Abstract:
A plurality of magnetic memories with respective ring-shaped magnetic layers therein are prepared. The magnetic layers have respective notches formed by partially cutting out the peripheries thereof in circular arc shape. The magnetic memories are arranged in plane so that the surfaces of the notches are parallel to one another.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    This invention relates to a nonvolatile magnetic memory array which is preferably usable as a magnetic random access memory (MRAM). Also, this invention relates to a method for recording in the nonvolatile magnetic memory array and a method for reading out from the nonvolatile magnetic memory array.  
           [0003]    2. Description of the Prior Art  
           [0004]    Various electronic devices have been employed under a specific condition such as an aero-space, and thus, it is desired to establish a recording device where once stored information can not be deleted by the irradiation of a radioactive ray. In this point of view, large radioactive-resistance and nonvolatile MRAMs having their respective simply structured magnetic memory cells are researched and developed.  
           [0005]    Conventionally, such a magnetic memory cell is shaped rectangular, and information “0” or “1” is stored on the magnetic direction of the magnetic memory cell. With the conventional magnetic memory cell, however, the magnetic flux originated from the magnetization is leaked outside from the magnetic memory cell due to the configuration thereof. In order to increase the recording capacity of the MRAM, in contrast, such an attempt is made as to arrange a plurality of magnetic memory cells in high density. In this case, however, the leaked magnetic flux affects significantly on the adjacent magnetic memory cells, and thus, the intended high density MRAM can not be realized.  
           [0006]    In this point of view, the inventors have developed a ring-shaped magnetic memory where a right handed (clockwise) magnetization or a left-handed (anticlockwise) magnetization is created in vortex, and information “0” or “1” is stored on the rotative direction of the magnetization thereof (Japanese Patent application 2002-73681).  
           [0007]    In this case, since a magnetic flux is not leaked from the magnetic memory, if a plurality of magnetic memories are arranged in high density as mentioned above, the leaked magnetic flux can not almost affect on the adjacent magnetic memories, so that a high density MRAM can be realized.  
           [0008]    As the thickness of the magnetic layer of the magnetic memory to store information is decreased, however, the vortex magnetization can not be created and thus, it may be that information recording utilizing the vortex magnetization can not be realized ([Physical Review Letters, 83, No. 5, pp1042-1045 (1999)].  
         SUMMERY OF THE INVENTION  
         [0009]    It is an object of the present invention to provide a magnetic memory array which can create a vortex magnetization, irrespective of the thickness of the magnetic layer of the magnetic memory composing the magnetic memory array. It is another object of the present invention to provide a recording method and a reading method for the magnetic memory array.  
           [0010]    In order to achieve the above-mentioned objects, this invention relates to a magnetic memory array comprising a plurality of magnetic memories with respective ring-shaped magnetic layers therein,  
           [0011]    the magnetic layers having respective notches formed by partially cutting out peripheries thereof in circular arc shape,  
           [0012]    the magnetic memories being arranged in plane so that surfaces of the notches are parallel to one another.  
           [0013]    The inventors found out through vast researches and developments that if the periphery of the ring-shaped magnetic layer composing the magnetic memory is partially cut so that the resultant cross sectional surface is perpendicular to the radial direction of the magnetic memory, the clockwise magnetization and the anticlockwise magnetization can be easily created in vortex even though the thickness of the magnetic layer is small. Then, if such a plurality of magnetic memories are arranged so that the cut lines of the notches of the magnetic layers are almost parallel to one another, to form a magnetic memory array, the recording operation for the magnetic memory array can be performed by applying a uniform external magnetic field. As a result, the magnetic memory array can be utilized as a high density recording medium.  
           [0014]    According to the present invention, therefore, even though the thickness of the magnetic layer of each magnetic layer composing the magnetic memory array is reduced within 1-10 nm, the vortex magnetization can be easily created in the magnetic layer, and information “0” or “1” can be recorded in the magnetic layer on the rotative direction of the vortex magnetization.  
