Magnetic element

A magnetic element includes a first magnetic layer and a first nonmagnetic layer. An angle θ0 between a first direction and the magnetization direction of the first magnetic layer satisfies 0°<θ0<90° or 90°<θ0<180° in a state in which neither a voltage nor a magnetic field is substantially applied to the first magnetic layer; and the first direction is from the first nonmagnetic layer toward the first magnetic layer. A resistance·area of the first nonmagnetic layer is 10 Ωμm2 or more.

TECHNICAL FIELD

Embodiments of the invention relate to a magnetic element.

BACKGROUND ART

A magnetic element is known in which the magnetization direction of a magnetic layer is changed according to information to be stored. It is desirable to obtain stable operations of the magnetic element.

PRIOR ART DOCUMENT

Patent Document

SUMMARY OF INVENTION

Problem to be Solved by the Invention

An embodiment of the invention provides a magnetic element in which the operational stability can be improved.

Means for Solving the Problem

According to an embodiment of the invention, a magnetic element includes a first magnetic layer and a first nonmagnetic layer. An angle θ0between a first direction and the magnetization direction of the first magnetic layer satisfies 0°<θ0<90° or 90°<θ0<180° in a state in which neither a voltage nor a magnetic field is substantially applied to the first magnetic layer; and the first direction is from the first nonmagnetic layer toward the first magnetic layer. A resistance·area of the first nonmagnetic layer is 10 Ω·μm2or more.

Effects of the Invention

According to an embodiment of the invention, a magnetic element can be provided in which the operational stability can be improved.

EMBODIMENTS OF INVENTION

Various embodiments of the invention are described below with reference to the accompanying drawings.

FIG. 1is a schematic perspective view illustrating a magnetic element according to an embodiment.

FIG. 2AandFIG. 2Bare schematic views illustrating characteristics of the magnetic element according to the first embodiment.

FIG. 3is a schematic cross-sectional view illustrating the magnetic element according to the embodiment.

A first magnetic element110according to the embodiment includes a first magnetic layer11, a first nonmagnetic layer21, and a second magnetic layer12.

A first direction from the first nonmagnetic layer21toward the first magnetic layer11is taken as a Z-axis direction. One direction perpendicular to the Z-axis direction is taken as an X-axis direction. A direction perpendicular to the Z-axis direction and the X-axis direction is taken as a Y-axis direction. An angle that is measured from the Z-axis is taken as a polar angle θ; and an angle in the XY plane measured from the X-axis is taken as an azimuth angle ϕ.

The second magnetic layer12is provided at the side opposite to the first magnetic layer11with the first nonmagnetic layer21interposed. The first nonmagnetic layer21is positioned between the first magnetic layer11and the second magnetic layer12in the Z-axis direction. For example, the first magnetic layer11, the first nonmagnetic layer21, and the second magnetic layer12spread parallel to the X-Y plane.

An anisotropic magnetic field Hkof the first magnetic layer11in a plane crossing the Z-axis direction satisfies Hk≠0. For example, as illustrated inFIG. 1, a length L1of the first magnetic layer11in the X-axis direction is different from a length L2of the first magnetic layer11in the Y-axis direction. Thereby, a shape anisotropic magnetic field is generated in the first magnetic layer11so that Hk≠0.

As illustrated inFIG. 2A, the angle θ0between the Z-axis direction and a magnetization direction m of the first magnetic layer11in a state in which neither a voltage nor a magnetic field is substantially applied to the first magnetic layer11satisfies 0°<θ0<90° or 90°<θ0<180° and is oblique to the Z-axis direction. The angle ϕ between the X-axis direction and the magnetization direction m is the same azimuth angle as Hkin the case where Hk≠0.

The first magnetic layer11includes a ferromagnetic material. For example, the c-axis of the ferromagnetic material included in the first magnetic layer11is aligned with the Z-axis direction. For example, in the state of Hk=0 before fine patterning, the magnetization direction m of the first magnetic layer11is at some position on a circular conic surface tilted at the angle θ0with respect to the c-axis (the Z-axis direction) as illustrated inFIG. 2B. Such a magnetization state satisfying 0°<θ0<90° or 90°<θ0<180° is called a cone magnetization state.

The first nonmagnetic layer21is, for example, a tunnel insulating layer. It is favorable for the resistance·area (RA: Resistance area product) of the first nonmagnetic layer21to be Ω·μm2or more. Thereby, for example, low power consumption is obtained in the voltage write operation. For example, the information that relates to the resistance-area of the first nonmagnetic layer21is obtained from the measurement results of the resistance of the element and the measurement results of the size of the element from a SEM (Scanning Electron Microscope), a TEM (Transmission Electron Microscope), etc.

