric power is not consumed. In the output portion  106 , electric power is consumed in order to read resistance. However, since the resistance is only read, extremely small power is consumed. Therefore, it can be said that the spin wave device is a device that hardly consumes electric power. 
       Second Embodiment 
       [0056]    In the spin wave device  100  described in the first embodiment, the spin wave having the information of “ 1 ” is the wave approximately π/2 different in the phase from the spin wave having the information of “ 0 ”. According to another viewpoint of the invention, the spin wave having the information of “ 1 ” may be a wave phase-shifted by π from the spin wave having the information “ 0 ”. A basic structure of the spin wave device  100  described in a second embodiment is the same as the basic structure shown in  FIG. 1 . Operation timings of a clock signal, a WP applied from the first electrode  103 , and an RP applied from the second electrode  104  are basically the same as the operation timings in  FIG. 5 .  FIG. 8  is a diagram showing a temporal change of an output signal obtained by measuring, via a reference resistor, as a voltage, the magnitude of an output current at the time when a micro-voltage is applied in the film surface perpendicular direction of the output portion  106 . In an output voltage waveform of a signal “ 0 ” in  FIG. 8 , at t 1 , a magnetization direction of the first ferromagnetic layer  101  is a film surface parallel left direction with respect to a film surface and antiparallel to magnetization of the second electrode  104 . Therefore, the resistance in the film surface perpendicular direction of the output portion  106  at t 1  increases and an output current decreases. Therefore, an output signal in  FIG. 8  decreases. In an output signal waveform of a signal “ 1 ” in  FIG. 8 , at t 1 , magnetization is in a film surface parallel right direction with respect to the film surface. Therefore, the output signal increases. It is seen from this result that, in the output portion  106  of the spin wave device  100  described in the second embodiment, it is possible to distinguish and detect a spin wave having information of “ 0 ” or “ 1 ”. Compared with the spin wave device  100  described in the first embodiment, in the spin wave device  100  described in the second embodiment, a maximum value and a minimum value of the resistance in the film surface perpendicular direction of the output portion  106  are detected. Therefore, there is an advantage that the detection is easy. 
       Third Embodiment 
       [0057]    In the spin wave device  100  described in the first embodiment and the second embodiment, the information of “ 0 ” or “ 1 ” of the spin wave is characterized by the phase of the spin wave. According to another viewpoint of the invention, information of “ 0 ” or “ 1 ” of the spin wave can be characterized by the amplitude of the spin wave.  FIG. 9  is schematically shows a spin wave having information of “ 0 ” and “ 1 ” propagated to the output portion  106  and a magnetization direction of the first ferromagnetic layer  101  at that point. In an example shown in  FIG. 9 , the amplitude of the spin wave having the information of “ 0 ” is plus. At t 1 , a magnetization direction of a portion of the first ferromagnetic layer  101  included in the output portion  106  is a parallel rightward direction with respect to a film surface. On the other hand, the amplitude of the spin wave having the information of “ 1 ” is minus. At t 1 , the magnetization direction of a portion of the first ferromagnetic layer  101  included in the output portion  106  is a parallel leftward direction with respect to the film surface. That is, the spin waves of “ 0 ” and “ 1 ” are spin waves phase-shifted by approximately π. A pulse width of a WP is controlled such that the spin wave is excited only for a half wavelength. 
         [0058]    In this way, in order to generate a spin wave having plus or minus amplitude, an external magnetic field only has to be applied in the film surface parallel rightward direction or leftward direction at t WP . Alternatively, a field-like torque (FLT) having effects same as the effects of a magnetic field may be controlled and used. In this case, it is possible to obtain a spin wave having amplitude in the rightward direction or the leftward direction by controlling the direction of an effective magnetic field by a FLT with the amplitude of a voltage. Further, it is also conceivable to adopt a method of designing the spin wave device  100  such that an electric current flows a little simultaneously when a voltage is applied in the film surface perpendicular direction of the input portion  105 . It is also conceivable to adopt a method of using spin-transfer torque (STT). In this case, it is possible to control a magnetization direction of a spin wave by changing a direction of the electric current, that is, a direction in which the voltage is applied. In both the methods, an effective magnetic field may be extremely small. A reason for that is that energy necessary for directing magnetization of the ideally manufactured first ferromagnetic layer  101  to the rightward direction or the leftward direction is equivalent and, if, for example, energy in the rightward direction decreases even a little because of the effective magnetic field, the magnetization easily turns to the right. Therefore, it is possible to induce a spin wave having amplitude in the rightward direction or the leftward direction with a small effective magnetic field. 