           [0015]    In the present invention, since a magnetic flux is not leaked from the magnetic layer due to the vortex magnetization, even though a plurality of magnetic memories having their respective magnetic layers are arranged in high density to form the magnetic memory array, no leaked magnetic flux affects on the adjacent magnetic memories.  
           [0016]    Other features and advantages of the magnetic memory array of the present invention will be described below. Also, a recording method and a reading method for the magnetic memory array will be described below. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]    For better understanding of the present invention, reference is made to the attached drawings, wherein  
         [0018]    [0018]FIG. 1 is a plan view schematically showing the configuration of a magnetic layer of a magnetic memory composing a magnetic memory array according to the present invention,  
         [0019]    FIGS.  2 ( a )-( c ) are plan views showing the magnetization states of the magnetic layer shown in FIG. 1,  
         [0020]    [0020]FIG. 3 is a plan view showing a concrete embodiment of the magnetic memory,  
         [0021]    [0021]FIG. 4 is a side view of the magnetic memory shown in FIG. 3, and  
         [0022]    [0022]FIG. 5 is a plan view showing a magnetic memory array according to the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0023]    This invention will be described in detail with reference to the accompanying drawings.  
         [0024]    [0024]FIG. 1 is a schematic view showing the configuration of a magnetic layer of a magnetic memory composing a magnetic memory array according to the present invention, and FIGS.  2 ( a )-( c ) are plan views showing the magnetization states of the magnetic layer shown in FIG. 1.  
         [0025]    As shown in FIG. 1, the magnetic layer  11  is shaped in ring, and the periphery of the magnetic layer  11  is partially cut out so that the resultant cross sectional surface is perpendicular to the radial direction of the magnetic layer  11 . As a result, a circular arc notch is formed at the periphery of the magnetic layer  11 . With the ring-shaped magnetic layer  11  having the notch  12 , even though the thickness of the magnetic layer  11  is reduced within 1-10 nm, for example, a vortex magnetization of right-handed (clockwise) direction or left-handed (anticlockwise) direction can be created in the magnetic layer  12  as shown in FIGS.  2 ( a ) and  2 ( b ).  
         [0026]    As shown in FIG. 2, therefore, if the right-handed (clockwise) magnetization is allotted to information “0” and the left-handed (anticlockwise) magnetization is allotted to information “1”, recording operation can be performed for the magnetic layer  11 .  
         [0027]    In the recording operation, the magnetization of the magnetic layer  11  is varied in FIG. 2( b ) from FIG. 2( a ) via FIG. 2( c ) or in FIG. 2( a ) from FIG. 2( b ) via FIG. 2( d ).  
         [0028]    If the height of the notch  12  is defined as “h” and the outer diameter of the ring-shaped magnetic layer  11  is defined as “H1”, the ratio (h/H1) is preferably set to 0.01 or over, particularly 0.05 or over. Therefore, if the notch  12  is formed by cutting the periphery of the magnetic layer  11  so as to satisfy the above-mentioned relation, the recording operation for the magnetic memory array of the present invention can be performed easily and precisely by a smaller external magnetic field.  
         [0029]    Although the upper limited value of the ratio (h/H1) is not restricted, it may be preferably set to 0.2. If the ratio (h/H1) is set over the upper limited value of 0.2, the effect/function of the present invention can not be enhanced, and it may be that a vortex magnetization can not be created in the magnetic layer  11  to be not able to be employed in the magnetic memory.  
         [0030]    In order to maintain the ring shape of the magnetic layer  11 , it is required to satisfy the relation of “h&lt;(H1−H2)/2 if the inner diameter of the magnetic layer  11  is defined as “H2”.  
         [0031]    The magnetic layer  11  may be made of a room temperature ferromagnetic material such as Ni—Fe, Ni—Fe—Co or Co—Fe, for example. The “room temperature ferromagnetic material” means a magnetic material showing ferromagnetic property at room temperature. Therefore, other magnetic materials may be employed, instead of the above-mentioned ferromagnetic material such as Ni—Fe or the like.  
         [0032]    The thickness of the magnetic layer  11  is preferably set within 1-10 nm, particularly within 3-5 nm. In this case, a sufficiently large vortex magnetization can be created in the magnetic layer  11 , and thus, information can be stably stored when information “0” or “1” is allotted to the rotative direction of the vortex magnetization.  
