JP2008166608A - Spin device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a spin device capable of controlling the magnetization direction of a free layer by spin injection.
In a spin device, a secondary tunnel barrier F is absorbed in a free layer C in order to prevent the flow of electrons having a specific polarized spin flowing from a nonmagnetic metal layer D to a ferromagnetic layer E. As a result, the spin magnetic moment of electrons of a specific polarized spin is increased, and the magnetization direction of the free layer C can be controlled by spin injection at a low current. When the material constituting the sub-tunnel barrier F as the insulating layer is ZnO, the tunnel resistance of the sub-tunnel barrier F can be lowered, so that the influence is suppressed and the magnetoresistance related to the other tunnel barrier layer B is suppressed. This is advantageous for reading out changes.
[Selection] Figure 1

Description

  The present invention relates to a spin device including a TMR (tunnel magnetoresistance) element.

  A TMR (tunnel magnetoresistive) element is known to be usable for a spin device such as a hard disk head or an MRAM (magnetoresistance memory). The basic structure of a TMR element is a structure in which an insulating layer constituting a tunnel barrier is sandwiched between two ferromagnets. If the directions of magnetization of both ferromagnets are the same, the resistance becomes small and polarization is achieved. If the amount of spin electrons passing increases and the magnetization directions of both ferromagnets are opposite, the resistance increases and the amount of polarized spin electrons passing decreases.

For example, Patent Document 1 below discloses a TMR element having a dual structure in which MR elements of a CPP (current perpendicular plane) type are stacked. According to this element, since two MR elements are laminated, two tunnel barrier layers are accidentally brought into contact with the free layer, but this is not relevant to the present invention.
JP 2002-157708 A

  FIG. 9 is a diagram showing a longitudinal sectional structure of a spin device including a TMR element as a comparative example.

  In this spin device, a pinned layer A having a unidirectional magnetization direction, a tunnel barrier layer B, a free layer (soft magnetic ferromagnet) C, a nonmagnetic metal layer D, and a magnetization direction opposite to the above. Are sequentially laminated. The order of stacking may be reversed. Among the electrons injected into the pinned layer A, electrons having a spin in one direction pass through the tunnel barrier layer B and flow into the free layer C. A part of the polarized spin injected into the free layer C gives the spin magnetic moment to the free layer C and flows into the nonmagnetic metal layer D and the ferromagnetic layer E.

  When electrons pass through the former three layers A, B, and C, the TMR effect occurs, so the tunnel barrier layer B has a predetermined magnetic resistance for each of the up and down spins. When electrons pass through the latter three layers C, D, and E, a GMR effect occurs, and therefore the nonmagnetic metal layer D has a predetermined magnetic resistance for each spin.

  A large spin magnetic moment is applied to the free layer C by the polarized spin injected from the pinned layer A through the tunnel barrier layer B to the free layer C, so that the magnetization direction of the free layer C can be controlled by this. It becomes possible. This is called a spin injection method. The latter three layers C, D, and E reduce the probability that a specific polarized spin will escape from the device.

  FIG. 10 is an equivalent circuit of the spin device shown in FIG.

  In the figure, R1 is the resistance to the up-spin electrons of the tunnel barrier layer B, R2 is the resistance to the down-spin electrons in the tunnel barrier layer B, R3 is the resistance to the up-spin electrons of the ferromagnetic layer E, and R4 is the strong resistance The resistance to down-spin electrons in the magnetic layer E, R5, is the spin resistance of the free layer C and indicates the difficulty of absorbing the spin of the free layer.

  Potentials V and 0 are respectively applied to both ends of the spin device, and spin currents (electron currents) I1, I2, I3, I4, and I5 flow through the resistors R1, R2, R3, R4, and R5, respectively. The potential V is negative.

  In the figure, I5 is a spin current absorbed by the free layer C, which is proportional to the spin magnetic moment absorbed by the free layer C. A part of the spin magnetic moment absorbed in the free layer C causes a change in magnetization of the free layer C.

