Abstract:
A memory device includes: a memory including a first magnetic layer having no retaining force and a second magnetic layer having a retaining force, the first magnetic layer and the second magnetic layer being stacked; a first magnet to magnetize the first magnetic layer in a first direction; and a second magnet to apply a magnetic field to a region through which the memory passes when the memory is removed and to magnetize the second magnetic layer in a second direction.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2011-229919, filed on Oct. 19, 2011, the entire contents of which are incorporated herein by reference. 
     FIELD 
     The embodiments discussed herein are related to a memory device and an electronic apparatus. 
     BACKGROUND 
     Magnetic memory devices that include magnetoresistive random access memory (MRAM) have a function as a non-volatile memory, and have high-speed access performance (for example, about 35 ns) that is equivalent to that of static random access memory (SRAM). 
     Memory cells of the magnetic memory devices store information using magnetic moment, and therefore allow data storage and highly reliable rewriting cycles under high-temperature circumstances. 
     Related technologies are disclosed in Japanese National Publication of International Patent Application No. 2006-511892 and International Publication Pamphlet No. WO 08/062686. 
     SUMMARY 
     According to an aspect of the invention, a memory device includes: a memory including a first magnetic layer having no retaining force and a second magnetic layer having a retaining force, the first magnetic layer and the second magnetic layer being stacked; a first magnet to magnetize the first magnetic layer in a first direction; and a second magnet to apply a magnetic field to a region through which the memory passes when the memory is removed and to magnetize the second magnetic layer in a second direction. 
     The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, as claimed. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  illustrates an exemplary magnetic memory device; 
         FIGS. 2A and 2B  illustrate an exemplary MRAM main body; 
         FIG. 3  illustrates an exemplary MRAM element; 
         FIG. 4  illustrates an exemplary magnetic memory device; 
         FIG. 5  illustrates an exemplary magnetic memory device; 
         FIG. 6  illustrates an exemplary magnetic memory device; 
         FIG. 7  illustrates an exemplary magnetic memory device; 
         FIG. 8  illustrates an exemplary magnetic memory device; 
         FIG. 9  illustrates an exemplary magnetic memory device; 
         FIG. 10  illustrates an exemplary magnetic memory device; 
         FIG. 11  illustrates an exemplary magnetic memory device; 
         FIG. 12  illustrates an exemplary magnetic memory device; 
         FIGS. 13A and 13B  illustrate an exemplary magnetic memory device; 
         FIG. 14  illustrates an exemplary magnetic memory device; 
         FIG. 15  illustrates an exemplary magnetic memory device; 
         FIGS. 16A and 16B  illustrate an exemplary magnetic memory device; 
         FIGS. 17A and 17B  illustrate an exemplary magnetic memory device; and 
         FIGS. 18A and 18B  illustrate an exemplary magnetic memory device. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Magnetic memory devices such as MRAM may be used in place of SRAM or battery-driven dynamic random access memory (DRAM). 
     Data in a magnetic memory device that has been removed from a personal computer or the like may be illegally read out or altered. 
       FIG. 1  illustrates an exemplary magnetic memory device (MRAM).  FIG. 1  illustrates a side view of the magnetic memory device (MRAM) in use. 
     In  FIG. 1 , reference numeral  1  denotes an MRAM main body (magnetic memory main body),  2   a  and  2   b  each denote a magnetic composite body (a magnetic field generating unit),  3  denotes a connector, and  4  denotes a substrate (for example, a motherboard of a target apparatus). 
     Reference numeral  11  denotes an MRAM element,  21   a  and  21   b  each denote a first anisotropic magnet (first magnetic field generating magnet) that generates a first magnetic field M 1 ,  22   a  and  22   b  each denote a shielding material, and  23   a  and  23   b  each denote a second anisotropic magnet (second magnetic field generating magnet) that generates a second magnetic field M 2 . 
     In the MRAM illustrated in  FIG. 1 , the MRAM main body  1  that includes a plurality of MRAM elements  11  may be independent. For example, the MRAM main body  1  may be coupled through the connector  3  to the substrate  4  of a personal computer or the like so as to be easily removable. 
     The MRAM main body  1  is electrically coupled to wiring of the substrate  4  via a plurality of metal terminals (connection pins)  101  included in the MRAM main body  1  and the connector  3 . 