The resistance·area of the first nonmagnetic layer21may be, for example, greater than 20 Ω·μm2. Thereby, for example, low power consumption that is ½ of the case of a current write operation is obtained. The resistance·area of the first nonmagnetic layer21may be, for example, 100 Ω·μm2or more. Thereby, for example, an even lower power consumption that is 1/10 of the case of a current write operation is obtained. The resistance·area of the first nonmagnetic layer21may be, for example, 500 Ω·μm2or more. Thereby, for example, even lower power consumption that is 1/50 of the case of a current write operation is obtained. The energy that is necessary to write increases abruptly when the resistance-area of the first nonmagnetic layer21becomes 20 Ω·μm2or less. The increase of the energy necessary to write accelerates further when the resistance·area of the first nonmagnetic layer21becomes less than 10 Ω·μm2.

On the other hand, in a voltage read operation, the time that is necessary to read lengthens as the resistance·area of the first nonmagnetic layer21increases. For example, the time that is necessary to read lengthens and is respectively 2 times, 10 times, and 50 times the case where the resistance·area of the first nonmagnetic layer21is 20 Ω·μm2, 100 Ω·μm2, and 500 Ω·μm2. Therefore, from the perspective of high-speed reading, it is favorable for the resistance·area of the first nonmagnetic layer21to be lower than the values recited above. In an actual magnetic memory device, it is sufficient to use an optimal resistance·area of the first nonmagnetic layer21for realizing both the power consumption and the read speed necessary for the individual application.

In the example illustrated inFIG. 3, the first magnetic element110is included in a magnetic memory device210. The magnetic memory device210further includes, for example, a second magnetic element120, a first conductive layer31, a second conductive layer32, a third conductive layer33, a fourth conductive layer34, an insulating portion40, a controller70, a first interconnect71, and a second interconnect72. The second magnetic element120includes a third magnetic layer13, a fourth magnetic layer14, and a second nonmagnetic layer22.

The third magnetic layer13is separated from the first magnetic layer11in the X-axis direction. For example, the third magnetic layer13has a structure similar to the first magnetic layer11. In other words, the anisotropic magnetic field of the third magnetic layer13in a plane crossing the Z-axis direction is greater than 0. The angle between the Z-axis direction and the magnetization direction of the third magnetic layer13is greater than 0° and less than 90° or greater than 90° and less than 180° in a state in which neither a voltage nor a magnetic field is substantially applied to the third magnetic layer13.

The fourth magnetic layer14is separated from the second magnetic layer12in the X-axis direction. The second nonmagnetic layer22is provided between the third magnetic layer13and the fourth magnetic layer14in the Z-axis direction.

The first magnetic layer11is provided between the first conductive layer31and the first nonmagnetic layer21in the Z-axis direction. For example, the first conductive layer31contacts the first magnetic layer11. The second magnetic layer12is provided between the second conductive layer32and the first nonmagnetic layer21in the Z-axis direction.

The third magnetic layer13is provided between the third conductive layer33and the second nonmagnetic layer22in the Z-axis direction. For example, the third conductive layer33contacts the third magnetic layer13. The fourth magnetic layer14is provided between the fourth conductive layer34and the second nonmagnetic layer22in the Z-axis direction.

A faint magnetic field such as geomagnetism, etc., in a range that substantially does not affect the magnetization directions of the first magnetic layer11and the third magnetic layer13may be applied to the magnetic memory device210. Here, the state in which a faint magnetic field such as geomagnetism or the like is applied also is included in the state of a magnetic field being substantially not applied.

The insulating portion40is provided between the first magnetic element110and the second magnetic element120in the X-axis direction.

The first conductive layer31and the third conductive layer33are electrically connected to the first interconnect71. The second conductive layer32and the fourth conductive layer34are electrically connected to the second interconnect72. For example, a first switch72ais provided between the second conductive layer32and the second interconnect72. For example, a second switch72bis provided between the fourth conductive layer34and the second interconnect72. The first switch72aand the second switch72bare, for example, select transistors. Thus, the state in which a switch or the like is provided in the current path also is included in the state of being electrically connected. The first switch72aand the second switch72bmay be provided respectively between the first conductive layer31and the first interconnect71and between the third conductive layer33and the first interconnect71.

The controller70applies the voltage between the first interconnect71and the second interconnect72and selectively applies the voltage to the first magnetic element110or the second magnetic element120by setting the first switch72aor the second switch72bON. When a voltage having the appropriate polarity is applied to the first magnetic element110, the magnetization direction of the first magnetic layer11precesses around the X-axis direction at the center; and the Z-axis direction component of the magnetization direction repeats a positive and negative reversal. The magnetization direction of the first magnetic layer11can be controlled to the desired direction by appropriately controlling the application time of the voltage to the first magnetic element110. In other words, in the magnetic memory device210, it is possible to perform bidirectional information writing by applying a unipolar voltage to the first magnetic layer11via the first nonmagnetic layer21.

