JP4297739B2 - Spin-injection magnetization reversal magnetoresistive element using quantum size effect - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a carrier spin injection magnetoresistive effect element, and more particularly to a magnetoresistive effect element using a technique for improving the efficiency of spin injection magnetization reversal by a quantum size effect.
[0002]
[Prior art]
A magnetoresistive effect element has attracted attention as an element used for a mass storage medium in an advanced information society. In particular, a magnetic head using the magnetoresistive effect has been put to practical use because it can achieve high sensitivity and high density.
[0003]
Recently, research on magnetoresistive films in which ferromagnets and nonmagnetic metals are alternately laminated has become active. The magnetoresistive film realizes a ferromagnetic parallel magnetization state and an antiparallel magnetization state by an external magnetic field, and utilizes a difference in electrical resistance in the film stacking direction in both states. For example, as a magnetic sensor Expected. In addition, research on a magnetic random access memory (MRAM) using a magnetoresistive effect film as a main component of a nonvolatile memory cell has been actively conducted. As shown in FIG. 15, the MRAM 100 has, for example, a structure in which an insulating layer 105 is sandwiched between two ferromagnetic layers 101 and 103, and one ferromagnetic layer that can be changed by a magnetic field. Lamination resulting from whether the relationship of the magnetization state between 101 and the other ferromagnetic layer 103 that cannot be changed by a magnetic field is a parallel magnetization state (low resistance) or an antiparallel magnetization state (high resistance) It is a non-volatile memory which reads the difference of the electrical resistance regarding a direction as memory | storage information. Since the structure of the MRAM cell is simple, a large number of MRAMs 100 are arranged on a two-dimensional plane and wirings L1 and L2 are connected to the ferromagnetic layers 101 and 103, respectively, as shown in FIG. An apparatus can be realized.
[0004]
In addition, a technique for realizing magnetization reversal without using an induced magnetic field has been proposed. For example, a carrier spin injection magnetization reversal type magnetoresistive effect film that performs magnetization reversal by injecting carrier spin in the stacking direction has also been proposed (see, for example, Non-Patent Documents 1 and 2). In the above carrier spin injection magnetization reversal type magnetoresistive effect film, when spin-polarized carriers are electrically injected from the injection layer to the inversion layer, the torque caused by the carriers to the magnetization of the magnetic material exceeds a certain inversion current. Magnetization rotation of the magnetization switching film occurs.
[0005]
[Non-Patent Document 1]
JCSlonczewski, Journal of Magnetism and Magnetic Materials 159 (1996) L1-L7.
[Non-Patent Document 2]
L. Berger, Physical Review B, Vol. 54 No. 13, 9353 (1996).
[0006]
[Problems to be solved by the invention]
By the way, a magnetoresistive film used for MRAM or the like needs to apply an induction magnetic field (external magnetic field) to a specific cell in order to realize either parallel magnetization or antiparallel magnetization of a ferromagnetic layer. There is. Therefore, there is a problem that it is necessary to build a magnetic field generator and power consumption is increased. In MRAM, the higher the density of a storage device, that is, the miniaturization of an element, the greater the influence of a leakage magnetic field on adjacent storage cells, and information is rewritten only on specific cells. It has the problem that it becomes difficult.
[0007]
On the other hand, the use of the carrier spin injection magnetization reversal magnetoresistive film can cope with the miniaturization of the element as compared with the case where a magnetic field is applied. ⁷ A / cm ² A large current is required. Moreover, since the intermediate layer is made of an insulator, it is difficult to realize the tunnel magnetoresistive element constituting the memory cell of the magnetic MRAM.
[0008]
The inventor previously proposed a technique that utilizes the fact that magnetization is rotated when spin-polarized carriers are injected according to an optical selection rule by circularly polarized light. This technique will be described with reference to FIGS. FIG. 1 is a diagram showing a conceptual configuration of an element using a spin-injection magnetization switching film according to the previous proposal, and is a diagram showing a configuration example of an element using a III-V group magnetic semiconductor. FIG. 2 is a schematic diagram showing a transition state between the conduction band and the valence band of the element shown in FIG. FIG. 3A and FIG. 3B are diagrams illustrating the interaction between photogenerated spin-polarized holes and Mn.