     Two magnetic composite bodies  2   a  and  2   b  are fixed to the substrate  4  on both sides of the MRAM main body  1 . The magnetic composite bodies  2   a  and  2   b  may be firmly secured to the substrate  4  using an adhesive or the like, for example. The magnetic composite bodies  2   a  and  2   b  may be attached to the substrate  4  so as not to be removable together with the MRAM main body  1 . 
     In one of the magnetic composite bodies,  2   a , the second anisotropic magnet  23   a  is provided above the first anisotropic magnet  21   a  via the shielding material  22   a . In the other magnetic composite body  2   b , the second anisotropic magnet  23   b  is provided above the first anisotropic magnet  21   b  via the shielding material  22   b.    
     Although both the direction of the first magnetic field M 1  based on the first anisotropic magnets  21   a  and  21   b  and the direction of the second magnetic field M 2  based on the second anisotropic magnets  23   a  and  23   b  are indicated as from the left to the right in  FIG. 1 , the directions of the magnetic fields may be opposite to each other. For example, the first magnetic field M 1  may be directed from the right to the left. 
     The shielding materials  22   a  and  22   b  may be disposed so that the first anisotropic magnets  21   a  and  21   b  and the second anisotropic magnets  23   a  and  23   b  do not affect each other in the magnetic composite bodies  2   a  and  2   b.    
     The first magnetic field M 1  based on the first anisotropic magnets  21   a  and  21   b  may be disposed so as to have an intensity that is sufficient for lower magnetic layers (first magnetic layers) of the MRAM elements  11  to function as MRAM and that does not affect magnetization reversal of upper free layers (second magnetic layers) of the MRAM elements  11 . The first magnetic field M 1  may be configured to have an appropriate intensity based on the distance between the first anisotropic magnets  21   a  and  21   b , for example. 
     The second magnetic field M 2  based on the second anisotropic magnets  23   a  and  23   b  may be disposed so as to have an intensity that forcedly reverses the direction of magnetization of the upper free layers ( 113 ) of the MRAM elements  11  when the MRAM main body  1  is removed and that does not affect the MRAM elements  11  in a normal state of use. The second magnetic field M 2  is configured to have an appropriate intensity based on the distance between the second anisotropic magnets  23   a  and  23   b , for example. 
     The first anisotropic magnets  21   a  and  21   b  and the second anisotropic magnets  23   a  and  23   b  of the magnetic composite bodies  2   a  and  2   b  may be something other than anisotropic magnets. When magnets with no directional properties are used, for example, the gap between the magnets  21   a  and  21   b  and between the magnets  23   a  and  23   b  may be set to be wide, for example, by changing the material of or adjusting the thickness of the shielding materials  22   a  and  22   b.    
       FIGS. 2A and 2B  illustrate an exemplary MRAM main body. The MRAM main body illustrated in  FIGS. 2A and 2B  may be disposed in the magnetic memory device illustrated in  FIG. 1 .  FIG. 2A  illustrates the MRAM main body  1 .  FIG. 2B  illustrates the MRAM elements  11  ( 11   a ,  11   b ). 
     The upper free layers (second magnetic layers)  113  correspond to a magnetic material (ferromagnetic material) that has a retaining force, and retain magnetization in the spin direction that corresponds to data to be written. The lower magnetic layers (first magnetic layers)  111  correspond to a magnetic material (ferromagnetic material) that has no retaining force, and are magnetized by an external magnetic force. When the magnetic force is lost, the lower magnetic layers  111  are demagnetized. 
     As illustrated in  FIG. 2A , for data to be written into each of the MRAM elements  11 , the spin direction of the upper free layers  113  ( 113   a ,  113   b ) is decided based on the direction of a writing current flowing through word lines WL, for example. Insulating layers  112  ( 112   a ,  112   b ) are provided between the upper free layers  113  ( 113   a ,  113   b ) and the lower magnetic layers  111  ( 111   a ,  111   b ). 
     As illustrated in  FIG. 2B , the direction of the first magnetic field M 1  that is based on the first anisotropic magnets  21   a  and  21   b  which prescribe the direction of magnetization of the lower magnetic layers  111 , may be substantially the same as (or may be substantially opposite to) the direction of magnetization of the upper free layers  113 . 
