JP2013069724A - Electromagnetic effect element using electromagnetic effect material having akermanite structure containing magnetic ion - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electromagnetic effect material exhibiting an electromagnetic effect even at a temperature higher than a magnetic transition temperature.SOLUTION: The electromagnetic effect element uses an electromagnetic effect material having an akermanite structure containing a magnetic ion. The electromagnetic effect material is an AMXO, wherein A is Ca, Sr, or Ba, X is Ge or Si, and M is a magnetic ion.

Description

  The present invention relates to an electromagnetism effect element using an electromagnetism effect material having an akermanite structure containing magnetic ions.

  In recent years, a phenomenon has been confirmed in which magnetization is induced when an electric field is applied from the outside, and on the contrary, electric polarization is induced when a magnetic field is applied from the outside, which is called an electromagnetic effect. A material that exhibits such an electromagnetic effect is called a multiferroic substance or an electromagnetic effect material. By using the electromagnetism effect, it is possible to control the magnetization using an electric field, and conversely to control the electric polarization using a magnetic field, which is expected to be applied to new electronic devices such as a magnetic memory described later. Yes.

In putting an electronic device using the electromagnetism effect into practical use, it is preferable that it can operate at room temperature. However, currently known electromagnetic materials often have low electromagnetism effect expression temperatures. Therefore, development of an electromagnetic effect material that exhibits an electromagnetism effect even at room temperature has been underway. It has been found that in an electromagnetic effect material, electric polarization is induced by applying a magnetic field at a temperature lower than the magnetic transition temperature. Therefore, in order to develop an electromagnetic effect material that exhibits an electromagnetism effect even at room temperature, an electromagnetism effect material having a magnetic transition temperature higher than room temperature (for example, 300 K or more) has been developed. For example, Non-Patent Document 1 discloses Z-type hexagonal ferrite (chemical formula Sr ₃ Co ₂ Fe ₂₄ O ₄₁ ) that exhibits a remarkable electromagnetic effect when a weak magnetic field of several hundred gauss is applied in a normal temperature region.

NATURE MATERIALS 9, 797-802 (2010) Physical Review Letters 105, 137202 (2010)

The above-described Sr ₃ Co ₂ Fe ₂₄ O ₄₁ is difficult to produce due to the similar structure and oxygen amount. For this reason, an electromagnetic effect material having a simple structure and easy to manufacture is desired. Sr ₃ Co ₂ Fe ₂₄ O ₄₁ has been reported to exhibit an electromagnetic effect at room temperature, but it is expected that the electromagnetism effect will not be exhibited when the magnetic transition temperature is exceeded. Therefore, an element using Sr ₃ Co ₂ Fe ₂₄ O ₄₁ cannot be used at a temperature exceeding the magnetic transition temperature. Therefore, an electromagnetic effect element that can be used regardless of temperature is desired.

The present invention has been made in view of the above problems, and according to an aspect of the present invention, there is provided an electromagnetism effect element using an electromagnetism effect material having an akermanite structure containing magnetic ions,
The electromagnetic effect material is A ₂ MX ₂ O ₇ , A is Ca, Sr, Ba, X is Ge, Si, M is a magnetic ion,
An electromagnetic effect element is provided that exhibits an electromagnetic effect at a temperature higher than the magnetic transition temperature of the electromagnetic effect material.

According to the present invention, there is provided an electromagnetic effect element that has a simple structure of A ₂ MX ₂ O ₇ (A = Ca, Sr, Ba, X = Ge, Si, M = magnetic ion) and can be easily produced. Is done. Conventionally, there has been no electromagnetism effect element that exhibits an electromagnetism effect at a temperature higher than the magnetic transition temperature. However, the electromagnetism effect element according to the present invention has an electromagnetism even at a temperature higher than the magnetic transition temperature. The effect is expressed. Therefore, it can be operated at an arbitrary temperature except for the restriction caused by the melting point of the crystal and the like as well as operating in the normal temperature region. In the electromagnetic effect element of the present invention, M may be any one of Mn, Co, Fe, and Cu.

