Patent Publication Number: US-2023165158-A1

Title: Magnetic memory devices and methods for initializing the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This U.S. non-provisional patent application claims priority under 35 U.S.C. § 119 to Korean Patent Application No. 10-2021-0164265, filed on Nov. 25, 2021, in the Korean Intellectual Property Office, the entire contents of which are hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     The present disclosure relates to magnetic memory devices, and more particularly, to magnetic memory devices using a movement phenomenon of a magnetic domain wall and methods for initializing the same. 
     High-speed and low-voltage memory devices have been demanded to realize high-speed and low-power electronic devices including memory devices. A magnetic memory device has been studied as a memory device satisfying these demands. The magnetic memory device has been spotlighted as a next-generation memory device because of its high-speed operation characteristics and/or non-volatile characteristics. In particular, a new magnetic memory device using a movement phenomenon of a magnetic domain wall of a magnetic material has been studied and developed. 
     SUMMARY 
     Embodiments of the present disclosure may provide a magnetic memory device capable of easily injecting a magnetic domain wall into a magnetic track including a synthetic antiferromagnetic structure. 
     Embodiments of the present disclosure may also provide a method for initializing a magnetic memory device capable of easily injecting a magnetic domain wall into a magnetic track including a synthetic antiferromagnetic structure. 
     In an aspect, a magnetic memory device may include a conductive line extending in a first direction, and a magnetic track extending in the first direction on the conductive line. The magnetic track may include a lower magnetic layer, a spacer layer, and an upper magnetic layer sequentially stacked on the conductive line, and a non-magnetic pattern on the spacer layer and adjacent a side of the upper magnetic layer. The non-magnetic pattern may vertically overlap with a portion of the lower magnetic layer. The lower magnetic layer and the upper magnetic layer may be antiferromagnetically coupled to each other by the spacer layer. 
     In an aspect, a magnetic memory device may include a magnetic track extending in a first direction. The magnetic track may include a lower magnetic layer extending in the first direction, an upper magnetic layer extending in the first direction on the lower magnetic layer, a non-magnetic pattern on the lower magnetic layer and adjacent a side of the upper magnetic layer, and a spacer layer extending in the first direction between the lower magnetic layer and the upper magnetic layer. The non-magnetic pattern may vertically overlap with a portion of the lower magnetic layer in a second direction substantially perpendicular to the first direction. The spacer layer may extend between the non-magnetic pattern and the portion of the lower magnetic layer. The lower magnetic layer and the upper magnetic layer may be antiferromagnetically coupled to each other by the spacer layer. 
     In an aspect, a method for initializing a magnetic memory device may be provided. The magnetic memory device may include a conductive line extending in a first direction, and a magnetic track extending in the first direction on the conductive line. The magnetic track may include a lower magnetic layer on the conductive line, an upper magnetic layer on the lower magnetic layer, a spacer layer between the lower magnetic layer and the upper magnetic layer, and a non-magnetic pattern on the spacer layer and adjacent a side of the upper magnetic layer. The non-magnetic pattern may vertically overlap with a portion of the lower magnetic layer. The magnetic track may include a synthetic antiferromagnetic region in which the lower magnetic layer and the upper magnetic layer are antiferromagnetically coupled to each other by the spacer layer, and a ferromagnetic region including the non-magnetic pattern and the portion of the lower magnetic layer which vertically overlaps with the non-magnetic pattern. The portion of the lower magnetic layer which vertically overlaps with the non-magnetic pattern may have an initial magnetization direction. The method may include applying a first external magnetic field to the magnetic track to reverse the initial magnetization direction of the portion of the lower magnetic layer which vertically overlaps with the non-magnetic pattern in the ferromagnetic region to a first magnetization direction and to form a lower magnetic domain wall in the portion of the lower magnetic layer which vertically overlaps with the non-magnetic pattern, and applying a current to the conductive line to inject the lower magnetic domain wall into the lower magnetic layer in the synthetic antiferromagnetic region. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a perspective view schematically illustrating a magnetic memory device according to some embodiments of the present disclosure. 
         FIG.  2    is a cross-sectional view illustrating a magnetic memory device according to some embodiments of the present disclosure. 
         FIGS.  3 A to  3 C  are cross-sectional views corresponding to a portion ‘A’ of  FIG.  2    to illustrate a method of manufacturing a magnetic memory device according to some embodiments of the present disclosure 
         FIGS.  4 A to  4 F  are cross-sectional views corresponding to the portion ‘A’ of  FIG.  2    to illustrate a method for initializing a magnetic memory device according to some embodiments of the present disclosure. 
         FIG.  5    is a cross-sectional view illustrating a magnetic memory device according to some embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Example embodiments of the present disclosure will now be described more fully with reference to the accompanying drawings. 
       FIG.  1    is a perspective view schematically illustrating a magnetic memory device according to some embodiments of the present disclosure. 
     Referring to  FIG.  1   , a magnetic memory device may include a conductive line CL, a magnetic track MTR on the conductive line CL, and a read/write unit  150  on the magnetic track MTR. Each of the conductive line CL and the magnetic track MTR may have a line shape extending in a first direction D 1 . The magnetic track MTR may be stacked on the conductive line CL in a second direction D 2  perpendicular to the first direction D 1 . Each of the conductive line CL and the magnetic track MTR may have a line shape in which a length in the first direction D 1  is greater than a width in a third direction D 3  perpendicular to both the first direction D 1  and the second direction D 2 . The read/write unit  150  may be adjacent to a portion of the magnetic track MTR. 
