JP2018186227A - Laminated structure and spin modulation element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laminated structure and a spin modulation element, capable of efficiently modulating spin polarizability of a ferromagnetic material by applying a uniform electric field to an interface between a ferroelectric layer and a ferromagnetic layer.SOLUTION: A laminated structure includes: a ferromagnetic layer; and a ferroelectric layer laminated on the ferromagnetic layer. An end face connecting a first surface of the ferroelectric layer at a side of the ferromagnetic layer and a second surface opposite to the first surface is inclined.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a laminated structure and a spin modulation element.

  Elements utilizing the spin of magnetic materials are used in various applications. For example, a magnetoresistive element such as a giant magnetoresistive (GMR) element composed of a multilayer film of a ferromagnetic layer and a nonmagnetic layer, or a tunnel magnetoresistive (TMR) element using an insulating layer (tunnel barrier layer or barrier layer) as the nonmagnetic layer. Effect elements are known. Magnetoresistive elements are used in magnetic sensors, high-frequency components, magnetic heads, magnetic recording media, non-volatile random access memories (MRAM), and the like.

  The magnetoresistive element outputs a change in resistance value associated with a difference in relative angle between the magnetization directions of the two ferromagnetic layers. By setting the state in which the magnetization directions of the two ferromagnetic layers are parallel to “0” and setting the state in which the magnetization directions of the two ferromagnetic layers are antiparallel to “1”, the magnetoresistive effect element has a binary value. Data can be output.

  On the other hand, with the recent increase in data capacity, it is required to accumulate data at a higher density. As one of the means, development of an element capable of recording data in multiple values of two or more values is underway. For example, Patent Documents 1 and 2 describe an element that can record data in multiple values by modulating the spin polarizability of a ferromagnetic layer using an electric field.

Japanese Patent Laid-Open No. 2006-63024 JP, 2006-63062, A

  However, in the elements described in Patent Documents 1 and 2, the end face of the element is damaged and deteriorated during manufacturing, and a uniform electric field may not be applied to the interface between the ferroelectric layer and the ferromagnetic layer.

  The present invention has been made in view of the above circumstances, and applies a uniform electric field to the interface between the ferroelectric layer and the ferromagnetic layer to efficiently modulate the spin polarizability of the ferromagnetic material and An object is to provide a spin modulation element.

  The present invention provides the following means in order to solve the above problems.

(1) The multilayer structure according to the first aspect includes a ferromagnetic layer and a ferroelectric layer provided on one surface of the ferromagnetic layer, and the ferromagnetic layer on the ferromagnetic layer side of the ferroelectric layer is provided. An end face connecting the first surface and the second surface facing the first surface is inclined.

(2) In the laminated structure according to the above aspect, the area of the first surface may be 0.02 times or more and less than 1 time the area of the second surface.

(3) In the laminated structure according to the aspect described above, the area of the first surface may be greater than 1 and less than or equal to 50 times the area of the second surface.

(4) In the laminated structure according to the above aspect, the area of the surface of the ferromagnetic layer on the ferroelectric layer side may be smaller than the area of the opposing surface.

(5) In the laminated structure according to the above aspect, the ferromagnetic layer may include a half metal.

(6) In the multilayer structure according to the above aspect, the ferromagnetic layer includes a Heusler alloy represented by a composition formula of Co ₂ XY, and X in the composition formula is selected from the group consisting of Cr, Mn, V, and Fe. One or more elements selected, and Y in the composition formula may be one or more elements selected from the group consisting of Al, Si, Ga, Ge, In, and Sn.

(7) In the laminated structure according to the above aspect, the ferroelectric layer may include a multiferroic material.

(8) In the multilayer structure according to the above aspect, the multiferroic material may have at least one crystal phase of a tetragonal crystal and a rhombohedral crystal.

