GSR sensor

Abstract

To provide a GSR sensor that uses negative magnetostrictive amorphous wire to significantly reduce magnetic noise.SOLUTION: A GSR sensor includes a negative magnetostrictive Co-Si amorphous wire, a magnetic field detection element formed by winding a coil around the wire, and a signal processing circuit for processing a voltage corresponding to a magnetic field signal generated by the magnetic field detection element, and a magnetic wire 1 constituting the GSR sensor is made of a negative magnetostrictive Co-Fe-B-Si soft magnetic alloy with an Fe / Co ratio of 0.65 or less, has an oxygen content of 10 ppm or less, a diameter of 10 μm or less, and has a two-layer magnetic domain structure consisting of a surface magnetic domain and a core magnetic domain.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a GSR sensor that reduces magnetic noise using a negative magnetostrictive amorphous wire.

Background Art

[0002] It is known that the GSR effect occurs when a high-frequency pulsed current is passed through an amorphous wire of a CoFeBSi-based alloy with zero magnetostriction or weak negative magnetostriction, causing the spins inside the wire to rotate rapidly. A GSR sensor is a highly sensitive magnetic sensor that utilizes a GSR element that detects this change with a detection coil wound around the amorphous wire.

[0003] Conventional GSR sensors use a magnetosensitive wire with zero magnetostriction or weak negative magnetostriction, as disclosed in Patent Document 1, which has a small anisotropic magnetic field and a high magnetic permeability, that is, a magnetic wall that moves easily. FIG. 4 shows a perspective view schematically showing the axial structure inside the amorphous wire. The magnetosensitive wire 4 is divided into two layers: a surface magnetic domain (spin arrangement in the circumferential direction) 41 and a core magnetic domain (spin arrangement in the magnetic domain direction) 42 due to differences in the magnetic domain structure. In the surface magnetic domain 41, the spins are divided into magnetic domains that rotate clockwise and counterclockwise in a certain circumferential direction, forming a bamboo structure, and there are 180 magnetic walls in the surface magnetic domain 41. On the other hand, the core magnetic domain 42 on the inner circumferential side of the surface magnetic domain 41 has a multi-magnetic domain structure and many magnetic walls exist. Also, at the interface between the surface magnetic domain 41 and the core magnetic domain 42, a 90-degree magnetic wall exists. Thus, the conventional magnetic wire 4 has a spin structure (arrangement) of clockwise and counterclockwise rotations with the spins facing a certain circumferential direction in the surface magnetic domain 41, and there is a 180-degree magnetic wall between the two. The core magnetic domain 42 has a multi-magnetic domain structure, and there is a 90-degree magnetic wall between the surface magnetic domain and the core magnetic domain, resulting in a magnetic composite structure as a whole.

[0004] Patent Document 2 states that "zero magnetostriction" means that the absolute value of magnetostriction is less than 10 -6 For example, on page 13 of "Magnetic Sensor Engineering" published by Corona Co., Ltd., "(CoFe) 80 (SiB) 20In this case, when Fe / Co is 0.07, the absolute value of magnetostriction becomes 10 -6 or less, and it is described that "the magnetostriction at that level is regarded as zero magnetostriction". Therefore, considering that the invention of Patent Document 1 used the amorphous wire that had been used in conventional MI sensors, the definition of zero magnetostriction or weak negative magnetostriction is consistent with the definition that the absolute value of magnetostriction in Patent Document 2 is 10 -6 or less.

[0005] Conventional GSR sensors are those that detect changes in magnetization due to spin rotation by suppressing the movement of magnetic walls because they are excited by GHz pulsed currents. However, in the process of the actual pulsed current reaching a high-speed change, it is industrially inevitable that it is accompanied by a process of gentle change at the initial and final stages of the pulse change. At this timing, it is possible that the 180-degree magnetic wall of the surface magnetic domain disappears or is generated along with the spin rotation. The 90-degree magnetic wall existing between the surface magnetic domain and the core magnetic domain can move inside the wire or move in the surface direction.