  The electro-magnetic effect element of the present invention may include a single crystal of the electro-magnetic effect material having a crystal structure in which a predetermined direction is a c-axis direction. A pair of electrodes may be formed at both ends. For example, in a single crystal having a crystal structure as shown in FIGS. 1A and 1B, when a pair of electrodes are formed at both ends in the c-axis direction, the plane is perpendicular to the c-axis. When a magnetic field is applied, an induced charge due to magnetically induced electric polarization appears on the electrode. As will be described later, in this specification, electric polarization induced by a magnetic field is appropriately referred to as magnetic field induced electric polarization.

  The electromagnetism effect element of the present invention may be a single crystal of the electromagnetism effect material, and may include a single crystal having a crystal structure having a predetermined direction as a c-axis direction. It may be a magnetic field sensor that detects the external magnetic field by expressing a magnetic field induced electric polarization in the c-axis direction when an external magnetic field that changes with time in a plane perpendicular to the c-axis is applied. . In this case, since the size and shape of the single crystal can be arbitrarily set, for example, a submicron-size extremely small magnetic field sensor can be manufactured.

  The electromagnetism effect element of the present invention is a single crystal of the electromagnetism effect material, and has a single crystal having a crystal structure having a predetermined direction as the c-axis direction, and is disposed at both ends of the single crystal in the c-axis direction. And a power generation element that outputs a magnetic field induced current from the electrode when a varying magnetic field is applied across the single crystal in a plane perpendicular to the c-axis of the single crystal. May be. In this case, since the size and shape of the single crystal can be arbitrarily set, for example, an extremely small power generation element of submicron size can be manufactured. As will be described later, in the present specification, a current generated in accordance with a change in magnetic field induced electric polarization is referred to as a magnetic field induced current. Furthermore, the power generation element includes a magnetic field generation mechanism that generates a magnetic field in a direction across the single crystal in a plane perpendicular to the c-axis of the single crystal, and a magnetic field variation mechanism that varies the magnetic field with time. Also good.

  ADVANTAGE OF THE INVENTION According to this invention, the electromagnetism effect element which can be used irrespective of temperature can be provided.

FIGS. 1A and 1B are schematic views showing an akermanite structure. 2A and 2B are schematic diagrams showing the relationship between the direction of magnetization and the direction of electric polarization. FIG. 3 is a schematic view of an electric polarization domain in a general electromagnetic effect material. The upper graph of FIG. 4 shows an external rotating magnetic field (8T) that rotates around the c-axis in the ab plane with the temperature of the single crystal of Sr ₂ CoSi ₂ O ₇ being 4.5K, 7K, 8K, and 10K. FIG. 5 is a graph showing the result of measuring the magnitude of electric polarization induced in the c-axis direction when applied, and the lower graph of FIG. 4 shows the state in which the temperature of the Sr ₂ CoSi ₂ O ₇ single crystal is 4.5K. When an external rotating magnetic field having a magnitude of 0T, 0.5T, 1T, 2T, 4T, or 8T is applied as an external magnetic field that rotates around the c-axis in the ab plane, the electricity induced in the c-axis direction It is a graph which shows the result of having measured the magnitude | size of polarization. The upper graph in FIG. 5 is a graph plotting the magnetic field dependence of magnetization at each temperature in Sr ₂ CoSi ₂ O ₇ , and the lower graph in FIG. 5 is the electric polarization at each temperature in Sr ₂ CoSi ₂ O ₇ . It is the graph which plotted the magnetic field dependence of. FIG. 6 is a flowchart showing a procedure of a method for producing a single crystal sample. FIG. 7 is a schematic view of the infrared heating single crystal manufacturing apparatus 10. FIG. 8 is a schematic view of the magnetic field induced electric polarization measuring device 60. The upper graph in FIG. 9 is a graph showing the time change of the component (μ ₀ H _a ) in the a-axis direction of the rotating magnetic field, and the graph shown by the bold line in the middle in FIG. 9 is the magnetic field induced by the rotating magnetic field. FIG. 10 is a graph showing a time change of a magnetic field induced current accompanying a change in induced electric polarization, and a graph indicated by a thin line in the middle stage of FIG. 9 is a half of the rotation period of the magnetic field among two components included in the magnetic field induced current signal. Only a component having a period is extracted, and the lower graph in FIG. 9 is a graph of the time change of the magnetic field induced electric polarization. FIG. 10 is a schematic view of the power generation element 100.