According to the embodiment, the angle θ0between the Z-axis direction and the magnetization direction m of the first magnetic layer11satisfies 0°<θ0<90° or 90°<θ0<180°. When the voltage is applied to the first magnetic layer11, for example, torque that changes the magnetization direction of the first magnetic layer11is applied by the anisotropic magnetic field Hkof the first magnetic layer11. As a result, the magnetization direction of the first magnetic layer11changes when the voltage is applied in a state in which there is substantially no external magnetic field.

Accordingly, it is unnecessary for the magnetic memory device210according to the embodiment to include a magnetic layer for applying a magnetic field in the in-plane direction to the first magnetic layer11, etc. For example, the magnetic memory device210does not include a magnetic layer having an easy magnetization axis in the in-plane direction. Because a configuration for applying a magnetic field to the first magnetic layer11is not included, the manufacture of the magnetic memory device210is easy. Further, the fluctuation of the change of the magnetization direction of the first magnetic layer11based on the fluctuation of the intensity of the external magnetic field can be suppressed; therefore, the operational stability of the magnetic memory device210can be improved.

For example, the magnetization direction of each magnetic layer included in the magnetic memory device210described above can be observed using spin-polarized SEM.

Specific examples of the components will now be described.

The first magnetic layer11, the second magnetic layer12, the third magnetic layer13, and the fourth magnetic layer14include, for example, at least one selected from the group consisting of Fe, Co, Ni, Cr, Mn, Gd, Nd, Sm, and Tb. The thicknesses of the first magnetic layer11, the second magnetic layer12, the third magnetic layer13, and the fourth magnetic layer14each are, for example, not less than 0.5 nm and not more than 10 nm.

Or, the first magnetic layer11and the third magnetic layer13may include first regions and second regions. The first region includes Co; and the second region includes at least one selected from the group consisting of Pt and Pd. In such a case, the first region is provided between the first nonmagnetic layer21and the second region.

Or, the first magnetic layer11and the third magnetic layer13may include multiple first regions and multiple second regions provided alternately in the Z-axis direction. In such a case, it is desirable for the first region to have a hexagonal close-packed structure (hcp) structure or a face-centered cubic (fcc) (111) structure. It is favorable for the second region to have a fcc (111) structure. Or, the first region may have a fcc (001) structure; and the second region may have an fcc (001) structure. It is favorable for the thickness (the length in the Z-axis direction) of one layer of the first region stacked on the second region including Pt to correspond to the size of 10 to 15 Co atoms. It is favorable for the thickness of one layer of the first region stacked on the second region including Pd to correspond to the size of 4.5 to 6 Co atoms.

The first region may include Co; and the second region may include Pt. For example, in such a case, the thickness of the first region is not less than 0.9 nm and not more than 1.1 nm; and the thickness of the second region is 2 nm. As an example, eight first regions and eight second regions are provided alternately in the Z-axis direction. Or, the first region may be Co that is 1 or 2 atomic layers thick; and the second region may be Pt that is 1 or 2 atomic layers thick. In such a case, for example, several layers to several tens of layers of the first region and the second region may be provided alternately in the Z-axis direction.

Or, the first magnetic layer11and the third magnetic layer13may include Co having an hcp structure.

Or, the first magnetic layer11and the third magnetic layer13may be configured by stacking a first magnetic film having an easy magnetization axis in the Z-axis direction, and a second magnetic film having an easy magnetization axis in the in-plane direction. In such a case, it is favorable for the first magnetic film and the second magnetic film to be relatively thin so that the magnetization direction of the first magnetic layer11and the third magnetic layer13as an entirety is tilted from the Z-axis direction.

The magnetization directions of the second magnetic layer12and the fourth magnetic layer14do not change easily. The magnetization directions of the first magnetic layer11and the third magnetic layer13change easily compared to the magnetization directions of the second magnetic layer12and the fourth magnetic layer14.

The first nonmagnetic layer21and the second nonmagnetic layer22include an oxide, a nitride, or a fluoride including at least one selected from the group consisting of Mg, Si, Al, Ti, Zr, Hf, Ta, Zn, Sr, and Ba. The thicknesses of the first nonmagnetic layer21and the second nonmagnetic layer22each are, for example, not less than 0.5 nm and not more than 4 nm.

The first conductive layer31, the second conductive layer32, the third conductive layer33, and the fourth conductive layer34are nonmagnetic. The first conductive layer31, the second conductive layer32, the third conductive layer33, and the fourth conductive layer34include, for example, at least one selected from the group consisting of Ta, Ru, W, Ir, Au, Ag, Cu, Al, Cr, Pt, and Pd. The thicknesses of the first conductive layer31, the second conductive layer32, the third conductive layer33, and the fourth conductive layer34each are, for example, not less than 1 nm and not more than 200 nm. More favorably, the thicknesses of these conductive layers are longer than the length L1or the length L2of the first magnetic layer11and are not more than 200 nm. Good flatness and a low resistance value are obtained thereby.

