JPWO2006028005A1 - Ferromagnetic ferroelectric and manufacturing method thereof - Google Patents

Abstract

The present invention was made for the purpose of providing a novel material having both ferromagnetism and ferroelectricity. The ferromagnetic ferroelectric material according to the present invention is a substance having a perovskite structure represented by a composition formula Bi2MM′O6 or Pb2MM′O6, and M is a transition metal ion having an electron in a part of an eg orbit, M ′ is a transition metal ion having no electrons in eg orbitals. In particular, Bi2CuMnO6 has a ferromagnetic transition temperature of 340K and has both ferromagnetism and ferroelectricity even at room temperature.

Description

  The present invention relates to a ferromagnetic ferroelectric that is a functional material having both ferromagnetism and ferroelectricity and capable of controlling ferroelectricity by a magnetic field, controlling ferromagnetism by an electric field, and the like, and a method of manufacturing the same.

  Ferroelectric materials are widely used in various devices such as storage media and sensors. In a ferroelectric, the magnitude of polarization can be controlled by applying an electric field and controlling the magnitude. Further, polarization remains even after the applied electric field is removed. Using this property, for example, a nonvolatile memory can be configured. On the other hand, a ferromagnetic material is also used in various devices such as a nonvolatile memory, and its control is performed by applying an external magnetic field.

  If a material having both ferroelectricity and ferromagnetism (hereinafter referred to as “ferromagnetic ferroelectric”) is obtained, devices having various functions can be realized by utilizing these two properties simultaneously. For example, a single material can be used to make a memory that performs recording by ferroelectricity and recording by ferromagnetism independently. In such a memory, the recording capacity (recording density) can be increased as compared with the case of using only one of ferroelectricity and ferromagnetism.

  In a ferromagnetic ferroelectric material, ferroelectricity can be controlled by a magnetic field, and conversely, ferromagnetism can be controlled by an electric field. For this reason, a device having a special function that cannot be obtained with a normal ferroelectric or ferromagnetic material can be constituted by such a ferromagnetic ferroelectric material.

  Furthermore, such materials can be used for spin filters. A spin filter is an element that generates an electron flow (current) with a uniform spin direction, and is a key device of spintronics (a technology that utilizes both the properties of electrons and electric charges). The material needs to be a ferromagnetic insulator. Since a ferroelectric is a good insulator, it can be said that a ferromagnetic ferroelectric is a material suitable for a spin filter.

Patent Document 1 describes that a ferromagnetic ferroelectric substance has been found in a compound having a perovskite structure (hereinafter, a perovskite type compound). Here, the perovskite structure is represented by the general formula ABX _3, are those having a structure in which a layer consisting of a layer and BX ₂ consisting of AX are alternately stacked, the BaTiO ₃ or giant magnetoresistive effect which is ferroelectric It is well-known for playing LaMnO _{3 and the} like. In this document, BiMnO ₃ is cited as a perovskite type compound which is a ferromagnetic ferroelectric substance. Certainly, this material has both ferroelectricity and ferromagnetism, but its ferromagnetic transition temperature is 110K, and it is necessary to cool the element in order to use it in a device such as a nonvolatile memory. Although this document describes that BiFeO ₃ is a ferromagnetic ferroelectric material, this material is actually a weak ferromagnetic material that generates magnetization when the spins of the antiferromagnetic material are tilted. is there.

  Patent Document 2 discloses an oxidation comprising an element capable of forming a perovskite type compound exhibiting ferromagnetism or antiferromagnetism and an element capable of forming a perovskite type compound having dielectric properties such as ferroelectricity and antiferroelectricity. A group of ceramic materials is shown. And the electromagnetic coupling constants representing the magnitude of the interaction between dielectric and magnetism are measured for these materials, which shows that there is a correlation between magnetism and dielectric properties in these materials . However, it is not clear whether these materials have both ferromagnetism and ferroelectricity. In addition, X-ray diffraction measurements indicate that these materials are amorphous and non-crystalline, and that it is not confirmed whether they are single-phase, and therefore identify which substances cause the above characteristics. I can't.