         [0033]    [0033]FIG. 3 is a plan view showing a concrete embodiment of the magnetic memory shown in FIG. 1, and FIG. 4 is a side view of the magnetic memory shown in FIG. 3. In the magnetic memory  30  shown in FIGS. 3 and 4, on a magnetic layer  21  as shown in FIG. 1 are successively formed an additional magnetic layer  23  and an antiferromagnetic layer  24  via a non-magnetic layer  22 . The magnetic layer  21  is shaped in ring, and the periphery of the magnetic layer  21  is partially cut out so as to form a notch thereat. The non-magnetic layer  22  through the antiferromagnetic layer  24  are also shaped in ring, which are concentrically for the magnetic layer  21 .  
         [0034]    In this embodiment, the peripheries of the non-magnetic layer  22  through the antiferromagnetic layer  24  are cut out to form the same notches as the one of the magnetic layer  21  thereat. The notches of the magnetic layer  21  through the antiferromagnetic layer  24  satisfy the above-mentioned relation relating to the notch of the magnetic layer  11 .  
         [0035]    The magnetic layer  21  is magnetized in right-handed (clockwise) direction or left-handed (anticlockwise) direction, and information “0” or “1” is allotted to the rotative direction of the resultant vortex magnetization. In this way, recording operation for the magnetic memory is performed.  
         [0036]    In the magnetic memory  30  shown in FIG. 3, the additional magnetic layer  23  is magnetized in right-handed (clockwise) direction or left-handed (anticlockwise) direction in advance, and the resultant vortex magnetization of the additional magnetic layer  23  is pinned through the bond with exchanging interaction to the antiferromagnetic layer  24 . The magnetic layer  21  and the additional magnetic layer  23  are magnetically divided by the non-magnetic layer  22 .  
         [0037]    The magnetic layer  21  may be made of a room temperature ferromagnetic material as mentioned above, and the thickness of the magnetic layer  21  may be set within 1-10 nm. The additional magnetic layer  23  may be made of such a room temperature ferromagnetic material as mentioned above, and the thickness of the additional magnetic layer  23  may be set within 1-10 nm.  
         [0038]    The non-magnetic layer  22  may be made of a non-magnetic material such as Cu, Ag or Au, and the antiferromagnetic layer  24  may be made of an antiferromagnetic material such as Mn—Ir, Mn—Pt or Fe—Mn. The thickness of the non-magnetic layer  22  is set so as to magnetically divide the magnetic layer  21  and the additional magnetic layer  23 . The thickness of the antiferromagnetic layer  24  is set so as to magnetically pin the magnetization of the additional magnetic layer  23  through the bond with exchanging interaction.  
         [0039]    [0039]FIG. 5 is a plan view showing a magnetic memory array according to the present invention. In the magnetic memory array shown in FIG. 5, a plurality of magnetic memories  30  shown in FIGS. 3 and 4 are arranged in 3×3 so that the surfaces of the notches  32  are directed upper left and almost parallel to one another. On the top and the bottom of the magnetic memory array are arranged top conducting wires  41 - 43  and bottom conducting wires  51 - 53  for the recording operation and the reading operation for the magnetic memory array.  
         [0040]    Although in this embodiment, the nine magnetic memories  30  are arranged, the arrangement number of the magnetic memory  30  is not restricted, but any arrangement number will do on the use of the magnetic memory array. Moreover, although in this embodiment, the magnetic memories  30  are arranged in 3×3, the arrangement configuration of the magnetic memory  30  is not restricted, but any arrangement configuration will do on the use of the magnetic memory array.  
