Patent Publication Number: US-2016240773-A1

Title: Self reference thermally assisted mram with low moment ferromagnet storage layer

Description:
DOMESTIC PRIORITY 
     This application claims priority to U.S. Non-provisional application Ser. No. 14/499,523, entitled “SELF REFERENCE THERMALLY ASSISTED MRAM WITH LOW MOMENT STORAGE LAYER”, filed Sep. 29, 2014, which claims priority to U.S. Provisional Application Ser. No. 61/903,598, entitled “SELF REFERENCE THERMALLY ASSISTED MRAM WITH LOW MOMENT STORAGE LAYER”, filed Nov. 13, 2013 and to U.S. Provisional Application Ser. No. 61/903,600, entitled “SELF REFERENCE THERMALLY ASSISTED MRAM WITH LOW MOMENT SYNTHETIC ANTIFERROMAGNET STORAGE LAYER”, filed Nov. 13, 2013, the contents of which are incorporated herein by reference in their entirety. 
    
    
     BACKGROUND 
     The present invention relates generally to magnetic memory devices, and more specifically, to thermally assisted MRAM devices that provide low moment ferromagnet storage and sense layers. 
     Magnetoresistive random access memory (MRAM) is a non-volatile computer memory (NVRAM) technology. Unlike conventional RAM chip technologies, MRAM data is not stored as electric charge or current flows, but by magnetic storage elements. The elements are formed from two ferromagnetic plates, each of which can hold a magnetic moment, separated by a thin insulating layer. One of the two plates is a reference magnet set to a particular polarity; the other plate&#39;s field can be changed to match that of an external field to store memory and is termed the “free magnet” or “free-layer”. This configuration is known as a magnetic tunnel junction and is the simplest structure for a MRAM bit. A memory device is built from a grid of such “cells.” In some configurations of MRAM, such as the type further discussed herein, both the reference and free layers of the magnetic tunnel junctions can be switched using an external magnetic field. 
     SUMMARY 
     According to one embodiment, a thermally assisted magnetoresistive random access memory device (TAS-MRAM) with reduced power for reading and writing is provided. The device includes a tunnel barrier disposed adjacent to a ferromagnetic sense layer and a ferromagnetic storage layer, such that the tunnel barrier is sandwiched between the ferromagnetic sense layer and the ferromagnetic storage layer. The ferromagnetic sense layer, the tunnel barrier, and the ferromagnetic storage layer together form a magnetic tunnel junction. An antiferromagnetic pinning layer is disposed adjacent to the ferromagnetic storage layer. The antiferromagnetic pinning layer pins a magnetic moment of the ferromagnetic storage layer until heating is applied. The ferromagnetic storage layer includes a non-magnetic material to reduce a storage layer magnetization of the ferromagnetic storage layer as compared to not having the non-magnetic material, and/or the ferromagnetic sense layer includes the non-magnetic material to reduce a sense layer magnetization of the ferromagnetic sense layer as compared to not having the non-magnetic material. A reduction at least one of in the storage layer magnetization of the ferromagnetic storage layer and in the sense layer magnetization of the ferromagnetic sense layer reduces the magnetostatic interaction between the ferromagnetic storage layer and the ferromagnetic sense layer, resulting in less power to read and write to the magnetic tunnel junction as compared to the ferromagnetic storage layer and the ferromagnetic sense layer not having the non-magnetic material. 
     According to another embodiment, a thermally assisted magnetoresistive random access memory device (TAS-MRAM) with reduced power for reading and writing is provided. The device includes a tunnel barrier disposed adjacent to a ferromagnetic sense layer and a synthetic antiferromagnet storage layer, such that the tunnel barrier is sandwiched between the ferromagnetic sense layer and the synthetic antiferromagnet storage layer. The synthetic antiferromagnet storage layer includes a first ferromagnetic storage layer disposed adjacent to the tunnel barrier, and a non-magnetic coupling layer sandwiched between the first ferromagnetic storage layer and a second ferromagnetic storage layer. An antiferromagnetic pinning layer is disposed adjacent to the second ferromagnetic storage layer of the synthetic antiferromagnet storage layer but opposite the non-magnetic coupling layer. A non-magnetic material included at least one of in the first ferromagnetic storage layer, in the second ferromagnetic storage layer, and in the ferromagnetic sense layer. The non-magnetic material reduces a first storage layer magnetization of the first ferromagnetic storage layer, reduces a second storage layer magnetization of the second ferromagnetic storage layer, and reduces a sense layer magnetization of the ferromagnetic sense layer as respectively compared to not having the non-magnetic material. A reduction in the first storage layer magnetization, the second storage layer magnetization, and the sense layer magnetization reduces magnetostatic interaction dispersions between the first ferromagnetic storage layer, the second ferromagnetic storage layer, and the ferromagnetic sense layer, resulting in less power to read and write as compared to the first ferromagnetic storage layer, the second ferromagnetic storage layer, and the ferromagnetic sense layer not having the non-magnetic material. The reduced magnetization permits a greater thickness for the first ferromagnetic storage layer, the second ferromagnetic storage layer, and the ferromagnetic sense layer as compared to not having the non-magnetic material. 
     Additional features and advantages are realized through the techniques of the present invention. Other embodiments and aspects of the invention are described in detail herein and are considered a part of the claimed invention. For a better understanding of the invention with the advantages and the features, refer to the description and to the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The forgoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a cross-sectional view of a thermally-assisted magnetoresistive random access memory (TAS-MRAM) device according to an embodiment. 
         FIG. 2A  illustrates a reading procedure of a self-referenced stack when the sense layer is switched in one direction according to an embodiment. 
         FIG. 2B  illustrates the reading procedure of the self-referenced stack when the sense layer is switched in the other direction according to an embodiment. 
         FIG. 3A  is a schematic diagram illustrating depositing an alloy by sputtering from a composite target A plus B made of the desired alloy to form a storage layer and/or sense layer with reduced magnetization according to an embodiment. 
         FIG. 3B  is a schematic diagram illustrating depositing the alloy by co-sputtering from different targets A and B containing the desired magnetic and non-magnetic elements to form the storage layer and/or sense layer with reduced magnetization according to an embodiment. 
         FIG. 3C  is a schematic diagram illustrating a multilayered stack comprising ferromagnetic and non-magnetic bilayers with multiple repetitions to form the storage layer and/or sense layer with reduced magnetization according to an embodiment. 
         FIG. 4A  is a chart illustrating the reduction of magnetization (M s ) for the storage layer and/or sense layer using various non-magnetic dopant materials according to an embodiment. 
         FIG. 4B  is a chart illustrating a reduction in stray fields (H bias ) generated by the storage layer on sense layer which is by the reduction in magnetization from the various non-magnetic dopant materials according to an embodiment. 
         FIG. 5  is a flow diagram illustrating a method of forming the thermally assisted magnetoresistive random access memory with device reduced power for reading and writing according to an embodiment. 
         FIG. 6  is a cross-sectional view of a thermally-assisted magnetoresistive random access memory (TAS-MRAM) device according to an embodiment. 
         FIG. 7A  illustrates a reading procedure of a self-referenced stack when the sense layer is switched in one direction according to an embodiment. 
         FIG. 7B  illustrates the reading procedure of the self-referenced stack when the sense layer is switched in the other direction according to an embodiment. 
         FIG. 8A  is a schematic diagram illustrating depositing an alloy by sputtering from a composite target A and B made of the desired alloy to form a storage layer and/or sense layer with reduced magnetization according to an embodiment. 
         FIG. 8B  is a schematic diagram illustrating depositing the alloy by co-sputtering from different targets A and B containing the desired magnetic and non-magnetic elements to form the storage layer and/or sense layer with reduced magnetization according to an embodiment. 
         FIG. 8C  is a schematic diagram illustrating a multilayered stack comprising ferromagnetic and non-magnetic bilayers with multiple repetitions to form the storage layer and/or sense layer with reduced magnetization according to an embodiment. 
         FIGS. 9A and 9B  together is a flow diagram illustrating a method of forming the thermally assisted magnetoresistive random access memory device with reduced power for reading and writing according to an embodiment. 