  When the ferromagnetic layer E is a normal ferromagnetic metal such as CoFe, since the resistance R3 to the up-spin current I3 of the ferromagnetic layer E is small, a large amount of spin current is not absorbed by the free layer C. Leaked from.

The spin current I5 absorbed in the free layer C is given by the following equation.

  From this equation, it can be seen that when the resistance R3 is small, the spin current I5 becomes small, so that the free layer C absorbs a lot of spins and the magnetization direction of the free layer C cannot be controlled.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a spin device capable of controlling the magnetization direction of a free layer by spin injection.

  In order to solve the above-described problems, the present invention provides the following spin device.

  A spin device according to a first aspect of the present invention is a spin device in which a pinned layer, a tunnel barrier layer, a free layer, a nonmagnetic metal layer, and a ferromagnetic layer are sequentially laminated, and between the nonmagnetic metal layer and the ferromagnetic layer. A secondary tunnel barrier is provided.

  This spin device functions as a TMR element by sandwiching a tunnel barrier layer between a pinned layer and a free layer. The secondary tunnel barrier prevents the flow of electrons with a specific polarization spin flowing from the nonmagnetic metal layer to the ferromagnetic layer, so that the spin magnetic moment of the electrons of the specific polarization spin absorbed in the free layer is increased. In addition, the magnetization direction of the free layer can be controlled by spin injection at a low current.

  A spin device according to a second aspect of the present invention is the above spin device, further comprising a second nonmagnetic metal layer between the ferromagnetic layer and the subtunnel barrier. As described above, even when the second nonmagnetic metal layer is interposed between the ferromagnetic layer and the subtunnel barrier, the subtunnel barrier has a specific polarized spin flowing from the nonmagnetic metal layer to the ferromagnetic layer. In order to prevent the flow of electrons having a certain amount, the spin magnetic moment of a specific polarized spin absorbed in the free layer increases, and the magnetization direction of the free layer is controlled by spin injection at a low current. Is possible.

  A spin device according to a third aspect of the present invention is a spin device having a free layer whose magnetization direction changes according to injected spin, and includes a pinned layer, a tunnel barrier layer, the free layer, a nonmagnetic metal layer, and a ferromagnetic layer. Is characterized in that a sub-tunnel barrier is provided between the free layer and the nonmagnetic metal layer.

  In this structure, since the secondary tunnel barrier is interposed between the free layer and the nonmagnetic metal layer, the secondary tunnel barrier has a specific polarized spin that flows from the free layer to the nonmagnetic metal layer. In order to prevent the flow, the spin magnetic moment of the electrons of a specific polarized spin absorbed in the free layer increases, and it becomes possible to control the magnetization direction of the free layer by spin injection at a low current. .

  A spin device according to a fourth aspect of the present invention is a spin device in which a pinned layer, a tunnel barrier layer, a free layer, a nonmagnetic metal layer, and a ferromagnetic layer are sequentially laminated, wherein the ferromagnetic layer is opposite to the nonmagnetic metal layer. And a secondary tunnel barrier and a second ferromagnetic layer.

  In this structure, the secondary tunnel barrier and the second ferromagnetic layer are absorbed in the free layer in order to prevent the flow of electrons having a particular polarized spin that is about to flow out of the first ferromagnetic layer. The spin magnetic moment of the electrons of a specific polarized spin is increased, and the magnetization direction of the free layer can be controlled by spin injection at a low current.

  A spin device according to a fifth aspect of the present invention is a spin device in which a pinned layer, a tunnel barrier layer, a free layer, a first nonmagnetic metal layer, and a second nonmagnetic metal layer are sequentially stacked. A sub-tunnel barrier is provided between the metal layer and the second nonmagnetic metal layer.

  This spin device functions as a TMR element by sandwiching a tunnel barrier layer between a pinned layer and a free layer. The secondary tunnel barrier prevents the flow of electrons having a specific polarization spin flowing from the first nonmagnetic metal layer to the second nonmagnetic metal layer, so that the specific polarization spin absorbed in the free layer is reduced. The spin magnetic moment of the electrons increases, and the magnetization direction of the free layer can be controlled by spin injection at a low current.

