Patent Publication Number: US-2020303632-A1

Title: Magnetic device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2019-049603, filed Mar. 18, 2019, the entire contents of which are incorporated herein by reference. 
     FIELD 
     Embodiments described herein relate generally to a magnetic device. 
     BACKGROUND 
     Magnetic devices including magnetic elements are known. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram to explain a configuration of a magnetic memory device according to a first embodiment. 
         FIG. 2  is a circuit diagram to explain a configuration of a memory cell array of the magnetic memory device according to the first embodiment. 
         FIG. 3  is a cross-sectional view to explain a configuration of the memory cell array of the magnetic memory device according to the first embodiment. 
         FIG. 4  is a cross-sectional view to explain a configuration of the memory cell array of the magnetic memory device according to the first embodiment. 
         FIG. 5  is a cross-sectional view to explain a configuration of a magnetoresistive effect element of the magnetic memory device according to the first embodiment. 
         FIG. 6  is a schematic view to explain a manufacturing method of the magnetoresistive effect element of the magnetic memory device according to the first embodiment. 
         FIG. 7  is a schematic view to explain a manufacturing method of the magnetoresistive effect element of the magnetic memory device according to the first embodiment. 
         FIG. 8  is a schematic view to explain effects according to the first embodiment. 
         FIG. 9  is a schematic view explain a configuration of a memory cell array of a magnetic memory device according to a modification of the first embodiment. 
         FIG. 10  is a cross-sectional view to explain a configuration of a memory cell of a magnetic memory device according to the modification of the first embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     In general, according to one embodiment, a magnetic device includes a magnetoresistive effect element. The magnetoresistive effect element includes a first nonmagnet, a second nonmagnet, a first ferromagnet between the first nonmagnet and the second nonmagnet, a third nonmagnet including a rare-earth oxide, the second nonmagnet between the first ferromagnet and the third nonmagnet, and a fourth nonmagnet between the second nonmagnet and the third nonmagnet and including a metal. 
     Hereinafter, the embodiments is described with reference to the drawings. In the description below, structural elements having the same functions and configurations is denoted by a common reference symbol. To distinguish a plurality of structural elements having a common reference symbol from each other, an additional symbol is added after the common reference symbol. If it is unnecessary to distinguish the structural elements, only a common reference symbol is assigned to the structural elements, and no additional symbol is added. Herein, additional symbols are not limited to subscripts or superscripts, and they may be lower-case alphabetical letters added to reference symbols, and indices meaning arrangements. 
     1. First Embodiment 
     A magnetic device according to a first embodiment is described. The magnetic device according to the first embodiment is, for example, a perpendicular magnetic magnetization-type magnetic memory device in which an element having a magnetoresistive effect provided by a magnetic tunnel junction (MTJ) (such an element may be called an MTJ element or a magnetoresistive effect element) as a resistance change element. 
     In the following, the magnetic memory device as an example of the magnetic device is explained. 
     1.1 Configuration 
     First, a configuration of the magnetic memory device according to the first embodiment is described. 
     1.1.1 Configuration of Magnetic Memory Device 
       FIG. 1  is a block diagram illustrating a configuration of the magnetic memory device according to the first embodiment. As illustrated in  FIG. 1 , the magnetic memory device  1  includes a memory cell array  10 , a row selection circuit  11 , a column selection circuit  12 , a decode circuit  13 , a write circuit  14 , a read circuit  15 , a voltage generation circuit  16 , an input/output circuit  17 , and a control circuit  18 . 
     The memory cell array  10  includes a plurality of memory cells MC, each associated with a row and a column. Memory cells MC arranged in the same row are coupled to the same word line WL, and memory cells MC arranged in the same column are coupled to the same bit line BL. 
     The row selection circuit  11  is coupled to the memory cell array  10  via word lines WL, To the row selection circuit  11 , a decoding result of an address ADD provided from the decode circuit  13  (row address) is supplied. The row selection circuit  11  sets a word line WL corresponding to a row which is selected based on the decoding result of an address ADD to a selected state. Hereinafter, the word line WL that has been set to a selected state is referred to as a selected word line WL. The word lines WL other than the selected word line WL are referred to as non-selected word lines WL. 
     The column selection circuit  12  is coupled to the memory cell array  10  via bit lines BL. To the column selection circuit  12 , a decoding result of an address ADD provided from the decode circuit  13  (column address) is supplied. The column selection circuit  12  sets a column which is selected based on the decoding result of an address ADD to a selected state. Hereinafter, the bit line BL that has been set to a selected state is referred to as a selected bit line BL. The bit lines BL other than the selected bit line BL are referred to as non-selected bit lines BL. 
     The decode circuit  13  decodes an address ADD from the input/output circuit  17 . The decode circuit  13  supplies the decoding result of the address ADD to the row selection circuit  11  and the column selection circuit  12 . The address ADD includes an address of a column to be selected and an address of a row to be selected. 
     The write circuit  14  writes data to a memory cell MC. The write circuit  14  includes, for example, a write driver (not illustrated). 
     The read circuit  15  reads data from a memory cell MC. The read circuit  15  includes, for example, a sense amplifier (not illustrated). 