         FIG. 10  is a block diagram illustrating an example of a computer which can be connected to, operate, and/or include the MRAM device(s) according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Thermally-assisted magnetoresistive random access memory (TAS-MRAM) requires heating of the magnetic tunnel junction stack to a write temperature (T write ) higher than the operating temperature (T op ) in order to write the device. This is typically done by heating from a bias current that is applied on the magnetic tunnel junction during the write process. The amount of power required to heat the device to T write  is strongly dependent on the thermal conductivity between the device and the surrounding structures and substrate, which are at T op &lt;T write . 
     In particular, the TAS-MRAM cell is composed of a magnetic tunnel junction with an antiferromagnetic (AF) pinning layer. This AF layer must be heated to T w &gt;T op  in order to allow writing data to (i.e., switch the magnetic moment) the storage layer (SL) of the TAS-MRAM device. Embodiments described herein reduce the power required to switch the magnetic moment in the storage layer and the sense layer (also referred to as a reference layer). 
     Now turning to the figures,  FIG. 1  illustrates a structure for a thermally-assisted magnetoresistive random access memory (TAS-MRAM) device  100  according to an embodiment.  FIG. 1  depicts a cross-sectional view of the device  100 . 
     The structure of the MRAM device  100  includes a magnetic tunnel junction (MTJ)  10 . The magnetic tunnel junction  10  may include a ferromagnetic sense layer  16  with a non-magnetic tunnel barrier  14  disposed at an interface of the ferromagnetic sense layer  16 . The magnetic tunnel junction  10  also includes a storage layer  12  disposed at an interface of the non-magnetic tunnel barrier  14 . The non-magnetic tunnel barrier  14  may be a semiconductor or insulator. The storage layer  12  includes ferromagnetic material as discussed further herein. Although not shown in  FIG. 1  ( FIG. 2 ), the reverse configuration is also contemplated for the magnetic tunnel junction  10  in which the sense layer is deposited on top of the tunnel barrier, and tunnel barrier is deposited on top of the storage layer. 
     An antiferromagnetic (AF) pinning layer  30  is disposed at an interface of the storage layer  12 . Note that in the reverse configuration the storage layer  12  can be disposed on top of the antiferromagnetic (AF) pinning layer  30 . The antiferromagnetic pinning layer  30  is an antiferromagnet and may include materials such as, e.g., IrMn, FeMn, PtMn, etc. The antiferromagnetic pinning layer  30  is composed of two magnetic sublattices. The two magnetic sublattices have opposite magnetic orientations (also referred to as magnetic moments), such that the net magnetic moment of the antiferromagnetic pinning layer  30  is zero. Since antiferromagnets have a small or no net magnetization, their spin orientation is only negligibly influenced by an externally applied magnetic field. 
     A contact structure  20  is disposed on top of the antiferromagnetic pinning layer  30  connecting the magnetic tunnel junction  10  (MRAM device  100 ) to a first wire  40 . The contact structure  20  may also be referred to as a non-magnetic cap. In the case of a reverse structure, the antiferromagnet is deposited on the top of the seed layer. 
     The magnetic tunnel junction  10  (particularly the ferromagnetic sense layer  16 ) is disposed on top of a seed layer  50 . However, in the case of a reverse structure, the antiferromagnet is deposited on the top of the seed layer. In  FIG. 1 , the seed layer  50  is the seed for growing the ferromagnetic sense layer  16 . Note that the seed layer  50  is optional, and in one implementation, the seed layer  50  may not be present. The seed layer  50 , when present, is disposed on top of a second wire  60 . When the seed layer  50  is not present, the ferromagnetic sense layer  16  is disposed on top of the second wire  60 . The seed layer  50  is disposed on and/or connected to the second wire  60 . The wires  40  and  60  connect the MRAM device  100  to a voltage source  70  (for generating the write bias current to heat the MRAM device  100 ) and ammeter  75  for measuring current. As such, the resistance of the MTJ  10  (i.e., MRAM device  100 ) can be determined. 
     The magnetic tunnel junction  10  comprises a tunnel barrier sandwiched by two ferromagnetic layers that can be used to store binary data. Indeed, the resistance of the magnetic tunnel junction  10  depends on the magnetic configuration (low resistance for parallel magnetizations, and high resistance for antiparallel magnetizations). The relative difference of resistance is called tunnel magnetoresistance (TMR). Due to the hysteresis of the ferromagnetic layers (i.e., the storage layer  12  and ferromagnetic sense layer  16 ), the magnetic tunnel junction  10  is used as a non-volatile cell. One ferromagnetic layer presents high anisotropy, and cannot be switched under the functioning conditions of the device. This layer is called the reference layer. The other ferromagnetic layer (i.e., the storage layer  12 ) is stable under the stand-by conditions, but can be switched by a combination of write magnetic field along with a write current sent through the junction. 
     In one reading scheme that improves the read margin of magnetic tunnel junction  10 , the ferromagnetic sense layer  16  replaces the reference layer.  FIGS. 2A and 2B  (generally referred to as  FIG. 2 ) illustrate a reading procedure of the self-referenced magnetic tunnel junction  10  in the thermally-assisted magnetoresistive random access memory (TAS-MRAM) device  100  according to an embodiment. 
     During reading in  FIG. 2A , the magnetic moment (shown by the solid arrow pointing to the right) of the ferromagnetic sense layer  16  is switched in one direction via current i (the “x” indicates that the current i is entering the plane of the page) applied in a field line  80  to generate a magnetic field shown by an open arrow pointing to the right. Note that the magnetic moment of the storage layer  12  continues pointing to the right and does not flip even when the magnetic field is applied via the field line  80 . This is because the write bias current is not applied by the voltage source  70  to de-pin (unpin) the storage layer  12  from the antiferromagnetic pinning layer  30 . 
     While on the other hand in  FIG. 2B , the magnetic moment (now shown by the solid arrow pointing to the left) of the ferromagnetic sense layer  16  is switched in the opposite direction via the current i (the dot “” indicates that the current i is exiting the plane of the page) applied in the field line  80  to generate the magnetic field shown by an open arrow pointing to the left. 
     The difference in resistance between the two reading steps (i.e., between the magnetic moments of the ferromagnetic sense layer  16  pointing to the right and then left) can be either positive or negative, depending on the direction of the magnetic moment of the storage layer  12 . The sign of the resistance change yields the stored information in the storage layer  12 . The storage layer  12  has an exchange bias pinned ferromagnetic layer that is pinned by the antiferromagnetic material of the antiferromagnetic pinning layer  30 . The exchange bias acting on the storage layer  12  can be overcome (in order to write to the storage layer  12 , i.e., flip its magnetic moment) by applying a current pulse (via the voltage source  70 ) through the stack (i.e., the MRAM device  100 ) that heats the junction (antiferromagnetic pinning layer  30 ) above its blocking temperature, in combination with the magnetic field (of the field line  80 ) that switches the now unpinned storage layer  12 . The (magnetic moment) storage layer  12  recovers to its new pinning direction during cooling when the write bias current is stopped. 
     Unlike embodiments but in a conventional MRAM device, this kind of stack lacks scalability. Indeed, due to the magnetostatic interactions between the sense and the storage layers, the sense layer reversal is biased. This shift increases when the pillar diameter decreases (width), so that the magnetic field required to switch the sense layer during reading becomes too high compared to the magnetic field that can be generated by field lines. Using standard materials, it is not possible to scale the magnetic tunnel junction diameter (width) below 250 nanometer (nm). 
     However, embodiments are able to scale the diameter of the magnetic tunnel junction  10  (including layers  20 ,  30 , and  50 ) below 250 nm and further below 100 nm (in diameter) by reducing the magnetization of the storage layer  12  and the ferromagnetic sense layer  16 . For example, the embodiments discussed herein address the problem of magnetostatic interactions between the ferromagnetic sense layer  16  and the storage layer  12  by using low magnetization ferromagnetic layers. Using low magnetization ferromagnetic layers in both the storage layer  12  and the ferromagnetic sense layer  16  reduces the strength/magnitude respectively of the magnetic moments (and stray fields) in the storage layer  12  and the ferromagnetic sense layer  16 . By reducing the magnetic moment in the storage layer  12 , the exchange bias field of the ferromagnetic sense layer  16  is reduced (which consequently reduces the required magnitude of the reading field (of the field line  80 ) that is needed). In order to reduce the magnitude of the writing field (of the field line  80 ), the magnetic moment of the ferromagnetic sense layer  16  and the magnetic moment in the ferromagnetic storage layer  12  are reduced which in turn reduces the magnetostatic interaction (of the layers  12  and  16 ) during the writing procedure. Reducing the magnetic moment of the ferromagnetic layers (i.e., the storage layer  12  and the ferromagnetic sense layer  16 ) is achieved by doping ferromagnetic materials with non-magnetic elements (discussed further in  FIG. 3 ). 