[0006] When the magnetic wall moves, there is a problem that Barkhausen noise is generated and large magnetic noise is accompanied. This problem is caused by the magnetic domain structure of the amorphous wire, which is a magnetosensitive wire, and the movement of the magnetic wall. That is, the magnetic walls existing in the multi-magnetic domain structure part of the core part 42 and the magnetic walls existing at the interface between the surface layer part 41 and the core part 42 have been a problem as the source of magnetic noise in the magnetosensitive wire or the GSR sensor using the same.

[0007] Patent Document 2 discloses a magnetosensitive wire having a vortex spin structure made of a soft magnetic alloy that becomes zero magnetostriction. According to the description, it is reported that hysteresis disappears due to the vortex spin structure, but no disclosure is made regarding magnetic sensor sensitivity or magnetic noise. Although it is considered that the large magnetic noise caused by Barkhausen noise et al. is suppressed by the vortex spin structure that does not include magnetic walls, it is expected that the magnetic anisotropy will increase and the sensitivity will decrease. Therefore, improving the detection output by the vortex spin structure is considered to be a research topic in the future.

Prior Art Documents

Patent Document

[0008]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0009] The problem of the present invention is to find a means for suppressing the movement of magnetic domains of amorphous wires used in current GSR sensors and to provide a GSR element and a GSR sensor with less magnetic noise. Suppressing the movement of magnetic domains also simultaneously suppresses the rotation of spins, which is the essence of the GSR effect, resulting in a decrease in sensor sensitivity. That is, magnetic noise and sensor sensitivity are mutually contradictory phenomena, and it is a difficult problem to improve them simultaneously.

Means for Solving the Problems

[0010] As a result of intensive research to solve the above problems, the inventors of the present invention have found that by using a Co-Si-based negative magnetostrictive amorphous wire with a large anisotropic magnetic field having an Fe / Co ratio of 0.065 or less, the movement of magnetic domains can be suppressed and magnetic noise can be significantly reduced. At the same time, for the suppression of spin rotation, the conversion pulse frequency is increased and the thickness of the surface magnetic domain layer is increased to offset the adverse effect on sensitivity, and it is possible to prevent a decrease in the overall magnetic sensor sensitivity. In addition, it has been found that minimizing impurities such as oxygen eliminates the damping phenomenon of local magnetic domain movement and realizes low noise, and the sensor sensitivity can be improved. Furthermore, when the wire diameter is reduced to 2 μm or less, the magnetic domain structure inside the wire disappears, and the vortex magnetic domain structure described in Patent Document 2 is generated. In the vortex magnetic domain structure, although the circumferential spin rotation caused by the pulse current is slightly suppressed and the sensor sensitivity decreases, it has been found that the magnetic noise associated with the movement of the magnetic wall almost disappears, so that the magnetic field detection output is significantly improved as a whole.

[0011] The configuration of the present invention will be described in the order of the magnetic wire, the GSR element, and the GSR sensor. <Magnetic wire> (1) The magnetic wire of the present invention has a two-layer magnetic domain structure composed of a surface magnetic domain and a core magnetic domain that are thicker than those of zero magnetic strain and weak negative magnetic strain, with a negative magnetic strain having an Fe / Co ratio of 0.065 or less. When the wire diameter is 2 μm or less, it has a vortex spin structure. The "vortex spin structure" means a structure in which each spin is continuously arranged in a certain circumferential direction in the surface layer portion of the wire, and in the inner peripheral portion which is the inner peripheral side of the surface layer portion, each spin gradually rotates from the circumferential direction to the axial direction as it approaches the center of the amorphous wire, and at the center of the wire, it becomes a continuous spin arrangement facing in the axial direction. It is described in detail in Patent Document 2. Here, the "spin" refers to the magnetic moment per atom.

[0012] (2) A perspective cross-sectional view of the vortex spin structure described in Patent Document 2 will be schematically shown in FIG. 1 and explained. Cross-section A is a plane perpendicular to the axial direction of the wire, and cross-section B is a plane cut at the central portion along the axial direction of the wire. The magnetosensitive wire 1 is composed of two layers, a surface layer portion 11 and an inner portion 12 with different spin arrangements. First, the surface layer portion 11 will be described. In the surface layer portion 11 of cross-section A, the spins are oriented in a certain circumferential direction. Therefore, the spins are continuously arranged as a whole and are closed (circulated or refluxed) in the circumferential direction, and there is no magnetic wall in the surface layer portion 11. And each spin existing in the X1-X2-X3-Y1 region (shown by the X1-X5 line as a representative example in FIG. 1) of cross-section B constituting the surface layer portion 11 has the same spin arrangement as the outermost surface of the surface layer portion 11.