         [0059]    When the spin wave propagates in the first ferromagnetic layer  101  and reaches the output portion  106 , in the second electrode  104 , a voltage (an electric current) is applied at time t RP  in synchronization with the clock signal in the second electrode  104 . An electric current (a voltage) in the film surface perpendicular direction of the output portion  106  is read. The spin wave propagated in the first ferromagnetic layer  101  changes to a magnetization direction shown in  FIG. 9  in the output portion  106 . That is, at t 1 , in the case of the spin wave of the signal “ 0 ”, the magnetization direction is a film surface parallel rightward direction. In the case of the spin wave of the signal “ 1 ”, the magnetization direction is a film surface parallel leftward direction. At this point, when the magnitude of an output current at the time when a micro-voltage is applied to the output portion  106  is shown as a temporal change of an output signal measured as a voltage via a reference resistor, the temporal change is as shown in  FIG. 10 . 
         [0060]    In an output voltage waveform of the signal “ 0 ” in  FIG. 10 , at t 1 , the magnetization direction of the first ferromagnetic layer  101  is a parallel rightward direction with respect to a film surface and is parallel to the second electrode  104 . Therefore, the resistance in the film surface perpendicular direction of the output portion  106  at t 1  decreases and an output current increases. Therefore, an output signal in  FIG. 10  increases. In an output signal waveform of the signal “ 1 ” in  FIG. 10 , magnetization is in a parallel leftward direction with respect to the film surface at t 1 . Therefore, the output signal decreases. 
         [0061]    As explained above, even when the information of “ 0 ” or “ 1 ” of the spin wave is characterized by the amplitude of the spin wave, it is possible to distinguish and detect which of the spin waves of “ 0 ” and “ 1 ” propagates. When the spin wave devices  100  in the first embodiment and the second embodiment are compared, in this system, a mechanism for applying an external magnetic field, a mechanism for generating FLT, or a mechanism for generating STT is necessary. However, there is an advantage that a mechanism for delaying the phase of the spin wave is unnecessary. 
       Fourth Embodiment 
       [0062]    In a spin wave device  1100 , movement of a magnetic domain wall  1101  may be used for detection of a spin wave propagated to the output portion  106 .  FIG. 11  shows a device structure for realizing detection of a spin wave using the magnetic domain wall  1101 . The magnetic domain wall  1101  is introduced into the first ferromagnetic layer  106  in  FIG. 11 . The direction of magnetization of the first ferromagnetic layer  106  changes to antiparallel in the magnetic domain wall  1101  serving as a boundary. On the inside of the magnetic domain wall  1101 , a magnetization direction spatially continuously changes. Therefore, when the spin wave propagates to the magnetic domain wall  1101 , magnetization inside the magnetic domain wall  1101  and the spin wave interact with each other. As a result, the magnetic domain wall  1101  can be moved. 
         [0063]      FIG. 12  shows, as an example, operation timings of a clock signal, a write pulse WP applied from the first electrode  103 , and a read pulse RP applied from the second electrode  104  in the spin wave device  1100  described in a fourth embodiment. 