     Embodiments use ferromagnetic layers doped with non-magnetic elements (i.e., in the storage layer  12  and/or in the ferromagnetic sense layer  16 ) in the self-referenced stack (of the thermally-assisted magnetoresistive random access memory (TAS-MRAM) device  100 ) that present a magnetization reduction as compared to the standard ferromagnetic materials that do not have the reduced magnetization for thermally-assisted magnetoresistive random access memory (TAS-MRAM) device. 
     To make the storage layer  12  and the ferromagnetic sense layer  16  with reduced magnetization (i.e., reduced magnetic moments in each),  FIGS. 3A, 3B, and 3C  (generally referred to as  FIG. 3 ) illustrate doping the ferromagnetic layers of the storage layer  12  and the ferromagnetic sense layer  16  to according to an embodiment. Note that such a doped ferromagnetic layer can be made by sputtering from an alloyed target, by co-sputtering from several targets, and/or by making a multilayer that consists of alternating ferromagnetic and non-magnetic thin layers. 
     The doped ferromagnetic layers can be utilized in the ferromagnetic sense layer  16 , the storage layer  12 , or both. In order to reduce the magnetic moment of the sense or storage layer magnetization, non-magnetic materials can be used to dope the ferromagnetic layers. The ferromagnetic materials include a Co, Fe, and/or Ni based alloy, while the non-magnetic doping elements can be Ta, Ti, Hf, Cr, Nb, Mo, Zr, and/or any alloy containing one of these elements. The doped ferromagnetic layer of the storage layer  12  has a magnetization that is (typically) below 1000 emu/cm 3 , where emu is electromagnetic unit. The doped ferromagnetic layer of the ferromagnetic sense layer  16  also has a magnetization that is (typically) below 1000 emu/cm 3 . This reduced magnetization in both the storage layer  12  and ferromagnetic sense layer  16  reduces the magnetostatic interaction between the storage layer  12  and ferromagnetic sense layer  16  (i.e., the stray fields between layers  12  and  16 ), which means that less current in the field line  80  is needed to write (i.e., flip the magnetic moment of the storage layer  12 ) and read (i.e., flip the magnetic moment of the ferromagnetic sense layer  16 ) the device  100 . As noted above, reducing magnetization in the layers  12  and  16  to reduce stray fields is what permits the diameter of the magnetic tunnel junction  10  (including layers  20 ,  30 , and  50 ) to be below 250 nm and further below 100 nm. 
     The storage layer  12  is typically 1-2 nm (nanometer) thick, but the thickness of the storage layer  12  can be between 0.2 and 10 nm. The ferromagnetic sense layer  16  is typically 1-2 nm thick, but the thickness of the ferromagnetic sense layer  16  can be between 0.2 and 10 nm. However, when there is no doping of the ferromagnetic layer in the storage layer and ferromagnetic sense layer (i.e., their magnetization is not reduced), a conventional system has a storage layer with a conventional magnetization of 1000 to 1700 emu/cm 3  and the sense layer has a conventional magnetization of 1000 to 1700 emu/cm 3 . 
     The storage layer  12  is pinned with a Mn based antiferromagnet in antiferromagnetic pinning layer  30 , and the antiferromagnetic pinning layer  30  may be PtMn, IrMn, IrCrMn, and/or FeMn. 
       FIG. 3  illustrates three example techniques to deposit the doped ferromagnetic layers for the storage layer  12  and the ferromagnetic sense layer  16 , which are part of the stack in the thermally-assisted magnetoresistive random access memory device  100  discussed herein.  FIG. 3A  shows depositing an alloy by sputtering from a composite target A plus B made of the desired alloy to form the desired storage layer  12  and/or ferromagnetic sense layer  16  with reduced magnetization. The material A is the ferromagnetic material (i.e., magnetic material discussed herein) and the material B is the non-magnetic material (discussed herein). The materials A and B have been made into an alloy in  FIG. 3A  for deposition to form the desired storage layer  12  and/or ferromagnetic sense layer  16 . 
       FIG. 3B  shows depositing the alloy by co-sputtering from different targets A and B containing the desired magnetic and non-magnetic elements to form the desired storage layer  12  and/or ferromagnetic sense layer  16  with reduced magnetization. The target A is the ferromagnetic material (i.e., magnetic material) and the target B is the non-magnetic material. The doped ferromagnetic layers of the storage layer  12  and/or ferromagnetic sense layer  16  respectively are formed by co-sputtering from the separate target A and separate target B. 
       FIG. 3C  shows depositing a multilayered stack comprising ferromagnetic and non-magnetic bilayers with n repetitions, where n ranges from 1 to 20. Again, the target A is the ferromagnetic material (i.e., magnetic material) and the target B is the non-magnetic material. For example, sputtering from target A is performed to deposit a ferromagnetic layer on the storage layer  12 /ferromagnetic sense layer  16 , and then the storage layer  12 /ferromagnetic sense layer  16  is shifted under the target B in order to perform sputtering from target B to deposit the non-magnetic layer on top of the previously deposited ferromagnetic layer (i.e., thus forming the first bilayer). Next, the storage layer  12 /ferromagnetic sense layer  16  is shifted back under target A to deposit another ferromagnetic layer on top of the non-magnetic layer, and then the storage layer  12 /ferromagnetic sense layer  16  is shifted under the target B in order to deposit the non-magnetic layer on top of the ferromagnetic layer. This process repeats for n repetitions. The thickness of each deposited ferromagnetic layer of the ferromagnetic material (FM) is between 0.1 to 2 nm while thickness of the non-magnetic material (NM) is below 1 nm. 
     In  FIG. 3 , the doped ferromagnetic layers (i.e., ferromagnetic layers doped with non-magnetic material) can present a gradient of doping. This gradient can be made by varying the sputtering conditions (pressure, flow, power, etc.) during the doped layer deposition, and/or by varying the relative thicknesses of ferromagnetic layer and non-magnetic material layer in the multilayer case. In the multilayer case, the multilayer stack comprises FM 1 /NM 1 / . . . /FMn/NMn, where FMk and NMk denote ferromagnetic and non-magnetic materials of different nature and thickness. 
     The ferromagnetic layers&#39; doping is designed to be compatible with these characteristics: TMR ratio above 10%, MTJ resistance-area product below 100 Ohm·μm 2 , and exchange bias field of the storage layer above 200 Oe at room temperature. 
       FIG. 4A  is a chart  405  illustrating the reduction of magnetization (M s ) for the storage layer and/or sense layer using various non-magnetic dopant materials according to an embodiment. With reference to  FIGS. 4A and 4B , the doping is accomplished by multilayering (as shown in  FIG. 3C ). The chart  405  shows the magnetization saturation, M s , (emu/cm 3 ) on the y-axis. On the x-axis, the chart  405  shows the lamination thickness (nm) of each non-magnetic layer in the multilayer storage layer  12 . As can be seen, as the lamination thickness of each non-magnetic layer increases (which is similar to increasing the percentage of non-magnetic material in the storage layer  12  as compared to the ferromagnetic material), the magnetization decreases. When the laminate thickness of each respective non-magnetic layer reaches 0.20 nm, the magnetization drops to about 570 emu/cm 3  for Hf dopants, to about 310 emu/cm 3  for Ti dopants, and about 95 emu/cm 3  for Ta dopants. 