     The voltage generation circuit  16  generates a voltage for various operations of the memory cell array  10  by using a power supply voltage provided outside (not illustrated) of the magnetic memory device  1 . For example, the voltage generation circuit  16  generates various voltages required for a write operation, and outputs the voltages to the write circuit  14 . The voltage generation circuit  16  also generates various voltages required for a read operation, and outputs the voltages to the read circuit  15 . 
     The input/output circuit  17  transfers an address ADD provided outside of the magnetic memory device  1  to the decode circuit  13 . The input/output circuit  17  transfers a command CMD provided outside of the magnetic memory device  1  to the control circuit  18 . The input/output circuit  17  transmits and receives various control signals CNT between the outside of the magnetic memory device  1  and the control circuit  18 . The input/output circuit  17  transfers data DAT provided outside of the magnetic memory device  1  to the write circuit  14 , and outputs data DAT transferred from the read circuit  15  to the outside of the magnetic memory device  1 . 
     The control circuit  18  controls the operations of the row selection circuit  11 , the column selection circuit  12 , the decode circuit  13 , the write circuit  14 , the read circuit  15 , the voltage generation circuit  16 , and the input/output circuit  17  in the magnetic memory device  1  based on a control signal CNT and a command CMD. 
     1.1.2 Configuration of Memory Cell Array 
     Next, a configuration of the memory cell of the magnetic memory device according to the first embodiment is described with reference to  FIG. 2 .  FIG. 2  is a circuit diagram showing a configuration of the memory cell array of the magnetic memory device according to the first embodiment. In  FIG. 2 , the word lines WL are classified by additional symbols such as two lower-case alphabets (“u” and “d”) and index (“&lt; &gt;”). 
     As shown in  FIG. 2 , the memory cells MC (MCu and Med) are arranged in a matrix in the memory cell array  10 , and are respectively associated with a set of one of a plurality of bit lines BL (BL&lt; 0 &gt;, BL&lt; 1 &gt;, . . . , BL&lt;N&gt;) and one of a plurality of word lines WLd (WLd&lt; 0 &gt;, WLd&lt; 1 &gt;, . . . , WLd&lt;M&gt;) or WLu&lt; 0 &gt;, WLu&lt; 1 &gt;, . . . , WLu&lt;M&gt;) (M and N are integers). In other words, the memory cell MCd&lt;i,j&gt; (0≤i≤M, 0≤j≤N) is coupled between the word line WLd&lt;i&gt; and the bit line BL&lt;j&gt;, and the memory cell MCu&lt;i,j&gt; is coupled between the word line WLu&lt;i&gt; and the bit line BL&lt;j&gt;. 
     The additional symbols “d” and “u” are used for convenience to identify a memory cell of the memory cells that is provided below or above a bit line BL. An example of a three-dimensional configuration of the memory cell array  10  is described later in detail. 
     The memory cell MCd&lt;i,j&gt; includes a switching element SELd&lt;i,j&gt; and a magnetoresistive effect element MTJd&lt;i,j&gt; coupled in series thereto. The memory cell MCu&lt;i,j&gt; includes a switching element SELu&lt;i,j&gt; and a magnetoresistive effect element MTJu&lt;i,j&gt; coupled in series thereto. 
     The switching element SEL has a function as a switch that controls a supply of a current to a corresponding magnetoresistive effect element MTJ when data is read from and written to the magnetoresistive effect element MTJ. More specifically, the switching element SEL in a memory cell MC, for example, serves as an insulator having a large resistance value and cuts off a current (in other words, is in an off state) when a voltage applied to the memory cell MC is below a threshold voltage Vth, and serves as a conductor having a small resistance value and allows a current to flow (in other words, is in an on state) when the voltage exceeds the threshold voltage Vth. In other words, the switching element SEL has a function of switching between the on state and the off state in accordance with a voltage applied to the memory cell MC, irrespective of a direction of a flowing current. 
     The switching element SEL may be, for example, a two-terminal type switching element having only two terminals. When a voltage applied between the two terminals is smaller than a threshold voltage, the switching element is in a “high resistance” state, such as an electrically non-conductive state. When a voltage applied between the two terminals is equal to or larger than the threshold voltage, the switching element is in a “low resistance” state, such as an electrically conductive state. The switching element may have this function regardless of the polarity of the voltage. For example, the switching element may include at least one type of chalcogen selected from a group of tellurium (Te), selenium (Se), and sulfur (S). Alternatively, the switching element may include chalcogenide, which is a compound containing the chalcogen element. This switching element may include at least one element selected from a group consisting of boron (B), aluminum (Al), gallium (Ga), indium (In), carbon (C), silicon (Si), germanium (Ge), tin (Sn), arsenic (As), phosphorus (P), antimony (Sb), titanium (Ti), and bismuth (Bi). More specifically, the switching element may include at least two elements selected from germanium (Ge), antimony (Sb), tellurium (Te), titanium (Ti), arsenic (As), indium (In), and bismuth (Bi). Furthermore, the switching element may include an oxide of at least one element selected from Ti, vanadium (V), chromium (Cr), niobium (Nb), molybdenum (Mo), hafnium (Hf), and tungsten (W). 
     A resistance value of the magnetoresistive effect element MTJ can be switched between a low-resistance state and a high-resistance state by a current of which the control is selected by the switching element SEL. The magnetoresistive effect element MTJ is capable of writing data in accordance with the change of its resistance state, and stores written data in a non-volatile manner to function as a readable memory element. 