         [0064]    At time t WP  synchronizing with the clock signal, when a voltage signal is applied to the first electrode  103 , an electric field is applied to the first ferromagnetic layer  101  via the first nonmagnetic layer  102 . A spin wave is generated in the first ferromagnetic layer  101 . The spin wave propagates in the first ferromagnetic layer  101  and reaches the introduced magnetic domain wall  1101 . At this point, the magnetic domain wall  1101  moves by interaction of the spin wave and the magnetic domain wall  1101 . A direction in which the magnetic domain wall  1101  moves depends on a direction in which magnetization of the spin wave tilts. 
         [0065]    In the following explanation, an example is explained in which a magnetization direction of the first ferromagnetic layer  101  is a perpendicular upward direction with respect to a film surface. The generated spin wave has information of a signal “ 0 ” or “ 1 ”.  FIG. 13  schematically shows a spin wave having information of “ 0 ” or “ 1 ” propagated to the output portion  106  in the spin wave device into which the magnetic domain wall  1101  is introduced. In an example shown in  FIG. 13 , the amplitude of the spin wave having the information of “ 0 ” is plus. At t 1 , a magnetization direction of a part of the first ferromagnetic layer  101  included in the output portion  106  is a parallel rightward direction with respect to the film surface. On the other hand, the amplitude of the spin wave having the information of “ 1 ” is minus. At t 1 , the magnetization direction of a part of the first ferromagnetic layer  101  included in the output portion  106  is a parallel leftward direction with respect to the film surface. That is, the spin waves of “ 0 ” and “ 1 ” are spin waves phase-shifted by n. A pulse width of the WP is controlled such that the spin wave is excited only by a half wavelength. 
         [0066]    When the spin wave reaches the magnetic domain wall  1101 , magnetization inside the magnetic domain wall  1101  and the spin wave interact with each other. As a result, the magnetic domain wall  1101  can be moved.  FIG. 14  schematically shows movement of the magnetic domain wall  1101  at the time when the spin wave of the signal “ 0 ” reaches the magnetic domain wall  1101 . A magnetization direction of the second electrode  104  is parallel to the film surface. In the example shown in  FIG. 14 , the magnetization direction is the rightward direction. In this example, the magnetic domain wall  1101  before the spin wave reaches is present on the left side of the output portion  106 . Therefore, the resistance in the film surface perpendicular direction of the output portion  106  is high resistance because of the magnetoresistance effect. When the spin wave of the signal “ 0 ” reaches, the magnetic domain wall  1101  moves to the right side of the output portion  106 . The resistance in the film surface perpendicular direction of the output portion  106  changes to low resistance. A temporal change of an output signal obtained by measuring, via a reference resistor, as a voltage, the magnitude of an output current at the time when a micro-voltage is applied to the output portion  106  before and after the spin wave reaches the magnetic domain wall  1101  is also shown in  FIG. 14 . In the figure, at t 1 , the output signal increases because the magnetic domain wall  1101  moves and the resistance changes. 
         [0067]    On the other hand,  FIG. 15  schematically shows movement of the magnetic domain wall  1101  at the time when the spin wave of the signal “ 1 ” reaches the magnetic domain wall  1101 . In this example, the magnetic domain wall  1101  before the spin wave reaches is present on the right side of the output portion  106 . Therefore, the resistance in the film surface perpendicular direction of the output portion  106  is low resistance because of the magnetoresistance effect. When the spin wave of the signal “ 1 ” reaches, the magnetic domain wall  1101  moves to the right side of the output portion  106 . The resistance in the film surface perpendicular direction of the output portion  106  changes to high resistance. Therefore, the output signal decreases because the magnetic domain wall  1101  moves and the resistance changes at t 1 . 
         [0068]    As explained above, in the spin wave device  1100  into which the magnetic domain wall  1101  is introduced, as a result of the propagation of the spin wave of “ 0 ” or “ 1 ”, the magnetic domain wall  1101  moves and the resistance of the output portion  106  changes. A characteristic of the spin wave device  1100  is that, even after the spin wave propagates to be attenuated, it is possible to continue to keep (latch) information. By controlling the amplitude of the electric field applied to the second electrode  104 , it is possible to locally fix a magnetization direction of a part of the first ferromagnetic layer  101  right under the second electrode  104 . This is because magnetic anisotropy changes, with an electric field, only in a part of the first ferromagnetic layer  101  right under the second electrode  104 . By making use of this, it is also possible to control the spin wave not to propagate in the first ferromagnetic layer  101  from the first electrode  103  passing over the second electrode  104 . 