[0009]
As shown in FIG. 1, the element using the spin transfer magnetization switching film according to the previous proposal has a structure in which, for example, a (Ga, Mn) As layer 3 is laminated on a GaAs layer 1. When this element is irradiated with circularly polarized light 5 in the stacking direction, an optical transition occurs as shown in FIG. In this case, the levels of heavy holes and light holes in the valence band are degenerated. As shown in FIGS. 3 (a) and 3 (b), in the magnetic mixed crystal semiconductor (Ga, Mn) As, the photogenerated spin-polarized holes give a torque to the Mn magnetic moment by interaction with Mn, Causes magnetization rotation. The direction of magnetization of a magnetic semiconductor is determined by the direction of carrier (electron / hole) spin excited in the semiconductor, and the quantization axis is determined by the direction of incidence of circularly polarized light. The direction of the carrier (electron / hole) spin about the quantization axis depends on whether the circularly polarized light is directed rightward or leftward.
[0010]
Here, the phenomenon that occurs when the structure shown in FIG. 1 is actually irradiated with circularly polarized light will be described with reference to FIG. First, in the structure shown in FIG. ₁ (LH ₁ ) Is degenerate in terms of energy, and E in the conduction band. ₁ Circularly polarized light σ having a wavelength corresponding to the energy difference ΔE between ⁺ , Only an optical transition with angular momentum L = + 1 occurs. Heavy hole HH ₁ And light hole LH ₁ Both electrons present in and are excited to the conduction band and holes are generated in the valence band. HH ₁ An electron with an electron transition from the valence band to the conduction band of, produces a spin-down electron, and LH ₁ As a result of the transition from the valence band to the conduction band, electrons with upward spin are generated. At this time HH ₁ Transition probability from LH ₁ As a result, the spin polarization rate of photogenerated electrons in the conduction band is 50% downward. Since all spins are conserved before and after transition, there are photogenerated holes with a 50% upward polarization in the valence band. Circularly polarized light σ ^- , An optical transition of L = −1 occurs. Again, circularly polarized light σ ₊ The spin polarization rate of photogenerated electrons / holes is 50% by the same selection side as in the case of irradiating.
[0011]
That is, in the structure shown in FIG. ⁺ And σ ^- Even when the above are selectively irradiated, the spin directions of photogenerated carriers cannot be completely aligned. Carriers having different spin directions exert different directions of torque on the magnetization, which means that the magnetization reversal is not performed efficiently.
[0012]
An object of the present invention is to increase the efficiency of magnetization reversal in order to reduce the power required for magnetization reversal.
[0013]
[Means for Solving the Problems]
According to one aspect of the present invention, the spin injection includes: providing a quantum magnetic semiconductor structure capable of quantum confinement of carriers; and irradiating the quantum magnetic semiconductor with elliptically polarized light A control method is provided. The quantum magnetic semiconductor structure has a magnetic semiconductor layer in which a magnetic metal is mixed in a semiconductor layer.
[0014]
In the above quantum magnetic semiconductor structure, the two levels of a heavy valence band and a light hole are split, for example, a wavelength corresponding to the energy difference between the heavy hole and the conduction band. By irradiating the elliptically polarized light, it is possible to selectively excite electrons present in heavy holes to the conduction band, improve the spin polarization rate of photogenerated carriers, and perform spin injection magnetization reversal. Can wake up efficiently.
[0015]
According to another aspect of the present invention, a magnetic semiconductor and an energy barrier for quantum mechanical confinement of the magnetic semiconductor, the degeneration of heavy holes and light hole states in the valence band of the magnetic semiconductor are solved. A quantum magnetic semiconductor microstructure having a semiconductor magnetic metal region is provided.
[0016]
In addition, an optical semiconductor device having a light source that selects an energy difference between quantum levels formed in a valence band and a conduction band in the semiconductor magnetic metal region and irradiates elliptically polarized light having energy corresponding thereto By using, it is possible to improve the spin polarization rate during irradiation with elliptically polarized light.
[0017]
A lower electrode; a fixed layer formed in the lower electrode and having a fixed orientation in magnetization; a first energy barrier layer formed in the fixed layer; and a magnetization inversion layer formed in the first energy barrier layer And a second energy barrier layer formed on the magnetization switching layer,
There is provided a quantum well spin-injection magnetization reversal magnetoresistive element having a transparent electrode formed on the second energy barrier layer.
[0018]
With the above structure, the degeneration between the hole levels in the magnetization switching layer can be solved, and electrons can be excited into the conduction band only from one level, and the spin polarization rate of the excited photogenerated carriers can be selected. Can be improved.
[0019]
Further, this quantum well spin-injection magnetization reversal magnetoresistive element, voltage detection means for detecting the voltage between the lower electrode and the transparent electrode, and energy for exciting the carriers of the magnetization reversal layer from the transparent electrode side And a light source capable of irradiating elliptically polarized light having a wavelength corresponding to the transition energy between the quantum levels formed in the conduction band and the valence band. In the non-volatile memory, carriers with a high spin polarization can be injected, so that spin injection magnetization reversal can be performed efficiently and the performance of the memory can be improved.