     The conductive line CL may be configured to generate spin-orbit torque by a current flowing therethrough. The conductive line CL may include a material capable of generating a spin hall effect or a Rashba effect by a current flowing in the first direction D 1  or an opposite direction to the first direction D 1  in the conductive line CL. The conductive line CL may include a heavy metal having an atomic number of thirty (30) or more and may include, for example, iridium (Ir), ruthenium (Ru), tantalum (Ta), platinum (Pt), palladium (Pd), bismuth (Bi), titanium (Ti), or tungsten (W). 
     The magnetic track MTR may include a lower magnetic layer  110 , a spacer layer  120  and an upper magnetic layer  130 , which are sequentially stacked on the conductive line CL. The lower magnetic layer  110 , the spacer layer  120  and the upper magnetic layer  130  may be stacked on the conductive line CL in the second direction D 2 . The lower magnetic layer  110  may be between the conductive line CL and the spacer layer  120 , and the spacer layer  120  may be between the lower magnetic layer  110  and the upper magnetic layer  130 . The lower magnetic layer  110 , the spacer layer  120  and the upper magnetic layer  130  may have line shapes extending in the first direction D 1 . The conductive line CL and the magnetic track MTR may have straight line shapes extending in the first direction D 1 , but embodiments of the present disclosure are not limited thereto. In certain embodiments, the conductive line CL and the magnetic track MTR may have U-shaped line shapes. 
     The lower magnetic layer  110  may include lower magnetic domains D_L arranged in the first direction D 1 , and lower magnetic domain walls DW_L between the lower magnetic domains D_L. Each of the lower magnetic domains D_L may be a region in the lower magnetic layer  110 , in which magnetic moments are aligned in a certain direction, and each of the lower magnetic domain walls DW_L may be a region in which directions of magnetic moments are changed between the lower magnetic domains D_L. The lower magnetic domains D_L and the lower magnetic domain walls DW_L may be alternately arranged in the first direction D 1 . 
     The upper magnetic layer  130  may include upper magnetic domains D_U arranged in the first direction D 1 , and upper magnetic domain walls DW_U between the upper magnetic domains D_U. Each of the upper magnetic domains D_U may be a region in the upper magnetic layer  130 , in which magnetic moments are aligned in a certain direction, and each of the upper magnetic domain walls DW_U may be a region in which directions of magnetic moments are changed between the upper magnetic domains D_U. The upper magnetic domains D_U and the upper magnetic domain walls DW_U may be alternately arranged in the first direction D 1 . The upper magnetic domains D_U may vertically overlap with the lower magnetic domains D_L in the second direction D 2 , respectively. As used herein, when element A is said to “overlap” or is “overlapping” element B, it may refer to the situation where element A is said to extend over or past, and/or cover a part of, element B in a given direction. Note that element A may overlap element B in a first direction, but may or may not overlap element B in a second direction. 
     The lower magnetic layer  110  and the upper magnetic layer  130  may be antiferromagnetically coupled to each other by the spacer layer  120 . Each of the lower magnetic layer  110  and the upper magnetic layer  130  may include a magnetic element and may include at least one of, for example, cobalt (Co), iron (Fe), or nickel (Ni). The spacer layer  120  may include a non-magnetic metal and may include, for example, ruthenium (Ru), iridium (Ir), tungsten (W), tantalum (Ta), or any alloy thereof. 
     The magnetic track MTR may further include a non-magnetic pattern  140  on the spacer layer  120  and adjacent a side of the upper magnetic layer  130 . The non-magnetic pattern  140  may vertically overlap with a portion of the lower magnetic layer  110  in the second direction D 2 . For example, the non-magnetic pattern  140  may vertically overlap with a corresponding lower magnetic domain D_L of the lower magnetic domains D_L in the lower magnetic layer  110  (e.g., in the second direction D 2 ). The non-magnetic pattern  140  may be in contact with a side surface  130 S of the upper magnetic layer  130 . The spacer layer  120  may be between the lower magnetic layer  110  and the upper magnetic layer  130  and may extend between the non-magnetic pattern  140  and the portion of the lower magnetic layer  110 . The non-magnetic pattern  140  may include a metal oxide. The non-magnetic pattern  140  may include a same magnetic element as a magnetic element in the upper magnetic layer  130  and may further include oxygen. 
     The magnetic track MTR may include a synthetic antiferromagnetic region SAF and a ferromagnetic region FM. The synthetic antiferromagnetic region SAF may be a region in which the lower magnetic layer  110  and the upper magnetic layer  130  are antiferromagnetically coupled to each other by the spacer layer  120 . The ferromagnetic region FM may include the non-magnetic pattern  140 , and the portion (i.e., the corresponding lower magnetic domain D_L) of the lower magnetic layer  110  which vertically overlaps with the non-magnetic pattern  140 . The magnetic track MTR may have a ferromagnet-synthetic antiferromagnet (FM-SAF) lateral junction structure in which the ferromagnetic region FM and the synthetic antiferromagnetic region SAF are joined to each other in the first direction D 1 . The ferromagnetic region FM of the magnetic track MTR may be a region used to inject a magnetic domain wall (e.g., the lower magnetic domain walls DW_L) into the synthetic antiferromagnetic region SAF of the magnetic track MTR for initialization of the magnetic memory device. 