As an electromagnetic effect material having an akermanite structure containing magnetic ions according to the present invention, Sr ₂ CoSi ₂ O ₇ will be described as an example. In the present specification, the substance “having an akermanite structure containing magnetic ions” is a compound having a crystal structure similar to that of mineral akermanite (Ca ₂ MgSi ₂ O ₇ ), Is replaced with magnetic ions such as Mn, Co, Fe, and Cu. Here, the production of crystals has been reported for those in which the Mg portion of the mineral akermanite is replaced with each element of Mn, Co, Fe, and Cu. However, the substance “having an akermanite structure containing magnetic ions” according to the present invention is not necessarily limited to a substance containing Mn, Co, Fe, or Cu as magnetic ions, and according to the knowledge of the inventors. It is considered that the substance may contain a group 3-11 element (transition element) in the periodic table. The Ca portion of the mineral akermanite may be replaced with other alkaline earth metals such as Sr and Ba, and the Si portion may be replaced with Ge.

As shown in FIGS. 1A and 1B, Sr ₂ CoSi ₂ O ₇ has a crystal structure including a tetrahedral structure in which Co and Si are each surrounded by four Os. Specifically, Sr ₂ CoSi ₂ O ₇ has a non-centrosymmetric tetragonal structure including a CoO ₄ tetrahedron and a SiO ₄ tetrahedron that share a vertex (O) with each other, and Sr ²⁺ ions sandwiched between them. (Space group P (−4) 2 ₁ m).

Here, consider a case where one CoO ₄ tetrahedron is arranged in the orientation shown in FIGS. 2 (a) and 2 (b). Against CoO ₄ tetrahedra, when an external magnetic field which rotates around the c-axis in a plane perpendicular to the c-axis (ab plane) is applied, the spin S of Co is in accordance with the rotation of the external magnetic field rotation To do. At this time, as shown in FIG. 2A, when the spin S of Co is parallel to the [110] direction, electric polarization + _Pz parallel to the c-axis direction is induced, and FIG. as shown, when the spin S of Co is parallel to [110] direction, antiparallel electric polarization -P _z in c-axis direction is known to be induced. Such electric polarization induced by a magnetic field is appropriately referred to as magnetic field induced electric polarization.

In the Sr ₂ CoSi ₂ O ₇ crystal, not all CoO ₄ tetrahedra are oriented in the same direction. And CoO ₄ tetrahedra are arranged at four corners in FIG. 1 (a), it is not equivalent to the CoO ₄ tetrahedra that are located in the center, facing different directions. Therefore, the direction and / or the magnitude of the electric polarization vector induced when the Co spin S is oriented in a predetermined direction (eg, [110] direction) in a plane (ab plane) perpendicular to the c-axis is The two types of CoO ₄ tetrahedrons are different from each other. However, these two types of CoO ₄ tetrahedrons are not arranged in such a positional relationship that induced electric polarization vectors cancel each other. Therefore, in the entire crystal of Sr ₂ CoSi ₂ O ₇ , the electric polarization vector induced when the Co spin S is rotated around the c-axis in the ab plane is not zero.

Note that, as shown in FIG. 3, a general electromagnetic effect material exhibits paraelectricity (PE) at a temperature higher than the magnetic transition temperature and exhibits ferroelectricity (FE) at a temperature lower than the magnetic transition temperature. In general, a ferroelectric includes a plurality of electric polarization domains inside, and each domain has spontaneous polarization. The spontaneous polarization of each domain is not in the same direction, but cancels each other. Therefore, in order to observe a large spontaneous electric polarization as a whole crystal, an electric field (E) is applied from the outside and the domain is It is necessary to perform a process of aligning in one direction, so-called polling processing. On the other hand, in the Sr ₂ CoSi ₂ O ₇ crystal according to the present invention, since the direction of electric polarization is determined by the direction of spin with respect to the two types of CoO ₄ tetrahedron as described above, polling by an external electric field is not performed. In both cases, large spontaneous electric polarization can be observed in the entire crystal.