       FIG. 4B  is a chart  410  illustrating a reduction in stray fields (H bias ) generated by the storage layer  12  on ferromagnetic sense layer  16  where the reduction in stray fields is caused by the reduction in magnetization from the various non-magnetic dopant materials according to an embodiment. The chart  410  shows the stray fields, H bias , measured in oersted (Oe) on the y-axis and shows the laminate thickness of each non-magnetic layer in the multilayer storage layer  12 . As can be seen, as the lamination thickness of each non-magnetic layer increases (which similar to increasing the percentage of non-magnetic material in the storage layer  12  as compared to the ferromagnetic material), the stray fields decrease. 
     In one case, the field line  80  may be a magnetic generating device  80  that is a combination of an (insulated) metal wire connected to a voltage source to generate the magnetic field as understood by one skilled in the art. Also, the magnetic generating device  80  may be a CMOS (complementary metal oxide semiconductor) circuit that generates the magnetic field as understood by one skilled in the art. 
       FIG. 5  illustrates a method  500  of reduced power for reading and writing the thermally assisted magnetoresistive random access memory device  100  according to an embodiment. Reference can be made to  FIGS. 1-4  along with  FIG. 10  discussed below. 
     At block  505 , the tunnel barrier  14  is sandwiched between the ferromagnetic sense layer  16  and the ferromagnetic storage layer  12 , in which the ferromagnetic sense layer  16 , the tunnel barrier  14 , and the ferromagnetic storage layer  12  together form the magnetic tunnel junction  10 . 
     At block  510 , the antiferromagnetic pinning layer  30  is disposed at an interface of the ferromagnetic storage layer  12 , where the antiferromagnetic pinning layer  30  pins the magnetic moment of the ferromagnetic storage layer  12  until heating at the writing temperature is applied. The voltage source  70  applies current that causes heating in the tunnel barrier  14  to unpin the ferromagnetic storage layer  12  from the antiferromagnetic pinning layer  30 . A write magnetic field is applied via the field line  80  to write (i.e., flip the magnetic moment) the ferromagnetic storage layer  12  when the ferromagnetic storage layer  12  is unpinned from the antiferromagnetic pinning layer  30 . 
     At block  515 , the ferromagnetic storage layer  12  is formed to include non-magnetic material (along with the ferromagnetic material) that reduces a storage layer magnetization (i.e., reduces the magnetic moment and stray fields) of the ferromagnetic storage layer  12  as compared to not having the non-magnetic material present in ferromagnetic storage layer  12 . 
     At block  520 , the ferromagnetic sense layer  16  is formed to include the non-magnetic material (along with the ferromagnetic material) that reduces the sense layer magnetization (i.e., reduces the magnetic moment and stray fields) of the ferromagnetic sense layer as compared to not having the non-magnetic material present in the ferromagnetic sense layer  16 . 
     At block  525 , the magnetostatic interaction between the ferromagnetic storage layer  12  and the ferromagnetic sense layer  16  are reduced by a reduction in the storage layer magnetization of the ferromagnetic storage layer  12  and a reduction in the sense layer magnetization of the ferromagnetic sense layer  16 , resulting in less power to read and write to the magnetic tunnel junction  10 . As such, the reduction in storage layer magnetization and sense layer magnetization require less power because a reduced magnitude write magnetic field and/or read magnetic field is required for the field line  80 , which means less voltage and current are needed to generate the write/read magnetic field. Due to the reduction of magnetostatic interaction, the device  100  can be read and/or written with magnetic fields below 200 Oe, while it requires more than 250 Oe to read or write a conventional device (i.e. without the reduction of storage layer and sense layer magnetizations). 
     The ferromagnetic storage layer  12  and the ferromagnetic sense layer  16  respectively include dopants of the non-magnetic material (along with their ferromagnetic material) as discussed in  FIG. 3 . 
     The magnetic tunnel junction  10  and the antiferromagnetic pinning layer  30  to have a diameter less than 250 nanometers based upon the reduction in both the storage layer magnetization of the ferromagnetic storage layer  12  and the sense layer magnetization of the ferromagnetic sense layer  16 . The reduction in both the storage layer magnetization of the ferromagnetic storage layer  12  and the sense layer magnetization of the ferromagnetic sense layer  16  reduce the magnetostatic interaction in order to allow reading and writing to the magnetic tunnel junction  10  that is less than 250 nanometers in diameter. Without the reduction in magnetization of layers  12  and  16 , at a diameter less than 250 nanometers the stray magnetic fields from both the ferromagnetic storage layer  12  and the ferromagnetic sense layer  16  become so large (and the required magnitude of the write and read magnetic fields generated by the field line  80  would have to be extremely large) that it is not feasible to have a diameter less than 250 nanometers in a conventional system. 
     As an example, the magnetic tunnel junction  10  (i.e., layers  12 ,  14 , and  16 ) and the antiferromagnetic pinning layer  30  are formed to have a diameter that is about 100 nanometers based upon the reduction in both the storage layer magnetization of the ferromagnetic storage layer  12  and the sense layer magnetization of the ferromagnetic sense layer  16 . The reduction in both the storage layer magnetization of the ferromagnetic storage layer  12  and the sense layer magnetization of the ferromagnetic sense layer  16  reduce the stray magnetic fields in order to allow reading and writing to the magnetic tunnel junction that is about 100 nanometers in diameter. 
     The ferromagnetic storage layer  12  is formed by sputtering, chemical vapor deposition, and/or physical vapor deposition applied to a composite material having both ferromagnetic material and the non-magnetic material (target A plus B combined) as shown in  FIG. 3A . The ferromagnetic storage layer  12  is formed from simultaneously co-sputtering a ferromagnetic material (target A) and the non-magnetic material (target B) as shown in  FIG. 3B . As shown in  FIG. 3C , the ferromagnetic storage layer  12  is formed of multilayers (i.e., the gray shaded layers and non-shaded layers) of the ferromagnetic material (target A) and the non-magnetic material (target B). 
     The ferromagnetic sense layer  16  is formed by sputtering, chemical vapor deposition, and/or physical vapor deposition applied to a composite material (targets A and B combined) having both ferromagnetic material and the non-magnetic material as shown in  FIG. 3A . The ferromagnetic sense layer  16  is formed from simultaneously co-sputtering a ferromagnetic material (target A) and the non-magnetic material (target B). The ferromagnetic sense layer  16  is formed of multilayers (i.e., the gray shaded layers and non-shaded layers) of the ferromagnetic material (target A) and the non-magnetic material (target B) in  FIG. 3C . 
     Ferromagnetic material is included in the first ferromagnetic storage layer, in the second ferromagnetic storage layer, and in the ferromagnetic sense layer. The ferromagnetic material includes Co, Fe, Ni and/or any alloy containing Co, Fe, and/or Ni. The non-magnetic material includes Ta, Ti, Hf, Cr, Nb, Mo, Zr, and/or any alloy containing Ta, Ti, Hf, Cr, Nb, Mo, and/or Zr. The non-magnetic material has a concentration between 1 and 40 atomic percent. 
     Now turning to  FIG. 6 , a cross-sectional view is illustrated of a structure for a thermally-assisted magnetoresistive random access memory (TAS-MRAM) device  600  according to an embodiment.  FIG. 6  is similar  FIG. 1  except that  FIG. 6  shows the storage layer  12  as a synthetic antiferromagnet (SAF) storage layer  12 . 
     The structure of the MRAM device  600  includes a magnetic tunnel junction (MTJ)  10 . The magnetic tunnel junction  10  may include the ferromagnetic sense layer  16  with the non-magnetic tunnel barrier  14  disposed at an interface of the ferromagnetic sense layer  16 . The magnetic tunnel junction  10  also includes the synthetic antiferromagnet (SAF) storage layer  12  disposed at an interface of the non-magnetic tunnel barrier  14 . The non-magnetic tunnel barrier  14  may be a semiconductor or insulator. Although not shown, it is contemplated that the reverse configuration may also be provided for the magnetic tunnel junction  10  in which the sense layer  16  is deposited on top of the tunnel barrier  14 , and the tunnel barrier  14  is deposited on top of the storage layer  12 . 