     The read/write unit  150  may be on the synthetic antiferromagnetic region SAF of the magnetic track MTR. The read/write unit  150  may include a GMR sensor using a giant magneto resistance effect or a TMR sensor using a tunnel magneto resistance effect. For example, the read/write unit  150  may include a magnetic pattern  154  on the upper magnetic layer  130 , a tunnel barrier pattern  152  between the upper magnetic layer  130  and the magnetic pattern  154 , and an electrode pattern  156  on the magnetic pattern  154 . The magnetic pattern  154  may be between the tunnel barrier pattern  152  and the electrode pattern  156 . The magnetic pattern  154  may include at least one of cobalt (Co), iron (Fe), or nickel (Ni). The tunnel barrier pattern  152  may include at least one of magnesium (Mg) oxide, titanium (Ti) oxide, aluminum (Al) oxide, magnesium-zinc (Mg—Zn) oxide, or magnesium-boron (Mg—B) oxide. The electrode pattern  156  may include a conductive material and may include, for example, a metal (e.g., copper, tungsten, or aluminum) and/or a metal nitride (e.g., tantalum nitride, titanium nitride, or tungsten nitride). 
     The read/write unit  150  may vertically overlap with a corresponding upper magnetic domain D_U of the upper magnetic domains D_U in the upper magnetic layer  130  and a corresponding lower magnetic domain D_L of the lower magnetic domains D_L in the lower magnetic layer  110  (e.g., in the second direction D 2 ). 
       FIG.  2    is a cross-sectional view illustrating a magnetic memory device according to some embodiments of the present disclosure. Hereinafter, the descriptions to the same features as mentioned with reference to  FIG.  1    will be omitted for the purpose of ease and convenience in explanation. 
     Referring to  FIG.  2   , the lower magnetic domains D_L in the lower magnetic layer  110  and the upper magnetic domains D_U in the upper magnetic layer  130  may have perpendicular magnetic anisotropy (PMA). Each of the lower magnetic domains D_L in the lower magnetic layer  110  may have a magnetization direction  110 M substantially perpendicular to an interface between the lower magnetic layer  110  and the spacer layer  120 , and the magnetization directions  110 M of lower magnetic domains D_L directly adjacent to each other may be opposite to each other. Each of the lower magnetic domain walls DW_L may define a boundary between the adjacent lower magnetic domains D_L having the magnetization directions  110 M opposite to each other. Each of the upper magnetic domains D_U in the upper magnetic layer  130  may have a magnetization direction  130 M substantially perpendicular to an interface between the upper magnetic layer  130  and the spacer layer  120 , and the magnetization directions  130 M of upper magnetic domains D_U directly adjacent to each other may be opposite to each other. Each of the upper magnetic domain walls DW_U may define a boundary between the adjacent upper magnetic domains D_U having the magnetization directions  130 M opposite to each other. 
     The upper magnetic domains D_U may vertically overlap with the lower magnetic domains D_L in the second direction D 2 , respectively, and the upper magnetic domains D_U and the lower magnetic domains D_L may be antiferromagnetically coupled to each other by the spacer layer  120 . The magnetization direction  130 M of each of the upper magnetic domains D_U may be antiparallel to the magnetization direction  110 M of a corresponding lower magnetic domain D_L of the lower magnetic domains D_L. In the synthetic antiferromagnetic region SAF of the magnetic track MTR, the upper magnetic domains D_U and the lower magnetic domains D_L may be antiferromagnetically coupled to each other by the spacer layer  120 . 
     The non-magnetic pattern  140  may vertically overlap with one of the lower magnetic domains D_L in the second direction D 2 . The corresponding lower magnetic domain D_L may have the magnetization direction  110 M substantially perpendicular to the interface between the lower magnetic layer  110  and the spacer layer  120 . The non-magnetic pattern  140  and the corresponding lower magnetic domain D_L may constitute the ferromagnetic region FM of the magnetic track MTR. The ferromagnetic region FM of the magnetic track MTR may be a region used to inject a magnetic domain wall (e.g., the lower magnetic domain walls DW_L) into the synthetic antiferromagnetic region SAF of the magnetic track MTR for initialization of the magnetic memory device. 
     When a current flows in the first direction D 1  or the opposite direction to the first direction D 1  in the conductive line CL, the lower magnetic domain walls DW_L in the lower magnetic layer  110  may move in the first direction D 1 . The movement of the lower magnetic domain walls DW_L may be due to spin-orbit torque and Dzyaloshinskii-Moriya interaction (DMI) generated at an interface between the conductive line CL and the lower magnetic layer  110 . A movement direction of the lower magnetic domain walls DW_L may be dependent on chirality of the lower magnetic domain walls DW_L. Since the lower magnetic domain walls DW_L in the lower magnetic layer  110  move in the first direction D 1 , the upper magnetic domain walls DW_U in the upper magnetic layer  130  may also move in the first direction D 1 . The movement of the upper magnetic domain walls DW_U may be due to the antiferromagnetic coupling between the lower magnetic layer  110  and the upper magnetic layer  130 . 