(9) In the multilayer structure according to the above aspect, the multiferroic material includes BiFeO ₃ , BiMnO ₃ , GaFeO ₃ , AlFeO ₃ , (Ga, Al) FeO ₃ , YMnO ₃ , CuFeO ₂ , Cr ₂ O ₃ , Any one selected from the group consisting of Ni ₃ Bi ₇ O ₁₃ I, LiMnPO ₄ , Y ₃ Fe ₅ O ₁₂ , TbPO ₄ , and LiCoPO ₄ may be included.

(10) A spin modulation element according to a second aspect includes the multilayer structure according to the aspect described above, and a nonmagnetic layer and a second ferromagnetic layer that are sequentially stacked on the ferromagnetic layer of the multilayer structure. .

  The laminated structure and the spin modulation element according to the above aspect can efficiently modulate the spin polarizability of the ferromagnetic material by applying a uniform electric field to the interface between the ferroelectric layer and the ferromagnetic layer.

It is the figure which showed typically the spin modulation element concerning this embodiment. FIG. 3 is a schematic cross-sectional view of a spin modulation element in which an end face connecting a first surface and a second surface of a ferroelectric layer is not inclined. It is a cross-sectional schematic diagram of a spin modulation element when the area of the first surface of the ferroelectric layer is larger than the area of the second surface. It is a cross-sectional schematic diagram of another aspect of a spin modulation element. It is a schematic diagram for demonstrating operation | movement of a spin modulation element.

  Hereinafter, the configuration of the present embodiment will be described with reference to the drawings. In the drawings used in the following description, in order to make the features easy to understand, the portions that become the features may be shown in an enlarged manner for the sake of convenience, and the dimensional ratios and the like of the respective components are not always the same as the actual ones. In addition, the materials, dimensions, and the like exemplified in the following description are examples, and the present invention is not limited to them.

(Spin modulation element)
FIG. 1 is a diagram schematically showing the spin modulation element according to the present embodiment. A spin modulation element 100 shown in FIG. 1 includes a laminated structure 10, a nonmagnetic layer 20, a second ferromagnetic layer 30, a first electrode 40, and a second electrode 50.

"Laminated structure"
The laminated structure 10 includes a ferroelectric layer 1 and a ferromagnetic layer 2. In FIG. 1, the laminated structure 10 is illustrated as a part of the configuration of the spin modulation element 100, but only the laminated structure 10 can be used as an AMR (magnetic anisotropy) sensor or the like.

  The ferroelectric layer 1 includes a material having ferroelectric characteristics. The spin polarizability of the ferromagnetic layer 2 is modulated by the ferroelectric characteristics of the ferroelectric layer 1. The charge generated by the dielectric polarization of the ferroelectric layer 1 induces a charge at the interface of the ferromagnetic layer 2 on the ferroelectric layer 1 side. The electric field due to the interface charge changes the band structure of the ferromagnetic layer 2 and modulates the spin polarizability of the ferromagnetic layer 2. When the spin polarizability is modulated, the spin modulation element 100 can be multi-valued. For example, when the spin polarizability of the ferromagnetic layer 2 is 1.0 and parallel to the second ferromagnetic layer 30, and when the spin polarizability of the ferromagnetic layer 2 is 0.5 and parallel to the second ferromagnetic layer 30 This is because the resistance value between the ferromagnetic layer 2 and the second ferromagnetic layer 30 is different.

Examples of the material having ferroelectric characteristics include La _x Sr _1-x MnO ₃ (0 ≦ x ≦ 1), Ba _x Sr _1-x TiO ₃ (0 ≦ x ≦ 1), PbZr _x Ti _1-x O ₃ (0 ≦ x ≦ 1)).