[0020]
Furthermore, a shutter that is provided on the elliptically polarized light irradiation side of the quantum well spin-injection magnetization switching magnetoresistive element and selectively irradiates the elliptically polarized light can be provided. For example, by circularly controlling the operation of the shutter, it is possible to irradiate only a specific element for which rewriting of stored information is desired with circularly polarized light.
[0021]
According to another aspect of the present invention, there is provided a magnetic semiconductor and an energy barrier that confines the magnetic semiconductor quantum mechanically, and degenerates heavy holes and light hole states in the valence band of the magnetic semiconductor. Light having a quantum magnetic semiconductor microstructure having a semiconductor magnetic metal region, a light receiving surface for receiving elliptically polarized light irradiated to the quantum magnetic semiconductor microstructure, and a measurement unit for measuring the potential of the magnetic semiconductor A sensor is provided.
[0022]
By using the sensor, for example, it is possible to sense the presence / absence or intensity of elliptically polarized light and the direction of elliptically polarized light.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
The inventor uses the fact that the spin polarization rate of the photogenerated carrier can be made almost 100% by forming quantum levels in the magnetic semiconductor layer by the quantum size effect, thereby effectively causing spin injection magnetization reversal. I came up with technology. As a result, it is possible to increase the efficiency of spin injection magnetization reversal and to reduce the power required for the magnetization reversal associated therewith. The principle of the quantum well spin-injection magnetization switching film according to one embodiment of the present invention will be described with reference to FIGS. FIG. 4 is a diagram showing a structure example of the quantum well spin-injection magnetization switching film according to the present embodiment. As shown in FIG. 4, the quantum well spin-injection magnetization switching film according to the present embodiment includes a first energy barrier layer 15 formed of, for example, an AlAs layer on the GaAs layer 11 and (Ga, Mn) As. It has a quantum well structure formed of a stacked structure including a formed quantum well layer 17 and a second energy barrier layer 21 formed of an AlAs layer. The first and second energy barrier layers 15 and 21 are made of Al. _x Ga _1-x An As layer (0 <x <1) may be used.
[0024]
FIG. 5 shows a schematic energy band structure related to the (Ga, Mn) As layer 17 forming the quantum well layer in the quantum well structure shown in FIG. As shown in FIG. 5, by confining carriers (holes) within a small size such that the quantum mechanical effect is noticeable, ₁ And LH ₁ Splitting the energy level with (energy difference = ΔE ₂ -ΔE _Three ). HH ₁ And LH ₁ By using energy level splitting with ₁ -HH ₁ Energy (wavelength) ΔE ₂ HH among the hole levels in the valence band when irradiated with circularly polarized light having ₁ Only the conduction band E ₁ Can be selectively excited. At this time, LH ₁ Holes in have circularly polarized energy (wavelength) E ₁ -LH ₁ Different from the energy (wavelength) of (ΔE _Three Therefore, LH ₁ Are not excited in the conduction band. Circularly polarized light is obtained by shifting the electric field vector of linearly polarized light by λ / 4 (λ is a wavelength) in the clockwise direction and the counterclockwise direction. For example, it can be obtained by a known technique such as passing linearly polarized laser light from a laser light source through a quarter-wave plate or passing an optical crystal to which an electric field such as a Pockel cell is applied.
[0025]
This phenomenon will be described more specifically. First, the valence band HH is compared with the structure shown in FIGS. ₁ And conduction band E ₁ Difference ΔE between ₂ Circularly polarized light with a wavelength corresponding to ⁺ , Only an optical transition with angular momentum L = + 1 occurs. HH ₁ Only the electrons inside are excited to the conduction band to generate heavy holes, and LH ₁ The electrons inside are not excited to the valence band. HH ₁ Only the transition from the valence band to the conduction band of the electrons inside occurs, so that the spin of photogenerated electrons in the conduction band is completely downward, and the spin polarization rate is 100%. At this time, all the spins are conserved, so that the photogenerated holes in the valence band are completely upward and the spin polarization rate is 100%. Valence band HH ₁ And conduction band E ₁ Difference ΔE between ₂ Circularly polarized light with a wavelength corresponding to ^- , An optical transition of L = −1 occurs. Again, circularly polarized light σ ⁺ As in the case of irradiation, the spin polarization of photogenerated carriers is 100%. That is, in the structure shown in FIG. 4 and FIG. ₁ -HH ₁ Σ of circularly polarized light selected for ⁺ And σ ^- , The spin directions of the electrons excited in the conduction band and the holes generated in the valence band can be perfectly aligned, and the photogenerated spin polarization degree is 100%. be able to. It is also possible to lengthen the relaxation time of photogenerated spin-polarized holes by strongly confining carriers in the quantum well, and this effect can be used to increase the magnitude of spin injection magnetization reversal. It is considered possible.