[0013] Next, the spin arrangement of the inner portion 12 will be described. In the Y1-X3-X6-Y3 region on cross-section B (shown by the X5-X6 line as a representative example in FIG. 1), the spins at the boundary (X5) between the surface layer portion 11 and the inner portion 12 have the same direction as the spins in the surface layer portion 11. As going from X5 to X6, that is, as approaching the axis center, the spins gradually tilt their direction from the circumferential direction toward the axial direction, and the directions coincide in the axial direction (the center line direction of the magneto-sensitive wire 1) at the axis center (X6). Such a spin tilt arrangement similarly exists also on the Y1-Y2 line of cross-section B and in any part within the Y1-X3-X6-Y3 region of cross-section B. Thus, there is no magnetic wall in the inner portion 12 of the magneto-sensitive wire 1 according to the present invention. Also, at the boundary surface between the surface layer portion 11S and the inner portion 12, the spins are continuously arranged and there is no magnetic wall. The present invention refers to such an entire spin arrangement as a vortex spin structure. Note that the "spin arrangement" as referred to in this specification means the distribution state of the magnetic moments of each spin in terms of species, but is also simply referred to as "spin" as appropriate instead of "spin arrangement".

[0014] (3) The outline of the GSR sensor using the magnetic wire of the present invention is as follows. All spins tilt in the direction of the applied magnetic field according to the magnitude of the applied magnetic field which is the applied magnetic field. When a pulse current flows through the magnetic wire, a magnetic field is formed in the circumferential direction of the magnetic wire by that pulse current, and the spins in the magnetic wire turn in the circumferential direction. The GSR sensor detects the change due to the rotation of the spins of this magnetic wire with a pickup coil.

[0015] <GSR element> (1) The present invention is also an element using, as a magnetic detector, a magnetic wire made of the above-described Co-Fe-Si-B alloy with negative magnetostriction and having a diameter of 10 μm or less. The GSR element of the present invention only needs to replace only the magnetic wire, which is the magnetic detector, of the conventionally known GSR element with the magnetic wire described above of the present invention. The configuration of the GSR element itself includes a substrate, the magnetic wire of the present invention described above, an insulator that encloses the magnetic wire, a detection coil wound around the magnetic wire, and electrode terminals extending from the magnetic wire and the detection coil, as described in Patent Document 1.

[0016] (2) Each spin in the magnetic wire of the GSR element is tilted in the direction of the external magnetic field according to the magnitude of the external magnetic field. When a pulsed current of 0.5 to 4 GHz generated by a pulse oscillation circuit is supplied thereto, a magnetic field is formed in the circumferential direction of the magnetic wire, and the spins in the magnetic wire rotate in the circumferential direction. The GSR sensor detects the change in the direction of this spin with a detection coil. A change also occurs when the pulsed current is cut off, and the change can be detected. By using the GSR element using the negative magnetostrictive amorphous wire with an Fe / Co ratio of 0.065 or less of the present invention in the GSR sensor, the excellent effects described below are exhibited.

[0017] <GSR sensor> (1) The present invention is understood not only as the above magnetic wire and GSR element, but also as a GSR sensor using them. The GSR sensor of the present invention only needs to replace only the magnetic wire, which is the magnetic detector, of the conventional GSR sensor with the magnetic wire described above of the present invention. That is, the GSR sensor of the present invention includes a negative magnetostrictive magnetic wire of the present invention, a detection coil wound around the magnetic wire, a pulse oscillation circuit that energizes the magnetic wire with a pulsed current, and a signal processing circuit that converts the detection voltage of the detection coil into a signal corresponding to the intensity of the external magnetic field. (2) Since the GSR sensor of the present invention uses the above-described magnetostrictive magnetic wire with negative magnetostriction, the movement of magnetic walls is suppressed, and it has the characteristic that magnetic noise is reduced. Also, it is possible to maintain high sensor sensitivity by increasing the converted pulse frequency of the pulse current and the thickness of the surface magnetic domain layer. The configuration of the GSR sensor itself is also known from the above-described publications and the like, and these known configurations and other known configurations can be used for the GSR sensor of the present invention.