This has been confirmed experimentally in, for example, a Ba ₂ CoGe ₂ O ₇ crystal having the same structure as the Sr ₂ CoSi ₂ O ₇ crystal (see Non-Patent Document 2). The present inventors also performed experiments as shown below for Sr ₂ CoSi ₂ O ₇ crystals to measure magnetic field induced electric polarization.

An external rotating magnetic field (8T) that rotates around the c-axis in the ab plane in a state where the temperature of the single crystal of Sr ₂ CoSi ₂ O ₇ produced by the method described later is set to 4.5K, 7K, 8K, and 10K. And the magnitude of electric polarization induced in the c-axis direction was measured. Note that the magnetic transition temperature of Sr ₂ CoSi ₂ O ₇ is about 7K. The measurement results at that time are shown in the upper graph of FIG. In addition, in the state where the temperature of the Sr ₂ CoSi ₂ O ₇ single crystal is 4.5 K, an external magnetic field rotating around the c-axis in the ab plane is 0T, 0.5T, 1T, 2T, 4T, and 8T. When an external rotating magnetic field having a magnitude was applied, the magnitude of electric polarization induced in the c-axis direction was measured. The measurement results at that time are shown in the lower graph of FIG.

From the upper graph of FIG. 4, when the temperature of the Sr ₂ CoSi ₂ O ₇ single crystal is a temperature near 8 K, which is a temperature near the magnetic transition temperature (7 K), a relatively large electric polarization is induced. I found out. It was found that the lower the crystal temperature compared to the magnetic transition temperature, the greater the induced electrical polarization. Further, from the lower graph of FIG. 4, it was found that the induced electric polarization increases as the magnitude of the applied external rotating magnetic field increases under a constant temperature condition. Further, while the external rotating magnetic field rotates 180 ° around the c-axis, the induced electric polarization vibrates once. In other words, it was found that the oscillation period of electric polarization was half that of the rotation period of the external rotating magnetic field.

Furthermore, the present inventor further investigated the temperature dependence of the electric polarization under a pulsed strong magnetic field of several T to about 50 T in order to observe the behavior of the electric polarization at the time of magnetization saturation and the behavior of the electric polarization in the paramagnetic state. In addition, the magnetic field dependency was measured. Sr ₂ CoSi ₂ O ₇ exhibits antiferromagnetism at a temperature lower than the magnetic transition temperature (about 7 K), and a magnetic ordered state is realized. When such a temperature under _{Sr 2} CoSi 2 O ₇ applies a strong magnetic field to the _sample, the magnetization of the Sr ₂ CoSi 2 O ₇ samples are expected to saturate. Therefore, the above-mentioned pulsed strong magnetic field was applied at a temperature lower than the magnetic transition temperature, and the behavior of electric polarization at the time of magnetization saturation was observed. At a temperature sufficiently higher than the magnetic transition temperature, the Sr ₂ CoSi ₂ O ₇ sample is in a paramagnetic state. Here, in the experiment in which an external magnetic field of about 8T was applied, almost no electric polarization was observed at a temperature of 10K. Therefore, it was decided to apply a pulsed strong magnetic field stronger than 8T and observe in detail the behavior of electric polarization in the paramagnetic state.

The upper graph in FIG. 5 is a plot of the magnetic field dependence of magnetization at each temperature in Sr ₂ CoSi ₂ O ₇ , and the lower graph in FIG. 5 is the electric polarization at each temperature in Sr ₂ CoSi ₂ O ₇ . This is a plot of the magnetic field dependence of. From the lower graph of FIG. 5, it was found that Sr ₂ CoSi ₂ O ₇ exhibits magnetic induction electric polarization even at temperatures of 30K, 100K, 200K, and 300K. Through this experiment, the present inventors have found that Sr ₂ CoSi ₂ O ₇ can induce electrical polarization by applying a strong magnetic field of more than a dozen Tesla even in a paramagnetic state.