[0026]
Next, an experiment relating to the formation of quantum levels in the AlAs / GaMnAs / AlAs quantum well in the structure shown in FIG. 4 will be described with reference to FIGS. FIG. 6 and FIG. 7 are diagrams showing the results of evaluating the characteristics regarding the AlAs / GaMnAs / AlAs quantum well used in the quantum well spin-injection magnetization switching film according to the present embodiment. FIG. 6 is a diagram showing the relationship between photon energy and reflected MCD (magnetic circular dichroism) when the well width of the GaMnAs quantum well structure is changed and irradiated with circularly polarized light, the measurement temperature is 7K, and the magnetic field It is a figure which shows the result measured on condition of H = 1.2T. The results are shown when the well width of GaMnAs is changed to 0.5 nm (AR4), 1.5 nm (AR3), 3 nm (AR2), 5 nm (AR1), and 10 nm (AR0). The arrows indicate E calculated for each well width. ₁ -HH ₁ Indicates the position of the transition. As shown in the figure, it can be seen that the peak of MCD shifts to the higher energy side as the quantum well width of GaMnAs is narrowed. As the quantum well width of GaMnAs becomes narrower, E ₁ -HH ₁ It is considered that the peak energy position of the MCD is also shifted to the higher energy side with the increase of the value (see FIG. 7B).
[0027]
FIG. 7A shows E obtained by theoretical calculation. ₁ -HH ₁ FIG. 7 is a diagram in which the relationship between the transition energy and the quantum well width obtained from the peak value of the MCD spectrum is plotted based on the curve of the value and the quantum well width and FIG. 6. As shown in FIG. 7A, the value obtained from the MCD spectrum is in good agreement with the curve based on the theoretical calculation value, and the quantum level is formed in the GaMnAs well layer in the AlAs / GaMnAs / AlAs quantum well structure. It was confirmed that
[0028]
Next, with reference to FIG. 8 to FIG. 10, an experimental result regarding optical spin injection magnetization reversal regarding the AlAs / GaMnAs / AlAs quantum well used in the spin injection magnetization reversal magnetoresistive element according to the present embodiment will be described. In addition, the experimental results when using bulk GaMnAs are shown correspondingly. 8 (a) and 8 (b) show 2.0 × 10 for the AlAs / GaMnAs / AlAs quantum well structure. ¹³ photon / cm ² It is a figure which shows the relationship between the delay time between the detection light with respect to Kerr rotation angle and excitation light at the time of irradiating / pulse circularly polarized light pulse. Σ having an energy of 1.61 eV at a measurement temperature of 30 K and a magnetic field of 0 T ⁺ Of circularly polarized light or σ ^- As shown in FIG. 8 (a), the time-resolved Kerr rotation shows a substantially target value in the positive and negative directions and approaches 0 as time passes. I understand that.
[0029]
Further, as shown in FIG. 8B, it can be seen that it has two components, a component that relaxes quickly and a component that slows. This is considered to be due to the presence of two components, a component having a fast relaxation related to spin relaxation of carriers and a component having a slow relaxation related to rotation of Mn. The magnetization change ΔM of the slow component at 0 ps is 13 mdeg.
[0030]
On the other hand, FIGS. 9A and 9B shown as comparative examples are 1.5 × 10 5 for the GaMnAs bulk structure. ¹² photon / cm ² It is a figure which shows the relationship between Kerr rotation angle and delay time at the time of irradiating the / pulse circularly-polarized-light pulse. Σ having an energy of 1.58 eV at a measurement temperature of 20 K and a magnetic field of 0 T ⁺ Of circularly polarized light or σ ^- As in FIG. 8 (a), the time-resolved Kerr rotation shows almost the target value in the positive and negative directions and approaches 0 with the passage of time (relaxation). I understand.)
[0031]
Comparing FIG. 8 (b) and FIG. 9 (b), ΔM, which is slower relaxation, which is a value related to the rotation of Mn, is larger in the quantum well structure, and at the moment of light irradiation (0 ps) It can be seen that the well structure is 13 mdeg and the GaMnAs bulk structure is 2 mdeg.