  A spin device according to a sixth aspect of the present invention is a spin device in which a pinned layer, a tunnel barrier layer, a free layer, and a nonmagnetic metal layer are sequentially laminated, and a sub-tunnel barrier is provided between the nonmagnetic metal layer and the free layer. It is characterized by that.

  This spin device functions as a TMR element by sandwiching a tunnel barrier layer between a pinned layer and a free layer. Since the secondary tunnel barrier is interposed between the nonmagnetic metal layer and the free layer, in order to prevent the flow of electrons having a specific polarized spin flowing from the free layer to the nonmagnetic metal layer, The spin magnetic moment of the electrons of the specific polarized spin that is absorbed is increased, and the magnetization direction of the free layer can be controlled by spin injection at a low current.

In the spin device according to the seventh invention, the sub-tunnel barrier includes at least one selected from the group consisting of MgO, ZnO and AlOx, TiO ₂ , ZrO ₂ , HfO ₂ , Ta ₂ O _5. Features. Since MgO has a large spin dependency of tunnel resistance, the spin polarizability can be improved. Since ZnO can reduce the tunnel resistance of the sub-tunnel barrier, it is advantageous for suppressing the influence and reading the magnetoresistance change related to the other tunnel barrier layer. Since AlOx such as Al ₂ O ₃ is known as an easily usable insulator, the cost can be reduced.

  The spin device according to an eighth aspect of the invention is characterized in that the sub-tunnel barrier is composed of an insulating layer or a Schottky barrier generated at a contact surface between a semiconductor and a metal by inserting a semiconductor layer. The Schottky barrier can be formed by inserting a semiconductor layer in contact with a metal layer adjacent to the insulating layer instead of the insulating layer. In the case where the sub-tunnel barrier is formed of an insulating layer, a layer whose thickness is accurately controlled can be formed, so that there is an advantage that a spin device with suppressed characteristic variation is obtained. When the sub-tunnel barrier includes a Schottky barrier formed by inserting a semiconductor layer, there is an advantage that the type of the Schottky barrier can be changed according to the semiconductor material to be inserted.

  In the above-described invention, the order of stacking may be reversed.

  According to the spin device of the present invention, the magnetization direction of the free layer can be controlled by spin injection.

Hereinafter, the spin device according to the embodiment will be described. Note that the same reference numerals are used for the same elements, and redundant description is omitted.
(First embodiment)

  FIG. 1 is a view showing a longitudinal sectional configuration of a spin device 1 including a TMR element according to the first embodiment.

  The spin device 1 is formed by sequentially laminating a pinned layer A, a tunnel barrier layer B, a free layer C, a nonmagnetic metal layer D, and a ferromagnetic layer (spin filter layer) E. The nonmagnetic metal layer D and the ferromagnetic layer E A secondary tunnel barrier F is provided therebetween. In each embodiment, the order of stacking may be reversed. Also, as shown in each drawing, adjacent layers are in contact.

Of the electrons injected into the pinned layer A having a unidirectional magnetization direction (+ Y direction) F _A , electrons having a unidirectional spin (having a negative charge) pass through the tunnel barrier layer B. , Flows into the free layer C. A portion of the injected polarized spin in the free layer C, giving the spin magnetic moment in the free layer C, to change the direction F _C of the magnetization of the free layer C, followed by the non-magnetic metal layer D, the sub-tunnel barrier F and the ferromagnetic layer E having the opposite magnetization direction F _E (−Y direction) sequentially flow to the outside. The injected electrons are conducted in each layer along the X direction.

The spin device 1 functions as a TMR element by sandwiching the tunnel barrier layer B between the pinned layer A and the free layer C. Orientation F _C of the magnetization of the free layer C is, for a same orientation F _A of magnetization of the pinned layer A (+ Y direction), the amount of electrons passing through the TMR element increases, the orientation F _C of the magnetization of the free layer C and the magnetization direction F _a of the pinned layer a case opposite (-Y direction), the amount of electrons passing through the TMR element is reduced.

