Classifications

• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11C—STATIC STORES
  • G11C11/00—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor
  • G11C11/02—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using magnetic elements
  • G11C11/16—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using magnetic elements using elements in which the storage effect is based on magnetic spin effect
  • G11C11/165—Auxiliary circuits
  • G11C11/1675—Writing or programming circuits or methods
• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11C—STATIC STORES
  • G11C11/00—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor
  • G11C11/02—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using magnetic elements
  • G11C11/16—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using magnetic elements using elements in which the storage effect is based on magnetic spin effect
  • G11C11/161—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using magnetic elements using elements in which the storage effect is based on magnetic spin effect details concerning the memory cell structure, e.g. the layers of the ferromagnetic memory cell

Definitions

• This disclosure relates generally to memory devices, and more specifically, to magnetic memory devices
• Non-volatile memory devices are an important component in electronic systems FLASH is the major non-volatile memory device in use today Typical non-volatile memory devices use charges trapped in a floating oxide layer to store information Disadvantages of FLASH memory include high voltage requirements, slow program and erase times, low endurance, and limitations of scalability
• MRAM magnetoresistive random access memory
• a memory state in MRAM is maintained by the direction of the magnetic moment, not by charges stored in a layer MRAM includes a magnetic tunnel junction (MTJ) structure
• the MTJ has a fixed magnetic layer separated from a free magnetic layer by a dielectric tunnel barrier
• data storage is accomplished by applying magnetic fields and causing the free layer to be magnetized either parallel or antiparallel to the fixed layer magnetization, corresponding to the two possible memory states
• Recalling data is accomplished by sensing the resistance of a current tunneling between the free and fixed magnetic layers If the magnetic moment of the free layer is parallel to the fixed layer moment, then the MRAM device has a low resistance If, instead, the magnetic moment of the free layer is antiparallel to the fixed layer moment, the MRAM device has a high resistance
• the magnetic fields for writing are created by passing currents through conductive lines external to the MTJ structure
• toggle MRAM bits are programmed using magnetic fields that are generated by passing currents down conducting lines that are in close proximity to the bits The same pulse sequence is used to switch from one state (e g , a "1 " or a "0") to another state (e g , a 'O" or a “1 ") While toggle MRAM has some advantages, it does not achieve a small write current, especially for small cell sizes
• STMRAM spin torque MRAM
• ST-MRAM the bits are programmed by allowing a spin-polarized electron current to impinge upon a magnetic free layer.
• the change of angular momentum associated with the spin-polarized current generates a torque on the free layer that can change its magnetization direction, for large enough currents.
• ST-MRAM uses substantially less write current than a toggle MRAM, particularly at small cell sizes, , the write current for STMRAM is still undesirably large and for some cells, requires a programming voltage that exceeds the breakdown voltage of the tunnel barrier (Vbd).
• Vbd breakdown voltage of the tunnel barrier
• a large write current requires a large pass transistor for selectively programming the bit in an array, thereby undesirably limiting the overall memory density. Therefore, a need exists to further decrease the programming currents for spin transfer effect devices.
• FIG. 1 illustrates a cross-sectional view of a memory device, such as an MRAM device, in accordance with one embodiment
• FIG. 2 illustrates a cross-sectional view of a free magnetic element in accordance with one embodiment
• FIG. 3 a flow chart illustrating a method writing a memory cell in accordance with one embodiment
• FIGs. 4-7 illustrates views of the free magnetic element in FIG. 2 during a write process in accordance with one embodiment
• FIG. 8 illustrates a schematic representation of an array of memory cells in accordance with an embodiment.
• the free magnetic element of the MTJ structure includes weakly coupled magnetic layers.
• the magnetic layers are weakly ferromagnetically coupled through thin nonmagnetic interlayers.
• each of the thin interlayers is approximately 0.1 to approximately 2 nanometers in thickness.
• the entire free layer reverses simultaneously due to the strong ferromagnetic coupling intrinsic to continuous magnetic materials.
• weakly magnetically coupled layers a low programming current is achieved, preventing or minimizing tunnel barrier breakdown.
• the memory cell can include smaller pass transistors than conventional STMRAM structures, which desirably decreases the size of the cell. Therefore, higher density and lower power MRAM devices are possible.
• a free magnetic element with weakly coupled magnetic layers can be used in any suitable magnetic memory cell.