  The inventors of the present invention have made further intensive studies, and even in the paramagnetic state, if the electric polarization can be induced by applying a strong magnetic field of 10 or more Tesla, the repetition period is very short instead of the strong magnetic field. The inventors have considered that electric polarization can be observed in a paramagnetic state even by applying a varying magnetic field, and the present invention has been achieved. Here, when investigating the magnetic field change of the magnetic field induced electric polarization by detecting the time change of the polarization charge (P) accumulated on the electrode on the sample surface as the current (i), the present inventors indicate that i is dP / Since it is proportional to dt, it has been noted that a large current flows if the time change of the electric polarization increases. We thought that it would be possible to observe magnetic field-induced electric polarization on a paramagnetic sample without using a strong magnetic field by rapidly changing the magnetic field, and the present invention was achieved.

Hereinafter, an experiment conducted by the inventors using a fluctuating magnetic field with a fast repetition period will be described in detail. Prior to the experiment, a single crystal sample of Sr ₂ CoSi ₂ O ₇ used in this experiment was prepared by the following procedure. FIG. 6 shows a procedure of a method for manufacturing a single crystal sample. First, a raw material powder (SrCO ₃ , CoO, SiO ₂ ) having a purity of 99.9% or more was weighed using an electronic balance so as to have a target composition ratio (weighing step S1), and mixed in an agate mortar. In mixing, a wet mixing method in which ethanol was added so that the raw material powders were sufficiently mixed was used (wet mixing step S2). After sufficiently mixing the raw material powder in this way, ethanol was evaporated to obtain a mixed powder.

  Next, the sufficiently mixed powder was transferred to an alumina crucible and calcined at 800 ° C. for about 12 hours in an air atmosphere using an electric furnace (calcination step S3). In addition, in order to make it react uniformly, after calcination, dry mixing was performed (first dry mixing step S4), and then, calcination was performed again at 900 ° C. for about 12 hours (second calcination step S5). ).

After calcination twice, dry mixing was further performed (second dry mixing step S6), and packed in a rubber balloon so as to have a uniform density. In order to make it into a straight bar shape, this rubber balloon is wrapped with paper and pressed using a hydraulic press machine with a pressure of about 300 to 400 kgf / cm ² to form a rod-like shape having a diameter of about 6 mm and a length of about 100 mm. A raw material rod was obtained (pressure forming step S7). The press-molded raw material bar was baked for about 48 hours at 1000 ° C. in an electric furnace to produce a sintered bar (main baking step S8).

  A single crystal sample was prepared by a floating zone melting method (Floating Zone method; hereinafter referred to as FZ method) using the sintered bar which was baked (crystal growth step S9). For the FZ method, an infrared heating single crystal production apparatus 1 (SC-M15HD) manufactured by Canon Machinery was used. As shown in FIG. 7, the infrared heating single crystal device 10 is a spheroid mirror in which two spheroid mirrors 11a and 11b are combined such that one of the respective focal points (first focal point) overlaps each other. 11, two halogen lamps 12 serving as heat sources respectively disposed at the other focal points (second focal points) of the spheroid mirrors 11 a and 11 b, and the first of the spheroid mirrors 11 a and 11 b. It is mainly provided with two main shafts 13a and 13b which are arranged so as to face each other vertically with one focal point interposed therebetween and fix the sample 20 from above and below, respectively. The main shafts 13a and 13b can move the sample 20 up and down while rotating the sample 20 with the center of the main shafts 13a and 13b as the rotation axis. The sample 20 is positioned at the first focal point of each spheroid mirror 11a, 11b.

  The infrared rays IR emitted from the two halogen lamps 12 respectively arranged at the second focal points of the spheroid-shaped mirrors 11a and 11b are converged to the first focal point, so that they are arranged at the first focal point. Infrared IR is irradiated to the sample 20 attached to the main shafts 13a and 13b. The portion of the sample 20 irradiated with the infrared IR is heated and melted to form a molten zone. By moving the upper and lower main shafts 13a and 13b downward in this state, the position of the melting zone of the sample 20 can be moved upward. Since the portion of the sample 20 that deviates from the first focus is hardly irradiated with the infrared IR, it is cooled and crystallized to produce a seed crystal. In this manner, by gradually moving the position of the melting zone of the sample 20 upward, the seed crystal can be grown and a single crystal sample can be obtained. At this time, the upper and lower main shafts 13a and 13b are rotated in reverse from each other in order to keep the melting zone stable and to eliminate the non-uniformity of the sample. In addition, since the molten zone is held by the sample 20 and the seed crystal having the same composition as that, there is no possibility of being contaminated by impurities.