     The magnetic pattern  154  of the read/write unit  150  may have perpendicular magnetic anisotropy (PMA). The magnetic pattern  154  may have a magnetization direction  154 M substantially perpendicular to an interface between the magnetic pattern  154  and the tunnel barrier pattern  152 , and the magnetization direction  154 M of the magnetic pattern  154  may be fixed in one direction. The magnetization directions  130 M of the upper magnetic domains D_U in the upper magnetic layer  130  and the magnetization directions  110 M of the lower magnetic domains D_L in the lower magnetic layer  110  may be changeable to be parallel or antiparallel to the magnetization direction  154 M of the magnetic pattern  154 . 
     The magnetic pattern  154  may vertically overlap with one of the upper magnetic domains D_U and a corresponding lower magnetic domain D_L of the lower magnetic domains D_L (e.g., in the second direction D 2 ). The magnetic pattern  154 , the corresponding upper magnetic domain D_U, and the corresponding lower magnetic domain D_L, which vertically overlap with each other, may constitute a magnetic tunnel junction MTJ. The magnetic pattern  154  may be a pinned layer having the magnetization direction  154 M fixed in one direction, and the corresponding upper magnetic domain D_U and the corresponding lower magnetic domain D_L may be antiferromagnetically coupled to each other to constitute a free layer having a synthetic antiferromagnetic structure. 
     In a read operation, a read current Iread may flow through the magnetic tunnel junction MTJ. A resistance state of the magnetic tunnel junction MTJ may be detected by the read current Iread. Whether the magnetic tunnel junction MTJ is in a high-resistance state or a low-resistance state may be detected by the read current Iread. Data (0 or 1) stored in the free layer may be detected from the resistance state of the magnetic tunnel junction MTJ. In a write operation, a write current Isw may flow through the magnetic tunnel junction MTJ. A magnitude of the write current Isw may be greater than a magnitude of the read current Iread. The magnetization direction  130 M of the corresponding upper magnetic domain D_U may be switched by spin transfer torque generated by the write current Isw. The magnetization direction  130 M of the corresponding upper magnetic domain D_U may be switched to be parallel or antiparallel to the magnetization direction  154 M of the magnetic pattern  154 , by the spin transfer torque generated by the write current Isw. The magnetization direction  110 M of the corresponding lower magnetic domain D_L may be switched to be antiparallel to the magnetization direction  130 M of the corresponding upper magnetic domain D_U, by the antiferromagnetic coupling between the corresponding upper magnetic domain D_U and the corresponding lower magnetic domain D_L. 
     In some embodiments, each of the lower magnetic layer  110 , the upper magnetic layer  130  and the magnetic pattern  154  may include at least one of cobalt (Co), iron (Fe), or nickel (Ni) and may further include at least one of non-magnetic materials such as boron (B), zinc (Zn), aluminum (Al), titanium (Ti), ruthenium (Ru), tantalum (Ta), silicon (Si), silver (Ag), gold (Au), copper (Cu), carbon (C), and nitrogen (N). For example, each of the lower magnetic layer  110 , the upper magnetic layer  130  and the magnetic pattern  154  may include at least one of a perpendicular magnetic material (e.g., CoFeTb, CoFeGd, or CoFeDy), a perpendicular magnetic material having a L 1   0  structure, a CoPt alloy having a hexagonal close packed (HCP) lattice structure, or a perpendicular magnetic structure. The perpendicular magnetic material having the L 1   0  structure may include at least one of FePt having the L 1   0  structure, FePd having the L 1   0  structure, CoPd having the L 1   0  structure, or CoPt having the L 1   0  structure. The perpendicular magnetic structure may include magnetic layers and non-magnetic layers, which are alternately and repeatedly stacked. For example, the perpendicular magnetic structure may include at least one of (Co/Pt)n, (CoFe/Pt)n, (CoFe/Pd)n, (Co/Pd)n, (Co/Ni)n, (CoNi/Pt)n, (CoCr/Pt)n, or (CoCr/Pd)n, where ‘n’ denotes the number of bilayers. In certain embodiments, each of the lower magnetic layer  110 , the upper magnetic layer  130  and the magnetic pattern  154  may include CoFeB or a Co-based Heusler alloy. 
       FIGS.  3 A to  3 C  are cross-sectional views corresponding to a portion ‘A’ of  FIG.  2    to illustrate a method of manufacturing a magnetic memory device according to some embodiments of the present disclosure. Hereinafter, the descriptions to the same features as mentioned with reference to  FIGS.  1  and  2    will be omitted for the purpose of ease and convenience in explanation. 
     Referring to  FIG.  3 A , a conductive line CL, a lower magnetic layer  110 , a spacer layer  120 , and an upper magnetic layer  130  may be formed to extend in the first direction D 1 . The lower magnetic layer  110 , the spacer layer  120 , and the upper magnetic layer  130  may be sequentially stacked on the conductive line CL in the second direction D 2 . 
     For example, the formation of the conductive line CL, the lower magnetic layer  110 , the spacer layer  120  and the upper magnetic layer  130  may include sequentially depositing a conductive layer, a first magnetic layer, a non-magnetic layer and a second magnetic layer, forming a first mask pattern M 1  on the second magnetic layer, and sequentially etching the second magnetic layer, the non-magnetic layer, the first magnetic layer and the conductive layer by using the first mask pattern M 1  as an etch mask. The conductive layer, the first magnetic layer, the non-magnetic layer, and the second magnetic layer may be formed using a chemical vapor deposition (CVD) method and/or a physical vapor deposition (PVD) method and may be formed using, for example, a sputtering deposition method. The first mask pattern M 1  may have a line shape extending in the first direction D 1  and may be a photoresist pattern or a hard mask pattern. The second magnetic layer, the non-magnetic layer, the first magnetic layer and the conductive layer may be sequentially etched by, for example, an ion beam etching process. The upper magnetic layer  130 , the spacer layer  120 , the lower magnetic layer  110 , and the conductive line CL may be formed by etching the second magnetic layer, the non-magnetic layer, the first magnetic layer, and the conductive layer, respectively. The lower magnetic layer  110  and the upper magnetic layer  130  may be antiferromagnetically coupled to each other by the spacer layer  120 . 