  In addition, in each of these documents, a series of substance groups written in a general formula is mentioned, but the reason for having both ferroelectricity and ferromagnetism common to those substance groups is not shown. . Therefore, it is not clear whether materials other than those shown in the experimental results in the series of substance groups actually have both ferroelectricity and ferromagnetism.

Japanese Patent Laid-Open No. 11-286774 ([0015] to [0017], FIGS. 1 to 4) JP 5-043227 A ([0003] to [0004])

A material having both ferroelectricity and ferromagnetism at room temperature is not yet known. Although it has been found that the ferromagnetic for the orderly arrangement of e _g orbitals occurs in BiMnO _3, no example of realizing by another substance ferromagnetic by similar orbital order. If a guideline for obtaining a ferromagnetic ferroelectric material can be established, a substance having both ferromagnetism and ferroelectricity can be obtained, and a series of substance groups consisting of not only one kind of substance but also many kinds of substances conforming to the guideline. Can be obtained. If such a substance group is obtained, it is expected that a ferromagnetic ferroelectric material having both ferroelectricity and ferromagnetism at room temperature can be obtained by searching for an optimum substance from among them.

  The problem to be solved by the present invention is to provide a novel substance group having both ferromagnetism and ferroelectricity. Another object is to provide a material having both ferromagnetism and ferroelectricity at room temperature.

The first aspect of the ferromagnetic ferroelectric material according to the present invention for solving the above problems is a substance having a perovskite structure represented by a composition formula Bi ₂ MM′O ₆ , t There is a 3d-5d transition metal ions with electrons only a portion of some or all and e _g orbitals of t _{2 g} trajectory of the d orbital of outermost, M 'is of the d orbital of outermost characterized in that a part or all of _2g orbitals is 3d-5d transition metal ions having no electrons e _g orbitals have electron.

A second aspect of the ferromagnetic ferroelectric material according to the present invention is a substance having a perovskite structure represented by a composition formula Pb ₂ MM′O ₆ , wherein M is t of d orbitals of the outermost shell. a 3d-5d transition metal ions with electrons only a portion of some or all and e _g orbitals of _2g orbitals, the electronic part or all of the t _2g orbitals of d orbitals of M 'is the outermost shell characterized in that it is a have e _g orbitals 3d-5d transition metal ions having no electrons.

  In the present application, the “3d-5d transition metal ion” refers to a transition metal ion in which electrons are present in any of the electron orbits of 3d, 4d, or 5d and does not have a closed shell structure. In addition, transition metal ions whose 3d orbitals do not have a closed shell structure are called “3d transition metal ions”. Similarly, transition metal ions whose 4d or 5d orbitals do not have a closed shell structure are referred to as “4d transition metal ions” and “5d transition metal ions”, respectively.

M and M ′ are preferably 3d transition metal ions. Among them, in Bi ₂ MM′O ₆ , M is any one of Co, Ni, and Cu, and the M ′ is preferably Mn. In particular, Bi ₂ CuMnO ₆ is more desirable in that it exhibits both ferromagnetism and ferroelectricity at room temperature.

Even if the ratio of each element shown in the above composition formulas Bi ₂ MM'O ₆ and Pb ₂ MM'O ₆ is slightly deviated, the material having both ferromagnetism and ferroelectricity according to the principle described later It is included in the technical scope of the invention.