     According to this embodiment of  FIG. 6  in contrast to  FIG. 1 , the storage layer is the synthetic antiferromagnet storage layer  12 , and the synthetic antiferromagnet storage layer  12  includes a first ferromagnetic layer  11  (also referred to as F 1 ) disposed at an interface of the tunnel barrier layer  14 . A non-magnetic coupling layer/material  15  is disposed at an interface of the ferromagnetic layer  11 . A second ferromagnetic layer  13  (also referred to as F 2 ) is disposed at an interface of the non-magnetic coupling layer  15 . The second ferromagnetic layer  13  (F 2 ), the non-magnetic coupling layer  15 , and the first ferromagnetic layer  11  (F 1 ) together form the synthetic antiferromagnet storage layer  12 . The non-magnetic coupling layer  15  may be a Ru spacer. For a given Ru thickness as understood by one skilled in the art, the RKKY coupling through the Ru spacer is antiferromagnetic. Thus, the net magnetization of the synthetic antiferromagnet storage layer  12  is the difference of the F 1  and F 2  magnetic moments, which is the difference between the magnetic moment of second ferromagnetic layer  13  (F 2 ) and the first ferromagnetic layer  11  (F 1 ). The non-magnetic coupling layer  15  causes the magnetic moment of the second ferromagnetic layer  13  to be opposite to the magnetic moment of the first ferromagnetic layer  11 . The magnetic moments of the second ferromagnetic layer  13  and the first ferromagnetic layer  11  both flip together. The magnetic moments are shown by arrows. 
     The antiferromagnetic (AF) pinning layer  30  is disposed at an interface of the synthetic antiferromagnet storage layer  12  and holds the magnetic moments of the second ferromagnetic layer  13  and the first ferromagnetic layer  11  in place until heating is applied by a write bias current. Particularly, antiferromagnetic (AF) pinning layer  30  is disposed at an interface of the second ferromagnetic layer  13  (F 1 ). The antiferromagnetic pinning layer  30  is an antiferromagnet and may include materials such as, e.g., IrMn, FeMn, PtMn, etc. A discussed above, the antiferromagnetic pinning layer  30  is composed of two magnetic sublattices, which have opposite magnetic orientations (also referred to as magnetic moments), such that the net magnetic moment of the antiferromagnetic pinning layer  30  is zero. Since antiferromagnets have a small or no net magnetization, their spin orientation is only negligibly influenced by an externally applied magnetic field. 
     The contact structure  20  (non-magnetic cap) is disposed on top of the antiferromagnetic pinning layer  30  connecting the magnetic tunnel junction  10  (MRAM device  600 ) to the first wire  40 . In the case of a reverse structure, the top contact structure  20  is deposited on top of the sense layer  16 . 
     As noted earlier, the magnetic tunnel junction  10  (particularly the ferromagnetic sense layer  16 ) is disposed on top of the seed layer  50 . However, in the reverse structure, the seed layer is disposed/lying below the antiferromagnet. In  FIG. 6 , the seed layer  50  is the seed for growing the ferromagnetic sense layer  16 . Note that the seed layer  50  is optional, and in one implementation, the seed layer  50  may not be present. The seed layer  50 , when present, is disposed on top of the second wire  60 . When the seed layer  50  is not present, the ferromagnetic sense layer  16  is disposed on top of the second wire  60 . The seed layer  50  is disposed on and/or connected to the second wire  60 . Note, in the case of a reverse structure, the second wire  60  is disposed below the antiferromagnet  12 . The wires  40  and  60  connect the MRAM device  600  to the voltage source  70  (for generating the write bias current to heat the MRAM device  600 ) and ammeter  75  for measuring current. As such, the resistance of the MTJ  10  (i.e., MRAM device  600 ) can be determined. 
     The first ferromagnetic layer  11  of the magnetic tunnel junction  10  can be used to store binary data. Indeed, the resistance of the magnetic tunnel junction  10  depends on the magnetic configuration (low resistance for parallel magnetizations, and high resistance for antiparallel magnetizations). The relative difference of resistance between the first ferromagnetic layer  11  in the synthetic antiferromagnet storage layer  12  and the ferromagnetic sense layer  16  is called tunnel magnetoresistance (TMR). Due to the hysteresis of the ferromagnetic layers (i.e., the synthetic antiferromagnet storage layer  12  and ferromagnetic sense layer  16 ), the magnetic tunnel junction  10  is used as a non-volatile cell. The reference layer presents high anisotropy, and cannot be switched under the functioning conditions of the device. The ferromagnetic layers  11  and  13  of the synthetic antiferromagnet storage layer  12  are stable under the stand-by conditions, but can be switched by an applied write/read magnetic field along with a write current sent through the junction. 
     The synthetic antiferromagnet storage layer  12  has exchange bias pinned ferromagnetic layers  11  and  13  which are pinned by the antiferromagnetic material of the antiferromagnetic pinning layer  30 . The exchange bias acting on the synthetic antiferromagnet storage layer  12  can be overcome (in order to write to the synthetic antiferromagnet storage layer  12 , i.e., flip the respective magnetic moments of ferromagnetic layers  11  and  13 ) by applying a current pulse (via the voltage source  70 ) through the stack (i.e., the MRAM device  600 ) that heats the junction (antiferromagnetic pinning layer  30 ) above its blocking temperature, in combination with the magnetic field (of the field line  80 ) that switches the now unpinned SAF storage layer  12 . The magnetic moment of the second ferromagnetic layer  13  and first ferromagnetic layer  11  of the synthetic antiferromagnet storage layer  12  recover to their new pinning direction during cooling. 
     As an example of writing to the MRAM device  100 , a write bias current (i) is generated from the voltage source  70 , which travels through the MRAM device  600 . Because of its high resistance, the tunnel barrier  14  heats up (as a result of Joule heating) when the write bias current flows through the tunnel barrier  14 . The heat unpins the synthetic antiferromagnet storage layer  12  from the antiferromagnetic pinning layer  30 . Since the synthetic antiferromagnet storage layer  12  is unpinned from the antiferromagnetic pinning layer  30 , a magnetic write field is generated by the field line  80  to flip the magnetic moment of the ferromagnetic sense layer  16  and the magnetostatic interaction (i.e., stray fields) acting on the storage layer  12  flips the magnetic moment of the first ferromagnetic layer  11  (of the SAF storage layer  12 ). Accordingly, because of the non-magnetic coupling layer  15 , the first ferromagnetic layer  11  reversal flips the second ferromagnetic layer  13  to have a magnetic orientation opposite of the magnetic orientation of the first ferromagnetic layer  11  (all while the heating is occurring). The write bias current is turned off to remove the heating. Accordingly, the magnetic moment of the first ferromagnetic layer  11  cools in place with its new direction, and the magnetic moment of the second ferromagnetic layer  13  cools in place with its new direction (opposite the first ferromagnetic layer  11 ). This is the process of storing data in the synthetic antiferromagnet storage layer  12 . 
       FIGS. 7A and 7B  illustrate a reading procedure of the self-referenced magnetic tunnel junction  10  in the thermally-assisted magnetoresistive random access memory (TAS-MRAM) device  600  according to an embodiment. 
     During reading in  FIG. 7A , the magnetic moment (shown by the solid arrow pointing to the right) of the ferromagnetic sense layer  16  is switched in one direction via bias current i (the “x” indicates that the current i is entering the plane of the page) applied in the field line  80  to generate a magnetic field shown by an open arrow pointing to the right. Note that the magnetic moment of the synthetic antiferromagnet storage layer  12  continues pointing in the same direction (i.e., the first ferromagnetic layer  11  continues pointing to the right while the second ferromagnetic layer  13  continues pointing to the left) and does not flip even when the magnetic field is applied via the field line  80 . This is because the write bias current (i.e., heating) is not applied by the voltage source  70  to de-pin (unpin) the synthetic antiferromagnet storage layer  12  from the antiferromagnetic pinning layer  30 . 
     While on the other hand in  FIG. 7B , the magnetic moment (now shown by the solid arrow pointing to the left) of the ferromagnetic sense layer  16  is switched in the opposite direction via the current i (the dot “” indicates that the current i is exiting the plane of the page) applied in the field line  80  to generate the magnetic field shown by an open arrow pointing to the left. The write bias current is also not applied in  FIG. 2B . 