The ferroelectric layer 1 preferably includes a multiferroic material having not only ferroelectric properties but also ferromagnetic properties. Multiferroic materials include BiFeO ₃ , BiMnO ₃ , GaFeO ₃ , AlFeO ₃ , (Ga, Al) FeO ₃ , YMnO ₃ , CuFeO ₂ , Cr ₂ O ₃ , Ni ₃ Bi ₇ O ₁₃ I, LiMnPO ₄ , YM Any one selected from the group consisting of ₃ Fe ₅ O ₁₂ , TbPO ₄ , and LiCoPO ₄ can be used. Among these materials, BiFeO ₃ is particularly preferable because it has a high Curie temperature and a Neel temperature and exhibits ferroelectric characteristics and ferromagnetic characteristics in a wide temperature range.

  When a multiferroic material is used for the ferroelectric layer 1, two effects can be exerted on the ferromagnetic layer 2. The first effect is an effect of modulating the spin polarizability of the ferromagnetic layer 2 by the above-described ferroelectric characteristics. The second effect is derived from the ferromagnetic properties of the multiferroic material.

  When the ferroelectric layer 1 exhibits ferromagnetic characteristics by using a multiferroic material, the magnetization direction of the ferromagnetic layer 2 is strongly oriented in one direction due to the influence of the magnetization generated in the ferroelectric layer 1. (Second effect). That is, by using a multiferroic material, the ferroelectric layer 1 has an effect of pinning the magnetization of the ferromagnetic layer 2 due to its ferromagnetic characteristics. When the magnetization of the ferromagnetic layer 2 is strongly fixed (pinned) in one direction, the magnetization direction of the ferromagnetic layer 2 is not disturbed by external factors such as heat, and the resistance value change rate associated with the magnetoresistance effect (MR ratio) increases.

  Multiferroic materials have different characteristics depending on the crystal structure. When the crystal structure is rhombohedral, it exhibits both ferroelectric properties and ferromagnetic properties, and is particularly excellent in ferromagnetic properties. On the other hand, when the crystal structure is a tetragonal crystal, the ferroelectric properties are excellent, but the ferromagnetic properties are not shown so much. Therefore, the multiferroic material preferably has at least one crystal phase of tetragonal and rhombohedral, and more preferably has both tetragonal and rhombohedral crystal phases.

  An end surface 1C connecting the first surface 1A on the ferromagnetic layer 2 side of the ferroelectric layer 1 and the second surface 1B facing the first surface 1A is inclined with respect to the stacking direction. When a voltage is applied between the ferromagnetic layer 2 and the first electrode 40 when the ferroelectric layer 1 is dielectrically polarized, an electric field is generated perpendicular to the first surface 1A and the second surface 1B. Therefore, if the end face 1C is inclined, it is possible to avoid an electric field from being generated along the end face 1C.

  FIG. 2 is a schematic cross-sectional view of the spin modulation element 101 in which the end surface 1C connecting the first surface 1A and the second surface 1B of the ferroelectric layer 1 is not inclined. As shown in FIG. 2, if the end face 1 </ b> C is not inclined, an electric field is generated along the end face 1 </ b> C of the ferroelectric layer 1.

  The end face 1C is produced by means of dry etching such as ion milling or reactive ion etching. The end face 1C subjected to these processes is damaged and deteriorated. Therefore, the dielectric characteristics in the vicinity of the end face 1 </ b> C are inferior to the dielectric characteristics in the central portion of the ferroelectric layer 1.

  As a first effect, the ferroelectric layer 1 induces a charge at the interface with the ferromagnetic layer 2 by a charge generated by dielectric polarization, and modulates the spin polarizability of the ferromagnetic layer 2 by the interface charge. The first effect that the electric field generated by the dielectric polarization of the end face 1 </ b> C having inferior dielectric properties has on the ferromagnetic layer 2 is smaller than the effect that the central portion of the ferroelectric layer 1 has on the ferromagnetic layer 2. That is, when a voltage is applied to achieve a sufficient dielectric polarization intensity at the end face 1C of the ferroelectric layer 1, an excessive voltage is applied at the center. That is, the intensity of the electric field applied to the interface between the ferroelectric layer 1 and the ferromagnetic layer 2 is not uniform, and the spin polarizability cannot be modulated efficiently.