The schematic diagram which shows the crystal structure of the ferromagnetic ferroelectric substance which concerns on this invention. The schematic block diagram of the apparatus used for manufacture of the ferromagnetic ferroelectric thin film of a present Example. X-ray (wavelength 0.0421Nm) diffraction chart of Bi ₂ NiMnO ₆ bulk sample produced in this example. Bi ₂ NiMnO ₆ X-ray of the bulk sample (wavelength 0.0421Nm) chart showing a temperature change of the diffraction. Graph showing the temperature change of the dielectric constant of the Bi ₂ NiMnO _6. Graph showing temperature variation of magnetic susceptibility of Bi ₂ NiMnO _6. Graph showing the magnetization curves of Bi ₂ NiMnO _6. Graph showing temperature variation of magnetic susceptibility of Bi ₂ CuMnO _6. Graph showing temperature variation of magnetic susceptibility of Bi ₂ CoMnO _6. X-ray diffraction chart of Bi ₂ NiMnO ₆ thin film fabricated in the present embodiment ((002) enlarged view of the vicinity of the peak). Graph showing the polarization P- electric field E curve in Bi ₂ NiMnO ₆ Temperature 100K of the thin film. Graph showing the change by the magnetic field of the Bi ₂ NiMnO ₆ thin film dielectric constant.

Explanation of symbols

11 ... Bi or Pb
12 ... MO ₆ octahedron 13 ... M'O ₆ octahedron 21 ... chamber 22 ... substrate holder 23 ... target holder 24 ... laser light source 25 ... pump 26 ... gas supply port 27a ... RHEED device electron gun 27b ... RHEED device screen 28 ... Substrate 29 ... Target 30 ... Laser beam 31 ... Evaporated target

Embodiments and effects of the invention

The ferromagnetic ferroelectric material of the present invention basically has a perovskite structure. The composition of the substance having a perovskite structure is represented by the general formula ABX ₃ as described above, but in the present invention, one unit is composed of two B sites, and this composition is expressed as A ₂ B ₂ X ₆ . To express. In the ferromagnetic ferroelectric material of the present invention, A is Bi (bismuth) or Pb (lead), and X is O (oxygen). B is the half t _{2 g} trajectories of some or all and e _g portion of the track only with electronic 3d-5d transition metal ions of the d orbital of the outermost shell (M ions), the other half There is a t _{2 g} trajectory of some or all have the electronic e _g no electrons orbit 3d-5d transition metal ions of the d orbital of the outermost shell (M 'ions). Therefore, the composition formula of the ferromagnetic ferroelectric material of the present invention is expressed as Bi ₂ MM′O ₆ or Pb ₂ MM′O ₆ .

The structure of the ferromagnetic ferroelectric material of the present invention will be described with reference to FIG. MO ₆ octahedron 12 (the octahedron shown in the light color in the figure) has M ions near the center and O ²⁻ ions at the apexes of the octahedron. The M′O ₆ octahedron 13 (the octahedron shown in the drawing in dark color) has M ions near the center and O ²⁻ ions at the vertices of the octahedron. The _six nearest octahedrons to the MO ₆ octahedron 12 are all M′O ₆ octahedrons 13, and the six nearest octahedrons to the M′O ₆ octahedron 13 are all MO _6. It is an octahedron 12. The nearest MO ₆ octahedron 12 and M′O ₆ octahedron 13 share one O ²⁻ ion one by one. Focusing only on M ions and M ′ ions, they are arranged in NaCl type. The A site 11 is in a position surrounded by eight octahedrons, and Bi ³⁺ ions or Pb ²⁺ ions are arranged.

Here will be described e _g orbitals. In the ferromagnetic ferroelectric material of the present invention, as described above, M ions and M ′ ions are arranged near the center of an octahedron having O ²⁻ ions at the apexes. In such an arrangement, the outermost d electrons of the M and M ′ ions are one of five orbitals called xy, yz, zx, 3z ² -r ² , x ² -y ² Placed in. Of these, the e _g orbit is a generic term for the 3z ² -r ² orbit and the x ² -y ² orbit. Xy, yz, and zx are collectively referred to as t _2g orbitals.

