Magnetic field sensor

Abstract

The objective is to provide a magnetic field sensor that utilizes the in-plane abnormal Hall effect. [Solution] A magnetic field sensor 100 comprises a sensor element 10 that generates an in-plane abnormal Hall effect, means for passing a current 22 in a first in-plane direction of the sensor element 10, and measuring means 30 for measuring the electromotive force in a second in-plane direction. The means for passing the current is, for example, a power supply circuit that connects terminals 20 and 21 via a power supply. The power supply is, for example, a DC power supply. The measuring means for measuring the electromotive force can, for example, be a known voltmeter. Alternatively, the measuring means may measure the resistance value of the sensor element.

Description

[Technical Field]

[0001] This invention relates to a magnetic field sensor. [Background technology]

[0002] Currently used magnetic field sensors include Hall sensors that detect vertical magnetic fields using the Hall effect, and anisotropic magnetoresistance sensors that detect horizontal magnetic fields using the magnetoresistance effect. Patent document 1 also discloses a magnetic field sensor that utilizes a combination of the anomalous Hall effect, anisotropic magnetoresistance effect, and unidirectional magnetoresistance effect. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Patent No. 7244157 [Overview of the project] [Problems that the invention aims to solve]

[0004] Hall sensors can detect the magnitude and direction of a vertical magnetic field, allowing for accurate measurement of geomagnetism, for example, by placing them on three mutually perpendicular surfaces. However, they have the disadvantage of a narrow detection area and limited placement flexibility. Anisotropic magnetoresistance sensors can detect horizontal magnetic fields and have a wide detection area, making them flexible in placement and widely used for detecting things like the opening and closing of laptops. However, they have the disadvantage of being able to determine the magnitude of a horizontal magnetic field but not its direction. Magnetic field sensors using the unidirectional magnetoresistance effect require applying an AC current of frequency ω and detecting changes in AC voltage of frequency 2ω, which limits the miniaturization of the device.

[0005] The present invention aims to provide a magnetic field sensor that utilizes the in-plane abnormal Hall effect. [Means for solving the problem]

[0006] One embodiment of the magnetic field sensor according to the present invention is: A sensor element capable of generating an in-plane abnormal Hall effect, Means for passing current in a first in-plane direction of the sensor element, The system includes means for measuring the electromotive force in a second in-plane direction.

[0007] One embodiment of the above-described magnetic field sensor includes a crystal whose crystal structure space group belongs to one of the following categories.

number

[0008] In one embodiment of the above magnetic field sensor, the crystal is one of the following compounds. III-V group compounds comprising one or more group III elements selected from Si, In, Ga, and Al, and one or more group V elements selected from Sb, As, and P; Permalloy alloy; Heusler compounds represented as XYZ or X2YZ (where X and Y represent different transition metal elements, and Z represents a p-block element); Cd3As2 doped with at least one of Zn and Sb; Compounds whose empirical formula is EuM2X2 (where M represents one or more elements selected from Cd, Zn, In, and Sn, and X represents one or more elements selected from P, As, and Sb); A compound whose chemical formula is represented by Co3Sn2S2, Fe3Sn2, Mn3Sn, SrRuO3, or Cd3As2.

[0009] One embodiment of the above-described magnetic field sensor further comprises a substrate for supporting the sensor element, wherein the substrate is CdTe, Al2O3, MgO, MgAl2O4, Si, SiC, InP, GaAs, ferrite, or SrTiO3.

[0010] One embodiment of the above magnetic field sensor is: A first member comprising the aforementioned sensor element and having a main surface, In an article having a second member that is made of a magnetic material, Detect the orientation of the second member with respect to the main surface of the first member.

Effect of the Invention

[0011] The present invention provides a magnetic field sensor utilizing the in-plane anomalous Hall effect.

Brief Description of the Drawings

[0012] [Figure 1] It is a schematic diagram used for explaining the in-plane anomalous Hall effect. [Figure 2] It is a schematic diagram showing an example of a magnetic field sensor. [Figure 3] It is a block diagram showing an example of control means. [Figure 4] It is a schematic diagram used for explaining the crystal structure of EuCd2Sb2. [Figure 5] It is a schematic side view showing an example of a sensor element. [Figure 6] It is a graph showing the in-plane anomalous Hall resistance of a EuCd2Sb2 single crystal thin film. [Figure 7] It is a graph showing the in-plane anomalous Hall resistance of a EuZn2Sb2 single crystal thin film. [Figure 8] It is a graph showing the in-plane anomalous Hall resistance of a SrRuO3 crystal thin film. [Figure 9] It is a schematic diagram showing an example of the use of a magnetic field sensor.