The single crystal sample produced by the above-described FZ method may have a small crystal distortion such as domain mixing due to being rapidly cooled. Therefore, in order to eliminate this distortion, after being held at 500 ° C. for 2 hours in an oxygen atmosphere, it was gradually cooled to room temperature over about 20 hours (annealing step S10). In this way, a single crystal sample of Sr ₂ CoSi ₂ O ₇ was produced.

Next, in order to observe the magnetic field induced electric polarization at room temperature, the following experiment was conducted. First, a rectangular parallelepiped sample 51 having a length of 2 mm and a thickness of 0.5 mm is cut out from a single crystal sample of Sr ₂ CoSi ₂ O ₇ produced by the above method so that the c-axis direction coincides with the thickness direction. It was. Electrodes 51a for observing a later-described current (magnetic field induced current) were formed on both surfaces in the c-axis direction of the sample 51, and the sample 51 was placed in the magnetic field induced electric polarization measuring device 60.

  As shown in FIG. 8, the magnetic field induced electric polarization measuring device 60 includes a cylindrical sample holder 61 that supports the sample 51 and a magnet that is concentrically disposed outside the sample holder 61 so as to cover the sample holder 61. A pair of neodymium magnets 63 arranged in the magnet holder 62 so as to sandwich the holder 62, the sample 51 supported by the sample holder 61, a pickup coil 64 fixed together with the sample 51 inside the sample holder 61, and a magnet Connected to the holder 62 and connected to the motor 65 for rotating the magnet holder 62 around the sample holder 61, the electrode 51a and the pickup coil 64, signals (current signals) from the electrode 51a and the pickup coil 64 are observed. A digital oscilloscope (not shown).

When the motor 65 is driven to rotate the magnet holder 62 around the sample holder 61, a pair of neodymium magnets 63 fixed to the magnet holder 62 rotate around the sample 51. Here, the direction of the magnetic field by the neodymium magnet 63 is parallel to the ab plane of the sample 51. Therefore, by driving the motor 65, a rotating magnetic field rotating around the c-axis of the sample 51 and oriented in parallel to the ab plane can be generated. In addition, it was found by measurement using a hall element (not shown) that the strength of the magnetic field created by the neodymium magnet 63 at the position of the sample 51 is about 0.222T. Further, the pickup coil 64 is arranged in parallel with the a-axis direction of the sample 51. Therefore, the magnitude (μ ₀ H _a ) of the component in the a-axis direction of the rotating magnetic field can be measured by the pickup coil 64.

  The sample 51 was placed on the sample holder 61 of such a magnetic field induced electric polarization measuring device 60 and the motor 65 was driven to generate a rotating magnetic field rotating around the c-axis of the sample 51 at high speed. Then, the magnetic field induced electric polarization induced by this rotating magnetic field was measured as a current generated with a change in the magnetic field induced electric polarization. In the present specification, a current generated with such a change in magnetic field induced electric polarization is referred to as a magnetic field induced current. Here, the magnitude of the magnetic field induced current is proportional to the time change of the electric polarization, and the time change of the electric polarization is proportional to the time change of the magnetic field. Therefore, it is expected that the observed magnetic field induced current increases as the time change of the magnetic field increases. Therefore, in order to increase the time change of the magnetic field as much as possible, a DC motor (about 20000 rpm) capable of high-speed rotation was adopted as the motor 65. This experiment was performed in an environment at room temperature.

FIG. 9 shows the result of this measurement. The upper graph of FIG. 9 shows the time change of the component (μ ₀ H _a ) in the a-axis direction of the rotating magnetic field measured based on the induced current generated in the pickup coil 64 by the rotating magnetic field rotating at high speed in the ab plane. It is a graph which shows. From this, it can be seen that the magnetic field is rotating at a period of 2.916 ms (frequency 342.9 Hz).