[0032]
Based on this result, FIG. 10 shows a summary of the characteristics in the case of using each of the bulk (single layer film) and the quantum well as the spin magnetization switching film. As shown in FIG. 10, in the GaMnAs layer in the case of bulk (x = 0.011), 7.0 × 10 ¹⁵ photon / cm ^Three / Pulse (1.5 × 10 ¹² photon / cm ² / Pulse) of about 0.5% of saturation magnetization (10 ¹⁸ cm ^-3 ) (ΔM = 2 mdeg, M _s = 400 mdeg.) Rotates. Therefore, about 170 Mn is rotated per photon. In addition, the influence which the difference of measurement temperature has on an experimental result is small.
[0033]
On the other hand, in the quantum well (x = 0.056) structure, 1.7 × 10 ¹⁷ photon / cm ^Three / Pulse (2.0 × 10 ¹³ photon / cm ² / Pulse) of about 52% of saturation magnetization (10 ^{twenty one} cm ^-3 ) (ΔM = 13 mdeg, M _s = 25 mdeg.) Rotates. Therefore, about 3600 Mn rotates per photon.
[0034]
From the above results, it can be seen that the use of the quantum well structure increases the spin polarization rate of the photogenerated holes and increases the magnetization change. In addition, the lifetime of hole spin can be expected to be longer. The lifetime of hole spin is considered to depend on the strength of carrier confinement in the quantum well. Therefore, when the relaxation time of the photogenerated hole spin is extended, it is expected that the holes can sufficiently interact with Mn and the magnetization change becomes larger. In another aspect, for example, by reducing the quantum well width or increasing the barrier height of the quantum well structure, the relaxation time of the hole spin can be lengthened and the irradiation of circularly polarized light is stopped. The storage time for later information can be lengthened. In this case, it is suitable for application as a nonvolatile memory element. On the other hand, for example, by increasing the width of the quantum well or lowering the barrier height of the quantum well structure, the relaxation time of the hole spin can be shortened according to the irradiation of circularly polarized light and its stoppage. Since it responds quickly, it is suitable for use as an optical switch or optical sensor. Further, since the direction of circularly polarized light can be known with high sensitivity by measuring Kerr rotation, it is also suitable as a sensor for measuring Kerr rotation.
[0035]
Next, an actual manufacturing method of the element according to the present embodiment will be described. As a material that can be used for the quantum well layer, there is a compound semiconductor quantum well, and a transition metal (Sc, Ti, V, Cr, Mn, Fe, Co, Ni) is highly concentrated in the well layer, for example, in the order of%. An added compound semiconductor quantum well layer can be used. For example, a III-V group compound semiconductor structure such as GaMnAs / AlGaAs heterostructure, InGaMnAs / InAlAs heterostructure, InMnSb / InAs heterostructure, InGaMnN / GaN, GaMnN / AlN heterostructure, or II-type such as ZnCrTe / ZnTe Group VI compound semiconductor structures can be used.
[0036]
The element can be produced, for example, by molecular beam epitaxy (MBE). In addition, it can be formed by metal organic vapor phase epitaxy (MOCVD), sputtering, or vacuum deposition.
[0037]
Hereinafter, an example of a specific element manufacturing process of the quantum well spin injection magnetization switching film will be described. First, a GaAs buffer layer is deposited on a GaAs substrate at 580 ° C., and then about 10 nm thick Ga _1-y Al _y An As (0 <y <1) layer (first barrier layer) is formed at 240 ° C. Next, Ga with a thickness of 5 nm _1-x Mn _x An As layer (0 <x <1, quantum well layer) is formed at 240 ° C. and Ga is about 10 nm thick. _1-y Al _y An As (0 <y <1) layer (second barrier layer) is formed at 240 ° C. Finally, a GaAs layer (protective layer) having a thickness of about 10 nm is formed at 240 ° C.
[0038]
Next, a magnetoresistive element using a quantum well spin-injection magnetization switching film will be described with reference to FIGS. The magnetoresistive effect element shown in FIG. ⁺ -GaAs layer 31, p-GaAs lower electrode layer 33, Ga _1-x Mn _x As (0 <x <1) fixed layer 35, Ga _1-z Al _z As (0 ≦ z ≦ 1) second barrier layer 37 and (In _1-y Ga _y ) _1-x Mn _x As (0 <x <1, 0 <y <1) magnetization switching layer 39, Ga _1-z Al _z As (0 ≦ z ≦ 1) has a laminated structure of a first barrier layer 41 and a transparent electrode layer 45. Ga _1-x Mn _x The magnetization direction of the As fixed layer 35 is fixed, while it is a quantum well layer (In _1-y Ga _y ) _1-x Mn _x As (0 <x <1, 0 <y <1) The magnetization switching layer 39 is a free layer, and the direction of magnetization can be changed by applying circularly polarized light. In the above structure, the voltage generated between the lower electrode 31 and the transparent electrode 45 can be measured. In this case, the carrier density p = 10 using a vapor deposition apparatus or the like. ¹⁹ cm ^-3 A p-type GaAs layer doped to some extent is formed by molecular beam epitaxy at 580 ° C., and an upper transparent electrode is formed thereon by an Au thin film or an ITO film.