     Next, a cross-section structure of the memory cell array  10  is described with reference to  FIG. 3  and  FIG. 4 .  FIG. 3  and  FIG. 4  show examples of cross sectional views illustrating a configuration of the memory cell array of the magnetic memory device according to the first embodiment.  FIG. 3  and  FIG. 4  show cross sections of the memory cell array  10  viewed from different directions intersecting each other. 
     As shown in  FIG. 3  and  FIG. 4 , the memory cell array  10  is disposed above a semiconductor substrate  20 . In the following description, a plane parallel to the surface of the semiconductor substrate  20  is defined as an XY plane, and a direction perpendicular to the XY plane is defined as a Z direction. The direction along the word lines WL is defined as an X direction, and the direction along the bit lines BL is defined as a Y direction. Thus,  FIG. 3  and  FIG. 4  are cross sectional views of the memory cell array  10 , taken along the Y direction and the X direction, respectively. 
     For example, a plurality of conductors  21  are disposed on an upper surface of the semiconductor substrate  20 . The conductors  21  have conductivity and each functions as a word line W 1   d . The plurality of conductors  21  are, for example, arranged in the Y direction, and each extending in the X direction. Although  FIG. 3  and  FIG. 4  illustrate a case in which the conductors  21  are disposed on the semiconductor substrate  20 , the embodiment is not limited to this case. For example, the conductors  21  may be disposed above the semiconductor  20 , not in contact with but apart from the semiconductor  20 . 
     On the upper surface of one conductor  21 , a plurality elements  22 , each functioning as a magnetoresistive effect element MTJd, are disposed. The elements  22  disposed on the upper surface of the conductor  21  are, for example, arranged in the X direction. In other words, the elements  22  arranged in line in the X direction are coupled to the upper surface of one conductor  21  in common. The details of the configuration of the elements  22  is described later. 
     On upper surfaces of the respective elements  22 , elements  23  that function as switching elements SELd are disposed. Each of upper surfaces of the elements  23  is coupled to any one of a plurality of conductors  24 . The conductors  24  have conductivity and each functions as a bit line BL. The conductors  24  are, for example, arranged in the X direction, and each extending in the Y direction. In other words, the elements  23  arranged in line along the Y direction are coupled to one conductor  24  in common. Although  FIG. 3  and  FIG. 4  illustrate a case in which each of the elements  23  is disposed on the element  22  and the conductor  24 , the embodiment is not limited to this case. For example, each of the elements  23  may be coupled to the element  22  and the conductor  24  via a conductive contact plug (not shown). 
     On an upper surface of one conductor  24 , a plurality of elements  25 , each functioning as a magnetoresistive effect element MTJu, are disposed. The elements  25  disposed on the upper surface of the conductor  24  are, for example, arranged in the Y direction. In other words, the elements  25  arranged in line along the Y direction are coupled to the upper surface of one conductor  24  in common. The elements  25  have a configuration equivalent to that of the elements  22 , for example. 
     On upper surfaces of the respective elements  25 , elements  26  that function as switching elements SELu are provided. Each of upper surfaces of the elements  26  is coupled to any one of a plurality of conductors  27 . The conductors  27  have conductivity and each functions as a word line WLu. The conductors  27  are, for example, arranged in the Y direction, and each extending in the X direction. In other words, the plurality of elements  26  arranged in line in the X direction are coupled to one conductor  27  in common. Although  FIG. 3  and  FIG. 4  illustrate a case in which each of the conductors  26  is disposed on the element  25  and the conductor  27 , the embodiment is not limited to this case. For example, each of the elements  26  may be coupled to the element  25  and the conductor  27  via a conductive contact plug (not shown). 
     The memory cell array  10  configured as described above has a structure in which a set of two word lines, WLd and WLu, corresponds to one bit line BL. Furthermore, the memory cell array  10  has a structure including a plurality of memory cells MC at different heights in the Z direction; in the structure, a memory cell MCd is arranged between a word line WLd and a bit line BL and a memory cell MCu is arranged between a bit line BL and a word line WLu. In the cell structure illustrated in  FIG. 3  and  FIG. 4 , the memory cell MCd is associated with the lower layer and the memory cell MCu is associated with the upper layer. In other words, of two memory cells MC coupled to one bit line BL in common, the memory cell MC disposed in the upper layer of the hit line BL is referred to with the additional symbol “u”, as “memory cell MCu”, and the other memory cell MC disposed in the lower layer is referred to with “d”, as “memory cell MCd”. 
     1.1.3 Magnetoresistive Effect Element 
     Next, a configuration of the magnetoresistive effect element of the magnetic device according to the first embodiment is described with reference to  FIG. 5 .  FIG. 5  is a cross-sectional view illustrating a configuration of the magnetoresistive effect element of the magnetic device according to the first embodiment.  FIG. 5  shows an example of a cross section of the magnetoresistive effect element MTJd shown in  FIG. 3  and  FIG. 4 , taken along a plane perpendicular in the Z direction (e.g., the YZ plane). Since the magnetoresistive effect element MTJu has a configuration similar to that of the magnetoresistive effect element MTJd, the illustration is omitted. 