The insulating portion40includes, for example, a nonmagnetic insulating compound. The insulating compound is, for example, an oxide, a nitride, or a fluoride of at least one element selected from the group consisting of Si, Al, Ti, Mg, and

The first magnetic layer11will now be described in detail.

FIG. 4A,FIG. 4B, andFIG. 5are schematic views illustrating characteristics of the first magnetic layer.

FIG. 4A,FIG. 4B, andFIG. 5illustrate the characteristics of the first magnetic layer11in a state in which a voltage is substantially not applied to the first magnetic element110.

InFIG. 4AandFIG. 4B, the horizontal axis is the angle θ between the magnetization direction of the first magnetic layer11and the Z-axis direction; and the vertical axis is an anisotropic energy εu. InFIG. 4A, the solid line illustrates a first-order term ε1of the anisotropic energy; and the broken line illustrates a second-order term ε2of the anisotropic energy. K1,effof the first-order term is the effective first-order anisotropy constant. For K1,eff, the contribution of the demagnetization energy is subtracted from a uniaxial first-order anisotropy constant Ku1. Ku2of the second-order term is the uniaxial second-order anisotropy constant.FIG. 4Billustrates the sum of the first-order term ε1and the second-order term ε2of the anisotropic energy illustrated inFIG. 4A.

In the first magnetic layer11as illustrated inFIG. 4B, multiple angles θ exist where the anisotropic energy εuis a minimum. Specifically, the angle θ where the anisotropic energy εUis a minimum exists where 0°<θ<90° and 90°<θ<180°. The angle θ where εuis a minimum is represented as θ0. In other words, the magnetization direction of the first magnetic layer11is tilted from the Z-axis direction in a state in which neither a voltage nor a magnetic field is substantially applied to these magnetic layers.

FIG. 5shows, as a contour diagram, the dependence on K1,effand Ku2of the angle θ0between the magnetization direction of the first magnetic layer11and the Z-axis direction. InFIG. 5, the horizontal axis on the lower side is the effective first-order anisotropy constant K1,eff; and the vertical axis is the uniaxial second-order anisotropy constant Ku2. The color bar on the right side illustrates the magnitude of θ0. Although θ0also can be 90°<θ0≤180°, the range of 0°≤θ0≤90° is focused on in the display ofFIG. 5. Also, because θ0and 360°−θ0are equivalent, a description is omitted for the case of 180°<θ0≤360°.

FIG. 5illustrates that 0°<θ0<90° is satisfied when the first-order anisotropy constant satisfies K1,eff<0 and the second-order anisotropy constant satisfies Ku2>−(½)K1,eff. In other words, the cone magnetization state of the first magnetic layer11is obtained by satisfying these conditions.

As θ0approaches 90°, processional switching easily occurs more stably as described below; and stable writing is possible. For example, relatively stable writing is possible in the case where 5°<θ0<90° or 90°<θ0≤175°. More stable writing is possible in the case where 15°≤θ0<90° or 90°<θ0≤165°. More stable writing is possible in the case where 30°≤θ0<90° or 90°<θ0≤150°. Yet even more stable writing is possible in the case where 45°≤θ0<90° or 90°<θ0≤135°.

On the other hand, the magnitude of the output signal when reading is proportional to the absolute value of cos θ0. Therefore, as θ0approaches 0° or 180°, the read output signal increases; and faster reading is possible. Therefore, from the perspective of high-speed reading, for example, relatively high-speed reading is possible in the case where 0°<θ0≤60° or 120°≤θ0<180°. Faster reading is possible in the case where 0°<θ0≤45° or 135°≤θ0<180°. Even faster reading is possible in the case where 0°<θ0≤30° or 150°≤θ0<180°. Yet even faster reading is possible in the case where 0°<θ0≤15° or 165°≤θ0<180°.

In the magnetic memory device210, it is sufficient to adjust the materials and the structures of the components to realize θ0to provide good balance between the write stability and the read speed necessary for each application.

EXAMPLE

FIG. 6toFIG. 11are figures illustrating simulation results relating to the first magnetic layer.

Here, a magnetic energy density ε(0)of the first magnetic layer11in a state in which a voltage substantially is not applied to the magnetic memory device210is illustrated in the following “Formula 1.” Here, μ0is the permeability; and Msis the saturation magnetization. (Nx, Ny, Nz) are demagnetizing factors; (mx, my, mz) are unit magnetization vectors; and the suffixes x, y, and z respectively illustrate the X-axis direction component, the Y-axis direction component, and the Z-axis direction component. (mx, my, mz) and (θ, ϕ) have the relationship (mr, my, mz)=(sin θ cos ϕ, sin θ sin ϕ, cos θ). Ku1(0)and Ku2(0)are respectively first and second-order anisotropy constants in a state in which a voltage substantially is not applied. The magnetic energy density ε of the first magnetic layer11in a state in which a finite voltage is applied is illustrated in the following “Formula 2.” Ku1and Ku2of “Formula 2” are respectively first and second-order anisotropy constants considering field effects. In the case where Ku1and Ku2change linearly with respect to an electric field E, Ku1and Ku2are expressed respectively in “Formula 3” and “Formula 4.” E represents the electric field. η1and η2respectively represent the field effects for Ku1and Ku2. t11represents the thickness of the first magnetic layer11.

