JP2009224563A - Multiferroic element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multiferroic element capable of inducing a current by magnetic field with an intensity around hundreds of gauss, and controlling the intensity and direction of electric polarization. <P>SOLUTION: A multiferroic nanogenerator has a structure formed of a multiferroic solid-state material 1 sandwiched between metal electrodes 2, is arranged to be applied with an A.C. magnetic field 5 parallel to the metal electrodes 2, and utilizes a current induced between the metal electrodes 2. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a new functional element multiferroic element having both ferroelectricity and ferromagnetism, and provides a nanometer-sized nano power generation device because a displacement current can be generated by repetitive magnetization reversal. . Further, an element capable of generating electric polarization by an external magnetic field and controlling the intensity and direction thereof is provided. Further, it is used for a magnetic sensor necessary for reading information stored by magnetization. Further, this element can be applied to a technology related to a memory element.

The inventors of the present application are multiferroic solid materials that combine ferroelectricity and ferromagnetism with a spin structure rotating so that the spin direction is along the outside of the cone, and generate electric polarization by an external magnetic field. Invented a multiferroic element using this (see Patent Literature 1 and Non-Patent Literature below).
Japanese Patent Application No. 2006-144309 Y. Yamazaki et al. Phys. Rev. Lett. 96, 207204 (2006)

However, in the MCr ₂ O ₄ (M = Mn, Fe, Co, Ni) compound in the present invention, in order to control this, a very large external magnetic field strength of about several thousand gauss is required.

  In view of the above situation, an object of the present invention is to provide a multiferroic element capable of inducing current with a magnetic field strength of about several hundred gauss and controlling the intensity and direction of electric polarization.

  [1] A multiferroic element is a multiferroic solid material having both ferroelectricity and ferromagnetism containing iron oxide as a main raw material, and is characterized in that current is induced by a weak external magnetic field of 300 gauss or less.

  [2] In multiferroic elements, a multiferroic solid material having both ferroelectricity and ferromagnetism containing iron oxide as the main raw material, and the intensity and direction of electric polarization can be controlled by a weak external magnetic field of 300 gauss or less. It is characterized by that.

[3] In the multiferroic element according to the above [1] or [2], the multiferroic solid material is a ferrite compound of A ₂ B ₂ Fe ₁₂ O ₂₂ , and A is Ca, Ba, Sr, or these It is composed of a mixture of two kinds of elements, and B is composed of Mg, Zn, Co, Ni, Cu.

[4] In the multiferroic element described in [1] or [2] above, the multiferroic solid material is a ferrite compound of A ₂ B ₂ —xCxFe ₁₂ O ₂₂ , and A is Ca, Ba, Sr, or these Characterized in that B is an element composed of Mg, Zn, Co, Ni, and Cu, C is an element composed of Zn, and the range of x is 0 <x ≦ 1. To do.

  [5] The multiferroic element according to [3] above, wherein the multiferroic solid material is further subjected to a heat treatment in oxygen at a temperature ranging from 400 ° C. to 800 ° C. for a time ranging from 100 to 400 hours. The temperature is increased to 260K.

  According to the present invention, the following effects can be achieved.

  (1) Repetitive alternating magnetic field (magnetic field reversal) Furthermore, since a displacement current continues to flow through the wiring due to a weak magnetic field strength of 300 gauss or less, it functions as a nano-sized generator incorporating a nanometer-sized power generation coil. For example, by applying a repetitive weak magnetic field from outside the human body, driving power can be applied to a micro motor in a blood vessel of the human body.

  (2) Since the magnetic sensor part and the electric polarization generating part can be made of the same solid material, it can be used as a data reading magnetic sensor that functions without having a special shape. As a result, the structure of the magnetic sensor element is simplified, resulting in significant cost merit. Since this magnetic sensor element can be miniaturized to the nano size, it becomes a magnetic sensor that can cope with the miniaturization of the magnetization region for storing information. Since this magnetic sensor can control polarization with a weak magnetic field, it becomes a highly sensitive magnetic sensor.

  (3) Since a multiferroic memory element (referred to as an MFM element) is electric field induced unlike a current induced magnetic field, significant current consumption can be suppressed. Furthermore, since the induced magnetization has hysteresis, it has a memory effect and becomes a nonvolatile memory element. Since the element structure is also simple, a minute memory can be formed, and a high-density memory becomes possible. Fewer layer configurations dramatically reduce process costs. A new low power consumption, high integration, low manufacturing cost multiferroic nonvolatile memory element (MFM element) becomes possible.