     The difference in resistance between the two reading steps (i.e., between the magnetic moments of the ferromagnetic sense layer  16  pointing to the right and then left) can be either positive or negative, depending on the direction of the magnetic moments of the synthetic antiferromagnet storage layer  12 . The sign of the resistance change yields the stored information in the first ferromagnetic layer  11  of the synthetic antiferromagnet storage layer  12 . Note that the resistance of the MRAM device  600  is based on whether the first ferromagnetic layer  11  (F 1 ) is parallel or antiparallel to the ferromagnetic sense layer  16 . For example, when the magnetic moments of the first ferromagnetic layer  11  (of the SAF storage layer  12 ) and ferromagnetic sense layer  16  are parallel (i.e., pointing in the same direction) as shown in  FIG. 7A , the resistance is low for the magnetic tunnel junction  10  (which represents a logical “1”). On the other hand, when the magnetic moments of the first ferromagnetic layer  11  (of the SAF storage layer  12 ) and ferromagnetic sense layer  16  are antiparallel (i.e., pointing in the opposite directions) as shown in  FIG. 7B , the resistance is high for the magnetic tunnel junction  10  (which represents a logical “0”). 
     Normally, in a conventional stack, one would need to make the layers  11 ,  13 , and  16  thin in order to tune the stray fields of the ferromagnetic sense layer  16  which flip the moment of the first ferromagnetic layer  11 . The stray fields of the magnetization of the ferromagnetic sense layer  16  couple to the magnetization of the first ferromagnetic layer  11 . However, embodiments use ferromagnetic layers doped with non-magnetic elements (i.e., in first and second ferromagnetic layers  11  and  13 , in the storage layer  12 , and in the ferromagnetic sense layer  16 ) in the self-referenced stack (of the thermally-assisted magnetoresistive random access memory (TAS-MRAM) device  600 ) that present a magnetization reduction as compared to the standard ferromagnetic materials that do not have the reduced magnetization for thermally-assisted magnetoresistive random access memory (TAS-MRAM) device. 
     By having the reduced magnetization, the layers  11 ,  13 , and  16  can be made thicker than in the conventional system without the reduced magnetization. In the conventional system without doping to reduce magnetization, the thickness of the ferromagnetic sense layer  16  is typically 20-30 Angstroms (Å), the thickness of the second ferromagnetic layer  13  is typically 15-30 Å, and the thickness of first ferromagnetic layer  11  is typically 15-30 Å. As understood by one skilled in the art, the accuracy of the deposition of the thin layers  11 ,  13 , and  16  in the conventional system is more difficult than for thicker layers in embodiments. 
     According to embodiments with the reduced magnetization, the thickness of the ferromagnetic sense layer  16  may be 10-60 (Å), e.g., the ferromagnetic sense layer  16  may be (about) 10 . . . 35, 40, 45, 50, 55, 60 Å thick (or more). With the reduced magnetization, the thickness of the second ferromagnetic layer  13  may be 10-60 Å, e.g., the second ferromagnetic layer  13  may be (about) 10 . . . 35, 40, 50, 55, 60 Å thick (or more). Also, with the reduced magnetization, the thickness of first ferromagnetic layer  11  may be 10-60 Å, e.g., the first ferromagnetic layer  11  may be (about) 35, 40, 50, 55, 60 Å thick (or more). Additionally, the accuracy of deposition is increased when depositing material at a thickness of 60 Å for the ferromagnetic sense layer  16 , 60 Å for the second ferromagnetic layer  13 , and 60 Å for the first ferromagnetic layer  11  as compared to the thinner deposition layers in conventional systems (discussed herein). 
     Also, if one tried to make the thick layers  11 ,  13 , and  16  (as discussed above for embodiments for the thicker deposition of materials) while using the conventional system without the reduced magnetizations, the stray magnetic dispersion among the pillars for layers  11 ,  13 , and  16  would be too large. For the conventional system, assuming a thickness dispersion of about 3% and a magnetization above 1200 emu/cm 3  makes the stray field dispersion among pillars too large when the first and/or second ferromagnetic thickness exceeds 30 Å (in thickness). Using ferromagnetic layers with reduced magnetization allows one to make a thicker layer, proportionally to the magnetization reduction, (since the magnetic moment is the product of the magnetization with the magnetic volume) according to embodiments. For example, a reduction by a factor of two of the magnetization of the first and second layers allows making up to 60 Å thick first and second ferromagnetic layers. 
     To make the second ferromagnetic layer  13  and first ferromagnetic layer  11  in synthetic antiferromagnet storage layer  12  and the ferromagnetic sense layer  16  with reduced magnetizations (i.e., reduced magnetic moments in each),  FIGS. 8A, 8B , and  8 C (generally referred to as  FIG. 8 ) illustrate doping the ferromagnetic layers  11  and  13  of the synthetic antiferromagnetic storage layer  12  and the ferromagnetic sense layer  16  to reduce magnetization according to an embodiment. Note that such a doped ferromagnetic layer can be made by sputtering from an alloyed target, by co-sputtering from several targets, and/or by making a multilayer that consists of alternating ferromagnetic and non-magnetic thin layers. Also note that the description of  FIG. 8  applies separately to each of the layers  11 ,  13 , and  16 . Some details in  FIG. 8  may be similar to  FIG. 3 . 
     In order to reduce the magnetic moment of the second ferromagnetic layer (F 2 ) magnetization, first ferromagnetic layer (F 1 ) magnetization, and sense layer magnetization, non-magnetic materials can be used to dope the ferromagnetic layers. As discussed above, the ferromagnetic materials include a Co, Fe, and/or Ni based alloy, while the non-magnetic doping elements can be Ta, Ti, Hf, Cr, Nb, Mo, Zr, and/or any alloy containing one of these elements. The first ferromagnetic layer  11  has a doped ferromagnetic layer in order to have a magnetization that is (typically) below 1000 emu/cm 3 , where emu is electromagnetic unit. Likewise, the second ferromagnetic layer  13  has the doped ferromagnetic layer in order to have a magnetization that is (typically) below 1000 emu/cm 3 . The doped ferromagnetic layer of the ferromagnetic sense layer  16  also has a magnetization that is (typically) below 1000 emu/cm 3 . This reduced magnetization in the ferromagnetic layers  11  and  13  in the synthetic antiferromagnet storage layer  12  and ferromagnetic sense layer  16  reduces the magnetostatic interaction between the first ferromagnetic layers  11  and the ferromagnetic sense layer  16  and between the second ferromagnetic layer  13  and the ferromagnetic sense layer  16 . As noted above, reducing magnetization in the layers  11 ,  13 , and  16  (to reduce the stray fields) is what permits a proper write field dispersion among the pillars in the memory device in embodiments. 
     When there is no doping of the ferromagnetic layers in the SAF storage layer and ferromagnetic sense layer (i.e., their magnetization is not reduced), a conventional system has a first ferromagnetic layer (F 1 ) and second ferromagnetic layer each with a conventional magnetization of 1000 to 1700 emu/cm 3 . A conventional system has a sense layer with a conventional magnetization of 1000 to 1700 emu/cm 3    
     The (magnetic moments of F 1  and F 2 ) synthetic antiferromagnetic storage layer  12  is pinned with a Mn based antiferromagnet in antiferromagnetic pinning layer  30 , and the antiferromagnetic pinning layer  30  may be PtMn, IrMn, IrCrMn, and/or FeMn. 
       FIG. 8  illustrates three example techniques to deposit the doped ferromagnetic layers for the first ferromagnetic layer  11 , the second ferromagnetic layer  13 , and/or the ferromagnetic sense layer  16 , which are part of the stack in the thermally-assisted magnetoresistive random access memory device  600  discussed herein.  FIG. 8A  shows depositing an alloy by sputtering from a composite target A plus B made of the desired alloy to form the desired storage layer  12  and/or ferromagnetic sense layer  16  with reduced magnetization. The material A is the ferromagnetic material (i.e., magnetic material discussed herein) and the target B is the non-magnetic material (discussed herein). The targets A plus B have been made into an alloy in  FIG. 8A  for deposition to form the desired the first ferromagnetic layer  11 , the second ferromagnetic layer  13 , and/or ferromagnetic sense layer  16 . 