In the calculations ofFIG. 6toFIG. 11, the conditions of the first magnetic layer11were set as follows.

A thickness t11of the first magnetic layer11is t11=1 [nm]; the length L1of the first magnetic layer11is L1=60 [nm]; the length L2of the first magnetic layer11is L2=46 [nm]; Nx=0.0242; Ny=0.0351; Nz=0.9407; the in-plane shape anisotropic magnetic field Hk=Ms(Ny−Nx)=15.2 [kA/nn] (192 [Oe]); a junction area A of the surface of the first magnetic layer11contacting the first nonmagnetic layer21is A=π(L1/2)(L2/2) [nm2]; a saturation magnetization Msof the first magnetic layer11is Ms=1400 [kA/m] (=1400 [emu/cm3]); the first-order anisotropy constant Ku1(0)=1109 [kJ/m3] for the magnetic anisotropy constant of the interface and the crystalline anisotropy of the first magnetic layer11when a voltage V applied to the first magnetic element110is V=0; the second-order anisotropy constant Ku2(0)=135 [kJ/m3]; temperature 300 [K]; a thermal stability factor Δ0=60.6; a thickness t21nof the first nonmagnetic layer21is t21n=1 [nm]; the magnitude E of the electric field is E=V/t21n[V/nn]; and an external magnetic field Hext=0 [kA/m]. The LLG equation is used in the calculation of the time evolution of the magnetization direction m=(mx, my, mz).

FIG. 6is simulation results illustrating contour curves of the magnetic energy density ε(0)when the applied voltage V=0 for the conditions recited above. The energy density appears to be highest at the mz=0 vicinity; and the energy density appears to decrease as mzapproaches the −1 or 1 vicinity. More correctly, the energy density has a minimum value at (mx, my, mz)=(mx(0), my(0), mz(0))=(sin θ0cos ϕ0, sin θ0sin ϕ0, cos θ0); and mz(0)=cos θ0is 0.96 or −0.96. ϕ0is 0° or 180°. From the simulation results, it can be seen that the magnetization direction θ0of the first magnetic layer11is tilted 15.8° or 164.2° toward the X-axis direction from the Z-axis direction. In other words, it can be seen that a cone magnetization state is realized. InFIG. 6, for example, the magnetization in the initial magnetization state is oriented toward a direction P0. InFIG. 7toFIG. 10, the initial magnetization direction was set to P0. P0is illustrated by an open circle inFIG. 6,FIG. 7A,FIG. 8,FIG. 9, andFIG. 10A.

FIG. 7AandFIG. 7Billustrate simulation results when a voltage is applied to the first magnetic element110in the state illustrated inFIG. 6.FIG. 7Aillustrates a trajectory of the magnetization direction. The trajectory in the time range of 0 ns to 50 ns is shown. InFIG. 7B, the horizontal axis is the time; and the vertical axis is the X-axis direction component mxand the Z-axis direction component mzof the magnetization direction. The solid line illustrates the Z-axis direction component mz; and the broken line illustrates the X-axis direction component mx. The conditions of the simulation were set as follows.

The field effect for Ku1is η1=−20 fJ/(V·m); the field effect for Ku2is η2=150 fJ/(V·m); and the Gilbert damping constant factor of the first magnetic layer11is α=0.005.

When the voltage is applied as illustrated inFIG. 7AandFIG. 7B, the magnetization direction of the first magnetic layer11precesses around the X-axis direction at the center. When the voltage is applied as illustrated inFIG. 7B, it can be seen that the Z-axis direction component mzreverses periodically between positive and negative. In other words, from the simulation results, it can be seen that the magnetization direction of the first magnetic layer11reverses in the Z-axis direction due to the voltage applied even when the external magnetic field Hext=0 [kA/m].

FIG. 8AtoFIG. 8Care simulation results illustrating the change of the energy contour curves when the applied voltage is changed. Here, the energy is the magnetic energy density s illustrated in “Formula 2.” Similarly toFIG. 7, the field effect for Ku1was set to η1=−20 fJ/(V·m); and the field effect for Ku2was set to η2=150 fJ/(V·m).

FIG. 8AtoFIG. 8Crespectively illustrate the energy contour curves when the applied voltage V=0.88 V, 0.89 V, and 0.90 V. In each drawing, the thick solid line illustrates the energy contour curve equal to s at the initial magnetization direction.