When A is Bi ³⁺ ion, the average valence of M ion and M ′ ion must be trivalent, so the combination of valences of both ions is “M ion: monovalent, M ′ ion: 5 "M ion: Divalent, M 'ion: Tetravalent", "M ion: Trivalent, M' ion: Trivalent", "M ion: Tetravalent, M 'ion: Divalent" or "M Ion: pentavalent, M ′ ion: monovalent ”. When A is a Pb ²⁺ ion, the average valence of M and M ′ ions must be tetravalent, so the combination of valences of both ions is “M ion: 2 valence, M ′ ion: 6 "M ion: trivalent, M 'ion: pentavalent", "M ion: tetravalent, M' ion: tetravalent", "M ion: pentavalent, M 'ion: trivalent" or "M Ion: Hexavalent, M 'ion: Divalent ".

The 3d-5d transition metal ions with electrons in a part of the e _g orbitals used as the M ion, Pd ¹⁺ (or, ^{monovalent), Cr 2+, Mn 2+,} Fe 2+, Co 2+, Ni ²⁺ , Cu ²⁺ , Pd ²⁺ , Ag ²⁺ , Pt ²⁺ , Au ²⁺ (above, bivalent), Mn ³⁺ , Fe ³⁺ , Co ³⁺ , Ni ³⁺ , Ru ³⁺ , Rh ³⁺ , Pd ³⁺ , Os ³⁺ , Ir ³⁺ , Pt ³⁺ (trivalent), Co ⁴⁺ , Fe ⁴⁺ , Ru ⁴⁺ , Rh ⁴⁺ , Pd ⁴⁺ , Re ⁴⁺ , Os ⁴⁺ , Ir ⁴⁺ , Pt ⁴⁺ (above, tetravalent), Rh ⁵⁺ , Ir ⁵⁺ , Pt ⁵⁺ (above, pentavalent), etc. The 3d-5d transition metal ions having no electrons e _g orbitals used as M 'ions, V ²⁺ (or ^{divalent), Ti 3+, V 3+,} Cr 3+, Nb 3+, Ta 3 ⁺ (More than trivalent), V ⁴⁺ , Cr ⁴⁺ , Mn ⁴⁺ , Nb ⁴⁺ , Mo ⁴⁺ , Tc ⁴⁺ , Ta ⁴⁺ , W ⁴⁺ , Re ⁴⁺ (more than tetravalent), Mo ⁵⁺ , Tc ⁵⁺ , Ru ⁵⁺ , W ⁵⁺ , Re ⁵⁺ , Os ⁵⁺ (above, pentavalent), Re ⁶⁺ , Os ⁶⁺ (above, hexavalent), etc.
It should be noted that both M ions and M ′ ions may be used in combination of two or more ions that satisfy the above conditions.

The reason why the ferromagnetic ferroelectric material of the present invention has both ferromagnetism and ferroelectricity will be described.
(i) Ferromagnet In the ferromagnetic ferroelectric material of the present invention, Bi ³⁺ or Pb ^{2+ at the} A site and O ^{2− at the} X site have no unpaired electrons, and are therefore non-magnetic. M and M 'ions are responsible. As described above, d electrons of the outermost shell in M ions occupy a portion or all of the t _{2 g} orbit, only a portion of the e _g orbitals, these d electrons provide magnetism. Then, the M ions, e _g orbitals are present so as to protrude toward the O ^2- ions in the vertices of the octahedron. On the other hand, in the M ′ ion closest to this M ion, the t _2g orbital exists so as to avoid the O ²⁻ ion. In such a case, the antiferromagnetic superexchange interaction via the O ^2- ion does not work between the M ion and the M ′ ion, and the ferromagnetic spin that tries to align both electron spins in the same direction. Only direct exchange interactions occur. Due to this interaction, ferromagnetism appears in the material according to the present invention.