Embodiments for Carrying Out the Invention

[0013] <00...​​​​In this specification, unless otherwise specified, the "~" indicating a numerical range includes the values ​​listed before and after it as the lower and upper limits. Furthermore, in this specification, characters with an overbar are referred to as " - It can sometimes be represented as "n" (where n is a character that should have an overbar).

[0014] [Summary of the Invention] First, let's outline the in-plane anomalous Hall effect. When an electric current is passed through a conductive sample under an external magnetic field, the Lorentz force generates an electric field (Hall field) perpendicular to both the magnetic field and the current, producing an electromotive force. This phenomenon is called the Hall effect. When a magnetic material is used as the conductive sample, in addition to the Hall field corresponding to the above Hall effect, a Hall field proportional to the magnetization is generated. This is called the anomalous Hall effect. For example, in Figure 1(A), when a magnetic field is applied in the z-axis direction while a current is flowing in the x-axis direction, a potential difference due to the anomalous Hall effect is generated in the y-axis direction. On the other hand, as shown in Figure 1(B), even when a magnetic field without a z-axis component (also called an in-plane magnetic field) is applied while a current Ix is flowing in the x-axis direction of the sample, it was expected that a potential difference would be generated in the y-axis direction. This is called the in-plane anomalous Hall effect. However, due to technical difficulties, no observational examples had been reported. The inventors have achieved observation of the in-plane anomalous Hall effect by using a crystal with a specific crystal structure as a sensor element. This invention was completed based on such knowledge and technology, and provides a magnetic field sensor based on a new principle that utilizes the in-plane anomalous Hall effect.

[0015] (Embodiment 1) The configuration of the magnetic field sensor will be described with reference to Figures 2 and 3. Figure 2 is a schematic diagram showing an example of a magnetic field sensor 100. The magnetic field sensor 100 comprises a sensor element 10 capable of generating an in-plane abnormal Hall effect, means for supplying current 22 in a first in-plane direction (e.g., the X-axis direction) of the sensor element, and means 30 for measuring the electromotive force in a second in-plane direction (e.g., the Y-axis direction). The means for supplying current is, as an example, a power supply circuit that connects terminals 20 and 21 via a power supply. The power supply is, as an example, a DC power supply. The means for measuring the electromotive force is, as an example, a known voltmeter. Alternatively, the resistance value of the sensor element may be measured. The means for measuring the resistance value may be, for example, means for measuring the current and voltage in the power supply circuit (ammeter, voltmeter), or, in the case of supplying a constant current, means for calculating it from the applied voltage. Furthermore, the means for supplying current and the various measuring means may each be integrated with control means, which will be described later. Furthermore, although not shown, the sensor element 10 may have means for further cooling as needed. Cooling improves sensitivity. Known means such as liquid nitrogen, liquid helium, or a Peltier element can be used for cooling.

[0016] Figure 3 is a block diagram showing an example of a control means 70. The control means 70 comprises an input unit 71, an output unit 72, a calculation unit 73, a control unit 74, and a storage means 80. The control means 70 may be electrically connected to the magnetic field sensor 100, or it may be connected by a wireless bidirectional communication means. As the control means 70, for example, a known personal computer, PDA, tablet terminal, etc. may be used, or it may be a small unit integrated with the magnetic field sensor 100.

[0017] The input unit 71 is an input means for receiving various types of information, and only needs to have means for acquiring measured values ​​related to the electromotive force (for example, terminals that can be connected to each component of the magnetic field sensor 100 or a wireless receiver), and may also be equipped with a keyboard, touch panel, various switches, etc., as needed.

[0018] The output unit 72 is an output means that outputs various necessary information, and may be configured as, for example, a display device, or in the case of a small magnetic field sensor, a buzzer or an LED. Alternatively, the output unit 72 may be a wireless transmission unit that transmits information to a remote information terminal device or the like.

[0019] The calculation unit 73 calculates the direction and magnitude of the magnetic field input to the sensor element 10, and / or the change in the direction and magnitude of the magnetic field, from the information obtained from the magnetic field sensor 100. Specifically, the calculation unit 73 is configured to include a CPU, various programs interpreted and executed on the CPU (including basic control programs such as the OS and application programs launched on the OS to realize specific functions), and internal memory such as RAM for storing programs and various data.