     As shown in  FIG. 5 , the magnetoresistive effect element MTJ includes, for example, a nonmagnet  31  serving as a top layer TOP, a nonmagnet  32  serving as a capping layer CAPa, a nonmagnet  33  serving as a capping layer CAPb, a ferromagnet  34  serving as a storage layer SL, a nonmagnet  35  serving as a tunnel barrier layer TB, a ferromagnet  36  serving as a reference layer RL, a nonmagnet  37  serving as a spacer layer SP, a ferromagnet  38  serving as a shift cancelling layer SCL, and a nonmagnet  39  serving as an under layer UL. 
     In the magnetoresistive effect element MTJd, the nonmagnet  39 , the ferromagnet  38 , the nonmagnet  37 , the ferromagnet  36 , the nonmagnet  35 , the ferromagnet  34 , the nonmagnet  33 , the nonmagnet  32 , and the ferromagnet  31  are stacked in this order, from the word line WLd side toward the bit line BL side (in the direction of the Z axis). In the magnetoresistive effect element MTJu, the nonmagnet  39 , the ferromagnet  38 , the nonmagnet  37 , the ferromagnet  36 , the nonmagnet  35 , the ferromagnet  34 , the nonmagnet  33 , the nonmagnet  32 , and the ferromagnet  31  are stacked in this order, from the bit line BL side toward the word line WLu side (in the direction of the Z axis). The magnetoresistive effect elements MTJd and MTJu function as, for example, perpendicular magnetization type MTJ elements, in which each of the magnetization directions of the magnets that constitute the magnetoresistive effect elements MTJd and MTJu is oriented in a direction perpendicular with respect to a film surface. The magnetoresistive effect element MTJ may further include an additional layer between two of the aforementioned layers  31  to  39 . 
     The nonmagnet  31  is a non-magnetic rare-earth oxide, and has a function of absorbing elements, such as boron (B), diffusing from the ferromagnet  34  during the process of producing the magnetoresistive effect element MTJ. The nonmagnet  31  includes an oxide of at least one rare-earth material selected from yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), scandium (Sc), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu). Furthermore, the nonmagnet  31  may include boron (B) as an element absorbed from the ferromagnet  34 . 
     The nonmagnet  32  is a conductive film of a nonmagnetic metal, and has a function of suppressing an increase of a parasitic resistance of the magnetoresistive effect element MTJ. The resistance value of the nonmagnet  32  is preferably, for example, a tenth or less of the resistance of the nonmagnet  35 , to suppress the increase of a parasitic resistance. Furthermore, the nonmagnet  31  is preferably disposed near the ferromagnet  34  so as not to reduce the effect of absorbing boron (B) from the ferromagnet  34 . Accordingly, to minimize the distance between the ferromagnet  34  and the nonmagnet  31 , the thickness of the nonmagnet  32  is preferably 2 nm (nanometers) or smaller. 
     Furthermore, the nonmagnet  32  preferably does not interfere with the function of the nonmagnet  31  absorbing boron (B) from the ferromagnet  34 . In other words, the nonmagnet  32  is preferably a material that can easily be boronized. 
     As materials that satisfy the requirements described above, the nonmagnet  32  may include at least one metal selected from, for example, tantalum (Ta), hafnium (Hf), zirconium (Zr), titanium (Ti), vanadium (V), and niobium (Nb). 
     The nonmagnet  33  is a non-magnetic insulating film, and includes, for example, magnesium oxide (MgO). The nonmagnet  33  may have a crystalline structure of a body-centered cubic (bcc) type (an NaCl crystalline structure having (001) planar orientation). In a crystallization treatment of the ferromagnet  34  adjacent to the nonmagnet  33 , the nonmagnet  33  functions as a seed material to be a nucleus for developing a crystalline film from the interface with the ferromagnet  34 . 
     A lattice spacing in the nonmagnet  33  is smaller than that in an oxide of a rare-earth element, for example. Therefore, the nonmagnet  33  does not prevent an element having a relatively small covalent radius (for example, boron (B) in the ferromagnet  34 ) from diffusing into the nonmagnet  31  from the ferromagnet  34 . On the other hand, the nonmagnet  33  has a function of preventing an element having a relatively large covalent radius (for example, iron (Fe) in the ferromagnet  34 ) from diffusing. 
     To suppress an increase of a parasitic resistance and minimize the distance between the nonmagnet  31  and the ferromagnet  34 , the nonmagnet  33  is preferably thinner than, for example, the nonmagnet  35 , more specifically, 1 nm (nanometer) or thinner. 
     The ferromagnet  34  has ferromagnetic properties, and has an axis of easy magnetization in a direction perpendicular to a film surface. The ferromagnet  34  has a magnetization direction oriented toward the bit line BL side or the word line WL side. The ferromagnet  34  includes at least one of iron (Fe), cobalt (Co), and nickel (Ni). The ferromagnet  34  may further include at least one of boron (B), phosphorus (P), carbon (C), aluminum (Al), silicon (Si), tantalum (Ta), molybdenum (Mo), chromium hafnium (Hf), tungsten (W), and titanium (Ti). More specifically, the ferromagnet  34  includes, for example, cobalt-iron-boron (CoFeB) or iron boride (FeB), and may have a crystalline structure of a body-centered cubic (bcc) type. 