(ii) Ferroelectricity In the ferromagnetic ferroelectric material of the present invention, Bi ³⁺ or Pb ^{2+ at the} A site has a lone pair of electrons in a 6s orbit that protrudes spatially. The Coulomb repulsive force acts between the O ²⁻ ions close to the A site and this lone pair, and the crystal structure is distorted in the temperature range below the Curie temperature, and the inversion symmetry is lost. This lack of inversion symmetry just means that the material according to the invention has ferroelectricity.

  As described above, each group of materials according to the present invention has both ferromagnetism and ferroelectricity. Therefore, it can be suitably used for devices that utilize both ferromagnetism and ferroelectricity, such as nonvolatile memories and spin filters.

  Qualitatively, the direct exchange interaction becomes larger as the distance between the M ion and the M ′ ion is shorter, so that the ferromagnetic transition temperature can be increased. Therefore, in order to shorten the distance between the M ion and the M ′ ion, it is desirable to use a 3d transition metal ion having an ion radius smaller than that of the 4d and 5d transition metal ions for the M ion and the M ′ ion.

Among the group of ferromagnetic ferroelectrics according to the present invention, Bi ₂ CuMnO ₆ is characterized by having both ferromagnetism and ferroelectricity at 340 K or higher, which is higher than room temperature. When a ferromagnetic ferroelectric material having both ferromagnetism and ferroelectricity at such a high temperature is used in the above device, it is not necessary to cool the device or simple cooling such as air cooling is performed. Since it only needs to be performed, the apparatus can be simplified and the cost can be reduced.

Next, the manufacturing method of the ferromagnetic ferroelectric substance of this invention is demonstrated.
Bulk ferromagnetic ferroelectrics can be manufactured by a high-pressure synthesis method. First, the raw materials are mixed so that the ratio of the number of atoms of A site atoms (Bi or Pb) and M and M ′ is 2: 1: 1. Here, in order to adjust the amount of oxygen, the ratio of the number of atoms of A, M, M ′ and O in the raw material may be 2: 1: 1: 6, but KClO ₄ , AgO ₂ If the amount of oxygen is adjusted by mixing a reducing agent such as an oxidizing agent or Ti metal with the raw material, O in the raw material may not follow the above ratio. The mixed raw material is heated to 600 ° C. to 1500 ° C. under a pressure of 1 GPa to 10 GPa. Note that when the temperature is 600 ° C. or lower or the pressure is 1 GPa or lower, the target ferromagnetic ferroelectric material is not generated. In addition, when the temperature is 1500 ° C. or higher, the raw material is decomposed. Furthermore, since a sample having sufficiently high purity can be obtained at a pressure of 10 GPa or less, application of a higher pressure only increases the cost and has no advantage. After heating, the product is cooled to room temperature and the pressure is removed. Thereby, the bulk-like ferromagnetic ferroelectric substance according to the present invention is obtained.

The ferromagnetic ferroelectric material according to the present invention is epitaxially grown on a single crystal substrate having a lattice constant close to that of the ferromagnetic ferroelectric material by a chemical vapor deposition (CVD) method, a sol-gel method, a laser ablation method, or the like. Thus, a thin film can be obtained. It is desirable to use a perovskite type compound such as SrTiO ₃ or BaTiO _{3 for the} single crystal substrate. When forming a thin film, Bi has a high vapor pressure and thus tends to precipitate alone. Therefore, epitaxial growth is preferably performed in a gas containing ozone gas. By using ozone gas, a strong oxidizing atmosphere can be obtained, thereby suppressing the precipitation (reduction) of Bi.