Advantages of the Invention

[0018] As described above, the GSR element and GSR sensor of the present invention can suppress magnetic noise and maintain high sensor sensitivity to obtain excellent magnetic field detection output by replacing the magnetosensitive wire of the conventional GSR element and GSR sensor with a magnetosensitive wire with negative magnetostriction.

Brief Description of the Drawings

[0019]

Figure 1

Figure 2

Figure 3

Figure 4

Best Mode for Carrying Out the Invention

[0020] The first embodiment will be described while appropriately comparing it with conventional examples. <Configuration> (1) Alloy Composition The magnetosensitive wire is a Co-Fe-Si-B-based soft magnetic alloy with negative magnetostriction having an Fe / Co ratio of 0.065 or less, and the diameter is 10 μm or less. Also, the oxygen content needs to be 10 ppm or less. This wire has a two-layer magnetic domain structure consisting of a surface magnetic domain and a core magnetic domain. The thickness of the surface magnetic domain increases as the Fe / Co ratio decreases. When the ratio exceeds 0.065 and reaches about 0.07, zero magnetostriction occurs, making it easier for magnetic walls to move, increasing magnetic noise, which is not preferable. Also, the total content of Co and Fe is preferably about 75% to 80%. If it is less than 75%, the strength of the saturation magnetization decreases, and the sensitivity of the sensor decreases. If it exceeds 80%, the content of Si or B, which is an amorphous forming element, decreases, making it difficult to manufacture the amorphous wire. Furthermore, the oxygen content is 10 ppm or less. If it exceeds 10 ppm and increases, local magnetic wall movement is likely to occur, causing magnetic noise. The diameter of the magnetosensitive wire is 10 μm or less. The smaller the diameter, the fewer the magnetic domain structures inside the wire. Also, when the diameter is 2 μm or less, a vortex magnetic domain structure occurs.

[0021] (2) Heat treatment This amorphous wire as the test material is preferably tension heat-treated at 250 to 350 °C after applying a tension of 40 to 76 kg / mm 2 to align it on the substrate and then applying a tension of 40 kg / mm 2 . By this tension heat treatment, the thickness of the surface magnetic domain can be increased to suppress magnetic domain noise and at the same time increase the sensor sensitivity.

[0022] (3) GSR element The configuration of the GSR element 2 according to the first embodiment of the present invention will be described using the conceptual diagram of FIG. 2. First, a detection coil 22 disposed via an insulator (not shown) around the magnetic wire 21 is arranged on the substrate 20. Electrodes 211 for applying a pulse current are connected to both ends of the magnetic wire 21. The detection coil 22 is connected to an electrode 221 for detecting a voltage that changes according to an external magnetic field. The length of the magnetic wire 1 is 0.2 to 2 mm, the coil pitch is 5 μm or less, and the number of turns of the detection coil 22 is 30 to 2,000 turns.

[0023] (4) GSR sensor The electronic circuit of the GSR sensor according to the present invention will be described with reference to FIG. 3. The GSR sensor 3 includes a GSR element 2, a pulse oscillation circuit 31, and a signal processing circuit 32. The pulse oscillation circuit 31 generates a converted pulse frequency corresponding to 0.5 to 4 GHz and supplies a pulse current of 50 to 100 mA to the magnetic wire 21 of the GSR element 2. Then, due to the action of the external magnetic field and the magnetic field in the circumferential direction of the wire caused by the pulse current, a voltage based on the rotation of the spins in the magnetic wire 21 is generated in the detection coil 22. The converted pulse frequency is calculated by first obtaining the rise or fall time Δt of the pulse of the pulse current waveform, and then assuming that the Δt corresponds to half of the period of the wave.

[0024] Next, after the pulse current rises, the analog switch 322 is switched (turned on - off) for a short time at a predetermined timing by the sample timing adjustment circuit 321. As a result, the analog switch 322 samples the voltage corresponding to the external magnetic field generated in the detection coil 3 and transmits it to the amplifier 323 via a buffer circuit. The same applies when the pulse current is cut off (falling edge). When the resistance of the detection coil is as small as 1 kΩ or less, the buffer circuit may be omitted. The configuration shown here is an example, and other known electronic circuits of GSR sensors may be employed.