     The nonmagnet  35  is a non-magnetic insulating film, and includes, for example, magnesium oxide (MgO). The nonmagnet  35  may have a crystalline structure of a body-centered cubic (bcc) type (an NaCl crystalline structure having (001) planar orientation). In a crystallization treatment of the ferromagnet  34  adjacent to the nonmagnet  35 , as well as the nonmagnet  33 , the nonmagnet  35  functions as a seed material to be a nucleus for developing a crystalline film from the interface with the ferromagnet  34 . The nonmagnet  35  is arranged between the ferromagnet  34  and the ferromagnet  36 , and constitutes a magnetic tunnel junction together with the two ferromagnets. 
     The ferromagnet  36  has ferromagnetic properties, and has an axis of easy magnetization in a direction perpendicular to a film surface. The ferromagnet  36  has a magnetization direction oriented toward the bit line BL side or the word line WL side. The ferromagnet  36  includes at least one of iron (Fe), cobalt (Co), and nickel (Ni), for example. The ferromagnet  36  may further include at least one of boron (B), phosphorus (P), carbon (C), aluminum (Al), silicon (Si), tantalum (Ta), molybdenum (Mo), chromium (Cr), hafnium (Hf), tungsten (W), and titanium (Ti). The ferromagnet  36  includes, for example, cobalt-iron-boron (CoFeB) or iron boride (FeB), and may have a crystalline structure of a body-centered cubic (bcc) type. The magnetization direction of the ferromagnet  36  is fixed, and in the example of  FIG. 5 , the magnetization direction is oriented to the ferromagnet  38 . In this description, “a magnetization direction is fixed” means that the magnetization direction is not changed by an electric current (spin torque) of such a magnitude that the magnetization direction of the ferromagnet  34  can be reversed. 
     Although the illustration is omitted in  FIG. 5 , the ferromagnet  36  may be a multi-layered body including multiple films. Specifically, the multi-layered body that constitutes the ferromagnet  36  may have a structure in which an additional ferromagnet is stacked on a surface of the ferromagnet  38  side of an interface layer containing cobalt-iron-boron (CoFeB) or iron boride (FeB), with a non-magnetic conductor being interposed between the ferromagnet  38  and the additional ferromagnet. The non-magnetic conductor in the multi-layered body constituting the ferromagnet  36  may include at least one metal selected from, for example, tantalum (Ta), hafnium (Hf), tungsten (W), zirconium (Zr), molybdenum (Mo), niobium (Nb), and titanium (Ti). The additional ferromagnet in the multi-layered body constituting the ferromagnet  36  may include at least one structure selected from, for example, a multi-layered film made of cobalt (Co) and platinum (Pt) (i.e., Co/Pt multi-layered film), a multi-layered film made of Co and nickel (Ni) (i.e., Co/Ni multi-layered film), and a multi-layered film made of Co and palladium (Pd) (i.e., Co/Pd multi-layered film). 
     The nonmagnet  37  is a non-magnetic conductive film, and includes at least one element selected from, for example, ruthenium (Ru), osmium (Os), iridium (Ir), vanadium (V), and chromium (Cr). 
     The ferromagnet  38  has ferromagnetic properties, and has an axis of easy magnetization in a direction perpendicular to a film surface. The ferromagnet  38  includes at least one alloy selected from, for example, cobalt platinum (CoPt), cobalt nickel (Coni), and cobalt palladium (Coed). The ferromagnet  38  may be a multi-layered body including multiple layers, similarly to the ferromagnet  36 . In this case, the ferromagnet  38  may include at least one structure selected from, for example, a multi-layered film made of cobalt (Co) and platinum (Pt) (i.e., Co/Pt multi-layered film), a multi-layered film made of Co and nickel (Ni) (i.e., Co/Ni multi-layered film), and a multi-layered film made of Co and palladium (Pd) (i.e., Co/Pd multi-layered film). 
     The ferromagnet  38  has a magnetization direction oriented toward the bit line BL side or the word line WL side. The magnetization direction of the ferromagnet  38  is fixed, as well as the ferromagnet  36 , and in the example of  FIG. 5 , the magnetization direction is oriented to the ferromagnet  36 . 
     The ferromagnets  36  and  38  are coupled in an anti-ferromagnetic manner by the nonmagnet  37 . In other words, the ferromagnets  36  and  38  are coupled in a manner in which they have magnetization directions mutually-antiparallel. For this reason, in the example illustrated in  FIG. 5 , the magnetization directions of the ferromagnets  36  and  38  are opposite to each other. Such a bonding structure of the above-described ferromagnet  36 , nonmagnet  37 , and ferromagnet  38  is called a synthetic anti-ferromagnetic (SAF) structure. It is thereby possible for the ferromagnet  38  to cancel an influence of the stray field of the ferromagnet  36  upon the magnetization direction of the ferromagnet  34 . For this reason, it is possible to suppress an occurrence of asymmetry in the susceptibility to magnetization reversal of the ferromagnet  34  (in other words, difference in the susceptibility to reversal of a magnetization direction of the ferromagnet  34  between the reversal in a certain direction and the reversal in the opposite direction) caused by external factors due to stray field, etc. of the ferromagnetic material  36 . 