(1) Example of manufacturing method of ferromagnetic ferroelectric material according to the present invention As an example of the present invention, a bulk sample and a thin film of Bi ₂ CoMnO ₆ , Bi ₂ NiMnO ₆ and Bi ₂ CuMnO ₆ were prepared. The result of measuring the magnetic and dielectric properties will be described.
First, a method for manufacturing a bulk sample will be described. Bi ₂ O ₃ , MnO ₂ and MO (CoO, NiO or CuO) are weighed and mixed in a ratio of Bi ₂ O ₃ : MnO ₂ : MO = 1: 1: 1 and enclosed in a gold capsule. . The capsule is pressurized to 6 GPa by a cubic anvil type high pressure generator. In this state, the capsule is heated to 700 to 1000 ° C. and held at this temperature for 30 minutes. In this example, the heating state was maintained for a sufficiently long time of 30 minutes so that the raw materials sufficiently reacted. After this time has elapsed, the capsule is slowly cooled over 8 hours. Then, the pressure is removed and the sample is taken out. Thereby, a bulk sample of Bi ₂ MMnO ₆ (M = Co, Ni or Cu) is obtained.

Next, a method for manufacturing a thin film will be described.
FIG. 2 shows a laser ablation apparatus used for thin film production. This apparatus has in a chamber 21 a substrate holder 22 for fixing a substrate and a target holder 23 for holding a target as a raw material for a thin film. Moreover, it has the laser light source 24 which irradiates a target with a laser beam. In this embodiment, an excimer laser is used as the laser light source 24. The chamber 21 is evacuated by a pump 25 and oxygen gas containing ozone is supplied from a gas supply port 26. The thin film formed on the substrate can be observed during film formation by an RHEED (reflection high-energy electron diffraction) apparatus including an electron gun 27a and a screen 27b. In addition, the thin film can be uniformly formed by rotating the substrate holder 22 and the target holder 23.

A SrTiO ₃ single crystal substrate 28 having a (001) surface is fixed to the substrate holder 22 with the surface facing the target 29 (downward). Target prepared by weighing and mixing Bi ₂ O ₃ , MnO ₂ and MO (CoO, NiO or CuO) in the same manner as above to a ratio of Bi ₂ O ₃ : MnO ₂ : MO = 1: 1: 1 29 is placed on the target holder 23. After evacuating the chamber 21, oxygen gas containing 10% ozone is supplied into the chamber 21. Then, while rotating the substrate holder 22 and the target holder 23, the laser light source 24 irradiates the target 29 with the laser light 30 having a wavelength of 248 nm and an intensity of ² J / cm ² W. The portion of the target 29 that has been irradiated with the laser is instantaneously evaporated, and the evaporated target 31 is deposited on the single crystal substrate. Thereby, a thin film of Bi ₂ MMnO ₆ (M = Co, Ni or Cu) is epitaxially grown on the single crystal substrate.

(2) Measurement of structure and characteristics of the ferromagnetic ferroelectric material produced by this example First, X-ray diffraction measurement of the bulk sample produced by this example was performed. FIG. 3 shows an X-ray diffraction chart of a bulk sample of Bi ₂ NiMnO ₆ at room temperature measured using an X-ray having a wavelength of 0.0421 nm (0.421Å). Using this X-ray diffraction chart, Rietveld analysis, which is analysis for specifying the crystal structure of the sample, was performed. As a result, when the crystal space group is C2 and the crystal structure of FIG. 1 in which Ni ²⁺ and Mn ⁴⁺ are regularly arranged is assumed, the measurement results and the calculation results agree well. As for Bi ₂ CoMnO ₆ and Bi ₂ CuMnO ₆ , since the same X-ray diffraction chart as Bi ₂ NiMnO ₆ was obtained, the space group is considered to be C2.

A crystal whose space group is C2 is a monoclinic crystal (a unit cell is shown by a one-dot chain line in FIG. 1). When the space group is C2, the crystal does not have inversion symmetry. This indicates that all of Bi ₂ CoMnO ₆ , Bi ₂ NiMnO ₆ and Bi ₂ CuMnO ₆ produced in this example have ferroelectricity.