Orientation F _C of the magnetization, since it is controlled by the spin injection, as the write current information, when injected into the free layer C a large amount of polarized spin from the pinned layer A, the magnetization of the free layer C direction F _C Is directed to the magnetization direction of the pinned layer A, and then a small amount of polarized spin is injected from the pinned layer A to the free layer C as a readout current, a large electron current is detected ( Magnetoresistance is reduced). On the other hand, electrons having a reverse polarization spin are injected from the ferromagnetic layer E into the free layer C, and electrons having a spin polarization opposite to the spin polarization of the injected electrons are caused to flow out of the pinned layer. In this case, the magnetization direction F _C of the free layer C is antiparallel to the magnetization of the pinned layer A, and then a small amount of polarized spin is injected from the pinned layer A into the free layer C as a readout current. In this case, a small electron current is detected (the magnetic resistance increases).

  In the spin device 1, the sub-tunnel barrier F prevents a flow of electrons having a specific polarization spin flowing from the nonmagnetic metal layer D to the ferromagnetic layer E, so that a specific polarization absorbed in the free layer C is obtained. The amount of electrons in the polar spin increases, and the magnetization direction of the free layer C can be controlled by spin injection at a low current. Polarized spins in the direction opposite to that of the ferromagnetic layer E are reflected by the sub-tunnel barrier F, but polarized spins having the same polarity are transmitted through the sub-tunnel barrier F. When spin injection is performed in the opposite direction, the tunnel barrier layer B positioned between the pinned layer A and the free layer C reflects polarized spins having a polarity opposite to that of the pinned layer A. .

  In the spin device of the comparative example described above, in order to increase the efficiency of spin injection into the free layer C, it is necessary to increase the spin accumulation potential. However, the structure of the comparative example described above is not sufficient. The reason is that the spin current flows out from the surface of the free layer C in contact with the metal opposite to the surface in contact with the tunnel barrier layer B. In the comparative example described above, the ferromagnetic layer E is provided as the spin filter layer facing the surface of the free layer C opposite to the surface in contact with the tunnel barrier layer B. When E is used, since the resistance of the ferromagnetic layer E to a small number of spins is not sufficient, most of the spin current flows out. In the case of performing reverse spin injection by flowing a current in the opposite direction, the resistance to the minority spin of the ferromagnetic layer E is not sufficient, so the spin accumulation potential in the free layer C does not increase. The spin magnetic moment of a specific polarized spin electron absorbed in the free layer C is small. For this reason, since the spin magnetic moment of the electrons of the specific polarized spin absorbed in the free layer C is small, the spin injection efficiency is low.

  On the other hand, in the spin device according to the embodiment, a sub-tunnel barrier F is provided. The ratio of the tunnel conductance of electrons with a large number of spins and electrons with a small number of spins when passing through the sub-tunnel barrier F is determined by the Fermi surface of the electrons having a large number of spins on both sides of the tunnel layer. It can be estimated as the ratio of the product of the density of states and the product of the density of states at the Fermi surface of electrons with a small number of spins on both sides of the tunnel layer. Moreover, the tunnel conductance is much smaller than the conductance of the ferromagnetic metal. Therefore, the difference in resistance of the ferromagnetic layer E with respect to the majority spin electrons and the minority spin electrons to which the tunnel resistance is added becomes larger than when the sub tunnel barrier F is not inserted. As a result, the spin current does not escape, and the injected spin current is effectively absorbed in the free layer C and used for the change in magnetization of the free layer.

The materials and preferred thickness ranges of the pinned layer A, tunnel barrier layer B, free layer C, nonmagnetic metal layer D and ferromagnetic layer E are as follows.

  In particular, the thickness of the nonmagnetic metal layer D is preferably set in the above-mentioned range because the magnetic coupling between the ferromagnetic layer E and the free layer C is prevented.

  The pinned layer A and / or the ferromagnetic layer E are each composed of a ferromagnetic layer alone or a layer in which a ferromagnetic layer and an antiferromagnetic layer such as IrMn are exchange-coupled to each other in order to fix the magnetization direction. It is good.

  FIG. 2 is an equivalent circuit of the spin device shown in FIG.