InFIG. 8A, the energy contour curve that passes through the initial magnetization direction does not pass through the region where mz<0; and the magnetization direction does not reverse. InFIG. 8BandFIG. 8C, the energy contour curve that passes through the initial magnetization direction passes through the region where mz<0; and the magnetization direction can reverse. From this result, it can be seen that the threshold voltage at which the reversal of the magnetization direction occurs is Vc=0.89 V. The threshold voltage Vccan be determined as the voltage for which the energy contour curve that passes through the initial magnetization direction passes through (mx, my, mz)=(1, 0, 0).

The threshold voltage Vcalso can be represented by the value of a threshold electric field Ecmultiplied by the thickness t21nof the first nonmagnetic layer21. In other words, the magnetization direction of the first magnetic layer11can be reversed by applying a voltage larger than Vc=Ec·t21nto the first magnetic element110. The threshold electric field Eccan be represented using the following “Formula 5” and “Formula 6.”

FIG. 9,FIG. 10A, andFIG. 10Bare figures illustrating other simulation results relating to the first magnetic layer. The applied voltage is V=0.78 V.FIG. 10Ashows a trajectory in the time range of 0 ns to 50 ns.

Here, the field effect η1for Ku1=10 fJ/(V·m) and the field effect η2for Ku2=150 fJ/(V·m) were set. In such a case, the threshold voltage that is estimated using “Formula 5” is 0.73 V; and the applied voltage is larger than the threshold voltage. Further, inFIG. 10, the Gilbert damping factor of the first magnetic layer11was set to α=0.005. Otherwise, the conditions are the same as those of the simulation results illustrated inFIG. 6andFIG. 7. Accordingly, the contour diagram of the magnetic energy density ε(0)when the applied voltage V=0 is the same asFIG. 6.

FIG. 9is simulation results illustrating the energy contour curves when the applied voltage V=0.78 V for the conditions recited above. Here, the energy is the magnetic energy density ε illustrated in “Formula 2.” The energy density is highest when my=1 or −1 and mz=0. The thick solid line illustrates the energy contour curve equal to ε for the initial magnetization direction.

In the simulation results as illustrated inFIG. 10AandFIG. 10B, it can be seen that the magnetization direction of the first magnetic layer11firstly rotates with the Z-axis direction at the center, and subsequently reverses in the Z-axis direction. In such a case, as illustrated inFIG. 10B, the time until the magnetization reversal occurs is slower than that of the simulation results illustrated inFIG. 7B. In other words, from the perspective of the reversal speed, the simulation results illustrated inFIG. 7are more favorable than the simulation results illustrated inFIG. 10. The switching illustrated inFIG. 7is called processional switching.

FIG. 11is a phase diagram illustrating an example of a switching condition.

InFIG. 11, the horizontal axis is the field effect η1for Ku1; and the vertical axis is the field effect η2for Ku2. InFIG. 11, the gray regions illustrate the regions where processional switching occurs; and the white regions illustrate the regions where processional switching does not occur. InFIG. 11, the broken lines illustrate (η1, η2) where D=0. D can be represented using the following “Formula 7” and “Formula 8.” In “Formula 7” and “Formula 8,” Ku1and Ku2are the anisotropy constants of the threshold electric field Ecdetermined using “Formula 5.” Also, inFIG. 11, the solid line illustrates the following “Formula 9.”

From “Formula 7” to “Formula 9” andFIG. 11, it can be seen that processional switching occurs if the contour curve of an energy εithat passes through the initial magnetization state does not reach mx=0 at the threshold voltage. To satisfy this condition, for example, it is sufficient for D<0. As described above, compared to other switching, the reversal speed of processional switching is fast; furthermore, it is favorable for η1and η2to be set to be included in the gray regions illustrated inFIG. 11to stably obtain successful switching for the voltage application of a constant pulse width.

The write stability can be improved not only by setting η1and η2but also by setting θ0. From “Formula 9,” it can be seen that as Ku2(0)decreases, the absolute value of the slope of the solid line ofFIG. 11decreases and the gray regions widen. It can be seen fromFIG. 5that a small Ku2(0)corresponds to θ0approaching 90°. From calculations using “Formula 7” and “Formula 8” as well, results are obtained in which as θ0approaches 90°, the absolute value of the slope of the broken line ofFIG. 11decreases and the gray regions widen. Also, even in the case where Ku1and Ku2do not change linearly with respect to the electric field E, processional switching occurs in a wider (Ku1, Ku2) range as θ0approaches 90°. Accordingly, as θ0approaches 90°, processional switching occurs easily; and stable writing is possible.

Although specific examples of the first magnetic layer11are described above, the third magnetic layer13may have similar characteristics.

Operational Example

Operational examples of the magnetic memory device according to the embodiment will now be described.

FIG. 12AtoFIG. 12Care schematic views illustrating operations of the magnetic memory device according to the embodiment.

In these figures, the horizontal axis is time. In these figures, the vertical axis is the potential of a signal S1applied between the first interconnect71and the second interconnect72. The signal S1substantially corresponds to a signal applied between the first magnetic layer11and the second magnetic layer12or between the third magnetic layer13and the fourth magnetic layer14.