         [0069]    Several methods are conceivable as a method of introducing the magnetic domain wall  1101  into the first ferromagnetic layer  101 . For example, a mechanism for strongly fixing magnetization in a part of the first ferromagnetic layer  101  may be provided. In an example shown in  FIG. 16 , a mechanism for locally applying a magnetic field to the first ferromagnetic layer  101  may be provided. In the example shown in  FIG. 16 , a spin wave device  1600  including magnetization fixing layers  1601  and  1602  is shown. The magnetization fixing layers  1601  and  1602  are desirably made of a ferromagnetic material having magnetic anisotropy larger than the magnetic anisotropy of the first ferromagnetic layer  101 . The magnetization fixing layers  1601  and  1602  are manufactured such that magnetization direction of the magnetization fixing layers  1601  and  1602  are antiparallel to each other. By manufacturing the magnetization fixing layers  1601  and  1602  in this way, magnetizations of parts  1603  and  1604  of the first ferromagnetic layer in contact with the magnetization fixing layers  1601  and  1602  are strongly fixed in antiparallel to each other. 
         [0070]    In order to more strongly fix the magnetization, a method of using an antiferromagnetic material as the magnetization fixing layers  1601  and  1602  is also effective. When the antiferromagnetic material is used, a magnetization direction is strongly fixed by exchange coupling of the antiferromagnetic material and the ferromagnetic material. As the antiferromagnetic material, IrMn, PtMn, and the like are representative. However, a material with which the exchange coupling strongly works is desirable. In this case as well, the magnetization fixing layers  1601  and  1602  are manufactured such that the magnetizations of the parts  1603  and  1604  of the first ferromagnetic layer in contact with the magnetization fixing layers  1601  and  1602  are strongly fixed in antiparallel to each other. 
         [0071]    The magnetization fixing layers  1601  and  1602  are desirably provided in positions apart from the first electrode  103  and the second electrode  104 . A reason for this is that, since the magnetizations of the parts  1603  and  1604  of the first ferromagnetic layer in contact with the magnetization fixing layers  1601  and  1602  are fixed in one direction according to the influence of the magnetization fixing layers  1601  and  1602 , it is conceivable that it is difficult to excite the spin wave or the amplitude of the spin wave decreases. 
         [0072]    In the spin wave device  1600  manufactured in this way, since the magnetizations of the parts  1603  and  1604  of the first ferromagnetic layer in contact with the magnetization fixing layers  1601  and  1602  are strongly fixed in antiparallel to each other, a boundary in the magnetization direction needs to be always present between the parts  1603  and  1604  of the first ferromagnetic layer. Therefore, at least one magnetic domain wall  1101  is introduced. 
         [0073]    As another method of introducing a magnetic domain wall, a mechanism for locally applying a magnetic field to the first ferromagnetic layer  101  may be provided. When this method is applied, it is possible to use a magnetic field generated by feeding an electric current. A wire for feeding an electric current is manufactured on the side of the first ferromagnetic layer  101  to be spaced apart from the first ferromagnetic layer  101 . When an electric current is fed to the wire, a magnetic field is generated. The magnetic domain wall is introduced by changing the magnetization direction of the first ferromagnetic layer  101  with the magnetic field. 
         [0074]    In the spin wave device manufactured by such a method, it is possible to continue to keep information as explained above. Therefore, the spin wave device can be used as a spin wave device capable of latching information. 
       Fifth Embodiment 
       [0075]    According to still another viewpoint of the invention, it is possible to convert two input signals respectively into spin waves and cause the two spin waves to interfere with each other to thereby cause the spin waves to operate like a logic gate, and output logic. By disposing the logic gate by the spin wave device in multiple stages, it is possible to form a logic circuit. In a fifth embodiment, an operation principle of a spin wave device that operate as an AND gate with respect to two inputs is explained as an example. 