  In the figure, R1 is the resistance to the up-spin electrons of the tunnel barrier layer B, R2 is the resistance to the down-spin electrons in the tunnel barrier layer B, R3 'is the resistance to the up-spin electrons of the ferromagnetic layer E, and R4 is The resistance to down-spin electrons in the ferromagnetic layer E, R5, is the spin resistance of the free layer C and indicates the difficulty of absorbing the spin of the free layer.

  Potentials V and 0 are respectively applied to both ends of the spin device, and spin currents (electron currents) I1, I2, I3 ′, I4, and I5 flow through the resistors R1, R2, R3 ′, R4, and R5, respectively. . The potential V in the figure is negative.

  In the figure, I5 is a spin current absorbed by the free layer C, which is proportional to the spin magnetic moment absorbed by the free layer C. A part of the spin magnetic moment absorbed in the free layer C causes a change in magnetization of the free layer C.

  A secondary tunnel barrier F is inserted between the nonmagnetic metal layer D and the ferromagnetic layer E, and electrons cause a spin-dependent tunnel at the interface between the nonmagnetic metal layer D and the ferromagnetic layer E. Resistance occurs. As a result, R3 'can be increased.

The spin current I5 absorbed in the free layer C is given by the following equation.

  From this equation, it can be seen that when the resistance R3 'is large, the spin current I5 becomes large, so that the efficiency of spin injection is improved.

  In the first embodiment and the following embodiments, the tunnel barrier F is preferably made of an insulating layer having a thickness that causes a tunnel effect, but this is made of a semiconductor layer and a (nonmagnetic) metal layer in contact with the semiconductor layer. It is good also as comprising by the Schottky barrier comprised. The Schottky barrier can be formed by inserting a semiconductor layer in contact with a metal layer adjacent to the insulating layer instead of the insulating layer. That is, a semiconductor layer is inserted at the position of the tunnel barrier F, and a Schottky barrier is formed on the contact surface with the nonmagnetic metal layer D or the like. The sub tunnel barrier F is composed of an insulating layer or a Schottky barrier. In the case where the sub-tunnel barrier F is formed of an insulating layer, a layer whose thickness is accurately controlled can be formed, so that there is an advantage that a spin device with suppressed characteristic variation is obtained. When the sub-tunnel barrier F is a Schottky barrier, there is an advantage that the type of the Schottky barrier can be changed according to the semiconductor material.

As a semiconductor material, for example, Si can be used. As a metal constituting a Schottky barrier with respect to n-type Si, φ is a Schottky barrier height, and Al (φ = 0.72 V), Mo (φ = φ = 0.68 V), Pt (φ = 0.90 V), W (φ = 0.67 V), TiSi ₂ (φ = 0.60 V), WSi ₂ (φ = 0.65 V), Au (φ = 0.80 V) ) And the like, and for p-type Si, Al (φ = 0.58 V), Mo (φ = 0.42 V), W (φ = 0.45 V), Au (φ = 0. 34V) is known. When a Schottky barrier is used, these metals may be used for the adjacent nonmagnetic metal layer.

Further, when the material constituting the sub-tunnel barrier F as the insulating layer is MgO, the spin resistance of the tunnel resistance is large, so that the spin polarizability can be improved. When this material is ZnO, it is possible to reduce the tunnel resistance of the sub-tunnel barrier F, which is advantageous in suppressing the influence and reading out the magnetoresistance change related to the other tunnel barrier layer B. Since AlOx such as Al ₂ O ₃ is known as an easily usable insulator, the cost can be reduced. These materials can be used for the tunnel barrier layer B. The sub-tunnel barrier F includes at least one selected from the group consisting of MgO, ZnO and AlOx, TiO ₂ , ZrO ₂ , HfO ₂ , Ta ₂ O ₅ .
(Second Embodiment)

  FIG. 3 is a view showing a longitudinal sectional structure of the spin device 1 according to the second embodiment.