As illustrated inFIG. 12A, the controller70performs a first operation OP1of applying a first pulse P1(e.g., a rewrite pulse) between the first interconnect71and the second interconnect72. In the first operation OP1, the first pulse P1is supplied between the first magnetic layer11and the second magnetic layer12. For example, the stored information is rewritten by the first pulse P1. The electrical resistance between the first magnetic layer11and the second magnetic layer12changes thereby.

For example, a second electrical resistance between the first magnetic layer11and the second magnetic layer12after the first operation OP1is different from a first electrical resistance between the first magnetic layer11and the second magnetic layer12before the first operation OP1.

For example, the change of the electrical resistance is based on the change of the magnetization direction of the first magnetic layer11due to the first pulse P1(the rewrite pulse). The relative relationship of the magnetization direction between the first magnetic layer11and the second magnetic layer12changes due to the first pulse P1(the rewrite pulse). Multiple states that have different electrical resistances correspond respectively to the stored information.

As shown inFIG. 12A, the controller70may further perform a second operation OP2. In the second operation OP2, the controller70applies a second pulse P2(a read pulse) between the first magnetic layer11and the second magnetic layer12(between the first interconnect71and the second interconnect72) before the first operation OP1. A third electrical resistance between the first magnetic layer11and the second magnetic layer12obtained using the read pulse is different from the second electrical resistance between the first magnetic layer11and the second magnetic layer12after the first operation. The third electrical resistance is the electrical resistance before the rewriting. The second electrical resistance is the electrical resistance after the rewriting. For example, the third electrical resistance is the same as the first electrical resistance.

For example, the polarity of the second pulse P2(the read pulse) is the reverse of the polarity of the first pulse P1(the rewrite pulse). In the case where the second pulse P2(the read pulse) having such a reverse polarity is used, the absolute value of a second pulse height H2of the second pulse P2may be less than, may be the same as, or may be larger than the absolute value of a first pulse height H1of the first pulse P1(the rewrite pulse). In the case where the magnetic anisotropy of the magnetic layer is controlled by a voltage, the change of the magnetization direction of the magnetic layer during reading can be suppressed by using a read pulse of the reverse polarity.

The case where the magnetic memory device210has the characteristics recited above is as follows.

In the first operation OP1, the controller70applies the first pulse P1between the first magnetic layer11and the second magnetic layer12. The second electrical resistance between the first magnetic layer11and the second magnetic layer12after the first operation OP1is different from the first electrical resistance between the first magnetic layer11and the second magnetic layer12before the first operation OP1. The first pulse P1has a first polarity, a first pulse width T1, and the first pulse height H1.

At this time, the case of applying another pulse having a second polarity that is the reverse of the first polarity, the first pulse width T1, and a pulse height having the same absolute value as the first pulse height H1is as follows.

The absolute value of the difference between the third electrical resistance between the first magnetic layer11and the second magnetic layer12after the other pulse is applied between the first magnetic layer11and the second magnetic layer12and a fourth electrical resistance before the other pulse is applied between the first magnetic layer11and the second magnetic layer12is less than the absolute value of the difference between the second electrical resistance and the first electrical resistance. In other words, the rewriting of the information is performed by the application of the first pulse P1; and the rewriting of the information does not occur due to the application of the other pulse.

The electrical resistance between the first magnetic layer11and the second magnetic layer12corresponds to the electrical resistance between the first interconnect71electrically connected to the first magnetic layer11and the second interconnect72electrically connected to the second magnetic layer12.

When the stored information should be maintained, the controller70performs a third operation OP3after the second operation OP2as shown inFIG. 12B. The first pulse P1recited above is not applied in the third operation OP3. At this time, the rewriting does not occur.

The rewriting of the information is possible when the appropriate first pulse P1is applied. When the appropriate first pulse P1is applied, the electrical resistance between the first magnetic layer11and the second magnetic layer12changes from the high resistance state to the low resistance state or from the low resistance state to the high resistance state. On the other hand, in the case where an inappropriate pulse is applied, the high resistance state does not become the desired low resistance state. In the case where an inappropriate pulse is applied, the low resistance state does not become the desired high resistance state.

The pulse width of the inappropriate pulse is, for example, about 2 times the appropriate first pulse width Ti. In the case where the inappropriate pulse is applied between the first magnetic layer11and the second magnetic layer12, the probability of the resistance change occurring is low.

For example, in the first operation OP1, the controller70applies the first pulse P1recited above between the first magnetic layer11and the second magnetic layer12. The first pulse P1has the first pulse width T1and the first pulse height H1. The rewriting is performed appropriately by the first pulse P1. In other words, the second electrical resistance between the first magnetic layer11and the second magnetic layer12after the first operation OP1is different from the first electrical resistance between the first magnetic layer11and the second magnetic layer12before the first operation OP1. In such a case, when another pulse P1xsuch as that shown inFIG. 12Cis applied, the change of the electrical resistance substantially does not occur. The other pulse P1xhas the first pulse height H1and a pulse width that is 2 times the first pulse width T1.