[0020] The storage means 80 is a storage means that stores various information necessary for the processing of the control means 70, and is composed of, for example, a hard disk or other recording medium. For example, it may include a database that stores the relationship between the deformation state of the member on which the magnetic field sensor 100 is installed and the direction and magnitude of the magnetic field input to the sensor element 10. The storage means 80 may also store information output from the magnetic field sensor 100 and the results calculated by the calculation unit 73, and the storage means 80 may also store various programs for executing the above processing.

[0021] The control unit 74 controls at least each part that constitutes the control means 70, and may also control the power supply and the voltmeter. Similar to the calculation unit 73, the control unit 74 is configured to include a CPU, various programs that are interpreted and executed on the CPU, and internal memory such as RAM for storing programs and various data.

[0022] The magnetic field sensor utilizing the in-plane abnormal Hall effect according to the present invention can detect the magnetic field in the in-plane direction, including its orientation, using DC power, and can be used in a wide range of applications by replacing known magnetic field sensors or by combining them with known magnetic field sensors. An example of the use of a magnetic field sensor will be explained with reference to Figure 9. Figure 9(A) shows an article 90 comprising a first member 40 equipped with a sensor element 10 and a second member 50 equipped with a magnet 55 that generates a horizontal magnetic field and is detachable from the first member 40. In such an article 90, the magnetic field sensor 100 can detect changes in the distance between the first member 40 and the second member 50 (see Figures 9(A) and (B)) (i.e., the detachment state), and furthermore, in this article 90, it is possible to distinguish between a state in which the first surface 51 of the second member 50 faces the first member 40 (Figure 9(C)) and a state in which the second surface 52 faces the first member 40 (Figure 9(B)). More specifically, if the item 90 is a notebook computer comprising a first component 40 equipped with a keyboard, etc., and a monitor (second component 50) having a display surface on its first surface 51, then a single sensor element 10 can detect the state of attachment or detachment of the monitor and the orientation of the first surface 51 relative to the first component 40, and automatically control operations such as turning the monitor or the touch panel on the monitor on or off according to that state. Also, although not shown, if the item 90 is a combination of a first component equipped with a touch panel and a second component which is an accessory device such as a stylus pen, then it can automatically control operations such as starting charging when the stylus pen is positioned in a specific orientation.

[0023] Next, as an example of a sensor element, we will describe an EuCd2Sb2 single-crystal thin film. Figure 4A is a schematic perspective view showing the unit cell of EuCd2Sb2, and Figure 4B shows the arrangement of each element as seen from the c-axis direction of Figure 4A. Note that the axis of symmetry is indicated in Figure 4B. The crystal structure of EuCd2Sb2 is a space group P in which Eu layers responsible for magnetism and Cd2Sb2 block layers are alternately stacked in the c-axis direction. - It is a trigonal crystal of 3m1, with a triple rotation axis (C3) along the c axis, a double rotation axis (C2) along the a axis and its equivalent axis, and a mirror plane m perpendicular to each C2 axis. In a zero magnetic field, the spin magnetic moments are ferromagnetically ordered on the ab plane of the triangular lattice and stack antiferromagnetically along the c axis, exhibiting a so-called type A antiferromagnetic order.

[0024] Figure 5 is a schematic side view showing an example of a sensor element 10. The single crystal thin film 12 is, for example, placed on a substrate 11. For example, by the molecular beam epitaxy method described below, an EuCd2Sb2 single crystal thin film 12 can be formed in which the c axis is positioned perpendicular to the main surface (XY plane) of the substrate 11 (in the Z-axis direction). A protective film or the like may be provided on the upper surface of the EuCd2Sb2 single crystal thin film 12.

[0025] A method for manufacturing a EuCd2Sb2 single-crystal thin film will be explained with an example. For the molecular beam epitaxy method, for example, an EpiQuest RC1100 can be used. As an example, first, a CdTe substrate with the (111)A surface exposed is prepared. The CdTe substrate may be surface-treated by etching with a bromine-methanol solution as needed, and then heating to approximately 650-800°C while supplying Cd flux. The temperature of the CdTe substrate is adjusted to approximately 300-400°C, and crystals are grown by molecular beam epitaxy. The molecular beam is supplied from a Knudsen cell containing Eu, Cd, and Sb. The equivalent pressure of the molecular beam is measured with an ionization gauge, and the pressure during simultaneous deposition is, for example, Eu = 1.0 × 10⁻⁶. -6 Pa~2.0×10 -5 Pa, Cd = 1.0 × 10 -4 Pa~8.0×10 -4 Pa, Sb = 2.0 × 10 -6 Pa~1.0×10 -5 It is preferable to set the density to around Pa. Increasing the supply amount of Cd makes it easier to obtain a single crystal film with a low carrier density. The thickness of the EuCd2Sb2 single crystal thin film is not particularly limited, but for example, it is preferably 10 to 200 nm. This method allows for the production of EuCd2Sb2 single-crystal thin films with such a small amount of 60° rotation domains (where Cd and Sb are swapped in Figure 4(B)) that they are negligible. Note that 60° rotation domains reduce the sensitivity of the sensor element, and the proportion of 60° rotation domains in the single-crystal thin film is preferably 5% or less, and more preferably 1% or less. The proportion of 60° rotation domains can be determined from the ratio of the peak intensities of Bragg reflections in X-ray diffraction.