  The multiferroic nanogenerator has a structure made of a multiferroic solid material sandwiched between metal electrodes, is arranged so as to apply an alternating magnetic field in parallel to the electrodes, and uses a current flowing between the electrodes. The magnetic sensor element has a structure made of a multiferroic solid material sandwiched between metal electrodes, and electric polarization generated in a direction substantially perpendicular to the magnetic field due to a weak magnetic field generated by a leakage magnetic field corresponding to information. May be detected by a voltmeter. The multiferroic memory element is made of a multiferroic solid material sandwiched between two metal electrodes. By applying a voltage between a specific selected bit line and a word line, magnetization is generated in a specific direction in a single memory element sandwiched between the selected lines. The generated magnetization has a memory function. A non-magnetic solid material is embedded between the memory elements. Data can be read by determining 0 or 1 based on the voltage intensity resulting from the polarization generated between a specific selected bit line and word line.

  Hereinafter, embodiments of the present invention will be described in detail.

  FIG. 1 is a schematic diagram of a multiferroic nanogenerator showing a first embodiment of the present invention.

  In this figure, 1 is a multiferroic solid material, 2 is a metal electrode formed on both sides of the multiferroic solid material 1, 3 is a wiring connected to the metal electrode 2, and 4 is connected to the wiring 3. The electrical device 5 is an alternating magnetic field that acts on the multiferroic solid material 1.

  As shown in FIG. 1, the multiferroic nanogenerator has a structure made of a multiferroic solid material 1 sandwiched between metal electrodes 2 and is arranged so as to apply an alternating magnetic field 5 in parallel to the metal electrodes 2. Then, the current flowing between the metal electrodes 2 may be used for the operation of the electric device 4. According to this embodiment, since the displacement current 6 continues to flow in the wiring 4 by a weak alternating magnetic field (magnetic field reversal) 5 of 300 gauss or less, nano-sized power generation in which a nanometer-sized power generation coil is incorporated. It functions as a machine. For example, by applying a repetitive magnetic field from outside the human body, driving power can be applied to a micro motor in a blood vessel of the human body.

  FIG. 2 is a schematic view of a multiferroic magnetic sensor element showing a second embodiment of the present invention.

  11 is a multiferroic solid material, 12 is a metal electrode formed on both sides of the multiferroic solid material 11, 13 is a wiring connected to the metal electrode 12, 14 is a voltmeter connected to the wiring 13, Reference numeral 15 denotes a perpendicular recording material in which data acting on the multiferroic solid material 11 is stored.

  As shown in FIG. 2, the magnetic sensor element has a structure made of a multiferroic solid material 11 sandwiched between metal electrodes 12, and is generated by a magnetic field generated by a leakage magnetic field of magnetization corresponding to information of the perpendicular recording material 15. The electric polarization generated in the direction substantially perpendicular to the magnetic field may be measured by the voltmeter 14.

  According to this embodiment, since the polarization can be generated by the magnetic field from the perpendicular recording material 15 in which data is stored, it functions as a data reading magnetic sensor.

  In this case, since the magnetic sensor unit and the electric polarization generating unit can be made of the same solid material, they function without having a special shape. As a result, the structure of the magnetic sensor element is simplified, resulting in significant cost merit. Since this sensor element can be miniaturized to a nano size, it becomes a magnetic sensor that can cope with the miniaturization of the magnetization region for storing information.

  The multiferroic memory element is made of a multiferroic solid material sandwiched between two metal electrodes. By applying a voltage from a DC power supply or an AC power supply via a wiring between a specific selected bit line and a word line, a single memory element sandwiched between the selected lines is magnetized in a specific direction. generate. The generated magnetization has a memory function. A multiferroic solid material is embedded between the memory elements.

3 is a layout diagram of a multiferroic memory cell according to the present invention, FIG. 4 is a configuration diagram of magnetic field induced current generation of the multiferroic element, and FIG. 5 is a Ba ₂ which is a multiferroic solid material according to the present invention. ₂ is a photograph substituted for a drawing showing a single crystal of Mg ₂ Fe ₁₂ O ₂₂ .