     The direction of magnetization of the MRAM elements  11  provided in the MRAM main body  1 , or the direction of a memory chip having a plurality of MRAM elements set to the direction of magnetization, may substantially coincide with the direction of the first magnetic field M 1  and the second magnetic field M 2 . 
     The MRAM element  11   a  is an element (magnetic tunnel junction (MTJ) element) with data “ 0 ” in which the spin directions of the lower magnetic layer  111   a  and the upper free layer  113   a  are substantially the same as each other. 
     The MRAM element  11   b  is an element (MTJ element) with data “ 1 ” in which the spin directions of the lower magnetic layer  111   b  and the upper free layer  113   b  are opposite to each other. A large current may flow through the MRAM element (1-MTJ element)  11   a  with data “ 0 ”. A small current may flow through the 1-MTJ element  11   b  with data “ 1 ”. 
       FIG. 3  illustrates an exemplary an MRAM element. The MRAM element illustrated in  FIG. 3  may be included in the MRAM main body  1  illustrated in  FIGS. 2A and 2B , and includes a transistor  12  for read out. The MRAM element  11 , which is provided at the intersection of the word line WL and a bit line BL, reads out data based on the magnitude of a current in the spin direction of the upper free layer  113 . 
     The transistor  12  is turned on based on a signal from the word line WL. A difference in magnitude of a current based on the spin directions of the lower magnetic layer  111  and the upper free layer  113  of the MRAM element  11  is detected via the bit line BL. Stored data is thus read out. 
     In  FIG. 3 , the MRAM element  11  stores data “ 1 ” where the spin directions of the lower magnetic layer  111  and the upper free layer  113  are opposite to each other and with a current flowing is small. Data “ 0 ” may be read out in substantially the same manner. The configuration of the MRAM element  11  is not limited to the configuration illustrated in  FIGS. 2A ,  2 B, and  3 . 
     The direction of magnetization of the upper free layer  113  is reversed by a magnetic field based on the writing current. The direction of magnetization may not be reversed by a magnetic force of the first anisotropic magnets  21   a  and  21   b  of the magnetic composite bodies  2   a  and  2   b.    
     The lower magnetic layer  111  may be a magnetic material having no retaining force. The direction of magnetization of the lower magnetic layer  111  is decided based on an external magnetic force from the first anisotropic magnets  21   a  and  21   b  of the magnetic composite bodies  2   a  and  2   b . When the external magnetic force is lost, the lower magnetic layer  111  is demagnetized. 
     In the MRAM element  11 , the direction of magnetization of the lower magnetic layer  111  is decided based on an external magnetic force, and the direction of magnetization of the upper free layer  113  is decided based on the magnetic field of a writing current. 
     When the spin directions of the lower magnetic layer  111  and the upper free layer  113  are substantially the same as each other, the electrical resistance of the MRAM element  11  becomes low, and data (logical value) “ 0 ” is retained. When the spin directions are opposite to each other, data “ 1 ” is retained. 
       FIGS. 4 to 6  illustrate an exemplary magnetic memory device.  FIG. 4  illustrates a state in which the MRAM main body  1  is disconnected from the connector  3 .  FIG. 5  illustrates a state in which the MRAM main body  1  is affected by the second magnetic field M 2 .  FIG. 6  illustrates a state in which the MRAM main body  1  is completely removed. 
     When the MRAM main body (magnetic memory main body)  1  is attached to the substrate  4  via the connector  3 , the magnetic memory device operates normally. When the MRAM main body  1  is disconnected from the connector  3 , data stored in the magnetic memory device may be disrupted. 
     When the MRAM main body  1  is disconnected from the connector  3  (substrate  4 ), as illustrated in  FIG. 4 , the MRAM main body  1  (MRAM elements  11 ) is displaced from the center of the first magnetic field M 1  that is based on the first anisotropic magnets  21   a  and  21   b  of the magnetic composite bodies  2   a  and  2   b.    