• the spin-transfer effect used in spin-torque memory cells involves a current becoming spin-polarized after the electrons pass through the first magnetic layer in a magnet/non-magnet/magnet trilayer structure, where the first magnetic layer is non responsive "fixed", either because it is substantially thicker than the second magnetic layer, or because of magnetic coupling to an adjacent layer.
• the spin-polarized electrons cross the nonmagnetic spacer and then, through conservation of angular momentum, place a torque on the second magnetic layer, which switches the magnetization direction of the second layer to be parallel to the magnetization direction of the first layer. If a current of the opposite polarity is applied, the electrons instead pass first through the second magnetic layer.
• the spin-transfer torque switches the magnetization direction of the second layer to be anti- parallel to the magnetization direction of the first layer.
• Spin-transfer as described so far involves transmission of the current across all layers in the structure.
• Another possibility is spin-transfer reflection mode switching. In reflection mode, the current again becomes spin- polarized as the electrons pass through the first magnetic layer.
• the electrons then cross the nonmagnetic spacer layer, but instead of also crossing the second magnetic layer, the electrons follow a lower resistance path through an additional conductor leading away from the interface between the nonmagnetic spacer and the second magnetic layer. In the process, some fraction of the electrons will reflect off this interface and thereby exert a spin- transfer torque on the second magnetic layer to align it parallel to the first magnetic layer.
• MRAM cell 100 a cross sectional view of an MRAM cell 100 is configured in accordance with one embodiment.
• an MRAM architecture or device will include many MRAM cells 100, which may be connected together in a matrix of columns and rows.
• MRAM cell 100 generally includes the following elements: a first conductor 102, which carries a write current 126; a spacer element 106; a free magnetic element or structure 108; an insulator 110; a fixed magnet element 112; and an isolation transistor or pass transistor 1 14.
• first conductor 102 may be connected to any number of similar MRAM cells (e.g., a column of cells) to provide a common write current 126 to each of the connected cells.
• First conductor 102 is formed from any suitable material capable of conducting electricity.
• first conductor 102 may include Al, Cu, Au, Ag, Ta, Ti, the like, or their combinations.
• Spacer element 106 may be located between first conductor 102 and free magnetic element 108.
• Spacer element 106 is formed from an electrically conducting nonmagnetic material, for example, Ta, TaN or other metallic materials. In one embodiment, spacer element 106 is not present.
• the free magnetic element 108 is located between spacer element 106 (or first conductor 102 if spacer element 106 is not present) and insulator 1 10.
• the free magnetic element 108 includes a first free magnetic layer (or first sub-layer) 109 and a second free magnetic layer (or second sub-layer) 1 13 separated from each other by an interlayer 1 11.
• Both first free magnetic layer 109 and second free magnetic layer 1 13 are formed from magnetic materials having a variable magnetization. The same or different materials can be used for the sub-layers 109 and 1 13.
• first free magnetic layer 109 and second free magnetic layer 1 13 may include Ni, Fe, Mn, Co, the like, their alloys, alloys with B and O, or so-called half- metallic ferromagnets such as NiMnSb, PtMnSb, Fe 3 O 4 , or CrO 2 .
• the first and second free magnetic layers 109 and 1 13 are each approximately 1 to approximately 5 nanometers thick.
• the direction of the variable magnetization of free magnetic element 108 determines whether MRAM cell 100 represents a "1" bit or a "0" bit. In practice, the direction of the magnetization of free magnetic element 108 is either parallel or anti-parallel to the direction of the magnetization of fixed magnet element 1 12.
• the interlayer 1 1 1 can be any nonmagnetic material.
• the interlayer 1 11 is a discontinuous nonmagnetic conductive material including Ta, Ti, Mg, Al, Cu, the like, or combinations of the above.
• the interlayer 1 1 1 is a discontinuous nonmagnetic insulating material, such as an oxide, nitride, or oxynitride of Si, Al, Mg, Ti, Ta, Hf, Fe, Ni, Co, V, Zr, the like, or combinations of the above.
• the interlayer 1 1 1 is an oxide or nitride, it can be formed by depositing an oxide or nitride layer or by exposing a layer (e.g., a layer of including Fe, Ni, Co, the like or combinations of the above) to an oxygen or nitrogen environment.
• a layer e.g., a layer of including Fe, Ni, Co, the like or combinations of the above
• the interlayer 1 1 1 is a discontinuous nonmagnetic material, it preferably is approximately 0.1 to approximately 1 nanometer thick. In one embodiment, the thickness is chosen to achieve the desired amount of ferromagnetic coupling between free magnetic layers 109 and 1 13. When there is no interlayer between layers 109 and 1 13, the maximum ferromagnetic coupling is achieved, which can be equivalent to a coupling field of greater than 10 4 Oe.