     The nonmagnet  39  is a nonmagnetic conductive film, and has a function of improving the electrical connectivity with respect to a bit line BL or a word line WL. The nonmagnet  39  includes, for example, a high-melting point metal. The high-melting-point metal refers to a material having a melting point higher than that of iron (Fe) and cobalt (Co); for example, at least one selected from zirconium (Zr), hafnium (Hf), tungsten (W), chromium (Cr), molybdenum (Mo), niobium (Nb), titanium (Ti), tantalum (Ta), vanadium (V), ruthenium (Ru), and platinum (Pt). 
     In the first embodiment, a spin injection write method is adopted, and the method includes supplying a write current directly to such a magnetoresistive effect element MTJ, injecting spin torque into the storage layer SL and the reference layer RL by this write current, and controlling the magnetization direction of the storage layer SL and the magnetization direction of the reference layer RL. The magnetoresistive effect element MTJ can take one of a low-resistance state and a high-resistance state, depending on whether the magnetization directions of the storage layer SL and the reference layer RL are parallel or antiparallel. 
     If a write current Iw 0  of a certain amplitude is supplied to the magnetoresistive effect element MTJ in the direction indicated by arrow A 1  in  FIG. 5 , i.e., from the storage layer SL to the reference layer RL, the relationship between the magnetization directions of the storage layer SL and the reference layer RL becomes parallel. In this parallel state, the resistance value of the magnetoresistive effect element MTJ is the lowest, and the magnetoresistive effect element MTJ is set to a low-resistance state. This low-resistance state is called a “P (parallel) state”, and is defined as a data “0” state. 
     If a write current Iw 1  larger than the write current Iw 0  is supplied to the magnetoresistive effect element MTJ in the direction indicated by arrow A 2  in  FIG. 5 , i.e., from the reference layer RL to the storage layer SL (the direction opposite to arrow A 1 ), the relationship between the magnetization directions of the storage layer SL and the reference layer RL becomes antiparallel. In this antiparallel state, the resistance value of the magnetoresistive effect element MTJ is the greatest, and the magnetoresistive element MTJ is set to a high-resistance state. This high-resistance state is called “AP (anti-parallel) state”, and is defined as a data “1” state. 
     The following description is given pursuant to the above-described data-defining method; however, how data “1” and data “0” are defined is not limited to the above-described example. For example, the P state may be defined as data “1”, and the AP state may be defined as data “0”. 
     1.2 Method for Manufacturing Magnetoresistive Effect Element 
     Next, a method for manufacturing the magnetoresistive effect element of the magnetic memory device according to the first embodiment is described. In the following description, a method for manufacturing the ferromagnet  34  (the storage layer SL) among the structural elements in the magnetoresistive effect element MTJ is specifically described, and a description of the other structural elements (the reference layer RL, the shift cancelling layer SGL, etc.) are omitted. 
       FIG. 6  and  FIG. 7  are schematic views illustrating the method for manufacturing the magnetoresistive effect element of the magnetic memory device according to the first embodiment.  FIG. 6  and  FIG. 7  show a process in which the ferromagnet  34  is changed from an amorphous state to a crystal state by an annealing treatment. The ferromagnet  36 , the nonmagnet  37 , the ferromagnet  38 , and the nonmagnet  39 , which are stacked under the nonmagnet  35 , are not shown for simplicity. 
     As shown in  FIG. 6 , the nonmagnet  35 , the ferromagnet  34 , the nonmagnet  33 , the nonmagnet  32 , and the nonmagnet  31  are stacked in this order from the semiconductor substrate  20 . 
     The nonmagnets  35  and  33  have the NaCl crystalline structure having a (001) planar orientation. Accordingly, in the nonmagnets  35  and  33 , magnesium (Mg) and oxygen (O) are alternately arrayed at the interfaces with the ferromagnet  34 . 
     The ferromagnet  34  is stacked as an amorphous layer including, for example, iron (Fe) and boron (B). 
     Next, as shown in  FIG. 7 , the annealing treatment is performed on each layer stacked as shown in  FIG. 6 . Specifically, the ferromagnet  34  is transformed from amorphous to crystalline by applying heat to each layer from outside. Here, the nonmagnets  35  and  33  function to control the orientation of the crystalline structure of the ferromagnet  34 . In other words, the ferromagnet  34  develops its crystalline structure by using the nonmagnets  35  and  33  as a seed material (a crystallization treatment). Since a mismatch in lattice spacing between iron (Fe) in the ferromagnet  34  and magnesium oxide (MgO) is small, the crystalline structure of ferromagnet  34  is oriented in the same crystal plane as the nonmagnets  35  and  33 . As a result, the crystalline orientation of the ferromagnet  34  can be improved and a greater tunnel magnetoresistive ratio (TMR) can be obtained. 
     Furthermore, at the interfaces between the ferromagnet  34  and each of the nonmagnets  35  and  33 , iron (Fe) in the ferromagnet  34  and oxygen (O) in the nonmagnets  35  and  33  are bonded to form an sp hybrid orbital. As a result, the ferromagnet  34  can develop a magnetic anisotropy in the vertical direction from both interfaces. 
     In the annealing treatment, the nonmagnet  31  absorbs boron (B) from the ferromagnet  34 . This promotes crystallization of the ferromagnet  34 . As described above, the thickness of the nonmagnet  32  is set to 2 nm (nanometers) or less, and the thickness of the nonmagnet  33  is set to 1 nm (nanometer) or less. Thus, the distance between the nonmagnet  31  and the ferromagnet  34  can be small, so that the nonmagnet  31  can absorb boron (B) from the ferromagnet  34 . This contributes to the promotion of the crystallization of the ferromagnet  34 . 