  On the other hand, in the ferroelectric layer 1 shown in FIG. 1, the area of the first surface 1A is smaller than the area of the second surface 1B, and the end surface 1C is inclined. Since the electric field is generated so as to connect the shortest distance between the conductors, the electric field is hardly generated in a region outside the perpendicular line 1Aa extending from the end of the first surface 1A to the second surface 1B. When the distance between the first surface 1A and the second surface 1B is large, the electric field may slightly leak out, but the first surface 1A and the second surface 1B are sufficiently close to each other. Therefore, the spin modulation element 100 shown in FIG. 1 has a uniform electric field strength applied to the interface between the ferroelectric layer 1 and the ferromagnetic layer 2 and can efficiently modulate the spin polarizability.

  The configuration in which the end surface 1C of the ferroelectric layer 1 is inclined is not particularly limited, but if the area of the first surface 1A and the area of the second surface 1B of the ferroelectric layer 1 are designed to be different, the ferroelectric layer 1 The end face 1C is inclined. The area of the first surface 1A may be larger or smaller than the area of the second surface 1B.

  For example, as shown in FIG. 1, when the area of the first surface 1A is smaller than the area of the second surface 1B, an electric field having a uniform strength is applied to the entire first surface 1A in contact with the ferromagnetic layer 2. Therefore, the amount of charge accumulated at the interface between the ferroelectric layer 1 and the ferromagnetic layer 2 can be increased, and the degree of modulation of the spin polarizability of the spin modulation element 100 can be increased. As the degree of modulation of the spin polarizability increases, the resistance value difference in each state increases.

  On the other hand, FIG. 3 is a schematic cross-sectional view of the spin modulation element 102 when the area of the first surface 1A of the ferroelectric layer 1 is larger than the area of the second surface 1B. The spin modulation element 102 shown in FIG. 3 has the stacking order opposite to that of the spin modulation element 100 shown in FIG. FIG. 3 shows an example of the case where the area of the first surface 1A of the ferroelectric layer 1 is larger than the area of the second surface 1B because the forward tapered shape whose area decreases in the stacking direction can be manufactured more easily. Although the spin modulation element 102 is illustrated, the spin modulation element 100 may be formed in the same order as the spin modulation element 100 illustrated in FIG.

  In the spin modulation element 102 shown in FIG. 3, the area of the first surface 1A on the ferromagnetic layer 2 side of the ferroelectric layer 1 is larger than the area of the second surface 1B. Therefore, an electric field having a uniform electric field strength is applied to a region inside the perpendicular line 1Ba extending from the end of the second surface 1B of the ferroelectric layer 1 to the first surface 1A. On the other hand, since an electric field is not applied to the end face 1C of the ferroelectric layer 1 having insufficient dielectric properties, the influence of the end of the element damaged during manufacturing can be removed.

  The spin modulation element 102 shown in FIG. 3 can provide an electric field having a uniform electric field strength in the region inside the perpendicular 1Ba at the interface between the ferroelectric layer 1 and the ferromagnetic layer 2, but the region outside the perpendicular 1Ba. Has almost no electric field. For this reason, the spin polarizability of the ferromagnetic layer 2 in the region outside the perpendicular line 1Ba cannot be efficiently modulated, which seems disadvantageous. However, the end face 2C of the ferromagnetic layer 2 may also be damaged during manufacture. Therefore, by applying a uniform electric field to the region inside the perpendicular line 1Ba, it is possible to avoid the influence of the region in the vicinity of the end face 2C where the characteristics may be deteriorated.