• the interlayer thickness is in the range of approximately 0.1 to approximately 1 nm, it is usually discontinuous so that coupling still exists between free magnetic layers 109 and 1 13, but the magnitude may be significantly reduced. If the nonmagnetic interlayer is continuous, there is no ferromagnetic coupling between layers 109 and 113, although antiferromagnetic coupling is possible for some oxides.
• the desired level of ferromagnetic coupling is in the range of approximately 50 Oe to approximately 500 Oe, which may vary based on layer thickness, bit size, and shape. A skilled artisan will recognize that this measurement of ferromagnetic coupling might be a net ferromagnetic coupling, as some antiferromagnetic coupling can exist at the ends of the layers, as described herein.
• interlayer 1 1 1 is a conducting material that, depending on its thickness, can produce antiferromagnetic coupling or ferromagnetic coupling between layers 109 and 1 13.
• Such materials may include Ru, Os, Re, Rh, Cu, , Cr, Ir, and the like.
• the interlayer is so thin as to be discontinuous (in the range of approximately 0.1 to approximately 0.5 nm,), there is ferromagnetic coupling between free magnetic layers 109 and 1 13.
• the interlayer is continuous, there is antiferromagnetic coupling between layers 109 and 1 13, having a maximum magnitude of several hundred Oe for a thickness in the range of approximately 0.7 to approximately 1.1 nm.
• the coupling can become weakly ferromagnetic again, typically in the thickness range of approximately 1.3 to approximately 1 .5 nm.
• AF antiferromagnetic
• Free magnetic element 108 has a magnetic easy axis that defines a natural or "default" direction of its magnetization.
• MRAM cell 100 is suitably configured to establish a particular easy axis direction for free magnetic element 108. From the perspective of FIG. 1 , the magnetization of free magnetic element 108 points either to the right or to the left.
• the anisotropy, such as shape or crystalline anisotropy, of the free magnetic layer, 108 determines the direction of the respective easy axis in the free magnetic element 108. In the embodiment illustrated in FIG.
• the free magnetic element 108 includes multiple magnetic layers and therefore, each magnetic layer has an easy axis.
• the easy axis for first magnetic layer 109 and second magnetic layer 1 13 are in one embodiment in the same direction .
• the magnetization of magnetic layers 109 and 113 are both pointing along their easy axis and to the right.
• insulator 1 10 is located between free magnetic element 108 and fixed magnet element 1 12.
• fixed magnet element 1 12 includes a fixed magnetic layer, a spacer layer, a pinned magnetic layer, and an antiferromagnetic pinning layer.
• insulator 1 10 is located between free magnetic element 108 and fixed magnetic layer 1 18.
• Insulator 1 10 is formed from any suitable material that can function as an electrical insulator.
• insulator 110 may be formed from a material such as oxides or nitrides including Al, Mg, Si, Hf, Sr, Ti, Zr or the like.
• insulator 1 10 serves as a tunnel barrier element and the combination of free magnetic element 108, insulator 1 10, and fixed magnet element 112 form a MTJ.
• fixed magnet element 1 12 is located between insulator 110 and isolation transistor 114.
• Fixed magnet element 112 has a fixed magnetic layer 1 19 whose magnetization is either parallel or anti-parallel to the magnetization of free magnetic element 108.
• the fixed magnet element is a single magnetic material, such as CoFe.
• the fixed magnet element 1 12 includes a fixed magnetic layer, a spacer layer, a pinned magnetic layer, and an antiferromagnetic pinning layer. In this embodiment, fixed magnetic layer and pinned magnetic layer have anti-parallel magnetizations.
• Fixed magnetic layer and pinned magnetic layer may be formed from any suitable magnetic material, such as at least one of the elements Ni, Fe, Mn, Co, their alloys or alloys with B or O, as well as so-called half-metallic ferromagnets such as NiMnSb, PtMnSb, Fe 3 O 4 , or CrO 2 .
• Antiferromagnetic layer may include, for example, IrMn, NiMn, and FeMn, RhMn, or PtMn.
• Spacer layer may be formed from any suitable nonmagnetic material, including Ru, Os, Re, Cr, Rh, Cu, or their combinations.
• the isolation transistor 1 14 includes a first current electrode coupled to a voltage potential, a second current electrode coupled to the fixed magnetic layer 122 and a gate that, when selected, allows electrons to flow through the cell 100 to the first conductor 102.