[0039]
As shown in FIG. 12A, in the state where the structure shown in FIG. 11 is not irradiated with circularly polarized light, the magnetization direction of the magnetization switching layer 39 (the direction indicated by the arrow) maintains the previous state. In FIG. 12A, the magnetization direction of the fixed layer 35 and the magnetization switching layer 39 is the same (parallel magnetization), and the resistance in the stacking direction is low. As shown in FIG. 12B, when the right-handed circularly polarized light is irradiated in the stacking direction, the magnetization once rises perpendicular to the film surface, and this generates a demagnetizing field in the opposite direction to the magnetization. By receiving the rotating torque and irradiating the circularly polarized light, the magnetization directions of the fixed layer 35 and the magnetization switching layer 39 are different (antiparallel magnetization), and the antiparallel magnetization state is maintained even in the absence of circularly polarized light, and the stacking direction The resistance remains low. That is, information is stored in a nonvolatile manner. As shown in FIG. 12C, when the circularly polarized light is irradiated in the stacking direction, the magnetization directions of the fixed layer 35 and the magnetization switching layer 39 are the same, and the parallel magnetization is maintained even in the absence of the circularly polarized light. Therefore, the state where the resistance value is low is kept non-volatile.
[0040]
In the above nonvolatile memory element, it is not necessary to distinguish between right and left circularly polarized light in order to realize parallel / antiparallel of two magnetic layers. That is, when circularly polarized light is applied, the magnetization rises in a direction perpendicular to the surface, and the force for reversing the magnetization in the surface at this time is a torque due to the demagnetizing field generated by the standing magnetization. The difference between right and left circularly polarized light only gives the difference between clockwise and counterclockwise rotation within the film surface, so if either + or-circularly polarized light is applied alternately, magnetization will occur within the film surface. Is reversed. Note that + and − of the circularly polarized light emitting element can be controlled by a magnetic field (magnetization direction).
[0041]
When the nonvolatile memory element is applied to an actual memory device, for example, first, the magnetization state (parallel magnetization or antiparallel magnetization) of the nonvolatile memory element according to the present embodiment to be rewritten is read. When the storage information different from the storage information to be rewritten is stored, the non-volatile storage element may be irradiated with circularly polarized light. If the same storage information as the storage information to be actually rewritten is stored, the subsequent processing is not particularly necessary.
[0042]
In each of the above embodiments, for example, when a large number of nonvolatile memory elements according to the embodiment of the present invention are formed on a two-dimensional plane, only a desired memory element is selectively irradiated with circularly polarized light. As a method for rewriting stored information, a light emitting element having (In, Ga, Mn) As having a smaller In composition than a magnetization switching layer as a light emitting layer is formed on the memory element structure as a light emitting element for irradiating circularly polarized light. To do. At this time, the band gap of the light emitting layer and the quantum level E of the magnetization switching layer ₁ -HH ₁ If the In composition of the light emitting layer and the magnetization switching layer is determined so that the transition energy between them is the same, circularly polarized light can be irradiated. The right and left circularly polarized light emission of the circularly polarized light emitting element can be controlled by a magnetic field (magnetization direction). In addition, by creating a storage element and arranging a λ / 4 plate directly below the device capable of controlling the polarization plane of transmitted linearly polarized light by switching the liquid crystal device, for example, the stored information can be rewritten individually. It may be configured. Further, when it is necessary to adjust the direction of circularly polarized light, it can be adjusted by the polarization plane of linearly polarized light and the λ / 4 plate. Furthermore, it is also possible to perform writing by irradiating each piece of circularly polarized light individually by scanning the optical fiber probe on the two-dimensionally arranged non-volatile storage element using a near-field microscope. .