FIG. 4 shows X-ray diffraction patterns of Bi ₂ NiMnO ₆ bulk samples measured at a wavelength of 0.0421 nm (0.421 mm) at temperatures of 300K and 500K. It has a P2 ₁ / n space group with inversion symmetry when the temperature is 500K, while it has a C2 space group without inversion symmetry when the temperature is 300K. This shows that the ferroelectric transition occurs at temperatures between 300K and 500K.

FIG. 5 shows the results of measuring the temperature change of the relative permittivity of Bi ₂ NiMnO ₆ . This relative dielectric constant has a maximum value at 485K. This temperature is the ferroelectric transition temperature of Bi ₂ NiMnO ₆ , which is consistent with the temperature change measurement result of the X-ray diffraction chart.

FIG. 7 shows the magnetic susceptibility of Bi ₂ NiMnO ₆ measured by applying an external magnetic field of 100 oersted. In the vicinity of 140K, the magnetic susceptibility increases rapidly with decreasing temperature. FIG. 7 (a) shows magnetization curves measured at a plurality of temperatures between 5K and 180K. When the temperature is 160K and 180K, the magnetization is almost proportional to the magnetic field, whereas when the temperature is 140K or less, the magnetization tends to increase rapidly as the absolute value of the magnetic field increases near the zero magnetic field. . Further, as shown in FIG. 7 (b), when the magnetization curve is measured while raising and lowering the magnetic field when the temperature is 5K, hysteresis peculiar to the ferromagnetic material is observed. These facts indicate that Bi ₂ NiMnO ₆ is a ferromagnetic material with a transition temperature of 140K.

As described above, it was confirmed that Bi ₂ NiMnO ₆ is a ferromagnetic ferroelectric material having a ferroelectric transition temperature of 485K and a ferromagnetic transition temperature of 140K.

FIG. 8 shows the results of susceptibility measurement for Bi ₂ CuMnO ₆ . From this result, it was confirmed that Bi ₂ CuMnO ₆ transitions to ferromagnetism at 340 K above room temperature. Further, as described above, Bi ₂ CuMnO ₆ has the same structure as Bi ₂ NiMnO ₆ at room temperature, so it can be said that it has ferroelectricity. Thus, Bi ₂ CuMnO ₆ was confirmed to be a material having both ferromagnetism and ferroelectricity at room temperature. Therefore, Bi ₂ CuMnO ₆ can be used as a device that utilizes both ferromagnetic and ferroelectric properties at room temperature, and can be said to be a material that has the advantage of not requiring cooling.

FIG. 9 shows the results of susceptibility measurement for Bi ₂ CoMnO ₆ . From this result, it was confirmed that Bi ₂ CoMnO ₆ transitions to ferromagnetism at a temperature of 80K. Further, this Bi ₂ CoMnO ₆ has ferroelectricity for the same reason as described above.

As described _{above, Bi 2 NiMnO 6, Bi 2} CuMnO 6, Bi 2 CoMnO 6 is a series of substance groups obtained in this example was confirmed that both a material having both ferromagnetic and ferroelectric It was.

Next, experimental results regarding the Bi ₂ NiMnO ₆ thin film produced in this example will be described. FIG. 10 shows an enlarged view near the (002) peak in the X-ray diffraction chart of the Bi ₂ NiMnO ₆ thin film at room temperature. The vertical axis represents the X-ray intensity in logarithm. The (002) diffraction peak of the Bi ₂ NiMnO ₆ thin film is clearly seen near the low angle side of the (002) peak of the SrTiO ₃ substrate. This indicates that the Bi ₂ NiMnO ₆ thin film is an epitaxial thin film whose (001) plane is grown in parallel on the (001) -SrTiO ₃ substrate. In addition, a satellite peak is observed around the (002) peak of the thin film. This satellite peak is a Laue peak due to the finite film thickness, indicating that a single crystal thin film with a uniform film thickness was obtained.