• the isolation transistor 114 is addressed when it is desired to write the cell 100 by providing a current from the first conductor 102 to the isolation transistor 1 14.
• MRAM cell 100 may employ alternative or additional elements, and one or more of the elements depicted in FIG. 1 may be realized as a composite structure or combination of sub-elements.
• the specific arrangement of layers shown in FIG. 1 merely represents one embodiment.
• FIG. 2 illustrates the free magnetic element 108 in accordance with another embodiment.
• the free magnetic element 108 includes multiple free magnetic layers 131 -134 (i.e., a first free magnetic layer 131 , a second free magnetic layer 132, and a third free magnetic layer 133, and a fourth free magnetic layer 134). Between pairs of the free magnetic layers 131 -134 are interlayers 136-138 (i.e., first interlayer 136, second interlayer 137, and third interlayer 138).
• the free magnetic layers 131 -134 can be any of the materials and have any of the dimensions discussed for the free magnetic layers 109 and 1 13.
• the interlayers 136-138 can be any of the materials and have any of the dimensions discussed for the interlayer 111.
• the free magnetic layers 131 -134 preferably have the same easy axis direction as each other. As shown in FIG. 2, each of the free magnetic layers 131 -134 has a magnetization direction as illustrated by the arrows 140-143. . Also shown in the embodiment illustrated in Fig. 2, there is a net ferromagnetic coupling between the free magnetic layers 131 -134, since their magnetization directions are parallel with no current applied.
• the free magnetic element 108 can be viewed as one free magnetic material with embedded interlayers. Although embodiments having two or four free magnetic layers with one to three interlayers, respectively, between the free magnetic layers are illustrated in FIGs. 1 and 2, a skilled artisan appreciates that these are only examples and any number of free magnetic layers and interlayers may be present (e.g., three magnetic layers and two interlayers, five magnetic layers and four interlayers, six magnetic layers and five interlayers, etc.). The more magnetic layers and interlayers in the free layer, the lower the switching current needed. Thus, it is advantageous to have more than one or two magnetic layers and more than one interlayer.
• a memory device includes a fixed magnetic layer; a tunnel barrier layer over the fixed magnetic layer, and a free magnetic layer formed over the tunnel barrier layer, wherein the free magnetic layer includes a first free magnetic layer; a second free magnetic layer, wherein the second free magnetic layer is weakly ferromagnetically or antiferromagnetically coupled to the first free magnetic layer; and a third free magnetic layer, wherein the third free magnetic layer is weakly ferromagnetically or antiferromagnetically magnetically coupled to the second free magnetic layer.
• the memory device further includes a first non-magnetic layer between the first free magnetic layer and the second free magnetic layer, and a second non-magnetic layer between the second free magnetic layer and the third free magnetic layer, wherein the first non-magnetic layer is a discontinuous insulator.
• the second nonmagnetic layer is also a discontinuous insulator; it can be the same or a different insulator than the first non-magnetic layer.
• FIG. 3 is a flow chart of an MRAM writing process 300 in accordance with one embodiment that may be performed when writing data to an MRAM array that includes MRAM cells 100.
• Process 300 may be performed or controlled by one or more logic or processor elements (see, for example, FIG. 5) such as those found in computer systems.
• process 300 may include any number of additional or alternative tasks, and process 300 may be incorporated into a more complex memory control read/write procedure.
• the tasks depicted in process 300 need not be performed in the order shown in FIG. 3 and one or more of the tasks may be performed concurrently.
• MRAM writing process 300 begins with a task 302, which designates an MRAM cell in the MRAM array for writing.
• task 302 may identify a row and a column to designate the MRAM cell.
• a write current is applied to a conductor line that is coupled to a row of MRAM cells (task 304)by selecting isolation transistor 1 14; the current will pass through the bit in the designated MRAM cell.
• MRAM writing process 300 applies a write current in a first direction to the designated MRAM cell (task 308); In response to the write current, the direction of the magnetization for the free magnetic element in the designated MRAM cell is switched to a written state (task 310). The direction of the magnetization for the free magnetic element in the designated MRAM cell is switched to become anti-parallel to the direction of the magnetization for the fixed magnetic element in the designated MRAM cell.
• MRAM writing process 300 applies a write current in a second direction to the designated MRAM cell (task 312).
• the direction of the magnetization for the free magnetic element in the designated MRAM cell is switched to become parallel to the direction of the magnetization for the fixed magnetic element in the designated MRAM cell.