     Furthermore, a material that can be easily boronized is selected as the nonmagnet  32 . Therefore, the nonmagnet  32  can also promote the absorption of boron (B) from the ferromagnet  34  together with the nonmagnet  31 . 
     Thus, the manufacturing of the magnetoresistive effect element MTJ is ended. 
     1.3 Advantages of Present Embodiment 
     According to the first embodiment, the magnetoresistive effect element can improve the perpendicular magnetic anisotropy, while suppressing an increase of the parasitic resistance. This advantage is described below. 
     In the magnetoresistive effect element MTJ of the first embodiment, the nonmagnet  35 , the ferromagnet  34 , the nonmagnet  33 , the nonmagnet  32 , and the nonmagnet  31  are stacked in this order above the semiconductor substrate  20 . The nonmagnet  31  includes a rare-earth oxide. Accordingly, boron (B) included in the ferromagnet  34  is absorbed by the nonmagnet  31  during the annealing treatment. As a result, high-quality crystallization of the ferromagnet  34  can be achieved. 
     Also, the nonmagnets  33  and  35  include magnesium oxide (MgO). Therefore, in the ferromagnet  34 , the crystalline structure can grow from both the interface with the nonmagnet  33  and the interface with the nonmagnet  35 . Therefore, iron (Fe)-oxygen (O) bonds, which improve the magnetic anisotropy, can be generated at both interfaces. 
       FIG. 8  is a schematic view illustrating effects according to the first embodiment. In  FIG. 8 , the horizontal axis represents the magnitude of magnetization (Ms×t) and the vertical axis represents the magnitude of an anisotropy field (Hk), based on which the magnitude of perpendicular magnetic anisotropy of a ferromagnet is indicated. Ms and t respectively represent a saturated magnetization and a film thickness of a subject ferromagnet. The magnitude of magnetization (Ms×t) is a product of the saturated magnetization and the film thickness. The perpendicular magnetic anisotropy is correlated to a product of a magnetization and an anisotropy field. Therefore, in the example shown in  FIG. 8 , as the line is nearer to an upper right corner, this represents greater perpendicular magnetic anisotropy. 
       FIG. 8  shows a line L 1  representing the magnitude of the perpendicular magnetic anisotropy of a ferromagnet of a comparative example, and a line L 2  representing the magnitude of the perpendicular magnetic anisotropy of the ferromagnet  34  according to the first embodiment. In the comparative example, a nonmagnet which includes magnesium oxide (MgO) is disposed on only one of the upper and lower surfaces of the ferromagnet. As shown in  FIG. 8 , the ferromagnet  34  of the first embodiment has greater perpendicular magnetic anisotropy than the ferromagnet of the comparative example. This is because the iron (Fe)-oxygen (O) bonds occur at only one of the upper and lower surfaces of the ferromagnet of the comparative example, whereas the bonds occur at both the upper and lower surfaces of the ferromagnet  34  of the first embodiment. Thus, the ferromagnet  34  of the first embodiment can provide perpendicular magnetic anisotropy theoretically about twice as high as the ferromagnet of the comparative example. 
     The thicknesses of the nonmagnets  32  and  33  are set smaller than 2 nm (nanometers) and 1 nm (nanometer), respectively. Accordingly, the distance between the nonmagnet  31  and the ferromagnet  34  can be small. Thus, high perpendicular magnetic anisotropy is obtained, while the effect of absorbing boron (B) from the ferromagnet  34  during the annealing treatment is also obtained. 
     Furthermore, a material that can be easily boronized is selected as the nonmagnet  32 . Therefore, reduction of the effect of absorbing boron (B) is suppressed though the nonmagnet  32  is interposed between the nonmagnet  31  and the ferromagnet  34 . 
     Moreover, a material having a resistance value of a tenth or less of the resistance of the nonmagnet  35  is selected as the nonmagnet  32 . Therefore, it is possible to suppress the increase of the parasitic resistance due to stacking of the nonmagnet  33  which includes magnesium oxide (MgO) with a relatively high resistance value. As a result, the increase of the resistance value of the magnetoresistive effect element MTJ can be suppressed, and accordingly, the increase of the write current Iw 0  and Iw 1  can be suppressed. Therefore, the magnetoresistive effect element MTJ can be easily applied to a magnetic memory device. 
     Further, the ferromagnet  34  is disposed above the ferromagnet  36 . The nonmagnet  33  is disposed under the nonmagnet  32 . Therefore, the magnetoresistive effect element MTJ is formed to have a structure in which the nonmagnet  33  is stacked on the upper surface of the ferromagnet  34 , and so that the nonmagnet  33  has a bcc crystal structure. 
     If the ferromagnet  34  is disposed under the ferromagnet  36 , the nonmagnet  33  is disposed above the nonmagnet  32 . More specifically, the nonmagnet  33  is disposed on the upper surface of the nonmagnet  32 . In this case, since the nonmagnet  32  does not contain boron (B) at the start of film forming, it can prevent the nonmagnet  33  from having a bcc crystal structure. Thus, it is preferable that the nonmagnet  33  be disposed under the nonmagnet  32 . According to the first embodiment, since the magnetoresistive effect element MTJ has a top free structure, the nonmagnet  33  is disposed under the nonmagnet  32 , so that the nonmagnet  33  may function as a seed material. 