       FIG. 8B  shows depositing the alloy by co-sputtering from different targets A and B containing the desired magnetic and non-magnetic elements to form the desired the first ferromagnetic layer  11 , the second ferromagnetic layer  13 , and/or ferromagnetic sense layer  16  with reduced magnetization. The target A is the ferromagnetic material (i.e., magnetic material) and the target B is the non-magnetic material. The doped ferromagnetic layers of the first ferromagnetic layer  11 , the second ferromagnetic layer  13 , and/or ferromagnetic sense layer  16  respectively are formed by co-sputtering from the separate target A and separate target B. 
       FIG. 8C  shows depositing a multilayered stack comprising ferromagnetic and non-magnetic bilayers with n repetitions, where n ranges from 1 to 20. Again, the target A is the ferromagnetic material (i.e., magnetic material) and the target B is the non-magnetic material. For example, sputtering from target A is performed to deposit a ferromagnetic layer of the first ferromagnetic layer  11 , the second ferromagnetic layer  13 , and/or ferromagnetic sense layer  16 , and then layer  11 ,  13 , and/or  16  is shifted under the target B in order to perform sputtering from target B to deposit the non-magnetic layer on top of the previously deposited ferromagnetic layer (i.e., thus forming the first bilayer). Next, the layer  11 ,  13 , and/or  16  is shifted back under target A to deposit another ferromagnetic layer on top of the non-magnetic layer, and then the layer  11 ,  13 , and/or  16  is shifted under the target B in order to deposit the non-magnetic layer on top of the ferromagnetic layer. This process repeats for n repetitions. The thickness of each deposited ferromagnetic layer of the ferromagnetic material (FM) is between 0.1 to 2 nm while thickness of the non-magnetic material (NM) is below 1 nm. 
     In  FIG. 8 , the doped ferromagnetic layers (i.e., ferromagnetic layers doped with non-magnetic material) can present a gradient of doping. This gradient can be made by varying the sputtering conditions (pressure, flow, power, etc.) during the doped layer deposition, and/or by varying the relative thicknesses of ferromagnetic layer and non-magnetic material layer in the multilayer case. In the multilayer case, the multilayer stack comprises FM 1 /NM 1 / . . . /FMn/NMn, where FMk and NMk denote ferromagnetic and non-magnetic materials of different nature and thickness. 
     The ferromagnetic layers&#39; doping is designed to be compatible with these characteristics: TMR ratio above 10%, MTJ resistance-area product below 100 Ohm·μm 2 , and exchange bias field of the second ferromagnetic layer of the storage layer above 200 Oe at room temperature. 
       FIGS. 9A and 9B  illustrate a method  900  of reduced power for reading and writing the thermally assisted magnetoresistive random access memory device  600  according to an embodiment.  FIGS. 9A and 9B  may generally be referred to as  FIG. 9 . Reference can be made to  FIGS. 4 and 6-8  along with  FIG. 10  discussed below. 
     At block  905 , the tunnel barrier  14  is sandwiched between the ferromagnetic sense layer  16  and the synthetic antiferromagnet storage layer  12 . 
     At block  910 , the synthetic antiferromagnet storage layer  12  is disposed at an interface of the tunnel barrier  14 , where the synthetic antiferromagnet storage layer  12  includes the first ferromagnetic storage layer  11  disposed at an interface of the tunnel barrier  14 , the non-magnetic coupling layer  15  disposed at the other interface of the first ferromagnetic storage layer  11 , and the second ferromagnetic storage layer  13  disposed at the other interface of the non-magnetic coupling layer  15 . 
     At block  915 , the antiferromagnetic pinning layer  30  is disposed at an interface of the ferromagnetic storage layer  13  of the synthetic antiferromagnet storage layer  12 . The antiferromagnetic pinning layer  30  pins the (opposite pointing) magnetic moments of the ferromagnetic storage layer  11  and  13  until heating is applied. The voltage source  70  applies current that causes heating in the tunnel barrier  14  to unpin the ferromagnetic storage layer  11  and  13  from the antiferromagnetic pinning layer  30 . A write magnetic field is applied via the field line  80  to write (i.e., flip the magnetic moment) the first ferromagnetic storage layer  11  via stray fields from the ferromagnetic sense layer  16  when the first ferromagnetic storage layer  11  is unpinned from the antiferromagnetic pinning layer  30 . As such, the non-magnetic coupling layer  15  then flips the second ferromagnetic storage layer  13  accordingly to maintain a magnetic moment opposite the first ferromagnetic storage layer  11 . 
     At block  920 , the first ferromagnetic storage layer  11 , the second ferromagnetic storage layer  13 , and the ferromagnetic sense layer  16  are each formed of ferromagnetic material (which may be the same or different ferromagnetic material) (along with the ferromagnetic material), in which a non-magnetic material reduces a first storage layer magnetization (i.e., reduces the magnetic moment and stray fields dispersions) of the first ferromagnetic storage layer  11 , reduces a second storage layer magnetization (i.e., reduces the magnetic moment and stray fields dispersions) of the second ferromagnetic storage layer  13 , and reduces a sense layer magnetization (i.e., reduces the magnetic moment and stray fields dispersions) of the ferromagnetic sense layer  16  as respectively compared to not having the non-magnetic material present in layers  11 ,  13 ,  16 . 
     At block  925 , the magnetostatic interaction between the first ferromagnetic storage layer  11 , the second ferromagnetic storage layer  13 , and the ferromagnetic sense layer  16  are reduced by a reduction in the first storage layer magnetization of the ferromagnetic storage layer  11 , a reduction in the second storage layer magnetization of the ferromagnetic storage layer  13 , and a reduction in the sense layer magnetization of the ferromagnetic sense layer  16 , resulting in less stray fields dispersions among pillars and thus in less power to read and write to the SAF storage layer  12  in the magnetic tunnel junction  10 . As such, the reduction in first storage layer magnetization, second storage magnetization, and sense layer magnetization require less power because a reduced magnitude write magnetic field and/or read magnetic field is needed for the field line  80 , which means less voltage and current are needed to generate the write/read magnetic field. As a result of the reduction of magnetostatic interaction dispersion, the device  600  can be read or written with magnetic fields below 200 Oe, while it requires more than 250 Oe to read or write a conventional device (i.e. without the reduction of storage layer and sense layer magnetization). 
     By having reduced magnetization, a greater thickness is permitted (or functions) for the first ferromagnetic storage layer, the second ferromagnetic storage layer, and the ferromagnetic sense layer as compared to not having the non-magnetic material at block  930 . 
     The first ferromagnetic storage layer  11 , second ferromagnetic storage layer  13 , and the ferromagnetic sense layer  16  respectively include dopants of the non-magnetic material (along with their ferromagnetic material) as discussed in  FIG. 8 . 
     The antiferromagnetic pinning layer, the synthetic antiferromagnet storage layer, the tunnel barrier, and the ferromagnetic sense layer each have a diameter less than 100 nanometers based upon the reduction in the first storage layer magnetization of the first ferromagnetic storage layer  11 , second storage layer magnetization of the second ferromagnetic storage layer  13 , and the sense layer magnetization of the ferromagnetic sense layer  16 . The reduction in the first storage layer magnetization of the first ferromagnetic storage layer  11 , second storage layer magnetization of the second ferromagnetic storage layer  13 , and the sense layer magnetization of the ferromagnetic sense layer  16  reduce the stray magnetic field dispersions in order to allow reading and writing to the SAF storage layer  12  that is less than 100 nanometers in diameter. Without the reduction in magnetization of layers  11 ,  13 , and  16 , at a diameter less than 100 nanometers the stray magnetic fields dispersion from layers  11 ,  13 , and  16  become so large (and the required magnitude of the write and read magnetic fields generated by the field line  80  would have to be extremely large) that it is not feasible to have a diameter less than 100 nanometers in a conventional system. 
     Also, the antiferromagnetic pinning layer  30 , the synthetic antiferromagnet storage layer  12 , the tunnel barrier  14 , and the ferromagnetic sense layer  16  may each have a diameter that is about 100 nanometers based upon the reduction in the first storage layer magnetization of the first ferromagnetic storage layer, the reduction in the second storage layer magnetization of the second ferromagnetic storage layer, and the reduction in the sense layer magnetization of the ferromagnetic sense layer. 