  The spin device 1 includes a second nonmagnetic metal layer G between the ferromagnetic layer E and the subtunnel barrier F in the spin device 1 of the first embodiment. Thus, even when the second nonmagnetic metal layer G is interposed between the ferromagnetic layer E and the subtunnel barrier F, the subtunnel barrier F is changed from the nonmagnetic metal layer D to the ferromagnetic layer E. In order to block the flow of electrons having a specific polarized spin that flows, the spin magnetic moment of the electrons of the specific polarized spin absorbed in the free layer C increases, and free by spin injection, which was impossible in the past, It becomes possible to control the magnetization direction of the layer C.

Note that the preferred thickness range of the second nonmagnetic metal layer G is equal to or less than the spin diffusion length of the nonmagnetic metal layer G because the spin polarization of conduction electrons is not attenuated. If the electron conduction between the nonmagnetic metal layer G and the ferromagnetic layer E is elastic, the same operation and effect as in the first embodiment can be obtained. An equivalent circuit is also expressed in the same manner.
(Third embodiment)

  FIG. 4 is a view showing a longitudinal sectional structure of the spin device 1 according to the third embodiment.

This spin device 1 has a free layer C in which the magnetization direction F _C changes according to the injected spin, and includes a pinned layer A, a tunnel barrier layer B, a free layer C, a nonmagnetic metal layer D, and a ferromagnetic layer E. A sub tunnel barrier F is provided between the free layer C and the nonmagnetic metal layer D.

In the case of this structure, since the secondary tunnel barrier F is interposed between the free layer C and the nonmagnetic metal layer D, the secondary tunnel barrier F has a specific bias that flows from the free layer C to the nonmagnetic metal layer D. In order to prevent the flow of electrons having a polar spin, the spin magnetic moment of electrons of a specific polarized spin absorbed in the free layer increases, and the magnetization of the free layer C due to spin injection, which has been impossible in the past, is increased. it is possible to control the orientation F _C.

The spin device 1 of this embodiment differs from the spin device of the first embodiment only in the insertion position of the sub-tunnel barrier F. Note that the preferable thickness range of the nonmagnetic metal layer D is equal to or less than the spin diffusion length of the nonmagnetic metal layer G because the spin polarization rate of conduction electrons is not attenuated. If the electron conduction between the nonmagnetic metal layer D and the ferromagnetic layer E is elastic, the same operations and effects as in the first embodiment can be obtained. An equivalent circuit is also expressed in the same manner. In addition, at the interface between the nonmagnetic metal layer D and the ferromagnetic layer E, a spin filter effect that selects the passage of electrons of a specific polarized spin occurs, and the spin polarizability is improved.
(Fourth embodiment)

  FIG. 5 is a view showing a longitudinal sectional structure of the spin device 1 according to the fourth embodiment.

  The spin device 1 includes a pinned layer A, a tunnel barrier layer B, a free layer C, a nonmagnetic metal layer D, and a ferromagnetic layer E, which are sequentially stacked. A sub-tunnel barrier F and a second ferromagnetic layer H are sequentially provided on the opposite side.

In the case of this structure, the functions of the layers A to E are as described above, but the specific polarized spin that the secondary tunnel barrier F and the second ferromagnetic layer H try to flow out of the first ferromagnetic layer E is used. In order to prevent the flow of electrons having the above, the spin magnetic moment of the electrons of a specific polarized spin absorbed in the free layer C increases, and the magnetization direction of the free layer C caused by spin injection, which was impossible in the past, it becomes possible to control the F _C.

That is, since the sub-tunnel barrier F is interposed between the ferromagnetic layers E and H having the same magnetization directions F _E and F _H , these three layers constitute a TMR element and serve as a spin filter. Functions and blocks the passage of electrons having spins of different polarity, and spins accumulate in the free layer C.

  Note that the preferable thickness range of the nonmagnetic metal layer D is equal to or less than the spin diffusion length of the nonmagnetic metal layer G because the spin polarization rate of conduction electrons is not attenuated. Also in this example, the same operation and effect as the first embodiment can be obtained.

  FIG. 6 is an equivalent circuit of the spin device 1 shown in FIG.