         [0076]      FIG. 17  schematically shows a spin wave device  1700  that operates as an AND gate. The spin wave device  1700  includes a thin line-shaped stacked body in which a first ferromagnetic layer  1701  and a first nonmagnetic layer  1702  are stacked in this order and includes a first electrode  1703  on the first nonmagnetic layer  1702 . Similar another thin line-shaped stacked body is present. The stacked body includes a second electrode  1704  on the first nonmagnetic layer  1702 . A part of the first nonmagnetic layer  1702  and the first ferromagnetic layer  1701  present right under the first electrode  1703  configure a first input portion  1705  including the first electrode  1703 . A part of the first nonmagnetic layer  1702  and the first ferromagnetic layer  1701  present right under the second electrode  1704  configure a second input portion  1706  including the second electrode  1704 . The two thin line-shaped stacked bodies merge in an interference portion  1707  to be one thin-line shape. Merged one thin line-shaped stacked body includes a third electrode  1708  on the first nonmagnetic layer  1702 . A part of the first nonmagnetic layer  1702  and the first ferromagnetic layer  1701  present right under the third electrode  1708  configure an output portion  1709  including the third electrode  1708 . The third electrode  1708  is made of a ferromagnetic material. 
         [0077]    In order to respectively apply electric fields between the first electrode  1703  and the first ferromagnetic layer  1701  and between the second electrode  1704  and the first ferromagnetic layer  1701 , an electrode is provided in the first ferromagnetic layer  1701 . The spin wave device  1700  includes a mechanism for reading resistance in a film surface perpendicular direction of the output portion  1709  (a mechanism for applying a micro-voltage of a degree not affecting magnetization of the third electrode  1708  and the first ferromagnetic layer  1701  and reading an electric current or a mechanism for applying a micro-current and reading a voltage). The spin wave device  1700  includes, on the outside, a mechanism for generating a clock signal. 
         [0078]      FIG. 18  is a diagram showing, as an example, operation timings of a clock signal, a write pulse  1  (WP 1 ) applied from the first electrode  1703 , a write pulse  2  (WP 2 ) applied from the second electrode  1704 , and a read pulse (RP) applied from the third electrode  1708  in the spin wave device  1700  described in the fifth embodiment. As it is seen from the figure, in the example of the fifth embodiment, the WP 1  and the WP 2  are applied at the same timing. 
         [0079]    As a generation method for a spin wave in the first input portion  1705  and the second input portion  1706 , the method described in any one of the first to third embodiments is applied. In the fifth embodiment, the spin wave generating method described in the third embodiment is applied. That is, the information of “ 0 ” or “ 1 ” of the spin wave is characterized by the amplitude of the spin wave. 
         [0080]    Spin waves simultaneously generated at time t WP  synchronizing with the clock signal in the first input portion  1705  and the second input portion  1706  propagate in the first ferromagnetic layer  1701  at the same speed and interfere with each other in the interference portion  1707 . As a result, the spin wave propagated to the output portion  1709  is different depending on the spin wave of “ 0 ” or “ 1 ” respectively input in the first input portion  1705  and the second input portion  1706 .  FIG. 19  shows a spin wave detected in the output portion  1709  with respect to signals input in the first input portion  1705  and the second input portion  1706 . 