  That is, if the area of the first surface 1A of the ferroelectric layer 1 is made smaller than the area of the second surface 1B, the entire interface can be charged, and the resistance value change in each state of the multivalued spin modulation element The amount can be increased. On the other hand, if the area of the first surface 1A of the ferroelectric layer 1 is larger than the area of the second surface 1B, the influence of the end regions of the ferroelectric layer 1 and the ferromagnetic layer 2 that may be deteriorated. And the signal output from the spin modulation element can be made sharper. The shape of the ferroelectric layer 1 can be selected according to the required performance and application.

  When the area of the first surface 1A of the ferroelectric layer 1 is smaller than the area of the second surface 1B, the area of the first surface 1A may be 0.02 times or more and less than 1 time the area of the second surface 1B. Preferably, it is 0.10 times or more and 0.998 times or less, more preferably 0.14 times or more and 0.97 times or less.

  On the other hand, when the area of the first surface 1A of the ferroelectric layer 1 is larger than the area of the second surface 1B, the area of the first surface 1A is larger than one area of the second surface 1B and not more than 50 times. It is preferably 1.002 times or more and 10 times or less, and more preferably 1.03 times or more and 6.8 times or less.

  FIG. 4 is a schematic cross-sectional view of another aspect of the spin modulation element. When a spin modulation element is incorporated into an integrated circuit, the first electrode 40 and the second electrode 50 may also serve as wiring. Therefore, as in the spin modulation element 103 illustrated in FIG. 4, the stacked structure 10, the nonmagnetic layer 20, and the second ferromagnetic layer 30 are interposed between the first electrode 40 and the second electrode 50 extending in the planar direction. Laminated. And the insulator 60 is provided in these side surfaces.

  The spin modulation element outputs a change in capacitance between the first electrode 40 and the second electrode 50. Since the electric field is applied perpendicularly to the first electrode 40 and the second electrode 50, if the inclination of the end face of the multilayer structure 10 is large, the proportion of the capacity of the insulator 60 in the output capacity increases. That is, when the first surface 1A and the second surface 1B of the ferroelectric layer 1 satisfy a predetermined area relationship, a capacitance unnecessary for the capacitance between the first electrode 40 and the second electrode 50 output from the spin modulation element. The occurrence of bonding can be reduced.

  The ferromagnetic layer 2 includes a magnetic material having magnetization oriented in one direction. It is preferable to use a substance having a strong magnetic anisotropy as the magnetic material constituting the ferromagnetic layer 2. For example, a metal selected from the group consisting of Cr, Mn, Co, Fe, and Ni and an alloy that includes one or more of these metals and exhibits ferromagnetism can be used. An alloy containing these metals and at least one element of B, C, and N can also be used. Specific examples include Fe and Co—Fe.

  The ferromagnetic layer 2 is preferably a half metal. Half metal is a substance in which one electron spin shows a metallic band structure and the other electron spin shows an insulating band structure. Half metal shows a large spin polarizability close to 1 ideally on the Fermi surface.

Further, as the half metal, Heusler alloy, magnetite (Fe ₃ O ₄ ), perovskite type Mn oxide and the like are known, and Heusler alloy is particularly preferable. Heusler alloys have characteristics such as high lattice matching with III-V semiconductors, a Curie temperature above room temperature, a large band gap near the Fermi surface, and the like, and can exhibit high spin polarizability even at room temperature.

The Heusler alloy includes an intermetallic compound having a chemical composition of X ₂ YZ, where X is a transition metal element or noble metal element of Co, Fe, Ni, or Cu group on the periodic table, and Y is Mn, V It is a transition metal of Cr, Ti or Ti, and can take the elemental species of X, and Z is a typical element of Group III to Group V. For example, Co ₂ MnGe, Co ₂ MnGa, Co ₂ FeGa, Co ₂ MnSn, Co ₂ MnAl, Co ₂ FeAl, Co ₂ CrAl, Co ₂ VAl, Co ₂ MnGaSn, Co ₂ Fe (Ge, Ga), Co ₂ Mn _{(Ge, Ga), Co 2} Fe (Ga, Si), Co 2 Fe (Ge, Si), Co 2 CrIn, Co 2 CrSn, Co 2 FeSi, Co 2 MnSi , and _{Co 2 Mn 1-a Fe a} Al b Si1 _-b (0 <= a <= 1, 0 <= b <= 1) etc. are mentioned.

  The area of the surface of the ferromagnetic layer 2 on the ferroelectric layer 1 side is preferably smaller than the area of the opposing surface. It is the electric charge at the interface between the ferroelectric layer 1 and the ferromagnetic layer 2 that modulates the spin polarizability of the ferromagnetic layer 2. When the area of the surface of the ferromagnetic layer 2 on the ferroelectric layer 1 side is smaller than the area of the opposing surface, the end face 2C of the ferromagnetic layer 2 is inclined so as to spread from the ferroelectric layer 1. In this case, the end face 2 </ b> C of the ferromagnetic layer 2 exists outside the end of the interface between the ferroelectric layer 1 and the ferromagnetic layer 2. The region outside the end of the interface between the ferroelectric layer 1 and the ferromagnetic layer 2 is not easily affected by the interface charge, and has little effect on the modulation of the spin polarizability of the spin modulation element. As described above, the end face 2C of the ferromagnetic layer 2 may be damaged due to manufacturing damage. Therefore, by providing this portion in a region outside the end portion of the interface, it is possible to suppress disturbance of the output signal.

"Nonmagnetic layer"
The nonmagnetic layer 20 may be an insulator, a semiconductor, or a metal. In the case where the nonmagnetic layer 20 is made of an insulator, the laminated body including the ferromagnetic layer 2, the nonmagnetic layer 20, and the second ferromagnetic layer 30 becomes a tunneling magnetoresistance (TMR) element, and the nonmagnetic layer 20 is In the case of being made of a semiconductor or metal, the laminated body including the ferromagnetic layer 2, the nonmagnetic layer 20, and the second ferromagnetic layer 30 is a giant magnetoresistance (GMR) element.

A known material can be used for the nonmagnetic layer 20.
For example, if the non-magnetic layer 20 is made of an insulator or semiconductor, as a material _{thereof, Hexagonal-BN, Graphene, HfO} 2, Y 2 O 3, TaO, GaO, TiO, InO, BaO, CaF 2, Al 2 O ₃ , SiO ₂ , MgO, MgAl ₂ O _4, or the like can be used. Among these, MgO and MgAl ₂ O ₄ are materials that can realize a coherent tunnel, so that the MR ratio can be increased. In addition, a material in which a part or all of Mg, Al, or Mg of MgO or MgAl ₂ O ₄ is substituted with Zn, Cd, Ag, Pt, Pb, Ga, In, Ge, or the like can also be used as the nonmagnetic layer 20. .

  Further, when the nonmagnetic layer 20 is made of a metal, Cu, Au, Ag, Cr, V, Al, AgZn alloy, AgMg alloy, NiAl alloy, or the like can be used as the material.

"Second ferromagnetic layer"
The second ferromagnetic layer 30 forms the ferromagnetic layer 2, the nonmagnetic layer 20, and the magnetoresistive element. When the ferromagnetic layer 2 is a fixed layer, the second ferromagnetic layer 30 is a free layer, and when the ferromagnetic layer 2 is a free layer, the second ferromagnetic layer 30 is a fixed layer.

  A known material can be used for the material of the second ferromagnetic layer 30. For example, a metal selected from the group consisting of Cr, Mn, Co, Fe, and Ni and an alloy that includes one or more of these metals and exhibits ferromagnetism can be used. An alloy containing these metals and at least one element of B, C, and N can also be used. Specifically, Co-Fe and Co-Fe-B are mentioned. In order to obtain higher output, a Heusler alloy may be used for the second ferromagnetic layer 30.

"First electrode, second electrode"
The first electrode 40 and the second electrode 50 are not particularly limited as long as they have conductivity. For example, metals such as gold, silver, copper, and aluminum, alloys thereof, and transparent conductors such as indium tin oxide (ITO) and indium zinc oxide (IZO) can be used.

  As described above, in the spin modulation device according to the present embodiment, the end face 1C of the ferroelectric layer 1 is inclined. Therefore, it is possible to avoid the occurrence of an electric field at the end of the ferroelectric layer 1 having inferior dielectric characteristics, and to efficiently change the spin state of the ferromagnetic layer 2.

(Method for manufacturing spin modulation element)
A method for manufacturing the spin modulation element 100 will be described. First, a base material is prepared. The substrate is preferably made of a conductive material in order to apply a voltage in the stacking direction of the stacked structure 10. In this case, the base material also serves as the first electrode 40.

  Next, the ferroelectric layer 1, the ferromagnetic layer 2, the nonmagnetic layer 20, and the second ferromagnetic layer 30 are sequentially laminated on the prepared base material. These layers can be laminated by the same method as the ferromagnetic layer and nonmagnetic layer of a magnetoresistive element such as a GMR element or a TMR element. For example, a sputtering method, a vapor deposition method, a laser ablation method, a CVD (chemical vapor deposition) method, a molecular beam epitaxial (MBE) method, or the like can be used.

  Next, the shape of the stacked structure is processed using a technique such as photolithography. For the processing, dry etching means such as ion milling or reactive ion etching through a mask can be used. The end face 1C of the ferroelectric layer 1 can be freely controlled by changing etching conditions and the like.

  Finally, the second electrode 50 is stacked on the surface of the second ferromagnetic layer 30 opposite to the nonmagnetic layer 20. By providing the electrodes, it is possible to flow a current uniformly over the entire surface of the ferromagnetic layer 2. Further, when the spin modulation element 102 shown in FIG. 3 is manufactured, the stacking order may be reversed.

(Operation of spin modulator)
Next, the operation of the spin modulation element will be described, and how multi-level processing is realized will be described.

  FIG. 5 is a schematic diagram for explaining the operation of the spin modulation element 100. In the spin modulation element 100, a switch SW1 for controlling a current flowing through the second ferromagnetic layer 30 and the ferromagnetic layer 2 and a switch SW2 for applying an electric field to the ferroelectric layer 2 are connected.

  First, as shown in FIGS. 5A and 5B, when the switch SW2 is open, an electric field is not applied to the ferroelectric layer 1. FIG. Therefore, in the spin modulation element 100, the second ferromagnetic layer 30 and the ferromagnetic layer 2 are in the first state (FIG. 5A) in which the magnetization directions of the second ferromagnetic layer 30 and the ferromagnetic layer 2 are antiparallel. Takes two states, ie, a second state (FIG. 5B) in which the magnetization directions are parallel. The magnetization direction of the ferromagnetic layer 2 is reversed by spin transfer torque (STT) by closing the switch SW1 and causing a spin-polarized current to flow in the stacking direction of the stack.

  Next, as shown in FIGS. 5C and 5D, the switch SW <b> 2 is closed and an electric field is applied to the ferroelectric layer 1. When an electric field is applied to the ferroelectric layer 1, the ferroelectric layer 1 reverses the direction of dielectric polarization. The electric field generated by the dielectric polarization changes the band structure of the ferromagnetic layer 2 and modulates the spin polarizability of the ferromagnetic layer 2.

For example, a positive voltage is applied to the ferroelectric layer 1 (FIG. 5 (c) voltage V _B direction), band bending is induced in the band structure of the down-spin ferromagnetic layer 2 by an electric field. Therefore, minority spin carriers are induced at the interface of the ferromagnetic layer 2 on the ferroelectric layer 1 side, and the spin polarizability of the ferromagnetic layer 2 decreases. 5C and 5D schematically show the decrease in the spin polarizability by the size of the arrow.