     After the formation of the conductive line CL, the lower magnetic layer  110 , the spacer layer  120  and the upper magnetic layer  130 , the first mask pattern M 1  may be removed. The first mask pattern M 1  may be removed by, for example, an ashing process and/or a strip process. 
     Referring to  FIG.  3 B , a second mask pattern M 2  may be formed on the upper magnetic layer  130 . The second mask pattern M 2  may expose a portion of the upper magnetic layer  130  and may at least partially cover a remaining portion of the upper magnetic layer  130 . The second mask pattern M 2  may be a photoresist pattern or a hard mask pattern. The second mask pattern M 2  may include a metal nitride and may include, for example, TaN. 
     An oxidation process may be performed on the upper magnetic layer  130 . The second mask pattern M 2  may be used as a mask of the oxidation process. The oxidation process may include, for example, an oxygen plasma treatment. 
     Referring to  FIG.  3 C , the portion of the upper magnetic layer  130  which is exposed by the second mask pattern M 2  may be oxidized by the oxidation process, and thus a non-magnetic pattern  140  may be formed at a side of the upper magnetic layer  130 . The non-magnetic pattern  140  may include a metal oxide. The non-magnetic pattern  140  may include the same magnetic element as the upper magnetic layer  130  and may further include oxygen. 
     The spacer layer  120  may be used as an oxidation stop layer of the oxidation process. Thus, a portion  110 P of the lower magnetic layer  110 , which vertically overlaps with the non-magnetic pattern  140  (e.g., in the second direction D 2 ), may not be oxidized by the oxidation process but may maintain a ferromagnetic property. 
     After the formation of the non-magnetic pattern  140  by the oxidation process, the second mask pattern M 2  may be removed. The second mask pattern M 2  may be removed by, for example, an ashing process and/or a strip process. 
     The lower magnetic layer  110 , the spacer layer  120 , the upper magnetic layer  130 , and the non-magnetic pattern  140  may constitute a magnetic track MTR. The conductive line CL and the magnetic track MTR may have line shapes extending in the first direction D 1 . 
     The magnetic track MTR may include a synthetic antiferromagnetic region SAF and a ferromagnetic region FM. The synthetic antiferromagnetic region SAF may be a region in which the lower magnetic layer  110  and the upper magnetic layer  130  are antiferromagnetically coupled to each other by the spacer layer  120 . The ferromagnetic region FM may include the non-magnetic pattern  140  and the portion  110 P of the lower magnetic layer  110  which vertically overlaps with the non-magnetic pattern  140 . The magnetic track MTR may have a ferromagnet-synthetic antiferromagnet (FM-SAF) lateral junction structure in which the ferromagnetic region FM and the synthetic antiferromagnetic region SAF are joined to each other in the first direction D 1 . 
     Referring again to  FIG.  2   , a read/write unit  150  may be formed on the synthetic antiferromagnetic region SAF of the magnetic track MTR. For example, the formation of the read/write unit  150  may include sequentially forming a tunnel insulating layer, a magnetic layer and an electrode layer on the magnetic track MTR, and etching the tunnel insulating layer, the magnetic layer and the electrode layer. A tunnel barrier pattern  152 , a magnetic pattern  154  and an electrode pattern  156  may be formed by etching the tunnel insulating layer, the magnetic layer and the electrode layer, respectively. 
       FIGS.  4 A to  4 F  are cross-sectional views corresponding to the portion ‘A’ of  FIG.  2    to illustrate a method for initializing a magnetic memory device according to some embodiments of the present disclosure. Hereinafter, the descriptions to the same features as mentioned with reference to  FIGS.  1  and  2    will be omitted for the purpose of ease and convenience in explanation. 
     Referring to  FIG.  4 A , a magnetic memory device may include a conductive line CL and a magnetic track MTR on the conductive line CL. The magnetic track MTR may include a lower magnetic layer  110 , a spacer layer  120 , and an upper magnetic layer  130  which are sequentially stacked on the conductive line CL, and may further include a non-magnetic pattern  140  on the spacer layer  120  and adjacent a side of the upper magnetic layer  130 . The non-magnetic pattern  140  may vertically overlap with a portion  110 P of the lower magnetic layer  110  in the second direction D 2 . The magnetic track MTR may include a synthetic antiferromagnetic region SAF in which the lower magnetic layer  110  and the upper magnetic layer  130  are antiferromagnetically coupled to each other by the spacer layer  120 , and a ferromagnetic region FM including the non-magnetic pattern  140  and the portion  110 P of the lower magnetic layer  110  which vertically overlap with each other (e.g., in the second direction D 2 ). 