[0026] Fig. 6(A) is a graph showing the dependence of the in-plane anomalous Hall resistance on the azimuthal angle φ of the in-plane magnetic field in a sensor element using a EuCd2Sb2 single crystal thin film. The graph has been background-processed. The in-plane magnetic field was changed in the range of 0.78 T to 9.00 T for measurement. The azimuthal angle φ indicates the angle shown in Fig. 6(B) with the direction of the current as the reference (φ = 0). Fig. 6(B) shows the arrangement of elements in the EuCd2Sb2 single crystal as viewed from the c-axis. As shown in Fig. 6(A), the in-plane anomalous Hall resistance exhibits symmetry with a 120° period, reflecting the symmetry of the crystal. Thus, a magnetic field sensor utilizing the in-plane anomalous Hall effect has excellent sensitivity to changes in the direction of the magnetic field.

[0027] (Embodiment 2) Embodiment 2 uses a EuZn2Sb2 single crystal thin film as the sensor element. First, a CdTe substrate with the (111)A plane exposed was prepared and heat-treated at 550 °C while supplying Cd flux. The temperature of the CdTe substrate was adjusted to about 265 °C, and crystals were grown by molecular beam epitaxy. The ratio of the equivalent pressures of the molecular beams was adjusted to P Eu :P Zn :P Sb = 1:7 to 15:1 to 3, and a small amount of EuZn2Sb2 single crystal thin film with a hole density of 10 19 cm -3 ~10 20 cm -3 and a thickness of 50 nm and a negligible amount of 60° rotation domains was produced. Fig. 7(A) is a graph showing the dependence of the in-plane anomalous Hall resistance on the azimuthal angle φ of the in-plane magnetic field in a sensor element using a EuZn2Sb2 single crystal thin film. As shown in Fig. 7(A), the in-plane anomalous Hall resistance exhibits symmetry with a 120° period, reflecting the symmetry of the crystal.

[0028] (Embodiment 3) Embodiment 3 uses a SrRuO3 single crystal thin film as the sensor element. The crystal structure of SrRuO3 is a cubic crystal of Pm - 3m (see Fig. 8(B)). As shown in Fig. 8(C), the SrRuO3 single crystal has a three-fold rotation axis (C3) along

[0111] , [1 -10] has a 2x rotation axis (C2) along its equivalent direction and a mirror plane m perpendicular to each C2 axis. Figure 8(A) is a graph showing the dependence of the in-plane anomalous Hall resistance on the azimuthal angle φ of the in-plane magnetic field in a sensor element using a SrRuO3 single crystal thin film. As shown in Figure 8(A), the in-plane anomalous Hall resistance exhibits a 120° periodic symmetry, reflecting the symmetry of the crystal.

[0029] (Other embodiments) As described above, a sensor element capable of producing an in-plane anomalous Hall effect must include a crystal with three rotation axes. On the other hand, a crystal with six rotation axes does not produce the above-mentioned in-plane anomalous Hall effect. For this reason, the magnetic field sensor of this disclosure is required to include a crystal whose crystal structure space group belongs to one of the following categories.

number

[0030] Examples of crystals having the above crystal structure include those having any of the following compositions. III-V group compounds comprising one or more group III elements selected from Si, In, Ga, and Al, and one or more group V elements selected from Sb, As, and P; Permalloy alloy; Heusler compounds represented as XYZ or X2YZ (where X and Y represent different transition metal elements, and Z represents a p-block element); Cd3As2 doped with at least one of Zn and Sb; Compounds whose empirical formula is EuM2X2 (where M represents one or more elements selected from Cd, Zn, In, and Sn, and X represents one or more elements selected from P, As, and Sb); A compound whose chemical formula is represented by Co3Sn2S2, Fe3Sn2, Mn3Sn, SrRuO3, or Cd3As2.