     The lower magnetic layers  111  ( 111   a ,  111   b ) of the MRAM elements  11  ( 11   a ,  11   b ) are no longer supplied with a sufficient magnetic field (for example, the first magnetic field M 1 ) for magnetization. Since the lower magnetic layers  111  of the MRAM elements  11  do not have a retaining force, the lower magnetic layers  111  may be affected by a magnetic field leaking from the upper free layers  113 . 
     For example, the lower magnetic layer  111   a  of the MRAM element  11   a , which stores data “ 0 ”, changes its direction from the direction ( 1 ), which is the same as the direction of the upper free layer  113   a , to the opposite direction ( 2 ). The lower magnetic layer  111   b  of the MRAM element  11   b , which stores data “ 1 ”, maintains its direction, which is opposite to the direction of the upper free layer  113   b.    
     The lower magnetic layers  111  ( 111   a ,  111   b ) of the MRAM elements  11  ( 11   a ,  11   b ) are magnetized in the direction opposite to the direction of magnetization of the upper free layers  113  ( 113   a ,  113   b ), and may lose a memory function that is for retaining data. As illustrated in  FIG. 4 , the upper free layer  113  of each MRAM element  11  retains a direction of magnetization corresponding to the stored data. 
     When the MRAM main body  1  is moved away from the substrate  4 , as illustrated in  FIG. 5 , the MRAM main body  1  (MRAM elements  11 ) may be located at the center of the second magnetic field M 2  that is based on the second anisotropic magnets  23   a  and  23   b  of the magnetic composite bodies  2   a  and  2   b.    
     Therefore, the lower magnetic layer  111   a  of the MRAM element  11   a , which stores data “ 0 ”, changes its direction from the direction ( 3 ) to the direction ( 4 ) in accordance with the second magnetic field M 2 . The upper free layer  113   b  of the MRAM element  11   b , which stores data “ 1 ”, changes its direction from the direction ( 5 ) to the direction ( 6 ) in accordance with the second magnetic field M 2 . 
     The second magnetic field M 2  based on the second anisotropic magnets  23   a  and  23   b  of the magnetic composite bodies  2   a  and  2   b  has an intensity that forcibly changes the direction of magnetization of the upper free layers  113  ( 113   a ,  113   b ) of the MRAM elements  11  ( 11   a ,  11   b ). Therefore, the upper free layers  113  are magnetized in substantially the same direction. 
     The second magnetic field M 2  forcibly magnetizes the lower magnetic layers  111  ( 111   a ,  111   b ) of the MRAM elements  11  ( 11   a ,  11   b ) in substantially the same direction. Therefore, the upper free layers  113  and the lower magnetic layers  111  of the MRAM elements  11  included in the MRAM main body  1  are magnetized in the direction of magnetization of the second magnetic field M 2 , which may disrupt data stored in the MRAM main body  1 . 
     When the MRAM main body  1  is moved away from the substrate  4 , as illustrated in  FIG. 6 , the MRAM main body  1  (MRAM elements  11 ) is displaced from the center of the second magnetic field M 2  that is based on the second anisotropic magnets  23   a  and  23   b  of the magnetic composite bodies  2   a  and  2   b.    
     The lower magnetic layers  111  ( 111   a ,  111   b ) of the MRAM elements  11  ( 11   a ,  11   b ) are no longer supplied with a sufficient magnetic field (second magnetic field M 2 ) for magnetization. Since the lower magnetic layers  111  of the MRAM elements  11  do not have a retaining force, the lower magnetic layers  111  may be affected by a magnetic field leaking from the upper free layers  113 . 
     The lower magnetic layers  111  ( 111   a ,  111   b ) of the MRAM elements  11  ( 11   a ,  11   b ) are affected by a magnetic field leaking from the upper free layers  113  ( 113   a ,  113   b ) to be magnetized out of the direction ( 7 ) into the direction ( 8 ), which is opposite to the direction of magnetization of the upper free layers  113  ( 113   a ,  113   b ). 
     The lower magnetic layers  111  of the MRAM elements  11  are magnetized into the direction opposite to the direction of magnetization of the upper free layers  113 , and data stored in the MRAM main body  1  may be disrupted (erased). The MRAM main body  1  is separated from the first anisotropic magnets  21   a  and  21   b , and therefore the function as a memory that stores data may be lost. 