• FIGs. 4-7 illustrate how the spin-torque reversal travels through the free magnetic element 108 of FIG. 2 in accordance with one embodiment. All of the cross-sections in FIGs. 4-7 are cross-sections taken in the x-z plane, as illustrated by axis 10 in each figure.
• FIG. 4 shows the free magnetic element 108 before a write current is applied; the spins 150- 153 of each sub-layer 131 -134 are all in the same direction. (Spins 150-153 represent the magnetization direction of each sub-layer 131 -134)
• Element 200 illustrates the direction of the spins 150-153 of each sub-layer 131 -134 in the x-y plane.
• the arrow in element 200 illustrates the spins 150-153 of all the sub-layers 131 -134.
• the layer nearest the tunnel junction which is the fourth free magnetic layer 134 in the embodiment illustrated, reverses first, as shown in FIG. 5.
• the third free magnetic layer 133 begins to reverse followed by the second free magnetic layer 132.
• the first free magnetic layer 131 may not have reversed yet. The reversal occurs in the x-y plane around the z-axis, as the axes are defined in the illustrations.
• spins 152 are rotated approximately 60 degrees relative to spins 153, as illustrated by element 210.
• spins 152 are illustrated as nearly pointing out of the plane of the paper by having a shorter arrow length.
• the spins 151 are rotated approximately 60 degrees relative to the spins 150 and approximately 60 degrees relative to the spins 152, as illustrated by element 210.
• the arrows denoting spins 151 in magnetic layer 132 of element 108 are also drawn as being shorter than arrows 150 because they are at an angle to the paper.
• the third free magnetic layer 133 like the fourth free magnetic layer 134, has completely reversed, the second free magnetic layer 132 has reversed more, and the first free magnetic layer 131 has begun to reverse, as shown in FIG. 6.
• the second free magnetic layer 132 has spins 151 that are approximately 60 degrees with respect to the spins 152 of the third free magnetic layer 133, and approximately 60 degrees with respect to the spins 150 of the first free magnetic layer 131.
• This direction of the spins 151 is illustrated in magnetic layer 132 of element 108 by the arrows denoting spins 151 being of shorter length than arrows denoting spins 152, but with the spins 151 pointing in the same direction as spins 152. Since the spins 150 of the first free magnetic layer 131 are nearly pointing out of the page, the spins 150 are also illustrated by arrows having a shorter length.. After additional time, all of the sub-layers have reversed as shown in FIG. 7. If the free magnetic element is approximately 4 nanometers thick and has 4 magnetic layers the entire write process may be approximately 1 nanosecond.
• Elements 230 shows the spins 150-153 being opposite (i.e., 180 degrees from) the spins 150-153 in element 200, which shows the spins 150-153 prior to application of a switching current.
• FIGs. 4-7 had the spins rotating or reversing in a clockwise direction in the x-y plane around the z- axis. However, the spins could rotate in a counterclockwise direction. If the spins rotated in a counterclockwise direction, some of the spins would point into the page, which could be illustrated by an x with a circle around it as opposed to dots with circles around each of them.
• Weakly coupled is any magnetic coupling that is substantially less than the exchange coupling of a ferromagnetic material, which is approximately 10 6 Oersted (Oe) or more.
• the weakly coupled layers are approximately -500 to approximately 1 ,000 Oe.
• a micromagnetic simulation showed that for a bit of size 0.08 um x 0.16 urn, having 4 weakly ferromagnetically coupled layers of NiFe, each 1 nm thick, the spin torque switching current was reduced by more than a factor of 2 compared to the case of a continuous 4 nm thick NiFe layer with strong coupling throughout. Furthermore, the overall thickness of the free magnetic element 108 is still sufficiently large enough (e.g., 4 nanometers) so that stability against thermal effects is maintained. This stability allows data to be retained.
• FIGs. 4-7 shows ferromagnetic coupling.
• the coupling can be ferromagnetic or antiferromagnetic.
• the switch of the free magnetization (task 310 or 314) is complete.
• the selective writing technique of MRAM writing process 300 maintains the magnetization direction of the free magnetic elements for all of the undesignated MRAM cells (task 316).
• the write current is removed (task 318).
• the isolation transistor that was selected in task 304 is deselected (task 320). The deselection of the isolation transistor and the removal of the write current are desirable to preserve the written state of the designated cell (task 322).
• a practical MRAM architecture may include an array or matrix of MRAM cells 100 having individual write selectivity.