[0043]
The magnetoresistive effect element shown in FIG. ⁺ -GaAs layer 71, p- (In, Ga) As lower electrode layer 73, Ga _1-z Al _z As (0 ≦ z ≦ 1) second barrier layer 75 and (In _1-y Ga _y ) _1-x Mn _x As (0 <x <1, 0 <y <1) magnetization switching layer 77, Ga _1-z Al _z As (0 ≦ z ≦ 1) first barrier layer 81, Ga _1-x Mn _x It has a laminated structure of As (0 <x <1) fixed layer 83 and transparent electrode layer 85. In this structure, the magnetic anisotropy of the magnetic layer is controlled by lattice distortion. (In _1-y Ga _y ) _1-x Mn _x The As magnetization reversal layer 77 is not strained and has an easy axis in the plane due to the demagnetizing field effect. _1-x Mn _x The As pinned layer 83 is subjected to tensile strain, and a structure having an easy axis of magnetization in the direction perpendicular to the surface can be realized. Ga _1-x Mn _x The magnetization direction of the As fixed layer 83 is fixed, while (In _1-y Ga _y ) _1-x Mn _x The As magnetization switching layer 77 is a free layer, and the direction of magnetization can be changed by irradiating circularly polarized light. The voltage generated between the lower electrode and the transparent electrode can be measured.
[0044]
As shown in FIG. 14A, in a state where circularly polarized light is not irradiated, the magnetization direction of the fixed layer 83 (the direction indicated by the arrow) is upward, and the magnetization direction of the magnetization switching layer 77 is in the plane of the film. Facing the direction. As shown in FIG. 14B, when the right-handed circularly polarized light is irradiated in the stacking direction, the magnetization directions of the fixed layer 83 and the magnetization switching layer 77 are both aligned upward, and the resistance value during irradiation is shown in FIG. It becomes lower than the case shown in a). As shown in FIG. 14C, when left circularly polarized light is irradiated in the stacking direction, the magnetization directions of the fixed layer 83 and the magnetization switching layer 77 are opposite to each other, and the resistance value during irradiation is shown in FIG. Higher than the case. In either case of FIG. 14B or FIG. 14C, when irradiation with circularly polarized light is stopped, a state (83, 77) substantially similar to FIG. 14A is obtained as shown in FIG. 14D. Return. That is, in the structure described above, the resistance value in the stacking direction can be changed depending on the direction of the circularly polarized light to be irradiated, and the element can be used as an optical switch that can change the resistance value depending on the direction of the circularly polarized light. can do. Since the resistance value takes a ternary state, it can be applied to a multi-value logic circuit. In addition, it can be used as an optical sensor capable of sensing circularly polarized light by sensing a resistance value.
[0045]
As described above, in the spin magnetization inversion type magnetoresistive element using the quantum size effect according to the present embodiment, HH and LH are split to selectively excite electrons from HH to the conduction band. Thus, it has been found that the spin injection magnetization reversal can be made more efficient by utilizing the fact that the spin polarization rate can be almost 100%. Thereby, the electric power required for magnetization reversal can be reduced.
[0046]
As described above, the present invention has been described according to the embodiment. However, the present invention relates to a magnetization reversal method of a magnetic material, and is not limited thereto. It will be apparent to those skilled in the art that other various modifications, improvements, and combinations can be made. For example, in the above-described embodiment, the case where the element is irradiated with circularly polarized light has been described as an example. However, elliptically polarized light (actually including circularly polarized light) may be irradiated.
[0047]
【The invention's effect】
In the spin-injection magnetization reversal magnetoresistive element using the quantum size effect according to the present invention, spin polarization is achieved by splitting HH and LH and selectively causing excitation of electrons from HH to the conduction band. Utilizing the fact that the rate can be almost 100%, the efficiency of spin injection magnetization reversal can be improved. Thereby, the electric power required for magnetization reversal can be reduced.
[Brief description of the drawings]
FIG. 1 is a diagram showing a conceptual configuration of an element using a spin-injection magnetization switching film according to a previous proposal, showing an example of the configuration of an element using a group III-V magnetic mixed crystal semiconductor (magnetic semiconductor). FIG.
FIG. 2 is a schematic diagram showing a transition state between a conduction band and a valence band of the element shown in FIG. 1;
FIGS. 3A and 3B are diagrams showing the interaction between photogenerated spin-polarized holes and Mn. FIG.
FIG. 4 is a diagram showing a structure example of a quantum well spin-injection magnetization switching film according to the first embodiment of the present invention.
5 is a diagram showing a schematic energy band structure related to a (Ga, Mn) As layer 17 forming a quantum well layer in the quantum well structure shown in FIG.
FIG. 6 is a diagram showing the relationship between photon energy and reflected MCD (deg) when the well width of a GaMnAs quantum well structure is changed and circularly polarized light is irradiated.