[0025] <Measurement> For the GSR characteristics, the GSR sensor 6 was placed in a magnetic field of ±240 A / m and 10 Hz, an 80 mA pulse current with a converted pulse frequency of 2 GHz was input to the magnetic wire 1 of the GSR element 2, the voltage signal generated in the detection coil 22 was signal - processed by the above - mentioned signal processing circuit 32, the voltage of each magnetic field output from the detection coil 22 was measured, and the magnetic noise and sensor sensitivity were obtained and evaluated. Both the rise time and the fall time of the pulse current were 0.25 ns. Here, the fall part of the pulse was detected, but the rise part may also be used, or both may be used.

[0026] <Characteristics of Magnetic Sensor> The magnetic noise characteristics showed that, for an element with the same number of coil turns compared to conventional zero magnetostriction wires, the magnetic noise decreased by about 1 / 10 and the sensor sensitivity was equivalent.

[0027] The second embodiment will be described below. The diameter of the magnetic wire was set to 2 μm or less, and other configurations were the same as those of the first embodiment. When the diameter of the magnetic wire is 2 μm or less, the magnetic domain structure becomes a vortex structure and the magnetic walls disappear. As a result, the magnetic noise associated with magnetic wall movement decreases significantly. Compared with the first embodiment, for the same number of coil turns, the sensor sensitivity becomes about 1 / 2 smaller, but the magnetic noise becomes 1 / 2 or less. Also, the strength of the excitation pulse current is about 25 to 50 mA, which is about 1 / 2 smaller than that of the first embodiment. The reason for the decrease in current is that the anisotropic magnetic field becomes about 2 times larger, but the circumferential magnetic field becomes about 4 times larger because it is inversely proportional to the wire diameter.

Example

[0028] [Example 1] Example 1 will be described in the order of magnetic wire, GSR element, and GSR sensor. (1) Magnetic wire An (Co 96 Fe4) 76 Si 12 B 12 (at%) alloy composition with an Fe / Co ratio of 0.041, an oxygen content of 5 ppm, and an amorphous wire with a diameter of 10 μm was used as the magnetic wire according to the embodiment of the present invention. After applying a tension of 76 kg / mm2 to align this amorphous wire on the substrate, a tension of 50 kg / mm2 was applied and tension heat treatment was performed at 300 °C. Note that, as a comparative example, (Co 93.7 Fe 6.3 ) 76 Si 12 B 12An amorphous wire with an alloy composition of (at%), having an Fe / Co ratio of 0.067, an oxygen content of 30 ppm, a diameter of 10 μm, a constant circumferential spin structure in the surface magnetic domain, and a core magnetic domain inside was prepared.

[0029] (2) GSR element The configuration of the GSR element 2 according to Example 1 of the present invention will be described with reference to the conceptual diagram of FIG. 2. First, a detection coil 3 arranged via an insulator (not shown) is disposed on the substrate 10 around the magnetic wire 1. Both ends of the magnetic wire 1 are connected to electrodes 51 for applying a pulse current. The detection coil 3 is connected to an electrode 52 for detecting a voltage that changes according to an external magnetic field. The length of the magnetic wire was set to 2 mm, the coil pitch was set to 3 μm, and the number of turns of the detection coil 30 was set to 560 turns.

[0030] (3) GSR sensor The electronic circuit of the GSR sensor 3 according to the embodiment of the present invention will be described with reference to FIG. 3. The GSR sensor 3 includes a GSR element 2, a pulse oscillation circuit 31, and a signal processing circuit 32. The operation of the sensor is as follows. A pulse current having a converted pulse frequency equivalent to 2 GHz generated by the pulse oscillation circuit 31 is supplied to the magnetic wire 21 in the GSR element 2. Then, due to the action of the external magnetic field and the magnetic field in the circumferential direction of the wire caused by the pulse current, a voltage based on the rotation of the spins in the magnetic wire 1 is generated in the detection coil 22. Next, after the pulse current rises, the analog switch 322 is switched (turned on - off) for a short time at a predetermined timing by the sample timing adjustment circuit 321. As a result, the analog switch 322 samples the voltage corresponding to the external magnetic field generated in the detection coil via the buffer circuit 320 and transmits it to the amplifier 323. The same applies when the pulse current is cut off (when it falls).