  In the figure, R1 is the resistance to the up-spin electrons of the tunnel barrier layer B, R2 is the resistance to the down-spin electrons in the tunnel barrier layer B, R3 'is the resistance to the up-spin electrons of the ferromagnetic layer E, and R4 is Resistance to down-spin electrons in the ferromagnetic layer E, R5 is the spin resistance of the free layer C, indicating that it is difficult to absorb the spin magnetic moment of the free layer, and R6 is the spin resistance in the ferromagnetic layer E This shows the difficulty of absorbing the spin magnetic moment of the ferromagnetic layer E.

  Potentials V and 0 are respectively applied to both ends of the spin device, and each of the resistors R1, R2, R3 ′, R4, R5, and R6 has spin currents (electron currents) I1, I2, I3 ′, I4, I5, Each I6 flows. The potential V in the figure is negative.

  In the figure, I5 is a spin current absorbed by the free layer C, which is proportional to the spin magnetic moment absorbed by the free layer C. A part of the spin magnetic moment absorbed in the free layer C causes a change in magnetization of the free layer C.

  By inserting the sub-tunnel barrier F between the ferromagnetic layers E and H, the resistance R3 'with respect to the up spin current I3 can be increased, so that most of the spin current can be absorbed by the free layer C. In this case, the spin current is also absorbed by the ferromagnetic layer E constituting the spin filter layer, but when the resistance R6 is large, the same spin injection efficiency as in the first embodiment can be obtained. The advantage of this embodiment is that the sub-tunnel barrier F is sandwiched between the ferromagnetic layers E and H selected from the ferromagnetic metal selected from the group selected from Co, Fe, CoFe, and CoFeB. The spin dependency of the tunnel resistance can be increased.

The spin current I5 absorbed in the free layer C is given by the following equation.

  This formula also shows that when the resistance R3 'is large, the spin current I5 becomes large, so that the efficiency of spin injection is improved.

  The spin device 1 described above can be used as a read head of a hard disk or an MRAM by arranging a pair of hard magnetic bodies at both ends in the Y-axis direction or both ends in the Z-axis direction.

  FIG. 7 is a view showing a longitudinal sectional structure of the spin device 1 according to the fifth embodiment.

  The spin device 1 is a spin device in which a pinned layer A, a tunnel barrier layer B, a free layer C, a first nonmagnetic metal layer D, and a second nonmagnetic metal layer K are sequentially stacked. A sub-tunnel barrier F is provided between the magnetic metal layer D and the second nonmagnetic metal layer K.

  In this spin device 1, the tunnel barrier layer B is sandwiched between the pinned layer A and the free layer C, thereby functioning as a TMR element. Since the sub-tunnel barrier F prevents the flow of electrons having a specific polarized spin flowing from the first nonmagnetic metal layer D to the second nonmagnetic metal layer K, a specific tunnel absorbed in the free layer C The spin magnetic moment of the polarized spin electrons increases, and the magnetization direction of the free layer can be controlled by spin injection at a low current. The materials of the nonmagnetic metal layers D and K are as described above. However, the nonmagnetic metal layer D is preferably a metal with small spin relaxation such as Mg.

In the case of this structure, the equivalent circuit is the same as that shown in FIG. 2, and the value of the resistor R4 is equal to the resistor R3 ′. That is, the current I5 is given by the following equation.

  As shown in FIG. 1, in the equivalent circuit in the case where the ferromagnetic layer E is present, R3 ′> R4, but in this example, R3 ′ = R4. However, when the resistance R3 ′ satisfies R5 <R3 ′ <R2, that is, the resistance R3 ′ is smaller than the resistance (R2) to the minority spin electrons of the TMR element and is smaller than the spin resistance (R5) of the free layer C. When it is large, it can be seen that the current I5 becomes large. Therefore, it can be seen that the efficiency of spin injection is improved in this case as compared with the case where there is no sub-tunnel barrier F.

  FIG. 8 is a view showing a longitudinal sectional structure of the spin device 1 according to the sixth embodiment.

  The spin device 1 is a spin device in which a pinned layer A, a tunnel barrier layer B, a free layer C, and a nonmagnetic metal layer D are sequentially stacked, and a sub-tunnel barrier between the nonmagnetic metal layer D and the free layer C. F is provided.