     In some embodiments, the lower magnetic layer  110  may have a magnetization direction  110 M substantially perpendicular to an interface between the lower magnetic layer  110  and the spacer layer  120 , and the upper magnetic layer  130  may have a magnetization direction  130 M substantially perpendicular to an interface between the upper magnetic layer  130  and the spacer layer  120 . The lower magnetic layer  110  and the upper magnetic layer  130  may be antiferromagnetically coupled to each other by the spacer layer  120 , and thus the magnetization direction  130 M of the upper magnetic layer  130  may be antiparallel to the magnetization direction  110 M of the lower magnetic layer  110 . For example, the magnetization direction  110 M of the lower magnetic layer  110  may be aligned in an up-direction, and the magnetization direction  130 M of the upper magnetic layer  130  may be aligned in a down-direction. 
     An initial magnetization direction  110 Mi of the portion  110 P of the lower magnetic layer  110  which vertically overlaps with the non-magnetic pattern  140  may be the same as the magnetization direction  110 M of the lower magnetic layer  110 . For example, the initial magnetization direction  110 Mi of the portion  110 P of the lower magnetic layer  110  may be aligned in the up-direction. 
     Referring to  FIG.  4 B , a first external magnetic field H 1  may be applied to the magnetic track MTR. A direction of the first external magnetic field H 1  may be an opposite direction to the initial magnetization direction  110 Mi of the portion  110 P of the lower magnetic layer  110 . For example. the direction of the first external magnetic field H 1  may be the down-direction. 
     A coercivity (Hc) of the synthetic antiferromagnetic region SAF of the magnetic track MTR may be greater than a coercivity (Hc) of the ferromagnetic region FM of the magnetic track MTR. Since the synthetic antiferromagnetic region SAF of the magnetic track MTR has the relatively great coercivity (Hc), the magnetization directions  110 M and  130 M of the lower magnetic layer  110  and the upper magnetic layer  130  in the synthetic antiferromagnetic region SAF of the magnetic track MTR may not be reversed by the first external magnetic field H 1 . Since the ferromagnetic region FM of the magnetic track MTR has the relatively small coercivity (Hc), the initial magnetization direction  110 Mi of the portion  110 P of the lower magnetic layer  110  in the ferromagnetic region FM of the magnetic track MTR may be reversed by the first external magnetic field H 1 . Thus, the portion  110 P of the lower magnetic layer  110  may have a first magnetization direction  110 M 1  aligned in the down-direction. 
     Since the initial magnetization direction  110 Mi of the portion  110 P of the lower magnetic layer  110  is reversed to the first magnetization direction  110 M 1  by the first external magnetic field H 1 , a lower magnetic domain wall DW_L may be formed in the portion  110 P of the lower magnetic layer  110 , which is adjacent to a junction between the ferromagnetic region FM and the synthetic antiferromagnetic region SAF. 
     Referring to  FIG.  4 C , a current I may be applied to flow in the conductive line CL in the first direction D 1  (or the opposite direction to the first direction D 1 ). Thus, the lower magnetic domain wall DW_L formed in the portion  110 P of the lower magnetic layer  110  in the ferromagnetic region FM may be injected into the lower magnetic layer  110  in the synthetic antiferromagnetic region SAF. For example, the lower magnetic domain wall DW_L may move in the first direction D 1 . 
     Referring to  FIG.  4 D , by the current I applied to the conductive line CL, the lower magnetic domain wall DW_L may be injected into the lower magnetic layer  110  in the synthetic antiferromagnetic region SAF and may move in the lower magnetic layer  110  in the synthetic antiferromagnetic region SAF in the first direction D 1 . With the movement of the lower magnetic domain wall DW_L, the magnetization direction  110 M of the lower magnetic layer  110  may be reversed to the first magnetization direction  110 M 1  aligned in the down-direction. 
     By the antiferromagnetic coupling between the upper magnetic layer  130  and the lower magnetic layer  110 , the magnetization direction  130 M of the upper magnetic layer  130  may be reversed to be antiferromagnetically coupled to the first magnetization direction  110 M 1  of the lower magnetic layer  110 . A reversed magnetization direction  130 M 1  of the upper magnetic layer  130  may be antiferromagnetically coupled to the first magnetization direction  110 M 1  of the lower magnetic layer  110  and may be aligned in, for example, the up-direction. Since the upper magnetic layer  130  has the reversed magnetization direction  130 M 1 , an upper magnetic domain wall DW U may be formed in the upper magnetic layer  130 . The upper magnetic domain wall DW U may vertically overlap with the lower magnetic domain wall DW_L (e.g., in the second direction D 2 ). 
     Referring to  FIG.  4 E , a second external magnetic field H 2  may be applied to the magnetic track MTR. A direction of the second external magnetic field H 2  may be an opposite direction to the first magnetization direction  110 M 1  of the portion  110 P of the lower magnetic layer  110 . For example, the direction of the second external magnetic field H 2  may be the up-direction. 
     Since the synthetic antiferromagnetic region SAF of the magnetic track MTR has the relatively great coercivity (Hc), the magnetization directions  110 M,  110 M 1 ,  130 M and  130 M 1  of the lower magnetic layer  110  and the upper magnetic layer  130  in the synthetic antiferromagnetic region SAF of the magnetic track MTR may not be reversed by the second external magnetic field H 2 . Since the ferromagnetic region FM of the magnetic track MTR has the relatively small coercivity (Hc), the first magnetization direction  110 M 1  of the portion  110 P of the lower magnetic layer  110  in the ferromagnetic region FM of the magnetic track MTR may be reversed by the second external magnetic field H 2 . Thus, the portion  110 P of the lower magnetic layer  110  may have a second magnetization direction  110 M 2  aligned in the up-direction. 