     2. Modification Etc. 
     The first embodiment is not limited to the above-mentioned example, and can be modified in various ways. In the following, modifications applicable to the first embodiment is described. For convenience of explanation, differences from the first embodiment is mainly explained. 
     In the memory cell MC of the first embodiment described above, a two-terminal type switching element is applied as the switching element SEL. However, a metal oxide semiconductor (MOS) may be applied as the switching element SEL. Thus, the memory cell array is not limited to the structure having a plurality of memory cells MC at different heights in the Z direction, but may be of any array structure. 
       FIG. 9  is a circuit diagram illustrating a configuration of a memory cell array of a magnetic memory device according to a modification.  FIG. 9  shows a structure corresponding to the memory cell array  10  of the magnetic memory device  1  of the first embodiment shown in  FIG. 1 . 
     The memory cell array  10 A shown in  FIG. 9  includes a plurality of memory cells MC, each associated with a row and a column. The memory cells MC arranged in the same row are coupled to the same word line WL, and both ends of each of the memory cells MC arranged in the same column are coupled to the same bit line BL and the same source line /BL. 
       FIG. 10  is a cross-sectional view illustrating a configuration of a memory cell of a magnetic memory device according to a modification.  FIG. 10  shows a structure corresponding to the memory cell MC of the first embodiment shown in  FIG. 3  and  FIG. 4 . Since the memory cell MC of the example shown in  FIG. 10  is not stacked on a semiconductor substrate, additional symbols, such as “u” and “d”, are not used. 
     As shown in  FIG. 10 , the memory cell MC is provided on the semiconductor substrate  40  and includes a select transistor  41  (Tr) and a magnetoresistive effect element  42  (MTJ). The select transistor  41  is provided as a switch for controlling supply and stopping of a current at the time of data write to and data read from the magnetoresistive effect element  42 . The configuration of the magnetoresistive effect element  42  is the same as that of the magnetoresistive effect element MTJ of the first embodiment shown in  FIG. 5 . 
     The select transistor  41  includes a gate (conductor  43 ) that serves as a word line WL, and a pair of source and drain regions (diffusion regions  44 ) provided on both sides of the gate in the x direction in a surface portion of the semiconductor substrate  40 . The conductor  43  is provided on an insulator  45  that functions as a gate insulation film provided on the semiconductor substrate  40 . The conductor  43  extends, for example, in the y direction, and is commonly coupled to a gate of a select transistor (not shown) of another memory cell MC arranged alongside in the y direction. The conductors  43  are arranged side by side, for example, in the x direction. A contact plug  46  is provided on the source region  44  at a first end of the select transistor  41 . The contact plug  46  is coupled to a lower surface (first end) of the magnetoresistive effect element  42 . A contact plug  47  is provided on an upper surface (second end) of the magnetoresistive effect element  42 , and an upper surface of the contact plug  47  is coupled to a conductor  48  that functions as a bit line BL. The conductor  48  extends, for example, in the x direction, and is commonly coupled to the second end of the magnetoresistive effect element (not shown) of another memory cell arranged alongside in the x direction. A contact plug  49  is provided on the source region  44  at a second end of the select transistor  41 . The contact plug  49  is coupled to a lower surface of a conductor  50  that functions as the source line /BL. The conductor  50  extends, for example, in the x direction, and is commonly coupled to the second end of the select transistor (not shown) of another memory cell arranged alongside in the x direction. The conductors  48  and  50  are arranged, for example, in the y direction. The conductor  48  is, for example, located above the conductor  50 . The conductors  48  and  50  are arranged to avoid physical and electric interference with each other, although this is not specifically shown in  FIG. 10 . The select transistor  41 , the magnetoresistive effect element  42 , the conductors  43 ,  48 , and  50 , and the contact plugs  46 ,  47 , and  49  are covered with an interlayer insulation film  51 . The other magnetoresistive effect elements  42  (not shown) arranged along the x direction or the y direction relative to the magnetoresistive effect element are, for example, provided on the same level. That is, in the memory cell array  10 A, a plurality of magnetoresistive effect elements  42  are arranged, for example, in the XY plane. 
     With the configuration described above, in the case of applying a MOS transistor, which is a three-terminal type switching element, as the switching element SEL, instead of the two-terminal type switching element, the same advantages as those of the first embodiment can be attained. 
     In the memory cell MC of the embodiment and modification described above, the magnetoresistive effect element MTJ is provided under the switching element SEL. However, the magnetoresistive effect element MTJ may be provided above the switching element SEL. 
     Furthermore, in the above first embodiment and the modifications, the magnetic memory device that includes the MTJ element is described as an example of a magnetic device that includes a magnetoresistive effect element; however, the configuration is not limited thereto. For example, the magnetic device may include another device that requires a magnetic element having a perpendicular magnetic anisotropy, such as a sensor and a medium. The magnetic element is, for example, an element that includes at least the nonmagnet  31 , the nonmagnet  32 , the nonmagnet  33 , the ferromagnet  34 , and the nonmagnet  35  shown in  FIG. 5 . 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions/present disclosure. Indeed, the embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit.