Laminate, magnetoresistive element, and method for manufacturing a laminate

Abstract

A laminate body (10) comprises: a first layer (110) which is made of a ferroelectric substance containing lead and the upper surface of which is a 011 plane; a second layer (120) which is made of Fe and is laminated on the upper surface of the first layer (110); and a third layer (130) which is made of Co3Mn and is laminated on the upper surface of the second layer (120), wherein the third layer (130) is thicker than the second layer (120).

Description

[Technical Field]

[0001] This invention relates to laminates, and more particularly to laminates having a multiferroic structure. [Background technology]

[0002] Conventionally, laminates having a multiferroic structure are known (see, for example, Non-Patent Document 1). [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] Fujii et al. “Giant converse magnetoelectric effect in a multiferroic heterostructure with polycrystalline Co2FeSi”, NPG Asia Materials (2022)14;43 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] A laminate with a larger magnetoelectric coupling coefficient is desired compared to the conventional laminate described in Non-Patent Document 1.

[0005] Therefore, the purpose of this disclosure is to provide a laminate with a higher magnetoelectric coupling coefficient compared to conventional laminates. [Means for solving the problem]

[0006] A laminate according to one aspect of the present disclosure comprises a first layer made of a lead-containing ferroelectric material having an O11 surface on its upper surface, a second layer made of Fe laminated on the upper surface of the first layer, and a third layer made of Co3Mn laminated on the upper surface of the second layer, wherein the third layer is thicker than the second layer.

[0007] A magnetoresistive element according to one aspect of the present disclosure is a magnetoresistive element having the above laminate, comprising a first ferromagnetic layer made of a ferromagnetic material, a second ferromagnetic layer made of a ferromagnetic material, and an insulator layer made of an insulator sandwiched between the first ferromagnetic layer and the second ferromagnetic layer, wherein the first ferromagnetic layer is the third layer of the above laminate.

[0008] A method for manufacturing a laminate according to one aspect of the present disclosure includes an Fe layer growth step of supplying a molecular beam of Fe to the upper surface of a first layer made of a ferroelectric material containing lead and having an upper surface of 011 plane by molecular beam epitaxy to laminate a second layer made of Fe on the upper surface of the first layer, and a Co3Mn layer growth step of supplying a molecular beam of Co and a molecular beam of Mn to the upper surface of the second layer by molecular beam epitaxy to laminate a third layer made of Co3Mn and thicker than the second layer on the upper surface of the second layer.

Advantages of the Invention

[0009] According to a laminate or the like according to one aspect of the present disclosure, a laminate or the like having a larger magneto-electric coupling coefficient is provided as compared with a conventional laminate.

Brief Description of the Drawings

[0010] [Figure 1] FIG. 1 is a perspective view showing the configuration of a laminate according to Embodiment 1. [Figure 2] FIG. 2 is a graph showing the result of X-ray diffraction analysis of the laminate according to Embodiment 1. [Figure 3A] FIG. 3A is a perspective view showing the configuration of a laminate according to the first comparative example. [Figure 3B] FIG. 3B is a perspective view showing the configuration of a laminate according to the second comparative example. [Figure 4A] FIG. 4A is a graph showing the result of X-ray diffraction analysis of the laminate according to the first comparative example. [Figure 4B] FIG. 4B is a graph showing the result of X-ray diffraction analysis of the laminate according to the second comparative example. [Figure 5]Figure 5 is a schematic diagram showing how the direction of the magnetic moment changes by controlling the applied electric field in the laminate according to Embodiment 1. [Figure 6] Figure 6 is a graph plotting the remanent magnetization values ​​of the magnetic moment when the applied electric field is changed for the laminate according to Embodiment 1. [Figure 7A] Figure 7A is a graph plotting the remanent magnetization values ​​of the magnetic moment for the laminate according to the first comparative example, when the applied electric field is changed. [Figure 7B] Figure 7B is a graph plotting the remanent magnetization values ​​of the magnetic moment for the laminate according to the second comparative example, when the applied electric field is changed. [Figure 8] Figure 8 is a flowchart of the first laminate manufacturing method according to Embodiment 1. [Figure 9] Figure 9 is a cross-sectional view showing the configuration of a magnetoresistive element according to Embodiment 1. [Figure 10] Figure 10 is a perspective view showing the configuration of the laminate according to Embodiment 2. [Figure 11] Figure 11 is a graph plotting the remanent magnetization values ​​of the magnetic moment when the applied electric field is changed for the laminate according to Embodiment 2. [Figure 12] Figure 12 is a flowchart of the second laminate manufacturing method according to Embodiment 2. [Figure 13] Figure 13 is a cross-sectional view showing the configuration of a magnetoresistive element according to Embodiment 2. [Modes for carrying out the invention]

[0011] (The circumstances that led to obtaining one aspect of this disclosure) Conventionally, a multiferroic laminate is known, in which a ferromagnetic layer made of a specific ferromagnetic material is laminated on the upper surface of a ferroelectric layer made of a specific ferroelectric material. This laminate has the characteristic that the direction of the magnetic moment in the ferromagnetic layer can be controlled by controlling the direction of the electric field applied to the ferroelectric layer. Due to these characteristics, laminates with such features are expected to have applications in various electronic devices.

[0012] For example, in the field of magnetoresistive random access memory (MRAM), conventional magnetoresistive elements change the direction of the magnetic moment in the magnetoresistive element at the desired memory location by inducing a composite magnetic field by passing current through mutually orthogonal word lines and bit lines when writing data to the desired memory cell. In contrast, a magnetoresistive element using a laminate with the above characteristics can change the direction of the magnetic moment in the magnetoresistive element of the desired memory cell by changing the electric field applied to the ferroelectric layer at the desired memory cell location when writing data to the desired memory cell. In other words, the direction of the magnetic moment can be changed without passing current to generate a composite magnetic field, which is expected to reduce power consumption during data writing by about five orders of magnitude.

[0013] Non-patent document 1 contains Pb(Mg 1 / 3 Nb 2 / 3 A laminate having a multiferroic structure is described, in which a ferromagnetic layer made of Co2FeSi is laminated on the upper surface of a ferroelectric layer made of O3-PbTiO3 (magnesium niobate titanate).

[0014] According to Non-Patent Document 1, the magnetoelectric coupling coefficient, which indicates the change in remanent magnetization for a unit change in the electric field in the laminate described in Non-Patent Document 1, is 1.8 × 10⁻⁶. -5 It is [s / m].

[0015] The inventors believed that if the magnetoelectric coupling coefficient of a laminate having a multiferroic structure could be increased, the range of applications for laminates having a multiferroic structure in electronic devices could be broadened. Therefore, they diligently conducted repeated experiments and studies to realize a laminate exhibiting a magnetoelectric coupling coefficient greater than that of the laminate described in Non-Patent Document 1.

[0016] As a result, the inventors determined that 2.8 × 10 -5 We have conceived of the laminates etc. described herein that achieve a magnetoelectric coupling coefficient of [s / m].

[0017] A laminate according to one aspect of the present disclosure comprises a first layer made of a lead-containing ferroelectric material having an O11 surface on its upper surface, a second layer made of Fe laminated on the upper surface of the first layer, and a third layer made of Co3Mn laminated on the upper surface of the second layer, wherein the third layer is thicker than the second layer.

[0018] According to the above configuration, a laminate with a higher magnetoelectric coupling coefficient is provided compared to conventional laminates.

[0019] Here, the ferroelectric material is Pb(Mg 1 / 3 Nb 2 / 3 It may also be considered as O3-PbTiO3.

[0020] Here, the third layer may have a body-centered cubic lattice structure.

[0021] A magnetoresistive element according to one aspect of the present disclosure is a magnetoresistive element having the above-mentioned laminate, comprising: a first ferromagnetic layer made of a ferromagnetic material; a second ferromagnetic layer made of a ferromagnetic material; and an insulating layer made of an insulator sandwiched between the first ferromagnetic layer and the second ferromagnetic layer, wherein the first ferromagnetic layer is a third layer of the laminate.

[0022] The magnetoresistive element with the above configuration provides a magnetoresistive element in which the direction of the magnetic moment in the first layer can be controlled more easily than a magnetoresistive element with a configuration in which a ferromagnetic layer in a conventional laminate is used as the first layer.

[0023] A method for manufacturing a laminate according to one aspect of the present disclosure includes: an Fe layer growth step of supplying a molecular beam of Fe to the upper surface of a first layer made of a lead-containing ferroelectric material having an O11 surface on its upper surface by molecular beam epitaxy, thereby laminating a second layer made of Fe on the upper surface of the first layer; and a Co3Mn layer growth step of supplying a molecular beam of Co and a molecular beam of Mn to the upper surface of the second layer by molecular beam epitaxy, thereby laminating a third layer made of Co3Mn, which is thicker than the second layer, on the upper surface of the second layer.

[0024] According to the above-described method for manufacturing laminates, it is possible to manufacture laminates with a higher magnetoelectric coupling coefficient compared to conventional laminates.

[0025] Here, the ferroelectric material is Pb(Mg 1 / 3 Nb 2 / 3 It may also be considered as O3-PbTiO3.

[0026] Hereinafter, the process may further include a substrate heat treatment step to ensure the flatness of the upper surface of the first layer, and in the Fe layer growth step, the second layer may be laminated on the upper surface of the first layer whose flatness has been ensured by the substrate heat treatment step.

[0027] The following describes specific examples of laminates and the like according to one aspect of this disclosure, with reference to the drawings. The embodiments shown here are all examples of this disclosure. Therefore, the numerical values, shapes, components, arrangement and connection configurations of components, as well as the steps (processes) and the order of steps shown in the following embodiments are examples and are not intended to limit this disclosure. In addition, each figure is a schematic diagram and is not necessarily a strict illustration. In each figure, substantially identical components are denoted by the same reference numerals, and redundant explanations are omitted or simplified.

[0028] (Embodiment 1) <Configuration of the laminate> FIG. 1 is a perspective view showing the configuration of the laminate 10 according to Embodiment 1.

[0029] As shown in FIG. 1, the laminate 10 includes a first layer 110, a second layer 120 laminated on the upper surface of the first layer 110, and a third layer 130 laminated on the upper surface of the second layer 120.

[0030] The first layer 110 is a layer made of a ferroelectric body containing lead whose upper surface is the 011 plane.

[0031] Hereinafter, the ferroelectric body containing lead will be described as Pb(Mg 1 / 3 Nb 2 / 3 )O3 - PbTiO3 (hereinafter, also referred to as "PMN - PT").

[0032] However, the ferroelectric body containing lead does not necessarily have to be limited to Pb(Mg 1 / 3 Nb 2 / 3 )O3 - PbTiO3.

[0033] Other examples of the ferroelectric body containing lead include Pb(Mg 1 / 3 Nb 2 / 3 )O3 - Pb(Zr,Ti)O3, Pb(In 1 / 2 Nb 1 / 2 )O3 - Pb(Mg 1 / 3 Nb 2 / 3 )O3 - PbTiO3, Pb(Zn 1 / 3 Nb 2 / 3 )O3 - PbTiO3, and the like.

[0034] In the following description, replacing Pb(Mg 1 / 3 Nb 2 / 3 )O3 - PbTiO3 with Pb(Mg 1 / 3 Nb 2 / 3 )O3 - Pb(Zr,Ti)O3 results in a similar discussion, and replacing Pb(Mg 1 / 3 Nb 2 / 3 )O3 - PbTiO3 with Pb(In 1 / 2 Nb 1 / 2)O3-Pb(Mg 1 / 3 Nb 2 / 3 The same argument holds true even if we substitute )O3-PbTiO3, and Pb(Mg 1 / 3 Nb 2 / 3 )O3-PbTiO3, Pb(Zn 1 / 3 Nb 2 / 3 The same argument holds true even if we substitute O3-PbTiO3.

[0035] PMN-PT is a ferroelectric material. Therefore, the first layer 110 functions as a ferroelectric layer. Furthermore, PMN-PT is known to exhibit a relatively large piezoelectric effect among ferroelectric materials. For this reason, PMN-PT is a useful ferroelectric material for exhibiting strain-induced magnetoelectric coupling effects. Additionally, it is known that the ferroelectric layer exhibits a large piezoelectric effect due to the inclusion of lead.

[0036] A typical thickness of the first layer 110 is, for example, 0.5 mm. However, the thickness of the first layer 110 is not necessarily limited to 0.5 mm.

[0037] The second layer 120 is a layer made of Fe.

[0038] The second layer 120 functions as a base (adhesive surface) for laminating the third layer 130, described later, onto the upper surface of the first layer 110. The second layer 120 is thinner than the third layer 130, described later. That is, the third layer 130, described later, is thicker than the second layer 120. A typical thickness of the second layer 120 is, for example, 2 [nm]. However, the thickness of the second layer 120 is not necessarily limited to 2 [nm].

[0039] The third layer, 130, is a layer consisting of Co3Mn.

[0040] Co3Mn is a ferromagnetic material. Therefore, the third layer 130 functions as a ferromagnetic layer.

[0041] A typical thickness of the third layer 130 is, for example, 30 nm. However, the thickness of the third layer is not necessarily limited to 30 nm.

[0042] Generally, in its bulk state, Co3Mn is stable in a face-centered cubic lattice structure or a hexagonal close-packed structure. However, it is known that by thinning Co3Mn, it is possible to realize Co3Mn with a body-centered cubic lattice structure, which is inherently unstable. Furthermore, in recent years, it has been discovered that a relatively large tunnel magnetoresistance effect (TMR effect) can be obtained in tunnel magnetoresistance elements using Co3Mn with a body-centered cubic lattice structure.

[0043] Therefore, considering the possibility of using the third layer 130 as a ferromagnetic layer in a tunnel magnetoresistive element, the inventors considered it preferable for the third layer 130 to be a layer made of Co3Mn having a body-centered cubic lattice structure rather than a layer made of Co3Mn having a face-centered cubic lattice structure or a hexagonal close-packed structure.

[0044] However, it is not possible to directly laminate Co3Mn having a body-centered cubic lattice structure onto the upper surface of PMN-PT, which has an O11 plane as its upper surface, that is, onto the upper surface of the first layer 110.

[0045] Therefore, the inventors diligently conducted repeated experiments and studies to realize the stacking of a layer made of Co3Mn having a body-centered cubic lattice structure on the upper side of a first layer 110 made of PMN-PT with an 011 plane on its upper surface.

[0046] As a result, the inventors discovered that by first laminating a layer of Fe having a body-centered cubic lattice structure, with a lattice constant of 0.286 [nm] which is relatively close to the lattice constant of Co3Mn, which is 0.285 [nm], onto the upper side of a first layer 110 made of PMN-PT with an upper surface of the 011 plane, and then using that Fe layer as a base (adhesive), laminating Co3Mn on top of that Fe layer, the Co3Mn can be made to have a body-centered cubic lattice structure. In other words, we found that by stacking a second layer 120 made of Fe on the upper surface of a first layer 110 made of PMN-PT with an O11 plane on its upper surface, and then stacking a third layer made of Co3Mn on top of the second layer 120, we can realize a laminate 10 having a stack of layers made of Co3Mn having a body-centered cubic lattice structure on the upper side of the first layer 110 made of PMN-PT with an O11 plane on its upper surface.

[0047] In the following, we will explain based on actual measurement data obtained from a sample of a laminate 10 having a first layer 110 with a thickness of 0.5 [mm], a second layer 120 with a thickness of 2 [nm], a third layer 130 with a thickness of 30 [nm], and the third layer 130 having a body-centered cubic lattice structure, as an example. However, in this disclosure, there is no intention to limit the configuration of the laminate 10 relating to this disclosure to the configuration of the sample used for the above measurements.

[0048] Figure 2 is a graph showing the results of X-ray diffraction analysis performed on the laminate 10.

[0049] In Figure 2, the horizontal axis represents the X-ray scattering angle, and the vertical axis represents the intensity of the scattered X-rays.

[0050] As shown in Figure 2, X-ray diffraction analysis was performed on the laminate 10 with the above configuration, and a diffraction peak originating from Co3Mn having a body-centered cubic lattice structure appeared at the position indicated by the arrow in Figure 2. Therefore, it can be confirmed that the third layer 130 of the laminate 10 with the above configuration is a layer made of Co3Mn having a body-centered cubic lattice structure.

[0051] Figure 3A is a perspective view showing the structure of laminate 10A according to the first comparative example, which was prepared by the inventors as a comparative sample, and Figure 3B is a perspective view showing the structure of laminate 10B according to the second comparative example, which was prepared by the inventors as a comparative sample.

[0052] As shown in Figure 3A, the laminate 10A comprises a first layer 110, a second layer 120A laminated on the upper surface of the first layer 110, and a third layer 130A laminated on the upper surface of the second layer 120A.

[0053] The second layer 120A is a layer in which Fe is replaced with Cr compared to the second layer 120, i.e., a layer made of Cr. Here, the thickness of the second layer is 2 [nm].

[0054] Furthermore, Cr has a body-centered cubic lattice structure, and its lattice constant is 0.288 [nm].

[0055] The third layer 130A is a layer made of Co3Mn, laminated on the upper surface of the second layer 120A, which is made of Cr. Here, the thickness of the third layer is 30 nm.

[0056] As shown in Figure 3B, the laminate 10B comprises a first layer 110, a second layer 120B laminated on the upper surface of the first layer 110, and a third layer 130B laminated on the upper surface of the second layer 120B.

[0057] The second layer 120B is a layer in which Fe is replaced with V compared to the second layer 120, i.e., a layer made of V. Here, the thickness of the second layer is 2 [nm].

[0058] Furthermore, V has a body-centered cubic lattice structure, and its lattice constant is 0.303 [nm].

[0059] The third layer 130B is a layer made of Co3Mn, laminated on the upper surface of the second layer 120B, which is made of V. Here, the thickness of the third layer is 30 nm.

[0060] Figure 4A is a graph showing the results of X-ray diffraction analysis performed on laminate 10A, and Figure 4B is a graph showing the results of X-ray diffraction analysis performed on laminate 10B.

[0061] In Figures 4A and 4B, the horizontal axis represents the X-ray scattering angle, and the vertical axis represents the intensity of the scattered X-rays.

[0062] As shown in Figure 4A, when X-ray diffraction analysis was performed on the laminate 10A with the above configuration, a diffraction peak originating from Co3Mn having a face-centered cubic lattice structure or a hexagonal close-packed structure appeared at the position indicated by the arrow in Figure 4A, but no diffraction peak originating from Co3Mn having a body-centered cubic lattice structure appeared. Therefore, it can be confirmed that the third layer 130A of the laminate 10A with the above configuration is a layer made of Co3Mn having a face-centered cubic lattice structure or a hexagonal close-packed structure, that is, the third layer 130A is not a layer made of Co3Mn having a body-centered cubic lattice structure.

[0063] As shown in Figure 4B, X-ray diffraction analysis was performed on the laminate 10B with the above configuration, and no diffraction peaks originating from Co3Mn having a body-centered cubic lattice structure, a face-centered cubic lattice structure, or a hexagonal close-packed structure appeared. Therefore, it can be confirmed that the third layer 130B of the laminate 10B with the above configuration is not a layer made of Co3Mn having a crystalline structure, that is, the third layer 130B is not a layer made of Co3Mn having a body-centered cubic lattice structure.

[0064] From these findings, it can be seen that in the laminate 10, the fact that the second layer 120 is made of Fe is an important factor in making the third layer 130 a layer made of Co3Mn having a body-centered cubic lattice structure.

[0065] Figure 5 is a schematic diagram showing how the direction of the magnetic moment in the third layer 130 changes by controlling the electric field applied in the thickness direction of the first layer 110 in the laminate 10.

[0066] As shown in Figure 5, the laminate 10 can change the direction of the magnetic moment in the third layer 130 by 90 degrees by controlling the electric field applied in the thickness direction of the first layer 110. In other words, the laminate 10 has a multiferroic structure in which a strain-induced magnetoelectric coupling effect is exhibited between the first layer 110 and the third layer 130.

[0067] Figure 6 is a graph plotting the remanent magnetization values ​​of the magnetic moment in the third layer 130 when the electric field applied to the laminate 10 in the thickness direction of the first layer 110 is changed.

[0068] In Figure 6, the horizontal axis represents the intensity of the electric field applied in the thickness direction of the first layer 110, and the vertical axis represents the value of the remanent magnetization of the magnetic moment in the third layer 130. In Figure 6, the solid line shows the change in the value of remanent magnetization when the applied electric field is changed from a positive value to a negative value, and the dashed line shows the change in the value of remanent magnetization when the applied electric field is changed from a negative value to a positive value.

[0069] As shown in Figure 6, it can be seen that the remanent magnetization of the laminate 10 changes sharply at the remanent magnetization conversion point. In other words, it can be seen that the laminate 10 achieves a good strain-induced magnetoelectric coupling effect.

[0070] The inventors calculated the magnetoelectric coupling coefficient of the laminate 10 from the measurement data and found that the magnetoelectric coupling coefficient of the laminate 10 is 2.8 × 10⁻⁶. -5 It was found to be [s / m]. This magnetoelectric coupling coefficient is 1.8 × 10⁻⁶, which is the magnetoelectric coupling coefficient for the laminate described in Non-Patent Document 1. -5 This indicates a magnetoelectric coupling coefficient greater than [s / m], i.e., a good one.

[0071] Thus, the laminate 10 with the above configuration provides a laminate that achieves a better magnetoelectric coupling coefficient than the laminate described in Non-Patent Document 1.

[0072] Figure 7A is a graph plotting the remanent magnetization values ​​of the magnetic moment in the third layer 130A when the electric field applied in the thickness direction of the first layer 110 is changed on the laminate 10A, and Figure 7B is a graph plotting the remanent magnetization values ​​of the magnetic moment in the third layer 130B when the electric field applied in the thickness direction of the first layer 110 is changed on the laminate 10B.

[0073] In Figures 7A and 7B, the horizontal axis represents the intensity of the electric field applied in the thickness direction of the first layer 110, and the vertical axis represents the value of the remanent magnetization of the magnetic moment in the third layer 130A or the third layer 130B. In addition, in Figures 7A and 7B, the solid line shows the change in the value of remanent magnetization when the applied electric field is changed from a positive value to a negative value, and the dashed line shows the change in the value of remanent magnetization when the applied electric field is changed from a negative value to a positive value.

[0074] As shown in Figures 7A and 7B, the laminates 10A and 10B are unable to control the direction of the magnetic moment in the third layer 130 by controlling the electric field applied in the thickness direction of the first layer 110. In other words, a significant strain-induced magnetoelectric coupling effect is not observed between the first layer 110 and the third layer 130.

[0075] From these findings, it can be seen that in the laminate 10, the fact that the second layer 120 is made of Fe is an important factor in generating a strain-induced magnetoelectric coupling effect between the first layer 110 and the third layer 130.

[0076] In Embodiment 1, it was explained that in the laminate 10, the first layer 110 is made of PMN-PT, the second layer 120 is made of Fe, and the third layer 130 is made of Co3Mn. However, the configuration is not necessarily limited to the first layer 110 being made only of PMN-PT, the second layer 120 being made only of Fe, and the third layer 130 being made only of Co3Mn.

[0077] The first layer 110 may contain elements other than those constituting PMN-PT as long as it is mainly composed of PMN-PT; the second layer 120 may contain elements other than Fe as long as it is mainly composed of Fe; and the third layer 130 may contain elements other than Co and Mn as long as it is mainly composed of Co3Mn.

[0078] With regard to the third layer 130, for example, a configuration in which some of the Co in the Co3Mn constituting the third layer 130 is replaced with Fe due to reasons such as some of the Fe constituting the second layer 120 seeping into the third layer 130 due to thermal diffusion, or due to reasons such as intentional addition of Fe, and a configuration in which Fe is added to the Co3Mn constituting the third layer 130 are also included in the scope of this disclosure. Furthermore, with regard to the second layer 120, for example, a configuration in which some of the Fe constituting the second layer 120 is replaced with Co due to reasons such as some of the Co or Mn in the Co3Mn constituting the third layer 130 seeping into the second layer 120 due to thermal diffusion, or due to reasons such as intentional addition of Co or Mn, and a configuration in which Co or Mn is added to the Fe constituting the second layer 120 are also included in the scope of this disclosure.

[0079] <Method for manufacturing laminates> The manufacturing method for the laminate 10 will be described below.

[0080] Figure 8 is a flowchart of the first laminate manufacturing method for producing the laminate 10.

[0081] As shown in Figure 8, the first laminate manufacturing method manufactures the laminate 10 by performing the substrate heat treatment step S210, the Fe layer growth step S220, and the Co3Mn layer growth step S230 in that order.

[0082] The following describes each step.

[0083] The substrate heat treatment process S210 is a process to ensure the flatness of the upper surface of the first layer 110.

[0084] More specifically, the substrate heat treatment step S210 is a step in which a PMN-PT substrate (for example, 0.5 mm thick) with an O11 top surface is heated at 400°C in, for example, a molecular beam epitaxy chamber, until the flatness of the top surface is ensured (for example, for 20 minutes), thereby ensuring the flatness of the top surface of the first layer 110 made of the PMN-PT substrate.

[0085] PMN-PT substrates with a 011 plane on the top surface can be obtained, for example, by purchasing commercially available products that are widely sold.

[0086] Furthermore, if a PMN-PT substrate with a flat top surface is available, this substrate heat treatment step S210 can be omitted.

[0087] The Fe layer growth process S220 is a process in which a molecular beam of Fe is supplied to the upper surface of a first layer 110 made of PMN-PT, whose upper surface is an O11 plane, by molecular beam epitaxy, thereby laminating a second layer 120 made of Fe onto the upper surface of the first layer 110.

[0088] More specifically, the Fe layer growth process S220 is a process in which, in a molecular beam epitaxy chamber, the temperature of the first layer 110, whose upper surface flatness has been ensured by the substrate heat treatment process S210, or the first layer 110 made of a PMN-PT substrate whose upper surface flatness has been ensured in advance, is set to 350°C, and in the molecular beam epitaxy chamber, a molecular beam of Fe is supplied to the upper surface of the first layer 110 by a Knudsen cell to laminate a second layer 120 made of Fe onto the upper surface of the first layer 110 until, for example, the thickness reaches 2 [nm].

[0089] The Co3Mn layer growth process S230 is a process in which a molecular beam of Co and a molecular beam of Mn are supplied to the upper surface of the second layer 120 by molecular beam epitaxy, thereby laminating a third layer 130 made of Co3Mn, which is thicker than the second layer 120, onto the upper surface of the second layer 120.

[0090] More specifically, the Co3Mn layer growth step S230 is a step in which, in a molecular beam epitaxy chamber, the temperature of the structure formed by stacking the first layer 110 and the second layer 120, which were created in the Fe layer growth step S220, is set to 200°C, and in the molecular beam epitaxy chamber, a Knudsen cell is used to supply a Co molecular beam and a Mn molecular beam to the upper surface of the second layer 120 in the structure, thereby stacking the second layer 120 to form a third layer 130 made of Co3Mn, for example, until the thickness reaches 30 [nm].

[0091] <Configuration of a magnetoresistive element> Figure 9 is a cross-sectional view showing the configuration of the magnetoresistive element 20 according to Embodiment 1.

[0092] As shown in Figure 9, the magnetoresistive element 20 has a laminate 10.

[0093] Furthermore, as shown in Figure 9, the magnetoresistive element 20 comprises a first ferromagnetic layer 210, a second ferromagnetic layer 220, and an insulating layer 230 sandwiched between the first ferromagnetic layer 210 and the second ferromagnetic layer 220.

[0094] The first ferromagnetic layer 210 is the third layer 130 constituting the laminate 10. Specifically, the first ferromagnetic layer 210 is made of Co3Mn having a body-centered cubic lattice structure, which is a ferromagnetic material whose magnetic moment direction can be controlled by controlling the electric field applied in the thickness direction of the first layer 110.

[0095] The second ferromagnetic layer 220 is a ferromagnetic material with a fixed magnetic moment direction and exhibits a TMR effect. This ferromagnetic material is, for example, Co3Mn having a body-centered cubic lattice structure. Alternatively, this ferromagnetic material may be, for example, a Heusler alloy or a Co-based alloy with a relatively high spin polarization rate.

[0096] The insulating layer 230 is made of an insulator in which the TMR effect has been observed. This insulator is, for example, MgO. Alternatively, as another example of a configuration, this insulator may be, for example, Al2O3 or MgAl2O4.

[0097] As shown in Figure 6, the third layer 130, that is, the first ferromagnetic layer 210, exhibits a discrepancy between the remanent magnetization value when the electric field applied to the first layer 110 is changed from a positive value to a negative value and the remanent magnetization value when the electric field applied to the first layer 110 is changed from a negative value to a positive value. Therefore, the magnetoresistive element 20, which has a configuration consisting of the first ferromagnetic layer 210, the second ferromagnetic layer 220, and the insulating layer 230 sandwiched between the first ferromagnetic layer 210 and the second ferromagnetic layer 220, functions as a magnetoresistive element.

[0098] It is known that the tunnel magnetoresistance ratio (hereinafter referred to as "the structure according to the example") of a structure (hereinafter also referred to as "the structure according to the example"), such as the magnetoresistive element 20, is 240% at room temperature, and comprises a first ferromagnetic layer made of Co3Mn having a body-centered cubic lattice structure, a second ferromagnetic layer made of Co3Mn having a body-centered cubic lattice structure, and an insulating layer made of MgO sandwiched between the first and second ferromagnetic layers.

[0099] In contrast, the tunnel magnetoresistance ratio of the laminate described in Non-Patent Literature 1, which consists of a first ferromagnetic layer made of Co2FeSi, a second ferromagnetic layer made of CoFeB, and an insulating layer made of MgO sandwiched between the first and second ferromagnetic layers (hereinafter also referred to as the "comparative structure"), is known to be 158% at room temperature.

[0100] From this, it can be seen that the magnetoresistive element 20 having the structure according to the above embodiment can achieve a larger, or better, tunnel magnetoresistance ratio than the magnetoresistive element having the structure according to the comparative example using Co2FeSi described in Non-Patent Document 1.

[0101] Thus, the magnetoresistive element 20 with the above configuration provides a magnetoresistive element that can achieve a better magnetoelectric coupling coefficient and a better tunnel magnetoresistance ratio compared to the magnetoresistive element of the comparative example.

[0102] (Embodiment 2) The following describes a laminate according to Embodiment 2, in which the second layer 120 is changed from the laminate 10 according to Embodiment 1 to the second layer according to Embodiment 2.

[0103] In the first embodiment, the second layer 120 is a single-layer structure made of Fe, whereas in the second embodiment, the second layer is a two-layer structure in which a layer made of V and a layer made of Fe are laminated together.

[0104] Here, regarding the laminate according to Embodiment 2, components similar to those of laminate 10 have already been described, so the same reference numerals are used and their detailed descriptions are omitted. The explanation will focus on the differences from laminate 10.

[0105] Figure 10 is a perspective view showing the configuration of the laminate 10C according to Embodiment 2.

[0106] As shown in Figure 10, the laminate 10C is constructed by changing the first layer 110 to the first layer 110C, the second layer 120 to the second layer 120C, and the third layer 130 to the third layer 130C, compared to the laminate 10 according to Embodiment 1.

[0107] The first layer 110C is the same as the first layer 110 according to Embodiment 1.

[0108] The third layer 130C is the same as the third layer 130 according to Embodiment 1.

[0109] The second layer 120C functions as a base (adhesive surface) for laminating the third layer 130C to the upper side of the first layer 110C, similar to the second layer 120 in Embodiment 1.

[0110] The second layer 120C comprises a fourth layer 121 laminated on the upper surface of the first layer 110, and a fifth layer 122 laminated on the upper surface of the fourth layer 121.

[0111] The fourth layer, 121, is a layer consisting of V.

[0112] The fifth layer, 122, is a layer made of Fe.

[0113] In the following, we will explain based on actual measurement data obtained from a sample of laminate 10C, which has the following configuration as an example: the first layer 110C has a thickness of 0.5 [mm], the fourth layer 121 has a thickness of 2 [nm], the fifth layer 122 has a thickness of 2 [nm], and the third layer 130C has a thickness of 5 [nm]. However, in this disclosure, there is no intention to limit the configuration of the laminate 10C related to this disclosure to the configuration of the sample used for the above measurements.

[0114] Figure 11 is a graph plotting the remanent magnetization values ​​of the magnetic moment in the third layer 130C when the electric field applied in the thickness direction of the first layer 110C is varied with respect to the laminate 10C.

[0115] In Figure 11, the horizontal axis represents the intensity of the electric field applied in the thickness direction of the first layer 110C, and the vertical axis represents the value of the remanent magnetization of the magnetic moment in the third layer 130C. In Figure 11, the solid line shows the change in the value of remanent magnetization when the applied electric field is changed from a positive value to a negative value, and the dashed line shows the change in the value of remanent magnetization when the applied electric field is changed from a negative value to a positive value.

[0116] As shown in Figure 11, the remanent magnetization of the laminate 10C changes sharply at the remanent magnetization conversion point. This indicates that the laminate 10C achieves a good strain-induced magnetoelectric coupling effect.

[0117] Furthermore, comparing Figure 11 and Figure 6, it can be seen that the degree of discrepancy between the remanent magnetization value when the electric field applied to the first layer 110C is changed from a positive value to a negative value and the remanent magnetization value when the electric field applied to the first layer 110C is changed from a negative value to a positive value is significantly larger than the degree of discrepancy between the remanent magnetization value when the electric field applied to the first layer 110 is changed from a positive value to a negative value and the remanent magnetization value when the electric field applied to the first layer 110 is changed from a negative value to a positive value.

[0118] In other words, it can be seen that the laminate 10C is able to achieve a significantly larger degree of deviation compared to the laminate 10.

[0119] <Method for manufacturing laminates> The manufacturing method for the laminate 10C will be described below.

[0120] Figure 12 is a flowchart of a second laminate manufacturing method for producing laminate 10C.

[0121] As shown in Figure 12, the second laminate manufacturing method manufactures the laminate 10 by performing the substrate heat treatment step S210C, the V layer growth step 215C, the Fe layer growth step S220C, and the Co3Mn layer growth step S230C in that order.

[0122] The substrate heat treatment process S210C and the Co3Mn layer growth process S230C are the same as the substrate heat treatment process S210 and the Co3Mn layer growth process S230 in the first laminate manufacturing method according to Embodiment 1, respectively, with the laminate 10 being read as laminate 10C, the first layer 110 as the first layer 110C, the second layer 120 as the second layer 120C, and the third layer 130 as the third layer 130C.

[0123] Therefore, this section will explain the second laminate manufacturing method, focusing on the V-layer growth process 215C and the Fe-layer growth process S220C.

[0124] The V layer growth process S215C is a process in which a V molecular beam is supplied to the upper surface of a first layer 110C made of PMN-PT, whose upper surface is the 011 plane, by molecular beam epitaxy, thereby laminating a fourth layer 121 made of V onto the upper surface of the first layer 110C.

[0125] More specifically, the V layer growth process S215C is a process in which, in a molecular beam epitaxy chamber, the temperature of the first layer 110C, whose upper surface flatness has been ensured by the substrate heat treatment process S210, or the first layer 110C made of a PMN-PT substrate whose upper surface flatness has been ensured in advance, is set to 300°C, and a molecular beam of V is supplied to the upper surface of the first layer 110C by a Knudsen cell in the molecular beam epitaxy chamber, thereby stacking a fourth layer 121 made of V on the upper surface of the first layer 110C until, for example, the thickness becomes 2 [nm].

[0126] The Fe layer growth process S220C is a process in which a fifth layer 122 made of Fe is deposited on the upper surface of the fourth layer 121 by molecular beam epitaxy.

[0127] More specifically, the Fe layer growth process S220C is a process in which, in a molecular beam epitaxy chamber, the temperature of the fourth layer 121 is set to 300°C, and a molecular beam of Fe is supplied to the upper surface of the fourth layer 121 using a Knudsen cell in the molecular beam epitaxy chamber, thereby stacking a fifth layer 122 made of Fe on the upper surface of the fourth layer 121 until, for example, the thickness reaches 2 [nm].

[0128] <Configuration of a magnetoresistive element> Figure 13 is a cross-sectional view showing the configuration of the magnetoresistive element 20C according to Embodiment 2.

[0129] As shown in Figure 13, the magnetoresistive element 20C is constructed by changing the laminate 10 to a laminate 10C, changing the second ferromagnetic layer 220 to a second ferromagnetic layer 220C, and changing the insulating layer 230 to an insulating layer 230C, compared to the magnetoresistive element 20 according to Embodiment 1.

[0130] Furthermore, the first ferromagnetic layer 210C is the third layer 130C that constitutes the laminate 10C.

[0131] The second ferromagnetic layer 220C is the same as the second ferromagnetic layer 220 according to Embodiment 1.

[0132] The insulating layer 230C is the same as the insulating layer 230 according to Embodiment 1.

[0133] As mentioned above, the third layer 130C, that is, the first ferromagnetic layer 210C, exhibits a discrepancy between the remanent magnetization value when the electric field applied to the first layer 110C is changed from a positive value to a negative value and the remanent magnetization value when the electric field applied to the first layer 110C is changed from a negative value to a positive value. For this reason, the magnetoresistive element 20C, which has a configuration consisting of the first ferromagnetic layer 210C, the second ferromagnetic layer 220C, and the insulating layer 230C sandwiched between the first ferromagnetic layer 210C and the second ferromagnetic layer 220C, functions as a magnetoresistive element.

[0134] Furthermore, as mentioned above, the degree of discrepancy between the remanent magnetization value when the electric field applied to the first layer 110C is changed from a positive value to a negative value and the remanent magnetization value when the electric field applied to the first layer 110C is changed from a negative value to a positive value is greater than the degree of discrepancy between the remanent magnetization value when the electric field applied to the first layer 110 is changed from a positive value to a negative value and the remanent magnetization value when the electric field applied to the first layer 110 is changed from a negative value to a positive value.

[0135] Therefore, it can be said that the magnetoresistive element 20C is more suitable as a magnetoresistive element than the magnetoresistive element 20 according to Embodiment 1.

[0136] (supplement) As described above, the technologies disclosed in this application have been explained based on Embodiments 1 and 2. However, this disclosure is not limited to these embodiments. Without departing from the spirit of this disclosure, various modifications to these embodiments that a person skilled in the art could conceive of, or forms constructed by combining components from different modifications, may also be included within the scope of one or more aspects of this disclosure. [Industrial applicability]

[0137] This disclosure can be widely applied to laminates having a multiferroic structure, magnetoresistive elements, and the like. [Explanation of Symbols]

[0138] 10, 10A, 10B, 10C laminate 20, 20C magnetoresistive element 110, 110C First layer 120, 120A, 120B, 120C: Second layer 121 The fourth layer 122 The fifth layer 130, 130A, 130B, 130C: Third layer 210, 210C First ferromagnetic layer 220, 220C Second ferromagnetic layer 230, 230C insulating layer

Claims

1. A first layer made of a lead-containing ferroelectric material, with its upper surface being a 011 plane, A second layer made of Fe is laminated on the upper surface of the first layer, Laminated on the upper surface of the second layer, Co ３ It comprises a third layer made of Mn, The third layer is thicker than the second layer. Laminated structure.

2. The ferroelectric material is Pb(Mg １／３ Nb ２／３ ) O ３ -PbTiO ３ That is The laminate according to claim 1.

3. The third layer has a body-centered cubic lattice structure. The laminate according to claim 1 or claim 2.

4. A magnetoresistive element having a laminate according to claim 1 or claim 2, A first ferromagnetic layer made of a ferromagnetic material, A second ferromagnetic layer made of a ferromagnetic material, The invention comprises an insulating layer made of an insulator sandwiched between the first ferromagnetic layer and the second ferromagnetic layer, The first ferromagnetic layer is the third layer. Magnetoresistive element.

5. An Fe layer growth step is performed by supplying a molecular beam of Fe to the upper surface of a first layer made of a lead-containing ferroelectric material, whose upper surface is a 011 plane, using molecular beam epitaxy, thereby laminating a second layer made of Fe onto the upper surface of the first layer. By molecular beam epitaxy, a molecular beam of Co and a molecular beam of Mn are supplied to the upper surface of the second layer, and Co ３ A third layer made of Mn, which is thicker than the second layer, is laminated to the Co ３ Mn layer growth process, Laminate manufacturing method.

6. The ferroelectric material is Pb(Mg １／３ Nb ２／３ )O ３ -PbTiO ３ and is The method for manufacturing a laminate according to claim 5.

7. Furthermore, the process includes a substrate heat treatment step to ensure the flatness of the upper surface of the first layer, In the Fe layer growth process, the second layer is laminated onto the upper surface of the first layer, whose flatness has been ensured by the substrate heat treatment process. A method for manufacturing a laminate according to claim 5 or claim 6.

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