     The magnetic memory device (MRAM) is used as a memory that stores data with the MRAM main body  1  inserted into the connector  3  as illustrated in  FIG. 1 , for example. After data is initialized, the magnetic memory device (MRAM) may be used as a new magnetic memory device. 
     The MRAM elements  11  built in the MRAM main body  1  may be formed as a single memory chip, or may be formed as a plurality of memory chips arranged horizontally or vertically. 
     A plurality of memory chips may be stacked on each other when the first magnetic field M 1  based on the first anisotropic magnets  21   a  and  21   b  of the magnetic composite bodies  2   a  and  2   b  magnetizes the lower magnetic layers  111  of the MRAM elements  11  during use of the MRAM. 
     With the magnetic memory device, electric power for disruption of stored data may become relatively low. Because data disruption is based on physical changes in the state of memory elements, the possibility of data read-out or decoding (alteration) after the data disruption may be reduced. 
     In the absence of an external magnetic field (first magnetic field M 1 ), the magnetic memory device does not function as a memory even if data are electrically rewritten by supplying electric power to the magnetic memory device. This reduces the possibility of data leakage that may occur when the magnetic memory device is taken out. 
     The magnetic memory main body  1  does not incorporate an external magnetic field supply source such as a magnet. Therefore, an external magnetic field supply source may be easily blocked from inappropriately removing data. The magnetic memory main body  1  is not broken by the blockage of an external magnetic field supply source. Therefore, the magnetic memory main body  1  may be reused. 
       FIG. 7  illustrates an exemplary magnetic memory device.  FIG. 7  may be a solid state drive (SSD) type magnetic memory device.  FIG. 7  is a bottom view of a laptop personal computer  5  on which an SSD-type magnetic memory device is mounted. 
       FIGS. 8 and 9  illustrate an exemplary magnetic memory device.  FIG. 8  illustrates the SSD-type magnetic memory device in use.  FIG. 9  illustrates a state in which an MRAM main body is removed from the SSD-type magnetic memory device. 
     An SSD that uses flash memory may be used in place of a hard disk drive (HDD) of the laptop personal computer  5 , for example. 
     With the SSD-type magnetic memory device, as illustrated in  FIG. 7 , an SSD unit  1  (with an MRAM main body) is removably attached to the substrate  4  that is at the bottom surface of the laptop personal computer  5 . 
     Shock absorbing materials  6   a  to  6   d  are provided at the four corners of the SSD unit  1 . A gap having a given distance is provided between the magnetic composite bodies  2   a  and  2   b  and the SSD unit  1 . The magnetic composite bodies  2   a  and  2   b  are fixed to the substrate (for example, a motherboard)  4  of the laptop personal computer  5 . Connection between the SSD unit  1  and a connector of the substrate  4  is not illustrated, and may be coupled in substantially the same manner as the attachment of the SSD. 
       FIGS. 8 and 9  may correspond to  FIGS. 1 and 5 , respectively.  FIGS. 8 and 9  illustrate mounting on the bottom surface of the laptop personal computer  5 , and therefore are inverted from  FIGS. 1 and 5  in the vertical direction. 
     As illustrated in  FIG. 8 , the SSD unit  1  is attached in tight contact with the substrate  4 . When the SSD unit  1  is attached to the substrate  4 , the first magnetic field M 1  may have an intensity that is sufficient for the lower magnetic layers of the MRAM elements  11  to function as MRAM and that does not affect magnetization reversal of the upper free layers. 
     When the SSD unit  1  is removed from the substrate  4 , for example when the SSD unit  1  is removed along with downward movement indicated by an arrow, as illustrated in  FIG. 9 , stored data may be disrupted (erased) as illustrated in  FIGS. 4 to 6 . 
     When the SSD unit  1  is removed from the substrate  4 , the second magnetic field M 2  may have an intensity that forcibly reverses the direction of magnetization of the upper free layers of the MRAM elements  11  and that does not affect the MRAM elements  11  in a normal state of use. 
     In the magnetic composite bodies  2   a  and  2   b , for example, the first anisotropic magnets  21   a  and  21   b , the shielding materials  22   a  and  22   b , and the second anisotropic magnets  23   a  and  23   b  are coated with plastic or the like, which may reduce the ease of disassembly. 