     The first ferromagnetic storage layer, the second ferromagnetic storage layer, and the ferromagnetic sense layer are formed by sputtering, chemical vapor deposition, and/or physical vapor deposition applied to a composite material having both ferromagnetic material and the non-magnetic material (target A and B combined) as shown in  FIG. 8A . The first ferromagnetic storage layer, the second ferromagnetic storage layer, and the ferromagnetic sense layer are formed from simultaneously co-sputtering a ferromagnetic material (target A) and the non-magnetic material (target B) as shown in  FIG. 8B . As shown in  FIG. 8C , the first ferromagnetic storage layer, the second ferromagnetic storage layer, and the ferromagnetic sense layer are formed of multilayers (i.e., the gray shaded layers and non-shaded layers) of the ferromagnetic material (target A) and the non-magnetic material (target B). 
     A thickness of the first ferromagnetic storage layer is 10-60 Angstroms (Å), a thickness of the second ferromagnetic storage layer is 10-60 Å, and a thickness of the ferromagnetic sense layer is 10-60 Å. 
     The ferromagnetic material is included in the first ferromagnetic storage layer, in the second ferromagnetic storage layer, and in the ferromagnetic sense layer. The ferromagnetic material includes Co, Fe, Ni and/or any alloy containing Co, Fe, and Ni. The non-magnetic material includes Ta, Ti, Hf, Cr, Nb, Mo, Zr, and/or any alloy containing Ta, Ti, Hf, Cr, Nb, Mo, Zr. The non-magnetic material has a concentration between 1 and 40 atomic percent. 
       FIG. 10  illustrates an example of a computer  1000  which includes the MRAM devices  100 ,  600  having the reduction in magnetization in layers  12  and  16  (along with the reduction in power requirements for the read and write magnetic fields discussed herein). The computer  1000  has capabilities that may be included in exemplary embodiments. The MRAM devices  100 ,  600  may be constructed in a memory array, e.g., multiple MRAM devices  100 ,  600  connected together as understood by one skilled in the art (for reading and writing data), and the memory array may be part of the computer memory  1020  discussed herein. Various methods, procedures, circuits, elements, and techniques discussed herein may also incorporate and/or utilize the capabilities of the computer  1000 . One or more of the capabilities of the computer  1000  may be utilized to implement, to incorporate, to connect to, and/or to support any element discussed herein (as understood by one skilled in the art) in  FIGS. 1-9 . 
     Generally, in terms of hardware architecture, the computer  1000  may include one or more processors  1010 , computer readable storage memory  1020 , and one or more input and/or output (I/O) devices  1070  that are communicatively coupled via a local interface (not shown). The local interface can be, for example but not limited to, one or more buses or other wired or wireless connections, as is known in the art. The local interface may have additional elements, such as controllers, buffers (caches), drivers, repeaters, and receivers, to enable communications. Further, the local interface may include address, control, and/or data connections to enable appropriate communications among the aforementioned components. 
     The processor  1010  is a hardware device for executing software that can be stored in the memory  1020 . The processor  1010  can be virtually any custom made or commercially available processor, a central processing unit (CPU), a data signal processor (DSP), or an auxiliary processor among several processors associated with the computer  1000 , and the processor  1010  may be a semiconductor based microprocessor (in the form of a microchip) or a microprocessor. 
     The computer readable memory  1020  can include any one or combination of volatile memory elements (e.g., random access memory (RAM), such as dynamic random access memory (DRAM), static random access memory (SRAM), etc.) and nonvolatile memory elements (e.g., ROM, erasable programmable read only memory (EPROM), electronically erasable programmable read only memory (EEPROM), programmable read only memory (PROM), tape, compact disc read only memory (CD-ROM), disk, diskette, cartridge, cassette or the like, etc.). Moreover, the memory  1020  may incorporate electronic, magnetic, optical, and/or other types of storage media. Note that the memory  1020  can have a distributed architecture, where various components are situated remote from one another, but can be accessed by the processor  1010 . 
     The software in the computer readable memory  1020  may include one or more separate programs, each of which comprises an ordered listing of executable instructions for implementing logical functions. The software in the memory  1020  includes a suitable operating system (O/S)  1050 , compiler  1040 , source code  1030 , and one or more applications  1060  of the exemplary embodiments. As illustrated, the application  1060  comprises numerous functional components for implementing the features, processes, methods, functions, and operations of the exemplary embodiments. The application  1060  of the computer  1000  may represent numerous applications, agents, software components, modules, interfaces, controllers, etc., as discussed herein but the application  1060  is not meant to be a limitation. 
     The operating system  1050  may control the execution of other computer programs, and provides scheduling, input-output control, file and data management, memory management, and communication control and related services. 
     The application  1060  may be a source program, executable program (object code), script, or any other entity comprising a set of instructions to be performed. When a source program, then the program is usually translated via a compiler (such as the compiler  1040 ), assembler, interpreter, or the like, which may or may not be included within the memory  1020 , so as to operate properly in connection with the O/S  1050 . Furthermore, the application  1060  can be written as (a) an object oriented programming language, which has classes of data and methods, or (b) a procedure programming language, which has routines, subroutines, and/or functions. 
     The I/O devices  1070  may include input devices (or peripherals) such as, for example but not limited to, a mouse, keyboard, scanner, microphone, camera, etc. Furthermore, the I/O devices  1070  may also include output devices (or peripherals), for example but not limited to, a printer, display, etc. Finally, the I/O devices  1070  may further include devices that communicate both inputs and outputs, for instance but not limited to, a NIC or modulator/demodulator (for accessing remote devices, other files, devices, systems, or a network), a radio frequency (RF) or other transceiver, a telephonic interface, a bridge, a router, etc. The I/O devices  1070  also include components for communicating over various networks, such as the Internet or an intranet. The I/O devices  1070  may be connected to and/or communicate with the processor  1010  utilizing Bluetooth connections and cables (via, e.g., Universal Serial Bus (USB) ports, serial ports, parallel ports, FireWire, HDMI (High-Definition Multimedia Interface), etc.). 
     When the computer  1000  is in operation, the processor  1010  is configured to execute software stored within the memory  1020 , to communicate data to and from the memory  1020 , and to generally control operations of the computer  1000  pursuant to the software. The application  1060  and the O/S  1050  are read, in whole or in part, by the processor  1010 , perhaps buffered within the processor  1010 , and then executed. 
     When the application  1060  is implemented in software it should be noted that the application  1060  can be stored on virtually any computer readable storage medium for use by or in connection with any computer related system or method. 
     The application  1060  can be embodied in any computer-readable medium for use by or in connection with an instruction execution system, apparatus, server, or device, such as a computer-based system, processor-containing system, or other system that can fetch the instructions from the instruction execution system, apparatus, or device and execute the instructions. 
     In exemplary embodiments, where the application  1060  is implemented in hardware, the application  1060  can be implemented with any one or a combination of the following technologies, which are each well known in the art: a discrete logic circuit(s) having logic gates for implementing logic functions upon data signals, an application specific integrated circuit (ASIC) having appropriate combinational logic gates, a programmable gate array(s) (PGA), a field programmable gate array (FPGA), etc. 
     The flowchart and block diagrams in the Figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods and computer program products according to various embodiments of the present invention. In this regard, each block in the flowchart or block diagrams may represent a module, segment, or portion of code, which comprises one or more executable instructions for implementing the specified logical function(s). It should also be noted that, in some alternative implementations, the functions noted in the block may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams and/or flowchart illustration, and combinations of blocks in the block diagrams and/or flowchart illustration, can be implemented by special purpose hardware-based systems that perform the specified functions or acts, or combinations of special purpose hardware and computer instructions. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one more other features, integers, steps, operations, element components, and/or groups thereof. 
     The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the present invention has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. The embodiment was chosen and described in order to best explain the principles of the invention and the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated 
     The flow diagrams depicted herein are just one example. There may be many variations to this diagram or the steps (or operations) described therein without departing from the spirit of the invention. For instance, the steps may be performed in a differing order or steps may be added, deleted or modified. All of these variations are considered a part of the claimed invention. 
     While the preferred embodiment to the invention had been described, it will be understood that those skilled in the art, both now and in the future, may make various improvements and enhancements which fall within the scope of the claims which follow. These claims should be construed to maintain the proper protection for the invention first described.