FIG. 7 shows E obtained by theoretical calculation. ₁ -HH ₁ FIG. 7 is a diagram in which the relationship between the transition energy and the quantum well width obtained from the peak value of the MCD spectrum is plotted based on the curve of the value and the quantum well width and FIG. 6.
FIGS. 8 (a) and 8 (b) show 2.0 × 10 4 for an AlAs / GaMnAs / AlAs quantum well structure. ¹³ photon / cm ² It is a figure which shows the relationship with the delay time of a Kerr rotation angle at the time of irradiating / pulse circularly polarized light pulse.
9 (a) and 9 (b) show 1.5 × 10 5 for a GaMnAs bulk structure. ¹² photon / cm ² It is a figure which shows the relationship between a Kerr rotation angle and its delay time at the time of irradiating the / pulse circularly polarized light pulse.
FIG. 10 shows a summary of characteristics when a bulk (single layer film) and a quantum well are each used as a spin-injection magnetization switching film.
FIG. 11 is a diagram illustrating a configuration example of a magnetoresistive element using a quantum well spin-injection magnetization switching film.
12 is a diagram showing the movement of the magnetization reversal layer when the element shown in FIG. 11 is irradiated with circularly polarized light. FIG.
FIG. 13 is a diagram illustrating a configuration example of a magnetoresistive element using strain.
14 is a diagram showing a state in which circularly polarized light is irradiated to the magnetoresistive element shown in FIG.
FIG. 15 is a diagram illustrating a configuration example of a TMR element.
FIG. 16 is a diagram illustrating a configuration example of a storage device using a TMR element.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 11 ... GaAs layer, 15 ... 1st energy barrier layer formed of AlAs layer, 17 ... Quantum well layer formed of (Ga, Mn) As, 21 ... 2nd energy barrier layer formed of AlAs layer .

Claims (8)

A quantum magnetic semiconductor structure capable of quantum confinement of carriers, the quantum magnetic semiconductor having a semiconductor magnetic region in which a degeneration between a heavy hole state and a light hole state in a valence band of the quantum magnetic semiconductor is solved by a quantum well structure Preparing a magnetic semiconductor structure;
Irradiating elliptically polarized light to the quantum magnetic semiconductor structure.   2. The spin injection magnetization control method according to claim 1, wherein the quantum magnetic semiconductor structure has a magnetic semiconductor layer in which a magnetic metal is mixed in a semiconductor layer.   A semiconductor having a magnetic semiconductor and an energy barrier that quantum mechanically confines the carriers of the magnetic semiconductor, wherein a degeneration between a heavy hole state and a light hole state in the valence band of the magnetic semiconductor is solved by a quantum well structure Quantum magnetic semiconductor microstructure with magnetic region. The quantum magnetic semiconductor microstructure according to claim 3,
An optical semiconductor device comprising: a light source that selects an energy difference between quantum levels formed in a valence band and a conduction band in the semiconductor magnetic region and irradiates elliptically polarized light having energy corresponding to the energy level. A magnetoresistive element that performs magnetization reversal by irradiation with elliptically polarized light,
A lower electrode;
A fixed layer formed on the lower electrode and fixed in the direction of magnetization;
A first energy barrier layer formed on the fixed layer; a magnetization reversal layer made of a magnetic semiconductor formed on the first energy barrier layer; a second energy barrier layer formed on the magnetization reversal layer; A magnetic semiconductor structure in which degeneration between a heavy hole state and a light hole state in the valence band of the magnetic semiconductor is solved by a quantum well structure, and on the second energy barrier layer magnetoresistive elements that have a transparent electrode formed. A magnetoresistive element according to claim 5,
Voltage detection means for detecting a voltage between the lower electrode and the transparent electrode;
A light source capable of irradiating an elliptically polarized light having a wavelength corresponding to a transition energy between a conduction band and a quantum level formed in a valence band of the energy for exciting the carriers of the magnetization switching layer from the transparent electrode side Non-volatile memory device. Furthermore, before being provided to the elliptically polarized light irradiation side of Ki磁 air resistance element, a non-volatile memory device according to claim 6 and a shutter for selectively irradiating elliptical polarization. Quantum magnetism that has a magnetic semiconductor and an energy barrier that confines the carriers of the magnetic semiconductor in a quantum mechanical manner and solves the degeneracy of heavy and light hole states in the valence band of the magnetic semiconductor by a quantum well structure Semiconductor microstructure,
A light receiving surface for receiving elliptically polarized light irradiated to the quantum magnetic semiconductor microstructure;
An optical sensor having a measurement unit for measuring the potential of the magnetic semiconductor.

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