The absolute value of the difference between the third electrical resistance between the first magnetic layer11and the second magnetic layer12after such an other another pulse P1xis applied between the first magnetic layer11and the second magnetic layer12and the fourth electrical resistance before the other pulse P1xis applied between the first magnetic layer11and the second magnetic layer12is less than the absolute value of the difference between the second electrical resistance and the first electrical resistance. In other words, when the other pulse P1xis applied, the electrical resistance substantially does not change. Or, the change of the electrical resistance when the other pulse P1xis applied is smaller than the change of the electrical resistance when the first pulse P1is applied.

The change of the electrical resistance recited above can be compared more reliably by using the average value of the resistance change over the operations of multiple times. For example, the process of applying the first pulse P1recited above and detecting the change of the electrical resistance before and after is performed multiple times. The average value of the absolute values of the change of the electrical resistance in such a case is determined. On the other hand, a process of applying the other pulse P1xrecited above and detecting the change of the electrical resistance before and after is performed multiple times. The average value of the absolute values of the change of the electrical resistance in such a case is determined. By comparing the two average values recited above, it can be seen more reliably that the change of the electrical resistance when the other pulse P1xis applied is smaller than the change of the electrical resistance when the first pulse P1is applied.

In the magnetic memory device210according to the embodiment, for example, the change of the electrical resistance when the other pulse P1xrecited above is applied is smaller than the change of the electrical resistance when the first pulse P1recited above is applied.

According to the embodiments described above, a magnetic memory device can be provided in which the operational stability is improved.

The embodiments may include the following configurations (proposals).

a first magnetic layer; and

a first nonmagnetic layer,

an angle θ0between a first direction and a magnetization direction of the first magnetic layer satisfying 0°<θ0<90° or 90°<θ0<180° in a state in which neither a voltage nor a magnetic field is substantially applied to the first magnetic layer, the first direction being from the first nonmagnetic layer toward the first magnetic layer,

a resistance·area of the first nonmagnetic layer being 10 Ω·μm2or more.

a first magnetic layer; and

a first nonmagnetic layer,

an angle θ0between a first direction and a magnetization direction of the first magnetic layer satisfying 0°<θ0<90° or 90°<θ0<180° in a state in which neither a voltage nor a magnetic field is substantially applied to the first magnetic layer, the first direction being from the first nonmagnetic layer toward the first magnetic layer,

bidirectional information writing being performed by applying a unipolar voltage to the first magnetic layer via the first nonmagnetic layer.

a first magnetic layer; and

a first nonmagnetic layer,

an angle θ0between a first direction and a magnetization direction of the first magnetic layer satisfying 0°<θ0<90° or 90°<θ0<180° in a state in which neither a voltage nor a magnetic field is substantially applied to the first magnetic layer, the first direction being from the first nonmagnetic layer toward the first magnetic layer,

a resistance·area of the first nonmagnetic layer being 10 Ω·μm2or more,

bidirectional information writing being performed by applying a unipolar voltage to the first magnetic layer via the first nonmagnetic layer.

The magnetic element according to any one of Configurations 1 to 3, wherein an anisotropic magnetic field Hkof the first magnetic layer in a plane crossing the first direction satisfies Hk≠0.

The magnetic element according to any one of Configurations 1 to 4, wherein the first nonmagnetic layer is a tunnel insulating layer.

The magnetic element according to any one of Configurations 1 to 5, wherein the first nonmagnetic layer includes an oxide, a nitride, or a fluoride including at least one selected from the group consisting of Mg, Si, Al, Ti, Zr, Hf, Ta, Zn, Sr, and Ba.

The magnetic element according to any one of Configurations 1 to 6, further comprising a second magnetic layer provided at a side opposite to the first magnetic layer with the first nonmagnetic layer interposed.

The magnetic element according to any one of Configurations 1 to 7, wherein the first magnetic layer has a cone magnetization state.

Hereinabove, exemplary embodiments of the invention are described with reference to specific examples. However, the embodiments of the invention are not limited to these specific examples. For example, one skilled in the art may similarly practice the invention by appropriately selecting specific configurations of components included in magnetic memory devices such as first magnetic layers, first nonmagnetic layers, second magnetic layers, third magnetic layers, second nonmagnetic layers, fourth magnetic layers, first conductive layers, second conductive layers, third conductive layers, fourth magnetic layers, insulating portions, controllers, first interconnects, second interconnects, first switches, second switches, etc., from known art. Such practice is included in the scope of the invention to the extent that similar effects thereto are obtained.

Moreover, all magnetic memory devices practicable by an appropriate design modification by one skilled in the art based on the magnetic memory devices described above as embodiments of the invention also are within the scope of the invention to the extent that the spirit of the invention is included.

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