     Since the first magnetization direction  110 M 1  of the portion  110 P of the lower magnetic layer  110  is reversed to the second magnetization direction  110 M 2  by the second external magnetic field H 2 , an additional lower magnetic domain wall DW_L′ may be formed in the portion  110 P of the lower magnetic layer  110  which is adjacent to the junction between the ferromagnetic region FM and the synthetic antiferromagnetic region SAF. 
     Referring to  FIG.  4 F , a current I may be applied to flow in the conductive line CL in the first direction D 1  (or the opposite direction to the first direction D 1 ). By the current I applied to the conductive line CL, the additional lower magnetic domain wall DW_L′ may be injected into the lower magnetic layer  110  in the synthetic antiferromagnetic region SAF, and the lower magnetic domain walls DW_L′ and DW_L may move in the lower magnetic layer  110  in the synthetic antiferromagnetic region SAF in the first direction D 1 . 
     The magnetization directions  110 M and  110 M 1  of the lower magnetic layer  110  may be reversed with the movement of the lower magnetic domain walls DW_L′ and DW_L. For example, with the movement of the lower magnetic domain wall DW_L, the magnetization direction  110 M of the lower magnetic layer  110  may be reversed to the first magnetization direction  110 M 1  aligned in the down-direction. In addition, with the movement of the additional lower magnetic domain wall DW_L′, the first magnetization direction  110 M 1  of the lower magnetic layer  110  may be reversed to the second magnetization direction  110 M 2  aligned in the up-direction. 
     By the antiferromagnetic coupling between the upper magnetic layer  130  and the lower magnetic layer  110 , the magnetization directions  130 M and  130 M 1  of the upper magnetic layer  130  may be reversed to be antiferromagnetically coupled to the reversed magnetization directions  110 M 1  and  110 M 2  of the lower magnetic layer  110 . For example, a reversed magnetization direction  130 M 1  of the upper magnetic layer  130  may be antiferromagnetically coupled to the first magnetization direction  110 M 1  of the lower magnetic layer  110  and may be aligned in the up-direction. In addition, a re-reversed magnetization direction  130 M 2  of the upper magnetic layer  130  may be antiferromagnetically coupled to the second magnetization direction  110 M 2  of the lower magnetic layer  110  and may be aligned in the down-direction. 
     Since the upper magnetic layer  130  has the reversed magnetization directions  130 M 1  and  130 M 2 , an additional upper magnetic domain wall DW_U′ may be formed in the upper magnetic layer  130 . The upper magnetic domain walls DW_U′ and DW_U may vertically overlap with the lower magnetic domain walls DW_L′ and DW_L (e.g., in the second direction D 2 ), respectively. 
     By applying an external magnetic field (e.g., the first and second external magnetic fields H 1  and H 2 ) to the magnetic track MTR, the lower magnetic domain wall DW_L may be formed in the portion  110 P of the lower magnetic layer  110  in the ferromagnetic region FM of the magnetic track MTR. By applying a current to the conductive line CL, the lower magnetic domain wall DW_L formed in the portion  110 P of the lower magnetic layer  110  may be injected into the lower magnetic layer  110  in the synthetic antiferromagnetic region SAF of the magnetic track MTR. The magnetic track MTR may be initialized by repeatedly performing the formation and injection of the lower magnetic domain wall DW_L as described with reference to  FIGS.  4 A to  4 F . The lower magnetic layer  110  of the initialized magnetic track MTR may include the lower magnetic domains D_L arranged in the first direction D 1  and the lower magnetic domain walls DW_L therebetween as described with reference to  FIG.  2   , and the upper magnetic layer  130  of the initialized magnetic track MTR may include the upper magnetic domains D_U arranged in the first direction D 1  and the upper magnetic domain walls DW_U therebetween as described with reference to  FIG.  2   . 
     According to the present disclosure, the magnetic track MTR may include the lower magnetic layer  110 , the upper magnetic layer  130 , the spacer layer  120  between the lower magnetic layer  110  and the upper magnetic layer  130 , and the non-magnetic pattern  140  on the spacer layer  120  and adjacent a side of the upper magnetic layer  130 . The non-magnetic pattern  140  may vertically overlap with a portion of the lower magnetic layer  110  in the second direction D 2 . The magnetic track MTR may include the synthetic antiferromagnetic region SAF in which the lower magnetic layer  110  and the upper magnetic layer  130  are antiferromagnetically coupled to each other by the spacer layer  120 , and the ferromagnetic region FM including the non-magnetic pattern  140  and the portion of the lower magnetic layer  110  which vertically overlap with each other (e.g., in the second direction D 2 ). The magnetic track MTR may have a ferromagnet-synthetic antiferromagnet (FM-SAF) lateral junction structure in which the ferromagnetic region FM and the synthetic antiferromagnetic region SAF are joined to each other in the first direction D 1 . In this case, by applying the external magnetic field to the magnetic track MTR, the lower magnetic domain wall DW_L may be easily formed in the portion of the lower magnetic layer  110  in the ferromagnetic region FM of the magnetic track MTR. In addition, by applying the current to the conductive line CL under the magnetic track MTR, the lower magnetic domain wall DW_L formed in the portion  110 P of the lower magnetic layer  110  may be easily injected into the lower magnetic layer  110  in the synthetic antiferromagnetic region SAF of the magnetic track MTR. 