     The magnetic composite bodies  2   a  and  2   b , in which the first anisotropic magnets  21   a  and  21   b , the shielding materials  22   a  and  22   b , and the second anisotropic magnets  23   a  and  23   b  are stacked on each other, are packaged to be fixed to the substrate  4 . 
     The magnetic composite bodies  2   a  and  2   b  may be fixed to the substrate  4  using various joining techniques so as not to be easily removable from the substrate  4 . The magnetic composite bodies  2   a  and  2   b  may be fixed so as not to be removable together with the SSD unit  1 . 
     The MRAM elements  11  illustrated in  FIGS. 8 and 9  may be formed as a memory chip that includes a plurality of MRAM elements. The SSD unit  1  may be used for apparatuses such as laptop personal computers, desktop personal computers, and other electronic devices. 
       FIGS. 10 and 11  illustrate an exemplary magnetic memory device. The magnetic memory device illustrated in  FIGS. 10 and 11  may be a small outline dual in-line memory module (SO-DIMM) type magnetic memory device for use in a laptop personal computer.  FIG. 10  is a perspective view of the magnetic memory device.  FIG. 11  is a bottom view of the magnetic memory device. 
     In the SO-DIMM-type magnetic memory device illustrated in  FIGS. 10 and 11 , for example, an SO-DIMM unit (with an MRAM main body)  1  is removably attached to a memory socket  4 ′ (substrate  4 ) via the connector  3 . 
     The SO-DIMM unit  1  may be shaped in substantially the same manner as an SO-DIMM for use in a laptop personal computer, for example, and may be attached and removed in substantially the same manner as the SO-DIMM for use in a laptop personal computer. 
     In the SO-DIMM-type magnetic memory device, the magnetic composite bodies  2   a  and  2   b  are fixed to both sides of the memory socket  4 ′ of the substrate (for example, a motherboard)  4  of the laptop personal computer  5 . 
       FIG. 12  illustrates an exemplary magnetic memory device.  FIG. 12  illustrates the SO-DIMM-type magnetic memory device in use.  FIGS. 13A and 13B  illustrate an exemplary magnetic memory device.  FIGS. 13A and 13B  illustrate a state in which an MRAM main body is removed from the SO-DIMM-type magnetic memory device. 
       FIG. 13A  is a bottom view illustrating a state in which the SO-DIMM unit (with an MRAM main body)  1  projects from a memory socket  4 ′.  FIG. 13B  is a side view of the state illustrated in  FIG. 13A , illustrating movement of the SO-DIMM unit  1 .  FIGS. 12 and 13A  and  13 B may correspond to  FIGS. 1 and 5  or  FIGS. 8 and 9 , respectively. 
     As illustrated in  FIG. 12 , the SO-DIMM unit  1  is fitted into the memory socket  4 ′ that has the connector  3  to be attached to the substrate  4 . When the SO-DIMM unit  1  is attached to the substrate  4 , the first magnetic field M 1  may have an intensity that is sufficient for the lower magnetic layers of the MRAM elements (memory chips)  11  to function as MRAM and that does not affect magnetization reversal of the upper free layers. 
     When the SO-DIMM unit  1  is removed from the substrate  4 , for example when the SO-DIMM unit  1  is rotated downward as indicated by an arrow to be removed from the memory socket  4 ′, as illustrated in  FIGS. 13A and 13B , stored data may be disrupted. 
     When the SO-DIMM unit  1  is removed from the memory socket  4 ′ (substrate  4 ), the second magnetic field  2  may not be applied to all the MRAM elements  11  (all the MRAM elements of the memory chips  11 ) at the same time, for example. However, all the data in the MRAM elements  11  may be disrupted. 
     The SO-DIMM-type magnetic memory device may be provided with the magnetic composite bodies  2   a  and  2   b , and may be provided as the SO-DIMM unit  1  for a laptop personal computer in substantially the same manner as an SO-DIMM for a laptop personal computer. 
       FIGS. 14 and 15  illustrate an exemplary magnetic memory device.  FIG. 14  illustrates an SO-DIMM-type magnetic memory device for use in a desktop personal computer.  FIG. 15  illustrates a state in which an SO-DIMM unit is attached to a memory socket. 