  The graph shown by the thick line in the middle of FIG. 9 is a graph showing the time change of the magnetic field induced current accompanying the change of the magnetic field induced electric polarization induced by the rotating magnetic field. By analyzing the frequency components of this graph, the magnetic field induced current signal contains two components: a component having the same period as the rotation period of the magnetic field and a component having a period that is half the rotation period of the magnetic field. I found out. Note that the graph indicated by the thin line in the middle stage of FIG. 9 is obtained by extracting only the component having a period that is half the rotation period of the magnetic field from the two components included in the magnetic field induced current signal.

  According to the knowledge of the inventors, the component having the same period as the rotation period of the magnetic field included in the magnetic field induced current signal is considered to be caused by the induced current generated by the rotating magnetic field. In terms of electrical circuit, since there is only the electrode 51a and wiring connected thereto, it seems that no induced current is generated at first glance. However, since the wiring inevitably contains an inductance component, it is considered that an induced current is generated due to this. On the other hand, a component having a period that is half the rotation period of the magnetic field included in the magnetic field induced current signal corresponds to a true magnetic field induced current accompanying a change in magnetic field induced electrical polarization induced by the rotating magnetic field. It is. Then, by integrating a component having a half of the rotation period of the magnetic field corresponding to the true magnetic field induced current, the time change of the magnetic field induced electric polarization can be obtained. The graph of the time change of the magnetic field induced electric polarization obtained in this way is shown in the lower part of FIG. Thus, the magnetic field induced electric polarization could be observed even at room temperature.

  Conventionally, it has been known that an electromagnetic effect material exhibits magnetic field induced electric polarization at a temperature lower than a magnetic transition temperature, that is, in a magnetic ordered state. As described above, an electromagnetic effect material that exhibits magnetic field induced electric polarization even at room temperature (for example, 300K) has been reported so far, but even in this case, the magnetic transition temperature is still above room temperature. In the sample in the paramagnetic state exceeding the magnetic transition temperature, no magnetic field induced electric polarization was observed.

On the other hand, as described above, since the magnetic transition temperature of Sr ₂ CoSi ₂ O ₇ is about 7K, Sr ₂ CoSi ₂ O ₇ exhibits paramagnetism at room temperature. Nevertheless, as in the experiment described above, by applying a rotating magnetic field rotating at high speed in the ab plane, it was possible to observe the magnetic field induced electric polarization induced by the rotating magnetic field.

Thus, the Sr ₂ CoSi ₂ O ₇ crystal exhibits magnetic field-induced electric polarization below the magnetic transition temperature, that is, in the magnetically ordered state, and also at a temperature higher than the magnetic transition temperature, that is, It was found that the magnetic field induced electric polarization was developed even in the paramagnetic state. In other words, it has been found that the electromagnetic effect is exhibited in any temperature range regardless of whether it is higher or lower than the magnetic transition temperature.

Next, the electromagnetic element using the electromagnetism effect material according to the present invention will be described with some examples. As described above, it has been found that Sr ₂ CoSi ₂ O ₇ exhibits an electromagnetic effect such as magnetic field induced electric polarization in any temperature range. Can be developed.

For example, an element in which electrodes are formed on both ends in the c-axis direction of a single crystal of Sr ₂ CoSi ₂ O ₇ like the sample 51 described above can be used as a variable magnetic field sensor. In the above experiment, when a rotating magnetic field was applied around the c-axis of the crystal, a magnetic field induced current was observed along with a change in magnetic field induced electric polarization induced by the rotating magnetic field. Conversely, it can be seen that when a magnetic field induced current was observed, a fluctuating magnetic field was generated around the c-axis of the crystal. In addition, the magnitude, polarity, frequency, etc. of the varying magnetic field can be detected from the magnitude, polarity, frequency, etc. of the magnetic field induced current. In addition, since there is no restriction | limiting in the magnitude | size of a crystal | crystallization, the magnetic field variation sensor of arbitrary magnitude | sizes and shapes can be produced. For example, a magnetic field sensor having a minimum size can be manufactured.