The results of the measurements of the dielectric properties of Bi ₂ NiMnO ₆ thin. FIG. 11 shows the results of dielectric polarization measurement at a temperature of 100K. The horizontal axis of this figure is the electric field E, and the vertical axis is the polarization P. From this PE curve, it can be seen that the Bi ₂ NiMnO ₆ thin film obtained in this example has a polarization of 15 μC / cm ^{2 at} 100K.

FIG. 12 shows the result of measuring the change of the dielectric constant of the Bi ₂ NiMnO ₆ thin film due to the magnetic field. Here, the vertical axis represents a value obtained by dividing the measured dielectric constant by the dielectric constant in a zero magnetic field. From this measurement result, it was clarified that Bi ₂ NiMnO ₆ can control the dielectric constant by applying a magnetic field. For example, when the temperature is 140 K, the dielectric constant when a magnetic field of 90000 oersted (7.2 × 10 ⁶ A / m) is applied is increased by about 4% from the dielectric constant in the zero magnetic field.

Claims (10)

A substance having a perovskite structure represented by a composition formula Bi ₂ MM'O _6, electrons only a portion of some or all and e _g orbitals of t _{2 g} trajectory of the d orbital of M is the outermost shell with a 3d-5d transition metal ions, M 'is t _{2 g} trajectory of some or all have the electronic e _g orbitals 3d-5d transition metal ions having no electrons within the d orbitals of the outermost A ferromagnetic ferroelectric material characterized by   2. The ferromagnetic ferroelectric material according to claim 1, wherein M is any one of Co, Ni, and Cu, and M ′ is Mn.   The ferromagnetic ferroelectric substance according to claim 2, wherein M is Cu. A substance having a perovskite structure represented by a composition formula Pb ₂ MM'O _6, electrons only a portion of some or all and e _g orbitals of t _{2 g} trajectory of the d orbital of M is the outermost shell with a 3d-5d transition metal ions, M 'is t _{2 g} trajectory of some or all have the electronic e _g orbitals 3d-5d transition metal ions having no electrons within the d orbitals of the outermost A ferromagnetic ferroelectric material characterized by   5. A ferromagnetic ferroelectric material according to claim 1, wherein M and M ′ are 3d transition metal ions.   6. The ferromagnetic ferroelectric material according to claim 1, wherein both the ferromagnetic transition temperature and the ferroelectric transition temperature are 340K or higher. A substance having a perovskite structure represented by a composition formula A ₂ MM'O _6, A is Bi or Pb, some or all of the t _{2 g} trajectory of the d orbital of M is outermost and e _g a 3d-5d transition metal ions with electrons only a part of the track, M 'has no electrons e _g orbitals have electrons into some or all of the t _{2 g} trajectory of the d orbital of the outermost shell 3d In a method for producing a ferromagnetic ferroelectric material that is a 5d transition metal ion,
A material containing A, M, and M ′ in a ratio of approximately 2: 1: 1 is reacted at a temperature of 600 ° C. to 1500 ° C. and a pressure of 1 GPa to 10 GPa. Production method. A substance having a perovskite structure represented by a composition formula A ₂ MM'O _6, A is Bi or Pb, some or all of the t _{2 g} trajectory of the d orbital of M is outermost and e _g a 3d-5d transition metal ions with electrons only a part of the track, M 'has no electrons e _g orbitals have electrons into some or all of the t _{2 g} trajectory of the d orbital of the outermost shell 3d In a method for producing a ferromagnetic ferroelectric material that is a 5d transition metal ion,
The ferromagnetic ferroelectric thin film characterized by using a raw material containing A, M and M ′ in a ratio of approximately 2: 1: 1 and epitaxially growing a thin film of composition A ₂ MM′O ₆ on a single crystal substrate. Manufacturing method.   9. The method of manufacturing a ferromagnetic ferroelectric thin film according to claim 8, wherein the substrate is made of a material having a perovskite structure.   10. The method for producing a ferromagnetic ferroelectric thin film according to claim 8, wherein the thin film is epitaxially grown in an atmosphere containing ozone.