     In the SO-DIMM-type magnetic memory device illustrated in  FIGS. 14 and 15 , for example, an SO-DIMM unit (with an MRAM main body)  1  is removably attached to a memory socket  4 ′ (substrate  4 ) via a connector  3 . In  FIG. 14 , reference numeral  6  denotes a central processing unit (CPU). 
     The SO-DIMM unit  1  may be shaped in substantially the same manner as an SO-DIMM for use in a desktop personal computer, for example, and may be attached and removed in substantially the same manner as the SO-DIMM for use in a desktop personal computer. 
     For example, the SO-DIMM unit  1  is inserted into the memory socket  4 ′ that has the connector  3 . The SO-DIMM unit  1  is firmly attached to the memory socket  4 ′ through connector levers (lock levers)  40   a  and  40   b.    
     In the SO-DIMM-type magnetic memory device, the magnetic composite bodies  2   a  and  2   b  are fixed to both sides of the memory socket  4 ′ of the substrate (for example, a motherboard)  4  of the desktop personal computer. 
     In  FIG. 14 , the magnetic composite bodies  2   a  and  2   b  are provided for one memory socket  4 ′, among a plurality of (four) memory sockets. However, the magnetic composite bodies  2   a  and  2   b  may be provided for all the memory sockets. 
     In  FIG. 15 , the magnetic composite bodies  2   a  and  2   b  are provided on both sides of a side surface of the SO-DIMM unit  1  on which the memory chips (MRAM elements)  11  are provided. 
     When the memory chips  11  are provided on both side surfaces of the SO-DIMM unit  1 , for example when the memory chips  11  are also provided on the back surface of the SO-DIMM unit  1 , the magnetic composite bodies  2   a  and  2   b  may also be provided on the back surface. 
       FIGS. 16A and 16B  illustrate an exemplary magnetic memory device.  FIGS. 16A and 16B  illustrate an SO-DIMM-type magnetic memory device in use.  FIGS. 17A and 17B  illustrate an exemplary magnetic memory device.  FIGS. 17A and 17B  illustrate a state in which an MRAM main body is removed from the SO-DIMM-type magnetic memory device. 
       FIGS. 16A and 17A  are each a front view of the SO-DIMM unit (MRAM main body)  1  and the memory socket  4 ′.  FIGS. 16B and 17B  are each a side view.  FIGS. 16A and 16B  may correspond to  FIG. 1 ,  8 , or  12 .  FIGS. 17A and 17B  may correspond to  FIG. 5 ,  9 , or  13 A and  13 B. 
     As illustrated in  FIGS. 15 ,  16 A, and  16 B, the SO-DIMM unit  1  is fitted into the memory socket  4 ′ that has the connector  3 , and the SO-DIMM unit  1  is attached to the memory socket  4 ′ through the connector levers  40   a  and  40   b.    
     When the SO-DIMM unit  1  is attached to the memory socket  4 ′ (substrate  4 ), the first magnetic field M 1  may have an intensity that is sufficient for the lower magnetic layers of the memory chips (MRAM elements)  11  to function as MRAM and that does not affect magnetization reversal of the upper free layers. 
     The magnetic composite bodies  2   a  and  2   b  are provided with spacers  20   a  and  20   b , respectively, so that the first magnetic field M 1  that is based on the first anisotropic magnets  21   a  and  21   b  is applied to the memory chips  11  of the SO-DIMM unit  1  at an appropriate position. 
     When the SO-DIMM unit  1  is removed from the substrate  4 , as illustrated in  FIGS. 17A and 17B , the connector levers  40   a  and  40   b  are opened to push up the SO-DIMM unit  1  from the memory socket  4 ′ for removal. Data stored in the memory chips (MRAM elements)  11  of the SO-DIMM unit  1  may be disrupted. 
     When the SO-DIMM unit  1  is removed from the memory socket  4 ′ (substrate  4 ), data in the MRAM elements  11  may be disrupted if the SO-DIMM unit  1  is removed in an inclined state. 
     The SO-DIMM-type magnetic memory device is provided with the magnetic composite bodies  2   a  and  2   b , but may be provided with the SO-DIMM unit  1  in substantially the same manner as an SO-DIMM for a desktop personal computer. 