     As a result, it is possible to provide the magnetic memory device capable of easily injecting a magnetic domain wall into the magnetic track MTR including the synthetic antiferromagnetic structure, and it is possible to provide the method for initializing the magnetic memory device, which is capable of easily injecting the magnetic domain wall into the magnetic track MTR. 
     In some embodiments, a plurality of magnetic tracks MTR spaced apart from each other may be provided. As described above, each of the plurality of magnetic tracks MTR may have the ferromagnet-synthetic antiferromagnet (FM-SAF) lateral junction structure in which the ferromagnetic region FM and the synthetic antiferromagnetic region SAF are joined to each other in the first direction D 1 . In this case, by applying an external magnetic field to the plurality of magnetic tracks MTR, a lower magnetic domain wall DW_L may be easily formed in the portion of the lower magnetic layer  110  in the ferromagnetic region FM of each of the plurality of magnetic tracks MTR. In addition, by applying a current to the conductive line CL under each of the plurality of magnetic tracks MTR, the lower magnetic domain wall DW_L formed in the portion  110 P of the lower magnetic layer  110  may be easily injected into the lower magnetic layer  110  in the synthetic antiferromagnetic region SAF of the magnetic track MTR. Thus, it is possible to provide a magnetic memory device and a method for initializing the same, which are capable of easily injecting magnetic domain walls into the plurality of magnetic tracks MTR including the synthetic antiferromagnetic structures. 
       FIG.  5    is a cross-sectional view illustrating a magnetic memory device according to some embodiments of the present disclosure. Hereinafter, differences between the present embodiments and the above embodiments of  FIGS.  1  and  2    will be mainly described for the purpose of ease and convenience in explanation. 
     Referring to  FIG.  5   , the lower magnetic domains D_L in the lower magnetic layer  110  and the upper magnetic domains D_U in the upper magnetic layer  130  may have in-plane magnetic anisotropy (IMA). Each of the lower magnetic domains D_L in the lower magnetic layer  110  may have a magnetization direction  110 M parallel to an interface between the lower magnetic layer  110  and the spacer layer  120 , and magnetization directions  110 M of lower magnetic domains D_L adjacent directly to each other may be opposite to each other. Each of the lower magnetic domain walls DW_L may define a boundary between the adjacent lower magnetic domains D_L having the magnetization directions  110 M opposite to each other. Each of the upper magnetic domains D_U in the upper magnetic layer  130  may have a magnetization direction  130 M parallel to an interface between the upper magnetic layer  130  and the spacer layer  120 , and magnetization directions  130 M of upper magnetic domains D_U adjacent directly to each other may be opposite to each other. Each of the upper magnetic domain walls DW U may define a boundary between the adjacent upper magnetic domains D_U having the magnetization directions  130 M opposite to each other. 
     The magnetic pattern  154  of the read/write unit  150  may have in-plane magnetic anisotropy (IMA). The magnetic pattern  154  may have a magnetization direction  154 M parallel to an interface between the magnetic pattern  154  and the tunnel barrier pattern  152 , and the magnetization direction  154 M of the magnetic pattern  154  may be fixed in one direction. The magnetization directions  130 M of the upper magnetic domains D_U in the upper magnetic layer  130  and the magnetization directions  110 M of the lower magnetic domains D_L in the lower magnetic layer  110  may be changeable to be parallel or antiparallel to the magnetization direction  154 M of the magnetic pattern  154 . 
     In some embodiments, each of the lower magnetic layer  110 , the upper magnetic layer  130 , and the magnetic pattern  154  may include a ferromagnetic material, and the magnetic pattern  154  may further include an antiferromagnetic material for pinning or fixing a magnetization direction of the ferromagnetic material. 
     Except for the aforementioned differences, other features and components of the magnetic memory device according to the present embodiments may be substantially the same as corresponding features and components of the magnetic memory device described with reference to  FIGS.  1  and  2   . In addition, the magnetic memory device according to the present embodiments may be formed by substantially the same method as described with reference to  FIGS.  3 A to  3 C  and may be initialized by substantially the same method as described with reference to  FIGS.  4 A to  4 F . 
     According to the present disclosure, the magnetic track may have the ferromagnet-synthetic antiferromagnet (FM-SAF) lateral junction structure in which the ferromagnetic region and the synthetic antiferromagnetic region are joined to each other in the first direction. In this case, by applying an external magnetic field to the magnetic track, a magnetic domain wall may be easily formed in the ferromagnetic region of the magnetic track. In addition, by applying a current to the conductive line under the magnetic track, the magnetic domain wall formed in the ferromagnetic region may be easily injected into the synthetic antiferromagnetic region of the magnetic track. 
     As a result, it is possible to provide the magnetic memory device capable of easily injecting the magnetic domain wall into the magnetic track including the synthetic antiferromagnetic structure, and it is possible to provide the method for initializing the magnetic memory device, which is capable of easily injecting the magnetic domain wall into the magnetic track. 
     While example embodiments of the present disclosure have been particularly shown and described, it will be understood by one of ordinary skill in the art that variations in form and detail may be made therein without departing from the spirit and scope of the attached claims.