Like the sample 51 described above, an element in which electrodes are formed at both ends in the c-axis direction of a single crystal of Sr ₂ CoSi ₂ O ₇ can also be used as a power generation element. As shown in FIG. 10, in a normal power generation element using electromagnetic induction, an induced electromotive force is generated in the coil by changing the magnetic flux density passing through the coil. On the other hand, the power generation element according to the present invention applies a magnetic field induced in the ab plane, such as a rotating magnetic field rotating in the ab plane of the crystal, to the power generation element 100 to thereby generate a magnetic field induced electric current on the c-axis of the crystal. Polarization is generated, thereby generating a magnetic field induced current. Again, since the size of the crystal is not limited, a power generation element having an arbitrary size and shape can be manufactured.

  In the above example, attention has been paid to the fact that the electric polarization can be controlled by applying a magnetic field, but conversely, the direction of magnetization can also be controlled by applying an electric field. If attention is paid to the fact that the direction of magnetization can be controlled by the electric field of the electromagnetism effect, the electromagnetism effect material according to the present invention can be applied to a magnetic memory capable of controlling the electric field. Alternatively, application to an optical element such as a magneto-optical element in which polarization control of light is performed by an electric field and a magnetic field is also possible.

In the above description, Sr ₂ CoSi ₂ O ₇ has been described as an example of an electromagnetic effect material having an akermanite structure containing magnetic ions, but the present invention is not limited to this, and for example, an akermanite structure It is applicable to A ₂ CoB ₂ O ₇ , A ₂ NiB ₂ O ₇ , A ₂ FeB ₂ O ₇ (where A is Ca, Sr or Ba, and B is Ge or Si).

  When the electromagnetic effect material according to the present invention is applied to a power generation element, it is difficult to manufacture a coil, and a power generation element that is too small to be handled by a power generation element using ordinary electromagnetic induction can be manufactured ( For example, power generation elements of micron order and submicron order). Thereby, it can utilize as an electric power generation element which supplies electric power to a very small machine.

60 Magnetic Field Induced Electrical Polarization Measuring Device 61 Sample Holder 62 Magnet Holder 63 Neodymium Magnet

Claims (6)

An electro-magnetic effect element using an electro-magnetic effect material having an akermanite structure containing magnetic ions,
The electromagnetic effect material is A ₂ MX ₂ O ₇ , A is any one of Ca, Sr, Ba, X is Ge or Si, M is a magnetic ion,
An electromagnetism effect element that exhibits an electromagnetism effect at a temperature higher than a magnetic transition temperature of the electromagnetism effect material.   2. The electro-magnetic effect element according to claim 1, wherein M is any one of Mn, Co, Fe, and Cu.   The electro-magnetic effect element is a single crystal of the electro-magnetic effect material, and includes a single crystal having a crystal structure in which a predetermined direction is a c-axis direction. Electrodes are provided at both ends of the single crystal in the c-axis direction. The electro-magnetic effect element according to claim 1, wherein the electro-magnetic effect element is formed. The electromagnetic effect element is a single crystal of the electromagnetic effect material, and includes a single crystal having a crystal structure in which a predetermined direction is a c-axis direction,
The magnetic effect element exhibits the magnetic field induced electric polarization in the c-axis direction when an external magnetic field that varies with time in a plane perpendicular to the c-axis of the single crystal is applied. The electromagnetic effect element according to claim 1, wherein the electromagnetism effect element is a magnetic field sensor that detects a magnetic field. The electromagnetic effect element is
A single crystal of the electromagnetic effect material having a crystal structure in which a predetermined direction is a c-axis direction;
Electrodes disposed at both ends of the c-axis direction of the single crystal,
The power generating element that outputs a magnetic field induced current from the electrode when a varying magnetic field in a direction crossing the single crystal is applied in a plane perpendicular to the c-axis of the single crystal. The electromagnetic effect element as described in any one of 1-3. The power generating element further includes a magnetic field generating mechanism that generates a magnetic field in a direction across the single crystal in a plane perpendicular to the c-axis of the single crystal.
The electromagnetic effect element according to claim 5, further comprising a magnetic field variation mechanism that temporally varies the magnetic field.

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