         [0041]    In the recording operation for the magnetic memory array shown in FIG. 5, currents are flowed in the top conducting wires and the bottom conducting wires of the magnetic memory  30  to be recorded to generate a magnetic field around the magnetic memory  30 . Then, the magnetic memory  30  is recorded by the magnetic field. When the recording operation is carried out for the upper right magnetic memory  30 , a current I 1  is flowed upward in the top conducting wire  41  and a current I 2  is flowed right in the bottom conducting wire  51 . In this case, the synthetic magnetic field B from the inductive magnetic field B 1  due to the upward current I 1  and the inductive magnetic field B 2  due to the right current I 2  is generated to create a left-handed (anticlockwise) magnetization as shown in FIG. 2( b ) in the magnetic layer  21 . Therefore, the recording operation for the magnetic memory  30  can be performed by allotting information “0” or “1” to the left-handed (anticlockwise) magnetization.  
         [0042]    It is desired to direct the synthetic magnetic field B in parallel with the surface  33  of the notch  32  of the magnetic memory  30  to be recorded. In this case, the recording operation for the magnetic memory  30  can be performed easily and precisely by a smaller magnetic field. In order to satisfy this requirement, the currents I 1  and I 2  and the position of the magnetic memory  30  are controlled appropriately.  
         [0043]    When a current I 3  is flowed downward in the top conducting wire  41  and a current I 4  is flowed left in the bottom conducting wire  51 , another synthetic magnetic field Ba, which is opposite to the synthetic magnetic field B and generated from the currents I 3  and I 4 , is applied to the magnetic memory  30  to create a right-handed (anticlockwise) magnetization as shown in FIG. 2( 2 ) in the magnetic layer  21 .  
         [0044]    In this case, too, it is desired to direct the synthetic magnetic field Ba in parallel with the surface  33  of the notch  32  of the magnetic memory  30  to be recorded.  
         [0045]    The recording operation for another magnetic memory  30  can be performed in the same manner as the upper right magnetic memory  30 . For example, when the current I 1  is flowed upward in the top conducting wire  42  and the current I 2  is flowed right in the bottom conducting wire  52 , the center magnetic memory  30  is recorded by the synthetic magnetic field B generated from the currents I 1  and I 2  to create a right-handed (clockwise) magnetization as shown in FIG. 2( a ) in the magnetic layer  21 .  
         [0046]    The recording operation can be performed at every magnetic memory  30 , but can be at some magnetic memories  30 .  
         [0047]    The reading operation for the magnetic memory array shown in FIG. 5 can be performed by utilizing the change in electric resistance of the magnetic memory  30  recorded on the relative direction in magnetization between the additional magnetic layer  23  and the magnetic layer  21 . In this case, the magnetization of the additional magnetic layer  23  is pinned by the antiferromagnetic layer  24  through the bond with exchange interaction. For example, when the magnetization of the magnetic layer  21  is parallel to the magnetization of the additional magnetic layer  23 , the electric resistance of the magnetic memory  30  is decreased. When the magnetization of the magnetic layer  21  is anti-parallel to the magnetization of the additional magnetic layer  23 , the electric resistance of the magnetic memory  30  is increased.  
         [0048]    Therefore, since the current of the magnetic memory  30  is varied on the change in electric resistance due to the relative direction in magnetization, as mentioned above, if the direction of the magnetization of the additional magnetic layer  23  is fixed, the direction of the magnetization of the magnetic layer  21  can be known, so that information “0” or “1” allotted to the direction of the magnetization of the magnetic layer  21  can be read out.  
         [0049]    With the magnetic memory array shown in FIG. 5, the information “0” or “1” recorded in the magnetic memory  30  can be read out by applying voltages to the corresponding top conducting wire and the corresponding bottom conducting wire and measuring the current from the magnetic memory  30 . For example, when the reading operation is carried out for the upper right magnetic memory  30 , voltages are applied to the top conducing wire  41  and the bottom conducting wire  51  to measure a current from the magnetic memory  30  through the conducting wires  41  and  51 .  
         [0050]    Although the present invention was described in detail with reference to the above examples, this invention is not limited to the above disclosure and every kind of variation and modification may be made without departing from the scope of the present invention.  
         [0051]    As mentioned above, according to the present invention can be provided a magnetic memory array which can create a vortex magnetization, irrespective of the thickness of the magnetic layer of the magnetic memory composing the magnetic memory array. In addition, according to the present invention can be provided the recording method and the reading method for the magnetic memory array.