  In FIG. 3, 21 is a multiferroic solid material, 22 is upper and lower metal electrodes, 23 is a multiferroic memory cell, 24 is a bit line, and 25 is a wort line.

  In this figure, in reading data, 0 or 1 is determined based on the voltage intensity caused by the polarization generated between a specific selected bit line 24 and word line 25.

  FIG. 4 is a configuration diagram in actual current measurement.

  In this figure, 31 is a multiferroic solid material, 32 is upper and lower metal electrodes, 33 is a magnetic field applied from the outside, and 34 is the direction of electric polarization generated. An ammeter 35 measures the current between the upper and lower metal electrodes 32 of the multiferroic solid material 31 generated by the induced electric polarization. A silver paste was used as the electrode material, but there is no problem with other metals such as aluminum and gold.

Of the compounds having a hexagonal ferrite structure as the multiferroic solid material 31, the arrangement of crystal orientations when Ba ₂ Mg ₂ Fe ₁₂ O ₂₂ is used is shown in 36. The sample used is a single crystal produced by a flux method (see FIG. 5). In FIG. 5, the photograph is the [001] plane.

The crystal structure and magnetic structure of Ba ₂ Mg ₂ Fe ₁₂ O ₂₂ are shown in FIG. Its magnetic structure is a helical spin structure with a propagation vector in the [001] direction. Although it is ferrimagnetic (a type of ferromagnetism) at room temperature, it is helical at temperatures below −78 ° C. and conical at temperatures below −223 ° C. The magnetic structure at the right end represents a state in which the cone is inclined with respect to [001] by the magnetic field, and electrical polarization occurs perpendicular to the plane of the paper (the back is positive).

FIG. 7 shows the measurement results of current and electric polarization generated when a weak external magnetic field of 300 gauss was vibrated in the [100] direction in a Ba ₂ Mg ₂ Fe ₁₂ O ₂₂ crystal material. The measurement temperature is −268 ° C. It can be seen that a current flows in response to the application of an alternating magnetic field, and that the electric polarization also alternates between positive and negative. FIG. 8 schematically shows the time change of the applied magnetic field and the generated electric polarization in this measurement. The arrow on the cone indicates the direction in which the spin rotates along the propagation vector direction.

  FIG. 9 is a diagram showing the magnetic field orientation dependence of electric polarization.

  In FIG. 9, a schematic configuration for the measurement of magnetoelectric (ME) polarization under a horizontal rotating magnetic field is shown in FIG. 9 (a), and in FIG. 9 (d) a vertical configuration is shown. Fig. 2 shows a schematic arrangement for the measurement of magnetoelectric (ME) polarization under a rotating magnetic field. Here, φ and θ are defined as relative angles between B and [120] and between B and [001], respectively.

  FIGS. 9B, 9C, 9E, and 9F show the φ-dependence and θ-dependence of magnetoelectric polarization under a rotating magnetic field of 300 Gauss and 10,000 Gauss.

The Ba ₂ Mg ₂ Fe ₁₂ O ₂₂ crystal material can control the intensity and direction of the generated current and electric polarization in the direction of the external magnetic field to be applied. When a 300 gauss magnetic field is turned around [001], the electric polarization also rotates in the same plane [FIG. 9 (b)]. On the other hand, when the magnetic field is rotated around [120], the magnitude changes with the direction of the electric polarization unchanged (FIG. 9E). When a magnetic field of 10,000 Gauss is applied, the electric polarization also rotates when rotating in the [001] plane [FIG. 9 (c)], but the ferroelectric polarization disappears when rotating in the [120] plane [FIG. 9]. (F)]. In this way, the intensity of the current generated in the direction of the magnetic field and the intensity and direction of the electric polarization can be controlled.

As described above, in the case of the multiferroic material Ba ₂ Mg ₂ Fe ₁₂ O ₂₂ , for the first time, it is possible to generate the current and electric polarization with a weak external magnetic field of 300 gauss and to control the intensity and direction of the electric polarization. Demonstrated. The applied magnetic field intensity was a weak magnetic field of about 300 Gauss in this example. In the conventional example, in order to obtain the same current intensity, a magnetic field intensity of about several thousand gauss is necessary. Furthermore, if the material is selected, the current density can be improved.