         [0081]      FIG. 19( a )  shows a spin wave at the time when a signal “ 0 ” is input in the first input portion  1705  and the second input portion  1706  and a spin wave propagated to the output portion  1709  via the interference portion  1707 . The spin wave propagated to the output portion  1709  has plus amplitude.  FIG. 19( b )  shows a spin wave at the time when the signal “ 0 ” is input in the first input portion  1705  and the signal “ 1 ” is input in the second input portion  1706  and a spin wave propagated to the output portion  1709  via the interference portion  1707 . In this case, since the input spin waves cancel each other according to interference, a spin wave is not observed in the output portion  1709 .  FIG. 19( c )  shows a spin wave at the time when the signal “ 1 ” is input in the first input portion  1705  and the signal “ 0 ” is input in the second input portion  1706  and a spin wave propagated to the output portion  1709  via the interference portion  1707 . Similarly, a spin wave is not observed in the output portion  1709 .  FIG. 19( d )  shows a spin wave at the time when the signal “ 1 ” is input in the first input portion  1709  and the second input portion  1706  and a spin wave propagated to the output portion  1709  via the interference portion  1707 . The spin wave propagated to the output portion  1709  has minus amplitude. 
         [0082]    In the output portion  1709 , an RP pulse is applied at time t RP  synchronizing with the clock signal. An electric current flowing in the film surface perpendicular direction of the output portion  1709  is read. In magnetization of a part of the first ferromagnetic layer  1701  included in the output portion  1709 , a magnetization direction changes with the generated spin wave. Therefore, since the resistance in the film surface perpendicular direction of the output portion  1709  changes with the magnetoresistance effect, it is possible to distinguish the propagated spin wave. 
         [0083]    From the result explained above, it is possible to use the spin waves as an OR gate by, for example, determining a threshold to set amplitude as Low when the amplitude is equal to or lower than 0. It is possible to manufacture a logic gate such as AND, NOR, or NAND by changing the threshold or combining the spin waves. It is also possible to configure a logic circuit by disposing, in multiple stages, the logic gate using the spin wave device manufactured in this way. 
         [0084]    Therefore, by using the spin wave device, it is possible to configure a logic circuit with power consumption reduced more than in the CMOS device currently in use.  FIG. 20  shows a schematic diagram of an FPGA configured using a spin wave device. The spin wave device is used in a configurable logic block (CLB)  2003 . In  FIG. 20 , as an example, a lookup table (LUT)  2005  is configured by a spin wave device. As it is seen from an LUT  2006  configured using the spin wave device, a logic circuit is realized by disposing the spin wave device  1700  in multiple stages. It is also possible to configure a switch box  2001 , a flip-flop (FF)  2004 , and the like with the spin wave device. 
       REFERENCE SIGNS LIST 
       [0000]    
       
         
           
               100  Spin wave device 
               101  First ferromagnetic layer 
               102  First nonmagnetic layer 
               103  First electrode 
               104  Second electrode 
               105  Input portion 
               106  Output portion 
               300  Circuit configuration of the spin wave device 
               301  First selection transistor 
               302  Second selection transistor 
               303  First bit line 
               304  Second bit line 
               305  Source line 
               306  First word line 
               307  Second word line 
               308  Bit line driver 
               309  Source line driver 
               310  Word line driver 
               311  Clock input line of the bit line driver  308   
               312  Clock input line of the source line driver  309   
               313  Clock input line of the word line driver  310   
               400  Circuit configuration of the spin wave device 
               1100  Spin wave device into which a magnetic domain wall is introduced 
               1101  Magnetic domain wall 
               1600  Spin wave device into which a magnetic domain wall including a magnetization fixing layer is introduced 
               1601  First magnetization fixing layer 
               1602  Second magnetization fixing layer 
               1603  Part of the first ferromagnetic layer in contact with the first magnetization fixing layer  1601   
               1604  Part of the first ferromagnetic layer in contact with the second magnetization fixing layer  1602   
               1700  Logic circuit using the spin wave device 
               1701  First ferromagnetic layer 
               1702  First nonmagnetic layer 
               1703  First electrode 
               1704  Second electrode 
               1705  First input portion 
               1706  Second input portion 
               1707  Interference portion 
               1708  Third electrode 
               1709  Output portion 
               2000  FPGA basic configuration using the spin wave device 
               2001  Switch box 
               2002  Global wire 
               2003  Configurable logic block (CLB) 
               2004  Flip-flop (FF) 
               2005  Lookup table (LUT) 
               2006  LUT configured using the spin wave device