     In the magnetic memory device discussed above, stored data may be disrupted with relatively low electrical power, and the possibility of data read-out or decoding (alteration) after the data disruption may be reduced. 
     When the magnetic memory main body is inappropriately taken out, stored data may be reliably disrupted, which may reduce the possibility of data leakage. When the magnetic memory main body which has been removed is attached, stored data has been disrupted, which allows the magnetic memory device to be reused after being newly initialized as a magnetic memory device. 
       FIGS. 18A and 18B  illustrate an exemplary magnetic memory device. The magnetic composite bodies  2   a  and  2   b  facing each other are fixed to the substrate  4 , for example a motherboard. Therefore, the magnetic composite bodies  2   a  and  2   b  may not be removed together with the MRAM main body, for example the SSD unit  1 . 
     In the magnetic memory device illustrated in  FIG. 18 , the magnetic composite bodies  2   a  and  2   b  facing each other are fixed to a dedicated substrate  30 , for example a substrate for the SSD unit  1  (unit substrate). Once attached to the motherboard  4 , the unit substrate  30  may not be removed from the motherboard  4 . 
       FIG. 18A  illustrates a state in which the SSD unit  1 , the unit substrate  30 , and the motherboard  4  are separated from each other.  FIG. 18B  illustrates a state in which the SSD unit  1 , the unit substrate  30 , and the motherboard  4  are fitted with each other. 
     The SSD unit  1  is removably provided on the unit substrate  30 , to which the magnetic composite bodies  2   a  and  2   b  are fixed, through connectors  100  and  310 . For example, the SSD unit  1  is electrically coupled through the connector  100  of the SSD unit  1  and the connector  310  of the unit substrate  30 . 
     The unit substrate  30  is electrically coupled through a connector  320  of the unit substrate  30  and a connector  400  of the motherboard  4 . Each of the connectors  100 ,  310 ,  320 , and  400  include a plurality of metal terminals (connection pins). 
     Lock mechanisms (female portions)  330   a  and  330   b  provided in the unit substrate  30  are fitted with lock mechanisms (male portions)  410   a  and  410   b  of the motherboard  4 . Hook portions  340   a  and  340   b  are formed in the lock mechanisms  330   a  and  330   b , respectively, of the unit substrate  30 . Once the lock mechanisms  330   a  and  330   b  are fitted with the lock mechanisms  410   a  and  410   b , respectively, of the motherboard  4 , the unit substrate  30  may not be removed because of the hook portions  340   a  and  340   b.    
     The motherboard  4  is provided with alignment portions  411   a  and  411   b  to allow the unit substrate  30  to be aligned at a given position of the motherboard  4 . 
     In  FIGS. 18A and 18B , the removal of the unit substrate  30  from the motherboard  4  may be reduced because of the lock mechanisms  330   a  and  330   b , the lock mechanisms  410   a  and  410   b , and the hook portions  340   a  and  340   b.    
     The unit substrate  30  may only be removed from the motherboard  4  using a dedicated removal tool that is difficult to obtain, for example. The unit substrate  30  may be attached to the motherboard  4  using an adhesive or the like so as not to be removable. 
     When the magnetic memory main body is inappropriately taken out, for example, stored data is disrupted (erased), which may reduce the possibility of data leakage. 
     Magnetic memory devices in which the magnetic composite bodies  2   a  and  2   b , the connectors  310  and  100 , and the SSD unit (MRAM main body)  1  are provided on the unit substrate  30  may be sold to other companies. 
     In the provided products, the positional relationship among the memory main body  1  and the magnetic composite bodies  2   a  and  2   b  (the anisotropic magnets  21   a  and  21   b  and  23   a  and  23   b ) has been set by the manufacturer of the magnetic memory devices. Therefore, the products may be managed strictly. 
     In personal computer assembly companies that have purchased the magnetic memory devices, the magnetic memory device (unit substrate  30 ) may be fixed to the motherboard  4  using technologies known in the art. An effect that is substantially the same as or similar to the effect of the magnetic memory device described above may be obtained. 
     The magnetic memory device may be applied to laptop personal computers, desktop personal computers, portable terminals, or various electronic devices. 
     All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiments of the present invention have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.