  The measurement temperature in the embodiment is a temperature region of −268 ° C. and a very low temperature region. However, since such a phenomenon occurs in a spin state exhibiting spiral magnetism, the spiral magnetic transition may be brought to a high temperature. It is possible to increase the helical magnetic transition temperature to 260 K by adding a heat treatment in the range of 400 to 800 ° C. in oxygen and in the range of 100 to 400 hours. Furthermore, the possibility of normal temperature is high by optimizing the temperature process.

In the multiferroic solid material Ba ₂ Mg ₂ Fe ₁₂ O ₂₂ having both ferromagnetism and ferroelectricity, it has been shown in the embodiment that the electric current and electric polarization can be controlled by an external magnetic field. It is possible to form electric polarization and generate magnetization. In a ferroelectric, the positive and negative directions of electric polarization can be controlled by an electric field. If the reversal of electric polarization occurs at this time, it is self-evident that the reversal of magnetization occurs simultaneously in a multiferroic material having a spin helical structure.

  In addition, this invention is not limited to the said Example, Based on the meaning of this invention, a various deformation | transformation is possible and these are not excluded from the scope of the present invention.

  The multiferroic element of the present invention can provide a nano-sized power generation device, a magnetic sensor that reads information on an element stored by magnetization, and a low-cost memory element.

It is a schematic diagram of the multiferroic nanogenerator which shows 1st Example of this invention. It is a schematic diagram of the multiferroic magnetic sensor element which shows 2nd Example of this invention. FIG. 3 is a layout diagram of multiferroic memory cells according to the present invention. It is a block diagram of the magnetic field induced current generation | occurrence | production of the multiferroic element concerning this invention. It is a drawing-substituting photograph showing a single crystal of Ba ₂ Mg ₂ Fe ₁₂ O ₂₂ is a multiferroic solid material according to the present invention. A magnetic structure view crystal structure of multiferroic Ba ₂ Mg ₂ Fe ₁₂ O ₂₂ is a solid state material and [001] direction with a propagation vector of the present invention. It is a figure which shows the measurement result of the displacement current when an external magnetic field is vibrated in the [100] direction to Ba ₂ Mg ₂ Fe ₁₂ O ₂₂ which is a multiferroic solid material according to the present invention. It is a schematic diagram showing the time change (upper stage) of the spin structure and the time change of the magnetic field / electric polarization when the magnetic field is vibrated in the [100] direction. It is a figure which shows the magnetic field orientation dependence of an electric polarization.

Explanation of symbols

1,11,21,31 Multiferroic solid material 2,12,22,32 Metal electrode 3,13 Wiring 4 Electrical equipment 5 AC magnetic field 6 Displacement current 14 Voltmeter 15 Vertical recording material 23 Multiferroic memory cell 24 Bit line 25 Wort line 33 Magnetic field applied from the outside 34 Direction of generated electric polarization 35 Ammeter 36 Arrangement of crystal orientation when using Ba ₂ Mg ₂ Fe ₁₂ O ₂₂

Claims (5)

  A multiferroic element which is a multiferroic solid material having both ferroelectricity and ferromagnetism containing iron oxide as a main material, and in which a current is induced by a weak external magnetic field of 300 gauss or less.   A multiferroic solid material that contains both iron and iron as its main raw material and has both ferroelectricity and ferromagnetism, and the strength and direction of electric polarization can be controlled by a weak external magnetic field of 300 gauss or less. element. 3. The multiferroic element according to claim 1, wherein the multiferroic solid material is a ferrite compound of A ₂ B ₂ Fe ₁₂ O ₂₂ , and A is Ca, Ba, Sr or a mixture of these two elements. A multiferroic element characterized in that B is an element composed of Mg, Zn, Co, Ni, and Cu. _{3. The} multiferroic element according to claim 1, wherein the multiferroic solid material is a ferrite compound of A ₂ B ₂ —xCxFe ₁₂ O ₂₂ , and A is Ca, Ba, Sr, or two kinds of these elements. A multiferroic device comprising a mixture, wherein B is an element composed of Mg, Zn, Co, Ni, and Cu, C is an element composed of Zn, and the range of x is 0 <x ≦ 1.   4. The multiferroic element according to claim 3, wherein the multiferroic solid material is further heat-treated in oxygen in the range of 400 ° C. to 800 ° C. in the range of 100 to 400 hours, and the helical magnetic transition temperature is increased to 260K. A multiferroic element characterized by high temperature.