  In this spin device 1, the tunnel barrier layer B is sandwiched between the pinned layer A and the free layer C, thereby functioning as a TMR element. Since the secondary tunnel barrier F is interposed between the nonmagnetic metal layer D and the free layer C, the flow of electrons having a specific polarized spin flowing from the free layer C to the nonmagnetic metal layer D is prevented. As a result, the spin magnetic moment of electrons of a specific polarized spin absorbed in the free layer C increases, and the magnetization direction of the free layer can be controlled by spin injection at a low current. The equivalent circuit of the spin device 1 is the same as that of FIG.

  Note that electrodes (not shown) are provided on layers at both ends in the X direction of the above-described spin device, and are connected to the wiring.

  The present invention can be used for a spin device having a TMR element.

It is a figure which shows the longitudinal cross-sectional structure of the spin device 1 provided with the TMR element which concerns on 1st Embodiment. 2 is an equivalent circuit of the spin device shown in FIG. 1. It is a figure which shows the longitudinal cross-section of the spin device 1 which concerns on 2nd Embodiment. It is a figure which shows the longitudinal cross-section of the spin device 1 which concerns on 3rd Embodiment. It is a figure which shows the longitudinal cross-section of the spin device 1 which concerns on 4th Embodiment. 6 is an equivalent circuit of the spin device 1 shown in FIG. It is a figure which shows the longitudinal cross-section of the spin device 1 which concerns on 5th Embodiment. It is a figure which shows the longitudinal cross-section of the spin device 1 which concerns on 6th Embodiment. It is a figure which shows the longitudinal cross-section of the spin device provided with the TMR element used as a comparative example. 10 is an equivalent circuit of the spin device shown in FIG. 9.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Spin device, A ... Pinned layer, B ... Tunnel barrier layer, C ... Free layer, D ... Nonmagnetic metal layer, E ... Ferromagnetic layer, F ... Sub tunnel barrier, G ... Nonmagnetic metal layer, H ... Strong Magnetic layer, K: nonmagnetic metal layer.

Claims (8)

In a spin device in which a pinned layer, a tunnel barrier layer, a free layer, a nonmagnetic metal layer, and a ferromagnetic layer are sequentially stacked, a sub-tunnel barrier is provided between the nonmagnetic metal layer and the ferromagnetic layer. Characteristic spin device. The spin device according to claim 1, further comprising a second nonmagnetic metal layer between the ferromagnetic layer and the sub-tunnel barrier. A spin device having a free layer in which the direction of magnetization changes according to injected spin, wherein the pinned layer, tunnel barrier layer, free layer, nonmagnetic metal layer, and ferromagnetic layer are sequentially stacked. A spin device comprising a sub-tunnel barrier between the free layer and the nonmagnetic metal layer. In a spin device formed by sequentially laminating a pinned layer, a tunnel barrier layer, a free layer, a nonmagnetic metal layer, and a ferromagnetic layer, a sub tunnel barrier and a second layer on the opposite side of the ferromagnetic layer from the nonmagnetic metal layer A spin device comprising a ferromagnetic layer and a sequential layer. In the spin device formed by sequentially laminating a pinned layer, a tunnel barrier layer, a free layer, a first nonmagnetic metal layer, and a second nonmagnetic metal layer, the first nonmagnetic metal layer and the second nonmagnetic layer A spin device comprising a secondary tunnel barrier between a metal layer and a spin layer. A spin device comprising a pinned layer, a tunnel barrier layer, a free layer, and a nonmagnetic metal layer sequentially stacked, wherein the spin device comprises a subtunnel barrier between the nonmagnetic metal layer and the free layer. . The sub-tunnel barrier includes at least one selected from an insulator group consisting of MgO, ZnO, AlOx, TiO ₂ , ZrO ₂ , HfO ₂ , and Ta ₂ O ₅ . The spin device according to any one of claims. 7. The sub-tunnel barrier is configured by an insulating layer or a Schottky barrier generated at a contact surface between a semiconductor and a metal by inserting a semiconductor layer. Spin device.

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