[0031] <Measurement> Regarding the GSR characteristics of this embodiment, the GSR sensor 6 was installed in a magnetic field of ±240 A / m and 10 Hz. An 80 mA pulse current with a converted pulse frequency of 2 GHz was input to the magnetic wire 1 of the GSR element 2. The voltage signal generated in the detection coil 22 was processed by the above signal processing circuit 32, and the voltages of each magnetic field output from the detection coil 3 were measured to obtain and evaluate the magnetic noise and sensor sensitivity. The rise time and fall time of the pulse current were both 0.25 ns. Here, the detection was performed at the falling edge of the pulse, but it may also be performed at the rising edge, or both.

[0032] The magnetic noise characteristic of Example 1 was 0.1 nT, a 1 / 10 reduction compared to the magnetic noise of 1.2 nT of the zero magnetostriction amorphous wire in the comparative example, and the sensor sensitivity was equivalent at 400 mV / G.

[0033] [Example 2] In Example 2, in Example 1, the magnetic wire was changed to an amorphous wire with a diameter of 10 μm having an alloy composition of (Co 98 Fe2) 76 Si 12 B 12 (at%) and having an Fe / Co ratio of 0.02 and an oxygen content of 5 ppm. As a result, the magnetic noise characteristic decreased to about 1 / 10 at 0.08 nT, and the sensor sensitivity was equivalent at 380 mV / G.

[0034] [Example 3] In Example 3, in Example 1, the diameter of the magnetic wire was changed to an amorphous wire having a vortex magnetic domain structure of 1 μm. As a result, the magnetic noise characteristic decreased to about 1 / 20 at 0.05 nT, and the sensor sensitivity improved to 600 mV / G.

[0035]

Table 1

Industrial Applicability

[0036] The magnetic wire, GSR element, and GSR sensor according to the present invention significantly suppress magnetic noise and improve magnetic detection output. Thereby, it can be applied to ultra-small magnetic sensors for small electronic devices such as medical devices and mobile phones.

Explanation of symbols

[0037] 1: Magnetic wire 11: Surface layer part 12: Inner part 2: GSR element 20: Substrate 21: Magnetic wire 211: Electrode 22: Detection coil 221: Electrode 3: GSR sensor 31: Pulse oscillation circuit 32: Signal processing circuit 320: Buffer circuit 321: Sample timing adjustment circuit 322: Analog switch 323: Amplifier 4: Conventional magnetic wire 41: Surface magnetic region 42: Core magnetic region

Claims

1. In a GSR sensor comprising a negative magnetostrictive Co—Si based amorphous wire (hereinafter referred to as a magnetic wire), a magnetic field detection element in which a coil is wound around the magnetic wire, and a signal processing circuit that processes a voltage corresponding to a magnetic field signal generated by the magnetic field detection element, the magnetic wire is a Co—Fe—B—Si based negative magnetostrictive soft magnetic alloy having an Fe / Co ratio of 0.065 or less and an oxygen content of 10 ppm or less, the magnetic wire has a diameter of 10 μm or less and a magnetic domain structure composed of a two-layer structure of a surface magnetic domain and a core magnetic domain, characterized GSR sensor.

2. According to Claim 1, the diameter of the magnetic wire is 2 μm or less, the magnetic domain structure has a vortex spin structure in which each spin is continuously arranged in a certain circumferential direction in the surface layer portion, and in the inner portion which is the inner circumferential side of the surface layer portion, the spins gradually rotate from the circumferential direction to the axial direction as they approach the center of the magnetic wire and are oriented in the axial direction at the center of the magnetic wire, which is a continuous spin arrangement, characterized GSR sensor.

3. According to Claim 1 or 2, the pulse current has a converted pulse frequency of 0.5 GHz to 4 GHz and a strength of the pulse current that generates a surface circumferential magnetic field that is 1.5 times or more the anisotropic magnetic field of the magnetic wire, characterized GSR sensor.

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