• FIG. 8 is a schematic representation of an example MRAM array 200 that may employ any number of MRAM cells 100.
• the dashed lines in FIG. 8 indicate that the MRAM array 200 can include any number of rows and any number of columns.
• each cell 100 is coupled to its own isolation transistor 202, and cells 100 in a given row share a common write line 210, 212, and 214.
• MRAM array 200 includes selection logic 218 that controls the selection of isolation transistor 202, and spin transfer write current selection logic 220 that controls the selection or application of current to the appropriate write line 210, 212, 214.
• An MRAM writing process similar to process shown in FIG. 3 can be utilized to write data to the MRAM array 200.
• a memory device and a method of switching a memory device that reduces the switching current compared to a memory device with a free magnetic layer that reverses simultaneously.
• this is achieved by using a free magnetic element that includes sub-layers that are weakly magnetically coupled so that the spin-torque induced reversal proceeds sequentially through the free magnetic element. This allows a lower programming voltage to be used, avoiding tunnel barrier breakdown, and a small pass transistor to be used, thus saving die real estate.
• a memory device includes a fixed magnetic layer; a tunnel barrier layer over the fixed magnetic layer; and a free magnetic structure formed over the tunnel barrier layer, wherein the free magnetic structure has a first layer and a second layer, the first layer is weakly magnetically coupled to the second layer with a coupling strength, and the coupling strength is chosen to produce a minimum spin- torque switching current.
• first layer is weakly ferromagnetically coupled to the second layer.
• first layer is weakly antiferromagnetically coupled to the second layer.
• a method of switching a memory device includes forming a fixed magnetic layer, forming a tunnel barrier layer over the fixed magnetic layer, forming a free magnetic layer formed over the tunnel barrier layer, wherein the free magnetic layer or structure includes forming a first sub-layer or layer formed over the tunnel barrier layer, wherein the first sub-layer is a first free magnetic material, forming a first interlayer formed in contact with the first sub-layer; and forming a second sub-layer or layer formed in contact with the first interlayer, wherein the second sub layer is a second free magnetic material, and the method further comprises applying a write current to the memory device, wherein when applying the write current the magnetic spins sequentially switch.
• the magnetic spins sequentially switch comprises having the magnetic spin of the first sublayer switch before the magnetic spin of the second sub-layer switches.
• a memory device comprising: a fixed magnetic layer; a tunnel barrier layer over the fixed magnetic layer; and a free magnetic structure formed over the tunnel barrier layer, wherein the free magnetic structure comprises: a first free magnetic layer; a first interlayer in contact with the first free magnetic layer; and a second free magnetic layer, wherein the second free magnetic layer is weakly ferromagnetically coupled to the first free magnetic layer and is in contact with the first interlayer; and wherein the memory device is capable of being programmed by impinging a spin-polarized electron current on the free magnetic structure.
• the first interlayer comprises an element selected from the group consisting of Ru, Rh, Os, and Re and wherein the first interlayer has a thickness in the range of approximately 1.2 to approximately 1.7 nanometers.
• the memory device of item 4, wherein the first interlayer comprises an oxide comprising an element selected from the group consisting of Si, Mg, Al, Ti, Ta, Hf, Fe, Ni, Co, V, and Zr.
• the first interlayer comprises a metal comprising an element selected from the group consisting of Ta, Ti, Mg, Hf, Al, Ru, Os, Re, Rh, V, Cu and B.
• a memory device comprising: a fixed magnetic layer; a tunnel barrier layer over the fixed magnetic layer; and a free magnetic structure formed over the tunnel barrier layer, wherein the free magnetic structure comprises a free magnetic material embedded within a non-magnetic insulating material.
• a memory device comprising: a fixed magnetic layer; a tunnel barrier layer over the fixed magnetic layer; and a free magnetic structure formed over the tunnel barrier layer, wherein the free magnetic structure comprises: a first free magnetic layer; a second free magnetic layer, wherein the second free magnetic layer is weakly magnetically coupled to the first free magnetic layer; and a third free magnetic layer, wherein the third free magnetic layer is weakly magnetically coupled to the second free magnetic layer and wherein: the memory device is capable of being programmed by impinging a spin-polarized electron current on the free magnetic structure.
• the memory device of item 16 further comprising a first interlayer between the first free magnetic layer and the second free magnetic layer.
• the first interlayer comprises an oxide comprising an element selected from the group consisting of Si, Mg, Al, Ti, Ta, Fe, Ni, Co, V, and Zr.

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