  As shown in FIGS. 5C and 5D, the third state in which the magnetization directions of the second ferromagnetic layer 30 and the ferromagnetic layer 2 are antiparallel even when the spin polarizability of the ferromagnetic layer 2 is decreased. (FIG. 5C) and a fourth state (FIG. 5D) in which the magnetization directions of the second ferromagnetic layer 30 and the ferromagnetic layer 2 are parallel to each other.

  That is, the spin modulation element 100 generates four states by controlling the switch SW1 and the switch SW2. The four states have higher resistance values in the order of the first state, the third state, the fourth state, and the second state.

  In the spin modulation device 100, the end face 1C of the ferroelectric layer 1 is inclined. Therefore, it is possible to avoid the occurrence of an electric field at the end of the ferroelectric layer 1 having inferior dielectric characteristics, and to efficiently change the spin state of the ferromagnetic layer 2.

  Although the embodiments of the present invention have been described in detail with reference to the drawings, the configurations and combinations of the embodiments in the embodiments are examples, and the addition and omission of configurations are within the scope not departing from the gist of the present invention. , Substitutions, and other changes are possible.

  For example, the spin modulation element is not limited to the forward taper shape whose area decreases in the stacking direction, but may be a reverse taper shape whose area increases in the stacking direction, and the end face of each layer may not be constant. Further, the central axes of the first surface 1A and the second surface 1B of the ferroelectric layer 1 do not have to coincide with each other.

DESCRIPTION OF SYMBOLS 1 ... Ferroelectric layer, 2 ... Ferromagnetic layer, 10 ... Laminated structure, 20 ... Nonmagnetic layer, 30 ... 2nd ferromagnetic layer, 40 ... 1st electrode, 50 ... 2nd electrode, 100 ... Spin modulation element , SW1, SW2 ... switch

Claims (10)

A ferromagnetic layer;
A ferroelectric layer provided on one surface of the ferromagnetic layer,
A laminated structure in which an end surface connecting a first surface of the ferroelectric layer on the ferromagnetic layer side and a second surface opposite to the first surface is inclined with respect to a laminating direction.   2. The stacked structure according to claim 1, wherein an area of the first surface is 0.02 times or more and less than 1 time of an area of the second surface.   2. The multilayer structure according to claim 1, wherein an area of the first surface is greater than 1 and less than or equal to 50 times an area of the second surface.   The multilayer structure according to any one of claims 1 to 3, wherein an area of a surface of the ferromagnetic layer on the ferroelectric layer side is smaller than an area of an opposing surface.   The laminated structure according to claim 1, wherein the ferromagnetic layer includes a half metal. The ferromagnetic layer includes a Heusler alloy represented by a composition formula of X ₂ YZ,
X in the composition formula is a transition metal element or noble metal element of Co, Fe, Ni, Cu group on the periodic table, Y is a transition metal of Mn, V, Cr, Ti group or an element species of X, The laminated structure according to any one of claims 1 to 5, wherein Z is a typical element from Group III to Group V.   The laminated structure according to claim 1, wherein the ferroelectric layer includes a multiferroic material.   The multilayer structure according to claim 7, wherein the multiferroic material has at least one crystal phase of a tetragonal crystal and a rhombohedral crystal. The multiferroic materials are BiFeO ₃ , BiMnO ₃ , GaFeO ₃ , AlFeO ₃ , (Ga, Al) FeO ₃ , YMnO ₃ , CuFeO ₂ , Cr ₂ O ₃ , Ni ₃ Bi ₇ O ₁₃ I, LiMnPO ₄ , YM _{3 Fe 5 O 12, TbPO 4} , is selected from the group consisting of LiCoPO ₄ comprising any multilayer structure according to claim 7 or 8. The laminated structure according to any one of claims 1 to 9,
A spin modulation element comprising: a nonmagnetic layer and a second ferromagnetic layer that are sequentially stacked on the ferromagnetic layer of the stacked structure.

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