[0031] Specific examples of the above-mentioned III-V group compounds include InP, GaAs, InGaAs, and InAs. Specific examples of the permalloy alloys mentioned above include alloys containing 35-80% by mass of Ni, which may also contain Cr and Mo, with the remainder being Fe and unavoidable impurities. Specific examples of Heusler compounds (half-Heusler compounds) represented by the above XYZ include VFeSb, NbFeSb, TaFeSb, TiCoSb, ZrCoSb, HfCoSb, TiNiSn, ZrNiSn, and HfNiSn. Specific examples of Heusler compounds (full Heusler compounds) represented by the above X2YZ include Cu2MnAl, Cu2MnIn, Cu2MnSn, Ni2MnAl, Ni2MnIn, Ni2MnSn, Ni2MnSb, Ni2MnGa, Co2MnAl, Co2MnSi, Co2MnGa, Co2MnGe, Co2NiGa, Co2MnSn, Pd2MnAl, Pd2MnIn, Pd2MnSn, Pd2MnSb, Co2FeSi, Co2FeAl, Mn2VGa, Co2FeGe, and Co2Cr x Fe 1-x Al, Co2Cr x Fe 1-x Si is one example.

[0032] Specific examples of compounds represented by the chemical formula EuM2X2 include, in addition to EuCd2Sb2 and EuZn2Sb2 mentioned in the above embodiment, EuCd2P2, EuCd2As2, EuZn2P2, EuZn2As2, EuIn2P2, EuIn2As2, EuIn2Sb2, EuSn2P2, EuSn2As2, and EuSn2Sb2.

[0033] Furthermore, for a sensor element that can generate an in-plane abnormal Hall effect, it is preferable that the axis of rotation three times is perpendicular to the plane direction. From this viewpoint, it is preferable to use CdTe, Al2O3, MgO, MgAl2O4, Si, SiC, InP, GaAs, ferrite, or SrTiO3 as the substrate.

[0034] As described above, the magnetic field sensor according to the present invention can detect magnetic fields in the in-plane direction, including their orientation, using direct current. Therefore, it can be suitably used for applications that detect the rotation of magnetic fields. Specifically, it can be suitably used for detecting the attachment and detachment of a laptop monitor, including its orientation, and for detecting the attachment and detachment of a tablet stylus pen, including its orientation.

[0035] The embodiments and modifications thereof described above are provided as examples for the purpose of illustrating the technical content of the present invention and are not intended to limit the technical scope of the invention to what is described herein. The technical scope of the invention includes modifications, substitutions, additions, and omissions made in the specification, drawings, and claims, or equivalents thereof, to the extent that a person skilled in the art can conceive of them. [Explanation of symbols]

[0036] 10 sensor elements, 11 base material, 12 single crystal thin films, Terminals 20 and 21, 22 current, 30 Measurement means; 70 Control means, 71 Input section, 72 Output section, 73 Calculation unit, 74 Control Unit, 80 Memory means; 100 magnetic field sensors.

Claims

1. A sensor element capable of generating an in-plane abnormal Hall effect, Means for passing current in a first in-plane direction of the sensor element, A magnetic field sensor comprising means for measuring the electromotive force in a second in-plane direction.

2. The magnetic field sensor according to claim 1, wherein the sensor element includes a crystal whose crystal structure space group belongs to any of the following.

3. The magnetic field sensor according to claim 2, wherein the crystal is any of the following: III-V group compounds comprising one or more group III elements selected from Si, In, Ga, and Al, and one or more group V elements selected from Sb, As, and P; Permalloy alloy; XYZ or X ２ Heusler compounds represented by YZ (where X and Y represent different transition metal elements, and Z represents a p-block element); Cd doped with at least one of Zn and Sb 3 As 2 ; The chemical formula is EuM 2 X 2 Compounds represented by (where M represents one or more elements selected from Cd, Zn, In, and Sn, and X represents one or more elements selected from P, As, and Sb); The composition formula is EuCd 2 Sb 2 、Co 3 Sn 2 S 2 、Fe 3 Sn 2 、Mn 3 Sn, SrRuO 3 or Cd 3 As 2 a compound represented by

4. Furthermore, the sensor element is supported by a substrate, the substrate being made of CdTe, Al 2 O 3 MgO, Mg Al 2 O 4 Si, SiC, InP, GaAs, ferrite, or SrTiO 3 The magnetic field sensor according to claim 1.

5. A first member comprising the aforementioned sensor element and having a main surface, In an article having a second member that is made of a magnetic material, The magnetic field sensor according to claim 1, which detects the orientation of the second member with respect to the main surface of the first member.

Images